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Passive acoustic monitoring has the potential to be a useful tool for population estimation of sound-producing fish and mammals (mostly whales). Previous work on population estimates of callers employed a simple cross-correlation technique with recordings from two acoustic sensors, and the current work extends the technique to two configurations of a 3-acoustic sensors array using two different sounds, i.e., chirps which is commonly generated by damselfish (Dascyllus aruanus), humpback whales (Megaptera novaeangliae), dugongs (Dugong dugon) etc., species, and grunts which is commonly generated by Japanese gurnard (Chelidonichthys kumu), Grey gurnard (Eutrigla gurnardus), gulf toadfish (O. beta), etc., species. We compared simulated results from this technique with values determined by theoretical approach. We have found that an increasing number of cross-correlation function (CCF) provide better results using this technique. However, the technique has some limitations including negligence of multipath interference, assuming the delays to be integer. Keywords: Passive acoustic monitoring, Cross-correlation function, Bin, Acoustic sensors

The current investigation represented the first anatomical description of the buccal cavity of the grey gurnard Eutrigla gurnardus. For the achievement of this study, 10 heads of mature fish were used for SEM examinations. The morphological characteristic appearance of the buccal cavity has shown several adaptations in relation concerning its feeding habits. The median fissure of the upper lip divided the upper lip into two halves, this fissure appeared to be formed from many micro-tubercles with numerous taste buds which aid in holding mucus secretion to the cell surface, help in mucus spread, and provide mechanical protection to the epithelium. Velum had two regions: median and peripheral region. The epithelium covering of the median region of the upper velum had dots-like epithelial protrusion that carrying numerous taste buds, meanwhile, the epithelium covering of the lower velum not carried taste buds but instead carried numerous small scales-like structures. The palate is divided into two semicircular regions by small region of microridges into the anterior and posterior region. The slightly bifid tongue had a median tubercle with numerous small taste buds on its dorsal surface. Concluded, these data were necessary to understand the adaptation of fish to its habitat and in developing a new and better method for fishing of this type of fish.

The grey gurnard Eutrigla gurnardus (L.) has been identified by ICES as a potential commercial species in the NE Atlantic with recommendations made to derive information on population biology for stock assessment purposes. However, data on the population biology of this species is limited. In this study, data on the age, growth and maturity of grey gurnard were collected by otter trawling in the coastal waters of northwest Wales and Eastern Anglesey. Total length (TL) of fish sampled ranged between 2.1–33.0 cm (male) and 1.9–36.9 cm (female) with the majority of female (70.8%) fish between 11 and 20 cm TL and male fish (70.5%) between 11 and 18 cm TL. The percentage of fish >20 cm TL was larger for females (30.4%) compared to males (17.6%). Total weight (TW) for female and male grey gurnard in the stratified subsample ranged from 1.9 to 499.9 g for females and 2.1–390.0 g for males, with the majority of female (66.3%) and male (76.1%) fish between 10 and 60 g. TL/TW relations for male and female fish and both sexes combined were: TW = 0.006TL3.07, TW = 0.007TL3.03 and TW = 0.007TL3.05 respectively. Age structure (based on otolith reading) ranged between 0.5 and 7.5 years old for females and 0.5 to 5.5 years old for male with the majority of female (41.7%) and male (46.0%) fish aged as 1.5 years old. The age structure of female and male grey gurnards was significantly different with the majority of older fish (>2.5 years) being female. The von Bertalanffy growth functions were calculated as Lt = 32.4[1 − e−0.24(t + 1.41)] for males, Lt = 45.9[1 − e−0.16(t + 1.37)] for females and Lt = 44.0[1 − e−0.18(t + 1.20)] for both sexes combined. Instantaneous rates of total mortality were similar for males and females and the combined Z value 1.00 year−1 with the natural mortality rate estimated as 0.33 year−1. The size at 50% maturity (L50) was estimated to be 25.3 cm TL for males, females and for both sexes combined. Age at 50% maturity (A50) was 3.2 years for both males and females. The results of this study provide the first information on the population biology of E. gurnardus in the Irish Sea, the first detailed study in the NE Atlantic since 1985 and helps to address the data gap identified by ICES in knowledge of the population biology of this species.

Triglidae is a family of benthic marine fishes known as gurnards and sea robins, and are distributed throughout all the tropical and temperate seas. Electrophoresis of PCR-RFLP and SDS-proteins were used for differentiation between three gurnards and to detect their genetic relationship. Twenty four fish samples of the grey, the red and the piper gurnards were taken as eight samples from each species. Protein bands varied from 10 to 13 bands in the studied fishes, i.e. 13 bands in the grey gurnard and 10 bands in each of the piper and the red gurnards. The red gurnard recorded the highest similarity to the piper gurnard, while the red gurnard recorded lower similarity to the grey gurnard. Two primers were used for PCR amplification of 360 bp long fragments of the mt DNA cytochrome b (Cyt b) gene and 655 bp of the mt DNA cytochrome oxidase subunit I (COI) gene. The PCR products were digested by two different restriction enzymes DdeI and HincII. Digestion by these enzymes produced highly polymorphic restriction profiles. This enables the differentiation of these fishes and showed that there is a wide intraspecific COI and Cyt b genes. The phylogenetic tree based on the sharing protein bands and PCR-RFLP fragments gave similar results and revealed the relationship between the studied gurnards.

