In order to assess the latitudinal variability in growth of the eastern Atlantic skipjack (Katsuwonus pelamis), conventional tagging data collected by the International Commission of the Conservation of Atlantic Tunas (ICCAT) since the 1960s are reanalyzed using a modified version of the von Bertalanffy-Fabens growth model. An analysis of the latitudinal patterns of recaptures showed that the lowest mixing rate between northern and southern regions was evidenced at 10° N Latitude. Since it is theoretically admitted that growth parameters L∞ and K are negatively correlated, we substituted L∞ into the growth equation model by a simple bioenergetic function of K fitted from existing studies on skipjack growth parameters. The likelihood for the meta-analysis of growth is combined with the likelihoods from the two regional tagging data with the aim of estimating simultaneously K in both areas and to transfer adequately uncertainties associated with the different data sets. From this study, it was showed that fish inhabiting waters south of 10° N latitude can be expected to grow generally larger but at slower rate than in the North (L∞ = 112.34 cm vs. 89.38 cm, and K = 0.14 vs. 0.38, respectively). Our results are consistent with the range of growth estimates obtained in the Atlantic Ocean and in different parts of the World's oceans. In contrast, the estimates of L∞ and K done in the Senegalese region in the 1980s within the framework of the Skipjack Year Program, and traditionally applied by ICCAT, are not supported by the present study. The findings concerning the phenotypic plasticity exhibited by growth of skipjack among latitudinal regions suggest potential differences in fish population productivity and consequently imply that non-conventional stock assessment methods such as catch-at size/growth transition matrix per region could be used to assess the responses of skipjack to exploitation.

The present study analyses the spatial and temporal distribution of the pelagic stingray (Pteroplatytrygon violacea) in the south-western Atlantic Ocean, based on data collected between April 1998 and March 2006 by the National Observers Program of the Uruguayan Tuna Fleet. During this period, data were recorded on 51 commercial fishing trips, in which a total of 2 306 851 hooks were set and 2740 stingrays captured. Of these, the sex was determined for 1329 individuals and the size for 944. The average disc width was 47 ± 8 cm (range: 24–82 cm) for females and 44 ± 5 cm (range: 28–84 cm) for males. The results indicate that the species seems to prefer warm temperate and tropical waters. There were no capture records in waters at <15.3 °C. The data collected suggest a mating season in late spring with a gestation period of 2 to 4 months and births occurring during late summer and early autumn. The increasing bycatch of this ovoviviparous species in pelagic longline fisheries, with an unknown survival rate after discard, coupled to its low reproductive potential, call for better monitoring in order to accurately determine its current conservation status.

Skin and gill parasites found in juvenile Atlantic bluefin tuna (Thunnus thynnus) caught in the Bay of Biscay, northeast Atlantic, were examined with the aim of finding biological tags. The degree of infection of different microhabitats was analyzed and the annual prevalence by species of parasite obtained. Of the specimens examined, 98% had parasites, and the gills were by far the most infected microhabitat, followed by the skin and the pectoral fin. Within the gill cavity, parasites were most commonly found in the afferent margins of the primary lamellae. Three species of Copepoda were identified, two species of Monogenea, and eleven Digenea. Thus, ten species (Digenea: Didymozoidae) and a new host record for Copiatestes thyrsitae (Digenea: Syncoeliidae) were recorded in Thunnusthynnus. The suitability of the different external parasites found is discussed and gill didymozoids are put forward as useful biological tags. Confusing taxonomy within this digenean family makes species identification of the different morphotypes difficult. However, their habitat specificity in hosts can be a good tool to differentiate morphotypes and characterise host individuals.

In order to address critical gaps arising from limited available data on historic shark catches in the Atlantic Ocean, a method was developed to estimate shark removals using shark fin trade data. A characterization of the global fin trade as of 2000, including number and biomass by shark species, was used as the basis of the methodology. A first step involved scaling Hong Kong trade-derived estimates for 2000 to annual global values for 1980-2006 based on the observed quantity of imports to Hong Kong and an approximation of Hong Kong's share of the global trade in each year. The resulting global fin trade figures for each year were then scaled to Atlantic-specific values using three different factors: (1) area of the Atlantic range relative to the global range of pelagic sharks; (2) Atlantic catches of tunas and billfishes relative to global catches of tunas and billfishes; and (3) Atlantic longline effort relative to global longline effort. The strengths and weaknesses of each scaling factor and the assumptions inherent in the methodology are discussed. These estimates are not intended to replace reliable fisheries dependent catch data compiled by ICCAT from submissions of members and cooperators, but can serve as one of a variety of useful cross-validation tools when historic catch data are missing or uncertain.

