Catchability is crucial for the economic performance of fisheries and their management. However, in many bio-economic simulation models it is assumed to be either constant or it is largely ignored, despite the fact that it is known to vary due to technical, environmental and behavioral factors. Such variation can cause the relationship between effort and fishing mortality to be nonlinear. This paper provides evidence for the possibility of nonlinear optimizing behavior from the Dutch beam trawl fishery, provides a methodology for estimating the curvature of the resulting relation, and a simple way of implementing these processes within a bio-economic model. Moreover, it shows the influence of a nonlinear relationship between effort and fishing mortality in a model of effort management (EU long-term flatfish management plan).

The long term influence of individual biological rhythms on group feed demand behaviour was investigated in European sea bass (Dicentrarchus labrax) held under controlled environmental conditions with an on-demand feeding system. The experiment was realized over 219 days with 190 fish distributed on 4 tanks. Sea bass had a mean body mass comprised between 139 g to 183 g. The number of feed demand acts by each individual was calculated daily, and the population could thus be partitioned into three categories (high-, low- and zero-triggering fish). The duration of the period that an individual held high-triggering status could vary, but was 63 ± 16 days on average. The transition period between two highest-triggering fish in one tank was on average 4 ± 4 days. The group feeding rhythm followed the same pattern of feed demand rhythm as the highest-triggering individual fish. When the highest-triggering fish was nocturnal, the totality of feed demand in the group was realized during the night with one peak at 22:00, corresponding to dusk under experimental conditions. When the highest-triggering fish was diurnal, the majority of feed demand in the group was realized during the light period with one peak at 06:00, corresponding to dawn, and/or another at 12:00. This study therefore highlights that sea bass group feeding behaviour is not the sum of individual feed demand behaviours, but is directed by the rhythm and behaviour of a few high-triggering fish. The regular changes of high-triggering fish in the group proved that it was not the identity of these particular fish that was most important for the group, but their role as a feed demand leader.

The loliginid squid Loligo forbesi has a flexible life-cycle, involving variable size and age at maturity, presence of summer and winter breeding populations, and extended periods of breeding and recruitment. This paper reviews life history data collected since 1983 from the commercial fishery in Scottish (UK) waters, alongside fishery data collected since 1970, and examines (a) the relationship between body size and timing of maturation, (b) evidence for shifts in the relative abundance of the summer and winter breeding populations, and (c) the possible role of environmental signals in determining the timing of breeding. Evidence from fishery data suggests that, since the 1970s, the summer breeding population has declined while the winter breeding population now dominates and breeds later than was previously the case. Length-weight relationships and size at maturity showed significant inter-annual and seasonal variation during the period 1983-2001. Males are shown to decline in relative weight as they mature while females increase in relative weight; possible interpretations are discussed. High autumn/winter temperatures (high winter NAO values) were associated with high squid abundance and precocious maturation and tended to favour high abundance in the following year, along with increased body weight at length and a decrease in the proportion of animals breeding in December. High abundance in summer, conversely, leads to a fall of body weight at length in the following year. Thus there may be alternation of precocious and slow maturation, and/or summer and winter breeding, driven by a combination of environmental conditions and intraspecific competition.

Short-term storage over several days as well as cryopreservation of turbot (Scophthalmus maximus) sperm were studied. Two extenders, Ringer 200 and artificial seminal liquid (ASL2), are suggested for semen collection in order to avoid the deleterious effect of urine contamination, and for the purpose of short-term storage between 0 and 15 °C. Oxygen atmosphere is not suitable for turbot sperm storage. Turbot spermatozoa undergo cryopreservation with a high rate of success especially in a sucrose solution with 10% dimethyl sulfoxide (DMSO) and 10% egg yolk.

