Virtual population analysis (VPA) is often used for assessing freshwater and marine fisheries resources. One important component in VPA is to calibrate abundance estimates with a time series of abundance indices. One of the commonly used calibration processes usually includes simultaneous estimation of cohort sizes across all ages and years. This reduces the flexibility of the model in accounting for age- and year-effects, in particular in the presence of an age-specific curvilinear relationship between abundance index and stock abundance. In this study, we compared this simultaneous method tuning approach with a stepwise approach which calibrates abundance age by age in tuning VPA. The simulation study suggests that the stepwise procedure tends to perform better with no obvious retrospective errors in the estimated stock biomass compared with the simultaneous method which tends to have large positive retrospective errors. In applying the stepwise procedure and simultaneous method to a cod fishery data set, we found large differences in the stock sizes estimated for the most recent year using these two methods, with the current stock size estimated using the stepwise method being substantially smaller than that estimated with the simultaneous method. Considering the likelihood of the presence of curvilinear relationship between abundance index and stock abundance, we conclude that the stepwise method yields more reliable results, and is less risk-prone in using VPA for fisheries stock assessment.

This study examines the trophic status and relationships of coral reef fish in the lagoon of New Caledonia, southwest pacific. The feeding habits of 34 fish species collected at three contrasted sites were first described using a compilation of gut contents observations and data from the literature. The carbon and nitrogen isotope signatures of these fish and of some of their potential ultimate food sources were also determined at each site. Despite some spatial variations in the isotopic signatures of most food sources and fish trophic groups, the overall trophic structures of fish assemblages were similar at the three sites. Stable isotope data were then used to re-assign fish species to trophic groups based on the δ 15N signatures of fish and their food sources. Herbivorous fish species were clearly distinguished from the other trophic groups by their lower δ 15N signatures, consistent with an estimated trophic position of ~2 for all species examined. Scaridae were however characterized by relatively higher δ 13C and lower δ 15N, which is probably linked with the role of detritus in their diet. The estimated trophic positions of planktivorous fish species were consistent with their gut contents-based classification. Conversely, the isotopic signatures of carnivorous and piscivorous fish species largely overlapped, and their estimated trophic positions were much lower than expected. This suggests that these species feed over a broader range of trophic levels and food sources than implied by the gut contents observations, and indicates that their diet is partly omnivorous. Finally, the relationships between body mass and the isotopic signatures of four fish species were significant for at least one isotopic ratio for each species. Since ontogenetic variations and omnivorous diets are difficult to assess with gut contents data only, stable isotopes revealed essential in estimating the actual trophic status and relationships characterizing the fish species under study.

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.

Contamination of shellfish by paralytic shellfish poisoning (PSP) toxins poses an economic threat to shellfish farmers. As contaminated shellfish cannot be harvested for long periods of time, it would be very useful to develop processes to optimise and shorten their detoxification. In this study, Pacific oysters Crassostrea gigas were first experimentally contaminated over a period of 13 days with a continuous flow of toxic Alexandrium minutum cultures at concentrations ranging from 150 to 200 cell ml-1 (toxin content after 13 days of contamination 438 $\mu $ g STX equiv. 100 g−1 wet weight). Then, two different detoxification treatments were tested and showed detoxification rates greater than those observed in coastal environments. The first treatment consisted of feeding oysters on Skeletonema costatum, at a concentration of 2000 cell ml−1 to speed up detoxification rates. The second detoxification method used the same Skeletonema costatum diet, supplemented with silt particles at a concentration of 20 mg L−1. A control was also set up by placing contaminated oysters in seawater with no additional algal food. The detoxification experiment lasted 8 days. Toxin contents were analysed by liquid chromatography with fluorescence detection (LC-FD). The S. costatum diet significantly reduced the time needed for oysters to reach the sanitary threshold (80 $\mu $ g STX equiv. 100 g−1 wet weight), but no effect of the silt supplement could be demonstrated conclusively. These different detoxification methods did not influence toxin biotransformations as observed in oyster tissues, i.e. epimerisation and decarbamoylation of gonyautoxins 2 and 3.

