Southwestern North Sea Research Articles

Detection and quantification of two commercial flatfishes (Solea solea and Pleuronectes platessa) in the North Sea using environmental DNA

AbstractSustainable fisheries management requires regular scientific monitoring of fish stocks. When information on certain fish stocks is limited, environmental DNA (eDNA) holds promise to complement traditional monitoring surveys. However, a better understanding of how eDNA concentrations relate to fish abundance and biomass is needed. Here, eDNA quantification of two commercially important flatfish species in the North‐East Atlantic, common sole (Solea solea) and European plaice (Pleuronectes platessa), was assessed. First, species‐specific, probe‐based assays for plaice and sole targeting the mitochondrial cytochrome b and cytochrome c oxidase subunit I gene, respectively, were developed (for sole) and validated (for both species). Subsequently, two mesocosm experiments revealed a significant and positive relationship between both abundance and biomass and eDNA concentrations for both species at three eDNA emission time periods (5 min, 1 h, and 24 h). Larger plaice shed significantly more eDNA (copies L−1) than smaller conspecifics. Finally, eDNA was obtained from seawater collected during research surveys in the Belgian part of the North Sea in spring 2020 (i.e., local scale) and the southwestern North Sea in autumn 2020 and 2021 (i.e., regional scale). eDNA concentrations were compared to the observed abundance (individuals per km2) and fish density in terms of biomass (kg per km2) as observed in the trawl at the same station. Local eDNA concentrations of both sole and plaice were positively correlated with observed abundance and fish density. The correlation between regional eDNA concentrations and fish density was positive and significant for sole in 2020 and 2021 and for plaice in 2020, but not in 2021. The correlation between regional eDNA concentrations and observed abundance was positive and significant for sole and plaice in 2020, but not in 2021. These results illustrate the potential of eDNA to estimate abundance and biomass parameters for stock assessments of flatfishes in the North Sea.

On the distribution of sand banks in the southwestern North Sea and an approach of predicting them

The morphology of the southwestern North Sea is greatly influenced by sand banks. With this paper these features have been identified by analysing bathymetric data and estimating their geometric properties. This allowed an assessment of the dimensions of the structures and enabled an economical evaluation of the associated sand resources. In fact, there are several aspects that are of economic interest, which include the sand as a potential exploitable resource and the interaction of the sand banks with submarine infrastructures, such as cables, pipelines and shipping channels. Therefore, this study aimed to evaluate and compare several oceanographic and sedimentary factors on the formation and distribution of the sand banks in the southwestern North Sea to create a prediction model for the bank occurance. The main focus was on the relation between critical shear stress of the bedload and the shear stress of currents and waves and it's effects on the sand bank formation. It has been figured out that the maximum bed shear stress needs to exceed the critical shear stress by a factor of nine to allow sand bank formation to a greater extend. Thus, this study contributes new knowledge about sand banks in the southern North Sea.

