This study aims to test the influence of size grading on self-feeding behaviour, social structure (measured by the percentage of triggering acts per individual), growth performances, and blood physiological variables of individually passive integrated transponder (PIT)-tagged sea bass juveniles, using a computerized on-demand feeding system coupled with a PIT tag monitoring device. Three consecutive periods of 27 days each were compared: a first period (P1) before grading (6 tanks of 100 fish; 40.2  ±  8.9 g) followed by a second period (P2) after grading. The protocol applied aimed to create two groups of fish of similar mean weight but with either a low or a high coefficient of variation of weight (CVw) corresponding to an imposed difference in social disruption (Tlow: CVw ~ 10%, 3 tanks of 60 fish each with social disruption; Thigh:CVw ~20%, 3 tanks of 60 fish each, without social disruption). Tlow and Thigh groups were studied over P2, and an additional 27-day period under identical conditions (P3). The grading protocol used and/or time modified the social structure when comparing P1 and P2. Thereafter, during P2 and P3, no difference could be observed in growth performances, feed demand, or physiological variables between Tlow and Thighgroups. Feeding rhythms and social structures were similar in both groups. In conclusion, such grading practice only transiently modifies feed demand behaviour and social structure built around the self-feeder, without further improvement in individual growth performances in sea bass.

Tropical shrimp fisheries are characterized by various interactions with their natural environment and with other fisheries. These latter interactions can be explained by the high quantity of bycatch taken by industrial trawler fleets, which has a significant impact on fish populations associated with shrimps and thus also on finfish fisheries. Bycatch also includes emblematic species, which are subject to strict conservation measures decided by the international community. It seems important to identify and assess the biological and economic consequences of different mitigation measures (increase of mesh size, turtle excluder devices and bycatch reducing devices). This communication is based on case studies undertaken on the Indian white prawn (Fenneropenaeus indicus) and speckled shrimp (Metapenaeus monoceros) fisheries in Madagascar and on the brown shrimp (Farfantepenaeus subtilis) and pink spotted shrimp (Farfantepenaeus brasiliensis) fishery in French Guiana. A review of the impacts of these fisheries on resources and ecosystems is made and some results of experiments on mitigation devices given. Finally, the results of simulations obtained using a multi-species, multi-fleet, age-structured bioeconomic model, including modifications of catchability and costs related to the adoption of these devices, is presented and discussed.

Among the strategies that can be used to improve fish welfare in a rearing environment, domestication and/or selective breeding was proposed to minimize fish responsiveness to husbandry practices. To verify this hypothesis on a recently domesticated species, the sea bass Dicentrarchus labrax, two experiments were realized, each using two populations differing according to their level of domestication or selection. For the first experiment, we used one population produced from wild parents (Wild; initial body mass: 106  ±  3 g), and one population from parents selected for growth for one generation (Selected 1; initial body mass: 129  ±  4 g). For the second experiment, we used one population produced from parents domesticated for two generations (Domesticated; initial body mass: 72  ±  3 g), and one produced from parents selected for growth for two generations (Selected 2; initial body mass: 89  ±  4 g). The first experiment was carried out over 112 days with 240 fish (60 fish per tank, 120 fish per population), and the second one over 84 days with 200 fish (50 fish per tank, 100 fish per population). Two variables, self-feeding behavior and growth performance, were measured over the time of the experiments. After a control period, the fish were submitted twice, at three-week intervals, to an acute stress treatment consisting of draining the tank and leaving the fish out of water for one minute. Both self-feeding behavior and growth performance were altered by the acute stress treatment. During the first post-stress period, the Domesticated and Selected (1 and 2) groups showed more pronounced post-stress exposure responses than the Wild fish: they modified their feeding rhythm, their feed intake, and their growth rate. During the second post-stress period, feeding rhythm was still affected (being more diurnal with a well defined peak), but the feed intake and growth rate results showed that the Domesticated and Wild groups seemed less affected than the Selected (1 and 2) populations, which continued to express a high post-stress response.

According to these results, it can be concluded that: (1) an application of two acute stress treatments, at three-week intervals, modified fish feeding behavior and growth performance; (2) the domestication process seemed to improve fish adaptation abilities to this kind of stress; and (3) the process of selection for growth led to a final, better growth, but did not seem to improve fish acute stress tolerance.

