An assessment of biological and population parameters of the Common whelk, Buccinum undatum (L.) in the region of the North West Irish whelk fishery

The Common whelk, Buccinum undatum (L.) is a conspicuous benthic scavenger in Irish waters, and is a valuable fisheries resource in South East Ireland. B. undatum is fished in many parts of its range, and previous studies have shown that certain life history parameters, which vary with location, make this species vulnerable to overexploitation. This makes research into each exploited stock essential to ensure sustainable fisheries management of the species. In 2003, interest in B. undatum as a complementary species in the inshore fishery east of the Inishowen Peninsula, North West Ireland, initiated investigation into fisheries related biological and population aspects of the species in this region. The current study presents estimates of spatial variation and density of the stock, size at age and growth rates, size and age at onset of sexual maturity, and timing of reproductive events in the region of the North West Irish whelk fishery for the period of June 2003 to May 2004. Analysis of variance of the total shell length of whelk landings to the fishery was conducted over spatial scales of fishing pot, fishing string and landings to vessels. Landings varied significantly in shell length at the spatial scale at which whelks are attracted to baited pots, but did not vary significantly over larger spatial scales. Depletion estimates of stock density from fisheries derived Catch per Unit Effort data and a mark re-capture experiment estimate 0.134 - 0.227 whelks per m2. Two independent methods of age determination found similar growth logistics functions for B. undatum.Modal analysis of length frequency distribution of landings to the fishery estimated symptotic length, Leo = 151.64 mm and Brody growth coefficient, K = 0.04. Analysis of the striae in individual opercula, where each stria was found to represent annual growth, estimated Loo = 137.73 mm and K = 0.12. Common whelks in the region of the North West Irish whelk fishery grow slowly and are long-lived, with 19 opercula striae recorded in one individual. Onset of sexual maturity is late, and no sex-specific differences in size or age at maturity were determined in the present study. Males were found to achieve sexual maturity at 83.30 ± 10.77 mm, and 8.9 - 11.1 years of age, and females at 82.62 ± 10.68 mm and 8.8 to 11.1 years of age. Systematic observations of reproductive events, including histological changes to the female ovary and male testis, and changes in the size and mass of body components, suggest that breeding occurred between the autumn and winter months of October and December 2003. Biological aspects of B. undatum in the study region are compared with previous studies from other regions, and discussed in relation to sustainable management of the fishery.

Abundance of sedentary consumers and sessile organisms along the wave exposure gradient of subtropical rocky shores of the south-west Atlantic

Sedentary consumers play an important role on populations of prey and, hence, their patterns of abundance, distribution and coexistence on shores are important to evaluate their potential influence on ecosystem dynamics. Here, we aimed to describe their spatio-temporal distribution and abundance in relation to wave exposure in the intertidal rocky shores of the south-west Atlantic to provide a basis for further understanding of ecological processes in this system. The abundance and composition of the functional groups of sessile organisms and sedentary consumers were taken by sampling the intertidal of sheltered and moderately exposed shores during a period of one year. The sublittoral fringe of sheltered areas was dominated by macroalgae, while the low midlittoral was dominated by bare rock and barnacles. In contrast, filter-feeding animals prevailed at exposed shores, probably explaining the higher abundance of the predator Stramonita haemastoma at these locations. Limpets were more abundant at the midlittoral zone of all shores while sea urchins were exclusively found at the sublittoral fringe of moderately exposed shores, therefore, adding grazing pressure on these areas. The results showed patterns of coexistence, distribution and abundance of those organisms in this subtropical area, presumably as a result of wave action, competition and prey availability. It also brought insights on the influence of top-down and bottom-up processes in this area.

