While fishing resources available to fishermen are becoming increasingly scarce, management actions that regulate these resources are becoming more restrictive, to such an extent that some fisheries remain closed for years. The anchovy fishery in the Bay of Biscay, which was closed for 5 years, from 2005 to 2009, is one of the most important sources of revenue for the Basque pelagic purse-seiner fleet. Throughout the course of this closure the fleet was forced to find alternative revenue streams. In the present study, the fishing alternatives were analysed before and during the anchovy fishery closure, defining an adaptability indicator to measure the ability of the fleet to cope with fisheries closures. Four differently-behaved segments were found within the purse-seiner fleet. Only one of these segments managed to maintain the same level of turnover during the anchovy closure, while the others could not reach a minimum level of adaptability. Compensation of the fishery closure through financial aid was studied, analysing the impact that public aid had on the profit of each segment and on the adaptability indicator.

Atlantic herring (Clupea harengus) in the offshore regions of the Gulf of Maine migrate each fall from their feeding grounds to the northern portion of Georges Bank to spawn. The Northeast Fisheries Science Center’s (NEFSC) herring acoustic survey has taken advantage of this behavior by conducting systematic surveys of the pre-spawning fish each year since 1999. Multi-frequency acoustic and midwater trawl data were collected along transects oriented perpendicular to bathymetric contours. Acoustic backscatter was analyzed to describe the aggregative patterns (e.g., size, location in the water column, and spatial and temporal distribution) of Atlantic herring during these surveys and regression trees were used to examine the aggregation characteristics. The positional variables of distance to spawning grounds and vertical location in the water column were the primary characteristics for describing pre-spawning aggregations. Secondary to these were the temporal variables of diel and survey timing, and the morphological characteristic of aggregation area. Lower numbers of aggregations were observed close to the herring spawning grounds but with higher acoustic energy than larger numbers of aggregations observed further from the spawning grounds but smaller in size and lower in acoustic energy. Most aggregations were in the lower portion of the water column, but those that were in the upper portion of the water column had higher acoustic energy. Consistently throughout the decade, 90% or more of herring aggregations were located within 40 nautical miles of their spawning grounds. The regression tree method provided valuable insight to the data series where it highlighted spatial and temporal patterns and was an effective way to quantitatively summarize relationships.

Bycatch in longline fisheries is considered one of the main threats for the conservation of albatrosses and petrels worldwide. However, the relative impact of fisheries on all the affected populations or species still remains poorly understood. This paper applied a Productivity and Susceptibility Analysis (PSA) and the concept of “Potential Biological Removal Level” (PBR) to assess the relative impact caused by the Uruguayan pelagic longline fishery on several populations. This two-step approach allowed us to obtain an objective view of the relative impact of the Uruguayan pelagic longline fleet on most of the populations or species of albatrosses and petrels with high association with this fishery. Of fifteen species considered, fourteen were finally assessed and a ranking of risk derived. The concept of PBR was applied to the nine most at-risk species. The impact of fishing on populations could not be straightforwardly inferred from their bycatch rates. Results indicate that large albatrosses (Diomedea spp.) and Thalassarche chlororhynchos are more affected than some of the main species caught by the fishery (i.e. Thalassarche melanophrys and Procellaria aequinoctialis). Diomedea exulans from South Georgia is likely to be the population most affected by the Uruguayan fleet. This work should be seen as a case study of the fisheries operating in the southwestern Atlantic. The Uruguayan fleet within its operation area was responsible for only the 4.3% to 12.5% of the total annual effort deployed by the different fleets during 2004–2008. The combined impact of these fleets could be sufficiently high to account for many of the observed declines in the populations of D. exulans, D. dabbenena and T. chlororhynchos. However, the seabird bycatch numbers for most of the pelagic longline fleets that operate in the southwest Atlantic remain unknown. Applying mitigation measures to reduce the impact of pelagic longline fleets operating in this region should be considered a high priority.

