VARIATION IN EARLY LIFE-HISTORY CHARACTERISTICS OF SYMPATRIC

RAINBOW SMELT POPULATIONS IN LAKE UTOPIA, NEW BRUNSWICK

by

Jennifer Lynn Shaw

Bachelor of Environmental Science, University of Guelph 1996

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

Masters of Science

In the Graduate Academic Unit of Biology

Supervisor: R.A. Curry, Ph.D., UNB, Biology

Examining Board: T.J. Benfey, Ph.D., UNB, Biology – Chair

R.A. Cunjak, Ph.D., UNB, Biology – Internal Examiner M. Wiber, Ph.D., UNB, Anthropology – External Examiner

This thesis is accepted by the Dean of Graduate Studies

THE UNIVERSITY OF NEW BRUNSWICK

January, 2006

© Jennifer L. Shaw, 2006

ii

ABSTRACT

Three sympatric morphotypes of rainbow smelt (Osmerus sp.) have been

identified in Lake Utopia, New Brunswick. The ‘giant’ form is larger (20.2 ± 2.8

cm SD), has fewer gill rakers, and spawns earliest before other forms and in

different streams. The ‘normal’ form is smaller (13.1 ± 1.9 cm) with increased

numbers of gill rakers. The ‘dwarf’ form is the smallest (9.9 ± 0.9 cm) and has the

highest gill raker count. Both normal and dwarf smelt spawn in the same

streams with normal forms beginning earlier and dwarf forms extending spawning

longer. If body size is the keystone biological feature among morphotypes, then

differences in egg size or differential growth rates exist at some time during their

ontogeny. We tested this prediction by comparing egg size, spawning date,

incubation time, hatch size, and growth to determine when a divergence in size

occurs. While some characteristics appeared stable, others displayed inter-

annual variability. Giant larvae hatched earlier, at a larger size and consistently

grew more rapidly as age 0+ fish. Divergence between normal and dwarf forms

was less stable, differing between years. The forms hatched at the same size,

however timing varied and divergence in growth occurred at age 0+, 1+ or 2+

fish. We suggest that genetic factors are most important for maintaining giant

morphotypes and environmental factors, such as lake and stream temperatures

are important in regulating the normal and dwarf morphotypes in Lake Utopia

today.

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ACKNOWLEDGMENTS

I would like to begin by thanking my supervisor, Dr. Allen Curry for giving

me this opportunity and for providing guidance, direction and support along the

way. Thank you to my supervisory committee, Dr. Stephan Peake and Mr. Steve

Currie for providing direction and constructive feedback at various stages of the

process.

This project would not have been completed without the help of many

individuals and organizations. Funding was provided by the New Brunswick

Wildlife Trust Fund and Fisheries and Oceans Canada’s, Student Subvention

Grant Program. Staff at the St. Andrews Biological Station, Marine Fish Division

of Fisheries and Oceans Canada provided equipment and lab support for otolith

microstructure procedures. The New Brunswick Department of Environment and

Local Government provided water temperature data. Thank you to Marcia

Chiasson, Emily Kitts, Chad Doherty, Mark Gautreau, Eric Chernoff and

Jonathon Freedman who provided much needed help in the field and in the lab. I

would also like to acknowledge and thank the many graduate students, summer

students, staff and faculty who provided help, shared ideas and were around to

talk when I needed it.

Lastly, I would like to thank my mom and dad, Karen and Ken, my sisters,

Lori and Michelle and my husband, Eric for always being there for me and

supporting me. You are what matters most.

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TABLE OF CONTENTS

ABSTRACT……………………………………………………………………………..ii

ACKNOWLEDGMENTS ..................................................................................... iii

TABLE OF CONTENTS ..................................................................................... iv

LIST OF FIGURES .............................................................................................vi

1 GENERAL INTRODUCTION ..................................................... 1

1.1 Life-History Variation ................................................................. 1

1.2 Evolutionary Significance of Size and Growth ........................... 3

1.3 Rainbow Smelt Biology.............................................................. 4

1.4 Life-history Variation in Rainbow Smelt ..................................... 5

1.5 Ecology of Morphotypes ............................................................ 6

1.6 Genetics .................................................................................... 8

1.7 Species At Risk Designation...................................................... 9

1.8 Research Objectives and Thesis Outline................................... 9

2 METHODS............................................................................... 11

2.1 Study Area............................................................................... 11

2.2 Early Life-History Characteristics............................................. 12

2.3 Growth ..................................................................................... 14

2.3.1 Field Sampling..........................................................................14

2.3.2 Otolith Microstructure Procedure ..............................................15

2.4 Statistical Analysis ................................................................... 18

3 RESULTS ................................................................................ 23

3.1 Early Life-History Characteristics............................................. 23

v

3.1.1 Spawning, Incubation, and Hatching Period.............................23

3.1.2 Water Temperature ..................................................................24

3.1.3 Egg and Hatch Size..................................................................25

3.2 Growth ..................................................................................... 26

3.2.1 Larval Growth ...........................................................................26

3.2.2 Adult Age and Growth ..............................................................27

3.2.3 Lake Temperature and Growth.................................................28

4 DISCUSSION .......................................................................... 41

4.1 Size Differences in Early Life ................................................... 41

4.2 Evolutionary Origin of Morphotypes......................................... 44

4.3 Summary ................................................................................. 48

5 LITERATURE CITED............................................................... 49

CURRICULUM VITAE

vi

LIST OF FIGURES

Figure 1: Lake Utopia (45°10’, 66°47’) and its smelt spawning tributaries. The giant form spawns in Mill Lake Stream, Trout Lake Stream and Spear Brook. Normal and dwarf forms spawn in Smelt, Unnamed and Second Brooks. ...............................................................................20

Figure 2: Relationship between otolith growth and somatic growth. Larval smelt captured in Lake Utopia in 2003 ( ▲ ), r2 = 0.93 (n=142) and 2004, r2 = 0.90 ( ○ ) (n=140). Adult giant, normal and dwarf smelt captured by dip-nets during spawning in Mill Lake Stream, Smelt Brook, Second Brook and Unnamed Brook in 1999 ( ■ ), r2 = 0.58 (n=158) and 2003 ( Δ ), r2 = 0.90 (n=108). ...................................................................21

Figure 3: Spawning ( ▄▄ ), incubation ( ▄▄ ) and hatching ( ▄▄ ) period of giant smelt in Mill Lake Stream, and normal and dwarf smelt in Smelt, Unnamed and Second brooks in Lake Utopia, 2004. Hatch marks indicate approximation of dates. ......................................................29

Figure 4: Mean daily water temperature (± 1 SD) of spawning tributaries in Lake Utopia for giant smelt (Mill Lake Stream and Spear Brook) and normal and dwarf smelt (Second Brook, Unnamed Brook and Smelt Brook), 2004.................................................................................................30

Figure 5: Mean egg size (± 1 SD) of giant ( ■ ), normal ( O ) and dwarf ( ▲ ) mature female smelt captured in Trout Lake Stream, Mill Lake Stream, Unnamed Brook, Smelt Brook and Second Brook in 2004 (total sample size n=120). Mean hatching length (± 1 SD) of larval smelt captured in Mill Lake Stream, Second Brook and Smelt Brook in 2004, and Smelt Brook and Unnamed Brook in 2002 (total sample size n=360). .....................................................................................31

Figure 6: Hatching date calculated from otolith daily growth rings of normal and dwarf larvae captured by Neuston trawls in Lake Utopia in summer 2003 (n=138) and 2004 (n=96). No larvae of giant smelt were captured...........................................................................................33