Harmful algal blooms and their effects in coastal seas of Northern Europe

Harmful algal blooms (HAB) are recurrent phenomena in northern Europe along the coasts of the Baltic Sea, Kattegat-Skagerrak, eastern North Sea, Norwegian Sea and the Barents Sea. These HABs have caused occasional massive losses for the aquaculture industry and have chronically affected socioeconomic interests in several ways. This status review gives an overview of historical HAB events and summarises reports to the Harmful Algae Event Database from 1986 to the end of year 2019 and observations made in long term monitoring programmes of potentially harmful phytoplankton and of phycotoxins in bivalve shellfish. Major HAB taxa causing fish mortalities in the region include blooms of the prymnesiophyte Chrysochromulina leadbeateri in northern Norway in 1991 and 2019, resulting in huge economic losses for fish farmers. A bloom of the prymesiophyte Prymnesium polylepis (syn. Chrysochromulina polylepis) in the Kattegat-Skagerrak in 1988 was ecosystem disruptive. Blooms of the prymnesiophyte Phaeocystis spp. have caused accumulations of foam on beaches in the southwestern North Sea and Wadden Sea coasts and shellfish mortality has been linked to their occurrence. Mortality of shellfish linked to HAB events has been observed in estuarine waters associated with influx of water from the southern North Sea. The first bloom of the dictyochophyte genus Pseudochattonella was observed in 1998, and since then such blooms have been observed in high cell densities in spring causing fish mortalities some years. Dinoflagellates, primarily Dinophysis spp., intermittently yield concentrations of Diarrhetic Shellfish Toxins (DST) in blue mussels, Mytilus edulis, above regulatory limits along the coasts of Norway, Denmark and the Swedish west coast. On average, DST levels in shellfish have decreased along the Swedish and Norwegian Skagerrak coasts since approximately 2006, coinciding with a decrease in the cell abundance of D. acuta. Among dinoflagellates, Alexandrium species are the major source of Paralytic Shellfish Toxins (PST) in the region. PST concentrations above regulatory levels were rare in the Skagerrak-Kattegat during the three decadal review period, but frequent and often abundant findings of Alexandrium resting cysts in surface sediments indicate a high potential risk for blooms. PST levels often above regulatory limits along the west coast of Norway are associated with A. catenella (ribotype Group 1) as the main toxin producer. Other Alexandrium species, such as A. ostenfeldii and A. minutum, are capable of producing PST among some populations but are usually not associated with PSP events in the region. The cell abundance of A. pseudogonyaulax, a producer of the ichthyotoxin goniodomin (GD), has increased in the Skagerrak-Kattegat since 2010, and may constitute an emerging threat. The dinoflagellate Azadinium spp. have been unequivocally linked to the presence of azaspiracid toxins (AZT) responsible for Azaspiracid Shellfish Poisoning (AZP) in northern Europe. These toxins were detected in bivalve shellfish at concentrations above regulatory limits for the first time in Norway in blue mussels in 2005 and in Sweden in blue mussels and oysters (Ostrea edulis and Crassostrea gigas) in 2018. Certain members of the diatom genus Pseudo-nitzschia produce the neurotoxin domoic acid and analogs known as Amnesic Shellfish Toxins (AST). Blooms of Pseudo-nitzschia were common in the North Sea and the Skagerrak-Kattegat, but levels of AST in bivalve shellfish were rarely above regulatory limits during the review period. Summer cyanobacteria blooms in the Baltic Sea are a concern mainly for tourism by causing massive fouling of bathing water and beaches. Some of the cyanobacteria produce toxins, e.g. Nodularia spumigena, producer of nodularin, which may be a human health problem and cause occasional dog mortalities. Coastal and shelf sea regions in northern Europe provide a key supply of seafood, socioeconomic well-being and ecosystem services. Increasing anthropogenic influence and climate change create environmental stressors causing shifts in the biogeography and intensity of HABs. Continued monitoring of HAB and phycotoxins and the operation of historical databases such as HAEDAT provide not only an ongoing status report but also provide a way to interpret causes and mechanisms of HABs.

Lipid and fatty acid dynamics by maternal Pacific bluefin tuna

Lipid and fatty acid composition of female Pacific bluefin tuna (PBF, Thunnus orientalis) reproductive and somatic tissues in southwestern North Pacific and Sea of Japan spawning grounds are compared. Total lipid (TL) levels are higher in liver than white muscle tissues. An increased gonadosomatic index (GSI) during the early spawning season coincided with decreased TL. Levels of triacylglycerols (TAG) in PBF liver tissues from the Nansei Islands and Sea of Japan, and white muscle in fishes from the Sea of Japan, decreased during the spawning season, while TAG in ovary tissues did not. Concurrent reductions in TL and increases in GSI early in the spawning season suggest TAG depletion was caused by allocation from liver and white muscle tissues to oocytes, that the liver is one of the important lipid-storage organs in PBF, and this species mostly reliant on capital deposits as a mixed capital-income breeder. Differences of docosahexaenoic acid (DHA) levels between spawning grounds were lower in ovary than in muscle and liver tissues. However, eicosapentaenoic (EPA) and arachidonic acid (ARA) levels that influence egg development and embryo and larval growth are significantly higher in PBF tissues from the Sea of Japan than Nansei Islands, which coincided with larval quality. These suggest a maternal effect exists, with egg quality influencing offspring survival, and that the reproductive strategy of PBF varies according to local variation at each spawning ground.

