Seabird biomass and food consumption in the North Sea

Calculations presented by Bourne (1983) contain some order-of-magnitude errors, and give the misleading impression that estimates of fish consumption by seabirds in the North Sea may be as low as 0.25%, or as high as 48%, of fish production, depending on the method of calculation. It is likely that the true figure is closer to 20% once the errors in Bourne's calculations are corrected, but several areas of uncertainty require further study; particularly seabird diets and foraging ranges, fish distributions and movements. Studies from other parts of the world show that seabird numbers can dramatically alter in response to changes in food abundance. Some changes result from natural perturbations and others from effects of overexploitation of fish stocks by man. Effects of overfishing seem likely to be potentially at least as serious as effects of oil or chemical pollution in many regions, possibly including the North Sea.     

Modelling exposure of oceanic higher trophic-level consumers to polychlorinated biphenyls: Pollution ‘hotspots’ in relation to mass mortality events of marine mammals

Marine mammals in the past mass mortality events may have been susceptible to infection because their immune systems were suppressed through the bioaccumulation of environmental pollutants such as polychlorinated biphenyls (PCBs). We compiled mortality event data sets of 33 marine mammal species, and employed a Finely-Advanced Transboundary Environmental model (FATE) to model the exposure of the global fish community to PCB congeners, in order to define critical exposure levels (CELs) of PCBs above which mass mortality events are likely to occur. Our modelling approach enabled us to describe the mass mortality events in the context of exposure of higher-trophic consumers to PCBs and to identify marine pollution ‘hotspots’ such as the Mediterranean Sea and north-western European coasts. We demonstrated that the CELs can be applied to quantify a chemical pollution Planetary Boundary, under which a safe operating space for marine mammals and humanity can exist.     

The use of the log-normal distribution of individuals among species in monitoring zoobenthos in the northern Baltic archipelago

The log-normal distribution of individuals among species of shallow, brackish water benthos is compared to other, more commonly used methods. This method, the use of which was introduced in marine monitoring in 1979, has not previously been tested on macrobenthos of the northern Baltic Sea. The relevance of other indices are discussed in relation to the log-normal distribution. Based on samples from three localities (soft littoral benthos, soft bottom benthos and sand bottom benthos) it is shown that the log-normal distribution could well be used as an important tool in interpreting benthic data sets from low-saline waters with few macrozoobenthic species. It illustrates natural and anthropogenic changes on the zoobenthic communities more adequately than the other parameters calculated.     

Seabirds indicate changes in the composition of plastic litter in the Atlantic and south-western Indian Oceans

I compare plastic ingested by five species of seabirds sampled in the 1980s and again in 1999-2006. The numbers of ingested plastic particles have not changed significantly, but the proportion of virgin pellets has decreased 44-79% in all five species: great shearwater Puffinus gravis, white-chinned petrel Procellaria aequinoctialis, broad-billed prion Pachyptila vittata, white-faced storm petrel Pelagodroma marina and white-bellied storm petrel Fregetta grallaria. The populations sampled range widely in the South Atlantic and western Indian Oceans. The most marked reduction occurred in great shearwaters, where the average number of pellets per bird decreased from 10.5 to 1.6. This species migrates between the South and North Atlantic each year. Similar decreases in virgin pellets have been recorded in short-tailed shearwaters Puffinus tenuirostris in the Pacific Ocean and northern fulmars Fulmarus glacialis in the North Sea. More data are needed on the relationship between plastic loads in seabirds and the density of plastic at sea in their foraging areas, but the consistent decrease in pellets in birds suggests there has been a global change in the composition of small plastic debris at sea over the last two decades.     

Increasing levels and biomagnification of persistent organic pollutants (POPs) in Antarctic biota

Representatives of the Antarctic food web (krill, cephalopod, fish, penguin, seal) of the area around Elephant Island and from the Weddell Sea were analysed for the most recalcitrant organochlorine compounds. Due to sorption of the compounds to sinking particles and accumulation in sediments, two benthic fish species (Gobionotothen gibberifrons, Chaenocephalus aceratus) feeding on benthos invertebrates and fish reflected significantly increasing concentrations within a decade (1987-1996), while a benthopelagic species (Champsocephalus gunnari) feeding on krill did not. In the pelagic food chain, lipid normalised concentrations of all compounds increased from Antarctic krill to fish proving that biomagnification of highly lipophilic pollutants (log octanol-water partition coefficient>5) occurs in water-breathing animals. As top predators Weddell and southern elephant seals (Leptonychotes weddellii, Mirounga leonina) biomagnified the persistent organic pollutants relative to krill 30-160 fold with the exception of hexachlorobenzene, the levels of which were lower than in fish indicating its intense specific elimination.     