The sea cucumber stocks off the east and northwest coasts of Sri Lanka were estimated bysurveying 1307 km2 and 1779 km2 by an underwater visual census (UVC)in June and October 2008 respectively. The presence of twenty-five sea cucumber speciesbelonging to seven genera; Actinopyga, Bohadschia, Holothuria, Pearsonothuria,Stichopus, Thelenota and Acaudina was identified in fivehundred sampling sites randomly selected in each area. The overall average density (± SD) of sea cucumbers was higher in the northwest (350 ± 648 ind ha-1) than inthe east (90 ± 130 ind ha-1) and low-value species were predominant in bothsurvey areas (79 ± 125 ind ha-1 in the east, 244 ± 488 in the northwest) whencompared with medium (10 ± 34 ind ha-1, 105 ± 175 ind ha-1,respectively) and high-value category (<2 ind ha-1).The estimated total biomass in the northwest (13 024 t) was roughly four times greaterthan the east (3027 t). Holothuria edulis was the most abundant speciesin numbers while Holothuria atra had the highest stock biomass in bothareas. Sea cucumber densities were significantly different among the habitat(p < 0.001) and depth categories. The highestdensity was reported in rocky habitat associated with seagrass and / or macroalgae. Thedensity of low-value species was significantly high in 1–10 m depth category(p < 0.001) in the northwest while othercommercial groups were dominant in 20–30 m depth range in both areas. Temporal banning ofthe fishery for high and medium-value species would be a better management option to avoidfurther stock depletion.

The phospholipid composition and fatty acid characteristics of diacyl and plasmalogen forms ofphosphatidylcholine and phosphatidylethanolamine of sperm of five marine and five freshwater speciesof fish have been determined. There was considerable variation in composition within each group offish, which obscured any differences which are related to the osmotic environment. Since such factors as temperature, nutrition, etc. probably greatly influence the lipid composition, we failed to determine a relationship between osmolality and phospholipid composition. We have also found certain phospho-lipid peculiarities, characteristic of sperm of various species of fish.Nevertheless, as we have found previously, the molar ratio of cholesterol to phospholipids in fishsperm is determined by the salinity of the habitat.

The early debate concerning the existence of several self-sustaining populations within the distributional limits of marine species centered on Atlantic herring in the northeastern Atlantic. Fr. Heincke convincingly resolved the controversy by extensive sampling of herring and sprat for the analysis of a large number of meristic and morphometric characters, and the development of new statistical methodology (including rudimentary multivariate statistics). He initially analysed the morphological variability at different parts of the life cycle of spring – and autumn – spawning herring aggregations off Kiel. This detailed study was accompanied by somewhat less-detailed sampling of herring and sprat from other locations in the Baltic Sea, North Sea, and Norwegian coastal waters. Heincke argued that a fundamental shift in both the species concept and the mechanism of speciation was required to account for the emerging empirical observations on marine fish. His observations and conclusions on the nature of geographic variability of fish species, even though revolutionary, were accepted rapidly. The influence of his studies on fisheries research, systematics, and evolutionary biology are evaluated. In addition, the contributions of J. Schmidt and J. Hjort to population thinking are briefly addressed. It is concluded that the studies by Heincke on herring populations, as well as having a major impact on subsequent developments in fisheries biology and management (in essence the definition of management units based on geographic populations or population complexes), also had an important impact on the biometricians (Weldon, Pearson) and the development of the evolutionary synthesis in the 1920s and 1930s (through Chetverikov, Dobzhansky, and Goldschmidt). Observations on geographic patterns in populations from terrestrial systems could be generalized to the oceans on the basis of Heincke's quantitative studies on herring and sprat (and the follow-up work on other fish species).

These early investigations on the very existence of marine populations by Heincke, Hjort and Schmidt are still pertinent to recruitment research and the studies underlying the definition of management units. An historical perspective may contribute to the resolution of present topical issues involving the regulation of populations.

The paper summarizes aspects of nutrition and growth in Clarias species. Of the many Clarias species cultured, Clarias gariepinus has been subject to particularly intensive research; the species has been widely introduced for aquaculture outside its natural range. Clarias are omnivorous fish. Their dietary protein requirements are about 40%, their energy requirements range between 13 and 17 kJ.g−1. Controversy exists on their ability to utilize carbohydrates, despite the fact that their natural feed may contain high levels of carbohydrates. Comparison of growth performances as recorded in literature indicate that C. gariepinus seems to perform better in terms of growth rates and feed conversion than other species (C. isheriensis, C. batrachus, C. fuscus). Monosex culture (in C. gariepinus) or triploidy (in C. gariepinus and C. batrachus) do not seem to hold much future for improving growth and feed utilization, in contrast to hybridization. Selection for improved growth could have drawbacks, such as an increased level of agression. To achieve improved growth, selection for lower maintenance requirements or better glucose metabolization seems preferable over selection for high feed utilization efficiencies.