The bivalve’s aquaculture industry is an important component of the economy in Eastern Canada. Seed collection is an initial and critical activity in most bivalve aquaculture industries including mussel farming in Prince Edward Island, production is entirely dependent on natural spat collection. Although seed supply is not a concern from a quantitative standpoint, there are growing concerns about the quality of natural seed. The general objective of this study was to identify and assess mussel seed quality criteria on the basis of physiological and biochemical status under laboratory and field conditions. The performance, as estimated by metabolic measurements, lipid class composition, multi-locus heterozygosity (MLH) and survival to stressful environment of seed from 6 different stocks sources was first compared under laboratory conditions at 12 °C and 25 °C. Results showed that MLH varied among the six sources of mussels in a way which is consistent with the physiological and biochemical indicators of seed quality. Mussels from Shippagan (New Brunswick) and Tracadie (Prince Edward Island) were found to have the highest quality scores and the best adaptive capacity to extreme water temperature under laboratory conditions. The results of the stock-site reciprocal field studies are in general agreement with those of the laboratory experiments with higher survival of mussels from Shippagan, Tracadie and St. Peters Bays in the various study sites. Our results suggest that the measure of MLH and survival curves at stressful temperature could be a good criteria combination to identify the improved survival potential of mussels stocks.

Water quality assessment is a key factor in the environmental management of freshwater networks, especially those including fish farms, which need cost-effective operational tools to monitor and control their waste output. In France, current legislation specifies limits in concentrations of dissolved compounds and suspended solids at fish-farm outlets. Despite the development of mass-balance modelling tools, chemical analysis of water (hydrological method) remains the most widely used method. To understand better the environmental impact of trout farms on aquatic ecosystems and to compare waste assessment methods, we monitored 20 commercial flow-through trout farms for 24 h, and we compared data obtained with the two methods (hydrological method and mass balance modelling) by linear regression. For total nitrogen and total phosphorus, the correlation between the two methods was high; thus, considering the uncertainty of both methods, this study was not able to determine which was more accurate. The high correlation between observed ammonia concentrations and predicted total nitrogen emissions provides a coefficient for estimating ammonia emissions at the farm level. The same approach is proposed for the evaluation of phosphate emissions. In conclusion, this study confirms the utility of simulation modelling for assessing nutrient release from fish farms.

High levels of larval mortality are a significant barrier to the artificial mass production of Pacific bluefin tuna (Thunnus orientalis). Mortality may occur when larvae sink and come into contact with the bottom of the rearing tank during the first 10 days after hatching. We evaluated the effect of flow control by aeration on the survival of T. orientalis larvae. These larvae were held in 500-L tanks in which the aeration rate was varied during the night. Larval survival increased with air supply. We documented the cross-sectional flow pattern and gravitational sinking velocities of larvae to assess the correlation between survival and circulation patterns in the tank. The sinking velocity of T. orientalis larvae at night increased with larval body density, which varied with swimbladder volume. Larvae with uninflated swimbladders sank significantly faster than larvae with inflated swimbladders. Both water circulation speed and survival increased at higher aeration rates. Our results suggest that aeration rates >900 ml min–1 may increase larval survival by counteracting sinking.

Mussel culture relies on the mussel self-attachment capacity through byssus production. By doing so, no cages or containment devices are needed. It has been previously suggested that thread production requires a non-negligible part of the energy expenditure in blue mussels Mytilus edulis. Therefore our work investigates the relationships between byssal thread production, mussels energetic reserves and phospholipids profiles in the foot. The relationship between thread production and heterozygosity was also examined. The study was realized in a small lagoon of the Îles-de-la-Madeleine, southern Gulf of St. Lawrence, Canada, on four sampling dates between June and September encompassing the pre- to post-spawning periods. Our results show a significant relationship between the thread numbers and attachment strength. However, no correlations were found between energy reserves, phospholipids composition of the foot or heterozygosity level and byssal production. Our results suggest that mussels in suspension culture in this lagoon were not energy-limited so that the energy reserves did not influence the byssal thread production.