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Figure 7: Size and age of 0+ larval fish captured by Neuston trawls throughout the summer in 2003 and 2004 in Lake Utopia. ................................35

Figure 8: Back-calculated, mean length-at-age of dwarf ( ▲, -SD ) and normal ( ○ , +SD) larval smelt captured in Lake Utopia on June 25, July 2, July 25, August 26 and September 18, 2003 (n=73), and on June 1, June 28, July 18, July 29 and August 28, 2004 (n=62). ...................36

Figure 9: Back-calculated mean length-at-age (± 1 SD) of adult giant ( ■ ), normal ( ○ ) and dwarf ( ▲ ) smelt captured by dip-nets during spawning in Mill Lake Stream, Smelt Brook, Second Brook and Unnamed Brook in 1999 (n=108) and in Mill Lake Stream, Trout Lake Stream, Smelt Brook, Second Brook and Unnamed Brook in 2003 (n=108). ..........38

Figure 10: Back-calculated mean yearly growth of adult smelt for age 1 (––––– ), age 2 (–— –—), age 3 ( — — —) and age 4 ( – – – – ) year classes . Mean summer air ( ········ ) and surface water (– · ·– · · ) temperature from 1996 to 2004............................................................................40

1

1 GENERAL INTRODUCTION

1.1 Life-History Variation

Many north-temperate fishes display variable life-history strategies, often

in sympatry, in the same lake or river system. Sympatric anadromous and

resident forms occur in Atlantic salmon, (Salmo salar), (Aubin-Horth and Dodson

2004), sockeye salmon (Oncorhynchus nerka) (Wood and Foote 1996; Foote et

al.1999), brook charr (Salvelinus fontinalis) (Power 1980; Nordeng 1983), brown

trout (Salmo trutta) (Ryman et al. 1979; Jonsson 1985), rainbow trout

(Oncorhynchus mykiss) (Kline et al. 1990) and pond smelt (Hypomesus

nipponensis) (Katayama et al. 2000). Differences in morphology are also

common in freshwater lacustrine systems. Trophic niche partitioning has

resulted in morphotypes (body types) that differ primarily in body size and gill

raker number that are typically correlated with habitats and resource use (e.g.

benthic or limnetic, planktivorous or piscivorous) (Skulason and Smith 1995).

These differences often result in a typical ‘normal’ form and a smaller, stunted

‘dwarf’ form as seen in lake whitefish, (Coregonus clupeaformis), (Fenderson

1964; Bernatchez et al. 1996), arctic charr (Salvelinus alpinus) (Jonsson and

Hindar 1982; Hindar and Jonsson 1993; Skulason et al. 1996), lake trout

(Salvelinus namaycush) (Moore 2001), least cisco (Coregonus sardinella) (Mann

and McCart 1981) and rainbow smelt (Osmerus mordax) (Lanteigne and

McAllister 1983; Nellbring 1989; Taylor and Bentzen 1993b).

2

Such life-history variation is a direct reflection of the processes driving

micro-evolutionary events such as natural selection, genetic differentiation, and

species formation (Schluter 2000; Barton 2001). However, natural selection

leading to speciation is slow to observe and speciation is often inferred from life-

history divergence (Gould and Johnson 1972; Futuyma 1986). Defining

taxonomic units has been a challenge for fisheries biologists and ichthyologists

for centuries. In north-temperate lakes the extent of genetic differentiation of

sympatric life-history variants is variable with either allopatric or sympatric

origins. Often differences in phenotype related to morphology and habitat use

within a single breeding population, referred to as resource polymorphism, can

also exists. Sympatric Arctic charr morphotypes can result from resource

polymorphism within a single breeding population in some lakes (Nordeng 1983;

Hindar and Jonsson 1993), while representing distinct genetic units in others

arising through sympatric divergence (Svendang 1990). Lake Thingvallvatn

morphotypes in Iceland seem to have arisen from evolutionary consequences of

both; sympatric divergence of a small benthivore, large benthivore and a

planktivore/piscivore group representing three reproductive units, with the

planktivore and piscivore group splitting further into two morphs due to an

ontogentic niche shift based on trophic polymorphism (Jonsson et al. 1988;

Skulason et al. 1989). Sympatric dwarf and normal lake whitefish display genetic

differentiation with multiple origins of trophic morphotypes. Evidence suggests

allopatric divergence followed by secondary contact of two monophyletic groups

due to isolation in separate refugia during the last glaciation, as well as a

3

polyphyletic origin where sympatric radiation has been expressed independently

more than once (Bernatchez and Dodson 1990; Bernatchez et al. 1996; Pigeon

et al. 1997). Rainbow smelt morphotypes in north eastern North America have a

polyphyletic origin and have arisen multiple times through sympatric divergence

(Taylor and Bentzen 1993b). Some populations display a significant genetic

divergence between forms (Taylor and Bentzen 1993b; Saint-Laurent et al. 2003;

Curry et al. 2004) while others may be examples of resource polymorphism

within a single breeding population (Rupp and Redmond 1966; Taylor and

Bentzen 1993b). Consequently, life-history variation challenges fisheries

biologists attempting to manage stocks based on taxonomic units, and more

recently for species at risk such as the Lake Utopia Dwarf Smelt.

1.2 Evolutionary Significance of Size and Growth

Body size is an important factor influencing many aspects of the

physiology, behaviour, and ecology of living organisms (Peters 1983). Different

sizes and growth rates can be achieved by a variety of mechanisms, particularly

when these mechanisms act on the larval and juvenile stage of development

(Miller et al. 1988; Pepin 1991). Egg size and subsequent hatch size has a

positive effect on size and growth of larvae and juveniles (Kazakov 1981; Kamler

and Kato 1983; Skulason 1986). Growth differences during the first growing

season can result from early spawning and hatching, which allows more time for

growth during the first growing season. Larger fish have a growth advantage and

better survival due to increased competitive ability (Arendt and Wilson 1997),

4

increased success as a predator (Blaxter 1986; Hayes and Taylor 1990),

decreased vulnerability to predation (Reznick 1983) and decreased over-winter

mortality (Schultz et al. 1998; Schindler 1999; Curry et al. 2005). Growth

differences in the first or subsequent growing seasons may also result from

ontogentic niche-shifts to different prey sources (Snorrasson et al. 1994).

1.3 Rainbow Smelt Biology

Rainbow smelt are a euryhaline fish native to north-eastern North America

and are found in coastal drainages from Labrador to New Jersey (Scott and

Crossman 1998). They reproduce in freshwater and populations can be

anadromous or strictly freshwater. Smelt are a small, schooling, pelagic species

that are primarily planktivorous, but larger individuals can be macrophagous and

piscivores (Nellbring 1989). Smelt are segregated within their habitat according

to age and size, which is strongly influenced by temperature (Heist and Swenson

1983; Burczynski et al. 1987). Young-of-the-year (YOY) are found in warm

epilimnion water, yearlings in cool water and adults in cold hypolimnion habitats

(Nellbring 1989). Like many zooplanktivorous fish, smelt display a diel migratory

behaviour, remaining deep during the day and moving up near the surface to

feed at night.