Trammel net is the main fishing gear used by artisanal fishers in Majorca Island (NW Mediterranean), and is representative of Mediterranean small-scale fisheries using static gear. The use of static gears close to the coast, where seasonal variability and spatial heterogeneity are high, promotes the diversification of fishing practices or metiers. We analyze the seasonal dynamics of the nets used, target species (red and black scorpionfish, red mullet and cuttlefish) exploitation patterns and the socio-economic conditions under which this fishery takes place, based on General Fisheries Directorate daily sale records (2002–2006). Additional personal socioeconomic interviews allowed the characterization of the trammel net fishery, its fishing behaviour, cost structure and conflicts. Catch and effort data and market surveys are used to evaluate the level of exploitation of the target species and allowed describing Majorca trammel net fishery as an activity based on a sustainable resource. The main target species were found to be near their maximum sustainable yield both by means of a surplus production model (with parameters estimated by CEDA-Catch Effort Data Analysis, software) and an age structured assessment model based on yield-per-recruit analysis. Management actions currently debated by local administration and fishers focus on improving fishers' economic situation, rather than on protecting a threatened resource. One of the management actions proposed is a one day effort reduction, which was analyzed here with the help of a bioeconomic simulation model. A 15-year (2005–2020) simulation allows providing advice to local managers to focus on the commercialization aspects, in order to obtain a higher value to the fish production, rather than expecting to obtain higher profits only by a reduction of the offer.

Based on the discrete optimal choice theory and a random utility model (RUM) framework, this paper focuses on the firm's long-term choices. A behavioural study on the stay and exit decisions of the fishing firms belonging to the inshore fleet of the Basque Country is undertaken by estimating a logistic model from a set of socio-economical sample panel data for the period 2003-04. Specifically, we aim to determine the set of vessels', skippers' and economic variables that may influence the probability of a fishing vessel to exit from the fishing activity. Special attention will be paid to the roll that incentives generated by decommissioning grants play in the fishermen's long-term behaviour. Our results indicate that the owner's age, years of experience being a skipper, the arrangement of continuity in the familiar business, the degree of dependency upon bank loan and lastly but not least decommissioning grants may significantly determine the decision to abandon the activity.

The paper analyzes the daily catch, fishing effort and fish size data of the purse seine fleet fishing in the western Indian Ocean in February 2005, when a major concentration of tuna occurred and was heavily exploited by this surface fishery. This tuna concentration event occurred over a period of just 12 days, in an area of about 3500 square nautical miles located to the west of the Seychelles. This small stratum produced a total catch of 22 000 t, corresponding to 6.5% of the total fishing mortality of all adult yellowfin (Thunnus albacares) in the entire Indian Ocean in 2005. Sets were made mainly on free schools and the catch mainly composed of large yellowfin tuna. The average CPUE and the average catch per set were very large, 65 t and 85 t per fishing day, respectively. This “event” took place in a precise area where a high concentration of chlorophyll had been localized 18 days before. The subsequent concentration of tuna schools probably arose due to the high densities of their prey feeding on this large phytoplankton biomass. This phytoplankton bloom was observed at the edge of an anticyclonic eddy, but its origin and its high density cannot be fully explained by available environmental data. The adult yellowfin were probably at a reproductive stage and actively feeding on the local food chain generated by the phytoplankton bloom. Such an event is extreme, but typical of tuna purse seine fisheries where fleets often search for such tuna patches. These events play an important role in tuna fisheries due to the increase in fishing effort and fishing efficiency of purses seiners, both of which increase their impact on the resource. The fine scale study of such events and their improved integration into tuna stock assessments is recommended.

The occurrence of new phytoplankton species in a coastal area may be explained by the import of shellfish containing whole live algal cells in their digestive tracts. Indeed, shellfish containing toxic algal cells can induce both primary contaminations in safe areas (initially free from toxic microalgae), and secondary contaminations of other shellfish growing in the same area via the faeces of the imported animals. To mitigate this problem, shellfish need to be placed in a separate holding tank and their intestinal content purged. For a deeper understanding of the risks associated with transferring contaminated shellfish, oysters (Crassostrea gigas) and mussels (Mytilus edulis) were purposely fed either Alexandrium minutum or A. catenella (Dinophyceae) or Pseudo-nitzschia calliantha (Bacillariophyceae) toxic algae for 2 h. They were then transferred into individual tanks where they were continuously fed with a non-toxic alga, Tetraselmis suecica. Biodeposit production, faeces composition, and filtration rates were monitored for the shellfish over a 6-h period. The effect of temperature differences and different initial toxic algae concentrations were compared. This study revealed a relationship between temperature and cell lysis in the oyster digestive tract. It also indicated that toxic algae concentration did not seem to influence gut passage time in oysters, while a significant effect was observed in mussels, and confirmed the existence of a difference between oyster and mussel feeding patterns.

