When measuring the flux of migrating salmon in rivers there are often multiple fish in the beam simultaneously. To obtain accurate measurements of flux, an understanding of the effects of multiple targets is required. Multiple targets in various configurations were passed through a horizontally-oriented 4° × 10° beam from a split-beam echo sounder. The effects on target strength, detection probability, spatial and temporal patterns of echoes, and measurement of target position are presented. When multiple targets were in the beam at the same range, the target strength was positively biased, whereas, when they were in-line at different ranges, the target strength and detection probability were negatively biased for the shadowed targets. Targets at the same range, but separated in the vertical or horizontal direction, produced characteristic patterns in the X vs. ping and Y vs. X plots. Similar patterns were found in routine observations of migrating salmon, allowing the identification of some multiple-target events. Identification of these events can aid in the correct interpretation of migrating fish data for flux measurement.

Marine populations are distributed heterogeneously in space and time because of the diversity of habitats and the requirements of species life cycles. Human exploitation of these resources also varies as a function of space, time and the type of fishing activities performed. These three factors determine fishing strategy at different levels of integration. The purpose of this study was to describe and analyse, with respect to different time scales, the relations between the modalities of resource exploitation and the biological or demographic characteristics of the species involved. These investigations relate to the more general task of acquiring the basic knowledge needed for spatialised management of fishing effort. A fleet of trawlers from La Rochelle, operating in the Bay of Biscay, was studied over a 15-year period (1979–1993), which led to the development of a reference resource exploitation scheme for these vessels. The degree of stability of this scheme over time was determined from landing profiles of the 18 most important species fished (94% of landings). An annual cycle for the species composition of landings was determined by multiple factor analysis. Two factors account for more than 55% of the inertia of the data. The first, of biological origin, is closely related to the breeding activity of species and associated migrations between the coast and the open sea. The second is spatial in nature, corresponding to the distribution and availability of resources according to a bathymetric gradient. This organisational scheme persisted over the first 13 years, but showed signs of change toward the end of the study period. Analysis of multi-year trends indicated four periods marked by sustained levels of landings per unit of effort for some species (decreasing for sole and wedge sole, or increasing for Norway lobster, striped red mullet, rays and the smallspotted catshark). These changes are attributable to restrictions on resource access imposed on the fleet (regulations and/or competition among the fishing gears for occupation of space), variations in the abundance of traditionally fished populations (hake, anglerfish) and changes in the professional behaviour of fishermen.

The catch from bottom longline stations sampled from a series of research cruises around Lanzarote and Fuerteventura (Canary Islands, NE Atlantic) was analysed in terms of fish distribution, density and diversity. The distribution of the number of species and individuals caught per station appeared to fit well the Poisson and Exponential distribution function, respectively. In particular, the parameter of the Poisson’s distribution appeared to provide an index of the point (at station scale) diversity, and its confidence interval, allowing for statistical comparisons. The relationships between point diversity, the alpha diversity (in the depth strata) and the beta diversity (along the depth gradient) were investigated. Around the islands, the density and the point diversity of the predator fish declined with depth down to about 800 m and then increased in the deeper stratum. The alpha diversity was the lowest in the deeper stratum but the taxonomic distinctness was similar to that of shallower strata. The beta diversity showed some faunal breaks along the depth gradient. The carnivorous fish fauna can be understood as comprised of three major assemblages: shelf, upper slope and mid-slope that are different both in terms of species composition and point, alpha and beta diversities. The relevance of this simple method for ecological studies of fish assemblage in the context of non-trawlable grounds is discussed, in particular for the slope and other areas of established or developing deep-water fisheries.

The scope of this study is to investigate the extent to which area-based management may have influenced the fishing efficiency of the Danish and Dutch demersal fleets harvesting cod, plaice and sole in the North Sea. Special consideration is given to the ‘plaice box’, a restricted area where fishing is prohibited to towed-gear fleets of horsepower exceeding 300 hp. An index of fishing power is calculated as the log-ratio between the catch per unit effort (CPUE) of any vessel and some survey abundance index. Annual trends in fishing are calculated as the year-effect derived from a general linear model (GLM) analysis of the index of fishing power. The fishing efficiency of Danish gill-netters and, to some extent, Danish seiners, has overall increased inside the ‘plaice box’, whilst remaining relatively stable outside. However, the fishing efficiency of the other exemption fleets has apparently been subject to little change. Overall, it is not possible to determine the extent to which the ‘plaice box’ has contributed to the fishing efficiency dynamics of the exemption fleets. However, some of the results of this study bear out the conclusions from recent investigations.

