While lognormal distributions have been proposed as useful descriptors of recruitment variability, the very nature of the recruitment distributions is still debated.To account quantitatively for recruitment distributions,I here propose a Weibull exponential model;it derives from a simple and natural hypothesis for uncorrelated recruitment processes of spawning, hatching, growth and survival through the early life stages to the point of vulnerability to the fishery.The quantification of Weibull exponentials is particularly important with regards to extrapolations to low recruits that have not yet been observed.To test the Weibull exponential null-hypothesis, I examine annual time-series of recruitment in major aquatic stocks.The Weibull exponential quite describes the bulk (95%) of the recruitment distributions of widely differing stocks,while the remaining 5% of the largest recruits are occurring with a much larger rate than predicted by the Weibull exponential.Further, I study the inter-event times between unusually high numbers in recruitment time-series data and find that intermittent pulses of strong recruitment follow non-Poisson statistics, which arises from year-to-year persistence of the magnitude of recruitment:large (or small) recruits are more likely to be followed by large (or small) recruits.This recruitment clustering effect is confirmed by the rescaled range analysis method.The empirical results imply that individual survivals on recruitment levels are independent of initial cohort sizes but year-to-year recruiting events exhibit long-term correlations.

We have analyzed a series of 22 groundfish surveys conducted between 1989 and 1999 on the Portuguese shelf and upper slope (97 sampling station grid, 36−710 m) in the summer, autumn, and winter, to address the hypotheses of latitudinal and depth trends in species richness (number of species) and whether these patterns changed over time and among seasons. Richness was modelled by means of a Generalized Additive Model (GAM) with significant covariates being latitude and longitude, in a joint-spatial smooth, and depth, chronological time, and season. A decrease in richness was detected along the continental margin, when moving higher in latitude, with lowest richness being found in the shallow northern area. Thus, although our study spanned only about 5 degrees in latitude, we found no exception to the equator-pole latitudinal decrease in richness commonly acknowledged by ecologists. There is no common agreement on the way marine fish species richness varies with depth, yet our findings were consistent for the entire eleven-year period: richness decreases slightly with depth, from the coastline to the shelf break (200−300 m), steadily increasing afterwards down the slope. The patterns of change in latitude and depth persisted in time and among seasons but their magnitude changed. Richness was higher in the winter compared to the other seasons.

A simulator dedicated to the modeling of individual search behaviors of fishing vessels has been built using multi-agents systems methodology. The harvesting activity of a virtual fleet is simulated and applied to a static virtual fish population, distributed in a bi-dimensional spatially explicit environment. The resource population can differ depending on different degrees of aggregation. Each vessel of the fleet is modeled as a singular and autonomous agent of the fishery system. The model focuses on the representation of information transfer among vessels, which results in an orientation of search effort. The informative search behavior is compared to a stochastic search, in order to estimate efficiency gains allowed by information transfers. Results show a strong dependence of the fleet's efficiency towards the level of aggregation of the resource. For higher levels of aggregation the informative behavior results in important gains in efficiency. Conversely, a misleading effect of information appears in the weakest aggregations. The informative behavior leads to the progressive convergence and the gathering of the agents. When the aggregation is strong, this “pack effect” is stable in time and enables the vessels to make quick catches. For the weakest aggregation levels, the “pack effect” is unstable and leads the ships to a perpetual pursuit state, without catches. Thus, the size of existing networks appears as a key parameter of vessel behaviors. This approach, using an individual-based simulator, seems quite appropriate to connect individual behaviors to the dynamics of the fishing efficiency, which are generally studied in an aggregated manner. It allows to quantify the effects of the exchange of information among vessels, which is commonly considered as a qualitative phenomenon. Such an approach should be enlarged to a more global modeling of all of the components of the individual search behaviors of vessels.

Using catch composition data collected on individual fishing trips between 1990 and 2001, we study fishing tactics and strategies of the coastal demersal trawlers operating in Senegal. Types of fishing actions (tactics) are defined through catch composition on fourteen stocks. Types of fishing units (strategies) are defined according to the tactics they can use. These two typologies are built using the K Means method, a non hierarchical classification approach. As results, twelve tactics and six strategies are primarily identified. Using expert knowledge some fishing tactics are gathered and eight tactics and five strategies are finally considered and discussed with a presentation of the articulations between stocks, tactics and strategies.

