Download E Case Study Trondheimsfjord

Kaiser part three; Impacts
Case study Trondheimsfjord
The Trondheimsfjord is a relatively selfsustaining ecosystem.
Of course, it is not hydrpgraphically 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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Kaiser part three; Impacts
Case study Trondheimsfjord
ABOUT THE TRONDHEIMSFJORD
The Trondheimsfjord is the third
longest and sevetnth deepest
fjord. 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.
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF FISHERIES
The Trondheimsfjord is very rich on fish species. More than a hundred fish
species are present, 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 later
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 human
population and is quite free. Also, leisure fisheries is a widespread 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, tuned to variation in the 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.
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF FISHERIES
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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EFFECTS OF FISHERIES
Norway pout
Gadoids (cod family) which
Cod
Poor cod
spawn in the Trondheimsfjord
Haddock
Whiting
Blue whiting
Saith
e
Hake
Pollack
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EFFECTS OF FISHERIES
100
80
Relativ årsklassestyrke torsk Verrabotn
60
40
20
0
1960
1965
1970
1975
1980
1985
1990
1995
Relative yearclass strengths of cod in the Trondheimsfjord 1963-1990 (Ekli 1997)
(cf next slide for extended period)
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EFFECTS OF FISHERIES
Kaiser part three; Impacts
Case study Trondheimsfjord
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EFFECTS OF FISHERIES
Kaiser part three; Impacts
Case study Trondheimsfjord
THE VERRAN COD (VERRATORSKEN)
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 gradually
reduced, and from the mid 80ies the fishery again became unprofitable for the boats
from 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 strong
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.)
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EFFECTS OF FISHERIES
Kaiser part three; Impacts
Case study Trondheimsfjord
/. 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% (Denstadli
1970, Mork 1976). On top of this comes the fishery mortality. In overexploited
stocks the total annual mortality (natural plus fishery-related) is often 70% or
more. The cod is a multiple spawner, and a spawning stock in good condition
consists of many yearclasses, included some big, old females for which a
superior egg quality and egg survival than younger females. In particular, first
time 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.
If high mortality (intense fishery), a 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) coinsides, 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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EFFECTS OF FISHERIES
Kaiser part three; Impacts
Case study Trondheimsfjord
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 of
the Trondheimsfjord (Beitstadfjord).
That this stock is genetically isolated
from the coastal herring and
Norwegian Springspawning herring
was confirmed by population
genetics methods at TBS in the
1990ies (Skjong 1994).
As common for herring stocks, the
Beitstadfjord herring has showed some
changes in spawning place and overwintering area in Beitstadfjord, but
it has still remained local.
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF FISHERIES
BEITSTADFJORDSILDA /. cont.
Apparently, the Beitstadfjord herring struggles somewhat with maintaining a proper size of the stock. It is
known to be relative small by size (slow-growing) and meager compared to e.g. coastal herring. It is mainly
a spring spawner. The spawning appears to have become more spread-out both geographically and temporally
since the 1980ies, but it still takes place in the inner fjord.
The local exploitation has traditionally been performed by ground-owners and fishermen/farmers who have used a few
herring nets, and also by the use of light and beach seines. Place for use of beach seines was a 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 lavere (2.500 tonn), at which time it was stopped due to bad recruitment to the
stock. Since 1996 there has been a full closing of the commercial fishery.. Today, it is only allowed to fish for personal
consumption using one herring net.
The traditional herring fishery in the Trondheimsfjord was not necessarily concerning only local herring. At the time
of the year when the fishery took place, there can easily be a contribution from other stocks, e.g. coastal herring and
Norwegian sprin-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 suficient natural
self-recruitment to with stand 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
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stocks in Norwegian coastal- and oceanic waters.
Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF FISHERIES
THE ANGLER FISH
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 10-15 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 catches are now reduced to one third,
and the large individuals have become more rare. This species needs a long time for the rebuilding of the local
stocks.
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EFFECTS OF FISHERIES
Kaiser part three; Impacts
Case study Trondheimsfjord
GENETIC EFFECTS OF FISHING
WITH SELECTIVE GEAR
According to evolutionary theory,
intensively exploited fish populations
are expected to undergo genetic shifts
toward 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, organized by C. T.
Marshall & H. I. Browman, discusses
probabilistic maturation reaction
norms in the context of disentangling
evolutionary vs. environmental (genetic
vs. physiological) influences on fish
maturation (see figure to the right).
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF AQUACULTURE
FARMING IN NET PENS.
RELEVANT SPECIES:
Salmon – cod – blue mussel
SALMON: The Trondheimsfjord is one of the
most important areas for salmon ascending to
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 suggested for the
status of National salmon fjord. 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-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 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 is the first application of its kind in the fjord, and triggered a legally
based process where The Ministry of Fisheries has sent the application out to a number of
hearing instances, both official and non-official. The Ministry will make its decision based on
the regulations of consessions and the the results of the hearings when these are available.
Among the conditions that probably will be treated by the hearing instances are:
From where will the codlings for farming be collected (local stock or central distributeur in Troms??)
Technical standard – security against wreckage and escape
Escape issues and potential effects on the local stock
Escape 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 MUSSEL: 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 establishe plants several places in the fjord, some
with good results.
The production is based on natural pelagic larvae which settles on ropes hanging in the water
column, and the larvae are not supported 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.
Concetrated faeces and dead mussels easily leads to local pollution of the bottom habitat. In later
years more consideration has been given to favourable current conditions and removal of debris
from theplants 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 implemented
by the authorities brought this problem under control.
Also, legislation against fertilization in winter has reduced the run-off of nutrients (nitrates,
phosphates) to rivers and the fjord. The earlier eutrophication effects with oxygen depletion
in 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 in
localities such as the Orkdalsfjord a large part of the toxic compounds are now covered by
natural sediments.
In Trondheim, industry that earlier used the Nidelva and the fjord as resipients has been
imposed strict rules for doscharge, and big cleansing plants for domestic waste has been
built.
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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 seawagw from a
large geographical area and a substantial popuulation.
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 centers 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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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
In the last 10-15 years the sea water on the Norwegian coast has undergone an
unusually 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 "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 "north boundary" for many marine
species, and that the biodiversity of the fjord becomes poorer and more like that
in 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 hegemony
as top predators, at least for a period.
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
The Figure on the next slide shows a plot of the development in bottom temperature
in 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 important
to monitor the physical and biological proceses in the fjord in order to learn and gain
experience in the effects that are triggered by climatic changes. Some of these effects
can be quite grim even at out latitudes.
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
The coronate jellyfish
(Periphylla periphylla) is an
example of an opportunist
which can strike in ecosystems out of balance.
It has some basic properties
which makes it a powerful
competitor for the hegemony
as top predator.
Not surprising, really; its basic
characteristics have survived
some 550 million years of
evolution.
Periphylla periphylla (kronemanet) i Trondheimsfjorden
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