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Abstract van Damme, C. J. G., Bolle, L. J., Fox, C. J., Fossum, P., Kraus, G., Munk, P., Rohlf, N., Witthames, P. R., and Dickey-Collas, M. 2009. A reanalysis of North Sea plaice spawning-stock biomass using the annual egg production method. – ICES Journal of Marine Science, 66: 1999–2011. Uncertainty about the quality of current virtual population analysis-based stock assessment for North Sea plaice (Pleuronectes platessa) has led to various abundance indices. We compared biomass estimates from the annual egg production (AEP) method with current stock assessments based on catch-at-age to validate the current and historical perception of exploitation. The AEP method was also used to investigate the dynamics of the spatial components of plaice in the North Sea. We corrected for fecundity down-regulation and changes in sex ratio. Estimates from both methods were similar in trend and absolute biomass. On the Dogger Bank, there was a dramatic decline in biomass from 1948 and 1950 to 2004, and in the Southern Bight, the stock appeared to increase from 1987 and 1988 to 2004, although not reaching the historically high levels of 1948 or 1950. The timing of spawning of North Sea plaice does not appear to have changed throughout the period of high exploitation. We conclude that the AEP method is a useful way to hindcast the spatial dynamics of heavily exploited flatfish stocks.

In order to estimate daily ration of juvenile Potamoschistus lozanoi and to evaluate the effect of tide and daylight on its feeding activity, two 24h samplings were performed, one (in 1985) with high water around midnight, the other (in 1986) with low water around midnight. Incidently, the sampling in 1985 was around neap tide and in 1986 it was around spring tide. The fish were observed to feed more intensively during the night. Daily ration in 1985 was estimated to be about 1% of body ash-free dry weight (ADW). For 1986, the estimate is about 5% of body ADW in spite of similar water temperatures at both sampling dates. It is suggested that a semilunar rhythm, either in the fish or in the invertebrate prey, is the basis of the observed difference. This phenomenon may also explain the prominent 14-ring bands observed in the otoliths. Because of the influence of the various rhythms on feeding activity in fishes living in a strongly tidal environment, an accurate estimate of daily ration from production estimates and a P:C ratio established in the laboratory may be logistically less demanding than an estimate from stomach-content data.

In 1988 juvenile bib (Trisopterus luscus) and whiting (Merlangius merlangus) were studied in a shallow coastal area by monthly sampling with fine-meshed nets. 0-group fish of both species are first caught in May. By the end of the first growth season bib reached about 150mm SL (standard length), whiting about 170mm SL. Maximal densities were recorded in June and by the end of the year most fish had left the area. The instantaneous mortality is estimated at 0.008 day-1 (0.77% day-1 for bib and 0.76% day-1 for whiting) for both species. In May both species depended almost exclusively on calanoid copepods. In June and July mysids and amphipods were the most important invertebrate prey, but small fishes such as gobies provided a substantial proportion of the energy requirements, especially in whiting. From August onwards shrimp and fish dominated the diet in both species. Using Jones' (1974) model, food consumption as per cent body weight day-1 varied between 4 and 6% during summer and declined to 2 to 3% in autumn. Total consumption per unit area of subtidal seafloor, by the 0-group fish of both species taken together, was estimated at 0.47 g ash-free dry weight (ADW) m-2 year-2 using Jones' (1974) model and at 0.57 g ADW m-2 year-1 using a conversion efficiency (P:C ratio) of 0.34.

