Download E English Case Study Trondheimsfjord

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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Kaiser part three; Impacts
Case study Trondheimsfjord
ABOUT THE TRONDHEIMSFJORD
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.
Verrabotn
Agdenes
Tautra
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF FISHERIES
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
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cod- and herring fishery in the fjord.BI 2060 V09
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
decreasing, 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 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.)
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EFFECTS OF FISHERIES
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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 with superior egg
quality and egg survival compared to 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.
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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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 Spring Spawning 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
local changes in spawning place and
wintering area in Beitstadfjord, but
it has still remained local.
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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 local stakeholders 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 legal right of the landowners 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 personal
consumption 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 and
Norwegian 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
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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 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.
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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
towards 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
norms in the context of disentangling
evolutionary vs environmental (genetic vs
physiological) influences on fish
maturation (cf illustr. to the right).
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF AQUACULTURE
FARMING IN NET PENS AND ON ROPES
RELEVANT 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-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 of
its 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 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 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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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 agriculture 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 discharge, and big cleansing plants for domestic waste has been
built.
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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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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 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 that
of 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 graph 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 latitrdes.
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
Mean bottom temperatures at three stations in the Trondheimsfjord in the period 1963-2007
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
INVASIVE SPECIES
The coronate jellyfish
(Periphylla periphylla) is an
example of an opportunist
which can strike when ecosystems are 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 (Coronatae) has invaded the Trondheimsfjord
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES, POLLUTION ETC
How did this jellyfish establish itself in the Trondheimsfjord in the first place?
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Kaiser part three; Impacts
Case study Trondheimsfjord
EFFECTS OF DISTURBANCES, POLLUTION ETC
Trondheimsfjorden, depths and bottom topography
The Trondheimsfjord has
three main basins
separated by tresholds at
Agdenes, Tautra and
Skarnsundet.
600 m
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.
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Kaiser part three; Impacts
Case study Trondheimsfjord
Verrasundet; the main
spawning place for
gadoids in the fjord.
Inner Trondheimsfjord
EFFECTS OF DISTURBANCES,
POLLUTION ETC
250 m
100 m
60 m
420 m
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EFFECTS OF DISTURBANCES,
POLLUTION ETC
Kaiser part three; Impacts
Case study Trondheimsfjord
Clips from Ukeadressa
25. 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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EFFECTS OF DISTURBANCES,
POLLUTION ETC
Kaiser part three; Impacts
Case study Trondheimsfjord
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.
Shrimp
(Calanus sp.)
Krill
Squid
Small herring and sprat
With this diet, the jelly is armed to
take over as a top predator in the
Trondheimsfjord ecosystem.
Cod larvae
Mesopelagic fish
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IMPACTS FROM DISTURBANCES,
POLLUTION, AND CLIMATE CHANGE
Kaiser part three; Impacts
Chapter 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.
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