The research was conducted on the parasite fauna and food composition of Eutrigla gurnardus caught as by-catch in commercial catches of the Atlantic cod Gadus morhua near the Shetland Islands. Thirteen species and two genera of pathogens were identified, including six species and one genus recorded for the first time in this host. Copepoda — Euphausiacea dominated in the stomach contents (they are also the intermediate hosts for most of the parasites found), while Gadidae dominated among the fish. A checklist of E. gurnardus parasites is included.

Specific features of feeding of grey gurnard Eutrigla gurnardus depending on vertical distribution and habitat conditions in the area of the Rockall Seamount in 2000 were considered. The intensity of feeding of grey gurnard from April to September decreased by several times. The main food of this species in spring are euphausiids and that in autumn are fish. Males feed slightly more intensively than females. The intensity of feeding, distribution, and behavior of grey gurnard in different seasons and at different depths near bottom and in the pelagial noticeably differ and depend on the composition of distribution and numbers of dominant food items (euphausiids, sand eel Ammodytes marinus, fish juveniles).

Previous studies have shown that Grey gurnard from the North Sea is comparatively heavily infected with the larvae of the parasitic and potentially consumer hazardous nematode Anisakis simplex (s.l.). Especially the high abundance of Anisakis larvae in the fish flesh is of concern regarding the possible intensified utilisation of Grey Gurnard as a food resource. To gain better knowledge of the nematode burden with emphasis on abundance and distribution in the fish flesh, various Grey gurnards from 6 localities across the North Sea, each representing either western, northern or eastern fishing grounds, were examined for anisakid nematodes during summer of 2010 and 2012. The overall prevalence of A. simplex (s.l.) larvae in the gurnards from all localities (n = 188) was nearly total, i.e. only a single fish from the northernmost locality (Viking Bank) was apparently not infected. GLM-analyses revealed that catching locality had by far the strongest effect on larval infection probability, both in total (flesh + viscera) and in the fish flesh, while body size (weight) was a weak but still significant predictor of overall A. simplex (s.l.) abundance, but not in the flesh. Thus, the overall larval abundance in the gurnards from the two western localities off the east-coast of British mainland was significantly higher compared to the other catching localities. In the former localities, the overall mean abundance of A. simplex (s.l.) larvae was 35.0 ± 23.9 and 92.2 ± 87.4, and ranged from 14 to 114 and 9 to 397, respectively. It was further shown that 93.8% of the larvae infecting the fish flesh were situated in the belly flaps, i.e. the ventral portion of each flesh side or fillet, independent of catching locality and fish size. However, trimming of the fillets by removing the belly flaps may reduce the abundance in the fillets to, on an average, 0.3 larvae.

Groundfish survey data from the German Bight from 1902–08, 1919–23, and 1930–1932 and ICES International Bottom Trawl Survey (IBTS) quarter 3 data from 1991 to 2009 were analysed with respect to species frequencies, maximum length, trends in catch-per-unit-effort, species richness parameters (SNR) and presence of large fish (Φ 40 ), the latter defined as average presence of species per haul with specimens larger than 40 cm given. Four different periods are distinguished: (a) before 1914 with medium commercial CPUE and low landings, Φ 40 ≈ 2, high abundance in elasmobranchs and SNR conditions indicating highly diverse assemblages, (b) conditions immediately after 1918 with higher commercial CPUE, recovering landings, Φ 40 at > 4 in 1919, and SNR conditions indicating highly diverse assemblages, (c) conditions from 1920 to the early 1930's with decreasing commercial CPUE, increased landings, decreasing Φ 40 , SNR conditions similar to later years indicating less diverse assemblages, and a decrease in elasmobranchs. In the IBTS series (d), Φ 40 remains low indicating an increased rarity of large specimens, and SNR characteristics are similar to the third period. Dab, whiting and grey gurnard have increased considerably in the IBTS series as compared to the historic data. Φ 40 is suggested an alternative indicator reflecting community functional diversity when weight based indicators cannot be applied.

Predation is one of the principle factors regulating the survival of early-life stages and recruitment success of marine fishes. Although challenging, it is important to understand how predation mortality varies in space and how this spatial variability affects the temporal dynamics of fish recruitment. We investigated the spatiotemporal variability in the magnitude of predation mortality and survival of Atlantic cod (Gadus morhua) in the North Sea by combining a Lagrangian individual-based model of cod early-life stages (eggs, larvae and age-0 juveniles) with an Eulerian representation of its fish predators based on field data collected quarterly from 1991 to 1997. The mean and variance (spatial and inter-annual) in survival of cod were different between simulations using homogeneous and heterogeneous spatial distributions of predators. Survival of cod through its early-life period was 1 order of magnitude higher in simulations using heterogeneous versus homogenous predator distributions, mainly due to reduced mortality of eggs and larvae in the former simulation. Our model predicted markedly different year-to-year changes in cod survival, when heterogeneous predator fields were implemented. In the heterogeneous simulation, Atlantic herring (Clupea harengus) and grey gurnard (Eutrigla gurnadus) emerged as the most important predators comprising, respectively, 68% and 13% of the predation mortality caused by 7 predators included in our study. A low (