The objective of this study was to investigate the effect on Mullus barbatus (red mullet) codend selectivity by increasing the codend mesh size or reducing the number of meshes in the codend circumference. This was performed through experimental sea trials and computer simulations. The sea trials were carried out in the Adriatic Sea using a polyamide codend in order to assess its selectivity, to record morphological (height, width and length) and population size structure parameters of red mullet (Mullus barbatus). The selectivity process in the codend was also simulated with an individual-based model (PRESEMO) and a finite element model (FEMNET) to calculate the codend shapes. By adjusting the behavioural description of red mullet in the simulation, the model results reached an agreement with the experimental results. Next these, behavioural parameters were used in the simulation model to predict the effect of changing mesh size and number of meshes around in new codend designs. The predicted effect and the benefit of enforcing these designs on catch efficiency below and above minimum landing size (MLS) were investigated. The results confirm that the reduction of number of meshes in the codend circumference will be more beneficial than increasing the mesh size.

We investigated spatial patterns of stony corals, molluscs and echinoderms among six habitat types within the lagoons of six atolls in the Tuamotu Archipelago (French Polynesia). Percent cover (stony corals only), abundance and richness were recorded within habitat types delineated by specific geomorphological features. Among six habitat types defined a priori, four encompassed distinct assemblages of corals and molluscs: (1) pinnacles possessed maximum richness, abundance and coverage, (2) passes showed relatively high abundance and coverage, (3) lagoon floors were marked by the commonness of a few coral genera, and minimum mollusc abundance and richness, and (4) inner reef flat stations, independent of their location in front of spillways, motu or rim zones, had low cover, abundance, and richness. While habitat associations were similar for stony corals and molluscs, echinoderms were preferentially found on the inner reef flat facing the rim. Lowest echinoderm abundances and species richness were recorded on pinnacles and in the vicinity of the pass. Such small-scale spatial heterogeneity appears to be one of the distinctive characteristics of coral communities in French Polynesian reefs. These results, along with those of the TYPATOLL program, demonstrate the importance of both local and regional factors in determining the diversity and structure of coral assemblages. Habitat fidelity was weak: many species/genera were poorly represented among habitats and restricted to a few atolls, while others were present across all lagoons and habitats. Therefore, marine protected areas design based solely on representativeness will require the protecting the vast majority of lagoon habitats.

Data on the diet of species are important for understanding ecosystem dynamics and are fundamental for the implementation of recent approaches in stock assessment and consequently for the establishment of more ecological management measures. In mainland Portugal, as in most European countries, skates and rays represent an important proportion of commercial landings. The four main species landed are Raja clavata and Raja brachyura, followed by Leucoraja naevus and Raja montagui. This paper analyses their diets based on the examination of stomach contents. Food items were identified to the lowest identifiable taxon and were further assembled into major taxonomic groups designated as prey. Intra- and interspecific comparisons were made according to size and sex. All four species had generalized diets with differences in prey preference among them. Decapods and bony fish were the most frequent prey. Furthermore, an ontogenetic dietary shift was evident in all species at around 45−55 cm total length. Both intra- and interspecific differences observed seem to be related to size and morphological characteristics of the species, as well as type of dentition. These variations allow different species, as well as small and large specimens from the same species, to exploit a larger diversity of habitats.

In this paper, we present an approach to compare the impact of different management options on the dynamics of a mixed fishery. We used ISIS-Fish, a simulation tool aimed at evaluating the impact of spatial and seasonal management measures on the dynamics of mixed fisheries. The French Nephrops norvegicus (Norway lobster) – Merluccius merluccius (hake) mixed fishery of the Bay of Biscay was chosen as a study case. First, we parameterised the population and exploitation models. We then selected several management measures, including marine protected areas (MPAs) and total allowable catches (TAC), and parameterised fishermen's reaction to each measure. Then, a sensitivity analysis was performed according to a fractional factorial experimental design. Management scenarios were assessed and compared using a statistical simulation design. The sensitivity analysis showed the large influence of some parameters, such as natural mortality, N. norvegicus fecundity, and catchability on both abundance and catches. Given model parameters, an improvement of trawl selectivity and several MPA designs (differing in size, seasonality and location) were found to result in a significant increase in abundance over 10 years, especially for N. norvegicus. This study illustrates the need for a pluri-specific approach to fisheries assessment and management.