We analyzed the small-scale fishery in the port of Vilanova i la Geltrú (NW Mediterranean) to assess the fishing practices in this fishery and produce economic indicators of its status. We defined the fishing tactics (or métiers) of this fishery with a multivariate analysis approach for evaluating the main fishery resources and fishing gears employed. Our results show that netters in this fishery practice 7 types of fishing tactics. Five of these fishing tactics, in terms of target species, gear and seasonality, are also used in other small-scale Mediterranean fisheries. The main types of fishing gear (trammel nets, gillnets) and target species (Sepia officinalis, Solea vulgaris, Mullus surmuletus and Merluccius merluccius), and a well defined seasonality, are also observed in other studies of Mediterranean small-scale fisheries. We show that the seasonal rotation of fishing tactics is determined by the availability of different fish species rather than market price. Identifying the fishing tactics, which in the Mediterranean are relatively limited in number, of small-scale fisheries provides information for developing monitoring and management strategies for these fisheries. We also assessed the economic performance of the small-scale fishery in Vilanova i la Geltrú and its conflicts with other uses of the coastal zone. We conclude that small-scale fisheries are an economically viable activity although seriously threatened by concurrent uses of the coastal zone (conflict with other extractive activities; competition for space with tourism and leisure activities; pollution). The integrated management of the uses of the coastal zone is necessary in order to sustain small-scale fisheries, which have become less important in economic terms, but which are an important social component of local coastal communities and are a source of high quality seafood with a low ecological impact.

The Chilean hake (Merluccius gayi gayi) is the predominant groundfish species inhabiting the southern Humboldt, mainly from Coquimbo (29° S) to Puerto Montt (42° S). At present there is only limited knowledge on the spatial distribution of juveniles of this species, particularly concerning its dependence on key physical characteristics. On the basis of annual surveys carried out during austral winters from 1997 to 2006, changes in the presence of juveniles were studied using Generalized Additive Model techniques. Temporal factors and spatial effects were more important than single physical variables in explaining the presence of juvenile hake (<34 cm total length). Juvenile hake had a preference for shallower waters. Although salinity and oxygen were significant, their contribution was marginal. Juvenile hake seem to prefer shallow oxygenated waters, but the nonlinear relationships and partial secondary peaks detected in salinity and oxygen probably only reflected the influence of three water masses found in the winter habitat. Endogenous factors could be more important in determining temporal and spatial changes in the proportion of juvenile hake. An important change in the presence of juveniles has occurred since 2004, coinciding with a significant decline in biomass of adult hake. It is postulated that cannibalism pressure from adults has probably declined and that spatial and temporal changes in the presence of juvenile hake seem to be more associated with fishery-induced demographic effects.

A series of physical characterization methods (UV fluorescence microscopy, X-ray microdiffraction, backscattered electron imaging and X-ray absorption spectroscopy) were applied to Polynesian pearls collected after different cultivation periods, varying from three weeks to eighteen months. Through this rigorous time-based sampling, 120 pearls produced by 20 different donor oysters were compared. Results show that the structure of the pearl layer can be understood as a sequence of distinct secretion processes whose progressive occurrence through time may lead to variously arranged and sometimes aberrant mineralized structures. By making comparisons with the structure and growth mode of the Pinctada margaritifera shell, this study shows that the currently accepted theory that views the pearl-bed as a “reversed shell” cannot account for the diversity of the microstructural patterns and mineralogical properties observed in the pearl layers. From a practical and economic view point, it appears that development of these pre-nacreous materials superposed onto a perfectly round-shaped nucleus is the main cause of shape irregularities in pearls and the consequent decrease in their value.

Water Framework Directive requires reliable and effective monitoring tools, and hydroacoustics has a potential to be one of them. The effect of pulse duration on in situ acoustical estimates of fish density and their size distribution was investigated. Measurements were performed in the oligo-mesotrophic Lake Hancza (Poland) using a SIMRAD EK60 split-beam echo-sounder at 70 kHz frequency. During the survey, two similar transducers pinged alternatively through the multiplexer using 4 different pulse lengths, from short to long ones. The results show that the volume backscattering coefficient (Sv) values, equivalent of the fish biomass, were not influenced by the pulse length. However, the number of the detected fish, the mean target strength (TS), and consequently the fish density, differed significantly for the long pulse duration data. This was especially noticeable in the layer above the thermocline with dense fish populations. In this upper layer, for the long pulse the Sawada index frequently exceeded value of 0.1 leading to overestimation of the mean TS and underestimation of the fish density.