The interdependence between groundfish assemblages and habitat properties was investigated on the Dogger Bank in the North Sea. Abiotic habitat parameters considered included topography, hydrographic conditions, sediment composition, and the biotic habitat variable the prevailing benthic invertebrates. Distinct epi- and infauna communities occurred at different locations on the Dogger Bank. Fish assemblages were clearly linked to both the biotic and abiotic habitat characteristics. Overall, fish and benthic communities revealed similar spatial distribution, represented in the respective clusters of characteristic and abundant species. Distribution patterns corresponded with the prevailing abiotic conditions such as depth and sediment composition, which appear to relate to autecological preferences of individual species. The apparently most generalist species, grey gurnard ( Eutrigla gurnardus ) and dab ( Limanda limanda ) occurred at all stations and dominated in terms of biomass in most cases. The absolute numbers of grey gurnards were related to the abundance of suitable prey, invertebrate and fish species, which stomach analyses revealed as part of the diet in an independent study during the same research cruise. Haddock ( Melanogrammus aeglefinus ) and whiting ( Merlangius merlangus ) were only abundant at deep stations along the flanks of the bank. The occurrence of lemon sole ( Microstomus kitt ), American plaice ( Hippoglossoides platessoides ) and cod ( Gadus morhua ) was also positively correlated with depth, whereas especially lesser weever ( Echiichthys vipera ), sandeel species and solenette ( Buglossidium luteum ) occurred predominantly at the shallower sites. At the same time, individual fish species such as solenette and lesser weever were associated with high densities of selected epi- or infauna species.

The understanding of spatio-temporal dynamics of marine ecosystems is crucial for ecosystem-based fisheries management and climate change impact assessments. We quantified temporal changes in the distribution of 0-group cod (Gadus morhua) and grey gurnard (Eutriglia gurnardus), a primary predator of 0-group cod, with the help of regression kriging and assessed the temporal dynamics of the related spatial predator–prey overlap of these two species at different spatial scales. We analysed the robustness of relationships among abiotic habitat properties (temperature, salinity and depth) and abundance. Small cod was mainly found in low salinity areas of the Skagerrak but larger year classes were able to expand their distribution area towards the central and northern North Sea. In contrast, grey gurnard was mainly found in waters with salinities above 33 and temperatures above 14°C. This species has expanded its high density areas in the central North Sea northward over the last two decades. Recruitment success of cod was negatively correlated to a Moran's I cross-correlation index, a proxy for the degree of spatial overlap between both species. Strong cod year classes overlapped less with grey gurnard at the large and medium spatial scale. In general, the relationships between abiotic habitat properties and abundance showed an increased inter-annual variability, which was likely caused by underlying factors not taken into account in the distribution models. Thus assemblage modeling approaches combining the strength of different model types should be considered in the future to predict potential distribution patterns under climate change scenarios.

Fishers and scientists have known for over 100 years that the status of fish stocks can be greatly influenced by prevailing climatic conditions. Based on historical sea surface temperature data, the North Sea has been identified as one of 20 ‘hot spots’ of climate change globally and projections for the next 100 years suggest that the region will continue to warm. The consequences of this rapid temperature rise are already being seen in shifts in species distribution and variability in stock recruitment. This chapter reviews currentevidence for climate change effects on fisheries in the North Sea—one of the most important fishing grounds in the world—as well as available projections for North Sea fisheries in the future. Discussion focuses on biological, operational and wider market concerns, as well as on possible economic consequences. It is clear that fish communities and the fisheries that target them will be very different in 50 or 100 years’ time and that management and governance will need to adapt accordingly

Lesser sandeels Ammodytes marinus are eaten by a range of predatory fishes including commercially fished species, but are also exploited at large scale by industrial fisheries. Is availability of sandeels, as key prey source, linked to the body condition of predatory fishes? In the North Sea, the largest sandeel biomass is concentrated in the Dogger Bank region. Here we studied predator–sandeel interactions at two sites differing widely in sandeel abundance and local sandeel fishing effort. Surveys took place in 2004, 2005, and 2006, years when local sandeel densities observed at these sites were low, intermediate, and high, respectively. Five predator species––whiting, lesser weever, grey gurnard, plaice, and haddock––showed better body condition indices in either the years or study area (or both) characterised by higher local sandeel densities, when compared to sandeel-poorer conditions. Moreover, whiting, weever, and gurnard condition was better for those individuals actually observed to have eaten sandeels (based on stomach contents) than for those that had not. As body condition relates to growth, reproduction, and survival, predators in sandeel-rich conditions may be inferred to have a higher fitness. These links between sandeel availability, sandeel consumption, and predator condition hint that, if large-scale localised depletions of sandeels were to occur, negative indirect effects on predatory fish might become apparent, underlining the importance of considering the sandeel fishery in an ecosystem context.