The clown loach Chromobotia macracanthus, endemic to Indonesia, is a major species on the international market of ornamental freshwater fish. In order to satisfy an increasing demand with a sustainable alternative to the massive capture of wild juveniles, research has been dedicated to the artificial propagation and domestication of this species. The present study, the first of a series, focused on favourable maintenance conditions for broodfish sexual maturation, criteria for identification of ripe fish, efficiency of hormone-induced breeding treatments, predictability of their latency response, and on the comparison of reproductive performances of fish from populations of Sumatra and Borneo Islands (in total, 112 females of 46 to 404 g body weight). When reared in fully controlled conditions in large water recirculation systems, broodfish originating from Sumatra had reproductive performances similar to or slightly higher than those maturing in the wild (ovulation rate of 93% vs. 82%, relative fecundity of 109 277 vs. 103 550 ova  kg-1 and fertilization rate of 73% vs. 61%, respectively). In the same rearing conditions, captive females from Borneo (n = 22) showed lower ovulation rate (77%), relative fecundity (76 262 ova kg-1) and fertilization rate (50%) than those originating from Sumatra (n = 28). By contrast, the mean individual weight of ova (around 0.8 mg) was independent from the origin or maintenance conditions of females. An initial modal follicle diameter  ≥1.02 mm generally led to high ovulation success (>80%) after hormonal treatment and is recommended as the main criterion for selecting female broodfish. Two hormonal treatments for inducing oocyte maturation and ovulation (T1: two successive injections of Ovaprim at a 6 h-interval; T2: one injection of human chorionic gonadotropin (hCG)- and one of Ovaprim 24 h later), produced similar results in terms of ovulation rate, quantity and quality of ova collected. With both treatments, the latency decreased with increasing water temperature, then increased again at temperatures  >28–29 °C. To our knowledge, such U-shaped relationship between the latency response and temperature has never been documented in teleost fishes.

This paper is based on recently recovered daily catch and effort data from the Algarve traps (south of Portugal) during the 1898−1900 period. These 18 traps targeted the two migrations of bluefin tuna, entering and leaving the Mediterranean Sea, each year during a period between mid April and the end of August. Their bluefin catches were significant, corresponding to average yearly catches of 61 000 bluefin, i.e., approximately 7900 t. Migration dates and durations towards and away from the Mediterranean Sea were estimated based on the daily catch per unit effort (CPUE) by the traps. Migration patterns were very stable during these three years. The entry migration took place over an average of 42 days, and the return lasted 53 days. Daily catches show large waves of tunas passing during the two migratory phases. It can be hypothesised that each of these waves of tuna spent about 52 days in the Mediterranean Sea, and that each group was stable and consistent during their arrival and return migrations. Migration trajectories along the Algarve coast can be estimated from the daily CPUEs of the different traps. They appear to be different between the arrival and return migrations. The daily data per trap show that most traps caught entering bluefin at quite low CPUE, whereas only a few traps were efficient for catching the returning bluefin, but with much larger catches and CPUEs. The analysis of catch and CPUEs during the entering and leaving phases allowed us to conclude that the catchability and fishing mortality of the bluefin stock in the Algarve trap fishery was much larger during the return migration. Additional daily data from other traps, both historical and contemporary, should be collected and analyzed in order to provide more comprehensive results on the patterns and changes in migration, stock structure and stock exploitation rate.

In comparison to older life stages, the embryonic stages of fishes generally have narrow tolerance ranges for environmental conditions, as regards water quality, temperature and mechanical shocks. The knowledge of these factors is indispensable to appraise the threats brought about by climate or anthropogenic changes upon their resilience, and to define adequate ways of incubating their eggs for an efficient propagation of the species under controlled conditions. Clown loach eggs have a narrow thermal tolerance range in comparison to other tropical and temperate fishes. Hatching occurs at 22–30 °C, and non-deformed larvae can only be obtained at 23.8–30.2 °C. Furthermore, the thermal tolerance of any particular progeny was found dependent on the maintenance temperature of the female parent, thereby making the actual tolerance no broader than 4.5 °C. The (log-log) relationship between the duration of the incubation period and temperature was characterized by a shallow slope, which is more typical of coldwater fishes, as is a narrow thermal tolerance range. On the other hand, clown loach hatched more rapidly (20 h at 26 °C) than predicted by existing models on the basis of water temperature and egg diameter, a feature that is shared by other warmwater fishes producing eggs that undergo a strong swelling process (about three times the ova diameter in clown loach). Clown loach embryos are strongly sensitive to mechanical shocks, but their development is not viable either in protracted steady state conditions, in absence of water movement, as they develop various deformities (e.g. pericardial oedema). This is thought to originate from a hypoxic microenvironment around the embryo, as a consequence of an oxygen gradient developing inside and outside the egg, since the boundary diffusion layer is not refreshed by water movement. This issue is worsened by strong egg swelling and incubation at warm temperature.

