The hydroacoustic estimation of fish abundance and distribution in the Solina reservoir was related to other biological and hydrological parameters. The increase of fish abundance corresponded to increased levels of eutrophication expressed by Secchi-disc visibility and chlorophyll a concentration. A negative correlation between fish and zooplankton abundances was observed, with changes in the zooplankton population structure, caused by fish grazing. Vertical distribution of zooplankton and fish were affected by the thermocline. Maximal concentrations were observed in a well-illuminated surface layer at the highest temperature and oxygen concentration.

Heritability of larval growth rate in diferent food environments and genotype-food environment interaction (during larval growth) are estimated in Mytilus chilensis, based on a nested design, involving 24 full-sib families (8 males each mated to 3 separated females) grown under three different algal concentrations. The heritability estimates for larval shell length ranged between 0.2 ± 0.1 and 0.9 ± 0.3 and showed a decreased towards the low food treatment; but the values suggest that selection would be effective. However, since there is a significant genotype-food interaction, selection should be done in each environment in which the animals are expected to perform. The significant interaction term (p<0.001) associated with a significant genetic variability for larval growth suggest the presence of genes in the population whose expression depends upon local food conditions.

Acoustic surveys of aquatic organisms are notorious for large data sets. Density distribution results from these surveys are traditionally graphed as two-dimensional plots. Increasing information content through wider acoustic frequency ranges or multiple angular perspectives has increased the amount and complexity of acoustic data. As humans are visually oriented, our ability to assimilate and understand information is limited until it is displayed. Computer visualization has extended acoustic data presentation beyond two dimensions but an ongoing challenge is to coherently summarize complex data. Our goal is to develop visualizations that portray frequency- and behavior-dependent backscatter of individual fish within aggregations. Incorporating individual fish behavior illustrates group dynamics and provides insight on the resulting acoustic backscatter. Object-oriented applications are used to visualize fish bodies and swimbladders, predicted Kirchhoff-ray mode (KRM) backscatter amplitudes, and fish swimming trajectories in three spatial dimensions over time. Through the visualization of empirical and simulated data, our goal is to understand how fish anatomy and behavior influence acoustic backscatter and to incorporate this information in acoustic data analyses.

Quantifying of sediment reworking processes provides new insights into benthic ecosystem functioning of the Thau lagoon, an important European shellfish farming area. In order to evaluate bioturbation rates of surface sediments, profiles of 7Be (half-life: 53 days) and 234Th (half-life: 24.1 days) were measured in cores collected since December 2001 to December 2006. Several sites were selected to sample the diversity of the Thau lagoon: C4, T10, and T11 in the middle of the lagoon, C5, T7 and T8 nearby oyster farming, T2 and T4 in the western edge, T12 in the eastern part closed to industry. 234Th in excess (234Thxs ; i.e. supplied to sediment by settling particles) and 7Be both show seasonal variations in activities and in penetration within sediment. Taking into account the moderate sedimentation rates of the Thau lagoon, sites (0.1–0.4 cm per year), the penetration of both short-lived radionuclides to variable depths, from 1 up to 8 cm, indicates efficient biological mixing of upper sediments. Bioturbation rates (D b) to the distribution of excess 234Th (234Pb-D b) and of 7Be (7Be-D b) range between 1 and 35 cm2 y−1, depending on site and season. Surface sediment mixing of the Thau lagoon is primarily controlled by the quality of particle input, i.e. the food supply to the benthic fauna, mainly governed by the hydrological and seasonal conditions. But locally shellfish production is a key parameter that influences bioturbation through biodeposition.

It is estimated that fish aggregating devices (FADs) are now used for over 40% of world tropical tuna catches, making this technique a major phenomenon for high seas fisheries worldwide, and one that has experienced great expansion over the past three decades. The question of whether the FAD is a good or a bad tool for the exploitation of marine resources depends on many parameters. To respond to this question, it is necessary to distinguish different scales of exploitation (artisanal vs. industrial) and various types of FADs (anchored vs. drifting), but it is also very important to gather more data and conduct further research on this topic to gain a better understanding of the phenomenon and of its impacts. As such, twelve years after the first international conference devoted to FADs, which was held in Martinique (French West Indies), a new multi-scalar global assessment of FAD fisheries development and a review of the progress of research in this field was deemed vital. The latest international conference, “Tuna Fisheries and Fish Aggregating Devices”, was held in Tahiti in November 2011, and it was an event that welcomed nearly 150 conference attendees from 40 different countries, three ocean regions, and the Mediterranean. This is an analysis of the relevant literature gathered by the author in the bibliographic database FADBASE. Then, the major issues already addressed by the scientific community are set out, and gaps and research priorities are highlighted for anchored and drifting FADs management.