Stomach contents of potential predators from a flatfish nursery ground on the Scot- tish west coast were examined visually and probed using a TaqMan real-time PCR based assay designed to detect plaice Pleuronectes platessa DNA. Stomachs from 1137 brown shrimp Crangon crangon, along with a lesser number of shore crab Carcinus maenas, grey gurnard Eutrigla gurnardus and Gobiidae were analysed. Overall 45% of shrimp tested positive for plaice DNA, a proportion considerably higher than in stomachs containing visually identifiable flatfish remains. When scaled to the population level, predation by shrimp generated an estimated mortality of ~9% d -1 , which compares with a decline in plaice abundance from mid-May to mid-June of ~4.4% d −1 . The discrepancy between mortality estimates based on molecular and catch-curve analysis might be due to sampling being conducted at low water between dusk and dawn, which would concentrate predators and prey at times coincident with peaks of shrimp feeding. In addition, the sensitivity of the TaqMan assay could have led to some over-estimation because non-fatal interac- tions may also have been detected, e.g. shrimp are known to nibble the fins of flatfish, that might result in a positive TaqMan result but not necessarily in mortality for the fish. The percentage of shrimp testing positive for presence of plaice DNA in their stomachs was also related to plaice density in a positive, linear manner. For less abundant predators, stomachs of 6% of shore crabs, 40% of gurnards and 11% of large gobies also tested positive.

A new species of parasitic nematode, Collarinema eutriglae n. sp. (Cystidicolidae), is described from the stomach of the marine scorpaeniform fish Eutrigla gurnardus (Linnaeus), the grey gurnard (Triglidae), collected in the North Sea in the vicinity of the Shetland Islands (61°12'N, 00°30'E) during March, 2011. The new species, studied using both light and scanning electron microscopy, is characterised mainly by the structure of the mouth (small pseudolabia with terminal projections, submedian labia and well-developed sublabia not exceeding the labia externally), very small simple deirids, the length of the spicules (405-423 and 117-135 μm) and non-filamented eggs. Collarinema Sey, 1970 is considered a valid genus and an amended diagnosis is provided. Ascarophis collaris Petter, 1970 is transferred to Collarinema as C. collaris (Petter, 1970) n. comb.

Grey gurnard ( Eutrigla gurnardus L.) is an abundant and widely distributed demersal fish in the North Sea. It is currently considered a sustainable stock, thus permitting future increased utilisation as a food resource. In order to address both consumer safety and aesthetical product quality, the occurrence and distribution of anisakid nematode larvae in Grey gurnard from two localities in the North Sea were investigated. Two anisakid species were recorded, i.e. Hysterothylacium aduncum in the viscera, and Anisakis simplex in both the viscera and flesh of the fish. Virtually all gurnards were infected with nematode larvae. However, H. aduncum was significantly less abundant than A. simplex in the fish from both localities. Only for the gurnards from the northernmost sampling locality there was a significantly positive correlation between host body weight and total A. simplex abundance. No such correlation was found for H. aduncum in either locality. Separate analyses of the Anisakis infection data in gurnards of marketable size (≥250 g) and pooled for both localities, revealed 83% prevalence of A. simplex larvae in the fish flesh, ranging 1–16 in intensity. The relative larval distribution between the viscera and flesh was 89 and 11%, respectively. Moreover, a significantly positive correlation was found between A. simplex occurring in the viscera and the flesh of this particular host size group, i.e. the number of larvae in the flesh appeared to increase with increasing infection level in the viscera. In general, Grey gurnard from the North Sea can be considered as heavily infected with nematode larvae. Especially the comparatively high abundance of A. simplex larvae in the flesh is of concern regarding the possible intensified utilization of Grey gurnard as a food resource.

Uhlmann, S. S., Bierman, S. M., and van Helmond, A. T. M. 2011. A method of detecting patterns in mean lengths of samples of discarded fish, applied to the self-sampling programme of the Dutch bottom-trawl fishery. – ICES Journal of Marine Science, 68: 1712–1718. In 2009, a self-sampling programme was organized in the Netherlands, fishers sampling ca. 80 kg of discards from randomly selected bottom trawls in the North Sea. A statistical procedure is proposed to highlight samples, trips (with multiple samples), or vessels (which may have multiple trips within a year) where extreme mean lengths of discarded fish were observed. Randomization methods were used to test for evidence of non-randomness in patterns of highlighted discard samples, e.g. repeated observations of extreme mean lengths for consecutive discard samples across trips from the same vessel. European plaice (Pleuronectes platessa), common dab (Limanda limanda), grey gurnard (Eutrigla gurnardus), and whiting (Merlangius merlangus) were considered because these were the most abundant species in most of the discard samples. A linear mixed model was used to estimate random-sample effects on the estimated mean lengths by species. These random effects were incorporated into uni- and bivariate procedures to identify extreme samples that were summed for each vessel, and the probability of observing such numbers was estimated. Excluding these samples from the dataset had marginal effects on estimated size distributions of fish.

Summary During a fisheries research cruise on the Dogger Bank in the central North Sea, we studied the role of diet for the condition of grey gurnard (Eutrigla gurnardus). Seventeen stations across the Dogger Bank were sampled with the GOV otter trawl in April/May 2006. Each fish sampled was categorised according to three feeding types: a predator specialised on fish, on invertebrates or having a mixed diet, depending on the percentage of fish and/or invertebrates in the stomach. These predator-prey categories were compared by means of three condition indices: Fulton’s condition factor, a hepatosomatic index (HSI) and a gonadosomatic index (GSI). Fulton’s condition factor provided evidence that a specialisation on fish prey increases the condition of grey gurnards in terms of the length-specific individual weight. In contrast, the HSI scored highest for predators feeding on a mixed diet. The GSI showed a tendency to be highest with a diet dominated by invertebrate prey, but differences between the three predator-prey categories were not significant. Based on the topography of the Dogger Bank, stations were allocated in shallow and deep regions. At shallow stations, the brown shrimp Crangon allmani and sandeels, combining basically the taxa Ammodytidae, Ammodytes juv. and Ammodytes marinus, were typically observed in stomach contents of gurnards whereas the amphipod Hyperia galba was predominantly found in gurnards sampled in deep regions.