Observers were placed on pelagic vessels in the Scottish fisheries for mackerel (Scomber scombrus), herring (Clupea harengus), "maatje" herring (herring caught just before their first spawning) and argentines (Argentina silus) to monitor by-catch composition and discarding practices. A total of 67 days was spent at sea, 11 on the argentine fleet, 28 on the herring fleet, 12 on the "maatje" herring fleet and 16 on the mackerel fleet. The level of by-catch generally ranged from <1% to around 2.5% of the total catch. The argentine fishery took a significant proportion of blue whiting (Micromesistius poutassou) (approx. 10% of the overall catch) but this was landed and sold in the market. The greatest range of by-catch species was found in the argentine fishery, including 11 species of fish and one species of squid. Discarding rates in the fisheries varied, with herring and argentine fisheries showing no discards, the mackerel fishery a discard rate of around 4% and the "maatje" herring fishery a discard rate of around 11%. By-catches included small numbers of gannets (Morus bassanus) but no marine mammals. If the sampled trips were representative, results indicate that marine mammal by-catch events typically occur during less than one in 20 hauls in the fisheries studied. A larger scale study is needed to confirm this. Cetaceans were sighted in the vicinity of the fishing boats during 4% of observed fishing activities.

Two methods for estimating bycatch-to-shrimp ratios were tested using Monte Carlo simulations. The Ratio Averager first calculates the ratio of bycatch to shrimp for each element of the sample and then averages all the entire sample. This method overestimated the ratio with a maximum bias as high as 4.5 times. In contrast, the Ratio Estimator or Ratio Estimation as termed in some literature first averages the sample catch rate of bycatch and shrimp and then calculates the ratio of the two averages. The Ratio Estimator performed quite well under all scenarios evaluated in this study, with a bias range from –1.7% to 2.8%. The reliability of the Ratio Estimator was also higher than the Ratio Averager, particularly when both bycatch and shrimp had high variability. Two sets of fishery survey data were used to demonstrate the difference in ratio estimates between the two methods.

Although there are numerous published accounts of studies utilizing heart rate (fH) transmitters in fish, few of these studies provide sufficient detail to aid other researchers in deploying these devices. Here, we detail the attachment, validation, and preliminary deployment of a commercially available ultrasonic fH transmitter. We used largemouth bass, Micropterus salmoides, for this study because they principally modulate cardiac output using fH, making them logical candidates for this technology. Using an external harness that balanced the battery on one side of the dorsum, and the transmitter on the other, we attached the device to 13 fish. Electrodes were positioned ventral-laterally to the pericardial cavity. Doppler flow probes were used to validate that the transmitter was detecting and emitting a signal when triggered by the depolarization of the ventricle (QRS wave), as indicated by peaks in blood flow. We then deployed the fH transmitters for periods of up to 32 days, generating one of the most complete series of fH data available. We present preliminary data illustrating the information available from fH transmitters at different temporal resolutions (real time vs. hourly means), including relationship of fH to temperature, behavioral correlates of fH, and diel patterns of fH.

An analysis of 273 samples taken at the filter screens of an estuarine power plant cooling water intake showed that herring and sprat were boldly associated with each other and formed mixed species schools. Herring-dominated schools were typically larger, more frequent and contained larger-sized individuals than schools dominated by sprat. The mean body length of both herring and sprat was biased as a function of their relative importance in the school suggesting that the fish schools were assorted by size. However, switching to a fish school dominated by the other species increased the individual body length variation relative to the group average. Diets of both species overlapped boldly but the feeding rate of sprat was significantly lower than that of herring. Our results suggest that during estuarine residency young sprat suffer the consequences of the school trap, possibly to profit from reduced predation risks in herring schools.

We analysed spatial and temporal patterns of condition factor (CF) of sprat (Sprattus sprattus) between 1986 and 2000 in different areas of the Baltic proper. Results showed a moderate increase in CF between 1986 and 1989. Afterwards, an abrupt decrease in CF, between 22% and 29%, occurred in all the areas of the Baltic proper. However, from 1998 and onwards, CF increased compared to the previous years. Weight-at-age and CF of Baltic herring showed a similar pattern in the same period. Several factors affecting variability of sprat CF were evaluated. Data showed that sprat CF was density-dependent and possibly related to the pelagic fish abundance and individual food intake. Temperature did not influence sprat CF while salinity seemed to affect variability of sprat CF in the northern Baltic proper. Changes in salinity levels may shape pelagic fish growth rates both indirectly changing the zooplankton community structure and abundance and/or directly via fish physiology and metabolisms.