Fish schools are aggregative structures encountered in all types of aquatic environments but have as yet been little studied in freshwaters except at small spatial scales. This study represents the three dimensional description of juvenile fish schools (Perca fluviatilis and Rutilus rutilus) in a lake environment using high resolution multibeam sonar system operating at a frequency of 455 kHz, composed of 60 beams of 1.5° allowing a 90° observation plane. The in situ diurnal schooling behaviour of young-of-the-year fish of both species is confirmed. The morphological, energetic and spatial variables of these schools are described and related to one another. The structures described are of the same order of magnitude as those described in the marine environment. The school shape is elliptical, they are shallow and they display a temporal and spatial stability over the course of a day but a highly variable morphology. The number of vacuoles, a descriptor of the internal morphology of the schools, was found to be significantly (p < 0.01) correlated with the volume of the school, and showed two distinct relationships, with proportions similar to the percentage occurrence of both species sampled by a pelagic trawl. The relation may be efficient for fish species discrimination by 3-D acoustics methods in this lake with two main aggregative fish species.

Selectivity studies usually describe the effects on target species, whereas information on by-catch and discards is scarce. Nevertheless, large quantities of undersized individuals and invertebrates are discarded in the Mediterranean multi-species bottom trawl fishery. The present work analyses the data from two surveys carried out on the shallow and deep continental shelf (50–78 m, and 147–189 m, respectively) off the Balearic Islands (western Mediterranean). In these surveys, the traditionally used 40 mm diamond mesh codend and an experimental square mesh codend were used under commercial conditions. Catch composition, yields, size selectivity of both target and by-catch species, and discards were compared between the two mesh types. The mean selection length (L 50) clearly increased for most species when using square mesh, escaping many more individuals under their minimum landing size. Yield of Spicara smaris was significantly lower by using the square mesh, changing the composition of the retained catch. Escapement ratio and economic loss were significantly higher with square mesh, although economic loss was almost negligible for both meshes on the deep continental shelf. The use of square mesh significantly reduced the discards of algae in the shallow waters and fish on the deep continental shelf. The results confirmed that square mesh codend reduces the fishing pressure on small specimens as well as the impact of trawling on the ecosystem. These benefits would not lead to a reduction of the yields neither of the main target species, the fishes Merluccius merluccius, Mullus surmuletus, Zeus faber, and the cephalopods Loligo vulgaris and Octopus vulgaris, nor of the rest of commercial categories, except for Spicara smaris.

The necessity to move from a traditional fishery management to an ecosystem approach is now acknowledged. Indicators are required to support the development of this approach. For example, community indicators have been proposed to assess the impact of fishing. We tested here the applicability of one such community indicator, the abundance-biomass comparison (ABC method), as a measure of the impact of bottom trawling (years of sampling: 2001 and 2003) on the benthic invertebrates – typically starfishes, crabs, squat lobsters, shrimps and large hard-shelled molluscs- of “Grande Vasière”, a major French fishing zone, in the Bay of Biscay. The ABC method is generally used as an impact indicator for different types of physical, biological and anthropogenic disturbances on benthic communities. This method is based on the assumption that increasing disturbance shifts communities from dominance by large-bodied species with low turnover rates toward dominance by small-bodied species with high turnover rates. At less disturbed areas the average biomass of individuals is greater than at more heavily disturbed areas. The ABC method measures this effect by comparing the ranked distributions of abundance and biomass within a given community. We applied the ABC method and compared the size structure and the species diversity at two areas exposed to moderate and high bottom trawl effort. Species diversity was lower in the most exploited area. The highly trawled area was dominated by opportunistic organisms, mainly one species of swimming crab Liocarcinus depurator, one species of squat lobster Munida rugosa and Norway lobsters Nephrops norvegicus, which are large-bodied species. Consequently, the results of the ABC method were inconsistent with the theoretical expectation for these particular macrofaunal communities and the measured levels of fishing intensity. 