Rainbow smelt are iteroparous, spawning in the spring (typically April and

May) as ice cover dissipates. They ascend small tributaries in large numbers

typically at night. Females are broadcast spawners with fecundities of 5,000-

5

40,000 eggs (Scott and Crossman 1998). Eggs are

6

The dwarf and normal smelt of Lake Utopia, New Brunswick have been

studied extensively (MacLeod 1922; Bajkov 1936; Lanteigne and McAllister

1983; Taylor and Bentzen 1993a,b; Taylor 1997). Taylor and Bentzen (1993a,b)

demonstrated morphological and genetic differences between a normal and

dwarf form, based on samples and observations from one or two nights. Curry et

al. (2004) examined the Lake Utopia smelt complex in detail and suggested the

smelt run reported as dwarfs by Taylor and Bentzen (1993a,b), spawned for a

three week period and actually consisted of two distinct forms, suggesting a third

‘intermediate’ morphotype also existed, i.e., dwarf, normal, and giant forms. This

suggestion was based on evidence from differences in timing of spawning, body

sizes and gill raker counts, with some corroboration from trophic analysis and

high levels of genetic divergence between the forms (average FST = 0.091).

Based on this evidence, the three morphotypes identified by Curry et al. (2004),

will be used in the current study and referred as the giant, normal and dwarf

form.

1.5 Ecology of Morphotypes

In Lake Utopia, smelt morphotypes spawn in two separate periods (Curry et

al. 2004). The giant form spawns first in early to mid-April, over a one week

period, in three streams (reported as the normal form by Taylor and Bentzen

1993a,b). This form is generally 17-23 cm and has the fewest gill rakers (31-33).

The normal and dwarf form (reported as the dwarf form by Taylor and Bentzen

1993a,b) spawn in a second run in late-April and May in three different streams,

7

over a 2-4 week period. The size of spawning smelt in this second run is largest

at the beginning and decreases throughout the spawning period. The normal

and dwarf form designation, is given respectively to individuals from the

beginning and end of this second run. These form designations are corroborated

by evidence of significant differences in body size, gill raker number and high

levels of genetic divergence (Curry et al. 2004). The normal form is generally

11-15 cm and has 33-35 gill rakers. The dwarf form overlaps in spawning with

the normal form, is generally 9-11 cm and has the highest gill raker count (35-37)

(Curry et al. 2004). Normal and dwarf forms have larger eyes and smaller jaws

in comparison with the giant form (Taylor and Bentzen 1993b). The estimated

population size of the giant form is 1,000-10,000, the normal form 100,000-

1,000,000, and the dwarf form >1,000,000 (Curry et al. 2004).

Trophic ecology promotes differentiation in smelt life-histories (Taylor and

Bentzen 1993). In Lake Utopia, dwarf and normal smelt are planktivorous and

feed on Diaptomus, Cyclops, Leptodora, Daphnia, Epischura and Bosmina

(Bajkov 1936). No study has looked at differences in stomach contents between

normal and dwarf forms to determine if differences in feeding exist. The giant

form is macrophagous and often piscivorous, preying on smaller smelts (Bajkov

1936; Curry et al. 2004). Stable isotope analysis indicates an increase in trophic

level from dwarf to giant forms, but a distinct trophic separation among forms is

not apparent (Curry et al. 2004).

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1.6 Genetics

Genetic analysis suggests multiple independent divergences of Osmerus

life-history types across eastern North American lakes (Taylor and Bentzen

1993b), that is, morphotypes are polyphyletic, arising independently from the

same ancestors in each lake. This example of parallel evolution shows

independent evolution of the same trait in a species, but with separate lineages

(Futuyma 1986). Within Lake Utopia, there is a genetic divergence between the

smelt morphotyes. Analysis of mitochondrial and nuclear mini-satellite DNA

indicated significant genetic differentiation between giant forms and what we now

assume was the dwarf form (Taylor and Bentzen 1993a). Curry et al. (2004)

using microsatellite DNA demonstrated a high level of genetic divergence among

the giant and normal and dwarf forms (average FST = 0.091) and between dwarf

and normal forms within spawning streams. The giant form was the most

genetically distinct from the others (average FST = 0.096), while the difference

between the normal and dwarf form was also relatively high (average FST =

0.083). The extent of differentiation among normal and dwarf smelt varied

among tributaries and morphotypes did not appear to be more similar by form or

stream. Measures of genetic divergence among forms in Lake Utopia exhibited

much greater differentiation than reported for a sympatric pair of dwarf and

normal smelt in Lac Saint-Jean, Quebec that synchronously use the same

spawning habitat (average FST = 0.019) (Saint-Laurent et al. 2003). The level of

genetic divergence among the Lake Utopia morphs were also higher than

commonly observed among populations of anadromous atlantic salmon

9

spawning in different tributaries within a river system (average FST = 0.007 to

0.036) (Garant et al. 2000). The large degree of genetic differentiation between

the normal and dwarf morphotypes in Lake Utopia suggests the groups are

reproductively isolated either through segregation in spawning, mate selection

and/or reduced hybrid viability.

1.7 Species At Risk Designation

The entire late smelt run, made up of normal and dwarf forms (reported as

dwarfs by Taylor and Bentzen 1993a), was designated as threatened by the

Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in 1998

and is now protected under the Species at Risk Act. The committee’s report

indicated the reasons were the small population size (1,000,000 and predation is not a

serious threat (Curry et al. 2004). An updated status report and designation will

be released in 2006.

1.8 Research Objectives and Thesis Outline

If body size is a keystone biological feature among morphotypes within a

population and the most apparent characteristic defining this life-history variation,

10

then differences in initial size or growth during the first or subsequent summers

are predicted. We tested these predictions for the rainbow smelt in Lake Utopia

by examining the following early life-history characteristics: spawning time, egg

and larvae size, stream temperature, incubation duration, hatch time and growth

of age 0+ larvae using otoliths. We then examined the growth of adults using

otoliths to determine if size differences from early life-history persisted to create

the final body sizes observed among forms.

Past research on smelt morphotypes has focused on studying

morphological and genetic differences between the forms. Understanding when

a divergence in growth occurs will help us understand what factors are important

in maintaining the smelt complex we observe in Lake Utopia today and what role

genetic and environmental factors may play in this process.

This thesis is organized into five chapters; introduction, methods, results,

discussion and literature cited. The thesis will be submitted for publication as

one paper.

11

2 METHODS

2.1 Study Area

Lake Utopia (45º10', 66º47') was formed after the last glaciation (~15,000

years ago) in south-western New Brunswick, Canada (Fig. 1). It is a large 1400

ha oligotrophic to mesotrophic lake with a mean depth of 11 m and a maximum

depth of 30 m. It is connected by a channel to the Magaguadavic River, which

flows 15 km into the Bay of Fundy at St. George, NB. A large waterfall and dam

downstream of the lake at St. George, are barriers to upstream movement of

anadromous smelt in the system (Carr, J. Atlantic Salmon Federation, St.

Andrews, N.B., pers. comm.). Lake Utopia has a fish community of 23 species

including stocked land-locked Atlantic salmon, brook charr, smallmouth bass

(Micropterus dolomieui), American eel (Anguilla rostrata), white sucker

(Catostomus commersoni), yellow perch (Perca flavescens), white perch

(Morone americana), alewife (Alosa pseudoharengus) and blueback herring

(Alosa aestivalis).

Lake Utopia has six known smelt spawning tributaries (Fig. 1; Curry et al.

2004). Normal and dwarf forms spawn in Smelt, Unnamed, and Second Brooks.

These streams are small, 1-2 m wide with 40-400 m of accessible spawning and

incubation habitats of sand and gravel substrate. The giant form spawns in Mill

Lake Stream, Trout Lake Stream, and Spear Brook. These spawning tributaries

are 3-5 m wide with 15 m (Mill Lake Stream and Trout Lake Stream) and 100m

12

(Spear Brook) of accessible spawning habitats of boulder and gravel substrate,

and are outlets of smaller lakes or ponds.

