Stuart I. Rogers

Temporal analysis of archived samples indicates marked genetic changes in declining North Sea cod (Gadus morhua)

Despite increasing evidence that current exploitation rates can contribute to shifts in life–history traits and the collapse of marine fish stocks, few empirical studies have investigated the likely evolutionary impacts. Here, we used DNA recovered from a temporal series of archived North Sea cod (Gadus morhua) otoliths, to investigate genetic diversity within the Flamborough Head population between 1954 and 1998, during which time the population underwent two successive declines. Microsatellite data indicated a significant reduction in genetic diversity between 1954 and 1970 (total number of alleles: 1954, 46; 1960, 42; 1970, 37), and a subsequent recovery between 1970 and 1998 (total number of alleles: 1970, 37; 1981, 42; 1998, 45). Furthermore, estimates of genetic differentiation (F and R) showed a significant divergence between 1998 and earlier samples. Data are consistent with a period of prolonged genetic drift, accompanied by a replacement of the Flamborough Head population through an increased effective migration rate that occurred during a period of high exploitation and appreciable demographic and phenotypic change. Other studies indicate that diversity at neutral microsatellite loci may be correlated with variability at selected genes, thus compromising a populations subsequent recovery and adaptive potential. Such effects are especially pertinent to North Sea cod, which are threatened by continuing exploitation and rising sea temperatures.

Demersal fish populations in the coastal waters of the UK and continental NW Europe from beam trawl survey data collected from 1990 to 1995

Samples of the demersal fish fauna have been collected by beam trawl from the coastal waters of northwest Europe (49–57°N, 8°W–9°E) by the UK, Netherlands, Germany and Belgium, since 1990, during the third quarter of the year. Changes in community structure within small spatial scales were subtle as species compositions formed part of a continuum over the entire continental shelf. Populations of low diversity were particularly evident in the German Bight and on the North Sea continental coast, where dab Limanda limanda were abundant. In the Channel and to the west of the UK the demersal assemblages were more species-rich than in the North Sea and, although dab was still an important member of the underlying fish assemblage, the abundance of other species, especially poor cod Trisopterus minutus, solenette Buglossidium luteum, plaice Pleuronectes platessa, and the lesser weever, Echiichthys vipera, allowed a range of different groups to be identified. Despite the greater species diversity in this westerly region only eight out of a total nineteen flatfish species were found in abundance. The dominance of different species in different size classes was a key feature of the community structure. Flatfish were the largest group by weight in the smaller-length classes (<30 cm), and in western areas the elasmobranchs dominated the larger-size classes. Observed patterns in community structure were partly explained by the zoogeography of the region and the presence of the British Isles at the boundary between two faunal types. The additional influence on demersal populations of depth and substrate type, which may regulate the abundance of flatfish at key stages in their life history, was also discussed. In addition to these natural processes, recent increases in fishing effort are thought to have affected the structure of the demersal assemblage, and an examination of aggregated length-frequency distributions from these surveys tends to support this conclusion. Without further information on the distribution of fishing effort, it is not possible to separate the influence of natural faunal changes between regions from that of artificial changes caused by fishing activity.

Relative contributions of different sole and plaice nurseries to the adult population in the Eastern Channel: application of a combined method using generalized linear models and a geographic information system

The Eastern Channel (ICES division 7d) is considered a unit for stock management of the common sole Solea solea and the plaice Pleuronectes platessa. At this scale, the aim of this work is to model the juvenile distribution of these flatfish. The database used, based on different surveys undertaken during the two last decades, includes 4500 coastal beam trawl hauls throughout the Eastern Channel coasts. Multivariate analyses are used to study the interannual fluctuations in flatfish recruitment of the region. This approach allows us to separate the Eastern Channel into homogeneous sectors with regard to these fluctuations. The physical parameters that contribute to the observed juvenile sole and plaice distributions are identified and their distributions are modelled using generalized linear models. The results of these models, and the areas of the different populations derived from a geographic information system, are used to identify the main nursery grounds and to compare their respective importance. This quantitative approach identifies the lack of estuarine dependence of the nursery grounds, and highlights those areas where anthropogenic disturbance could influence these populations.