La fécondité par acte de ponte du listao Katsuwonus pelamis de l'ouest de l'océan Indien a été étudiée à partir de 281 femelles dont les tailles (longueur à la fourche) sont comprises entre 43 et 73 cm et dont les ovaires étaient à un stade de maturité sexuelle avancé. Le liquide de Gilson, utilisé comme agent conservateur et dissociateur des ovocytes, a une action importante et rapide (5 jours) sur le rétrécissement des ovocytes. Des comptages effectués à l'aide d'une cuve de Dollfus sur des sous-échantillons d'ovocytes dissociés, montrent que pour une même période d'activité sexuelle (février), la fécondité du listao du canal de Mozambique est semblable à celle des listaos du sud du plateau des Seychelles. Bien qu'une activité sexuelle du listao soit notée tout au long de l'année, la fécondité individuelle varie d'une saison à l'autre et ce, pour un même secteur géographique. Cette fécondité individuelle par acte de ponte varie de 80 000 œufs pour des femelles de 44 cm provenant de la côte nord-ouest de Madagascar à 1,25 millions d'œufs pour des femelles de 75 cm pêchées autour des Seychelles. La fécondité relative correspondante évolue donc entre 40 et 130 œufs/g de poids de corps. Pour cette espèce, le nombre de pontes successives a été estimé à 4 par an.

Bioassays were carried out with the ‘blue diatom' Haslea ostrearia Simonsen, which is responsible for oyster greening during the fattening period of Crassostrea gigas Thunberg in oyster ponds. Samples of seawater were taken from two oyster ponds: one without oysters and the other with 20 oysters per m[sup2 ], maximal density allowed by the French AFNOR norm for ‘refinement'. The aims were to clarify the nutrient requirements of this diatom, also to elucidate the eventual influence of C. gigas at this density on the seawater fertility and to envisage the mass production of this diatom by pond fertilization. Examination of cell numeric densities at the end of bioassays allows us to conclude that silicate was the first limiting nutrient, closely followed by phosphate. Chlorophyll a concentrations led to different conclusions: phosphate was the first limiting factor, but after the seawater storage period in ponds, seawater quality evolved to a deficiency of nitrogen. Silicate addition increased cell division rate, and silicate depletion increased chl a synthesis for this species. Examination of nutrient assimilation ratios confirms that H. ostrearia requires a large amount of silicon. From these results, it was possible to prepare a N + P + Si simplified medium which has been tested in laboratory and field mesocosm conditions. In both conditions, similar results were observed: a significant increase in H. ostrearia cell concentrations and consequently an evolution up to the greening stage. Applications of this work are numerous; the principal permits us to envisage the production of this species in 25-m3 ponds, with the aim of allowing constant production of the greening phenomenon.

While the pineal organ in poikilothermic vertebrates consistently influences a number of physiological processes, its precise role, and what controlling signal (hormonal and/or neural) is abolished by its removal, is still uncertain. For this reason, the effect of long-term pinealectomy (PINX) on seasonal growth and reproductive development was investigated in Atlantic salmon, Salmo salar, parr. Mean daytime plasma melatonin level in the control, sham-operated and PINX fish was 35 pg·mL–1 in all groups, while mean night-time levels were 296, 255 and 25 pg·mL–1, respectively, indicating that PINX abolished the natural nocturnal rise in melatonin. Pinealectomy did not influence the incidence or timing of early sexual maturation in the male parr. However, pinealectomy significantly affected growth, its effect being boldly seasonally dependent. Compared to sham-operated and control fish, pinealectomized fish showed significantly lower specific growth rates (SGRs) during the period of lengthening photoperiod up until the summer solstice. Thereafter, corresponding to the season of decreasing photoperiods, the pinealectomized fish exhibited higher SGRs. These results suggest a functional relationship between the pineal organ and somatic growth in the Atlantic salmon, although what controlling signal from the pineal (melatonin or neural) is involved has yet to be determined.