2.2 Early Life-History Characteristics

The spawning period was monitored in all known spawning brooks three

times per week, beginning at the end of March and continuing to the end of May,

by observing spawning activity at night and egg deposition in the spawning

brooks in 2003 and 2004. Spawning females from each brook were collected by

dip-net and a random sample (n=25) selected for gonad collections in 2003.

Ovaries were removed and weighed fresh. Three egg sub-samples of

approximately 0.2 g wet weight were stored in 10% buffered formalin. The

number of eggs were counted in each sub-sample to determine the average egg

weight.

ACR® Smart Button temperature loggers were deployed in Mill Lake

Stream, and Spear, Smelt, Unnamed, and Second Brooks for the entire

spawning, incubation, and hatching period in 2004. The ACR® Smart Button has

a resolution of 0.5 °C and an accuracy of ± 1.0 °C from -10 to 45 °C. Eggs were

not discovered in Trout Lake Stream until the end of the incubation period, so

temperature was obtained from manually using a thermometer during site visits.

13

Larval drift nets (250 μm mesh size) (Johnston 1997) were placed at the

mouth of Mill Lake Stream, Smelt Brook, Unnamed Brook and Second Brook at

the end of the spawning period to catch hatched and drifting larvae in 2002 and

2004. Newly hatched larvae immediately begin to drift out of spawning streams

(Scott and Crossman 1998). Drifting larvae from Mill Lake Stream were assigned

a giant form. Curry et al. (2004) gave evidence that the spawning period of the

normal and dwarf forms were temporally segregated with some overlap. Since

embryos were incubating at the same location within the brooks, it was assumed

the hatching period would also be temporally segregated with some overlap.

Using this assumption, larvae that hatched at the beginning of the hatching

period were assigned as normal forms. Larvae that hatched at the end of the

period were assigned as dwarf forms. Larvae that hatched during the middle of

the period were not assigned a form. This assumption was supported by

predicting the hatch time from the number of degree days for incubation of smelt

embryos from spawning until hatch from the literature. The predicted hatch date

(giant May 10, normal May 24, and dwarf June 9) based on the mean number of

degree days from studies conducted by McKenzie (1958) and Cooper (1978) fall

within the designation of the hatch period for giant, normal and dwarf larvae.

Larval fish were collected from the drift nets three times per week, stored in 95%

ethanol, and lengths were later measured to the nearest 0.001 mm using

Optimus® 6.5 imaging software. Shrinkage in larval smelt due to preservation in

ethanol is not significant, so no mathematical correction was applied (Sirois et al.

1998).

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2.3 Growth

2.3.1 Field Sampling

Samples of adult smelt were dip-netted in the spring of 1999 and 2003.

Giant smelt were collected from Trout Lake Stream and Mill Lake Stream on April

3, 1999 and April 14, 2003. Normal and dwarf individuals were collected in

Second Brook, Unnamed Brook and Smelt Brook. The normal forms were dip-

netted at the beginning of the second run on April 20-21, 1999 and May 4-8,

2003. The dwarf forms were collected at the end of the second spawning run on

May 3, 1999 and May 20, 2003. The length (1 mm) and weight (0.01 g) of each

fish was measured and then fish were frozen for later otolith removal and growth

analysis.

Age 0+ larval smelt were collected from Lake Utopia once a month from

June to November in 2003 and 2004. In 2003, larval fish were first captured on

June 25 and then again on July 2, July 25, August 26, September 28, and

November 3. In 2004, larval fish were captured on June 1, June 28, July 18, July

29, August 28 and October 4. An attempt was made to collect samples from

fixed, randomly selected sites within the lake. However, larval smelt remained in

specific shallow, offshore areas of the lake and were subsequently targeted in

these areas. In attempts to sample larval fish throughout the lake, the lake was

divided into three areas based on surface area and an equal number of smelt

targeted for collection from each area on each sampling day. Smelt were

15

collected at night with a 1 x 2 m Neuston net (1.8 mm mesh). The net was towed

at the surface behind a boat at 4 km/h. Larvae were stored in 95% ethanol and

lengths measured upon returning to the lab.

Lake and air temperatures were recorded from June to October. This

period corresponds to the 5 month growing season for rainbow smelt. Monthly

temperature profiles were taken at the same location in the deep basin of the

lake to record lake water temperature in 2003 and 2004. Data for 1996-2002

was obtained from New Brunswick, Department of Environment and Local

Government. Summer lake temperatures were calculated from the mean

epilimnion temperature (0- 6 m) from June to October. Average summer air

temperature from 1996-2004 was obtained from Environment Canada at Point

Lepreau, New Brunswick (25 km east)

2.3.2 Otolith Microstructure Procedure

Studies using otoliths to infer age and growth have been used extensively

in fisheries science (Jones 1992). Otoliths are found in the inner ear canal and

aid the fish in balance and hearing. Growth is a one-way process as layers of

calcium carbonate crystals and fibro-protein are added to form daily increment

rings which result from the 24 hour light and dark cycle (Pannella 1971).

Alternating light and dark bands of fast and slow growth represent daily growth in

larval fish and yearly growth in adults.

16

Back-calculations use otolith increment widths and fish lengths to

determine length at a given age. Back-calculation methods are based on the

assumptions of constant periodicity in the formation of the otolith and

proportionality between otolith growth and somatic growth (Campana 1992). The

assumption of constant periodicity in otolith formation has been validated in larval

smelt (Sirois et al. 1998). The second assumption is demonstrated empirically by

strong correlations between fish size and otolith size. This relationship is seen

for Lake Utopia’s larval smelt in 2003 (r2 = 0.93, P < 0.001) and 2004 (r2 = 0.90,

P < 0.001) and for adults in 1999 (r2 = 0.58, P < 0.001) and 2003 (r2 = 0.90, P <

0.001; Fig. 2).

Traditional back-calculation methods have been found to have a growth

effect bias (Francis 1990), which occurred because the otoliths of slow growing

fish were larger than those of faster growing individuals. To eliminate the growth-

effect bias, the Biological Intercept Method was developed (Campana 1990),

which uses a biologically, rather than a statistically determined intercept. The

biological intercept occurs when daily increment formation begins, which in larval

smelt occurs at hatching (Sirois et al. 1998).

Larval fish (n=30) were randomly selected from the six sampling dates for

2003 and 2004 (total n=360 smelt). Sagittal otoliths were removed, mounted in

thermoplastic glue, polished with 3 µm and 0.3 µm photographic lapping film and

viewed under a microscope at 400x magnification (Secor et al. 1992). Age

17

(days) and hatching date were determined from the number of daily growth rings

and morphotype assigned to the individual based on their hatching date. Due to

the difference in spawning periods for normal and dwarf forms that were

identified by Curry et al. (2004), hatch dates at the beginning of the period were

assigned as normal forms and those hatching at the end of the period were

assigned as dwarf forms. Individuals that were estimated to have hatched during

the middle of the period were not assigned a form.

Adults of the giant, normal and dwarf forms were randomly selected in

1999 and 2003 for otolith microstructural analysis (total n=320). Sagittal otoliths

were removed, embedded in epoxy resin and sectioned with a slow-speed

Isomet saw. The section was placed in water and viewed under a microscope at

100x magnification. Age (years) was determined from the number of annual

growth rings. The size of growth increments of otoliths were measured using a

video camera, connected to a light microscope and a computer with Optimus®

6.5 imaging software.

Back-calculations were performed to determine length-at-age using the

following biological intercept (BI) method which eliminates the growth effect bias

(Campana 1990).

L t = L c + (O t – O c) (L c – L 0) -1

18

where L is fish length at age t (Lt), at the BI (L0) and at capture (Lc) and O is

otolith radius at age t (Ot), at the BI (O0), and at capture (Oc).

