Thesis for the degree of Doctor of Philosophy, Sundsvall 2012

NOBLE CRAYFISH (ASTACUS ASTACUS) IN A CHANGING WORLD – IMPLICATIONS FOR

MANAGEMENT

Jenny K. M. Zimmerman

Supervisors:

Professor Thomas Palo

Professor Nils Ekelund

Department of Natural Sciences, Engineering and Mathematics

Mid Sweden University, SE-851 70 Sundsvall, Sweden

ISSN 1652-893X,

Mid Sweden University Doctoral Thesis 126

ISBN 978-91-87103-17-9

ii

Akademisk avhandling som med tillstånd av Mittuniversitetet i

Sundsvall framläggs till offentlig granskning för avläggande av filosofie

doktorsexamen fredagen den 25 maj, 2012, klockan 10.15 i sal L 111,

Mittuniversitetet Sundsvall.

Seminariet kommer att hållas på svenska.

NOBLE CRAYFISH (ASTACUS ASTACUS) IN A CHANGING WORLD – IMPLICATIONS FOR MANAGEMENT

Jenny Zimmerman

The picture of the front cover page illustrates the success of the

reintroduction of noble crayfish to the River Ljungan. (Photo: Jenny

Zimmerman 2011).

The picture of the back cover page illustrates the noble crayfish in a

changing world (Figure: Karin, Edit & Irma Zimmerman 2012).

© Jenny Zimmerman, 2012

Department of Natural Sciences, Engineering and Mathematics

Mid Sweden University, SE-851 70 Sundsvall

Sweden

Telephone: +46 (0)771-975 000

Printed by Kopieringen Mid Sweden University, Sundsvall, Sweden,

2012

iii

NOBLE CRAYFISH (ASTACUS ASTACUS) IN A CHANGING WORLD – IMPLICATIONS FOR MANAGEMENT

Jenny K. M. Zimmerman

Department of Natural Sciences, Engineering and Mathematics

Mid Sweden University, SE-851 70 Sundsvall, Sweden

ISSN 1652-893X, Mid Sweden University Doctoral Thesis 126;

ISBN 978-91-87103-17-9

ABSTRACT

The noble crayfish (Astacus astacus) is critically endangered in

Sweden. This is mainly due to the crayfish plague (Aphanomyces astaci), a

lethal disease that, among other things, can be spread through the

stocking of fish from contaminated water or contaminated fishing gear.

The largest single propagation path is the illegal introduction of infected

signal crayfish (Pacifastacus leniusculus). A conservation measure for

crayfish is to re-introduce it to where it has a chance to survive, though a

sustainable, locally regulated fishing can also serve as an indirect

protection for the species. When the local inhabitants are allowed to keep

their fishing culture and when fishing is acceptable, the incentive for

illegal stocking of signal crayfish is low. However, it is important to

avoid overfishing because the recovery, especially in the northern

regions, can take several years. Therefore, it is important to know how

crayfish respond long-term to fishing and environmental factors.

Crayfish populations became extinct in the River Ljungan for

unknown reasons in 1999. The water flow of the river has been used for

activities such as fishing, timber transport and hydroelectric power since

the 1500s, and the noble crayfish has been part of the fauna since the last

century. The River Ljungan was known as one of Sweden's best fishing

areas for crayfish and fishing became an important part of the local

tradition. When the crayfish populations became extinct, a

reintroduction program was a natural step, and crayfish are nowadays

re-established in the river.

From 1963 to 1990 the Swedish Board of Fisheries collected data from

crayfish fishing in the River Ljungan to determine the economic damage

to fishery owners caused by the construction of a power plant. After

iv

each season the fishermen reported the catch. In this thesis, the data was

used to investigate which factors influence the long-term size of the

crayfish catch and how the crayfish catches were affected by the power

plant building. After re-introduction of the crayfish to the River Ljungan,

the local fishermen monitored the population development in a simple,

standardized way. To examine the validity of their measurements and to

investigate the body growth of the individuals, a capture-recapture

technique with a permanent marking of the crayfish was used.

The crayfish catches were primarily impacted by the previous years'

catch size, and a large catch the previous year resulted in a reduced catch

the following year. A mild winter climate (NAO-index > -0.7) six years

before the catch implied a large catch, whereas a high water flow during

the autumn or spring (>95m3s-1) two years before the catch, implied a

poor catch. Major habitat changes in the form of greatly reduced water

flow (~90%) were negative for crayfish catches. The standardized

method of fishing used by the local fishermen to monitor the

development of the crayfish population was precise enough to detect

population trends and this method can therefore be recommended to

monitor future re-introductions of crayfish. Although the River Ljungan

is located at the northern edge of the species' range, noble crayfish in the

river presently have a body growth rate that is close to the maximum

measured for crayfish (8 mm/moult for females and 10 mm/moult for

males).

Based on the results, the most important advice for sustainable

fisheries in Ljungan and other northern rivers is to:

Monitor the population trends, NAO-index and water flow

in May and October.

Use the results from the monitoring to determine the number

of allowed fishing days and traps.

Collect data about the catch size and efforts from legal

fishing and use it to evaluate the sustainability of the fishing.

Enhance the buildup of the harvestable cohort by

-saving reproductive females

-introduce a size limit of 10 cm

-provide proper shelters for the non-harvestable

cohort.

Keywords: Noble crayfish (Astacus astacus), CPUE, climate change,

water regulation, body growth, reintroduction,

sustainable fishing, monitoring.

v

SVENSK SAMMANFATTNING

Flodkräftan i en föränderlig värld – förutsättningar för skötsel

Flodkräftan (Astacus astacus) är akut hotad i Sverige främst på grund

av kräftpest (Aphanomyces astaci). Kräftpest är en dödlig sjukdom som

bland annat kan spridas vid fiskutsättningar från smittade vatten eller

med smittade fiskeredskap. Den enskilt största spridningsvägen är

illegala introduktioner av smittade signalkräftor (Pacifastacus

leniusculus). En bevarandeåtgärd för flodkräfta är att återintroducera den

till lokaler där den har chans att överleva, men ett hållbart fiske med

lokal styrning kan också fungera som ett indirekt skydd för arten. När

lokalbefolkning tillåts att behålla sin fiskekultur och fisket är bra, blir

incitamentet för illegal inplantering av signalkräfta lågt. Men det är

viktigt att undvika överfiske då återhämtning, speciellt i nordlig miljö

kan ta åtskilliga år. Därför är det betydelsefullt att veta hur flodkräftan

svarar på fiske och omgivningsfaktorer i det långa loppet.

Flodkräftbeståndet dog, av okänd anledning, ut i Ljungan 1999. I

Ljungans flöde har det fiskats, flottats timmer och utvunnits vattenkraft

etc. sedan 1600-talet och under det senaste århundradet har flodkräftan

varit en del av Ljungans fauna. På sin tid var det en av Sveriges bästa

lokaler för flodkräfta. Kräftfisket blev en viktig del av den lokala

traditionen, så när kräftbeståndet dog ut var återintroduktion en

självklarhet och flodkräftan har åter sin hemvist i älven.

Under perioden 1963 till och med 1990 samlade Fiskeriverket in data

från kräftfisket i Ljungan för att fastställa den ekonomiska skadan som

fiskerättsägarna åsamkats i samband med ett kraftverksbygge. Efter

varje säsong fick fiskarna rapportera hur fisket gått. I den här

avhandlingen, har det materialet använts för att undersöka vilka faktorer

som påverkar kräftfångstens storlek på lång sikt och hur kräftfångsterna

påverkades av kraftverksutbyggnaden. Efter återintroduktionen av

flodkräfta till Ljungan mättes beståndsutvecklingen på ett enkelt, men

standardiserat sätt av de lokala fiskevårdsområdena. För att undersöka

validiteten av deras mätningar och hur kräftornas individuella

utveckling fortskred, användes fångst- och återfångstteknik, med

permanent märkning av kräftorna.