The purpose of this study was to determine biochemical changes occurring in blue mussels (Mytilus edulis) fed effluent from an Atlantic cod (Gadus morhua) aquaculture facility over a period of ten weeks, compared to those in mussels fed a commercial shellfish diet and those supplied only filtered seawater. The total lipid and fatty acid content (mg g-1 wet weight) significantly decreased for mussels fed effluent during the experiment. The only change in the lipid class composition (% total lipid) at the end of the experiment was a significant increase in the proportion of acetone mobile polar lipids. There were several significant changes in the fatty acid composition (% total fatty acid) including an increase in the proportion of 18:1ω9, 18:2ω6, 20:4ω6, 21:5ω3 and the dienoic non-methylene-interrupted fatty acids 20:2a and 22:2b and significant decreases in the proportions of 16:0, 18:4ω3 and 20:5ω3. The increase in non-methylene interrupted dienes suggests that the amount of essential fatty acids in the effluent may be insufficient for optimal mussel growth. The presence of the terrestrial plant marker 18:2ω6 in both the fish feed and the effluent and its increased proportion in mussels fed effluent suggest that this fatty acid may have potential as a marker for aquaculture wastes.

Flatfishes represent an important resource in Portuguese fisheries. Although flatfish landings represent a low percentage of total fish weight landed, their importance is higher when commercial value is considered (11%). Official data on flatfish landings from 1992 to 2005 for all landing ports in Portugal were analysed, together with vessel characteristics, in order to detect patterns in flatfish fisheries. Fleet characteristics were heterogeneous, but most of the vessels were multi-gear. Three landing profiles were identified in the flatfish fishery, and the target species of these métiers showed variation in space and in time. Small vessels caught species that occur in coastal areas, mainly soles, bastard sole, flounder, turbot and brill, and usually also presented high landings of octopuses, cuttlefish and rays. Megrims and spotted flounder were caught with others species, like small pelagic fishes and seabreams by coastal trawlers. For this fleet component, catches of flatfish were usually bycatch. Generalized Linear Models (GLM) were used to analyse flatfish landings (LPUE, landings per unit effort and landings in terms of value) between 1992 and 2005 and to evaluate their relationships with several variables. The main effects in the models included year, month, landing port, vessel length class and total landings (kg). The models explained between 15% and 60% of the variability of the LPUE, and 46% to 82% of the variability of landing value, for the flatfish groups considered, with the most important factors being landing port, vessel length class, month, total landing (kg) and landing port: vessel length interaction. These results suggest high spatial and temporal variability. The results of this study may have implications for fishery management, because the LPUE was highest during the important periods of flatfish life cycles, like the spawning season. This fishing pattern has a negative impact on the stocks because of increased fishing pressure during a sensitive period for these species. The adoption of spatial and temporal closures should be implemented.

Dramatic declines in American eel (Anguilla rostrata) recruitment have resulted in strong conservation measures being implemented. Recovery actions in Ontario have included stocking of glass eels. Given the financial costs and imperative to undertake effective recovery actions, post-stocking monitoring is essential. In this study, point- and transect electrofishing sampling were compared in terms of eel detection, catch rates, size-selectivity, and power to detect changes in abundance. Transect sampling was more likely to detect eels and captured over twice the number of eels than point-sampling. Differences in catch rates and statistical power were dependent on the catch-per-unit-effort measure (i.e. sampling unit vs. time). Results support a transect-based sampling program for stocked eels in Lake Ontario tributaries.