The recruitment of Strangomera bentincki (common sardine) and Engraulis ringens (anchovy) and the relationships with oceanographic conditions in the upwelling ecosystem of central-south Chile were investigated from 1990 to 1998, with emphasis on the 1997–1998 El Niño. Time series of recruitment, biomass, local sea surface temperature, and a coastal upwelling index were used to explore relationships during the spawning (July–August) and pre-recruitment (August–December) periods. The 1997–1998 El Niño caused physical changes in the small pelagic fish habitat off central-south Chile. Anomalous sea surface temperatures (SST) and upwelling indexes began to be detected from May 1997 and persisted into 1998. Recruitment of common sardine showed significantly negative relationship with SST anomalies during the pre-recruitment period, as well as with the upwelling index during the peak of spawning. However, the recruitment of anchovy did not seem to be affected by the environmental changes observed in the 1990s. Instead, the recruitment rate of anchovy showed negative relationship with the recruitment rate of common sardine. We conclude that the conditions of the 1997–1998 El Niño off central-south Chile affected the survival of common sardine offspring, and that the recruitment success of anchovy could be determined by less-abundant cohorts of common sardine through a biological mechanism of interaction.

An advection diffusion reaction model was used to estimate movement and tag attrition parameters from skipjack tuna tagging data off the Maldives. Two sets of data were available from the experiments carried out during two distinct periods: 1990–1991 and 1993–1995. The results of the analysis were compared with the previous analyses and discussed in relation to management of skipjack fisheries in the Maldives and in the Indian Ocean. The movements were found to be highly variable in space and time, and few consistent patterns were observed between the two data sets. Similarly, significantly different estimates of fishing and natural mortality rates were observed from the two data sets. These differences were found, in part, to be due to the uneven distribution of tag releases in both space and time. Estimates of movement and attrition rates show that emigration from the Maldivian fishery to the rest of the Indian Ocean’s was small. The exploitation rate was found to be substantial, contributing about 30-40% of the total attrition in the fishery area. Such levels of localized exploitation may be maintained by steady immigration from outside of the Maldives, but more extensive tagging is required to be certain. The impact of tuna fisheries elsewhere in the Indian Ocean on the domestic Maldivian fishery cannot be determined until a comprehensive large-scale tagging program, including all the fisheries in the Indian Ocean, is completed.

To understand the ecology of the exotic silver European eel Anguilla anguilla introduced into Japanese waters, the migratory behavior of 106 specimens captured in the coastal waters of Japan between April 1997 and March 2002 was analyzed. Their migratory behavior was apparently correlated with various environmental factors, particularly photoperiod, water temperature, lunar phase, and passage of atmospheric depressions, and was similar to the behavior of the species in European waters. These findings suggest that transplanted European eels retain their ability to respond to environmental cues for seaward migration in similar temperate habitats. The timing of the migration of silver European eels coincided with that of the native Japanese eels A. japonica, suggesting that the silver European eel was synchronized physiologically with the native eel by the same environmental factors.

This work is aimed at demonstrating the influence of insulin in the triggering of hepatic cholestasis in young gilt-head sea bream larvae reared under experimental conditions. The results are based on an immunological assay of insulin and an ultrastructural study of the yolk syncytial layer and the liver. Compared to fed larvae, fasting gilt-head sea bream larvae displayed a substantial increase in insulin level correlated with dysfunction of the yolk syncytial layer and hepatic histopathology. This correlation was verified in larvae reared in sea water containing insulin. Ultrastructural observations suggested that insulin affects lipoprotein secretion by the yolk syncytial layer. The failure of plasmatic lipoproteins would then cause dysfunction of the biliary lipid secretion mechanisms and, hence, trigger hepatic cholestasis. These results in gilt-head sea bream show for the first time the influence of insulin in the triggering of hepatic cholestasis during the early development of a vertebrate.

17α-ethynylestradiol sex-reversed males of Oreochromis aureus (pseudofemales, ΔF, genotype ZZ) are used in aquaculture to produce a male monosex population by crossing with ZZ homogametic normal males. When placed with males (M) and females (F) in the same spawning tank, the spawning rate of F is higher than for ΔF. In order to understand this phenomenon, comparisons were made between the behaviour of 18 F (446 ± 96 mm) and 18 ΔF (401 ± 59 mm). ΔF showed a more aggressive behaviour and were significantly more dominant than normal F in fighting pair experiments (F × ΔF) or in fighting group experiments in four different stocking densities (8, 12, 16 and 83 fish 10–3 l with F/ΔF RATIO = 1). ΔF were also more aggressive towards males than F were. The results support the idea that behavioural differences exist between F and ΔF. These differences are probably due to the effect of the sexual genotype on behaviour.