Kräftfångsternas storlek påverkades främst av tidigare års

fångststorlek; en stor fångst föregående år innebar minskad fångst

vi

följande år. Ett milt vinterklimat (NAO-index > -0.7) sex år före fångst

innebar bättre fångster, medan höga vattenflöden höst och vår (>95m3s-1)

två år före fångsttillfället innebar sämre fångst. Större

habitatförändringar i form av kraftigt reducerade vattenflöden (~90%)

var negativt för kräftfångsterna. Den standardiserade metoden som

fiskevårdsområdena använt för att mäta beståndsutvecklingen var

tillräckligt precis för att påvisa populationsutvecklingen och kan därför

rekommenderas också för uppföljning av andra återintroduktioner av

flodkräfta. Trots att Ljungan ligger i norra kanten av flodkräftans

utbredningsområde har flodkräftorna i Ljungan för närvarande en

kroppstillväxt som är nära den maximala som uppmätts för flodkräfta (8

mm/ömsning för honor och 10 mm/ömsning för hannar).

Utifrån resultaten är de viktigaste råden för ett hållbart fiske i

Ljungan och andra nordliga vattendrag att:

Övervaka kräftstammens utveckling, NAO-index samt

vattenflöde i maj och oktober.

Använda resultaten från övervakningen för att bestämma

antalet tillåtna fiskedagar och burar.

Samla in data om fångststorlek och hur många burnätter

som faktiskt gjordes under säsongen. Använda data för att

utvärdera fiskets hållbarhet.

Stärka uppbyggnaden av den fångstbara storleken genom

att

-spara reproduktiva honor

-införa en storleksgräns på 10 cm

-tillse att det finns gömslen för kräftor av icke-fångstbar

storlek.

vii

TABLE OF CONTENTS

ABSTRACT III SVENSK SAMMANFATTNING V Flodkräftan i en föränderlig värld – förutsättningar för skötsel v TABLE OF CONTENTS VII LIST OF PAPERS VIII 1 INTRODUCTION 1 1.1 Thesis background 1

1.2 Noble crayfish 2 2 THE PRESENT THESIS 6

2.1 Research area 6 2.2 Long-term studies 8

2.2.1 Catch data 8 2.2.2 Modeling population dynamics 8 2.2.3 Climatic impact 9 2.2.4 Water regulation 12

2.3 Field study 14 2.3.1 Experimental setup 14 2.3.2 Capture-recapture methods 14 2.3.3 CPUE versus capture-recapture methods 17 2.3.4 Body growth after reintroduction 18

3 GENERAL DISCUSSION 19

3.1 Methodologies to monitor noble crayfish 19 3.2 Management of noble crayfish 21

3.2.1 Reintroduction 21 3.2.2 Sustainable fishing 22

3.3 Future research 24 3.4 Noble crayfish in a changing world 25

4 REFERENCES 27 5. TILLKÄNNAGIVANDEN 39

viii

LIST OF PAPERS

This thesis is mainly based on the following four papers, herein

referred to as their Roman numerals:

Paper I Zimmerman J.K.M. and Palo R.T. 2012. Time series

analysis of climate related factors and their impact on red

listed noble crayfish population in northern Sweden.

Freshwater Biology 57: 1031–1041.

Paper II Zimmerman J.K.M. and Palo R.T. 2010. Influence of water

regulation and water flow on noble crayfish (Astacus

astacus) catch in the River Ljungan, Sweden. Freshwater

Crayfish 17: 141-144.

Paper III Zimmerman J.K.M. and Palo R.T. 2011. Reliability of catch

per unit effort (CPUE) for evaluation of reintroduction

programs – A comparison of the mark-recapture method

with standardized trapping. Knowledge and Management of

Aquatic Ecosystems. 401: 07.

Paper IV Zimmerman J.K.M. 2012. Body growth of noble crayfish

(Astacus astacus) after reintroduction to a northern river

(Ljungan, Sweden). Manuscript.

In paper I-II Jenny Zimmerman conducted most of the planning, data

analyses and writing.

In paper III Jenny Zimmerman conducted most of the planning, field

work, data analyses and writing.

In paper IV Jenny Zimmerman conducted all of the planning, field

work, data analyses and writing.

Papers I-III are reprinted in this thesis with the permission of the

publishers concerned.

ix

Till Mormor,

Morfar, Farmor och Farfar –

Ni gjorde detta möjligt!

1

1 INTRODUCTION

1.1 Thesis background

Knowledge on the impact of climate change and how habitat

alterations may affect organisms is needed when determining of

conservation management objectives to achieve economically and

ecologically sustainable actions. An evaluation of such actions is crucial,

but often ignored in conservation projects (Seddon et al. 2007). The

availability of reliable techniques that are inexpensive and easy to

perform is essential and could increase any incitements for evaluation.

Thereby, knowledge of ecological mechanisms that lead to successful or

failed conservation measures could increase.

In Europe, reintroductions are common conservation actions for

noble crayfish (Astacus astacus) (Šmietana et al. 2004, Sint & Füreder

2004, Taugbøl 2004b, Taugbøl & Peay 2004, Jussila et al. 2008, Edsman &

Schröder 2009, Erkamo et al. 2010, Kozák et al. 2011 ). A conjecture is that

this action will be used more frequently in the future to compensate for

the loss of populations due to the increased spread of crayfish plague or

to enhance the possibilities for weak populations in restored habitats. In

Scandinavia where crayfish traditionally is important, a sustainable

fishing of noble crayfish might serve as a tool for conservation of the

species. The possibility for exploitation and economical as well as

recreational benefits among local inhabitants may make them more

eager to protect the species (Taugbøl 2004a, Jones et al. 2006).

In present thesis, the focus is mainly on factors that influence the

sizes of adult noble crayfish populations in a northern river. This might

give a clue how to manage noble crayfish in a northern climate. Research

into the reintroductions of crayfish, especially noble crayfish to lotic

ecosystems is limited, and the purpose of the present thesis has been to

gain knowledge of the long-term climatic impact and habitat alteration

on noble crayfish in the northern Swedish River Ljungan (I-II),

methodology of evaluation after reintroduction (III), and noble crayfish

body growth after reintroduction (IV).

2

1.2 Noble crayfish

In terms of commercial importance, crayfish are among the same

order as shrimps, crabs and lobsters that belong to the class Malacostraca

of the subphylum Crustacea (Ahyong & O’Meally 2004, Meland &

Willassen 2007). Over 650 freshwater crayfish species are found

worldwide and are indigenous to all continents, with the exception of

Africa and Antarctica (Taylor 2002, Crandall & Buhay 2008).

Figure 1. The two crayfish species that is present in Sweden. The indigenous noble crayfish (Astacus astacus) is to the left and the introduced signal crayfish (Pacifastacus leniusculus) to the right. The noble crayfish is mainly recognized by the scratchy carapace (A) and by the red spot (B) at the joint between the two fingers of the claw. The most distinctive signs of signal crayfish are the smooth carapace (A) and the white-turquoise patch (B) on top of their claws at the joint between the two fingers of the claw. Figure: Linda Nyberg.

Two crayfish species are present in Sweden (Fig. 1) belonging to the

Astacideae family. The indigenous noble crayfish (Astacus astacus,

Linnaeus) is widely distributed in Eurasia and native to 28 European

countries (Edsman et al. 2010) and the North American signal crayfish

(Pacifastacus leniusculus, Dana), which was introduced to Sweden in the

late 1960s (Fjälling & Fürst 1985). Nowadays the signal crayfish has

3

become more common than the noble crayfish (Bohman & Edsman

2011).

Crayfish, especially noble crayfish, have been consumed in

continental Europe since the medieval times (Gherardi 2011). A search

for crayfish recipes in Google gave 2 830 000 hits (Google 2012),

indicating the importance of crayfish in food culture. Crayfish parties

have been a part of Swedish folklore since the 16th century when

crayfish was served by the Vasa dynasty at celebrations. However, the

general public did not consume crayfish until the end of the 19th century

but nowadays the “Kräftskiva” (crayfish party) is a well-known Swedish

tradition that is celebrated annually each August (Swahn 2004) and the

recreational catch of crayfish in Sweden is approximately 10 times larger

than the professional catch (Fiskeriverket 2000, SCB 2011).

