Simon P. R. Greenstreet

Fishing and the ground-fish assemblage structure in the north-western North Sea : an analysis of long-term and spatial trends

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.

Fishing effects in northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. V. Changes in structure of the North Sea groundfish species assemblage between 1925 and 1996

Abstract We examine long-term changes in the structure and composition of the groundfish species assemblage in four regions of the northwestern North Sea during the period 1925–96. Species diversity in the whole groundfish assemblage has declined in the three areas where fishing pressure has been greatest. In the area where fishing pressure was least, no trend in species diversity was detected. Only in the most intensively fished area was there a negative trend in species diversity in the non-target species assemblage. Marked spatial variation in species diversity was observed. For the whole groundfish assemblage, diversity was greatest in the inshore and southern regions and least in the offshore northern area. For the non-target species assemblage, the spatial diversity gradient was reversed. Multi-variate analyses indicated long-term changes and between-area differences in the species composition of both the whole groundfish assemblage and the non-target species subset. However, these changes consisted mostly of subtle variations in the relative and absolute abundance of a few key species, rather than major species replacement events. Only one species showed any marked increase in abundance: a dominant species which became more abundant. Examination of species aggregated length-frequency distributions indicated a shift towards an assemblage dominated by smaller fish in the whole assemblage, but not in the non-targeted assemblage.

Fishing effects in northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. II. Trends in fishing effort in the North Sea by UK registered vessels landing in Scotland

Abstract North Sea fishing effort data (expressed as hours fishing) for UK vessels landing in Scotland over the period 1960–1994 are analysed. Long-term temporal, spatial and seasonal trends in the use of particular gears are described. Pelagic fishing effort trends were clearly related to changes in the target species. Pelagic effort, mainly pair-trawling targeted at sprats in the 1960s and early 1970s, declined markedly in the late 1970s. In the early 1980s pelagic fishing effort increased again, but was predominantly purse-seining targeted at herring. The spatial distribution of pelagic effort shifted northwards, and changed from winter to summer. Demersal fishing effort varied little over three decades, but marked changes in the type of gear used were apparent. The use of seine nets decreased, particularly in the northwestern North Sea, and otter trawl fishing increased. The spatial distribution of demersal effort is now more widespread than in earlier years, but there has been little change in seasonal patterns.

Bridging the Gap between Policy and Science in Assessing the Health Status of Marine Ecosystems

Human activities, both established and emerging, increasingly affect the provision of marine ecosystem services that deliver societal and economic benefits. Monitoring the status of marine ecosystems and determining how human activities change their capacity to sustain benefits for society requires an evidence-based Integrated Ecosystem Assessment approach that incorporates knowledge of ecosystem functioning and services). Although there are diverse methods to assess the status of individual ecosystem components, none assesses the health of marine ecosystems holistically, integrating information from multiple ecosystem components. Similarly, while acknowledging the availability of several methods to measure single pressures and assess their impacts, evaluation of cumulative effects of multiple pressures remains scarce. Therefore, an integrative assessment requires us to first understand the response of marine ecosystems to human activities and their pressures and then develop innovative, cost-effective monitoring tools that enable collection of data to assess the health status of large marine areas. Conceptually, combining this knowledge of effective monitoring methods with cost-benefit analyses will help identify appropriate management measures to improve environmental status economically and efficiently. The European project DEVOTES (DEVelopment Of innovative Tools for understanding marine biodiversity and assessing good Environmental Status) specifically addressed these topics in order to support policy makers and managers in implementing the European Marine Strategy Framework Directive. Here, we synthesize our main innovative findings, placing these within the context of recent wider research, and identifying gaps and the major future challenges.

Length–weight relationships of 216 North Sea benthic invertebrates and fish

Size-based analyses of marine animals are increasingly used to improve understanding of community structure and function. However, the resources required to record individual body weights for benthic animals, where the number of individuals can reach several thousand in a square metre, are often prohibitive. Here we present morphometric (length weight) relationships for 216 benthic species from the North Sea to permit weight estimation from length measurements. These relationships were calculated using data collected over two years from 283 stations. For ten abundant and widely dispersed species we tested for significant spatial and temporal differences in morphometric relationships. Some were found, but the magnitude of differences was small in relation to the size-ranges of animals that are usually present and we recommend that the regression relationships given here, based on pooled data, are appropriate for most types of population and community analyses. Our hope is that the availability of these morphometric relationships will encourage the more frequent application of size-based analyses to ben hue survey data, and so enhance understanding of the ecology of the benthic/demersal component of marine ecosystems and food webs.