IMPOSEX AS AN INDICATOR OF ORGANOTIN POLLUTION AT RIO DE JANEIRO SOUTH COAST: SEPETIBA AND ILHA GRANDE BAYS

Imposex is the development of male sexual characteristics, i.e., penis and/or vas deferens in females of dioecious gastropods. This phenomenon has been associated to the use of the organotin based marine antifouling paints and used worldwide as a bioindicator of pollution by the TBT (antifouling agent) as well as to evaluate the related ecological impact. This study reports imposex in Stramonita haemastoma at south coast of Rio de Janeiro State (Brazil), specifically at Sepetiba and Ilha Grande Bays. All the stations where snails were found have shown imposex. Ilha Grande Bay presented the highest values of imposex indices when compared to Sepetiba Bay. The results suggest that high concentration of shipping activities and coastal morphology are the principal causes at the most polluted sites.

Populations of Pacific Oysters Crassostrea gigas Respond Variably to Elevated CO2 and Predation by Morula marginalba

Ocean acidification is anticipated to decrease calcification and increase dissolution of shelled molluscs. Molluscs with thinner and weaker shells may be more susceptible to predation, but not all studies have measured negative responses of molluscs to elevated pCO2. Recent studies measuring the response of molluscs have found greater variability at the population level than first expected. Here we investigate the impact of acidification on the predatory whelk Morula marginalba and genetically distinct subpopulations of the Pacific oyster Crassostrea gigas. Whelks and eight family lines of C. gigas were separately exposed to ambient (385 ppm) and elevated (1000 ppm) pCO2 for 6 weeks. Following this period, individuals of M. marginalba were transferred into tanks with oysters at ambient and elevated pCO2 for 17 days. The increase in shell height of the oysters was on average 63% less at elevated compared to ambient pCO2. There were differences in shell compression strength, thickness, and mass among family lines of C. gigas, with sometimes an interaction between pCO2 and family line. Against expectations, this study found increased shell strength in the prey and reduced shell strength in the predator at elevated compared to ambient pCO2. After 10 days, the whelks consumed significantly more oysters regardless of whether C. gigas had been exposed to ambient or elevated CO2, but this was not dependent on the family line and the effect was not significant after 17 days. Our study found an increase in predation after exposure of the predator to predicted near-future levels of estuarine pCO2.

Age and growth of Nassarius reticulatus in the Ria de Aveiro, north-west Portugal

Shell growth of the whelk Nassarius (¼Hinia) reticulatus was studied in the Ria de Aveiro (north-west Portugal) between 1995 and 1998. Temporal analysis of shell height frequency distributions demonstrated that growth occurs during the ¢rst ¢ve years of life, whelks attaining a size of 6.7^7.8 mm in the 1st year, 12.1^14.5 mm in the 2nd year, 18^19.5 mm in the 3rd year, 22.7^23.6 mm in the 4th year and by the 5th year males have achieved an average size of 25 mm whilst females have reached 27 mm. Age estimates from internal microscopic annual growth lines present in the shell lip suggest that large whelks may achieve a longevity of at least 11 years. External annual rings become less discernible as the whelks increase in size and estimates of their age based solely on ring counts can underestimate their age. In males sexual maturation is reached between the 3rd and 4th years whilst in females it is attained between the 4th and 5th years. Imposex was visible in 2 year old females and attained maximum development by the 5th year.

Evaluation du stock de coquilles Saint-Jacques de la Baie de Seine et du Proche Extérieur. COMOR 32 (8-23 juillet 2002)

Scientific scallop surveys called COMOR are carried out in the bay of Seine since 1976. Results are used by fishermen’ associations and by fishing administration to lead management measures. In this report, the scientific results of the survey COMOR 32 realised in July 2002 are described. Abundance and growth indices for scallop, by age and area, are presented. During these surveys, data about most abundant benthic species are also collected since 1998. A first assessment with five years data is made here. A global descriptive analysis is undertaken about all the species present on scallops grounds. A special zoom is applied on both species whitch could be exploited (whelk Buccinum undatum and queen scallop Aequipecten opercularis) and three competitive species (starfish Asterias rubens, American slipper-limpet Crepidula fornicata and brittle star Ophiothrix fragilis)