BI 2060 V091 Kaiser part three; Impacts Case study Trondheimsfjord The Trondheimsfjord is a...

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Kaiser part three; Impacts Case study Trondheimsfjord

The Trondheimsfjord is a relatively selfsustaining ecosystem. Of course, it is not hydrographically or biologically isolated from coastal waters, but it is so big and diverse with respect to biotopes and habitats that many species can complete full life-cycluses in the fjord. This applies to both evertebrates, fishes, seabirds and mammals.

Thus, one can use practical examples from the ecosystem Trondheimsfjord to examplify effects of human activity, viz:

• Fisheries• Aquaculture• Habitat disturbances and pollution • and• Conservation activity

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The Trondheimsfjord is the third longest and seventh deepest fjord in Norway. The distance from Agdenes (the outlet) to Steinkjær is 140 km, and the largest depth is 614 m. The fjord is divided into three main basins by thresholds at Agdenes, Tautra and Skarnsundet.

ABOUT THE TRONDHEIMSFJORD

Agdenes

Tautra

Verrabotn

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The Trondheimsfjord is very rich in fish species. More than a hundred fish species are represented, including many of the most important Norwegian commercial fish (cod, saithe, haddock, whiting, blue whiting, hake, herring, sprat, and several flatfishes).The most important fisheries have been on cod, saithe and herring. In recent years the commercial catch of herring has been closed due to the danger of recruitment failure. The traditional home fishery on cod and herring has long traditions in the local population and is free of any charge. Also, leisure fishery is a widespread pastime activity for a large part of the population along the fjord. The output from the cod fishery has been an On/Off situation in the last 50 years, reflecting variation in the cod stock size.The stock size variation show signs of being correlated with both milieu factors and exploitation pressure, as argumented for in the following treatment of the cod- and herring fishery in the fjord.

EFFECTS OF FISHERIES

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Trondhjem Biological Station (TBS) has performed fisheries biological studies in the Trondheimsfjord for more than a hundred years. Many research vessels has been serving during these years.

Sunrise mood onboard RV "Harry Borthen I". The Skarnsund bridge at the inlet to the Beitstadfjord

is a wellknown landmark.


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Gadoids (cod family) which

spawn in the TrondheimsfjordCod

Haddock

Whiting

Saithe

Pollack

Norway pout

Poor cod

Hake

Blue whiting


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Relative yearclass strengths of cod in the Trondheimsfjord 1963-1990 (Ekli 1997)

(cf next slide for extended period)


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Like many other fish stocks, the cod benefitted greatly from the catch stop during the second world war. After the war, the catches were good up to the 1960ies, and so also in the Trondheimsfjord. Then the output gradually decreased, making it more or less economically unprofitable to fish commercially in the fjord. This gave the stock a chance to recover for some years. From the middle of the 1970ies the fishery was good based on several strong yearclasses. This again lead to higher exploitation,e.g. by the participation of 20-30 large vessels from the coastal areas which used chains of up to 80 modern monofilament nets on the spawning grounds in Verrasundet(inner parts of the fjord). Apparently, this intense fishery was too much for the stock. The catches were graduallydecreasing, and from the mid 80ies the fishery again became unprofitable for the boatsfrom the coast. The stock was left in relative peace, but the recruitment and yearclass strength were low in a substantial perion after that. Only in the mid 90ies stronger yearclasses started to appear again. The causal relations are complex in marine ecosystems, but this story of the Trondheimsfjord cod seems to fit into some wellknown patterns (/. cont.)

THE VERRAN COD (VERRATORSKEN)


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/. cont.The size of a fish stock is a balance between annual recruitment and mortality.The natural annual mortality of cod in the Trondheimsfjord is ca 40% (Denstadli1970, Mork 1976). On top of this comes the fishery mortality. In overexploitedstocks the total annual mortality (natural plus fishery-related) is often 70% ormore. The cod is a multiple spawner, and a spawning stock in good conditionconsists of many yearclasses, included some big, old females with superior egg quality and egg survival compared to younger females. In particular, firsttime spawning females has a comparatively low survival of their eggs.In a heavily exploited stock the spawners will consist of a large portion of young females which, due to low quality eggs, will result in weaker yearclasses.In situations when high mortality (intense fishery), low mean age in the spawning stock (low egg survival), and non-optimal natural milieu conditions (temperature, mismatch relative to the plankton bloom, predation on eggs) coinside, a stock can collapse and stay at a low size for many generations. There are reasons to assume that this is part of the explanation for the history of the Trondheimsfjord cod since the second world war. Apparently, periods with a lower exploitation have given the stock a possibility to recover to natural size.