Crayfish are found in both lentic and lotic ecosystems and are used as

indicator species for good water quality (Richardson 2012). Three factors

are critical for crayfish; oxygen content, pH and temperature (Nyström

2002). The abundance of crayfish is also influenced by the presence of

predators, water flow velocity, urban influence, proportion of arable

land and sun exposure (Gherardi 2002, Schulz et al. 2006). At the

northern limit of the distribution area for noble crayfish successful

crayfish populations are more frequent in streams than lakes (Odelström

& Johansson 1999, SCD 2010).

The body temperature of poikilothermic organisms varies with that

of the surrounding environment (Rastogi 2007). This makes their

physiological processes and thus their life cycles temperature dependent

(Giller & Malmqvist 1998). Crayfish is poikilothermic and consequently,

its growth rate and activity pattern are governed by temperature

(Abrahamsson 1983, Westin & Gydemo 1986, Bubb et al. 2004, Nyström

2002, Salkonen et al. 2010).

During the autumn, a decreasing temperature and shortened days

induce the reproduction cycle for Astacideae. Noble crayfish in northern

environments begins with moult in July, followed by mating in

September-October (Abrahamsson 1983, Zimmerman, personal

observation). The maturity age and size are individual and postponed in

cold climate compared to warmer (Abrahamsson 1972, Reynolds 2002).

Females breed every second or third year depending on the availability

of high quality foods and temperature (Reynolds 2002, Skurdal et al.

2010, Zimmerman, personal observation). The embryonic development

4

of noble crayfish eggs demands a period of time below 5˚C for high

survival (Reynolds 2002, Skurdal & Taugbøl 2002), with the hatching of

juveniles occuring in July (Abrahamsson 1972). A cold spring might

delay hatching and thereby cause less growth and difficulties for

juveniles to survive the winter (Gydemo & Westin 1989, Pursiainen &

Erkamo 1991, Reynolds 2002, Skurdal & Taugbøl 2002).

Crayfish spend most of their time in shelters and an ideal habitat is

heterogeneous with the bottom substrate consisting of stones, gravel and

silt, tree roots and driftwood (Gherardi 2002, Nyström 2002). The

shelters serve as refuges from predators or from currents during floods.

Juvenile crayfish prefer shallow hard-bottom areas with rocks,

vegetation or both (Hamrin 1987, Skurdal & Taugbøl 2002). Substrate

availability (shelters) sets the upper limit of the population size in lakes

and streams, though for streams, there are also ecological top-down

processes, i.e. the abundance of predator fish seems to be more

important for crayfish abundance than substrate availability (Stenroth

2005).

Noble crayfish live long and can reach an age of 20 years (Edsman et

al. 2010). Mortality declines with increasing body size. Almost 95% of the

juveniles are probably lost during their first summer due to predation,

cannibalism or incomplete moult (Ackefors et al. 1989, Skurdal &

Taugbøl 2002). Adults are most vulnerable to predation during moult

when the carapace is soft and not protective.

Perhaps one of the most important mortality factors is diseases. This

could be viral, bacterial, parasites or caused by fungus (Evans &

Edgerton 2002). Among diseases the Crayfish plague (Aphanomyces astaci

Schikora) is the most fatal for European crayfish since whole populations

of crayfish can be obliterated within several weeks (Evans and Edgerton

2002, Edsman et al. 2010). The infection is mainly spread through illegal

introductions of infected crayfish, but other human activities like the

stocking of fish from contaminated water, fishing with contaminated

fishery tools and fishing nets or boats can act as agents (Evans &

Edgerton, 2002, Edsman & Schröder 2009).

The food web structure of crayfish is complex since their feeding

habits change depending on age and situation. They could be regarded

as prey, predators, omnivores or detrivores and eat algae, periphyton,

aquatic vascular macrophytes, invertebrates, vertebrates, fish, fish eggs,

carrion and detritus (Usio 2000, Nyström 2002, Dorn & Wojdak 2004,

5

Stenroth 2005, Setzer et al. 2011). A lack of alternative food generates

cannibalism and in certain situations crayfish is a top-predator (Nyström

et al. 1999, Nyström 2002,). The consumption of detritus from land-based

material adds nutrition and organic material to the water. Fish, birds

and mammals are predators of adult crayfish, whereas invertebrates and

fish eat juvenile crayfish (Skurdal & Taugbøl 2002, Stenroth 2005).

Crayfish are keystone engineers because they bioturbate its

environment, i.e. they displace and mix sediment particles by

excavating, lifting and jostling small stones with their walking legs,

scrape and flick with the abdomen or telson when walking or swimming

and thereby move sediments from the bottom to the water column

(Parkyn et al. 1997). Crayfish influence lower trophic levels directly via

selective consumption of macrophytes and invertebrates, especially

“slow” preys such as snails (copepoda) (Nyström et al. 1999, Dorn &

Wojdak 2004). In a long-term perspective, high densities of crayfish may

cause destruction of the macrophyte community (Abrahamsson 1966).

Indirect effects, so-called trophic cascade effects, arise through the

crayfish consumption of snails, resulting in increased periphyton

biomass due to the reduction of predating snails, or the consumption of

midges (Tanopodinae), the predatory invertebrates, leading to an indirect

increase of its prey (Chironomidae), or when crayfish prefer Chara macro

algae and Cladophora spp. macrophyton as food, thus shifting the species

composition to blue-green algae that is less favourable to the crayfish

(Abrahamsson 1966, Parkyn et al. 1997, Nyström et al. 1999, Usio &

Townsend 2002, Dorn & Wojdak 2004, Stenroth 2005).

Crayfish compete for food, shelter and females (Nyström 2002).

Interspecific competition occurs, for example, between fish and crayfish

when they compete for the same food resources. Trout (Salmo trutta) was

more effective in foraging and the abundance of crayfish was therefore

low when the trout was present (Olsson et al. 2006). Interspecific

competition between crayfish species is important when the distribution

of the crayfish species is determined. Most NICS (non indigenous

crayfish species) are more aggressive and have a higher capacity for

population increase than ICS (indigenous crayfish species). The large

capacity for a NICS population increase is derived from a higher

individual growth rate, earlier sexual maturity and a higher per capita

egg production that makes them invasive and outrivals ICS (Gherardi

2002).

6

One-third to one-half of the crayfish species in the world are

threatened by population decline or extinction (Taylor 2002, Crandall &

Buhay 2008). The current status of the noble crayfish is alarming. Present

day the catches of noble crayfish in Europe are below 1/10 of the catches

in the 19th century (Skurdal & Taugbøl 2002) and known Swedish

populations have decreased by 97% during the last century with an

accelerating trend since the 1960s (Bohman et al. 2006). The species is

classified as vulnerable on the IUCN Red list of Threatened Species

(Edsman et al. 2010) and as critically endangered on the Swedish Red

List (Gärdenfors 2010).

The most immediate threat to European crayfish is the introduction

of NICS (Taylor 2002, Holdich et al. 2009). Crayfish plague is mainly

spread through illegal introductions of signal crayfish (Edsman et al.

2010, Gärdenfors 2010). In addition, crayfish are sensitive to degraded

habitats. Therefore, impoundment or channelization of streams,

drainage of wetlands, urban development, increased siltation and

changes in water chemistry along with over-fishing and climate change

are factors that threaten populations (Taylor 2002, Holdich et al. 2009).

2 THE PRESENT THESIS

2.1 Research area

The research area in the River Ljungan is centred around 62˚31´59”N

and 15´27”0˚E, a 60 km long stretch of the river (Fig. 2). The western

border of the study area was situated immediately upstream Holmsjön,

with power plant at Ljungaverk along the eastern border. The River

Ljungan flows from the Scandinavian Mountains in the west to the Baltic

Sea in the east and stretches about 400 km with a catchment area of

12,851 km2 (Thoms-Hjärpe 2002). The River Ljungan has been influenced

and exploited by man since at least the sixteenth century until today.

Fisheries, sawmills, watermills and the transport of timber dominated

before small hydroelectric power plants were built and energy-

demanding factories, such as nitrate and chlorate plants, were

constructed near the river close to the electric power in the early

twentieth century (Nordberg 1977). The expansion of modern

hydroelectric power took place from the 1950s to mid-1970s and today

the river is regulated along its entire length and the effects of the dams

are pronounced throughout the river ecosystem (Giller & Malmqvist

1998).