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

The Seasonal Variability in The Genus-Family Structure of Free-Living Nematode Communities in Organic Shrimp Farming Ponds, Ca Mau Province

Tsunami propagation over a wide, shallow continental shelf caused by the Storegga slide, southeastern North Sea, Denmark

The large Storegga slide, which occurred on the Norwegian Atlantic shelf ∼8150 yr ago, triggered a tsunami that has been identified in sediment deposits along the coasts of Greenland, Norway, the Faroe Islands, the Shetland Islands, Scotland, and the northernmost coasts of England, but hitherto not along the southeastern shores of the North Sea. It has generally been assumed that the shallow continental shelf of the North Sea attenuated and dissipated the energy of the tsunami before it reached those coastlines. We used radiocarbon and optically stimulated luminescence dating as well as stratigraphic, lithologic, chemical, and palynological analyses of sediment cores to identify tsunami deposits on the barrier island of Romo located on the southwestern North Sea coast of Denmark. We show that tsunami sediments were deposited in a freshwater paleolake that is located ∼16 m below present-day mean sea level. The tsunami sediment run-up was between 1.5 m and 5.5 m above the contemporaneous sea level. Our results demonstrate that the Storegga slide tsunami propagated across the wide (>500 km) and relatively shallow (depth <95 m) continental shelf of the North Sea and resulted in run-up along adjacent coastlines. In contradiction to earlier theoretical studies, the coastline of the southeastern North Sea cannot be regarded as being sheltered from impacts of North Atlantic tsunami incidents.

Modelling survival and connectivity of &amp;lt;i&amp;gt;Mnemiopsis leidyi&amp;lt;/i&amp;gt; in the south-western North Sea and Scheldt estuaries

Abstract. Three different models were applied to study the reproduction, survival and dispersal of Mnemiopsis leidyi in the Scheldt estuaries and the southern North Sea: a high-resolution particle tracking model with passive particles, a low-resolution particle tracking model with a reproduction model coupled to a biogeochemical model, and a dynamic energy budget (DEB) model. The results of the models, each with its strengths and weaknesses, suggest the following conceptual situation: (i) the estuaries possess enough retention capability to keep an overwintering population, and enough exchange with coastal waters of the North Sea to seed offshore populations; (ii) M. leidyi can survive in the North Sea, and be transported over considerable distances, thus facilitating connectivity between coastal embayments; (iii) under current climatic conditions, M. leidyi may not be able to reproduce in large numbers in coastal and offshore waters of the North Sea, but this may change with global warming; however, this result is subject to substantial uncertainty. Further quantitative observational work is needed on the effects of temperature, salinity and food availability on reproduction and on mortality at different life stages to improve models such as used here.

A supplement to the amphipod (Crustacea) species inventory of Helgoland (German Bight, North Sea): indication of rapid recent change

The surroundings of the rocky island of Helgoland (German Bight, south-western North Sea) are one of the best-studied sites in European seas with species occurrence data available for nearly 150 years. As the area is strongly affected by global change (e.g. increase in mean sea surface temperature at Helgoland by 1.67°C since 1962), ecosystem structure and function are expected to change more than those of average marine systems. The paper presents a supplement to the local amphipod species inventory (5 nautical miles around the island). At least seven species of this ecologically important taxon seem to have newly established themselves at Helgoland since the late 1980s: Ampelisca typica, Amphilochus brunneus, Caprella mutica, Cheirocratus assimilis, Monocorophium acherusicum, Orchestia mediterranea and Orchomenella crenata. Most of them are not only new for the Helgoland area, but also for the German Bight; and two species (Amphilochus brunneus and Orchomenella crenata) are even new to the North Sea as a whole. Out of the seven new species, one (Caprella mutica) is a neozoon from the north-western Pacific. The other six species show clear warm water affinities (oceanic–Lusitanian species) which suggest a recent range expansion in the context of climate warming. The establishment of an increasing number of species formerly probably absent from the area does not seem to be compensated by losses of species, so that local species diversity is expected to increase.