Pouting, Trisopterus luscus is harvested commercially on the Galician shelf by the Spanish inshore artisanal fleet. In spite of a substantial decrease in pouting catches, fishery regulations are limited to size length restrictions. This study provides biological data including length-at-maturity based on histological methods, seasonal maturation, spawning and fecundity. A collection 443 females, from 17 to 42 cm in total length, were sampled from landings (December 2003 to December 2004). Pouting length-at-maturity was estimated as 19.2 cm on average. Pouting females in spawning condition were observed throughout the year and the number of developing oocytes ranged from 20 000 to 1 327 000. Peak spawning was observed between February and April, which correlated well with trends in gonadosomatic index, and inverse to condition factor and hepatosomatic index. Histological examination of the gonads revealed that pouting ovarian development organization is asynchronous, and fecundity is probably determinate.

It has been previously shown that two guilds of predators, the sea kraits and their prey, the anguilliform fish (predator themselves), are far more abundant and diverse than previously suspected in coral reefs of the Indo-Pacific area. Based on diet, foraging range, feeding rate, and population size of two sea krait species, we estimated the annual uptake of anguilliform fish around Signal Island, New Caledonia. We found that more than 4000 snakes live on this 15 ha islet and that they can take up to 45 000 fish (>1.3 t) per year, essentially from 10 fish species previously considered as rare. One third of these fish are captured on the reef flat, the two other thirds within a 17 km radius surrounding Signal Island. We suggest that the foraging areas of the different snake populations belonging to numerous islets (and the surrounding reef flats) overlap greatly.

The change in catches and mean size of one-year-old perch (Perca fluviatilis) in Lake Geneva was studied between 1957 and 2005, and related to trophic changes and average temperature. The status of Lake Geneva, assessed on the basis of total phosphorus concentrations, switched from being oligotrophic before 1960 to eutrophic, with total phosphorus concentration reaching nearly 90 µg L−1 in 1976-1979. In response to management measures, the trophic status then returned to mesotrophy in the early 2000s. Zooplankton is the main food consumed by young perch, and quantities present (annual biovolumes of zooplankton) were recorded throughout the study period. The lake water temperature was also recorded. Data obtained from perch catches and perch spawns enabled eleven strong cohorts of perch to be identified. Strong cohorts dominated the stock for three years, until they were massively caught by fishermen. Yields have fluctuated widely, increasing rapidly until 1975, and subsequently decreasing, with an exceptional decline between 1976 and 1981. During the period 1977-1981, unfavourable climatic conditions in spring were probably the main cause of this fall in perch yields. For the other periods, perch yields and the mean size of one-year-old perch were significantly correlated with trophic parameters, total phosphorus concentration and zooplankton biovolume. Correlations are higher if only strong cohorts are taken into account. As a result of the re-oligotrophication process, perch growth has been progressively reduced, age at first maturity delayed and strong cohorts become less frequent; the mean size of 0+ individuals in strong cohorts is significantly smaller than in the other cohorts, suggesting a population density effect in the context of a limited supply of zooplankton. During the study period, trophic changes in Lake Geneva have had more impact on perch growth and yield than has temperature, since no significant correlation could be detected between water temperature and perch growth.