The biological intercept occurs when otolith increment deposition begins.

In larval smelt, increment growth begins the day of hatching (Sirois et al. 1998);

therefore, length at the biological intercept (L0) was 5.19 ± 0.59 mm (X̄ ± 1SD) for

dwarf smelt, 4.91 ± 0.53 mm for normal smelt, and 5.30 ± 0.36 mm for giant

smelt (calculated from the mean length of hatched larvae captured in larval drift

nets). The otolith radius at the biological intercept (O0) (12.19 ± 1.97 µm) was

calculated from the mean core radius of otoliths from age 0+ fish captured in the

lake.

Otoliths were read in random order by two readers. A total of 139 larval

otoliths were examined in 2003 and 21 (15 %) were discarded because

discrepancy between readers was >10%. In 2004, 115 larval otoliths were

examined and 19 (17 %) were discarded. A total of 158 adult otoliths were

examined in 1999 and 25 (16 %) were discarded because a discrepancy in age

existed between readers. In 2003, 108 adult otoliths were examined and 16

(15%) were discarded.

2.4 Statistical Analysis

Egg size was compared between forms using one-way analysis of

variance (ANOVA) on log10 transformed data with a Bonferroni post-hoc

19

comparison test. Hatch size was compared between dwarf and normal forms for

2002 and between giant and normal forms for 2004 using a one-way ANOVA on

log10-transformed data. Stream temperatures were compared using a one-way

ANOVA with repeated measures. A Tukey post-hoc comparison was done once

a month from April to June.

Larval growth was compared between forms on log10-transformed data

using a one-way ANOVA at time = 15, 30, 45 and 60 days with a post-hoc

Bonferroni test for comparison (α = 0.05 adjusted to 0.05/k, where k is the

number of tests; Rice 1989). Adult growth was compared between forms on

log10-transformed data using a one-way ANOVA at time = 1, 2 and 3 years with a

post-hoc Bonferroni test for comparison (α = 0.05 adjusted to 0.05/k). Adult age

was compared using a one-way ANOVA with a Bonferroni test for comparison.

All assumptions of parametric analysis were met prior to analyses. Statistical

computations were done using SYSTAT®10.2 software.

20

Figure 1: Lake Utopia (45°10’, 66°47’) and its smelt spawning tributaries. The

giant form spawns in Mill Lake Stream, Trout Lake Stream and Spear Brook.

Normal and dwarf forms spawn in Smelt, Unnamed and Second Brooks.

21

Figure 2: Relationship between otolith growth and somatic growth. Larval smelt

captured in Lake Utopia in 2003 ( ▲ ), r2 = 0.93 (n=142) and 2004, r2 = 0.90 ( ○ )

(n=140). Adult giant, normal and dwarf smelt captured by dip-nets during

spawning in Mill Lake Stream, Smelt Brook, Second Brook and Unnamed Brook

in 1999 ( ■ ), r2 = 0.58 (n=158) and 2003 ( Δ ), r2 = 0.90 (n=108).

22

Adults1999 and 2003

Fork length (mm)

100 150 200 250

Oto

lith

radi

us (m

m)

0.5

1.0

1.5

2.0

2.5

Larvae 2003 and 2004

10 20 30 40 500.0

0.2

0.4

0.6

0.8

1.0

23

3 RESULTS

3.1 Early Life-History Characteristics

3.1.1 Spawning, Incubation, and Hatching Period

The giant form of the Lake Utopia smelt spawned first from 16-20 April in

Mill Lake Stream and Trout Lake Stream in 2004 (Fig. 3). This was the first time

spawning was confirmed in Trout Lake Stream. Giant smelt were observed in

Spear Brook at this time, but no eggs were ever found. The normal and dwarf

form spawned next from 27 April - 11 May in Unnamed, Second and Smelt

brooks. Normal morphs spawned first, followed by dwarfs resulting in a partial

temporal segregation over the spawning period. The giant form had a shorter

spawning period of 5 d compared to the normal and dwarf forms which spawned

over 15 d in 2004 and 28 d in 2003.

The larvae of giants hatched first and were captured in drift nets placed in

Mill Lake Stream from May 8-12 (5 d; Fig.3). The normal and dwarf form hatched

from May 19-June 12 in Smelt, Unnamed and Second Brooks (23 d). The mean

incubation period for giants was 22 d and 28 d for the normal and dwarf form

(calculated from the difference between mean spawning and hatching time of the

early giant run and the later normal and dwarf run).

24

3.1.2 Water Temperature

In general, water temperatures in giant streams (Mill Lake Stream and

Spear Brook) were higher than in normal and dwarf streams (Unnamed, Smelt

and Second brooks) during spawning and they warmed quicker during the

incubation and hatching period (Fig. 4). During spawning in April, giant streams

were 5.0 °C and were significantly warmer than dwarf and normal streams

(ANOVA, Tukey, April 5, F4,10 = 20.3, P < 0.001). During the period when the

giants spawn, normal and dwarf steams were 3°C. By May and June both

streams used by giant smelt were significantly warmer than the normal and dwarf

streams (ANOVA, Tukey, P < 0.001: May 11, F4,10 = 244.9; Jun 16 F4,10 = 228.8).

There was no significant difference among the streams used by normal and

dwarf smelt in April (ANOVA, April 5, Tukey, F4,10 = 20.31, P > 0.999). By May,

Second Brook was slightly (but significantly) warmer than Smelt and Unnamed

Brooks (ANOVA, May 11, Tukey, F4,10 = 244.9, P < 0.001).

The number of degree days experienced by incubating embryos,

calculated from mean spawn date to mean hatch date, was 214 for the early

giant run in Mill Lake Stream with a mean daily temperature of 9.3°C and 192 for

the late normal and dwarf run in Second, Unnamed and Smelt brooks with a

mean daily stream temperature of 6.9°C.

25

3.1.3 Egg and Hatch Size

Eggs from giant smelt were significantly larger than normal and dwarf

smelt (ANOVA, Bonferroni, F2,116 = 20.9, P < 0.001; Fig. 5). Mean egg size for

giant, normal, and dwarf smelt was 0.43 ± 0.06 mg, 0.36 ± 0.05 mg and 0.35 ±

0.04 mg, respectively. Normal and dwarf egg sizes were not significantly

different (P > 0.05).

Mean egg size did not differ significantly among streams used by giant

smelt (ANOVA, F1,28 = 0.75, P = 0.394; Fig.5). Eggs from normal smelt (earliest

of second run) were significantly smaller in Smelt Brook than Unnamed and

Second Brooks (ANOVA, Bonferroni, F2,42 = 6.16, P < 0.05). Dwarf eggs from

Unnamed Brook were slightly (but significantly) smaller than those in Second

Brook (ANOVA, Bonferonni, F2,41 = 3.618, P < 0.5).

Size-at-hatch patterns were similar to egg size (Fig. 5). At hatching, giant

smelt were 5.32 ± 0.46 mm, normal smelt 4.71 ± 0.53 mm, and dwarf smelt 5.30

± 0.59 mm. Giant larvae were significantly larger than normal larvae (ANOVA,

F1,243 = 72.18, P < 0.001); however, there were no significant differences between

dwarf and normal larvae (ANOVA, F1,113 = 13.56, P = 0.36).

26

3.2 Growth

3.2.1 Larval Growth

Larval smelt were captured in shallow offshore areas throughout the lake,

and only at night when they moved up to the surface. Normal and dwarf

morphotypes were assigned in 2003 and 2004, but no giant larvae were captured

in either year. Normal and dwarf larvae captured in 2003 and 2004 had similar

hatching dates (Fig. 6), which were consistent with timing of larvae captured in

drift nets (Fig. 3). Normal and dwarf larvae were captured in all parts of the lake

in both years.