Several methods have been used to indirectly estimate copepod production in the southern Benguela region, based on field sampling of copepod stages and laboratory measurements of growth and development rates under variable food and temperature regimes. Estimates of production have steadily increased from 11 gC m-2 y-1 in 1979 to 80 gC m-2 y-1 in 1987. Since 1988, extensive measurements of copepod egg production and moulting rates of Calanus agulhensis at sea during hydro-acoustic fisheries surveys over the south and west coasts of South Africa in November have provided more direct estimates of copepod production. Daily Mean Production: Mean Biomass (P: B) ratios varied between 0.1 and 0.3 and annual production ranged between 17 and 150 gC m-2 y-1 Copepod biomass, distribution, and demographic structure varied between cruises in different years, apparently linked to both the abundance of predators and shifts in hydrology. Production appeared to be due more to shifts in distribution of biomass and demography of Calanus than to variations in growth rates. Poor correlations existed between juvenile growth and female egg production, suggesting one is unable to predict population growth from egg production rates only. Weak correlations between growth rates of different stages also suggest that the only meaningful measure of copepod production requires all stages to be incubated.

in a recent publication von Brandt (1) gives a survey of all determinations of the calcium content of Baltic water hitherto published. He records in all 39 analyses made during the last century, which give us an idea of the order of magnitude of the calcium concentration; they cannot, however, serve for comparative purposes as in many cases chlorine determinations on the same water samples are lacking. Neither have we any clue for judging the accuracy of these analyses, the latest of which date from 1884. Fifty years later, in 1935, Za rin s and O z o 1 ins (8) published an extensive investi­gation of the water in the Bay of Riga and in the Baltic off the Latvian coast, their most westerly station nearly coinciding with the Finnish station F81 (Lat. 57° 22'N., Long. 19°57'E.) above the central depression of the Baltic. Their material comprised about 70 calcium analyses on water from all depths. Finally v o n B r a n d t in the above-mentioned paper publishes nearly 300 analyses of surface water collected in 1935 and 1936 during several voyages from Pillau to Helsingfors and back, and along the German coast as far as Kiel and back. The present material comprises analyses of only 48 samples of surface and bottom water collected during the summer cruise, in July 1935, of the s.s. "Nautilus" from the Gulf of Finland, the Gulf of Bothnia, and the northern half of the Baltic proper. In spite of the smaller number of samples this material is more comprehensive than the two preceding investigations in so far as it covers a greater area of the sea. I t was originally meant as a survey of the calcium content in these parts of the Baltic, but the surprisingly simple relationships between calcium content and chlorinity which it revealed, give the results far more scope than was expected.

Abstract Marine recreational fisheries (MRF) have important social and economic benefits, but can impact fish stocks and the environment. The diverse and dispersed nature of these fisheries makes them challenging to study; a lack of data has made it more difficult to include them in fisheries management and the varied motivations of fishers makes their response to management measures hard to predict. Research into MRF is growing rapidly, so this themed article set aims to bring together MRF research to highlight the current evidence base and identify future opportunities. New survey methods were presented alongside analyses of existing data, which highlighted issues with methods, reconstruction of missing data, and factors influencing catch and effort. The manuscripts demonstrated the biological and economic impacts of MRF, and its self-subsidizing nature was recognized. Novel approaches for management, including improving compliance, were identified. Finally, the lack of funding for MRF was highlighted. Key research gaps are: governance that embeds MRF in fisheries management; integration of novel approaches and traditional surveys; risk-based approaches to identify impacts; understanding fish welfare; management that balances economic, social, and biological impacts and allows allocation between sectors; and understanding social benefits and their impacts on management and compliance. 

Although estuarine zooplankters are generally believed to be detritivorous, high clearance rates by the estuarine copepods Eurytemora affinis and Acartia tonsa on natural estuarine microplankton have been reported in the literature. In order to enable detection of possible selectivity for these microplankton organisms over detritus, a method that measures clearance rates on total particulate matter is proposed. Image analysis is used to measure copepod gut contents, and combined with Coulter counter measurements of total particulate matter concentration, allows one to calculate clearance rates on the latter. The first results indicate that, in the Westerschelde estuary (SW Netherlands), both E. affinis and A. tonsa are capable of selecting dominant phytoplankton cells over the total particulate matter. The possibility of using image as a sole technique in these studies is discussed.