The aim of this study was to quantify the efficiency of different lengths of beach seine nets for each diel period in freshwater reservoirs. Only fish older than young-of-the-year were considered. Nets of 10, 20 and 50 m length (“in-nets”) were tested in an enclosed area framed by a 200 m long net (block net). The net efficiency estimate was calculated as the ratio of fish catches with the in-net and block net divided by the ratio of their respective areas. The net efficiency estimate was significantly different between day and night catches. At night, the efficiency estimate of nets depended on the size of the fish. The efficiency estimate of a 10 m long net decreased significantly in reverse correlation with fish size. A similar trend was found when using a 20 m long net. The efficiency estimate of a 50 m long net was independent of fish size. The variance in efficiency estimate between samples with a given net length was high, but decreased with longer nets. Of five species tested, only the efficiency estimate for catching bream (Abramis brama) increased significantly with the length of net. The biomass and abundance of larger fish was generally higher at night, although especially short nets exhibited a spuriously high efficiency estimate during the day, probably due to the concentrating (chasing) effect of the hauling ropes. We therefore recommend the use of a 50 m long net, since its nighttime efficiency estimate was about 0.9 in terms of both sampling abundance and biomass. A model relating the efficiency estimate and net length was developed with the data acquired.

The swimming, air-gaping, and agonistic behaviours of Heterobranchus longifilis (318 ± 67 mm) were examined while fish were in a fasted state under 12L:12D and variable group size (2, 5, 10 and 15 fish) in a 1000-L aquarium. Fish exhibited a predominantly nocturnal activity pattern independent of group size. A diurnal peak of activity occurred, however, at the usual feeding time. A reduction in frequency of agonistic interactions was observed in larger groups. Five fish were then observed under 72L:0D and 0L:72D. The nocturnal activity pattern remained, contrary to the diurnal peak, and was independent of the duration of illumination or darkness. These results suggest the absence of biological clock in H. longifilis, although fish may somehow be influenced by past feeding experience. Behavioural plasticity in this species may provide potential for aquaculture in northern latitudes.

Bonamiosis is a parasitic disease (causative agent: Bonamia ostreae) affecting the European flat oyster Ostrea edulis, responsible for a drastic decline in its aquaculture production. Selective breeding programs for resistance to bonamiosis have been undertaken to counter this disease. In the present study, a 6-month cohabitation challenge experiment was performed in order to transmit the disease from wild oysters injected with the parasite to two tested families of oysters (20 and 8-month old at the beginning of the experiment, with different genetic backgrounds) originating from a selective breeding program developed by IFREMER in France. Mortalities were checked daily and ventricular heart smears were performed on dying or moribund oysters to detect the level of infection by B. ostreae. Mortality started after 4 months of cohabitation in the tested oysters. The cumulative mortalities after 6 months were 58% for the wild oysters, 9% for Family 1 (20-month old) and 20% for Family 2 (8-month old). In the dying oysters, the parasite could be detected in 67% of the wild oysters, 68% of Family 1 and 89% of Family 2. It was detected in only 11% of the surviving oysters of Family 2. The mortality and the level of infection by the parasite were significantly higher in Family 2 than in Family 1. Our results demonstrate that prespawning oysters as young as 1 year-old can become infected with the parasite and, most importantly, can die from bonamiosis. This result is inconsistent with the commonly accepted critical age of 2 years-old for the disease development. Additionally, no clear relationship between shell length and level of infection was observed. We also review the different methods for infection of the European flat oyster O. edulis with B. ostreae under experimental conditions and their main results.

Hatchery produced pearl oyster spat are generally transferred to the ocean on spat collectors which may, or may not, be covered with fine mesh to prevent spat loss. This study examined the effectiveness of mesh bag covers on culture units for spat of the blacklip pearl oyster, Pinctada margaritifera. It assessed spat retention and growth in culture units without mesh bags (REMOVE) and in those where mesh bags were replaced weekly (REPLACE), washed weekly (WASH) or left unwashed (NO WASH) for the duration of the six-week experiment. Culture units in the REPLACE treatment had the greatest number of spat at the end of the experiment and 41% more spat than in the REMOVE treatment. Grading of the spat from each treatment at the end of the experiment showed that the REPLACE treatment had the highest number of spat in large and medium size classes with mean (± SE) dorso-ventral height of 23.9 ± 0.5 mm and 17.4 ± 0.5 mm, respectively. Mean wet weight of the mesh bags at the end of the experiment differed between treatments with bags from the WASH and NO WASH treatments having significantly greater mean wet weights than those from the REPLACE treatment. The results show that the presence of a mesh bag around spat culture units may improve retention of spat by between 18–41%. However, protective mesh bags may foul quickly and, to maximise retention and spat growth, weekly replacement of mesh bags should be undertaken.