The moral is...?


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THE BEITSTADFJORD HERRING (BEITSTADFJORDSILDA)

It has been known for more than a hundred years that there is a local selfsustained and selfrecruiting herring stock in the inner part ofthe Trondheimsfjord (Beitstadfjord).That this stock is genetically isolatedfrom the coastal herring and Norwegian Spring Spawning herringwas confirmed by population genetics methods at TBS in the1990ies (Skjong 1994).

As common for herring stocks, the Beitstadfjord herring has showed somelocal changes in spawning place and wintering area in Beitstadfjord, butit has still remained local.


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BEITSTADFJORDSILDA /. cont.

Apparently, the Beitstadfjord herring struggles somewhat with maintaining a proper size of the stock. It isknown to be relative small by size (slow-growing) and meager compared to e.g. coastal herring. It is mainlya spring spawner. The spawning appears to have become more spread-out both geographically and temporallysince the 1980ies, but it still takes place in the inner fjord. The local exploitation has traditionally been performed by local stakeholders and fishermen/farmers who have used a fewherring nets, and also by the use of light and beach seines. Place for use of beach seines was a legal right of the land-owners and was listed in official documents for the Beitstadfjord.

Herring in the Trondheimsfjord was opened for catch for up to 10.000 tons per year in the 1950ies, but considerably lower (2.500 tons) from 1980 to 1985 (2.500 tonn), at which time it was stopped due to low recruitment to the stock. Since 1996 there has been a full closing of the commercial fishery. Today, it is only allowed to fish for personalconsumption using one herring net. The traditional herring fishery in the Trondheimsfjord was not necessarily for local herring only. At the time of the year when the fishery took place, there can very well be contributions from other stocks, e.g. coastal herring andNorwegian Spring Spawning herring in the mid part of the Trondheimsfjord.

The moral in this case is that the local herring stock in the Trondheimsfjord does not have sufficient natural self-recruitment to withstand any substantial exploitation with modern, effective catch gear. For this reason, it must be subject to a more restrictive management and regulation than more productive stocks in Norwegian coastal- and oceanic waters.


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The angler fish (Lophius piscatorius) is found along the Norwegian coast up to Vesterålen. It gained its latin name from the "fishing rod" on its head, with which it lures its prey. The species was almost unattended in Norway until for 15-20 years ago. At that time it became a popular restaurant food and gave a good income for the fishermen. Old and very large individuals were caught in the beginning. Specimens of more than 40 kg was relatively common, and a record weight of over 70 kg is reported from the Trondheimsfjord. From being an almost unexploited stock with a large portion of old, large individuals, the situation has changed, so that the catches are now reduced to one third, and the large individuals have become more rare. This species needs a long time for the restitution of local stocks.

THE ANGLER FISH


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According to evolutionary theory, intensively exploited fish populations are expected to undergo genetic shiftstowards maturation at smaller sizes and/or younger ages, given that early maturing individuals will be more likely to reproduce prior to capture. Fisheries-induced evolution could thus lead to a loss of genetic diversity in life history traits. The Theme Section (right), organized by C. T. Marshall & H. I. Browman, discusses probabilistic maturation reaction reaction normsnorms in the context of disentangling evolutionary vs environmental (genetic vs physiological) influences on fish maturation (cf illustr. to the right).

GENETIC EFFECTS OF FISHINGWITH SELECTIVE GEAR


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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF AQUACULTURE

FARMING IN NET PENS AND ON ROPESRELEVANT SPECIES:Salmon – cod – blue mussel

SALMON: The Trondheimsfjord is Norway's most important fjord for salmon ascending their rivers. Several large salmon rivers drain to the fjord (Orkla, Gaula, Nidelva, Stjørdalselva, Verdalselva, Steinkjærselva, Figga). From 1989 the entire fjord was regulated as temporary (5 years) security zone for salmonids; i.e. no new licenses for salmon and trout farming will be given within the zone. Later, the fjord has been granted the status of National Salmon Ford. This will mean very strict bans on all farming activity which bear the risk of escapees, disease or other danger for the natural populations.

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF AQUACULTURE

COD: Feeding of wild-caughtwild-caught cod to market size has been going on for some time in the Trondheimsfjord, but this is not regarded as an activity which represents a danger for the natural cod population. Some production of codlings for farming also takes place, but is land-based and not regarded as a danger to nature.