7

Noble crayfish were probably introduced to the river in the early 1900s

(Odelström & Johansson 1999). Local folklore tells that it happened on

two separate occasions. The first was in 1910 when the managing

director of the Alby Chlorate Plant planned a crayfish party, but lost a

corf with crayfish from southern Sweden into the river. The second

occasion is a similar occurrence and interestingly with some support for

these stories in the genetic variation of the crayfish in the River Ljungan,

showed similarity to crayfish populations with Southern and Western

Swedish origin (Edsman et al. 2002, Gross et al. 2012). The

“introduction” was successful and the crayfish fishing was

extraordinary. It was not unusual with 50 crayfish per trap (Ahl 1957).

Figure 2. The research area along the River Ljungan. The large ellipse (I)

indicates the river stretch where the analysis of climatic and weather impact on crayfish catches was performed (paper I). The small ellipses (1, 2, 3) indicate

Sections 1, 2 and 3 that together with the catch areas a, b, c, d and e (orange circles) were analysed with regards to impact of a new water flow regulation scheme (paper II). The red circles A, B, C, D and E indicate the areas where capture-recapture experiments were performed (paper III & paper IV). The

direction of water flow is indicated by small arrows in the major reservoirs.

In the 1960s, the crayfish in the river were subjected to research. The

population structure, growth and fecundity were investigated and

compared with other Swedish sites (Abrahamsson 1965, Abrahamsson

1972). Fishing was a tradition in the region until the crayfish became

extinct for unknown reasons in 1999. Soon after extinction the local

fishery owners associations, the local municipality, the county board and

the Swedish board of fisheries decided to run a reintroduction program

for the crayfish. The location of the reintroduction sites and the numbers

of introduced crayfish at these sites were determined by the fishery

8

owners associations. So far, more than 80,000 adult crayfish have been

reintroduced to the river at 35 sites (Ånge kommun 2010).

2.2 Long-term studies

2.2.1 Catch data

A prerequisite for long-term studies is the comprehensive time series

of reliable quality. These are difficult to achieve, but from the fishing of

crayfish in the River Ljungan data was collected by the Swedish Board of

Fisheries from 1963 to 1990. Fishing took place in August-September and

the fishermen reported the site, the efforts used and the catch size after

each season. The number of fisherman reports totaled about 10,000

during the period and the data was transformed to catch per unit effort

(CPUE), i.e. number of captured crayfish per trap and night. The CPUE

was used for two purposes in this thesis; to investigate the impact on

crayfish catches by climatic factors (I) and the decreased water flow after

the power plant was built (II).

2.2.2 Modeling population dynamics

In conservation management and fishing, predicting future

population development is important. Population modelling can be a

useful tool to determine when actions are needed to preserve a species or

to the size of fishing quotas for sustainable fishing.

The population size of a species at a certain future time Nt+1, is

generally described by the sum of the total population size (Nt) at the

current time (t), the births (B), deaths (D), immigrants (I) and emigrants

(E) (eqn 1). The population size is then a consequence of the population

success of survival (B - D) and the number of individuals that have been

permanent to the site (I – E) during the actual time.

EIDBNN tt 1 (eqn 1) (Gotelli 2001)

This model is simple, but reality is complex and many factors act

upon the population. For example, the number of females that are

mature, successfully mated, and the quantity of spawned eggs determine

the amounts of births (B). The number of births is then a consequence of

the female physical status and the amount of newborn crayfish is then a

result of how successful the female has been in taking care of the eggs

during maturation and how well she has defended the eggs from

predators. However, senescence, diseases, accidental events and

9

predation including cannibalism and fishery are setting the amount of

deaths (D). The physical status of the crayfish determines the “death

risk”, e.g. a weak and starved crayfish runs a greater risk of being

consumed by a predator/infection than a healthy one. The population

rate of migration (I+E) is determined by several factors. The low

presence of populations in the vicinity at the sites and the high

availability of unoccupied sites imply a fast overall migration rate

(Gotelli 2001), whereas favourable physical and biological conditions,

such as site area, availability of critical habitats (e.g. shelters and food),

and the absence or scarcity of predators and competitors, inhibit

emigration (E).

A logistic model can describe the population growth with density-

dependent birth and death rates, assuming that the availability of

resources at a site does not vary over time and that every future

individual added to the population imply a decreased per capita growth

(eqn 2).

K

NrN

dT

dN1 (eqn 2) (Gotelli 2001)

In other words, the change in population size (dN) over time (dT) is a

function of a site specific constant (r), the population size (N) and the

carrying capacity (K) of the site. (1 – N/K) corresponds to the unused

proportion of available resources, where r is the population success of

survival (B-D, eqn 1). This means that a population will stop growing

when either r or N equals 0, as well as when N = K. The population is in

equilibrium when dN/dT=0 i.e. N = K, when the population growth

reaches carrying capacity. This model can be used to predict the size of a

crayfish population at a certain site before and after changes in

environmental factors (K) and changes in survival (for example, the time

a population needs to recover after a disease or increased fishing).

However, a more complicated model incorporating climatic factors, and

weather and population density dependent factors was used to

investigate the cause of crayfish catch fluctuations in the River Ljungan

(I).

2.2.3 Climatic impact

The size of the annual crayfish harvest for adults longer than 9 cm in

the River Ljungan fluctuated throughout the years. A prerequisite for

the catch is that the crayfish reach the harvestable size and are actively

10

seeking food during the harvest occasions. The size of the harvest is

therefore a consequence of the size of the harvestable crayfish cohort and

the behavior of the crayfish. The size of the harvestable crayfish cohort is

the result of a long-term process over several years, whereas the

behavior is short-term. As mentioned before, the crayfish is a

poikilothermic organism and, hence, the life cycle and behavior are

largely governed by temperature. Crayfish catches in a southern

Swedish lake were shown to respond to winter temperatures with time

lags of several years (Olsson et al. 2009).

Regional weather is partly a consequence of large scale climate. The

North Atlantic Oscillation (NAO) directs primarily the winter weather

pattern in the northern hemisphere, and when the NAO index is high,

winter in northern Europe is humid and warm, whereas low index

implies the opposite weather pattern (Hurrel & Deser 2009). Climate

impact is difficult to predict because it affects the life cycle of crayfish,

both directly and indirectly and in different ways, at different scales and

at different stages. In paper I the influence of both large scale climatic

and regional weather patterns in terms of the NAO index, air

temperature and water flow on crayfish catches was investigated.

CPUE was assumed to reflect population size and the time series of

crayfish catches from the River Ljungan was compared pair-wise with

cross correlation analysis (CCA) using the NAO index, air temperature

and water flow time series from measurement stations in the vicinity of

the river. When large coefficients appear in a time lag, you may suspect

that the time series are dependent (Huitema & Laraway 2007).

Significant correlations were therefore used to develop two separate

linear regression models (Model 1, Model 2) that predicted the

magnitude of crayfish catches based on the climatic and weather

variables. Model 1, a modified Ricker Model, predicted the catch growth

rate from population density dependent factors and environmental

variables, and Model 2 predicted the magnitude of catch from the

environmental variables only (Ricker 1954, Kölzsch et al. 2007, Olsson et

al. 2009). The most parsimonious models that were significant (p>0.05) in

all variables were chosen from a stepwise approach with a forward and

backward selection of variables and determined with Akaike´s

Information Critera (AIC) and the relative importance of regressors for

the models (Burnham & Anderson 2002, Grömping 2007). The predictive

power of the models was tested with correlations to two independent

datasets from the river.

11

The two models gave almost the same results, but with a better fit to

data for Model 1. The models showed that crayfish catches were

influenced by the NAO index with a time lag of 6 years and by water

flow in May and October with a time lag of 2 years. Model 1 also

included density dependent factors with a time lag of 1 year (i.e. the

magnitude of catch current year was dependent of the previous catch

size).

Weather and climatic factors influenced the size of crayfish catches in

the River Ljungan, but the single most important factor was the

magnitude of the annual harvest. This implies that the population is

affected by intrinsic competition but effects of fishing cannot be ruled

out. The population might need at least a season to replace the captured

cohort with a large body size (i.e > 9 cm) by a smaller cohort after a large

catch.

