Jim R. Ellis

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 ).

Temporal changes in allele frequencies but stable genetic diversity over the past 40 years in the Irish Sea population of thornback ray, Raja clavata

Rays and skates are an unavoidable part of the by-catch in demersal fisheries. Over the past 40 years, the thornback ray (Raja clavata) has decreased in numbers and even disappeared in some areas, leading to concerns about genetic risk. For this reason, the effective population size (Ne), the migration rate (m) and temporal changes in the genetic diversity were estimated for the population of thornback rays in the Irish Sea and Bristol Channel. Using genotyped, archived and contemporary samples (1965 and 2003–2004), Ne was estimated at 283 individuals (95% CI=145–857), m at 0.1 (95% CI=0.03–0.25) and the Ne/N ratio between 9 × 10–5 and 6 × 10−4. Although these results must be treated with caution, due to the small sample sizes, this is the first attempt to estimate Ne in an elasmobranch species. The low Ne/N ratio suggests that relatively few individuals contribute to the next generation. The combined effect of sex bias, inbreeding, fluctuations in population size and, perhaps most important, the variance in reproductive success may explain the low Ne/N ratio. In addition, the relatively high gene flow between Irish Sea population and other source populations is likely to have had an impact on our estimate, which may be more relevant at the metapopulation scale. No significant loss of genetic diversity was found over the 40-year timeframe and long-term maintenance of the genetic diversity could be due to gene flow.

A tale of two seas: contrasting patterns of population structure in the small-spotted catshark across Europe

Elasmobranchs represent important components of marine ecosystems, but they can be vulnerable to overexploitation. This has driven investigations into the population genetic structure of large-bodied pelagic sharks, but relatively little is known of population structure in smaller demersal taxa, which are perhaps more representative of the biodiversity of the group. This study explores spatial population genetic structure of the small-spotted catshark (Scyliorhinus canicula), across European seas. The results show significant genetic differences among most of the Mediterranean sample collections, but no significant structure among Atlantic shelf areas. The data suggest the Mediterranean populations are likely to have persisted in a stable and structured environment during Pleistocene sea-level changes. Conversely, the Northeast Atlantic populations would have experienced major changes in habitat availability during glacial cycles, driving patterns of population reduction and expansion. The data also provide evidence of male-biased dispersal and female philopatry over large spatial scales, implying complex sex-determined differences in the behaviour of elasmobranchs. On the basis of this evidence, we suggest that patterns of connectivity are determined by trends of past habitat stability that provides opportunity for local adaptation in species exhibiting philopatric behaviour, implying that resilience of populations to fisheries and other stressors may differ across the range of species.

Geographic variation in the abundance and morphology of the bryozoan Alcyonidium diaphanum (Ctenostomata : Alcyonidiidae) in UK coastal waters

The ctenostome bryozoan Alcyonidium diaphanum is widespread and abundant in the coastal waters of England and Wales. It was recorded in 77-90% of beam trawl catches in the eastern English Channel and southern North Sea, and in 53-73% of catches in the Bristol Channel and Irish Sea. The maximum catch rates in these two study areas were 1410 and 751 kg h -1 respectively. Alcyonidium diaphanum was most abundant in the greater Thames Estuary. Additional data from the North Sea indicated that A. diaphanum is widely distributed throughout the southern North Sea. Alcyonidium diaphanum was found intertidally in only seven of 99 locations sampled. Several different morphotypes were observed, ranging from cylindrical to lobate forms. The distribution patterns of various morphotypes are discussed.

Concentrations of mercury and other trace elements in two offshore skates: sandy ray Leucoraja circularis and shagreen ray L. fullonica

Trace metal concentrations in muscle and liver tissues from two offshore species of skate were examined. Concentrations of mercury in muscle of Leucoraja circularis (n=20; 23-110.5cm total length, 157-490m water depth) and L. fullonica (n=24; 28.5-100cm total length, 130-426m water depth) were 0.02-1.8 and 0.04-0.61mgkg-1, respectively. Concentrations of both As and Hg increased with total length. Only the largest specimen had a concentration of Hg in muscle >1.0mgkg-1. Data were limited for specimens>90cm long, and further studies on contaminants in larger-bodied skates could usefully be undertaken.