Recently, a company has applied for concession to establish a plant for farming cod in the inner part of the fjord. This was the first application ofits kind in the fjord, and triggered a legal process where The Ministry of Fisheries sent the application out to a number of hearing instances, both official and non-official. On February 18, 2009, the Director of Fisheries made a decision based on the regulations of consessions and the the results of the hearings. The application was rejected, and a temporary consession which had been granted was lifted.

Among the factors that have been considered in the process are:From where will the codlings for farming be collected (local stock or central distributeurs Troms)Technical standard – security against wreckage and escape issues and potential effects on the local stockEscape issues related to the predation on salmon in the fjord Disease and infection issues – related to wild cod and other species Pollution effects on local bottom habitats Norwegian legislation, consession rules, international obligations

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF QUACULTURE

BLUE MUSSLE:Blue mussel farming has existed for many decades in the Trondheimsfjord, with variable success. Particularly in the early phases the trials were characterized by lack of knowledge and planning, and many producers went bancrupt because of algal blooms, wreckage, predation losses by seabirds, and an in general bad caretaking of the plants. In later years, more serious producers have established plants several places in the fjord, some with good economic results. The production is based on natural pelagic larvae which settles on ropes hanging in the water column, and the larvae are not supplied with feed of any kind. This industry is sensible for algal blooms. However, because a veterinary control is taken care of by the authorities, the risk has been reduced for dramatic production losses by harvesting in the wrong periods.Potential harm to natural habitats lies in detoriation of the bottom substrat below the plants. Concentrated faeces and dead mussels lead to local pollution of the bottom habitat. In later years more consideration has been given to favourable current conditions and removal of debris from the plants during the planning and localization process. The authorities has placed considerable work in coastal zone planning and localization criteria for blue mussel plants as well as other forms of farming and ranching.

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF DSTURBANCES,

POLLUTION ETC

POLLUTION: The Trondheimsfjord has traditionally been debited with considerable pollution because it has had both a substantial industry (mining, erts shipping, quarries etc) and a substantial agriculture activity with run-off to rivers and ultimately to the fjord.

While mercury pollution from agriculture earlier was serious problem, regulations implementedby the authorities brought this problem under control.

Also, legislation against agriculture fertilization in winter has reduced the run-off of nutrients (nitrates,phosphates) to rivers and the fjord. The earlier eutrophication effects with oxygen depletionin the bottom waters of local basins has to a large degree been solved.

In former industy societies such as Orkanger the pollutioning industry are terminated, and inlocalities such as the Orkdalsfjord a large part of the toxic compounds are now covered bynatural sediments.

In Trondheim, industry that earlier used the Nidelva and the fjord as resipients has been imposed strict rules for discharge, and big cleansing plants for domestic waste has beenbuilt.

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Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF DISTURBANCES,

POLLUTION ETC

The Trondheimsfjord acts as resipient for poisons, plant nutrients, waste and sewage from a large geographical area and a substantial population.Several large studies on the pollution status of the Trondheimsfjord have been done. These have identified local problems, mostly quite near to the largest population centres and shipping harbours. However, the general picture is that the situation in the fjord is good, especially in comparison with fjords with industry in south and east Norway.

This is explained by the fact that the Trondheimsfjord is a very good recipient due to its large volume which has a good water exchange with the coast. The normal picture is that the fjord water is completely renewed by twice a year, one in the spring (April – Atlantic water) and one in the autumn (coastal water). In addition, the Trondheimsfjor has a substantial tidal water amplitude of 180 cm. Together with a typical estuarine run-off due to the large rivers this results in a stable ingoing net current on the south and east side, and an outgoing rest current on the north and south side of the fjord. Together these physical factors gives good water renewal for the fjord, and makes it a very effective and robust resipient.

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POLLUTION ETC

In the last 10-15 years the sea water on the Norwegian coast has undergone anunusually strong temperature increase, some places on the coast as much as 2-3 degrees Celcius. This situation is also valid for the Trondheimsfjord. The monthly hydrographic measurements by Trondhjem Biological Station show that the temperature in the bottom water have increased unusually much since the 1990ies, and has set frequent "all time highs", latest in February 2007.

If this continues without the periodic "correction" that was common in earlier periods, it will probably result in changes in the fjord's ecosystem. One of the probable scenarios is that the fjord looses its position as the "northern boundary" for many marine species, and that the biodiversity of the fjord becomes poorer and more like thatof the fjords in southwest Norway today.