Prevalence and composition of fishing gear debris in the nests of northern gannets (Morus bassanus) are related to fishing effort

Bycatch and indirect mortality associated with global fishing operations affect non-target species. Northern gannets (Morus bassanus) and other seabirds incorporate marine debris, much of it originating in fisheries, into their nests, at times resulting in entanglement. We compared the prevalence and composition of marine debris in nests at two gannet colonies in Newfoundland before and after a basin-wide ground fish closure in 1992, and at the species' largest colony in the Gulf of St. Lawrence, where fishing effort is low. The proportion of nests with marine debris decreased following the fishery closure, and the proportion of nests with fishing gear was related exponentially to the number of gillnets set around breeding colonies. Assessing the composition of gannet nests could provide a useful index of the prevalence of fishing debris and could be used to assess entanglement risk of other animals in the marine environment over decadal scales.     

Increase of organochlorines and mercury levels in common guillemots Uria aalge during winter in the southern North Sea

Beached seabirds, mainly common guillemots Uria aalge, were collected on the Belgian coast during winter from 1990 to 1995. Concentrations of total and organic mercury, and of organochlorines (PCBs and pesticides) were determined in muscle, liver and kidney. They were high compared to summer data (up to one order of magnitude), and increased during winter. This increase is not due to changes of total body weight nor polar lipid content, and thus reflects an actual increase of the seabirds' contamination while wintering in the southern North Sea. The observed annual cycle can be understood by assuming differences in prey contamination: higher during winter in the southern North Sea ecosystem than during summer in the Atlantic water ecosystem.     

Mortality of seabirds and fish in a lost salmon driftnet

Large numbers of seabirds have been killed in offshore salmon driftnets. Mortality of seabirds occurs not only in the nets being fished but also in lost or discarded gear. In 1978, we recovered ninety-nine seabirds of five species, two salmon sharks, one ragfish and over two hundred chum and silver salmon from a lost salmon dirftnet in the western North Pacific. Our observations indicate that such nets may be a hazard to marine organisms for extended periods on time.     

Birds,fish and offal in the North Sea

Estimates that birds take 6–29% of North Sea fish production are examined in the light of revised census results, which on the same basis would suggest that it was 13–48%, and the fishery statistics, which suggest it is more likely to be 0.25–4%. Possible causes for the ten-fold discrepancy include inadequate past allowances for the food contained in the Atlantic inflow to the North Sea and its continued high productivity, the trophic level at which the birds feed, the variety of food which they take, and the movements of both the birds and their prey. It seems likely that the offal discarded by fishermen is more important to birds than the fish that they take, and unlikely that the activity of birds makes much difference to fishermen, but any effect is masked by the slow rate of change of bird populations.     

Trypanosome infections of marine fish in the southern Barents Sea and the invasive red king crab Paralithodes camtschaticus

The red king crab Paralithodes camtschaticus was introduced to the Barents Sea from the North Pacific in the 1960s. A previous study concluded that it may be indirectly responsible for increased transmission of Trypanosoma murmanense to cod Gadus morhua in the southern Barents Sea by promoting an increase in the population of the leech vector Johanssonia arctica. Eleven species of fish, totalling 681 individuals, caught in October 2002 along the coast of Finnmark, were examined for trypanosome infections. The aims were to investigate changes in levels of infection in cod since 1999–2001, and to extend the sampling to other fish species. Relatively high infection levels were found in cod, haddock Melanogrammus aeglefinus and long rough dab Hippoglossoides platessoides, while other species were lightly infected or uninfected. In cod, no significant geographical differences in levels of infection were found, but haddock were significantly more heavily infected in western Finnmark.     