Growing pressures from development activities, on aquatic environments in South American countries, have created an urgent need for tools to measure the quality of aquatic systems. The index of biotic integrity, based on fish assemblages, elaborated in North America, constitutes a basis for the development of these tools. However, its direct application is problematic in regions having a rich and diverse ichthyofauna and where the knowledge of fish species ecology is incomplete. The response of taxonomic or trophic groups is often unknown and the selection of fish assemblage metrics cannot be based on previous knowledge, as in intensely studied regions. This work proposes a method, similar to the approach recently pursued in Europe, based on comparing the variability of fish assemblages in reference situations with their variability influenced by human-induced perturbations. The method was developed from 53 samples of 27 reaches in 7 hydrographic basins of French Guiana. For each of 28 fish assemblage descriptors, stepwise multiple linear regressions with 28 habitat variables were carried out. The residuals of the models obtained were used as candidate metrics independent of natural environmental factors. Nine metrics showing significant differences between reference and disturbed samples were selected to constitute the index. The index was validated by analysing a temporal data series obtained from a reach disturbed by dam construction.

The objective is to study different factors of variations in the body shape of trout (Salmo trutta) belonging to the Mediterranean lineage (indigenous trout) or Atlantic lineage (introduced trout), and their hybrids. Using thin plate-spline (TPS) method by pointing landmarks, it made possible to provide a graphical representation of the characteristic conformation of the individuals. The characteristics of form highlighted let appear – that the male trout have a dorsal part more prominent than that of the female trout and a larger head – the existence of a general curvature of the body related to the size of trout, independently of the sex. In addition, characteristics of form provide satisfactory results to distinguish the Mediterranean lineage from the Atlantic lineage. The recognition of hybrid trout is more random because very near to Mediterranean trout. The existence of a sexual dimorphism could be established in spite of the absence of information on the sex. Comparative with the sexual dimorphisms in spawning period reveals morphological transformations during the reproduction, mainly for the males. Independently of the genotypic and sexual dimorphisms, a general curvature of the body related to the size was detected.

Competent larvae of 4 tropical reef fish species, i.e. two pelagic spawners (Parupeneus barberinus and Acanthurus triostegus) and two benthic spawners (Abudefduf sexfasciatus and Dascyllus aruanus) were collected over two years in Wallis Islands, in order to compare 1) their size and age at settlement, 2) the variability of these parameters and 3) their spatial and temporal variations. The larvae were collected in three sites approximately 10 km apart in September 2002, December 2002, March 2003 and June 2003. The otoliths were examined to obtain early life history information: pelagic larval duration and timing of settlement. Size at settlement varied from 3 mm for A. sexfasciatus, D. aruanus and A. triostegus to 10 mm for P. barberinus. For the benthic spawners, settlement occurred after 17 and 19 days within a narrow age interval (7 to 9 days) and mainly in the middle of the interval. For the pelagic spawners, settlement occurred later (after 35 and 42 days), within a larger age interval (13 days). These estimates are lower than those from other locations in the Pacific but their range is larger. Size at settlement differed significantly between sampling sites only for D. aruanus and between surveys only for A. sexfasciatus. Age at settlement differed significantly between sampling sites only for A. sexfasciatus and between surveys only for D. aruanus. For the pelagic spawners the variability of size and age within site and survey was up to ten times greater than for the benthic spawners. This flexibility would be an advantage for larvae of the pelagic spawners that have to travel greater distances to settle.

This study investigated the size, diversity, dominance and trophic structures of the exploited inshore fish community of the Sinazongwe area, Lake Kariba, Zambia, for the period 1980-1995. It was based on fish records of scientific gillnet surveys and on data available in the literature. The size and diversity spectra exhibited, like those of exploited demersal marine fish communities, regular decreasing patterns, indicative of high fish numbers and diversity in smaller sizes and vice versa among larger sizes. The size spectra patterns were recurrent from year to year and well fitted by quadratic functions. The diversity (Shannon index) and dominance (J' index) decreased and increased linearly, respectively, with fish length. Diversity for larger lengths has decreased as evidenced by the annual variations of diversity spectra's slopes. The abundance-biomass comparison plots indicated years of undisturbed, strongly and moderately stressed fish community. The proportions of predators, especially of Hydrocynus vittatus, and the mean trophic level decreased linearly over years. The average diversity trophic spectra remained unchanged. The mean abundance and biomass trophic spectra indicated a top-predator controlled community over 1980-1984, and vice versa thereafter. The trophic structure descriptors better captured the fish community changes under increasing fishing pressure and revealed for the first time the “fishing down marine food webs” effects for Lake Kariba. The community attributes studied are potentially promising alternatives for the assessment and management of tropical exploited freshwater fish communities.