Middle and Late Weichselian (Devensian) glaciation history of south-western Norway, North Sea and eastern UK

Data from eastern England, Scotland, the northern North Sea and western Norway have been compiled in order to outline our current knowledge of the Middle and Late Weichselian glacial history of this region. Radiometric dates and their geological context from key sites in the region are presented and discussed. Based on the available information the following conclusions can be made: (i) Prior to 39 cal ka and most likely after ca 50 cal ka Scotland and southern Norway were extensively glaciated. Most likely the central North Sea was not glaciated at this time and grounded ice did not reach the shelf edge. (ii) During the time interval between 29 and 39 ka periods with ameliorated climate (including the Ålesund, Sandnes and Tolsta Interstadials) alternated with periods of restricted glaciation in Scotland and western Norway. (iii) Between 29 and 25 ka maximum Weichselian glaciation of the region occurred, with the Fennoscandian and British ice sheets coalescing in the central North Sea. (iv) Decoupling of the ice sheets had occurred at 25 ka, with development of a marine embayment in the northern North Sea (v) Between 22 and 19 ka glacial ice expanded westwards from Scandinavia onto the North Sea Plateau in the Tampen readvance. (vi) The last major expansion of glacial ice in the offshore areas was between 17.5 and 15.5 ka. At this time ice expanded in the north-western part of the region onto the Måløy Plateau from Norway and across Caithness and Orkney and to east of Shetland from the Moray Firth. The Norwegian Channel Ice Stream (NCIS), which drained major parts of the south-western Fennoscandian Ice Sheet, was active at several occasions between 29 and 18 ka.

국내 5기의 석조문화재에 분포하는 기중조류와 생물학적 등급에 관한 연구

The purpose of research was to find aerial algae and to investigate the change of color in each class of photosynthetic pigments in five stone cultural properties of Korea. It turned out to be a total of 29 taxa, including as 26 species, 1 variety and 2 unidentified species. Among them, Haplaosiphon fontinalis and Stigonema turfaceum were found to be newly recorded species of Korea. The average Chl-a concentration from the change of color in the stone cultural properties increased as its class; however, the class 5 showed lower values than the class 4, which was shown in previous studies. From the studies of algal distribution, chlorophytes appeared earlier than cyanophytes in stone cultural properties of algal infestation. Also, 50% or more of the five stone cultural properties already appeared to have bio-pollution.ഀ䡹摲潢楯汯杩愀5㔀3㌭㐴Ѐㄹ㜷਀ㄹ㜷ⴰ〰琁Ų
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Contrasting behaviour of anthropogenic gadolinium and natural rare earth elements in estuaries and the gadolinium input into the North Sea

All major rivers in northwestern Germany that flow into the North Sea, including the Weser River, display rare earth element (REE) patterns with large positive gadolinium (Gd) anomalies that indicate the presence of anthropogenic Gd derived from contrast agents used in magnetic resonance imaging. This microcontaminant cannot be removed by common sewage treatment technology and enters rivers and lakes with the discharge from waste water treatment plants. As elsewhere, a large fraction of the natural dissolved REE in the Weser River are associated with colloids. These colloids aggregate during mixing of freshwater and seawater in the low-salinity part of the Weser Estuary and the dissolved REE are partially removed from the river water together with the colloids. In marked contrast to the natural REE, the anthropogenic Gd behaves conservatively during this estuarine mixing and transits through the Weser Estuary almost unaffected. This indicates that the speciation of anthropogenic Gd is different from that of natural Gd and suggests a long environmental half-life of the anthropogenic Gd complexes used as contrast agents. The amount of anthropogenic Gd introduced into seawater via rivers is significant and produces anthropogenic positive Gd anomalies in coastal seawater. This is observed in the southwestern North Sea, off the coast of the East Frisian Islands, where anthropogenic Gd is mostly derived from the rivers Rhine and Thames. Its long environmental half-life and conservative estuarine behaviour suggest that anthropogenic Gd might be utilized as a pseudo-natural far-field tracer for truly dissolved riverine REE input into seawater and for discharge from waste water treatment plants and for sewage in river, ground and drinking water. The widespread distribution of anthropogenic Gd is an example of how the increasing use of “exotic” (ultra)trace elements in high-tech processes will in the future significantly hamper studies of the distribution and geochemical behaviour of such elements in natural systems.