Temperature affects the timing of spawning and migration of North Sea mackerel

Climate change accentuates the need for knowing how temperature impacts the life history and productivity of economically and ecologically important species of fish. We examine the influence of temperature on the timing of the spawning and migrations of North Sea Mackerel using data from larvae CPR surveys, egg surveys and commercial landings from Danish coastal fisheries in the North Sea, Skagerrak, Kattegat and inner Danish waters. The three independent sources of data all show that there is a significant relationship between the timing of spawning and sea surface temperature. Large mackerel are shown to arrive at the feeding areas before and leave later than small mackerel and the sequential appearance of mackerel in each of the feeding areas studied supports the anecdotal evidence for an eastward post-spawning migration. Occasional commercial catches taken in winter in the Sound N, Kattegat and Skagerrak together with catches in the first quarter IBTS survey furthermore indicate some overwintering here. Significant relationships between temperature and North Sea mackerel spawning and migration have not been documented before. The results have implications for mackerel resource management and monitoring. An increase in temperature is likely to affect the timing and magnitude of the growth, recruitment and migration of North Sea mackerel with subsequent impacts on its sustainable exploitation.     

Climate induced temperature effects on growth performance, fecundity and recruitment in marine fish: developing a hypothesis for cause and effect relationships in Atlantic cod (Gadus morhua) and common eelpout (Zoarces viviparus)

Effects of global warming on animal distribution and performance become visible in many marine ecosystems. The present study was designed to develop a concept for a cause and effect understanding with respect to temperature changes and to explain ecological findings based on physiological processes. The concept is based on a wide comparison of invertebrate and fish species with a special focus on recent data obtained in two model species of fish. These fish species are both characterized by northern and southern distribution limits in the North Atlantic: eelpout (Zoarces viviparus), as a typical non-migrating inhabitant of the coastal zone and the cod (Gadus morhua), as a typical inhabitant of the continental shelf with a high importance for fisheries.Mathematical modelling demonstrates a clear significant correlation between climate induced temperature fluctuations and the recruitment of cod stocks. Growth performance in cod is optimal at temperatures close to 10°C, regardless of the population investigated in a latitudinal cline. However, temperature specific growth rates decrease at higher latitudes. Also, fecundity is less in White Sea than in North and Baltic Sea cod or eelpout populations. These findings suggest that a cold-induced shift in energy budget occurs which is unfavorable for growth performance and fecundity. Thermal tolerance limits shift depending on latitude and are characterized by oxygen limitation at both low or high temperatures. Oxygen supply to tissues is optimized at low temperature by a shift in hemoglobin isoforms and oxygen binding properties to lower affinities and higher unloading potential. Protective stimulation of heat shock protein synthesis was not observed.According to a recent model of thermal tolerance the downward shift of tolerance limits during cold adaptation is associated with rising mitochondrial densities and, thus, aerobic capacity and performance in the cold, especially in eurythermal species. At the same time the costs of mitochondrial maintenance reflected by mitochondrial proton leakage should rise leaving a lower energy fraction for growth and reproduction. The preliminary conclusion can be drawn that warming will cause a northern shift of distribution limits for both species with a rise in growth performance and fecundity larger than expected from the Q₁₀ effect in the north and lower growth or even extinction of the species in the south. Such a shift may heavily affect fishing activities in the North Sea.     

Chemically-induced genetic damage in fish: Isolation and characterization of the dab (Limanda limanda) ras gene

Polycyclic aromatic hydrocarbons (PAHs) have been implicated in the aetiology of carcinogenesis in fish liver. In mammalian models, such compounds cause characteristic DNA mutations at codons 12, 13 and 61 of the ras gene, leading to oncogene activation. In this report, the isolation and characterization of the normal ras gene of the North Sea flatfish dab (Limanda limanda) is described. Two ras genes have been identified using polymerase chain reaction (PCR) which showed extensive sequence homology to other fish and mammalian ras gene counterparts. The sequence information reported here will enable the subsequent identification of mutated dab ras alleles in feral fish taken from areas of high PAH contamination in the North Sea, and from fish exposed experimentally to specific PAHs under controlled laboratory conditions.     

Environmental policy and regulation for oil exploration and shipping activities in the Barents Sea

The Barents Sea has one of the highest levels of biological production of all the world's oceans, and holds some of the largest fish stocks and concentrations of seabirds. Environmental conditions in the area make it particularly vulnerable to damage from human activities. Given the vulnerability of this ecosystem to the effects of human activity, and the fact that physical factors (e.g. reduced visibility, ice) increase risks due to oil exploitation and shipping activities, environmental authorities will work towards more stringent discharge limits and higher standards for emergency preparedness for both oil exploitation and shipping in the Barents Sea. The Norwegian Pollution Control Authority gives priority to preventive measures that can lower the probability of accidents and particular emphasis will be given to conditions attached to production licences and controls on activities in areas that have not yet been opened for petroleum activities. Within the Arctic Environmental Protection Strategy (the Rovaniemi-process), Norway has proposed that efforts should be made to improve the protection of Arctic marine areas, and further that a working group including representatives of all the Arctic countries should assess various legal instruments and possible measures, and make recommendations for action. Currently, no special international requirements apply to ships sailing in ice-infested waters, and the recommendations from the working group will therefore be of great importance in protecting the area from damage from shipping.     