This work presents a method to observe pelagic fish around drifting fish aggregating devices (DFADs). A triple-frequency vertical echosounder was employed to observe fish distributions in the vicinity of DFADs. Surveys were conducted in a star pattern that was centred at the DFADs. The objective of the study was to define a methodology for future acoustic studies. This goal was pursued by (i) studying the spatial distribution of fish aggregations, (ii) developing concepts for the grouping of observed aggregations and (iii) developing specifications for future autonomous acoustic tools. For this purpose 5 cruises were carried out in the western Indian Ocean. The multi-frequency approach proved useful as a means of separating acoustic detections into sound-scattering layers (e.g. plankton and micronekton), fish aggregations and individual fish. Fish target strength (TS) was measured. Four types of aggregations were found near DFADs: (i) dense structure (ii) medium structure (iii) loose structure and (iv) structure consisting of separated targets. More than 90% of these structures were found within a radius of 400 m and about 75% within 200 m of the DFADs. The spatial configuration of DFAD fish aggregations appeared to be more dynamic compared to aggregations near moored FADs. The spatial distribution and structure of DFAD aggregations have direct implications for their catchability by tuna purse-seiner. We have carried out the first quantitative acoustic recordings around DFADs, and obtained a better understanding of the spatiotemporal dynamics of fish aggregations around DFADs in the Indian Ocean. Based on this knowledge we are now working on specifications for instrumented buoys that are intended as autonomous data recording observatories for such pelagic environments.

The reproductive dynamics of swordfish (Xiphias gladius) was investigated from catches of the Reunion Island-based longline swordfish fishery between 19–25 °S and 48–54 °E. Thus, 1727 swordfish (size range 75–289 cm, lower jaw-to-fork length, LJFL) were sampled on board commercial fishing vessels during the period of May 1998 to January 2001. Reproductive activity was assessed using macroscopic gonad characteristics, trends of gonadal indexes for both sexes, oocyte size-frequency distributions and microscopic investigation of oocyte development stages. Size at first maturity (L50) for female and male swordfish was estimated in Indian Ocean for the first time. L50 was estimated at 170 cm and 120 cm (LJFL) for females and males, respectively. Spawning occurred from October to April in the vicinity of Reunion Island where sex ratio of caught populations fluctuated seasonally. The seasonal changes in sex ratio and the incidence of larger individuals at the beginning of the spawning season provide some preliminary indications of synchronized movements of swordfish between spawning grounds and neighboring regions. Our results add significantly to knowledge about the reproductive biology of swordfish in the southwestern Indian Ocean. An overview of the available information on reproductive biology and dynamics of swordfish in Indian Ocean and eastern Pacific indicated that spawning activity is localized in discrete areas, and showed that there is incomplete information on spawning grounds in this extended area.

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.

In aquaculture, a diet both nutritionally sound and organoleptically pleasing is essential to guarantee satisfactory intake. This has not been fully achieved with soleids (Solea solea and Solea senegalensis) because of their special palatability requirements, which are difficult to satisfy with conventional diets. Nevertheless, soleids have long been considered interesting species for aquaculture. To improve the palatability of diets for this family, various substances have been tried. Betaine has been the most effective substance by far, for all the species studied and especially for sole, reporting good results but at too high a cost. In other areas of animal production, the problems of palatability are solved with commercial flavours, which offer scope for specialisation to satisfy the most demanding organoleptic requirements. The aim of the present work is to evaluate the use of a bivalve commercial flavour as an alternative to betaine in sole diets. An ethological methodology, adapted to the feeding behaviour of sole, is developed to qualify and quantify behavioural changes when faced with experimental diets containing either this commercial flavour or betaine. Results show that the commercial flavour externally applied to feed particles performs efficiently as an attractant and as an arrestant, being able to attract the animal to the food source from some distance, provoke the ceasing of locomotion close to the food particle and promote initiation of feeding. In this step of the feeding sequence, it may be considered a viable alternative to betaine from the organoleptic point of view and economic cost. When the commercial flavour is applied internally to the feed, its performance as a stimulant, to encourage the continuation of feeding, is not distinguishable from betaine. Other factors such as time of feeding and size of fish, also assessed in the experiment, boldly influenced the level of acceptation of diets, even more than the composition of the diet itself. The distribution of feed at a time out of the endogenous rhythm of the species provoked a lower feed acceptation. Slight differences in the size of fish also affected the degree of acceptation, this being lower in the smaller fish.