We sampled 27 month-old mussel populations grown on collector ropes in Cascapédia Bay,Quebec, to test whether density-dependent growth was present concomitantly toself-thinning, a process which was previously shown to occur in this system and thought tobe driven by spatial constraints. Biomass-density curves of raw samples were curvilinear,suggesting density-dependent growth. However, at least two cohorts were present.Fractionating the samples on the basis of age yielded a linear relationship for the main,2 year-old cohort. This implies density-independent growth and rules out food regulationin these populations. Therefore, our results are consistent with inferences drawnpreviously from the values of the self-thinning exponent, that is, space-regulatedself-thinning. Our results suggest that curvilinearity of the raw biomass-density curvesresulted from a bias caused by including the 1 year-old cohort and spat of the year in theanalysis. This conclusion is supported by a model showing that samples with mixed cohortscan yield linear, concave or convex biomass-density curves without density-dependentgrowth. The shape of the curves depends on the scaling relationships between cohortabundances. It appears that the shape of biomass-density curves may be a usefulcomplementary criterion – in addition to the value of self-thinning exponents – for theidentification of food or space as factors regulating cultured populations.

The impact of the “Erika” oil spill on the tidal rock pool community, and particularly on two species of sea urchin (Paracentrotus lividus and Psammechinus miliaris), was investigated over a 3-year period, at Piriac-sur-Mer (Department of Loire-Atlantique, France, 47°21.6' N; 2°31.7' W). A dramatic increase in the abundance of two macroalgae Ulva sp. and Grateloupia doryphora occurred following a 100% mortality of sea urchins observed three weeks after the oil spill. The density of sea urchins and of other main herbivores, the periwinkle Littorina littorea and the trochid mollusks Gibbula umbilicalis and Gibbula pennantii, were monitored between January 2000 and March 2003. There was significant inverse relationship between the overall density of herbivores (sea urchins, periwinkles and trochid mollusks) and the percent cover of algae in the tidal pools. The first urchins in the tidal pools were observed two years after the oil spill and it took three years to reach sea urchin densities comparable to the reference value of 63 ind.m−2 obtained before the oil spill.

After the population increase of introduced Nile perch (Lates niloticus) in Lake Victoria, a decrease in the relative abundance of herbivorous cladocerans and calanoids was reported for the pelagic zone. The shift from large herbivores to small-bodied predatory cyclopoids has been attributed to the increase of the zooplanktivorous cyprinid dagaa (Rastrineobola argentea), which rose concomitantly with the Nile perch. However, we observed that in the Mwanza Gulf of the lake cyclopoids dominated the zooplankton community already before the rise of dagaa. Furthermore, there are indications that dagaa takes fewer calanoids than expected from their representation in the environment, although a slight preference for cladocerans may exist. Calanoids dominated the diet of small Nile perch of about 4 cm length, but juvenile Nile perch did not occur in the study area until after the size shift in zooplankton. The lumped biomass of dagaa and small Nile perch is lower than the biomass of the original haplochromine-dominated community of zooplanktivorous fish. Thus, the decline of large zooplankters in the lake cannot be explained by intensified predation after the replacement of zooplanktivorous haplochromines by dagaa and Nile perch. Increased eutrophication, resulting in a shift in predominance from diatoms to cyanophytes, is suggested as an alternative explanation for the shift in zooplankton composition.

The swimming path of a reared Pacific bluefin tuna, Thunnus orientalis, was measured in a submerged aquaculture net cage to understand how reared fish use the space in such a cage. A bluefin tuna (fork length, FL, 0.51 m) was captured by angling in the cage, and two micro data loggers (PD3GT, Little Leonardo; DST Comp-Tilt, Star-Oddi) were attached to its body. The fish was then released back into the net cage. The PD3GT measured its swimming speed and depth at 1-s intervals and recorded these in flash memory. The DST Comp-Tilt measured the magnetic field strength at 1-s intervals and recorded the heading estimated from the magnetic field strength in flash memory. The fish moved through the water in the cage at speeds of 0.7–0.8 m s-1 and attained a maximum speed of 3.6 m s-1. Burst swims exceeding 2 m s-1 were confirmed only after dark and a significant difference was found between the daytime and night-time swimming speeds (p < 0.001). The fish moved at depths between 2 and 22 m, swimming near the bottom during the day and at 10–15 m at night, with a significant difference in swimming depth between day and night (p < 0.001). The swimming path reconstructed by dead reckoning was visualised using night-time data. For this period, the absolute speed was corrected from 0.75  ±  0.09 m s-1 to 0.71  ±  0.15 m s-1 by removing the accumulated error from the reconstruction vector. This study allowed us to examine the behaviour of a tagged tuna in three dimensions and is the first to monitor the behaviour of a bluefin tuna in a submerged net cage. Although only one fish was analysed, this study provides useful information on the space use of reared fish in aquaculture net cages. Future studies must obtain sufficient data to understand the underlying generalities of tuna behaviour.