The impact of an alien species is correlated with its abundance and potential to colonise new environments. Consequently, the crucial aspects that give a mytilid species invasive potential include its strength and capacity for adhesion to a wide variety of substrates and its ecological tolerance to environmental conditions. The alien black pygmy mussel Xenostrobus securis settles together with the indigenous and raft cultured mussel Mytilus galloprovincialis on hard substrates of the inner coastline of the Ría de Vigo (Atlantic Coast NW Spain). Key parameters for the ecological success of these species could include their byssus structure and ecological plasticity. In this study, we assessed their comparative ability to attach to different substrates under different environmental conditions, using both in situ and laboratory approaches. Byssus threads secreted by X. securis were found to be extremely thin and their thickness did not vary with mussel size. This thinness of byssus filaments in X. securis was compensated by the secretion of a huge number (up to thousand of byssus filaments). Although no increase in attachment strength was found with increasing mussel size in this species, multiple byssus thread secretion might be a key factor in the successful invasion of inner areas of the estuary. Furthermore, X. securis exposes a much lower shell area to lift and drag forces in mussel conglomerates. By contrast, the indigenous species M. galloprovincialis secretes thicker byssus threads, which provide stronger in situ attachment displaying a linear increase in strength relative to the size of mussels. The exposure of both mytilid species to different abiotic factors in the laboratory confirmed the weaker byssus secretion and limited variation in attachment strength in the alien species. On one hand, X. securis seemed to be better adapted to life on soft bottoms and not capable of much plasticity when attached to different substrates. However, X. securis might be also well adapted to variable environmental conditions, e.g., salinity fluctuations, with no need to modify its byssus properties to ensure secure attachment. Attachment strength of M. galloprovincialis was higher than X. securis in all abiotic conditions tested. Results are discussed in relation to the ecological tolerance and impact of these mytilid species.

The Central Mediterranean provides important neritic habitats for loggerhead turtles (Caretta caretta), but Mediterranean bottom trawlers catch an estimated 30 000 turtles a year, with 25% mortality. Mortality by trawling is mainly due to enforced apnoea during towing activity. In order to reduce the submergence time and consequent turtle mortality, a specific technical modification was developed in the early 1980s: the Turtle Excluder Device (TED). In this paper, we field-tested a typical Supershooter TED and three new types of low-cost TED, built with different designs and materials, incorporating aspects of US and Australian TEDs, as well as design features to improve handling and catch rates. The performance of the TEDs was investigated under commercial fishing conditions in diverse trawling grounds in the Adriatic Sea (Mediterranean). All TEDs were easy to operate and did not require changes to normal fishing operations. Due to lack of entry of turtles it was not possible to evaluate the ability of the different TEDs to release turtles, but one large loggerhead turtle (C. caretta) was captured during the experimental tows and was successfully excluded by the Supershooter. The TEDs reduced anthropogenic debris and, consequently, sorting operations on board. Among the four TEDs tested, both the semi-rigid TED and the Supershooter performed in accordance with the design objectives: total discards were reduced but total commercial catches were not significantly reduced. With the Supershooter, all European hake (Merluccius merluccius) individuals equal to or above 16 cm were found in the codend and 10–15% of those between 5.0 and 15.5 cm were released. In general, the total discard rate of the TED-equipped nets was reduced to around 20–60%. Since the Council Regulation (EC) No. 1967/2006 called for a discard reduction policy in waters under the jurisdiction of the European Union, TEDs may have some broader value in this context.

The common whelk Buccinum undatum (Neogastropoda, Buccinidae) is widespread along the north Atlantic coasts of France. In west Cotentin (Normandy), an important local fishery exists that depends exclusively on this marine resource and represents about 90% of French whelk production. Despite successive restrictive measures, fishing yields have decreased since 2000. Shell length frequency distributions of Buccinum undatum caught in west Cotentin were studied in 2005 (N = 2910), in 2007 (N = 2032) and in 2009 (N = 4145) ranging from 7 to 85 mm. In order to preserve this fishery and to characterise the whelk stock at this site, the reproductive biology of this species was studied in relation to age, sex and size, for whelks of commercial size (45 to 61 mm) over the complete annual cycle in 2008. Age was determined by reading the number of operculum striae: animals between 45 and 59 mm had 2 to 4 striae. Four reproductive stages were defined for males and females on the basis of histological analysis. The time course of reproductive events was described according to size and sex: the highest percentages of ripe stages were found in October for both sexes. Spawning events occurred between October and December. The shell length that corresponded to 50% of animals having mature gonads (49 mm and 52 mm for males and females, respectively, corresponding to 3 and 4 years old animals) exceeded the minimal landing size (45 mm). Fifty percent maturity was reached for males in their third year and for females in their fourth year. Reproductive investment was evaluated by quantitative analysis of the gonadal thickness or surface and was found to be proportional to shell size. We found that less than 20% of females under 49 mm in length were sexually mature and that these produced only a few eggs. This information, collected in a major fishing area, should assist fishery management decisions.