Growth patterns between normal and dwarf larvae differed between years.

In 2003, different size classes of smelt of the same age appeared to emerge by

early summer (Fig.7), and by July/August, there was a large difference in size of

larvae of the same age. A divergence in growth began 10 days after hatching

and continued until the end of the first growing season (Fig.8). The back-

calculated size of normal and dwarf larval smelt differed significantly at T = 15, 30

and 45 days (ANOVA, p < 0.001, at T = 15 days F1,69 = 16.60; T = 30 days F1,61 =

56.57; and T = 45 days F1,30 = 13.55). At 60 days, there was no significant

difference (ANOVA, p = 0.029, F1,16 = 5.72), but sample sizes were small (n =18).

Normal larvae hatched at 5 mm, were 8.4 mm after 10 d, and tripled in size to

17.0 mm after 25 d. Dwarf larvae also began at 5 mm total length, were 8.1 mm

after 10 d, and 13.3 mm after 25 d. In 2004, body size of normal and dwarf

larvae did not diverge during the first growing season (Fig. 7). The difference in

27

back-calculated length-at-age of normal smelt and dwarf smelt is not significant

at any time (ANOVA, p>0.05 at T = 15 days, F1,57 = 0.163; at T = 30 days, F1,50 =

0.442; at T = 45 days, F1,17 = 0.03). After 45 days the sample size was not large

enough to perform any statistical analyses (n =8).

3.2.2 Adult Age and Growth

The size of giant (20.2 ± 2.8 cm), normal (13.1 ± 1.9 cm) and dwarf (9.9 ±

0.9 cm) smelt were similar to the sizes observed by Curry et al. (2004). Mature

giant smelt were slightly older than the other forms, although differences were

not always significant. In 1999, giant smelt were significantly older (3.5 ± 0.9

years; ANOVA, Bonferonni, F2,155 = 8.638, P < 0.001) than mature normal (3.0 ±

0.7 years) and dwarf (2.7 ± 0.7 years) smelt, which were statistically identical in

age (P > 0.05). In 2003, no significant difference was found in the age of mature

giant smelt (3.5 ± 0.8 years) relative to normal smelt (3.4 ± 0.9 years); however,

dwarf smelt were significantly younger (2.5 ± 0.7 years; ANOVA, Bonferonni,

F2,105 = 16.388, P < 0.001) than giant or normal fish.

Back-calculated sizes for given ages of adult smelt showed a divergence

in growth between forms at different times (Fig. 9). Giants diverged in growth in

the first growing season and were significantly larger at all ages (ANOVA,

Bonferroni, 1999 - P < 0.05; age 1 F2,155 = 5.74; age 2 F2,155 = 11.02; age 3 F2,155

= 24.43; age 4 F2,24 = 4.18; 2003 - P < 0.001; age 1, F2,105 = 40.28; age 2, F2,105 =

156.42; age 3, F2,76 = 256.68; age 4, F2,27 = 71.92). No significant differences in

28

mean size were found between normal and dwarf adults at age 1; however,

significant differences in the time of divergence between sample years were

apparent. In 2003, divergence in size occurred during their second growing

season at age 1+ (age 1 - P = 0.87; age 2 - P < 0.05); in 1999, divergence

occurred during their third growing season at age 2+ (age 1 - P = 0.26; age 2 - P

= 0.35; age 3 - P < 0.05).

3.2.3 Lake Temperature and Growth

Mean summer lake temperature (19.7 – 21.2 ºC) and air temperature (5.4

– 7.8 ºC) showed a similar pattern and were strongly correlated (r = 0.98, P <

0.001) from 1999 to 2004 (Fig. 10). No inter-annual effects of summer growing

periods related to temperature among year classes or ages were apparent.

Yearly growth of age 1 and 2 smelt were strongly correlated with air temperature

(age 1 - r = 0.87; age 2 - r = -0.78); however, this correlation weakened by age 3

(r = -0.46) and 4 (r = 0.25; Fig. 10). Fish of all age classes, especially age 1 and

2, grew more in years when the water temperature was warmer and less in

cooler years.

29

Apr-12 Apr-26 May-10 May-24 Jun-07

Giant

Normal

Dwarf

Figure 3: Spawning ( ▄▄ ), incubation ( ▄▄ ) and hatching ( ▄▄ ) period of

giant smelt in Mill Lake Stream, and normal and dwarf smelt in Smelt, Unnamed

and Second brooks in Lake Utopia, 2004. Hatch marks indicate approximation of

dates.

30

Normal and dwarf Streams

05-Apr 19-Apr 03-May 17-May 31-May 14-Jun

Tem

pera

ture

oC

0

5

10

15

20

Giant Streams

05-Apr 19-Apr 03-May 17-May 31-May 14-Jun

Tem

pera

ture

oC

0

5

10

15

20

spawn hatch

spawn hatch

Figure 4: Mean daily water temperature (± 1 SD) of spawning tributaries in Lake

Utopia for giant smelt (Mill Lake Stream and Spear Brook) and normal and dwarf

smelt (Second Brook, Unnamed Brook and Smelt Brook), 2004.

31

Figure 5: Mean egg size (± 1 SD) of giant ( ■ ), normal ( O ) and dwarf ( ▲ )

mature female smelt captured in Trout Lake Stream, Mill Lake Stream, Unnamed

Brook, Smelt Brook and Second Brook in 2004 (total sample size n=120). Mean

hatching length (± 1 SD) of larval smelt captured in Mill Lake Stream, Second

Brook and Smelt Brook in 2004, and Smelt Brook and Unnamed Brook in 2002

(total sample size n=360).

32

Egg Size

Trout Mill Unnamed Smelt Second

Egg

siz

e (m

g)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Hatch Size

Mill Second Smelt Smelt Unnamed

Tota

l len

gth

at h

atch

(mm

)

0

1

2

3

4

5

6

7

20022004

33

Figure 6: Hatching date calculated from otolith daily growth rings of normal and

dwarf larvae captured by Neuston trawls in Lake Utopia in summer 2003 (n=138)

and 2004 (n=96). No larvae of giant smelt were captured.

34

2004

19-May 26-May 02-Jun 09-Jun 16-Jun 23-Jun

Freq

uenc

y

0

2

4

6

8

10

12

14

2003

16-May 23-May 30-May 06-Jun 13-Jun 20-Jun 27-Jun 0

1

2

3

4

5

6

7

8Normal Unknown Dwarf

Emergence date

Normal DwarfUnknown

35

2004

Age (days)0 20 40 60 80 100 120 140

Tota

l len

gth

(mm

)

10

15

20

25

30

35

40

45

50

June 1June 28July 18July 29Aug 23Oct 4

2003

0 20 40 60 80 100 120 140 160 18010

15

20

25

30

35

40

45

50

June 25July 2July 25Aug 26Sept 28Nov 3

Figure 7: Size and age of 0+ larval fish captured by Neuston trawls throughout

the summer in 2003 and 2004 in Lake Utopia.

36

Figure 8: Back-calculated, mean length-at-age of dwarf ( ▲, -SD ) and normal

( ○ , +SD) larval smelt captured in Lake Utopia on June 25, July 2, July 25,

August 26 and September 18, 2003 (n=73), and on June 1, June 28, July 18,

July 29 and August 28, 2004 (n=62).