Assessment of a Bayesian Belief Network-GIS framework as a practical tool to support marine planning.

For the UK continental shelf we developed a Bayesian Belief Network-GIS framework to visualise relationships between cumulative human pressures, sensitive marine landscapes and landscape vulnerability, to assess the consequences of potential marine planning objectives, and to map uncertainty-related changes in management measures. Results revealed that the spatial assessment of footprints and intensities of human activities had more influence on landscape vulnerabilities than the type of landscape sensitivity measure used. We addressed questions regarding consequences of potential planning targets, and necessary management measures with spatially-explicit assessment of their consequences. We conclude that the BN-GIS framework is a practical tool allowing for the visualisation of relationships, the spatial assessment of uncertainty related to spatial management scenarios, the engagement of different stakeholder views, and enables a quick update of new spatial data and relationships. Ultimately, such BN-GIS based tools can support the decision-making process used in adaptive marine management.

Estimating limits to the spatial extent and suitability of sole (Solea solea) nursery grounds in the Dover Strait

There is a growing need for accurate and interpretable maps that describe the spatial extent and suitability of flatfish habitats. A common approach to developing such maps is to construct spatially explicit habitat models from fisheries-independent survey data. As the entire range of factors that define fish habitats can never be fully quantified, habitat models are invariably built from a small subset of factors, which typically consist of physical seabed and water column characteristics. If important physical and biological habitat features have not been measured, conventional modelling techniques may underestimate habitat use and quality. We present a spatial modelling technique capable of estimating the maximum extent and suitability of flatfish habitats, i.e. the potential or upper limits of the habitat, using juvenile sole (Solea solea L.) in the Dover Strait as an example. To develop the models, juvenile sole catch densities and environmental habitat data were first acquired and assembled within a Geographical Information System (GIS). Regression quantiles were then estimated for models of change in juvenile sole catch density according to changes in a number of habitat variables. Finally, spatial models were constructed within a GIS by combining the quantile regression models with digital maps of the environmental variables. The use of regression quantiles allowed linear model parameters to be estimated near to the upper bounds of the sole-habitat relationships, thereby providing estimates of the limiting effects of the habitat. In turn, the habitat map built from the upper regression quantiles provided robust estimates of the maximum spatial extent and suitability of sole nursery grounds in the Dover Strait region, as confirmed by model tests using independent data. Habitat maps developed using this approach may be desirable from a species conservation perspective, as the likelihood of underestimating the extent and quality of the habitat is reduced.

The distribution, relative abundance and diversity of echinoderms in the eastern English Channel, Bristol Channel, and Irish Sea

The distribution and relative abundance of macroepibenthic echinoderms in the eastern English Channel and Irish Sea is described from beam trawl catches. Echinoderms accounted for approximately 29% (by biomass) of fauna captured. A total of 24 species were recorded, including 12 species of starfish. The most frequently encountered species were Asterias rubens and Psammechinus miliaris , which were recorded at 85.5% and 56.0% of stations respectively. Asterias rubens and Ophiothrix fragilis accounted for 63.7% and 25.5% (by biomass) respectively of the echinoderms sampled. Mean echinoderm catches ranged from 0.8-kg h −1 in the north-eastern English Channel to 329-kg h −1 in the south-eastern Irish Sea. The echinoderm fauna was more diverse in the St Georges Channel and western Irish Sea (6.7–7.0 species haul −1 ) than in the north-eastern English Channel (1.9 species haul −1 ).

Fishing effects in northeast Atlantic shelf seas: patterns in fishing effort, diversity and community structure. IV. Can comparisons of species diversity be used to assess human impacts on demersal fish faunas?