Recently, a significant amount of attention has been devoted to the determination of polybrominated biphenyls in food and the environment. In this study, PBB contamination of fish from the North and Baltic Seas, with a special focus on samples from Poland and France, was investigated. North Sea fish like salmon, herring, scarp, gilthead seabream and grey gurnard were collected from a French fish market. Baltic Sea fish like salmon, tunny, trout, herring, and freshwater fish such as carp were purchased from a Polish fish market. Cod livers in oil were also analyzed in this study. As additional food samples, butter, pork fat and beef fat were tested. Concentrations of PBBs in North Sea fish (except herring) were higher than in fish from the Baltic Sea. The highest total PBB concentration was measured in scarp muscle tissue (635 ± 107 pg g −1 wet weight), and the lowest was in carp samples (0.567 ± 0.245 pg g −1 wet weight). The PBB content in tunny oil samples was below the detection limits (0.45–1.05 pg g −1 fat). Our study also demonstrated that PBBs may bioaccumulate in the liver, where PBB concentrations were 2116 ± 351 pg g −1 wet weight and 841 ± 147 pg g −1 wet weight. In fish species from Poland, the most dominant congeners were tetrabromobiphenyls, followed by pentabromobiphenyls and hexabromobiphenyls. In some species of fish from the North Sea, the most dominant groups were hexabromobiphenyls and tetrabromobiphenyls. Although the relative abundances of structurally known and unknown isomers varied from species to species, all fish (except tunny) were contaminated with PBBs.

Understanding the links between large scale spatial structuring of fish assemblages and shaping factors is essential to develop comprehensive ecosystem-based fisheries management. In this study, we investigated spatial patterns of bottom fish assemblages in the North Sea in relation to prevailing water masses in the region. We based our analysis on catch data from the German Small-Scale Bottom Trawl Survey conducted between 1987 and 2005 and used both ordination techniques and Mantel tests. Spatial variability of bottom fish assemblages was larger than inter-annual variability. Five significantly different bottom fish assemblages were associated with the following prevailing hydrographical regimes: i) the English Channel, ii) Continental Coastal, iii) central North Sea, iv) northern North Sea, and v) northern Atlantic water masses. Associations were generated by gradients in relative proportions of abundant species such as grey gurnard (Eutrigla gurnardus), dab (Limanda limanda), whiting (Merlangius merlangus), haddock (Melanogrammus aeglefinus) and Norway pout (Trisopterus esmarki). Taking into account large scale spatial structuring of catch data Mantel tests confirmed significant correlation between the fish assemblages and hydrographical variables. In summary, our results strongly support the hypotheses that hydrographical features such as water masses, fronts, and residual currents could shape bottom fish associations in the North Sea. Spatial demarcations of bottom fish assemblages indicated by this study can be used to support ecosystem-based fisheries management strategies.

This paper presents the first estimation of discarding levels by the demersal fishery in the waters around Ireland. The analysis is based on the Irish discard programme, involving observer's onboard commercial vessels that participate on a voluntary basis. The programme started in 1993 and, until 2002, 225 trips were sampled, corresponding to 2189 sampled tows. Approximately one-quarter of the catch of otter trawlers and “Scottish” seiners is discarded, while two-thirds of the catch of beam trawls is discarded. Furthermore, otter trawl fleet components (defined by the area visited, targeted species and gear used) discard between 20 and 60% of their catch. Discards usually comprise 11 fish species per haul in the 3 gears types studied. Whiting (Merlangius merlangus), haddock (Melanogrammus aeglefinus), bluemouth (Helicolenus dactylopterus), megrim (Lepidorhombus whiffiagonis) and dogfish (Scyliorhinus spp.) are the main species discarded by otter trawlers. “Scottish” seiners discard mostly whiting, haddock and grey gurnard (Eutrigla gurnardus). Dab (Limanda limanda) and plaice (Pleuronectes platessa) are the most species discarded by beam trawls. The majority of these discarded species consist of immature fish. Discarding appears to be increasing in recent years, especially in traditionally bycaught species such as haddock and whiting.

Grey gurnard (Eutrigla gurnadus) is a widely distributed demersal species in the North Sea that has been ranked frequently among the 10 dominant species. Since the late 1980s, grey gurnard catch rates in the international bottom trawl surveys showed a pronounced increase and it was included as an "other predator" in the North Sea multispecies virtual population analysis (MSVPA) in 1997. The MSVPA results estimated grey gurnard to be responsible for approximately 60% of the total predation mortality on age-0 Atlantic cod (Gadus morhua). Long-term MSVPA predictions led to the extinction of North Sea cod. As a possible technical reason, the Holling type II functional response implemented in the model was discussed. In the current analysis, it was demonstrated that the Holling type II functional response was not responsible for the extinction of cod in the model, which was rather a true effect of high grey gurnard predation. Further, it was shown that grey gurnard predation had a significant top-down effect on whiting (Merlangius merlangus) and potentially also on cod recruitment, which was linked to the spatial distribution of the three species. Eventually, the implications of the results for North Sea cod stock recovery plans were discussed.