Figure 3. Tree diagram of Model 1 and Model 2, show implications of the sizes

of previous catch (CPUE), water flow in May two years before catch and NAO index six years before catch, on the crayfish catches in the River Ljungan. The size of the crayfish in the figure corresponds to the size of the modeled catch i.e. a large crayfish means that the catch is large and vice versa. The tree models are built up from a process of several binary splits. An unordered factor is divided into two non-empty groups and the process will stop when the terminal nodes are too small or too few to be split (Ripley 2011). It is noteworthy that during the study period between 1963 and 1990 CPUE was below 6.1 seven times, the average water flow in May was below 95 m

3s

-1 nine times and winter NAO-index

was below -0.69 eight times.

12

In addition to intrinsic competition and harvesting, winter climate

and water flow during the spring and autumn seem to play a role in

population dynamics and act on different cohorts of the population (Fig.

3). The NAO signal with a time lag of 6 year might be related to survival

of eggs or juvenile stages; a positive NAO index 6 years before harvest

implied larger catches. A high water flow seems to be negative for

crayfish, where a large water flow in May or October two years before

harvest implied smaller catches. The results imply that the size of the

crayfish catch is mainly governed by the size of the harvestable cohort

and that the behavior of crayfish (i.e. timing of molt) is of minor

importance in the long-term.

Global climate change is forecasted with high NAO index and raised

precipitation in northern Europe (IPCC 2007, Hurrel & Deser 2009).

Based on the models in paper I, the climate is forecasted, thus providing

a prediction of the effects on noble crayfish in northern environments.

This prediction shows that the effects of climate change might be non-

existent to slightly negative on crayfish catches and therefore on crayfish

populations.

2.2.4 Water regulation

The regulation of water for hydroelectric power leads to large-scale

ecological effects, with the loss of river ecosystems and fragmentation of

habitats and aquatic organism populations (Dynesius & Nilsson 1994).

Former rapids become inundated or lost, and the river becomes more or

less similar to a lake. To satisfy electrical demands, water regulation is at

different time scales with long-term dampening of flow seasonality and

short-term daily fluctuations (Malmqvist et al. 2009).

The life strategies of many organisms are adapted to natural flow

schemes with low flow during the winter, a flow peak in the spring and

high flow in the summer. A long-term regulation with an even water

flow throughout the year might alter the timing of events and have a

negative impact on these organisms (Bunn & Arthington 2002). The

diversity of macro invertebrates located downstream from power plants

is also negatively affected by sudden flushes that occur when the

reservoirs are filled and when a rain fall makes it necessary to open the

dam gates (Malmqvist et al. 2009).

The effects of short-term regulation include changes in discharge,

water depth, temperature and increased siltation (Cushman 1985). A

rapid lowering and rising of the water level increase the risk of stranding

13

and catastrophic drift of invertebrates, while increased siltation might

destroy refuges and prevent production of vegetation (Bunn &

Arthington 2002, Bruno et al. 2010). An effect of lowered water depth is

that shallow shelters become stranded forcing the crayfish to seek new

shelters into deeper water. This unintended movement exposes the

animals to predators and thus increases the predation risk and mortality

(Hamrin 1987, Tulonen et al. 2010).

A new water regulation scheme was introduced in a section of the

River Ljungan in 1976, when the water from this river stretch was

redirected to a power plant located on land. The consequences for

crayfish in the river in relation to this water regulation are discussed in

Paper II.

CPUE was assumed to reflect population size and catch data was

sorted by geographical position (sections 1, 2 and 3; catch areas a, b, c, d

and e; Fig. 2) and catch date before or after the building of the power

plant. Differences in the mean annual values for water flow and median

values of annual crayfish catch between the sites and between the times

before and after the building of the power plant were confirmed with the

Kruskal-Wallis test, followed by the Dwass-Steel-Chritchlow-Fligner-

test. In Section 1, the differences between CPUE within the catch areas

were compared to determine if these were associated with changes in

water flow.

The most upstream section of the study area (section 1) had the

lowest annual water flow already before the water from this river stretch

was redirected to the power plant on land. But the difference was even

more pronounced after this measure when the annual water flow was

lowered by about 90% in this stretch of river and the other sections were

unaffected.

The median CPUE after the new water regulation scheme decreased

in Section 1 and decreased slightly in Section 3, with Section 2

unaffected. Within Section 1, CPUE decreased significantly in the

upstream catch areas A, B, C and D with no significant difference in

catch area E.

The building of a new power plant with water from the river

redirected to the plant, inferred a new water regulation scheme in

Section 1. This implied a low and even water flow with occasional peaks

compared to the scheme with a maintained flow and seasonal variation

14

that persisted for Section 2 and 3 during the study period. The new

scheme was negative for the crayfish in Section 1 and the effects were

most pronounced immediately downstream from the water intake to the

bypass tunnel. For Sections 2 and 3 these effects were negligible.

The regulation of water flow combined with the reduced water flow

decreased the species richness of invertebrates, which was not the case

where only regulation occurred (Giller & Malmqvist 1998). This might

perhaps explain the reduced crayfish catches in Section 1, where the

water flow was decreased and regulated after 1976, while the water flow

in Sections 2 and 3 only were regulated.

2.3 Field study

2.3.1 Experimental setup

Five reintroduction sites were chosen for capture-recapture

experiments (A, B, C, D and E; Fig. 2). In total, 120 baited traps, evenly

allocated on 24 lines, were positioned over-night along both sides of the

river bed (Fig. 7). Covering a total area of 1 hectare, the experimental

setup stretched downstream 100 metres from the reintroduction sites (A,

B, C, D and E; Fig. 2). The distance between the traps was 10 metres,

which is within the range that crayfish can spot and be attracted by bait

(Acosta & Perry 2000, Cukerzis 1989 and Fedotov 1993, cited by

Kholodkevich et al. 2005).

At each site 700 animals were caught, marked individually with

Passive Integrated Transponders (PIT-tags) and released at the same

spot during the second weeks of June, August and September from 2007

to 2010 (Fig. 4). Data were collected using a protocol that noted the

length, moult phase, fecundity and existent injuries.

2.3.2 Capture-recapture methods

Population trends are essential knowledge in the decision-making of

management actions and evaluation of conservation measures (IUCN

1998, Vié et al. 2009). There are plenty of methods to choose between;

from simple counts and indices to more complicated capture-recapture

methods (Seber 1986, Williams et al. 2002).

A capture-recapture method consists of several capture occasions. At

the first occasion, all animals are marked and released at the same spot

as for capture. During subsequent occasions unmarked animals are

marked and the relationship between the marked and unmarked

15

Figure 4. A male noble crayfish released to the River Ljungan, after marking with

the PIT-tag. In a few minutes the crayfish will locate a shelter to avoid exposure to predators, such as perch (Perca fluviatilis) and pike (Esox lucius). Photo: Jenny Zimmerman.

animals is used to estimate the animal abundance. The simplest capture-

recapture model is the Lincoln-Petersen estimation, which only requires

two sampling occasions (Petersen 1896, Lincoln 1930). It is a so-called

closed population model, which assumes a constant population size

during the study. This implies neither events of birth and death nor the

occurrence of any immigration and emigration between sampling

occasions (Pollock et al. 1990). The Lincoln-Petersen estimation assumes

equal catchability during sample occasions. With several recapture

occasions other closed population models considering heterogeneity,

temporal and behavioral effects of trapping can be used (Pollock et al.

1990).

In long-term studies, the assumption of constant population size is

not realistic and open population models considering events of birth and

death are used instead. The population abundance can be estimated with

the Jolly-Seber model from the probability to catch an individual (Jolly

1965, Seber 1965). A prerequisite for this model is that all individuals

caught during previously sampling occasions are marked and released

to the study area. The Cormack-Jolly-Seber model, however, gives

survival rates based on the probability that an individual has survived

until the sampling and only the capture history of each individual is

16

therefore needed for estimation (Pollock & Alpizar-Jara 1985, Pollock et

al. 1990). Pollock (1982) presented the robust design, where sampling

occurs on two temporal scales; several short-term investigations where

closed models can be used and a long-term investigation that applies to

open models.