An ecosystem in change often gives opportunistic species a chance to establish themselves in free or new niches. Such species can easily take over the hegemonyas top predators, at least for a period.

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POLLUTION ETC

The graph on the next slide shows a plot of the development in bottom temperaturein the three main basins in the Trondheimsfjord. The upgoing trend in clearly seen,and the latest measurements are "all time high”, with a good margin, since these measurements started early in the 1960ies.

In the latest 10-15 years or so, reports have been more frequent on the occurrence of fish with a more southern distriburence which have been found in the Trondheimsfjord (sworfish, tuna, horse mackerell, sea bass, goatfish, blackfish). At the same time, a specific jellyfish, the Periphylla periphylla, has established a large, selfrecruiting and seemingly stable population in the innermost basin of the fjord.It is still an open question if all these observations in any way are coupled to the ongoing temperature increase.

If an extensive change in the fjord's ecosysten is going on, it is even more importantIf an extensive change in the fjord's ecosysten is going on, it is even more importantto monitor the physical and biological proceses in the fjord in order to learn and gainto monitor the physical and biological proceses in the fjord in order to learn and gainexperience in the effects that are triggered by climatic changes. Some of these effectsexperience in the effects that are triggered by climatic changes. Some of these effectscan be quite grim even at out latitrdes. can be quite grim even at out latitrdes.

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POLLUTION ETC

Mean bottom temperatures at three stations in the Trondheimsfjord in the period 1963-2007

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POLLUTION ETC

Periphylla periphylla (Coronatae) has invaded the Trondheimsfjord

The coronate jellyfish(Periphylla periphylla) is anexample of an opportunistwhich can strike when eco-systems are out of balance.

It has some basic propertieswhich makes it a powerfulcompetitor for the hegemonyas top predator.

Not surprising, really; its basiccharacteristics have survivedsome 550 million years ofevolution.

INVASIVE SPECIES

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How did this jellyfish establish itself in the Trondheimsfjord in the first place?


EFFECTS OF DISTURBANCES, POLLUTION ETC

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Trondheimsfjorden, depths and bottom topography

The Trondheimsfjord has three main basins separated by tresholds at Agdenes, Tautra and Skarnsundet.

Atlantic water regularly flows over the tresholds and into the fjord. This water is heavy and sinks to the bottom. It brings with it organisms which get a chance to establish themselves in the fjord.

600 m

Kaiser part three; Impacts Case study Trondheimsfjord EFFECTS OF DISTURBANCES, POLLUTION ETC

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Inner Trondheimsfjord

Verrasundet; the main spawning place for gadoids in the fjord.

250 m

100 m

60 m420 m



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Clips from Ukeadressa25. November 2006.

Over: The catch after a 30 min hawl at 100 m depth in Verrasundet. Mainly jellies in the codend.

Right: After sampling the jellies are shuffled overboard. They are probably so damaged by the gear that they will not survive long.



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What is the diet of this jelly?• Mesopelagic species: Small fishes and squids• Pelagic larvae and young stages of gadoids, flatfishes, herring• Shrimps, krill, calanoids (i.e. it is a competitor for e.g. cod, addock, whiting and saithe.

Small herring and sprat

Cod larvae

KrillShrimp(Calanus sp.)

Squid



Mesopelagic fish

With this diet, the jelly is armed totake over as a top predator in theTrondheimsfjord ecosystem.

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IMPACTS FROM DISTURBANCES, POLLUTION, AND CLIMATE CHANGE

Kaiser part three; ImpactsChapter 14: Disturbances etc

Interaction between factors

In the foregoing, different factors that influence the marine ecosystems have been treated separately for the sake of simplicity. In reality they often work in concert, and the effects can be additive or synergetic.

It is notoriously difficult to predict the end outcome of the change in one factor in an ecosystem, because the interplay is so intense and complex between organisms, and between organisms and their environment. The outcomes may be very different, depending on the particular situation in time and space.

The occurence of cascade reactions is wellknown, where originally small disturbances can ”run away” and lead to substantial overthrowings of the ecosystems.

Times with extensive changes are Bonanzas for opportunistic species. Many of these are evolutionary very old forms with simple life functions. Having survived through hundreds of millions of years of evolution, one can say that they have proved the success of their design.

BI 2060 V091 Kaiser part three; Impacts Case study Trondheimsfjord The Trondheimsfjord is a...

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