Although sound production in teleost fish is often associated with territorial behaviour, little is known of fish acoustic behaviour in other agonistic contexts such as competitive feeding and how it changes during ontogeny. The grey gurnard, Eutrigla gurnardus, frequently emits knock and grunt sounds during competitive feeding and seems to adopt both contest and scramble tactics under defensible resource conditions. Here we examine, for the first time, the effect of fish size on sound production and agonistic behaviour during competitive feeding. We have made sound (alone) and video (synchronized image and sound) recordings of grey gurnards during competitive feeding interactions. Experimental fish ranged from small juveniles to large adults and were grouped in four size classes: 10–15, 15–20, 25–30 and 30–40 cm in total length. We show that, in this species, both sound production and feeding behaviour change with fish size. Sound production rate decreased in larger fish. Sound duration, pulse duration and the number of pulses increased whereas the peak frequency decreased with fish size, in both sound types (knocks and grunts). Interaction rate and the frequency of agonistic behaviour decreased with increasing fish size during competitive feeding sessions. The proportion of feeding interactions accompanied by sound production was similar in all size classes. However, the proportion of interactions accompanied by knocks (less aggressive sounds) and by grunts (more aggressive) increased and decreased with fish size, respectively. Taken together, these results suggest that smaller grey gurnards compete for food by contest tactics whereas larger specimens predominantly scramble for food, probably because body size gives an advantage in locating, capturing and handling prey. We further suggest that sounds emitted during feeding may potentially give information on the motivation and ability of the individual to compete for food resources.

Size preference for prey fish of North Sea whiting, saithe, and grey gurnard was analysed. The analysis combined size-specific prey abundance estimates derived from bottom-trawl surveys with size frequencies of prey in predator stomachs from the International North Sea Stomach Database. To estimate the abundance of all potential prey fish in the sea, predator-specific length-based number spectra were calculated. Prey spectra were weighted by local predator abundance to take the spatial–temporal overlap between predator and their prey into consideration. Species-specific prey size preference models are presented. Contrary to former results, the preferred predator–prey weight ratio of whiting and grey gurnard is an exponentially increasing function of predator size and an exponentially decreasing function of the slope of the number spectrum. When predators grow, they prefer larger prey in absolute units. However, from a species-specific body size onwards they increasingly shift their prey preference towards relatively smaller prey sizes. From a bioenergetic point of view, this behaviour most likely maximizes the predator's foraging efficiency by reducing the expenditure of costly, anaerobically generated energy expended during burst swimming.

The acoustic repertoire of captive grey gurnard Eutrigla gurnardus during competitive feeding consisted of three types of sound: knocks, grunts and growls. Knocks were audible as a single sound, whereas grunts and growls were perceived as longer, pulsed sounds to the human ear. Typically, knocks were composed of 1–2 pulses, grunts of 4–8 pulses and growls >10 pulses. Growls were longer and had shorter pulse periods than grunts. All sound types had peak frequencies of c. 500 Hz. The sequences of behaviours observed during feeding interactions suggest that grey gurnard obtain food both by scramble and contest tactics. Competing fish emitted knocks mainly while grasping a food item and also during other non-agonistic behaviour, suggesting that knock production may reflect a state of feeding arousal but could also serve as a warning of the forager’s presence to nearby competitors. Grunts were mainly emitted during frontal displays, which were the most frequent behavioural act preceding grasps, suggesting that they may play a role in deterring other fish from gaining access to disputed food items.

Effort in trawl surveys is standardized by using a common gear and fixing haul duration and vessel speed. Such standardization should result in a fairly constant distance trawled and area or volume swept. Protocols for the North Sea International Bottom Trawl Survey (IBTS) establish hauls of 30 min at a target speed of 4 knots over ground with a standard GOV (Grande Ouverture Verticale) trawl. Primarily to evaluate the effect of departures from the target speed and of trawl speed through water, a fishing experiment was performed under IBTS protocol conditions. The experiment consisted of 30 hauls made by RV “Walther Herwig III” in a small area in the northern North Sea during 5 days in November 1997. Speed over ground was calculated from the distance between GPS shooting and hauling positions. Current speed and direction were continuously recorded by a current metre set a few metres above the sea bottom in the centre of the area to allow trawl speed through water to be calculated. We used generalized additive and linear models to analyse variation in catch rates of Norway pout (Trisopterus esmarki), haddock (Melanogrammus aeglefinus), whiting (Merlangius merlangus), dab (Limanda limanda) and grey gurnard (Eutrigla gurnardus) with speed over ground and through water, and also with area and volume swept by the gear, together with time of day to account for diel fluctuations. Catch rates of small haddock and whiting, grey gurnard and dab increased significantly with speed over ground while rates of Norway pout and large whiting increased with speed through water. We propose that this difference is indicative of the vertical distribution of the fish. Most affected by speed were small haddock and whiting: catches in numbers doubled within the range of 3.9 to 5.2 knot ground speed observed during the experiment. Catches of large haddock were stable. Area swept affected small haddock and whiting and volume swept affected small haddock only. With the exception of large whiting, catch rates of all species and sizes varied with time of day typically within a factor of 2 between day and night. Copyright 2002 International Council for the Exploration of the Sea. Published by Elsevier Science Ltd. All rights reserved.