Patterns in the abundance of commercially important and non-target demersal fish species collected by beam trawl survey from the coastal waters of the northeast Atlantic are described. Catches were dominated by a small number of species, which occurred in large numbers and at high biomass. The most abundant species (plaice and dab) were typical of shallow, uniform sandy and muddy seabed which occurred extensively throughout the southern North Sea, and to a limited extent in UK western waters. Renyis diversity index family was used to rank the diversity of coastal sectors throughout the region. The less species-rich North Sea fauna, partly a result of the uniform nature of the seabed, was largely responsible for lower diversity of North Sea coastal faunas compared to those in the Channel and west of the UK. West of the Dover Strait, the more heterogeneous substrate supported a more diverse fauna of smaller sized fish, with the occurrence of southern species such as red gurnard and thickback sole and an increasing abundance of elasmobranchs. In the Irish Sea, fish biomass was dominated by plaice and dab, but to a lesser extent than on the continental coast of the North Sea. Sole, lesser spotted dogfish and cod were also important in this assemblage. Patterns in community structure over such a wide spatial scale, and without historical perspective, can be explained by biogeographic factors, seabed structure and the influence of regional hydrography. Inferring from these patterns an impact of anthropogenic factors (such as towed fishing gears) is unlikely to be achieved. Identifying vulnerable species, and use of fishing effort distribution data of high resolution, may be a more fruitful approach.

Assessing Marine Ecosystem Health: The Long-Term Effects of Fishing on Functional Biodiversity in North Sea Benthos

Assessments based on the taxonomic composition and relative abundance of taxa provide valuable information about the effects of anthropogenic activities on benthic systems. However, international agreements also require active conservation of ecosystem functioning as well as biological assemblages. We must therefore learn more about how ecosystems function and why changes occur within them in order to fully understand the implications of human activities. Biological traits analysis allows systems to be described in terms of the characteristics of member taxa, describing functional diversity whilst retaining information on taxa distributions. This study used biological traits analysis to investigate the long-term effects of fishing on benthic infaunal communities. Infaunal abundance was recorded over three decades at two stations, one within and one outside a fishing ground in the central western North Sea. Each taxon present was categorised for the degree to which it exhibited certain biological traits. The distribution of these traits within a sample produced a picture of functional diversity. Multivariate analyses were used to compare trait composition at the stations over time, thus depicting how community functioning responded to physical disturbance. The assemblages at the two stations were functionally distinct at the onset of the study; with differences in size, feeding type and reproductive method. The functional structure changed over time at the station within the fishing ground as the level of exploitation varied. Large animals, predators, scavengers and those eating invertebrates or carrion dominated years of light effort in the fishing ground but were less represented when effort increased. No such changes occurred at the station outside the fishing ground. Fishing seems to have some effect on benthic functional biodiversity and this effect is most obvious when moving from low to moderate levels. The differences between stations at the start of the timeseries may reflect variations in the physical environment or may result from effects of fishing that predate the timeseries.

Marine strategy framework directive : Task Group 4 report : food webs

The Marine Strategy Framework Directive (2008/56/EC) (MSFD) requires that the European Commis-sion (by 15 July 2010) should lay down criteria and methodological standards to allow consistency in ap ...

Sampling strategies to evaluate the status of offshore soft sediment assemblages

Reliable descriptions of the status of offshore seabed habitats usually require substantial investment in field data collection and sample analysis. While assessment of, for example, biogenic reef habitat can often include simple physical parameters (e.g. spatial extent), comparative measures for soft sediment habitats generally rely on the distribution and relative abundance of species, with a description of the associated sedimentary environment. To investigate the power of surveys to detect significant trends in assemblage structure, samples of meiofauna, macroinfauna and megafauna (i.e. representing ecological components from nematodes to demersal fish), were collected from four offshore mud and sand habitat sites in western UK shelf seas during July 2004 and 2005. Spatial arrays of samples within these sites, up to 23 km apart, were designed to optimise descriptions of assemblage structure and the patterns of spatial distribution at a local scale. Analyses of species abundance, biomass and taxonomic relatedness of the species complement at each site suggested that most assemblages represented relatively unimpacted regional conditions. The power of the sampling programme to detect a significant change in univariate community attributes was assessed. The variability in many of the community attributes indicated that intensive replicate sampling would be required to detect ecologically important changes. Improving the power of such benthic surveys to detect trends would therefore require substantial additional time and effort to be invested in sample collection and analysis. Resource analysis showed that the time from gear deployment to complete sample identification was gear-dependent, lowest per sample for meiofauna (10h) and megafauna (6-12h), and highest for macroinfauna (12-22 h). These results have implications for the development of meaningful indicators of habitat status for offshore soft sediment habitats, and the resources required for effective monitoring of change.