Le cycle sexuel de Cerastoderma edule a été étudié durant l'année 1987 sur plusieurs sites le long du littoral atlantique français, de la baie de Somme au bassin d'Areachon. Cette étude vise à définir les modalités de la ponte et les facteurs qui la régissent, afin d'identifier à ce niveau, les causes de la variabilité du recrutement. Dans ce but, une méthode commune est mise en œuvre. Elle repose essentiellement sur la reconnaissance des stades de maturité sexuelle et sur les fluctuations de l'indice de condition. Les pontes peuvent être : précoce, printanière, estivale ou tardive, et, selon leur nombre et leur importance, variables selon les sites. La première ponte apparaît toujours en réponse au stimulus thermique qui correspond, au printemps, à l'amélioration des conditions climatiques et trophiques. A l'intérieur de l'espace latitudinal défini, il n'apparaît pas de net gradient au niveau des pontes, ce qui démontre que celles-ci ne sont pas déclenchées par une valeur définie de la température. L'efficacité de la ponte printanière est liée à une valeur seuil de l'indice de condition. Le nombre et l'intensité des pontes estivales et automnales sont fonction de l'importance de la ponte printanière. Il en résulte une forte variabilité dans les conditions de recrutement. Dans l'optique recherchée, certains principes prédictifs peuvent cependant être avancés.

Data concerning the planktonic food web and the farmed pearl oysters of the lagoon of Takapoto Atoll were assembled into a steady state model of carbon flows. A method of optimisation, using constraints from the literature, called ‘inverse analysis’ was chosen as the numerical tool for estimating the missing flow values. The resulting food web is characterised by: 1) high primary production, achieved by low phytoplankton biomass, 2) high production of non-living matter, especially as dissolved organic carbon, 3) low bacterial production, 4) zooplankton dominated by protozoa (biomass and processes) and mesozooplankton (processes), and 5) very low consumption of plankton by farmed bivalves compared to planktonic fluxes. When considering the whole lagoon, the farmed oysters (Pinctada margaritifera) and associated bivalves (Pinctada maculata) consume 0.24% of the planktonic gross primary production. In addition, the consumption by natural populations of the main benthic bivalves in this lagoon (Chama iostoma, Arca ventricosa, Pinctada margaritifera and Pinctada maculata) is also low compared to the high planktonic primary production (4.1%). The oyster farming in this lagoon is thus very far from being food-limited.

The first successful case of transgenic fish was achieved in 1984. It is in a model system that the integration and expression of recombinant human growth hormone (hGH) in host red common carp (Cyprinus carpio, red var.) have been thoroughly studied. Recently, the integration sites have been recovered and characterized. Compared with non-transgenic peers, hGH-transgenic fish are prior in dietary utilization and growth performance. In view of bio-safety and bio-ethics, an "all-fish" construct CAgcGH, grass carp growth hormone fused with common carp β-actin promoter, has been generated and transferred into Yellow River carp (C. carpio, local strain in Yellow River) fertilized eggs. Under middle-scale trial, CAgcGH-transgenics show higher growth rate and food conversion efficiency than the controls, which is consistent to laboratory findings. To avoid the potential impact of transgenic fish on the environment, a sterile strain of transgenic triploid fish has been successfully produced. The "all-fish" transgenic common carp is also approved safe enough as daily food, according to a test based on the pathological principles of new medicines issued by the Ministry of Health of China. The "all-fish" transgenic common carp with growth enhancement is now ready for market, but looking for governmental authorization.