This study was carried out to investigate the effect of feeding diets containing herring or anchvoy oil, on flesh quality parameters of Atlantic salmon (Salmo salar). Two extruded experimental diets with the same basal composition but one coated with herring oil and the other with anchovy oil, were each fed during 24 weeks to salmon with an average initial weight of 1.8 kg. Salmon grew to a final weight of 3.9 kg. Growth, condition factor and biometric parameters were not affected by the dietary treatment. No significant differences were found for intramuscular fat. Monounsaturated fatty acid (MUFA) concentrations were highest in the group fed the diet containing herring oil, in both neutral and polar lipids, while the group fed the diet containing the anchovy oil showed a higher concentration of n-3 fatty acids in both fractions of intramuscular lipids. The n-3/n-6 ratio was higher in the neutral lipid fraction of fish fed the southern hemisphere oil, while no significantly differences were found for the polar lipid fraction. No differences were found on muscle α-tocopherol levels. Muscle homogenates from fish fed the anchovy oil showed the highest thiobarbituric acid reactive substances (TBARS) after 9 days of storage. However no differences were found between groups on the induced oxidation tests. It is concluded that the origin of the fish oil has no effect on growth perfomance, but there is a marked effect on fatty acid composition and susceptibility to lipid oxidation.

Few studies have compared the suitability of different artificial reef construction materials in terms of their efficacy in acquiring diverse faunal assemblages. We compared the fishes associated with 12 co-located reefs constructed of limestone quarry boulders, concrete-gravel aggregate, or concrete-tire aggregate (four of each substrate) in 7 m of water, 200 m offshore Miami Beach, Florida, USA. All 12 reefs were deployed 100 m apart the same day in two lines of six. The four quarry stone reefs consist of a pile of 50 boulders each. The remaining eight reefs, of concrete-gravel aggregate and concrete-tire aggregate, were each constructed with 25 1.5 m edge and 25 1.2 m edge tetrahedron modules. Every two months from October 1998 to February 2001, SCUBA divers recorded fish species, abundance, and length, as well as spiny lobster, Panulirus argus, abundance. One hundred and forty-six species of fishes were recorded during the study period. The abundance and species richness of fish on each treatment exhibited a significant (p<0.05) seasonal variation with summer months having the greatest numbers and winter the lowest. There was no significant difference in total fish or spiny lobster abundance or fish biomass amongst the three reef types (p>0.05). Likewise, multi-dimensional scaling of Bray-Curtis dissimilarity indices did not indicate clustering of fish assemblages by reef type. Comparison of pre-deployment fish counts from the reef sites and neighboring hard bottom and jetty with counts from the same sites two years post-deployment indicate the artificial reefs increased both fish abundance and richness in the local area.

In the Mediterranean Sea, the fish Sarpa salpa (Sparidae) is the only vertebrate grazer of Posidonia oceanica meadows. In order to gain knowledge about the behaviour of S. salpa and a better understanding of the meadow's primary production recycling, an original study was designed using ultrasonic telemetry to investigate activity patterns and space utilisation in the field. During June–September 2000, we compared diel movements of six adult S. salpa (249–317 mm FL and 313–633 g) in the Bay of Calvi. These fish were tagged by intraperitoneal insertion of ultrasonic transmitters. Their positions were recorded with a directional hydrophone from a small boat with an accuracy between 10 and 50 m, depending on the local environment. The tracking duration ranged from 3 to 22 days (average 11.8 ± 7.3). Locations were performed from at least dawn to dusk or early night, and one fish was tracked during the entire 24-h cycle. Fish were more mobile during the twilight periods, but statistical analysis indicated individual differences for the precise period of mobility. Two major behavioural patterns were observed: first, the fish remained in close vicinity of the harbour during the day and moved away to the north or the south at dusk to access nocturnal sites, occupying a home range of about 4.3 ha. The second behavioural pattern involved persistent occupation of the same sites during day and night within a relatively restricted home range (about 0.8 ha). Great variation in mobility was found and the same individual fish could show both kinds of behaviour.