Viral haemorrhagic septicaemia virus (VHSV) was isolated from five species of wrasse (Labridae) used as biological controls for parasitic sea lice predominantly, Lepeophtheirus salmonis (Kroyer, 1837), on marine Atlantic salmon, Salmo salar L., farms in Shetland. As part of the epidemiological investigation, 1400 wild marine fish were caught and screened in pools of 10 for VHSV using virus isolation. Eleven pools (8%) were confirmed VHSV positive from: grey gurnard, Eutrigla gurnardus L.; Atlantic herring, Clupea harengus L.; Norway pout, Trisopterus esmarkii (Nilsson); plaice, Pleuronectes platessa L.; sprat, Sprattus sprattus L. and whiting, Merlangius merlangus L. The isolation of VHSV from grey gurnard is the first documented report in this species. Nucleic acid sequencing of the partial nucleocapsid (N) and glycoprotein (G) genes was carried out for viral characterization. Sequence analysis confirmed that all wild isolates were genotype III the same as the wrasse and there was a close genetic similarity between the isolates from wild fish and wrasse on the farms. Infection from these local wild marine fish is the most likely source of VHSV isolated from wrasse on the fish farms.

Catches of demersal fish from research vessel surveys in three areas around the British Isles from 1901 to 1907 were compared with survey catches in the same areas from 1989 to 1997. Mesh size and other characteristics of the trawls used suggested that some of these data were comparable, and could be used to describe changes in demersal fish assemblages over the last 80 years. In Start Bay (NW English Channel) and the Irish Sea, species diversity was the same in both periods, although the most abundant species in each period were not the same. In English coastal regions of the southern North Sea, fish populations became more diverse, as plaice Pleuronectes platessa and whiting Merlangius merlangus became less abundant, and the relative abundance of several non-target species such as dragonet Callionymus spp., bib Trisopterus luscus, and bull-rout Myoxocephalus scorpius increased. The proportion in the catch of small fish species (maximum body length 30 cm) in catches decreased in all regions during the time period, except in the Irish Sea where plaice replaced grey gurnard Eutrigla gurnardus as a dominant species. There was a decline in abundance of large sharks, skates and rays, including the common skate, Raja batis, white skate R. alba and the angel shark Squatina squatina. During historic surveys, 60% of the elasmobranch fauna consisted of thornback ray Raja clavata, whereas in contemporary surveys the lesser spotted dogfish Scyliorhinus canicula was the most abundant elasmobranch. Changes in length-frequency distribution of fish in both target and non-target categories, and other observed changes, were thought to be a response to commercial exploitation, and corresponded to similar observations recorded elsewhere. (C) 2000 British Crown Copyright.

The most obvious effect of fishing on non-target species is direct mortality. To quantify this effect on the vulnerability of species requires measurement of the current fishing mortality rate and of the tolerance of the species to fishing mortality. These are difficult to estimate for the little-studied non-target species. We describe two potential methods for estimating current fishing mortality rate when data are limited. Their application is illustrated for dab (Limanda limanda) and grey gurnard (Eutrigula gurnardus), two common non-target species in the North Sea. We also develop approaches to define tolerance levels for fishing mortality for little-studied and rare species, based on the potential jeopardy level: the fishing mortality that causes a reduction in spawning stock biomass per recruit relative to the unexploited situation. We propose that for non-target species, models founded on basic knowledge of life history parameters, and on generally established relationships between these parameters, may offer the only practical approach.

Fish predation on 0-group flatfish (plaice Pleuronectes platessa, dab Limanda limanda and flounder Pleuronectesflesus) populations on Tralee Beach. Scotland (56" 31' N, 5" 29' W) was studied by stomach content analysis during the summers of 1992 and 1993. I-group grey gurnard Eutrigla gurnardus, poor-cod Trisopterus minutus and whiting Merlanyius inerlangus and 0-group cod Gadus rnorhua were the major fish predators of the 0-group flatfishes. Flatfishes >45 mm total length appeared to have a refuge in size from predation by the fishes sampled. Predation by fishes was shown to be negatively size-selective, concentrated on the smaller size-classes of flatfishes. Smaller individuals were eaten by a greater taxonomic variety and a larger size range of predators than larger flatfishes. Smaller flatfishes'were therefore vulnerable to a larger number of predators. The size distributions of predators affected the pattern of predation because only the larger individuals ate flatfishes. It is therefore proposed that the degree of overlap in the size distributions of predators and prey determine the magnitude of predation. Growth rates and the timing of settlement in any one year will therefore have a considerable influence on predation, with the potential to result in a 'match or mismatch' of predator and prey size distributions.