37

2004

Age (days)

0 10 20 30 40 50 60 70 80 90

Tota

l len

gth

(mm

)

0

10

20

30

40

2003

0 10 20 30 40 50 60 70 80 900

10

20

30

40

38

Figure 9: Back-calculated mean length-at-age (± 1 SD) of adult giant ( ■ ), normal

( ○ ) and dwarf ( ▲ ) smelt captured by dip-nets during spawning in Mill Lake

Stream, Smelt Brook, Second Brook and Unnamed Brook in 1999 (n=108) and in

Mill Lake Stream, Trout Lake Stream, Smelt Brook, Second Brook and Unnamed

Brook in 2003 (n=108).

39

1999

0

50

100

150

200

2003

Age (years)

0 1 2 3 4 5

Fork

leng

th (m

m)

0

50

100

150

200

250

40

1996 1998 2000 2002 2004

Gro

wth

rate

(mm

/yea

r)

10

20

30

40

50

60

70

Tem

pera

ture

(C)

5

6

7

818

20

22

24

Figure 10: Back-calculated mean yearly growth of adult smelt for age 1 (––––– ),

age 2 (–— –—), age 3 ( — — —) and age 4 ( – – – – ) year classes . Mean

summer air ( ········ ) and surface water (– · ·– · · ) temperature from 1996 to 2004.

41

4 DISCUSSION

4.1 Size Differences in Early Life

Differences in egg or larvae size provide an early growth advantage that

may lead to differences in size among morphotypes of smelt in Lake Utopia.

Giant smelt eggs and larvae were significantly larger than the other forms, which

lead to differences in growth rates (Kazakov 1981; Reznick 1982). While we did

not capture any giant larvae during their first summer, the back-calculated size of

adults was already significantly larger at age 1+ showing a divergence in growth

during their first 5 months in the lake.

Early hatching is another possible mechanism for promoting a divergence

in growth among morphotypes in sympatric populations of fish, including the

Lake Utopia smelt complex. Individuals that hatch earlier have a longer growth

period that can be critical for north-temperate fishes (e.g., Schindler 1999; Curry

et al. 2005). Smelt spawning appears to be controlled by water temperature and

begins when temperatures reach critical values of 5-10°C depending on locality

(McKenzie 1958; Bailey 1964; Scott and Crossman 1988). In Lake Utopia,

streams where the earliest spawning, giant smelt morphotypes reproduce were

warmer earlier. Stream temperatures at spawning time were 7oC, while streams

used by normal and dwarf morphotypes were 3°C and partially covered with ice

and snow.

42

Length of embryo incubation is also largely controlled by water

temperature (McKenzie 1958; Hale 1960; Cooper 1978; Scott and Crossman

1998) and will affect time of hatching. Streams used by giants were warmer

resulting in a shorter mean incubation period of 22 d, compared to 28 d for

normal and dwarf morphotypes. Giant embryos have a higher number of degree

days (214) compared to 192 for normal and dwarf embryos. Even though giant

embryos require more degree days to hatch, early spawning and warmer

incubation temperatures result in giant larvae hatching 2-4 weeks earlier.

The larger eggs and larvae, earlier hatching, and shorter incubation period

suggest that genetic factors have the principle control over tactics used by

spawning giant smelt that sustains their large body size and leads to

macrophagous/piscivorous feeding.

Giant larvae were not captured in the lake probably due to the probability of

encounter. The estimated spawning population size of the giant form is 1,000-

10,000, the normal form 100,000-1,000,000, and the dwarf form >1,000,000

(Curry et al. 2004). We captured, aged, and assigned forms to 360 larval fish,

thus the chance of catching giant larvae were low. It is possible that age 0+

giants were using a different habitat in the lake, however without a hydroacoustic

survey of the lake, distribution and habitat use of the forms and age classes in

the lake is uncertain.

43

Differences between normal and dwarf morphotypes were more subtle

and displayed inter-annual variation. Egg and larvae sizes were similar (Fig. 5),

while spawning and hatch time were variable between morphotypes (Fig.3) and

displayed inter-annual variation. Normal smelt spawn two weeks after giants

when stream temperatures reach 6°C, followed by dwarfs such that there was a

partially segregation of initial spawning of a few days to weeks. The duration of

their spawning periods varied from 2-4 wks between years (and from 1996-2004:

Curry et al. 2004; R.A. Curry, unpublished data). Larger temporal segregation in

spawning and a longer spawning period in 2003 could cause the bimodal

hatching frequency of larvae not apparent in 2004. Such a temporal segregation

may allow normal forms to hatch earlier, thus imparting a growth advantage

during their first summer as suggested for 2003. Spring 2004 was colder (Fig.

10), which may be a factor shortening spawning periods for the normal and dwarf

forms. Colder lake temperatures in 2004 may also contribute to the lack of

divergence between forms as growth in many larval pelagic species is strongly

dependent on temperature (Pepin 1991). In Lake Utopia fish grew more in years

when lake temperatures were warmer, which was most evident for age 0+ and

1+ year classes (Fig.10). Years with cooler temperatures may reduce growth

and hinder a growth divergence between 0+ normal and dwarf morphs.

In addition to divergence between normal and dwarf smelt that can take

place already as larvae, size differences also occurred at age 1+ and 2+ (Fig.9),

also with inter-annual variability. Such variation probably results from

44

environmental conditions that influence spawning and incubation, lake

temperatures and growth. Environment may be the most important factor

regulating production of normal and dwarf forms of smelt in Lake Utopia. Curry

et al. (2004) indicated that genetic separation of these two forms was apparent,

however, the inter-annual variations in spawning and growth of distinctly early

(normal) and late (dwarf) spawned smelt suggests that environmental factors are

also important.

4.2 Evolutionary Origin of Morphotypes

Trophic specialization and ontogenetic niche partitioning are known to play

an important role in the evolution of fishes in landlocked lakes (Echelle and

Kornfield 1984, Schluter 2000). During the end of last glaciation as the ice sheet

receded, anadromous rainbow smelt would have colonized Lake Utopia. Through

trophic radiation, a smaller form with increased number of gill rakers appears to

have adapted to planktivory, while the larger, giant form adapted to piscivory with

fewer gill rakers (Taylor and Bentzen 1993a). These differences could have

initially resulted from polymorphism within the single breeding population, but at

some point reproductive isolation occurred possibly through size differences

influencing mate selection, predation/competition, reduced hybrid viability, and/or

habitat availability producing the genetic divergence between the giant and

smaller stunted forms we see today (Taylor and Bentzen 1993a; Curry et al.

2004).

45

There are fitness advantages associated with fast growth and attaining a

large body size. In Lake Utopia, larval smelt probably incur significant intra-

specific competitions as well as competition from alewife and blueback herring

larvae that occupy the same habitats and compete for the same food resources

(Scott and Crossman 1998). Larger body size may help an animal to overcome

competition (Blaxter 1986; Arendt and Wilson 1997) especially with limiting food

resources. Although zooplankton abundance in north temperate lakes is high in

early summer, it declines throughout the summer (Kalff 2002). A large size

would be advantageous with limited food resources for abundant larval smelt as

well as other planktivorous larvae in the lake. Larger size and gape also imparts

an advantage for prey selection allowing individuals to eat larger and more

nutritious foods (Hayes and Taylor 1990). Dwarf and normal fish remain

planktivorous due to their gape limitation while the giant form attains a large

enough gape size to switch to piscivory.

Fish that grow fast also reduce risk of predation (Reznick 1983). Larger

size can incur greater survival by influencing encounter rates, predator avoidance

abilities, and predator gape limitation (Blaxter 1986). In north-temperate lakes,

body size can be a critical factor regulating first winter survival in fishes

(Schindler 1999; Pratt and Fox 2002; Curry et al. 2005). All of these factors

suggest that larger smelt gain fitness advantages from their larger body size that

are selected for among the smelt forms.