Common to capture-recapture models is the assumption that marks

are neither lost between capture occasions nor unobservable at recapture

(Pollock et al. 1990). This requires synchronization between the time

duration of the marking method and the choice of capture-recapture

model. Temporary methods such as paints (Fig. 5), attached streamers

and radio isotope marking last for a limited time and can be used if the

study period is short. Semi-permanent methods like tags, neck collars

and radio telemetry, or permanent tattoos, branding, passive integrated

transponders (PIT-tags, Fig. 6) or visible implant fluorescent elastomer

(VIE) are more convenient for long-term studies (Beausoleil et al. 2004).

The moulting behavior of crustaceans makes long-term marking

difficult. Paints and fluorescent marking only last until the next moult,

whereas branding or piercing may last for several moults (Abrahamsson

1965, Brandt & Schreck 1975 and references herein, Guan 1997). Only

recently after the development of PIT-tags, VIE and coded microwire

tags (CWT) could crayfish be individually, permanently marked

(Haddaway et al. 2011).

In papers I-III CPUE was used as an index of population size, in

paper III the CPUE index was compared with capture-recapture models

based on PIT-tags and in paper IV capture-recapture models were used

for population estimations and to follow individuals over several years.

Figure 6. Noble crayfish marked

permanently with PIT-tag. The PIT tag has a unique code that is read with a reading device. Photo: Renée Lindblom

Figure 5. Noble crayfish marked

temporarily with paint. The mark will be lost when the crayfish moults next time. Photo: Jenny Zimmerman

17

2.3.3 CPUE versus capture-recapture methods

There is a need for scientifically-based, accurate and cost-efficient

methods to monitor and evaluate reintroduction programs. The

monitored indicators should be measurable, precise, consistent, and

sensitive to the target (IUCN/SSC 2008). CPUE is an index that has been

used for population estimations for fish (Maunder et al. 2006) and

crayfish (Skurdal & Taugbøl 2002, Westman et al. 2002, Olsson et al.

2009, Erkamo et al. 2010). But the accuracy of this population estimation

method has been questioned (Harley et al. 2001, Goodyear et al. 2003,

Maunder et al. 2006, Laloë 2007). Local fishermen have used CPUE

calculated from the standardized trapping of crayfish in the River

Ljungan since 2004 to evaluate the success or failure of the

reintroduction program. The aim of paper III was to investigate if their

efforts were enough to reliably evaluate the program.

The relationships between CPUE using different efforts (15

traps/hectare and 120 traps/hectare) and population estimations were

investigated at five sites (A, B, C, D and E; Fig. 2). The population

estimations were made with log linear closed population models and

followed Pollock´s robust design. The Mann Whitney U-test was used to

compare the differences in CPUE, and the Pearson correlation test and

linear regression were used to investigate the relationships between log

transformed CPUE and the estimated population sizes.

In all, CPUE with low and high efforts and population estimations

with capture-recapture models showed an increasing trend during the

study. The variation of CPUE was larger with low effort and the values

of CPUE were larger compared to high effort. CPUE was positively

correlated to the population estimations and the CPUE with a high effort

had a greater correlation to the abundance than CPUE with low effort.

CPUE might be considered suitable for monitoring only if it is

properly standardized (Hockley et al. 2005). The number of traps is

obviously important for reliable estimates regarding the abundance and

population trends from CPUE. The more traps, the more accurate the

result (III). However, when the effective radius from the traps overlap;

i.e. there are more than one trap within the range that crayfish can spot

and be attracted by bait, further traps will not improve the accuracy

(Peay 2004).

The trapping procedure performed by the fishermen in the River

Ljungan was standardized and performed with the same equipment, at

18

the same time of the year (late-August) and at the same spots from year

to year. These actions seem sufficient for a qualitative estimation of

population trends and to handle the limitations of CPUE concerning the

bias of size and sex on the estimation caused by the trapping or by

crayfish moulting behavior (Abrahamsson 1966, Rabeni et al. 1997,

Westman & Pursiainen 1982, Dorn et al. 2005, Price & Welch 2009). The

minimalistic monitoring design used by the fishermen is a less accurate,

though it is a reasonable method for estimating population trends. The

accuracy can be improved by increasing the number of traps. The simple

design that can be done by amateurs makes the method inexpensive

compared to capture- recapture methods. Therefore, the method is

valuable for the evaluation of reintroduction programs.

2.3.4 Body growth after reintroduction

The body growth of crayfish and other crustaceans over several

seasons has been studied very little due to their behavior, which makes

simple marking techniques impossible to apply. A marking on the

crayfish shell is lost simply through moulting. In recent years the

development of new marking techniques have made it possible to

reliably follow individuals in the wild for several years (Bubb et al. 2002,

Camp et al. 2011, Haddaway et al. 2011).

In the harsh climatic conditions with low temperatures that prevail in

waters at high latitudes, such as the River Ljungan (62˚N), the rate of

physiological processes and digestion decrease and cause a shorter

growth season. This can influence organisms into a less somatic growth,

longer life span and delayed maturation compared to conspecifics at

lower latitudes (Momot 1984, Karasov & Martinez del Rio 2007). A result

of delayed maturation is that the build-up of populations may be slow

and sensitive to disturbance.

The body growth of noble crayfish in relation to water temperature

and other physical and chemical properties was investigated at the sites

A, B, C, D and E (Fig. 2). Differences in size structures and body growth

rates were confirmed between sites with the Kruskal Wallis test

followed, by the Conover-Inman posthoc test. Linear growth models

were developed from recapture data. The powers of the models were

tested with Pearson's product moment correlation tests, between

predicted values from the models and values from measurements of

animals that were measured two or three years earlier.

19

Most animals moulted once a year with length increments close to the

maximum that is reported for the species (Skurdal & Taugbøl 1994). The

male growth was larger than the female growth and the size of the

length increment did not differ among the sites, which was apparently

not associated to differences in habitats or water temperatures.

Body growth measurements were conducted on noble crayfish in the

River Ljungan during the 1960s (Abrahamsson 1972), when the length

increments were 31 % smaller for females and 19 % smaller for males

compared to today. Obviously, other conditions were prevalent in the

river 50 years ago, such as more fishing and a different water regulation

scheme (I, II). As well, the water temperatures were lower and the noble

crayfish population was denser. Therefore, it cannot be precluded that

these differences in climate and population density positively enhance

the body growth rate as observed presently in the River Ljungan.

From paper IV it is concluded that it is possible to individually

follow noble crayfish in the wild for several years using PIT-tags and

that noble crayfish have the ability to grow equally as fast in the

northern edge of its distribution area as in southern locations (<60˚N).

3 GENERAL DISCUSSION

3.1 Methodologies to monitor noble crayfish

Two methodologies were used in this thesis to monitor and

investigate noble crayfish. The investigations at the population level

were made with CPUE as the population index and estimations of

population abundance from capture-recapture methods based on PIT-

tags. PIT-tags were used to identify crayfish at the individual level.

The CPUE index was sufficient for long-term population studies in

relation to climate (I), for the evaluation of population alterations after a

large-scale habitat change (II) and for the evaluation of population

trends after reintroduction (III). In addition, the capture-recapture

method based on PIT-tags was suitable for estimations of population

trends (III).

The accuracy of the CPUE-index seems adequate provided that

crayfish behavior is considered. Investigations should be performed

when the crayfish are actively entering baited traps, i.e. in between

moult and mating season. Paper III also showed that it is possible to

increase the accuracy of the CPUE-index by increasing the number of

20

traps. The accuracy of estimates from the capture-recapture method

seemed to gradually increase (III). This was most likely a consequence of

the increased proportion of marked crayfish in the study area and

several marking occasions are needed to achieve an improved accuracy

from capture-recapture methods.

The CPUE-index was standardized in that the yearly trapping

occasion occurred during the same season and the numbers of traps and

their locations were the same throughout the years (III). The use of the

CPUE-index can be expanded with analyzes of size structure, fecundity

and proportion of injured crayfish among the years, if measurements of

length, maturity of eggs and injuries are included in the investigation

protocol.