Icelanders gradually adopted an Individual Transferable Quota (ITQ) in their waters. This property-rights based system yielded benefits to the economy but was not applied to all fishermen. Some fishermen remained outside of the ITQ system and were subject to other management measures. In this paper we investigate the effects of various effort restrictions on the behaviour of fishermen outside of the ITQ system. Empirical estimates from duration model analysis are presented which measure the effects of various management measures aimed at affecting the behaviour of those “outsiders” as well as the indirect effect of the ITQ system on the behaviour of those who stayed outside of it. The results show that outsiders had incentives to stay outside of the ITQ system and free-ride on the behaviour of the ITQ fleet. Management measures aimed at restricting their effort proved to be ineffective. The conclusions can be generalized to other situations where property rights based management systems are used and economic agents harvest a common resource pool.

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.

The bigeye cigarfish (Cubiceps pauciradiatus) is a small pelagic nomeid of the tropical world ocean, often recovered in the stomach contents of top predators such as tunas, billfishes and marine mammals. In the Indian Ocean, a few studies have investigated the biology and the ecology of this species that is one of the most abundant fish of the intermediate trophic levels. In this paper, we investigated the spatial distribution of C. pauciradiatus in the Indian Ocean using pelagic trawl catches carried out between 20°N and 45°S, and the importance of bigeye cigarfish in the diet of 9 piscivorous fishes sampled by different fishing gears in the western part of the Indian Ocean. The highest densities were observed along the eastern coast of Africa and in the Arabian Sea (87 000 individuals per square nautical mile) during the South-West Monsoon and in the eastern part of the Seychelles archipelago (62 200 ind. square nmi) during the North-East Monsoon. Small sized bigeye cigarfish (20–80 mm SL) was a regular and abundant prey (20 to 200 ind. per stomach) for schooling predators exploited by purse seine fishery such as large yellowfin and bigeye tunas chasing prey near the sea surface. Large sized bigeye cigarfish (61–150 mm SL) occurred in small numbers (3 to 20 ind. per stomach) in the stomach contents of swordfish and of large yellowfin and bigeye tunas caught by longline sets at great depths. Large concentrations of bigeye cigarfish occurred in zones of high productivity, and that species constituted seasonally a strong link in the transfer of energy from low to high trophic levels in this part of the Indian Ocean.

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.

The taxonomic status of the cupped oysters Crassostrea angulata and C. gigas has received considerable attention in the last decades. Based on larval shell morphology, experimental hybridization, allozymes and nuclear DNA studies several authors have considered these two taxa as being synonymous. However, mitochondrial data showed clear genetic differences between the two taxa. In addition, microsatellite-based studies and cytogenetic studies have also provided evidence that supports their differentiation. Considerable differences have also been observed at the phenotypic level in terms of growth rate and ecophysiological parameters. In the present study, C. angulata from Sado estuary (Portugal) and C. gigas from Seudre estuary (France) were collected and factorial crosses were performed. Juveniles of the different progenies were reared in Ria Formosa (Portugal) under common conditions to determine if they exhibited differences in shell shape and in pigmentation of the adductor muscle scar. Significant morphometric differences between C. angulata and C. gigas progenies were indicated by univariate and multivariate analyses. Univariate analysis of size-adjusted shell measurements revealed significant differences between the two taxa for shell depth, muscle scar height, and length of ligamental area. Both reciprocal hybrids showed intermediate morphometric characters between parental lines. In addition, significant differences were also observed between C. angulata and C. gigas progenies in terms of pigmentation of adductor muscle scar. C. angulata and both reciprocal hybrid progenies showed highly pigmented adductor muscle scars whereas in C. gigas progeny the pigmentation was lighter. The differences in shell shape and muscle scar pigmentation observed in the present study support the distinction of the two taxa.