46

Attaining an absolute, maximum body size alone is not the sole factor

regulating the survival and evolution of the smelt in Lake Utopia otherwise the

three morphotypes would not have arisen over the last 15,000 years (Taylor and

Bentzen 1993a) and persist today. Trophic niche partitioning within the smaller,

planktivorous population may have occurred again, allowing the different forms to

use different resources giving the normal and dwarf forms a distinct niche to fill.

The giant smelt population may be limited by spawning habitat availability as

most individuals spawn in Mill Lake Stream with a 15 m section of suitable

spawning habitat. Lower temperatures and a longer distance from the lake (2

km) may deter the sporadic spawning in Spear Brook, while the poor spawning

habitat (metal culvert, 2 m depths, with boulder and cobble substrate) in Trout

Lake Stream may also be a factor. Reproductive isolation may be influenced by

schooling behaviour of like-sized individuals resulting in mate selection (Nellbring

1989). Smaller stunted forms may be deterred from spawning with the giant form

that are known predators (Bajkov 1936; Curry et al. 2004). Evidence of larger

bodied smelt of the same age spawning together early has also been

documented in the Miramichi River, NB (McKenzie 1964) and in two lakes in

Maine (Rupp 1959).

Giant morphs display the largest difference in morphology, are

completely temporally and spatially segregated while spawning and display the

largest amount of genetic separation. It appears genetic factors are largely

maintaining the difference between the giant form and other morphotypes.

47

Phenotypic and genetic divergence between the normal and dwarf form may

have occurred after this initial divergence event and may have emerged from the

smaller stunted plantivorous form. Both dwarf and normal fish are planktivorous,

there is less genetic divergence between them (Curry et al. 2004) and they

display inter-annual variation in timing of divergence in growth. Our findings

suggest that environment, and in particular temperature regulation of spawning

period initiation and duration, and growth of 0+ age classes, also controls the

creation of divergent body size groups, i.e., the normal and dwarf forms. The

resultant fitness advantages of attaining a larger size and trophic niche

partitioning may contribute to the divergence of dwarf and normal forms in this

earlier stage of divergence.

The monophyletic population of Arctic charr, morphotypes of

Thingvallavatn, Iceland also diverge in growth at different times during the

ontogeny of four morphotypes (Jonsson et al. 1988). Large and small benthivore

morphs emerge at different sizes, diverge in growth immediately at age 0+ and

are separate reproductive units; large piscivores and small plantivores belong to

the same reproductive unit, emerge at different sizes, but don’t diverge in growth

until age 3+ due to ontogenetic niche shift partitioning (Jonsson 1988; Skulason

et al. 1989; Danzmann et al. 1991; Snorrason et al. 1994). Both charr and smelt

complexes appear to be evolving from selection consequences of: 1) genetic

control of body size at first exogenous feeding (benthic charr and giant smelt); 2)

environmental control of body size at first exogenous feeding (normal and dwarf

48

smelt); 3) environmental control of food resources during ontogeny (pelagic charr

and all smelt); and 4) isolating factors associated with habitat (benthic vs. pelagic

charr). We would suggest that body size is an important determinant of

morphotypes in fish population complexes, but more specifically it is relative body

size within a cohort related to ontogenic development.

4.3 Summary

Morphotypes in Lake Utopia appear to diverge in growth at different times

during their ontogeny and display different levels of stability. Giant larvae are

more stable emerging earlier, at a larger size and consistently diverging in growth

during their first growing season as age 0+ fish. Divergence between the normal

and dwarf form appears to be unstable and shows inter-annual variation. The

normal and dwarf form emerge at the same size, however hatching varies and

divergence in growth varies annually from age 0+ to 2+ suggesting it has an

environmental basis. Environmental factors associated with spawning time and

lake temperatures may affect the degree of divergence between these

morphotypes. We suggest that genetic factors appear to be more important in

maintaining giant morphotypes where environmental factors may play more of a

role in maintaining the normal and dwarf morphotypes in Lake Utopia today.

49

5 LITERATURE CITED

Arendt, J. D. and D. S. Wilson. 1997. Optimistic growth: competition and an

otogenetic niche-shift selected for rapid growth in pumpkinseed sunfish

(Lepomis gibbosus). Evolution. 51: 1946-1954.

Aubin-Horth, N. and J. J. Dodson. 2004. Influence of individual body size and

variable thresholds on the incidence of a sneaker male reproductive tactic

in Atlantic Salmon. Evolution. 58(1): 136-144.

Bailey, M. M. 1964. Age, growth, maturity and sex composition of the American

smelt, Osmerus mordax (Mitchill), of western Lake Superior. Transactions

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0

CURRICULUM VITAE

Candidate: Jennifer Lynn Shaw Mailing Address: University of New Brunswick

Department of Biology Canadian Rivers Institute

PO Box 45111 Fredericton, New Brunswick E3B 6E1 Phone: 506-458-7247 Email: jennifer.shaw@unb.ca

Home Address: 3393 Woodstock Road

Fredericton, New Brunswick E3E 1A5 Phone: 506-454-8842

Universities Attended: September 2003 – December 2005 University of New Brunswick, Fredericton, New Brunswick Master of Science (Biology) September 1992 – May 1996 University of Guelph, Guelph, Ontario Bachelor of Environmental Science (Ecology/Environmental Impact Assessment) Conference Presentations: Shaw, J.L. and R.A. Curry. 2005. Early life-history characteristics and growth of sympatric rainbow smelt in Lake Utopia, New Brunswick. Canadian Conference for Fisheries Research, January 9-11, Windsor, Ontario. Poster Presentations: Shaw, J.L., R.A. Curry and S.L. Currie. 2004. Intravariation in early life-history characteristics of rainbow smelt in Lake Utopia, New Brunswick. Atlantic International Chapter - American Fisheries Society, September 19-21, Fairmont, Vermont.

1

Shaw, J.L., R.A. Curry and S.L. Currie. 2004. Early life-history characteristics and growth of sympatric rainbow smelt in Lake Utopia, New Brunswick. Canadian Conference for Fisheries Research, January 6-8, St. John’s, NL. Publications: Shaw, J.L. and R.A. Curry. 2005. Lake Utopia Rainbow Smelt Field Studies 2004. New Brunswick Cooperative Fish and Wildlife Research Unit, Fisheries Report #05-01. Shaw, J.L. and R.A. Curry. 2004. Lake Utopia Rainbow Smelt Field Studies 2003. New Brunswick Cooperative Fish and Wildlife Research Unit, Fisheries Report #04-02.

1 GENERAL INTRODUCTION1.1 Life-History Variation1.2 Evolutionary Significance of Size and Growth1.3 Rainbow Smelt Biology1.4 Life-history Variation in Rainbow Smelt1.5 Ecology of Morphotypes1.6 Genetics1.7 Species At Risk Designation1.8 Research Objectives and Thesis Outline

2 METHODS2.1 Study Area2.2 Early Life-History Characteristics2.3 Growth 2.3.1 Field Sampling2.3.2 Otolith Microstructure Procedure

2.4 Statistical Analysis

3 RESULTS 3.1 Early Life-History Characteristics3.1.1 Spawning, Incubation, and Hatching Period3.1.2 Water Temperature3.1.3 Egg and Hatch Size

3.2 Growth3.2.1 Larval Growth3.2.2 Adult Age and Growth3.2.3 Lake Temperature and Growth

4 DISCUSSION4.1 Size Differences in Early Life 4.2 Evolutionary Origin of Morphotypes 4.3 Summary

5 LITERATURE CITED5