In addition to estimations of population trends, population growth

rates, survival rates and population densities, permanent marking with

PIT-tags also provides an opportunity to follow the performance of an

individual crayfish. Marking lasts for at least 3 years in noble crayfish

(IV). Depending on which measurements are made during capture

occasions, information about body growth (IV), fecundity, moult

frequency, history of injuries, migration pattern, etc. can be achieved.

The PIT-tag is implanted inside the crayfish body and is therefore not

recognized without a reading device. This is an advantage because the

appearance of marked animals does not differ compared to unmarked

and their behavior or survival is not affected (Bubb et al. 2002).

However, a disadvantage is that special equipment to recognize a

marked crayfish is needed. This is unsuitable in fishing areas, where an

obvious risk is that fishermen will remove marked crayfish by mistake.

The CPUE method only requires baited traps compared to the

capture-recapture method, which also needs PIT-tags and a reading

device. Besides the extra equipment needed for the capture-recapture

method, it is also based on multiple capture occasions. Overall, this

makes the CPUE method easier to perform and less expensive compared

to the capture recapture method based on PIT-tags. However the costs of

the capture-recapture method can be decreased if the PIT-tags are

replaced with a less expensive marking method.

21

Table 1. A brief comparison between the CPUE-method and the capture-

recapture method based on PIT-tags (CRM).

CPUE CRM

Population abundance X

Population trends X X

Population density X

Population growth rate X X

Population survival X

Migration rate X

Individual performance X

Tags and reading equipment are needed X

Cost Low High

Effort Low High

Method handiness Easy Complicated

The choice of method has to be adapted to the situation, with Table 1

perhaps supporting this. A comparison of the most important properties

of the CPUE-method and the capture-recapture method based on PIT-

tags show that if the need is only to know crayfish population trends, the

best choice is the CPUE method because it is easy to perform, with less

effort and less cost than the capture recapture approach (Table 1).

Otherwise, the capture-recapture method should be used.

3.2 Management of noble crayfish

3.2.1 Reintroduction

The reintroduction of noble crayfish to the River Ljungan is so far

successful. The body growth of individual crayfish is remarkably high

(IV) and the sub-populations show an increasing trend (III) , though it is

difficult to know exactly why. However, the reintroduced crayfish were

from the same county and had the same genetic origin (Gross et al. 2012).

It could therefore be expected that the crayfish were well suited to the

seasonal climatic variations of the region. Many specimens were

reintroduced. Thus providing a boosted start for population

development (Taugbøl & Peay 2004)

Still, one of the most important measures in the project has been the

involvement of the local inhabitants in deciding the reintroduction sites

and in the practical work with introduction and monitoring (Ånge

kommun 2010). To ensure the long-term nature of the project, the locals

22

were trained in management and the local papers annually reported the

progress of the project to the general public (Zimmerman 2011).

3.2.2 Sustainable fishing

It may seem contradictory to argue for the fishing of an endangered

species. However, in Scandinavia noble crayfish have long been a part of

the culture. The risk that future generations of local population will not

have the opportunity to experience recreational fishing is a strong

incentive to conserve the species. This commitment was manifested in

the voluntary work to reintroduce noble crayfish to the River Ljungan by

the local inhabitants (Ånge kommun 2010, Zimmerman 2011). To

maintain this kind of commitment among locals, they must have the

privilege to retain their fishing traditions. Hence there is a need for local

management and sustainable fishing.

Fishing affects the sizes and size structures of populations and as

indicated in paper (I), recovery and buildup of the population after a

large catch in the River Ljungan required at least a season. The time

needed depends on the recruitment rate, which in turn is a consequence

of body growth rate and fecundity. A high body growth rate implies that

the time between birth and sexual maturity as well as the time needed to

reach a harvestable size may be shortened. Females will have the ability

to reproduce additional times during their lifetime and juveniles will

rapidly reach adult size. The result will be a faster build up of the adult

cohort. This process might be enhanced with increased water

temperature, low population density or a combination of these factors

(IV).

Sustainable fishing is a challenge, though some lessons can be learned

from the fisheries industry. A common strategy is to harvest down to a

very small population size and expect recovery. This destroys ecological

interactions when the dominant predator fish is suppressed and its

ecological niche is occupied by other organisms, making recovery

difficult. For example, cod (Gadus morhua) in Alaska has not yet

recovered after the population collapse in the 1990s (Frank et al. 2007).

Overfishing is especially dangerous for species with a slow process of

recruitment, e.g. noble crayfish in northern environments, and should be

avoided (Momot 1984).

The strategy called maximum sustainable yield (MSY) aims to

maximize the population growth and thereby increase the recruitment to

23

the harvestable cohort. It is based on the logistic model described in

section 2.2.2, where the maximum population growth rate occurs when

the population size is half of the carrying capacity of the habitat (Gotelli

2001). The size of the carrying capacity must be determined, from which

the fishing quotas are drawn up. MSY may be hazardous because the

value of the carrying capacity is not constant, but varies with changes in

habitat and without updated quotas there is a risk of overfishing. The

consequence of a change in carrying capacity was shown in paper II,

where a large-scale habitat change implied dramatic decreased catches of

noble crayfish in a section of the River Ljungan.

Hence, the regulations for the fishing of crayfish have to be adapted

to the population size and be robust to environmental changes.

Regulating the numbers of traps is important, but the most effective

recovery measure after overfishing seemed to be a shortening of the

legal fishing period (Skurdal & Taugbøl 2002). The use of size limits, no-

take zones and avoiding reproductive females have been suggested as

tools for a sustainable harvest (Jones et al. 2006).

Figure 7. The goal with a sustainable, recreational fishing of noble crayfish is to

have an acceptable catch from year to year and to maintain an interest for the species among the public. The equipment at this photo was used for the trapping of crayfish for capture-recapture estimations and for the standardized fishing, performed by the fishermen, to monitor the population development after reintroduction of the noble crayfish to the River Ljungan. Five traps were attached to the blue line, with a snap hook. The yellow boxes contained pelleted, bait. Photo: Anna Broich.

24

The aim of reintroducing noble crayfish to the River Ljungan is to re-

establish the species to the river and then establish a recreational fishing

(Fig. 7) (Ånge kommun 2010). Paper (I) showed that the most important

factor determining the size of the catch was the size of the previously

year´s catch. Hence, when the crayfish stock is large enough, there will

be additional pressure on the population from fishing besides the

environmental pressure. To avoid overfishing and realize a sustainable

fishing of crayfish in the River Ljungan, my suggestions to the fishermen

are:

Monitor the population trends, NAO-index and water flow

in May and October.

Use the results from the monitoring to determine the number

of allowed fishing days and traps.

Collect data about the catch size and effort from legal fishing

and use it to evaluate the sustainability of the fishing.

Enhance the buildup of the harvestable cohort by

-saving reproductive females

-introduce a size limit of 10 cm

-provide proper shelters for the non-harvestable

cohort.

3.3 Future research The more knowledge gained, the more questions are raised, and my

research has raised my curiosity with regards to

Flow effects on the survival of different cohorts of crayfish. What are

the biological mechanisms that imply a decreased crayfish catch two

years after a large water flow in May or October?

The body growth rate of crustacea is the result of length increment

per moult and the number of moults (Hartnoll 1982). The extreme length

increments of noble crayfish found in the River Ljungan lead to a

number of issues. Are large length increments common in harsh

climates? What is the breaking point regarding the profitability with

several moults instead of one? Will the crayfish in the River Ljungan

moult twice a year in the future? If so, will the extreme length

increments remain?

25

The reintroduction of noble crayfish to the River Ljungan has gone

well, but why? Is it the massive introduction with numerous specimens?

How many crayfish need to be inserted for success? Does it matter

where you put them? What is the migration from the release sites? What

affects the migration?

3.4 Noble crayfish in a changing world

The noble crayfish population in the River Ljungan was established at

almost the same time as when the first cars were registered in Sweden.