Functional diversity of nematode communities in the southwestern North Sea

A range of biological traits of nematode species were combined to identify patterns in the functional composition of their assemblages collected at 19 soft-bottom stations in the southwestern North Sea with the primary aim to determine which environmental variables control communities. We used 19 categories of five biological traits thought or known to represent an important ecological function. These were related to buccal morphology, tail shape, body size, body shape and life history strategy. Data on trait membership was provided by biological information on species and genera. A total of 79 different trait combinations were recorded. Results from correlation analyses revealed several significant relationships between traits. Some trait combinations were shared by different species and genera, and the ratio of realised versus total number of possible trait combinations of < 1 suggested that some trait combinations were not represented by the nematode fauna from this region. The functional composition of nematodes was strongly linked to median particle diameter and silt content of the sediment and water depth. The approach adopted and our attempts at defining and analysing functional attributes of nematode communities raised a number of conceptual and methodological issues which are discussed.

Patterns of nematode populations in the southwestern North Sea and their link to other components of the benthic fauna

This article describes the major features of nematode assemblages collected at 19 stations in the southwestern North Sea and identifies dominant species within communities in relation to environmental parameters and anthropogenic activities. Patterns observed for meiobenthic nematodes were compared with those from larger-sized benthic fauna. Correlation analyses of nematode populations with the varied substrate occurring in the study area revealed that locations with similar sediment type and water depth were also most similar faunistically. The combined analysis of different faunal groups showed a notable similarity between species distribution patterns and this was partly based on common affinities for particular habitat conditions. The influence of factors related to sediment granulometry generally decreased with increasing size and mobility of the faunal group investigated. In terms of diversity and species composition, nematode communities encountered were similar to those occurring in comparable environments worldwide. As evident from sediment, contaminant and faunal analyses, acute effects of human activities on nematode populations seem unlikely.

Reproductive cycle of the spatangoid echinoid Echinocardium cordatum (Echinodermata) in the southwestern North Sea

Summary The reproductive cycle of the spatangoid echinoid Echinocardium cordatum is described from a 3-year survey of a population located in Wimereux (the southwest part of the North Sea). From monthly measurements and histological observations of gonads, seven distinct gonadal stages were described. These are based on the changes observed in the two-cell populations forming the germinal epithelium (germinal cells vs. nutritive cells). The gonad index (GI) and maturity index (MI) were established, and their variations were related to the seasonal changes in temperature. The species has an annual reproductive cycle with spawning beginning in April/May (variable between years) and ending suddenly in June/July. The gonads then enter a resting/recovery period until the onset of the new gametogenic process which starts in December/January. Fully mature individuals were rarely found, suggesting that gametes do not accumulate in the gonads for a long period. Empty gonads were never observed either, suggesting a regulation/interruption of gametogenesis due to the development of the somatic cells of the germinal epithelium. This could account for the annual abrupt cessation of spawning in the species. Calculation of the MI allowed a precise determination of the spawning period, and showed that reproduction is highly synchronized between males and females and well synchronized from year to year in the population. However, changes in GI values revealed different patterns between years, and this index could not be used to characterize the reproductive cycle in this species. A correlation was found between temperature and MI, with gametogenesis beginning each year after the minimal temperature has been reached. However, no clear link appears for E. cordatum between temperature and spawning events. During the resting/recovery period, there is clear evidence of nutrient accumulation resulting in both gamete resorption and food acquisition. The influence of food supply on the annual gonad development in E. cordatum is discussed, particularly with respect to the ecological constraints to which this species is subject.

The use of market sampling to generate maturity ogives and to investigate growth, sexual dimorphism and reproductive strategy in central and south-western North Sea sole (Solea solea L.)