The pout, Trisopterus luscus, is one of the most important gadoid fish captured by northern Portuguese traditional fisheries. In spite of a substantial decrease in fish catches, little data are available either on the population structure or on the management of the species. In this study, chemical analysis with inductively coupled plasma mass spectrometry of whole otoliths of 90 pouts (age group 2, total length: 17.9–25.0 cm) provided location-specific elemental signatures. Sampling took place in shallow waters along the coastline in three fishing grounds off the Portuguese north coast (Viana do Castelo, Matosinhos and Aveiro) between February and March 2010. Otolith fingerprint analysis detected the presence of several informative trace elements. Molar concentrations for each site were analysed through uni- and multivariate statistical tests. Strontium, barium, magnesium and lithium (Sr, Ba, Mg and Li) differed significantly among locations, while no significant differences were found for manganese (Mn) and nickel (Ni). Canonical analysis allowed us to discriminate the tested individuals with respect to their sampling origin with a mean classification accuracy of 69%. The observed site-specific elemental differences in pout otoliths suggest a high level of site-fidelity in relation to their growing/feeding areas. Pouts from these locations can be regarded as a single, although not necessary homogenous, stock. Furthermore, this study also suggests that the populations of juvenile fish mix partially and, therefore, cannot be assumed to be separate units for fisheries management purposes.

Juveniles of the mussel Mytilus chilensis were exposed to a diet containing paralytic shellfish poisoning (PSP) toxins produced by the dinoflagellate Alexandrium catenella (strain ACC02). The feeding behaviour and the dynamics of intoxication and detoxification were evaluated over an intoxication period of nine days, followed by a detoxification period of eight days. A significant reduction in the feeding activity was measured during the first days of exposure to the PSP toxins (days 0 and 2), followed by a period of recovery observed on days 5 and 9, when the clearance rate of the contaminated mussels significantly increased. During the detoxification period, the contaminated bivalves showed a total recovery of clearance rate, and no significant differences were observed between contaminated and control groups. The intoxication dynamic was characterised by a rapid and sustained increase in the amount of PSP toxins accumulated in the tissues of the bivalves. Due to this increase, the level of PSP toxins critical for human consumption was reached on the first day, and at the end of the intoxication period, the mussels had accumulated 1601 μg STX eq. 100 g-1 tissue. During the detoxification period, a decrease of PSP toxins was observed, down to 319 μg STX eq. 100 g-1 tissue. The lower clearance rates observed over the first days of exposure would produce a decrease in the energy intake and could affect the rate of growth of juveniles. Despite this initial effect, the rapid intoxication capacity of M. chilensis corroborates that this species is a good indicator for the early detection of harmful algal blooms.

Argentina is one of the countries with the largest overall landings of skates and rays (24 000 t/year). As a consequence of high levels of exploitation and deficient management tools, many of these species are threatened with extinction. In the bottom trawl fishery of San Matías Gulf, northern Patagonia, skates and rays are caught as bycatch and all have historically been recorded in the fishery logbook under the category “rays”. Therefore, species composition and their characteristics were unknown. The aim of this study was to characterize the commercial exploitation of batoid species in this fishery. Our results indicate that commercial landings include nine species of skate, six of which are common. Among these, Atlantoraja platana, Sympterygia bonapartii and Dipturus chilensis were considered the main species of this fishery. Their combined relative abundance and weight made up about 90% of the batoid catch throughout the year. Sexual segregation was detected in four species in which individuals of one sex dominated commercial landings. The commercial fraction was composed of individuals with a wide range of sizes. Immature individuals could represent 90% of the individuals landed for some species. At present, lack of data prevents us from quantifying the impact that this fishery is having on these species, but our findings highlight the importance of conducting research surveys to assess the abundance and geographic extent of these populations. The information presented here provided the basis for the proposal of a new logbook format incorporating species-level identification. The new logbook was implemented on 1 January 2010.