Twelve diel surveys were carried out in three reservoirs of Sri Lanka viz. Minneriya, Udawalawe and Victoria, to investigate diel feeding patterns, daily ration and relative food consumption in fish populations. Stomach content weights of different size classes of various fish species in the three reservoirs in 12 diel surveys were analysed using an iterative method, MAXIMS. Predominantly herbivorous or detritivorous fish species such as Amblypharyngodon melettinus and Oreochromis niloticus exhibited one peak in the diel feeding pattern. Two peak feeding periods were evident in predominantly insectivores and/or zooplanktivores (e.g., Puntius chola and Rasbora daniconius) and interestingly in macrophyte feeders (i.e., Etroplus suratensis, Puntius filamentosus and Tilapia rendalli). It might be possible that all species with two feeding peaks in diel feeding patterns rely on vision for feeding.Food consumption per biomass (Q/B ratio) defined as amount of food consumed per unit weight of an age-structured population of fish was estimated on the basis of the average quantities of food consumed over a long period of time by various size classes in order to minimize the bias of estimates.

Neosalanx reganius is a poorly studied salangid fish restricted to the upper reaches of the Chikugo and the Midori River flowing into the Ariake Bay, Kyushu, Japan. Samples of N. reganius were collected from brackish water areas of the Chikugo River by eight cruises in 1998-2004 to characterize the distribution pattern, feeding ecology in relation to ambient prey concentrations, fecundity and condition of the fish. A total of 244 specimens were collected, 36 to 71 mm total length, and 111 to 1301 mg body weight. The catch per unit of effort (CPUE; number of fish collected by towing a larva net for 20 min) correlated positively with turbidity and negatively with salinity. N. reganius is a planktivorous fish, fed on a single calanoid copepod species Sinocalanus sinensis, which was the single most dominant prey item in all stations during all cruises, contributing as high as 97.0% of the total diet of the fish; the other prey items (other calanoids and cyclopoids, Daphnia sp. and decapod mysid) together contributed only 3%. S. sinensis also dominated in the environmental copepod composition. The CPUE showed significant correlation with copepod dry biomass which increased upstream (r = 0.90; p < 0.05). Fecundity ranged 347-995 (mean 583 173) oocytes individual−1 and relative fecundities ranged 6.8-15.6 (mean 10.1 ± 2.4) oocytes mm−1 TL and 0.8-2.5 (mean 1.6 ± 0.5) oocytes mg−1 of net body weight (weight taken after gonad extraction). Fecundity showed significant positive relationship with fish length and body weight. GSI ranged 29.4-58.8% (mean 43.5 ± 7.9%) and had significant relationship with fish length and body weight. Spawning individuals had higher allometry coefficient (b) and condition factor (K) than the non-spawning individuals. The oligohaline upper Chikugo estuary provides important feeding and spawning grounds for the fish with sufficient prey abundance and turbidity maximum that seemed advantageous for feeding and spawning of N. reganius in the Chikugo estuary. We suggest that future research should emphasize on the spawning and early life ecology of the fish in order to formulate effective conservation action.