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.

This work focuses on investigating the potential of calcein and manganese as growthmarkers of the common cockle (Cerastoderma edule) in the bay of Somme(France). Recapture of shells, previously marked using a chemical marking and then bred innatural conditions, was performed in order to determine the shell growth patterns. Calceinmarking has shown a fluorescent increment in shells after only 30 min immersion time at150 mg L-1, but also for shells immersed 3 h at 50 mg L-1. Likewise,manganese shell marking was revealed under cathodoluminescence for shells immersed 1 h at120 mg L-1 as well as for shells which spent 4 h at 90 mg L-1. Anumerical analysis performed on each marked cockles has revealed 23 micro-incrementsbetween the mark and the ventral edge of the valves, corresponding to the 23 tides thatoccurred during the 12 days at liberty post marking. The periodicity of incrementformation is thus validated for a tidal frequency. The growth rates of C.edule, ranged from 11.67 to 19.94 μm d-1, decreasedsignificantly with increasing shell length. This preliminary study gives a clue to theunderstanding of cockle growth and could be used in shellfish production for cockle agemonitoring, but also for chemical analysis to learn more about biomineralization processof this species.

To study the behavior of dolphinfish (Coryphaena hippurus) around drifting Fish Aggregating Devices (FADs), we tagged individuals with long-lived, coded sonic transmitters and attached automated sonic receivers to drifting FADs in two regions of the Western Indian Ocean. Among the three tagging methods used in this study (surgery, external hooks, underwater bait without capture), the latest resulted in residence times significantly shorter than the other ones, likely due to regurgitation. Dolphinfish tagged with the two other methods usually stayed several days associated to FADs (Kaplan-Meier survival analysis 5.09 days, mean 6.25 days, SD 4.39 days, maximum 15.26 days), drifting with them. There was no significant difference in the residence times of dolphinfish in equatorial and tropical areas. While associated to FADs, dolphinfish spent most of their time close to floating object (<365 m). The total time spent away from FADs was low (median 8%), and likely corresponded to making feeding excursions. Dolphinfish did not form a single school while associated to a given FADs, but formed multiple small schools. FADs are likely to be sites with exchanges of individuals between schools. These results are discussed in regards to the possibility of FADs acting as ecological traps and the validity of meeting-point hypotheses as an explanation for fish aggregations under floating objects.

Age and growth of four tropical marine fish species: Lethrinus choerorynchus, Lutjanus kasmira, Nemipterus furcosus and Scomberomorus brasiliensis, were determined by means of otolith interpretation and length-frequency analysis. The results showed the presence of annual rings in the studied species. These rings were consistently interpreted and their annual periodicity tested by means of various methods. The annuli are composed of distinct daily increments, of different thickness depending of the otolith area. Growth determination by means of length-frequency analysis was problematic in some species due to the lack of clear modal classes (in the length distributions). The joint analysis of the age and the length-frequency data improved the estimation of growth parameters, and allowed the selection of results that were biologically acceptable.

L'étude de la croissance linéaire, rapportée au modèle particulier de von Bertalanffy, de l'espèce Epinephelus guaza échantillonnée dans le canal sicilo-tunisien donne : L∞ = 114,49 cm ; K = 0,0928 ; t0 = -0,7508 an, et la relation entre la taille et le poids : Log Wi = 3,073 Log Li - 4,377. Le taux de croissance présente un infléchissement significatif à l'âge de 5 ans qui traduit une réorientation de l'allocation énergétique du métabolisme vers une activité gonadique ovogénétique (maturité sexuelle). Ce poisson hermaphrodite protérogyne manifeste ensuite, à l'échelle de la population, une inversion sexuelle qui se produit entre 9 et 16 ans avec un maximum d'intensité à 12 ans. A partir de cette période d'inversion, la dispersion des tailles corporelles à l'intérieur de chaque classe d'âge s'amplifieau point qu'il devient probablement illusoire d'utiliser les paramètres de croissance comme critères d'identification des unités de population. Des critères issus de l'étude du développement sexuel et replacés dans des analyses démographiques qualitatives et quantitatives menées conjointement pourraient se révéler plus performants.