The effect of different parameters on short-term storage capacity of turbot ova was assessed over a 45-h period after ova collection for fertilization rates and over a 9-h period after ova collection for hatching rates. Increasing the volume of ova sampling from 0.5 to 2.5 mL, as well as adding an antibiotic-antimicotic solution or oxygen did not significantly change the storage capacity of ova. Regarding the hatching rates, a higher storage ability was recorded at 8 and 13 °C, compared to 3 °C. The mean composition of the ovarian fluid was determined (n = 57 spawns). Use of a diluent mimicking the ovarian fluid significantly decreased the storage ability as assessed by the fertilization rates but did not modify the hatching rates. Diluting ova in an artificial ovarian fluid deprived of calcium significantly decreased the fertilization and hatching rates during the storage period. Furthermore, addition or not of soybean trypsin inhibitor (Sigma T 9003) to the artificial ovarian fluid deprived of calcium did not significantly change the results. Storage capacity of control batches of ova was low: at 13 °C, without any diluent and when ova were fertilized 3 h after stripping, the hatching rate was lowered to 62.4 ± 29.4 % (mean ± SD) of the initial value.

This paper reviews a selection of nine indicators for assessing the biological state of a fish population monitored only by using trawl surveys in which catchability is assumed constant from time to time and place to place. The intention is to inform or remind of the range of possibilities and of associated practical and statistical issues. The indicators, grouped according to relationships with abundance, length, age, weight, and reproduction, are documented in a standard format covering estimation, interpretability, sensitivity, considerations for reference points where possible, and an example of their application. Lastly, selected indicators together with year-class curves fitted to abundance indices-at-age are applied to the North Sea cod to demonstrate the feasibility of an assessment based on only one trawl survey. Results support findings of the International Council for the Exploration of the Sea (ICES) working group on the assessment of demersal stocks in the North Sea and Skagerrak.

The western Mediterranean is an important fishing area in which the Spanish longline fleet operates. Longline fisheries affect several species of marine mammals, sea turtles, sharks and seabirds, all of which are especially sensitive to fishing mortality. Given international efforts to identify and reduce the bycatch of sensitive species, an onboard observer program was implemented by the Spanish Oceanographic Institute (IEO, Instituto Español de Oceanografía). The aim of the present study was to report data on marine mammal bycatch in the western Mediterranean. The additional aim was to improve knowledge about the possible effects of the Spanish longline fisheries on cetacean populations, particularly Risso’s dolphin, and to suggest improvements to fisheries management. Data on marine mammal bycatch were collected during the period 2000–2009. Differences are reported for catch per unit effort (CPUE, defined as marine mammals per 1000 hooks) for each type of gear (n = 7), as well as their effect on specific marine mammal species. A total of 5 398 297 hooks were monitored, which yielded 56 marine mammals belonging to 4 different species. Our results indicate that Risso’s dolphin is the species most affected by the longline fishery in the western Mediterranean (n = 33). We built a predictive model for Risso’s dolphin bycatch using variables associated with the technical characteristics of the fishery, geographic location and seasonality. We performed a binary logistic regression of the presence/absence of Risso’s dolphin bycatch to test whether the probability of incidentally catching one or more dolphins may be predicted by some of the explanatory variables selected. Our results indicate that Risso’s dolphin was mainly caught using Japanese longline (LLJAP) or an experimental home-based longline (LLHBexp) over the continental shelf. Because LLHBexp is an experimental type of gear that was only used occasionally by the fleet, controlling the use of LLJAP over the continental shelf could strongly reduce the impact of these fisheries on populations of Risso’s dolphin in the western Mediterranean.