Seaweed farming is often depicted as a sustainable form of aquaculture, contributing to poverty reduction and financial revenues in producer countries. However, farms may negatively affect seagrasses and associated organisms (e.g. invertebrate macrofauna) with possible effects on the flow of ecosystem goods and services to coastal societies. The present study investigates the influence of a seaweed farm, and the farmed seaweed Eucheuma denticulatum in particular, on fishery catches using a traditional fishing method (“madema” basket traps) in Chwaka bay (Zanzibar, Tanzania). The results suggest that a seaweed farm, compared to a seagrass bed, had no influence on catch per unit effort (no. of individuals per catch, or catch weight) or no. of species per catch, but significantly affected catch composition (i.e. how much that was caught of which species). The two species contributing most to differences between the sites were two economically important species; the herbivorous seagrass rabbit fish Siganus sutor, which was more common in the seaweed site and is known to graze on the farmed algae; and the benthic invertebrate feeder chloral wrasse Cheilinus chlorourus, more common in the seagrass site. Compared to vegetation-free bottoms, however, the catches were 3−7 times higher, and consisted of a different set of species (ANOSIM global R > 0.4). As traps placed close to the seaweeds fished three times more fish than traps placed on sand patches within the seaweed farm, the overall pattern is attributed to the presence of submerged vegetation, whether seagrass or seaweed, probably as shelter and/or food for fish. However, qualitative differences in terms of spatial and temporal dynamics between seagrass beds with and without seaweed farms, in combination with other factors such as institutional arrangements, indicate that seaweed farms cannot substitute seagrass beds as fishing grounds.

This study describes the current status of the small fish community in Niushan Lake in China, and examines the spatial and seasonal variations of the community in relation to key environmental factors. Based on macrophyte cover conditions, the lake was divided into three major habitat types: (1) Potamogeton maackianus habitat, (2) Potamogeton maackianus and Myriophyllum spicatum habitat, and (3) uncovered or less-covered habitat. Fish were sampled quantitatively in the three habitat types by block nets seasonally from September 2002 to August 2003. A total of 10 469 individuals from 27 fish species were caught, among which 20 species were considered as small fishes. Rhodeus ocellatus, Paracheilognathus imberbis, Pseudorasbora parva, Micropercops swinhonis and Cultrichthys erythropterus were recognized as dominant small fishes according to their abundance and occurrence. It was noted that (1) small fishes predominated the total number of fish species in the lake, which reflected to some degree the size diminution phenomenon of fish resources; (2) many small fishes had plant detritus as their food item, which was consistent with the abundance of macrophyte detritus in the lake and implied the importance of detritus in supporting small fish secondary production. Canonical correspondence analysis suggested that the spatial distributions of most small fishes were associated with complex macrophyte cover conditions. Macrophyte biomass was positively correlated with species richness, diversity index and the catch per unit of effort (CPUE) of the fish community. Water depth had no significant effects on species diversity and distribution of the small fishes. Correspondence analysis revealed a higher occurrence of the small fishes and higher abundance of individuals in summer and autumn. Seasonal length-frequency distributions of several species indicated that more larval and juvenile individuals appeared in spring and summer. This study provides some baseline information which will be essential to long-term monitoring of small fish communities in the Yangtze lakes.

Tilapia species are able to hybridize in captivity or in natural conditions following introduction of alien species. Here, we report a case of hybridization between two (and perhaps three) autochthonous species, Tilapia zillii and T. guineensis, resulting from a modification of their environment due to human activities. The man-made dam Ayamé (Côte d'Ivoire) transformed the River Bia into a lake (Lake Ayamé, area: 197 km2). In this new environment, both tilapia species have hybridized. In order to study hybridization along the Bia System, 25 allozyme loci have been screened in 470 specimens from ten locations. Two loci LDH-1 and PGI-2 were diagnostic between the two different species and can be used to identify hybrids in each sampling location of the River Bia basin. The percentage of pure T. zillii individuals in Lake Ayamé varied from 18.1% in Ebikro to 4.2% in Kétesso while percentage of pure T. guineensis varied from 81.3% in Yaou to 50.0% in Ebikro. The proportions of hybrids varied from 8.3% in Yaou to 31.9% in Ebikro. The existence of private alleles observed in tilapia from Lake Ayamé compared to what has been observed in both reference populations, T. zillii and T. guineensis led to the hypothesis that a third species could have been engaged in this hybridization. This third species is likely to be T. busumana, formerly present in the lake but now rarely observed. If this natural hybridization is due to the dam construction and the correlated ecological changes, then other hybridizations could result since many dams have been constructed within the range of these species in Côte d'Ivoire.