The influence of body size, age, geographical distribution, year and season on the sexual maturation of Dover sole (Solea solea L.) in the North Sea was investigated using market sampling data collected from fish landed by commercial fishing vessels at English ports on a monthly basis since 1983. A comparison was made with maturity estimates for sole derived from research vessel survey data. The market sampling data were summarized using general linear modelling and used to generate maturity ogives for sole. There are a number of uncertainties with this approach, stemming from the use of the commercial fishery to provide the fish samples and reliance on visual (macroscopic) staging to ascertain the stage of sexual maturation of the gonads. Despite the inability to resolve all uncertainties, it was felt that it should be feasible to derive general-purpose maturity ogives from market sampling data, and that these should be sufficiently reliable for use in assessing the spawning stock biomass of North Sea Dover sole. Male and female sole were shown to have different growth and reproductive strategies, with the emphasis being directed towards maximizing egg production.Current stock assessments for sole assume that sexual maturation is knife-edged, with all fish maturing at 3 years of age. Evidence is presented to show that this approach is likely to inflate estimates of spawning stock size, since not all 3-year-olds spawn, and the proportion that do spawn varies annually. Size selection pressures resulting from commercial fishing practices are also likely to further inflate estimates of the spawning stock size. In addition, reproductive investment in first time spawning females was found to be substantially lower than in older established spawners, and it is the latter which are the first to become depleted through the pressure of sustained size-selective fishing. As a consequence, the current view of the state of well being of the North Sea sole spawning stock is likely to be overly optimistic.

Investigation of multi-phase erosion using reconstructed shale trends based on sonic data. Sole Pit axis, North Sea

Estimates from sonic data of removed overburden (burial anomalies) rely on identification of normal velocity–depth trends for relatively homogenous lithological units. In the North Sea, such trends are difficult to establish for Mesozoic formations that rarely are found at maximum burial and hydrostatic pressure. The analysis of erosional history based on sonic data can, however, be developed further where two homogeneous units are encountered in the same wells, because the two units may or may not have been simultaneously at maximum burial at a given location. If the two units were at maximum burial depth simultaneously prior to the most recent erosional event, the burial anomalies for the two units should be identical. If, however, the lower unit was at maximum burial before the upper unit, due to an intervening erosional event, the burial anomaly for the lower unit should exceed that of the upper unit. In the North Sea, Neogene erosion can be estimated from burial anomalies for the Upper Cretaceous–Danian Chalk Group. This allows corrections to be made of the depths of pre-Chalk formations to the situation prior to the onset of Neogene erosion. The normal trend for the pre-Chalk formation can now be traced more easily in a plot of velocity versus corrected depth, because the pre-Chalk formation was at maximum burial at more locations prior to Neogene erosion. This procedure is used to derive baselines for a Lower Jurassic shale unit, and for the Lower Triassic Bunter Shale and Bunter Sandstone using data from 123 British and Danish wells. The dominance of smectite/illite in the marine Lower Jurassic shale, and of kaolin in the continental Bunter Shale may explain why these two baselines diverge, and why those for the Bunter Shale and Bunter Sandstone converge. Burial anomalies for the Chalk Group and the Bunter Shale/Sandstone are calculated for 210 wells in the southwestern North Sea. Of these wells, 81 have data for both the Chalk and the Triassic level. The burial anomaly for the Triassic level exceeds that for the Chalk only along the Sole Pit axis. There, the Triassic deposits are suggested to have experienced maximum burial prior to an erosion event, in probably the Late Cretaceous or locally in the latest Jurassic. The erosion removed more than 2 km of mainly Jurassic–Lower Cretaceous or locally Triassic–Jurassic sediments. The burial anomalies for the Chalk and the Bunter levels are about identical over the rest of the southwestern North Sea Basin where they were both at maximum burial prior to Neogene erosion of up to 1 km of sediments of mainly Cenozoic age.

Storm surges and erosion of coastal dunes between 1957 and 1988 near Dunkerque (France), southwestern North Sea

Abstract The comparison of aerial photographs of eroding coastal dunes located between Dunkerque (Northern France) and the Belgium border revealed that the retreat rate of the dune front increased between 1957 and 1988. Analyses of hourly water levels from the Dunkerque Harbour tide gauge showed an increase in the frequency of high water levels associated with storm surges during the same period. Significant wave heights that could be generated during these high water level events were computed according to a wave hindcast model and using wind data collected at Dunkerque. These analyses show an increase in storm magnitude and frequency during the last two decades of the study period, and suggest a strong relationship between dune front erosion and frequency of storm surge conditions. Since relative sea-level is rising in the southern North Sea, coastal dunes will probably be more frequently reached by storm waves in the future. Consequently, more severe coastal dune erosion may take place during the next decades, increasing the risk of flooding of coastal lowlands.