Towards ecosystem-based management: identifying operational food-web indicators for marine ecosystems

Modern approaches to Ecosystem-Based Management and sustainable use of marine resources must account for the myriad of pressures (interspecies, human and environmental) affecting marine ecosystems. ...

The impact of the sandeel fishery closure in the northwestern North Sea on seabird food consumption, distribution and productivity

In the North Sea, the lesser sandeel (Ammodytes marinus) is the target of an industrial fishery and the principal prey of many top predators. Because of concerns about potential effects on predators, the sandeel fishery off eastern Scotland was closed in 2000, and local sandeel abundance increased subsequently. To examine whether closure benefitted sandeel-dependent seabirds, we compared summer sandeel consumption, at-sea distributions, and breeding success of seven species with fishery removals and abundance of older (1+ group) and young-of-the-year (0 group) sandeels from 1996 to 2003. Breeding success of black-legged kittiwake (Rissa tridactyla), a species that has declined in recent decades, was related to abundance of both 1+ group (the age class targeted by the fishery) and 0 group sandeels. The proportion of 0 group consumed by kittiwakes and proportion of the kittiwake population foraging in the area were linked to 0 group abundance. None of these parameters in the other seabird species were associated with sandeel abundance. Our results suggest that fishery closure can have a beneficial impact on top predators sensitive to variation in abundance of the target species, although environmental conditions before and after closure are also likely to be critically important.In the North Sea, the lesser sandeel (Ammodytes marinus) is the target of an industrial fishery and the principal prey of many top predators. Because of concerns about potential effects on predators, the sandeel fishery off eastern Scot- land was closed in 2000, and local sandeel abundance increased subsequently. To examine whether closure benefitted sandeel-dependent seabirds, we compared summer sandeel consumption, at-sea distributions, and breeding success of seven species with fishery removals and abundance of older (1+ group) and young-of-the-year (0 group) sandeels from 1996 to 2003. Breeding success of black-legged kittiwake (Rissa tridactyla), a species that has declined in recent decades, was related to abundance of both 1+ group (the age class targeted by the fishery) and 0 group sandeels. The proportion of 0 group consumed by kittiwakes and proportion of the kittiwake population foraging in the area were linked to 0 group abundance. None of these parameters in the other seabird species were associated with sandeel abundance. Our results suggest that fishery closure can have a beneficial impact on top predators sensitive to variation in abundance of the target species, although environmental conditions before and after closure are also likely to be critically important.

Resolution of biodiversity and assemblage structure in demersal fisheries surveys: the role of tow duration

Resolution of biodiversity and assemblage structure in demersal fisheries surveys: the role of tow duration M. Moriarty*, A. F. Sell, V. M. Trenkel, C. P. Lynam, F. Burns, E. D. Clarke, S. P. R. Greenstreet, and C. McGonigle Marine Scotland Science, 375 Victoria Road, Aberdeen AB11 9DB, UK Environmental Sciences Research Institute, Ulster University, Cromore Road, Coleraine, BT52 1SA, UK Thünen Institute of Sea Fisheries, Palmaille 9, 22767 Hamburg, Germany Ifremer, Rue de I’lle d’Yeu, BP 21105, 44311 Nantes Cedex 03, France CEFAS, Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK

Exploring the influence of food and temperature on North Sea sandeels using a new dynamic energy budget model

The zooplanktivorous schooling fish sandeels A. marinus comprise a quarter of North Sea fish biomass and are essential food for a number of marine mammals and birds. However, in recent decades there has been a decline in the abundance of older sandeels, with increased overwinter mortality proposed as a contributor. To survive winter animals require a minimum energy reserve which is determined by temperature, prey abundance, and possibly prey size. Here a new dynamic energy budget model is created to determine the influence of food and temperature on sandeel energy dynamics. The model hindcasts changes in energy and survival between 2000 and 2008, a period of pronounced stock decline in the northwestern North Sea. Overwinter starvation mortality was a large contributor towards a recent decline in sandeels in northern UK waters. Highest over-winter mortality rates were recorded for juveniles and not individuals aged 1 or over due to the effect of weight-specific metabolism. However, a sensitivity analysis of the model suggests that mortality rates are more sensitive to changes in copepod abundance in the build up to overwintering rather than temperature during overwintering. Further, projections show that temperature rises are negated by increases in large, but not small copepods. The conclusion is that food-driven size-selective starvation mortality contributed to the northwestern North Sea stock decline and that indirect food web effects of climate change are greater than direct physiological effects on sandeels.