Fischereiliche Veränderungen in kulturbedingt eutrophierenden Seen

Mainly from the trends of fish yield four stages of fish succession in European lakes under cultural eutrophication are described. Trends of transparency, phosphorus, weed, benthos, and plankton are included. Supplementary interrelated effects of eutrophication on fish biology (growth, fat content, condition, distribution, reproduction, parasites, fish kills, introgression, feeding) have been collected from literature. The effects, mainly observed on planktivores, are not specific for species or localities.     

Response of the Arctic benthic community to excessive amounts of nontoxic organic matter

The paper presents a study of the effect of excessive amounts of organic matter (OM) on Arctic benthos. The source of nontoxic OM is from the mariculture of blue mussels in the White Sea (north-western area of Russia). The use of multivariate analysis procedures made it evident that in the Arctic conditions benthos is incapable of annual utilization of more than 1.5 kg dry OM m⁻² from an external source. Mineralization of OM accumulated in sediments will deteriorate the oxygen regime. The critical concentration of OM in sediments is 9–10%. An excess over this threshold leads to the formation of oxygen-free zones at the bottom, and degradation of benthos community.     

The incidence of plastic ingestion by fishes: From the prey’s perspective

One of the primary threats to ocean ecosystems from plastic pollution is ingestion by marine organisms. Well-documented in seabirds, turtles, and marine mammals, ingestion by fish and sharks has received less attention until recently. We suggest that fishes of a variety of sizes attack drifting plastic with high frequency, as evidenced by the apparent bite marks commonly left behind. We examined 5518 plastic items from random plots on Kamilo Point, Hawai’i Island, and found 15.8% to have obvious signs of attack. Extrapolated to the entire amount of debris removed from the 15 km area, over 1.3 tons of plastic is attacked each year. Items with a bottle shape, or those blue or yellow in color, were attacked with a higher frequency. The triangular edges or punctures left by teeth ranged from 1 to 20 mm in width suggesting a variety of species attack plastic items. More research is needed to document the specific fishes and rates of plastic ingestion.     

Seabird mortality in the north Irish Sea and firth of clyde early in 1974

Heavy mortality of guillemots in the Irish Sea was recorded in 1969 and was the subject of a detailed enquiry. Organochlorine contamination was thought to be a contributory factor, although this could not be conclusively established. These persistent pollutants remain in the environment and further mortalities might be expected if they were indeed responsible. In January, 1974 there was a further heavy loss of seabirds in the area and, this time, investigators were prepared and the incident was carefully monitored.     

The application of a Marine Biotic Index to different impact sources affecting soft-bottom benthic communities along European coasts

Following the European Water Framework Directive (2000/60/EC), the authors proposed, in a previous contribution, a Marine Biotic Coefficient (BC) to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments. The present study examines the application of the BC to the Atlantic (North Sea; Bay of Biscay; South of Spain) and Mediterranean (Spain and Greece) European coasts. The investigation assesses also the usefulness of the BC, in relation to different impact sources (e.g. drilling cuts with ester-based mud, submarine outfalls, heavy metals, industrial and mining wastes, jetties and sewerage works). The results obtained are consistent with those obtained using several methods and parameters, such as richness, diversity, evenness, Abundance-Biomass comparison plots and univariate and multivariate statistical analyses. The BC values provide a simple and clearly defined way to establish the ecological quality of soft-bottom benthos, complementary to the above mentioned methods.     

Ingested plastic in a diving seabird, the thick-billed murre (Uria lomvia), in the eastern Canadian Arctic

Plastic debris has become ubiquitous in the marine environment and seabirds may ingest debris which can have deleterious effects on their health. In the North Atlantic Ocean, surface feeding seabirds typically ingest high levels of plastic, while the diving auks which feed in the water column typically have much lower levels. We examined 186 thick-billed murres from five colonies in the eastern Canadian Arctic for ingested plastic debris. Approximately 11% of the birds had at least one piece of plastic debris in their gastrointestinal tracts, with debris dominated by user plastics. This is the first report of ingested plastics in an auk species in Canada’s Arctic, and the highest incidence of plastic ingestion to date for thick-billed murres (Uria lomvia).