Even with the rapid changes in the level of complexity and the uncertainty of the environment in which Belgian sea fisheries operate, fisheries management in Belgium is still mainly based on restrictive policy instruments founded in the biological approach of fisheries management science. Since they will continue to play an important role, this paper evaluated changes in three restrictive policy instruments and their effect on future fleet performance and dynamics, i.e. maximum fishing days, total quota-restrictions and licences. These effects are tested through scenarios in a microeconomic simulation model, including sensitivity analysis. This study opts for a dynamic simulation model based on a microeconomic approach of fleet dynamics using system dynamics as a modelling technique (operational base: Vensim®DSS). The results indicated that changes in maximum fishing days and total quota resulted in higher fluctuations in fleet performance and dynamics compared to changes in licences. Furthermore, changes in maximum fishing days and total quota had a direct impact on fleet performance, though not always as expected, whereas licences only affected fleet performance indirectly since they only limit the entry of new vessels to the fleet and they can block the growth of successful sub fleets. The outcomes of this study are translated into practical recommendations for improving fisheries management. Firstly, policy makers need to be more aware of misperceptions of feedback. Secondly, the results proved that altering only one type of restrictive policy instrument at a time often fails to meet desired outcomes. Therefore, policy makers need to find a balance in combining policy instruments. Finally, this paper opens the discussion on the future value of restrictive policy instruments in the rapidly changing, complex and uncertain fisheries environment. It suggests rethinking their use from “preserving a status quo and social peace” toward a driving factor in “stimulating fleet dynamics”.

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.

A number of European fishing fleets have been regulated through a combination of quota and effort (sea days) controls since 2004. These two regulation schemes are, however, interrelated, i.e. a given quota limit will necessarily determine the effort used and vice versa. A bioeconomic feedback model is presented which takes this causality between effort and harvest control into account, and switches back and forth between these two regulation schemes depending on which is the binding rule. The model is based on biological stock projection, and quotas are set using the Pope approximation while an economic production function is used to estimate the harvest when the effort is binding. The economic response of the fleet is modelled through a dynamic investment/disinvestment module which evaluates the change in the fleet capacity given the economic outcome of the fishery. A simple example is presented for the Danish seiners catching cod in the North Sea. The model has been constructed as part of the 6th framework project “Operational Evaluation Tools for Fisheries Management Options (EFIMAS)”.

Fisheries bycatches and discards constitute a significant problem in many fisheries worldwide. Unlike the pelagic purse-seine, the demersal purse seine usually targets high commercial value demersal species such as sea breams (e.g., Diplodus spp., Pagellus spp., Sparusaurata) and the European sea bass (Dicentrarchuslabrax), while discards consist mainly of pelagic species and juveniles of the above mentioned species. In order to evaluate the efficiency of a selectivity device in reducing bycatch and consequently of discards in a demersal purse seine fishery, experimental deployments were carried out. The bycatch reducing device (BRD) consisted in the use of a panel of diamond-shaped mesh netting of 70 mm stretched mesh in the posterior part of the purse seine. Data from 61 experimental fishing trials allowed the evaluation of discards, with Scomberjaponicus, Boops boops, Sardina pilchardus, Diplodus bellottii and Belone belone being the main discarded species. The mean discard ratio per set was 0.49 (± 0.30 standard deviation). The causes for discarding were also identified, with low commercial value being the most important reason. The results of the trials with BRD, were promising, with an average of 49% (± 24%) of the fish escaping per set, especially from those species that are most discarded. Overall, the use of this method for reducing discards can be considered positive for the following reasons: there is no need for structural modification of the fishing gear, the BRD is easy to deploy, and it is efficient in terms of species, sizes and quantities of fish that manage to escape. It therefore has significant benefits for the demersal purse seine fishery and possibly for other “métiers” as well.

Parameters of hemocyte populations have been considered as relevant indicators of bivalve health and are currently used in immunotoxicological studies. Hemocytes in hemolymph can be collected by puncturing either the pericardial cavity or the adductor muscle sinus with a syringe. Flow cytometry is a methodological approach that is increasingly being used in laboratories for the study of hemocyte parameters in aquatic invertebrates. However, various protocols for hemocyte processing in laboratories equipped with different types of cytometers have been published. In this context, two flow cytometers (EPICS XL4®, Beckman Coulter and FacsCalibur®, Becton Dickinson) and two sites of hemocyte collection (pericardial cavity and adductor muscle sinus) were compared for the analysis of hemocyte parameters in the Pacific oyster, Crassostrea gigas. Hemolymph cells were analyzed in terms of their number and organelle contents. Cell mortality, phagocytosis, non specific esterase, extension of the lysosomal compartment and production of reactive oxygen species were quantified. The results showed that the phagocytic index was higher for hemocytes obtained in the muscle sinus hemolymph. The results are discussed with respect to the potential use of flow cytometry as a tool for hemocyte studies in bivalves.