Clay mineral associations in fine-grained surface sediments of the North Sea

With the help of about 500 samples of surface sediments from the North Sea crude maps of the distributions of the clay minerals illite, chlorite, smectite and kaolinite were constructed. Illite, with 51%, is the dominant clay mineral, followed by smectite (27%), chlorite (12%), and kaolinite (10%). There are well-distinguished areas of different concentrations of the individual clay mineral associations. Illite and chlorite show highest values in the north, kaolinite concentrations are high in a corridor a few hundred kilometres wide between the east coast of the UK and the Danish/south Norwegian coast. Smectite is high in the German Bight and in the southwestern North Sea. The distribution patterns of the clay mineral associations are mainly explained by late Quaternary history and by recent to sub-recent sedimentary processes. During the Pleistocene cold periods illite- and chlorite-rich sediments from the Fennoscandian Shield were transported by the great inland ice-masses in a southward direction. The present high sea-level erosion on the east coast of Great Britain provides the North Sea with kaolinite-rich fine-grained sediments. Smectites inherited from Elsterian deposits in the southeast corner and probably from sub-recent Elbe sediments are responsible for their higher values in the German Bight. The high values of smectite in the southwest may have originated from Cretaceous sediments eroded on the banks of the Strait of Dover. The present contribution of riverine suspended load to the North Sea appears to be low.

Cold Induced Abnormal Catches of Sole

Large catches of sole (Solea solea) were made in early 1996 from the south-western North Sea. Sole suffer physiological damage in waters below 3–4 C. In February 1996 cold water of 3–4 C unusually extended from the Continental coast onto the Dogger Bank. It is likely that the increased catches were due to the consequential distribution and behaviour of the sole, making them more susceptible to capture.Exceptionally large catches of mature sole (Solea solea (L.)) were made in February 1996 by Lowestoft fishermen from the south-western North Sea. Surprisingly this was not welcome. The UK allocation of the North Sea sole is -4 % of the EU Total Allowable Catch (TAC), and fishermen are restricted nationally, and by the fishing companies, to a tightly managed ration. The Lowestoft Journal (8 March 1996) reported the suspension of a local fishing skipper for not throwing back 5000 kg of sole caught in the Silver Pits. We will show that the abnormal catches were due to exceptionally cold waters.Sole in the North Sea are at the northern extremity of their range, with sole seldom living in waters below 5°C (Horwood, 1993). In fact, North Sea sole were successfully introduced into Lake Quarun, Egypt, where they lived in temperatures in excess of 30°C (El-Zarka, 1965). Young sole migrate from their shallow inshore nursery grounds, such as the Waddensea, as winter approaches (Creutzberg &amp; Fonds, 1971).

Seasonal variation in the diet of harbour seals in the south-western North Sea

Seasonal vanation in harbour seal diet in the south-western North Sea was investigated from faeces collected monthly, over a 2 yr period, from a high-water haulout site in the Wash on the east coast of England. A total of 12444 fish otoliths from 31 species was recovered from 708 faeces; otolith measurements were corrected for partial digestion and used to estimate the proportion, by weight, of each species in the diet. Overall, the diet was dominated by whiting (24 L ) , sole (15%), drayonct (13''~) and sand goby (11 '16). Other flatfish (dab, flounder, plaice: l'.?%), other gadoids (blb, cod: 11 %) , bullrout (7 % and sandeels (3 'h) were also consumed. A strong seasonality in diet was apparent which can be summarised as: whiting, bib and bullrout dominated from late autumn through early spnng; sand goby peaked during winter and early spnng; dragonet, sandeels and flatfish (except sole) dominated from late spring to early autumn; and sole peaked In spring. Harbour seal diet composition in general, and seasonal changes in diet in particular, appeared mainly to be llnked to availablllty (in terms of prcy distribution and abundance, feeding or spawning activity and, perhaps, prey si: ,~) but this was not always the case. In a few species (whiting, dab and plaice), seasonal changes in consumption appeared to be related to the availability of other species. Differences in harbour seal and grey seal diets In the same area were consistent with the 2 species feeding in different areas, but there was also evldence of a maximum preferred prey size for harbour seals.