Since then, automobiles in Sweden have increased to over 4 million,

society has undergone revolutionary changes and the River Ljungan has

received profound alterations (SCB 2012). A century ago the river was

free flowing; today the water flow is regulated both daily and seasonally

in separated reservoirs. The climate has changed. This has been

Figure 8. The present distribution areas for the noble crayfish (blue dots) and the

signal crayfish (red dots) in Sweden. The ellipse in the right figure shows recently made illegal introductions of signal crayfish to water courses in the northern Sweden. These introductions are an immediate threat to the noble crayfish populations and have a low probability for success (Sahlin et. al 2010). Figure: Patrik Bohman, SCD, Swedish University of Agricultural Sciences, Institution of Freshwater Research.

26

manifested with an increased NAO index during the winter since the

1960s (I) and increased water temperature during the summer (IV) with

a prolonged growth season as a result. Not much is known about the

crayfish population in the River Ljungan from the early 20th century, but

the population has been subject to fishing since the 1950s. A sudden

extinction occurred for unknown reasons in 1999. However, in the early

21st century the noble crayfish population was reintroduced and is

today re-established in the river (III). During the century when noble

crayfish were found in the River Ljungan they have become an

important element of the local culture. The local inhabitants are

concerned about the species and have been working to reestablish the

species for future conservation. The future survival and development of

this crayfish population in particular and noble crayfish in northern

environments in general is unpredictable. Global climate change is

forecasted to raise the NAO index, summer seasonal temperatures and

precipitation in northern Europe (IPCC 2007, Hurrel & Deser 2009,

Kjellström et al. 2011). This will probably enhance body growth (IV),

perhaps with an increased number of moults, while the population

development will probably be more or less stable or slightly decreased

(I). Still, there is the increasing threat of illegal introductions of signal

crayfish that in recent years have appeared in several water courses in

the vicinity of the River Ljungan (Fig. 8). An introduction of signal

crayfish may eradicate the noble crayfish population in the river within a

few weeks.

It is our responsibility to conserve this species for future generations

and thus the future of the noble crayfish is determined by us.

“We do not inherit the Earth from our

parents but we borrow it from our children.”

(Native American proverb)

27

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stream food webs: roles of omnivory, substrate heterogeneity and sex.

Oikos, 98, 512-522.

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Tong R. 2009. The IUCN Red List: a key conservation tool. Pages 1-14 in

Wildlife in a changing world An analysis of the 2008 IUCN Red List of

Threatened Species™. Vié J., Hilton-Taylor C. and Stuart S.N. eds.,

IUCN, Gland, Switzerland

Westin L. and Gydemo R. 1986. Influence of light and temperature on

reproduction and moulting frequency of the crayfish, A. astacus L.

Aquaculture, 52, 43-50.

Westman K. and Pursiainen M. 1982. Size and structure of crayfish

(Astacus astacus) populations on different habitats in Finland.

Hydrobiologia, 86, 67−72.

Westman K., Savolainen R. and Julkunen M. 2002. Replacement of the

native crayfish Astacus astacus by the introduced species Pacifastacus

leniusculus in a small, enclosed Finnish lake: a 30-year study. Ecography,

25, 53−73.

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Williams B.K., Nicholls J.D. and Conroy M.D. 2002. Analysis and

Management of Animal Populations. Academic Press, San Diego,

California, USA, 242-243.

Zimmerman J. 2011. Slutrapport Förstudie för Älvens Hus - Ett

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Jordbruksverket. Journalnummer 2009-3844.

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5. TILLKÄNNAGIVANDEN

Det här projektet har varit ett samarbete mellan Ånge kommun och

Mittuniversitetet. Jag riktar ett alldeles speciellt tack till Fredrik Westin

som gjorde detta möjligt. Under projektets gång har det varit

fruktsamma samarbeten med både ”Återplantering av flodkräfta till

Ljungan” och Leader-projektet ”Förstudie för Älvens Hus”. Jag vill

också passa på att tacka för stipendier från Makarna Öhrns fond, Helge

Ax:son Johnsons stiftelse, Stiftelsen Markussens studiefond, samt från

IAA18 organizing committe, som har möjliggjort att jag kunnat resa och

få internationella kräftkompisar.

Det här med att doktorera har varit fantastiskt skoj och jag hade inte

fixat det utan hjälp. Jag vill rikta ett stort tack till ALLA som bidragit till

att jag fått en bra doktorandtid och till att mitt projekt kunnat

genomföras!

Tack alla som bidragit med data; Sötvattens-laboratoriet och Eva Sers,

Vattenregleringsföretagen, EON, Ljungandalens forskarverkstad,

fiskevårdsområdena speciellt Borgsjö Mellersta och Viken för långa

dataserier, samt Åsa och Johan på Ånge kommun för att ni sammanställt

data när jag behövt det. Ett särskilt tack till Magnus Fürst som förklarade

hur fångstdata i Ljungan kommit till och till Bertil Eriksson som samlat

in data och dessutom visste att det fanns data ända sedan 1963 och vart

de gick att hitta! Alla assistenter genom åren ska få en stor kram; Anna -

den första, Gustav - den största, Tita - den riktiga kräftfiskaren, Carina -

den mesta, Kim - den hungrigaste och Tom - den starkaste. Praktikanter,

examensarbetare och andra som hjälpt till är Jonas - legitimerad

kräftmålare, Rocio - utbildad roddare, Reneé – fotograf och Tobias –

känd från TV. Ett tack också till Johan som sprut-målade flöten (som jag

sedan rationaliserade bort). Jag hade inte kunnat drömma om det

engagemang som finns i bygden för flodkräftan. Tack Permascand AB,

Ånge Judoklubb och Karlsro Flyers för att vi fick tak över huvudet.

Det har varit kul att få lära känna alla fiskevårdsområden och

ingenting kommer någonsin vara omöjligt för er. Ni har ställt upp för

mig på ett otroligt sätt, vare sig det handlat om roddhjälp, utlåning av

båtar, burar, flöten, eller om att lyssna på min svada. En del av er har jag

haft lite extra mycket att göra med genom åren; Kjell – organisatören och

stöttepelaren, Berit – kvinnan som har hand med både människor och

kräftor, Åke och framlidne Lennart Nordin; ni lärde mig fiska kräftor på

riktigt. Kurt och Elsy - det var gudomligt att efter fyra timmars ösregn få

40

torka upp i er varma bastu. Sören – alltid beredd att låsa upp bommen,

Kenth-abborrdödaren, Håkan – sambandscentral för kräftutsättningar

och Janne – det du inte vill veta om kräftor det finns inte!

Jag hade inte klarat mig utan mina speciella kräftmentorer Anders,

Ivar, Tommy och Lelle. Inga frågor har varit för små för era öron. Ljunga

Frukostklubb lärde mig att frukost intas på tåget i trevligt sällskap,

medan tonhallsgänget diskuterade högt och lågt under lunchen. Jag tror

att våra nya fotbollsregler med stildomare kommer att göra succé. FIFA

here we come! NAT, denna trivsamma arbetsplats, tog emot mig med

öppna armar. Vad hade fikarummet, expeditionen och labben varit utan

Ingrid, VIK/VER, Torborg och Håkan? Jag har gillat den osannolika

mixen på NAT och i doktorandgruppen. Till min nuvarande

rumskompis Sara - jag hoppas att vi haft lika villkor på rummet och att

du och hararna kommer fortsätta att trivas ihop! Jag tänkte också passa

på att tacka vaktmästeri, städ och bibliotek för god service.

Vad glad jag blev när du Nils läste och gav kommentarer på kappan.

Thomas – tack för att du trott på mig från vårt första möte. Vilka

intressanta diskussioner vi har haft. Jag har uppskattat att du vågat

släppa ut mig på djupt vatten och att du inte blev arg när jag körde

sönder bilen…

Ett stort tack också till mina föräldrar, svärföräldrar, syskon med

familjer för att ni ”älskat” kräftor och statistiska analyser under de

senaste åren. En extra kram till min mormor för att du alltid bryr dig om.

Ni som står mig allra närmast; Irma, Edit, Karin och Erik har sett att jag

under de här fem åren blivit äldre, klokare och mer förvirrad än

någonsin. Jag har glömt saker, varit på fel ställe och fastnat framför

datorn. Men jag är så innerligt glad över att ni finns och nu går vi mot

nya djärva mål - eller som det står på vår dörr – we interrupt this family

for football season!

Johannisberg 11 april, 2012