Download consso nov 98/2/ngo - CHARLIE

CONSSO NOV 98/2/NGO.
Committee of North Sea Senior Officials
Oslo: 19 - 20 November 1998
__________________________________________
Pollution Impacts on North Sea Fish Stocks *)
Presented by
World Wide Fund For Nature (WWF)
Background
In para 10 of the IMM 97 Statement of Conclusions, the need for the protection of fisheries
resources and the North Sea ecosystem from activities other than fisheries - particularly
pollution - is highlighted.
Through WWF's newest report with regard to pollution impacts on North Sea fish stocks, an
in depth review of this issue is now available. The non-technical summary is attached.
Action requested
CONSSO is invited to
take note of the attached information and consider follow up actions to implement para 10 of
the IMM SoC 97.
*)
This report to the European Commission DGXIV (Ref. 96-083) has been produced by Alison Parrett, WWF
UK. This report does not necessarily reflect the views of the European Commission and in no way anticipates
any future opinion of the Commission. The contents of this report may not be reproduced unless the source of the
material is indicated. This study has been carried out with the financial assistance of the European Commission. Full copies of the report will be provided at the CONSSO Meeting. Copies can also be ordered from WWF,
Living Seas Programme, Panda House, Weyside Park, Catteshall Lane, Godalming, Surrey GU7 1XR United
Kingdom
Pollution Impacts on North Sea Fish Stocks
NON-TECHNICAL SUMMARY
The North Sea is a relatively shallow, semi-enclosed sea into which rivers from densely
populated, highly industrialised and intensively farmed catchment areas flow. It is biologically
productive and hosts a diverse range of marine wildlife including important fisheries.
Commercial fisheries cause large-scale disturbance of the ecosystem and are often held
responsible for the decrease in size of some fish stocks. However, changes in fisheries
abundance may be exacerbated or even caused by other human influence such as
eutrophication, toxic pollution, climatic change or by natural changes in the ecosystem.
Marine areas ultimately become sinks for chemicals released directly or indirectly into the
environment. The last 50 years have witnessed a large number of diverse, naturally occurring
and synthetic contaminants being released into the ecosystem, and particular concern has been
expressed over the release of persistent and highly toxic organic pollutants.
Contaminants enter the marine environment from land-based and offshore sources. The
majority originate from land-based sources, so coastal areas are considered to be more
contaminated than offshore areas. A number of fish and shellfish species spend at least part of
their life-cycle in near shore areas (for example, nursery grounds) so they can be exposed to
contaminants for considerable periods.
Establishing that an impact or change in fisheries abundance is exclusively the result of
pollution is extremely difficult. Long-term data sets go some way to distinguishing between
natural and anthropogenic changes - but even if a trend is identified, establishing a single
cause can be difficult. In addition, biological factors and variation such as sex, age and
reproductive status can obscure data and conceal the effect that contaminants may have on
populations. Determining cause and effect relationships between biological effect and
contaminants is further complicated by the mobility of fish species.
Conclusive evidence that pollutants impact on fish stocks or populations is currently lacking however, evidence in scientific literature indicates that marine fish and invertebrates are
impacted sub-lethally by chemical contamination and nutrient inputs. Some circumstantial
evidence suggests that pollution, at least in part, may be responsible for some fish diseases.
Studies in the North Sea reveal a number of contaminant ‘hot spots’ - for example the
titanium dioxide waste dumping sites in the German Bight area - but other factors (for
example salinity and dissolved oxygen concentration) are also known to be involved in
causing external fish disease. Based on current information, there is no clear evidence that
contaminants are responsible for external fish disease. More likely, they may exert an effect
on fish immune response.
There is clear evidence from field and laboratory studies in the USA that specific chemical
groups (PAHs) are involved in the development of liver tumours and other lesions, and that
contaminant levels in some North American polluted marine environments are high enough to
induce these effects. Some European studies also indicate that pollutants can cause liver
disease. A series of pre-cancerous lesions have been identified and are used in monitoring
-2-
programmes as biomarkers of biological effects. Liver carcinomas normally develop over a
number of years, so it is unlikely that liver tumours add significantly to fish mortality in the
North Sea.
Successful reproduction and recruitment is vital for fish stock maintenance. Concern has been
expressed over the last decade that certain groups of chemicals such as PCBs can disrupt or
mimic fish reproductive hormones. Recently, male fish sampled from estuarine and coastal
sites around the UK were found to be exhibiting signs of feminisation and in the USA, female
fish at polluted sites showed premature vitellogenesis (egg yolk production). Additional
information is required on these and other endocrine disrupting effects (behavioural,
developmental and immune response) that may effect fish.
High levels of malformed fish eggs and larvae have been correlated to high levels of
pollutants detected at sites in the North Sea. However, environmental factors such as
temperature are also known to influence egg viability, so it has not been possible to establish
conclusively if pollutants are responsible.
Although there is evidence that fish and shellfish are exposed to contaminants, these
biomarkers offer little information of potential effects on the population as a whole. There is a
need to relate biomarker response to physiological change.
Nutrient levels have been increasing in many marine coastal waters throughout the world,
including the North Sea. Moderately enhanced nutrient levels have been said to have a
beneficial effect on primary production and fisheries abundance, but this is hypothesis.
Negative effects of anthropogenic eutrophication (stimulated algal growth by enrichment with
nutrients) have been shown to induce oxygen-depleted water resulting in widespread mortality
and/or migration of fish and shellfish populations out of the affected area. Vegetation cover
appears to be of major importance for fish diversity, community structure and predator-prey
relationships. In addition, a number of algal species produce toxins harmful to other aquatic
life. Although the production of harmful algal blooms is a natural phenomenon, observations
show an increase in the occurrence of novel, unusual and/or toxic phytoplankton blooms.
More work is required to establish nutrient and energy flow through the ecosystem and
determine harmful algal bloom dynamics in order to predict and identify long-term ecosystem
changes.
Furthermore, potential threats to fish stocks also exist as a result of climate change. For
example, temperature increases are likely to modify fish stock range and contaminant
detoxification in enzyme systems. Sea level rise, another predicted consequence of climate
change, is likely to cause disturbance in coastal zones, and will have implications for inshore
habitats of a number of commercial fish species . Ozone depletion resulting in enhanced
levels of harmful UV-B radiation reaching the sea surface may also impact on fish stocks.
Fish eggs and larvae floating at the sea surface may be directly impacted, whereas impacts on
phytoplankton and bacteria (at the base of the food web) could have longer-term implications
for fisheries.
On the basis of all this, there is clearly a need for a precautionary approach. In addition,
current gaps in knowledge must be addressed through continued environmental monitoring,
including long-term data sets, and through effort directed at research and the development of
monitoring and predictive techniques including a modelling approach.
-3-
-4-