Onchocerciasis is a widespread disease in intertropical Africa, which, ultimately, causes irreversible blindness. The disease is transmitted by a small blackfly, Simulium damnosum (Diptera), which has aquatic larval and pupal stages. The breeding sites of the blackflies are riffles. These river reaches are the targets of the control campaign of the Onchocerciasis Control Programme in West Africa (OCP). An aquatic monitoring network covering the totality of the area exposed to the insecticide was set up to evaluate environmental impact. In this paper, we present results from the OCP 20-year period of monitoring of the ichthyofauna regularly exposed to larvicides. We do not record any measurable effects of pesticides on the CPUE, abundance of species, trophic structure, community structure or fish health. However, we detect the emergence of a number of medium-term tendencies. These tendencies may relate to climatic conditions that have a consequent effect on hydrology. Thus, we note a constant decrease in the CPUE from the beginning of the monitoring until 1995. The rivers were treated during that time until 1990 or 1993, depending on the station. But even after the treatments ended, the number of catches continued to decrease. As a result, we consider other factors to be the cause of that decline. The average level of annual discharges in this region has been decreasing regularly from the beginning of the 1970s. The production of fish fluctuates in all the rivers according to the flood rate. Important floods inundate larger areas, making greater quantities of food available, and thus improving the conditions for reproduction. The determining factor of the ichthyological stock abundance seems to depend both on the extent and the duration of the flood. In our catches, the observed effect was not immediately evident but appeared a few years later as a cumulative effect of poor hydrological conditions. An increase in the CPUE since 1996 has been related to improved hydrological conditions. In these last few years, we have observed an intensification of the basic flow leading to a ground water renewal. Furthermore, on three of the stations investigated, it appeared that the impediment of rivers (dams) could induce different and/or antagonistic effects. In some cases, we have observed that in spite of unfavourable hydrological conditions, certain species appear to be favoured by the presence of the dam. But, the damming of the river has a negative effect on other species, particularly on the coefficient of condition of migratory fishes. The impact of these factors is enhanced by the fact they exist conjointly.

At the onset of sexual maturation, European eels Anguilla anguilla exhibit high locomotor activity which may correspond to migratory restlessness. We measured activity of captive eels and determined whether it correlated with downstream runs of silver eels as well as changes in environmental factors. Groups of eels at different stages of the silvering process (yellow to silver stage) were tagged and placed in separate tanks supplied with either river or tap water. Activity was measured by means of a flat-board antenna placed vertically in the middle of the tank at the surface of the water. Wild migrating silver eels were caught in the nearby river. Activity of eels in the river water tanks increased 1 to 2 days before downstream migrating eels were caught in the trap, and concurrently with a rise in turbidity and a decrease in conductivity. Activity of eels in the tap water tank showed a different pattern, which did not correspond to downstream runs. A peak in activity corresponded to a drop in tap water pH. It is concluded that eels do show periods of high locomotor activity at the onset of migration and this could be used to predict downstream migration. Movements are triggered by changes in water composition (as opposed to changes in discharge, atmospheric pressure and lunar cycle) measured using turbidity and/or conductivity as proxies. If eels are able to detect such small changes in water conductivity (80 µS cm−1), they may use it to find their way to the estuary.

Intense local fishing pressure is likely to induce significant local decreases in both resource biomass and fishing yields. This is what we term ‘local overfishing’. Such a phenomenon and its consequences for stock assessment are investigated with the fisheries simulator SHADYS (Simulateur halieutique de dynamiques spatiales: spatialized simulator of fisheries dynamics). In SHADYS, resource dynamic is based on an advection–diffusion–reaction equation. After a brief presentation, the simulator is used to characterize the ‘local overfishing’ phenomenon as a ‘wound’ of the population. The latter is subsequently able to ‘heal’ and to recover its initial distribution. We show that, associated with cooperation tactics of the fishing fleets, local overfishing may induce non-linear relationships between catches per unit of effort (CPUE) and fishing effort calculated locally. In particular, it is shown that there is a strictly decreasing relationship between catchability and effort when fishing vessels apply intense local fishing pressure but do not cooperate; that the relationship may increase when vessels cooperate but do not apply intense local fishing pressures; and finally, that it may go through a maximum when, simultaneously, ships cooperate and have high local exploitation rates. These three main types of theoretical relationships correspond well with those observed in reality. The existence of such relationships could be an important source of biases in stock assessment.

The cladocerans Moina micrura and Diaphanosoma excisum and the copepod Thermocyclops decipiens were studied in microcosms (0.8 m3) under semi-controlled experimental conditions at 25–29 °C for 32 days, by daily sampling after an initial monospecific inoculation. For each species, the time series began with an exponential population growth phase. M. micrura showed a higher daily population growth rate (mean = 1.19) than D. excisum (0.78) and T. decipiens (0.45). The growth phase of M. micrura coincided with bacterial and phytoplanktonic peaks while the growth phase of the two other species followed these peaks. After this phase, M. micrura quickly disappeared (day 10), while D. excisum biomass decreased but showed a second increase, followed by a stabilization sequence. T. decipiens biomass had a slower increase and stabilized after day 17. The passage to sexual reproduction in relation to crowding was the main regulating factor for M. micrura, whereas food limitation was important for D. excisum. For T. decipiens, population growth was limited by decreased recruitment to copepodite stages which could have resulted from cannibalism exerted by older stages.