In the tropics, there is very little information on fish reproduction in intermittent streams and most of the studies are from the neotropic regions. In temporary rivers, environmental conditions are sharply contrasted and the variation amplitude of hydrological and physicochemical characteristics is high. In the Baoulé River (Mali), during the peak of the dry season, the remaining pools comprise only 10% of the total length of the river. During the wet season, there is a short (three months) but intense period of flooding. In this study, the reproductive strategies of 18 species of fishes were investigated in the upper reach of the Baoulé drainage. They belong to eight families, show variation in feeding guilds, and vary in size and habitat preferences. Fishes were collected from February 1985 to November 1988 using gillnets. Two main types of spawning strategies may be distinguished among these species. The first, the ‘total spawners’, have generally a short annual spawning period just before the flood. The second, the ‘small-brood spawners’, produce small batches of eggs at frequent intervals for most of the year. Most of the species inhabiting the Baoulé River exhibit a breeding strategy in relation to the flood seasonality. This type of strategy, common in harsh but predictable environments, favours a synchronous reproduction in phase with the optimal environmental conditions and the production of large number of juveniles that require no parental care. Concerning the Baoulé River, 12 variables related to life-history theory were measured for 18 species. Clustering of these species based on Euclidean distances resulted in two groups. The first corresponds to developed parental care, large oocytes and low fecundity (about a hundred eggs). Two species, Chrysichthys auratus and Sarotherodon galilaeus, belong to this ‘equilibrium strategy’. Others species have a ‘seasonal strategy’, which is adapted to the harsh local conditions. In the Nilo-Sudanian area, most fishes appeared to be associated with a seasonal life history strategy that exploits an annual expansion of aquatic production. In the Baoulé River, the ‘seasonal strategy’is characterised by high fecundity, absence of parental care, limited breeding season and for some species large adult size and upstream spawning migrations to floodplains.

At present, European marine fish farming is based on sea bream and sea bass. A trend for diversification is sustained by the diversity of environmental conditions, by the availability of new production techniques such as recirculating systems, by an increase in rearing yields, by new market trends and by the possibilities to reduce risks of disease outbreak. Already reared fish species were chosen considering a limited number of criteria such as a high selling price and the availability of juveniles or breeders in the wild. This paper proposes a new selection method of fish species as candidates for aquaculture development on the French Atlantic, the Channel and the North Sea coasts. Using a three-phase procedure, candidates were selected among 20000 fish species. Final classification was carried out using a panel of 22 criteria, taking into account inquiries conducted in France with aquaculturists but also with the main actors of distribution and transformation channels and with consumers. Cod (Gadus morhua) was selected by the present work as the first candidate for aquaculture development on the western coasts of France. This work also highlights the high interest of Gadoids for aquaculture development in this area.

The combined effects of feeding time (morning and evening) and dietary fat concentration on feed intake, growth, body composition and lipid tissue distribution were examined in rainbow trout fed on demand. To that purpose, diets with low (LE, 6% lipid) or high energy concentrations (HE, 24% lipid) were used in four treatments that combined provision of the same (HE–HE or LE–LE) or different (HE–LE, LE–HE) diets at morning and evening meals. Digestible energy intakes of the LE–HE (229 kJ kg–1 d–1) and HE–HE (269 kJ kg–1 d–1) groups were significantly different. There was no significant difference in the amount of energy intake between the two meals of the day in any of the treatments. The main effect of dietary treatment was on lipid intake; fish in the HE–HE, HE–LE and LE–HE treatments ingested approximately 3, 2.2 and 1.8 times more lipid than those on the LE–LE treatment. Growth, weight gain and protein gain were not affected by dietary treatment, but lipid gain reflected lipid intake; fish in the HE–HE, HE–LE and LE–HE treatments gained approximately 2.6, 2.1 and 1.7 more lipid than did fish on the LE–LE treatment. Body composition was significantly affected by dietary treatment; whole body lipid content reflected lipid gain, and visceral lipid concentration was affected in a similar way to whole-body lipid. On the other hand, muscle lipid concentrations were similar in fish submitted to the HE–LE, LE–HE, and LE–LE treatments (< 4%), and were lower than in fish on the HE–HE treatment (ca. 5.5%). Consequently muscle lipid concentration was not directly related to lipid intake, because lipid intakes of fish on HE–LE and LE–HE treatments was higher than in those on the LE–LE treatment, while muscle lipid concentration was lower. Thus feeding fish with different diets in the morning and evening might have potential as a tool for manipulating lipid distributions and concentrations without major adverse effects on growth.