The myxosporean specimens were noted in grey gurnard Eutrigla gurnardus (L.) from the area near the Shetland Islands. The structure and dimensions of its vegetative stage differ from earlier descriptions. A sequence of small subunit ribosomal RNA gene obtained during the current study differs from other Ceratomyxa spp. available in GenBank. A phylogenetic position of parasite based on the 18S rDNA fragment was estimated. The proposed name for this myxosporean is Ceratomyxa gurnardi sp. n.

The stomach content of 589 specimens of Eutrigla gurnardus (collected at quarterly intervals) have been analyzed to determine diet according to fish size and season. The results show that crustaceans (% No = 93%, %Weight = 81%) are the basic food and that teleostean fishes are quite important in the adult diet. The importance of nycthemeral migrators decreases significantly as size increases, whilst the importance of benthic prey increases inversely. In every size, the feeding intensity is greater at midday than in the morning. Larger prey are eaten in winter than in summer although feeding intensity is lower in winter.

This paper examines long-term changes in the structure and composition of the groundfish species assemblage in three regions of the north-western North Sea. Scottish fisheries research vessel data collected during the months July-September over the period 1929-53 are compared with more recent August groundfish survey data covering the period 1980-93. Trends in the whole groundfish assemblage, and in a subset of the assemblage that is not targeted by commercial fisheries, are described. Long-term differences in species assemblage were subtle, and were most apparent in the dominance structure. Species diversity in the whole groundfish assemblage was marginally greater in the period 1929-53, but no difference was apparent within the non-target species assemblage. For the whole groundfish assemblage, diversity was greatest in the inshore region and least in the offshore area, but there was no obvious spatial gradient for the non-target species assemblage. Multivariate analyses indicated long-term changes and between-area differences in the species composition for both the whole groundfish assemblage and the non-target species subset. More detailed examination of the data revealed that the long-term changes resulted from relatively small and subtle differences in the relative abundance of rarer species, such as grey gurnard Eutrigla gurnardus (L.) and spur-dog Squalus acanthius L.. In contrast, changes in the relative abundance of the more common species, such as Norway pout Trisopterus esmarkii (Nilsson) and whiting Merlangius merlangus (L.), explained much of the between-area variation. Examination of species aggregated length-frequency distributions suggested that by the 1980s there had been a shift towards assemblages in which smaller fish were more highly represented. This was only apparent, however, in the whole groundfish species assemblage ; the length-frequency distributions of non-targeted species were almost identical in the two time periods. Overall, the results suggest that, although differences in the structure of the whole fish assemblage can be detected, the non-target groundfish assemblage appears to have remained relatively unchanged, despite a century of intensive fishing activity.

Complete parasitological analysis of the grey gurnard Trigla gurnardus (L.) had been carried out on Shetland Islands fishing grounds. Material was collected at random from commercial catches in March 1976. Generally, the presence of 14 species of parasites was ascertained (Protozoa - 1; Cestoda - 1; Trematoda - 7, Nematoda - 3, Crustacea-Copepoda - 1, and Fungi - 1 species). Frequency of their prevalence, as well as intensity and incidence were determined. Ten species were found first time as occurring on the grey gurnard.

A main feature of the data here presented is the number of new records. For the sake of brevity these are tabulated below, under their respective headings.Another feature is the wide geographical distribution of a large percentage of the parasites herein recorded, particularly of such forms as Zoogonoides viviparus (Olsson), Derogenes varicus (Mueller) and Hemiurus communis Odhn. The former has been recorded for St Andrews, Millport, Aberdeen, Plymouth, Northumberland, Liverpool, Galway, and also for foreign seas. Derogenes varicus has been recorded for St Andrews, Millport, Plymouth, Aberdeen, Northumberland, Galway, and for foreign seas. Hemiurus communis has been recorded for St Andrews, Millport, Plymouth, Northumberland, Liverpool, Aberdeen, Galway, and for foreign seas.This suggests that the intermediate host of the larval stages of these parasites must be some common marine form, in all probability an invertebrate, which itself enjoys a very wide geographical distribution.A further feature is the tendency of certain parasites to infect a variety of fish, the more notorious being Derogenes varicus (Mueller) and Hemiurus communis Odhn. Of the twenty-six species of marine fishes examined at Galway, eleven (42 per cent.) were found to harbour Derogenes various. The infected fishes were the bib (G. luscus), cod (G. morrhua), pollack (G. pollachius), dab (Pleuronectes limanda), plaice (P. platessa), tub (Trigla hirundo), grey gurnard (T. gurnardus), brill (Rhombus laevis), hake (Merluccius vulgaris), common sole (Solea vulgaris), common sea bream (Sparus centrodontus).Hemiurus communis was found parasitising eight species of fish, i.e. 31 per cent, of the total number of species examined. The hosts affected were the bib (G. luscus), whiting (G. merlangus), cod (G. morrhua), pollack (G. pollachius), flounder (P. flesus), tub (T. hirundo), plaice (P. platessa), and the common sea bream (S. centrodontus).At the moment it is a little premature to prophesy to what extent the discovery of encysted specimens of Prosorhynchus crucibulum (Rud.) in the gill tissues of the cod (Gadus morrhua) will assist in elucidating the life-history of this parasite. Mature specimens of Prosorhynchus crucibulum have previously been recorded as occurring in the alimentary canal of the conger eel (Conger niger). The writer discovered partly digested specimens of small cod to form a considerable bulk of the stomach contents of the conger eel.