A lightweight sorting grid was developed to reduce bycatch in the Danish small-meshed trawl fishery (22 mm full mesh in the cod end) for Norway pout in the North Sea. Experimental fishing with the grid demonstrated the possibility to capture Norway pout with only a minimum of unintended bycatch. Fishing with two different grid orientations, backwards and forwards-leaning, in distinct day and night hauls, resulted in an estimated release of between 88.4 and 100% of the total number of haddock (Melanogrammus aeglefinus) and whiting (Merlangius merlangus) entering the trawl. However, bycatch reductions were not significantly different between day and night or between grid orientations, indicating that the grid rejection of haddock and whiting is not influenced by fish behaviour. The loss of the target species, Norway pout, was low (between 5.6% and 13.7%) in comparison with the bycatch excluded, and clearly length dependent. Consequently, loss of target species would vary with the size structure of the population fished. Although results were not statistically significant, length-based analyses indicated that the grid rejection likelihood for particularly smaller Norway pout (<16 cm) was higher when fishing with the forwards-leaning grid during the night; this might be explained by behavioural and visual aspects of the fish-grid encounter process for Norway pout.

Several fleets with various fishing strategies operate as a mixed fishery in the Bay of Biscay. Among the main fleets, bottom trawlers target Norway lobster (Nephrops norvegicus) and, together with gillnetters, they also catch hake (Merluccius merluccius). Trawling leads to average-size catches that are below the minimum landing size (MLS); such catches are discarded since they cannot be sold. These discards result in negative impacts on stock renewal, as most of them do not survive. This also results in an economic loss for both bottom trawlers and gillnetters since these discards represent a future loss of rent. This study, based on the 2009 and 2010 selectivity experiments at sea, assesses the short- and long-term bio-economic impacts of four experimental selective devices aimed at reducing N. norvegicus and M. merluccius discards over a 20-year simulation period. Tests were conducted at sea on a research trawler. Using the impact assessment model for fisheries management (IAM model), selectivity scenarios for trawlers in the Bay of Biscay were compared to a theoretical selective scenario of adopting an optimal device that catches only N. norvegicus and M. merluccius above MLS (9 cm and 27 cm total length, respectively). Costs and benefits were analyzed with the objective of finding the best compromise between a reduction in discards of undersized fish and a loss of valuable catches among the experimental devices. Selectivity scenarios show positive impacts on stocks but different economic impacts between fleets. The combination of a square mesh cylinder with a grid and square mesh panels gives the closest results to the theoretical scenario tested in terms of stock recovery and economic benefits. This experimental device leads to low economic losses in the short term and eventually to higher N. norvegicus yields, which would be favourable for fleets that greatly contribute to N. norvegicus fishing efforts.

Hatchlings of clown loach (3.8 mm in total length, TL) are pelagic. When reared at 26−28 °C, they become benthic 3 days after hatching (dah), when their swim bladder is inflated. The fin development sequence (pectorals  <  caudal  <  dorsal  =  anal  <  pelvic) is typical of the clade Ostariophysi. All fins and finrays are fully elongated at 20 mm TL, but the finfold persists until 25 − 26 mm TL (start of juvenile stage). Melanophores appear at 3 dah, they form a 5-bar pattern at 5 dah, then two bars (III and V) vanish progressively, producing at 26 mm TL the 3-bar pattern that is typical of adults. Throughout the ontogeny, the pigment pattern exhibits a structural regularity (bars spaced at regular intervals), which is interpreted in a functional perspective by reference to the maintaining of crypsis and signalling throughout. Exogenous feeding commences at 4 dah (5.5 mm TL). Food intake (FI) increases rapidly, from 6% wet body mass (WM) at 5.5 mm TL to  >20% WM in fish  > 7 mm TL. Gut evacuation rate (Rg) increases with increasing meal size and fish size, as a result of gut coiling (from 8 to 15 mm TL), and is highest at 11 mm TL (about 10% WM h-1 in fish feeding maximally). The allometric increase of FI and Rg during the early larval stages is accompanied by increasing capacities for growth, so early sizes differences amplify rapidly during the ontogeny. Nevertheless, growth remains slow (mean of 0.4 mm TL day-1 from 4 to 29 dah; 0.9 mm TL day-1 for top growers). By contrast, unfed fish display long resistance to starvation (until 14−15 dah). The combination of slow growth and long resistance to starvation is discussed in respect to the reproductive phenology of the species, as the capacity of making metabolic economies prevails over fast growth for seasonal strategists spawning mainly at the start of the rainy season.

Hooking (or “at-haulback”) fishing mortality was analysed in elasmobranchs captured by Portuguese longliners targeting swordfish in the Atlantic Ocean. Information was collected by on-board fishery observers who monitored 834 longline fishing sets between August 2008 and December 2011, and recorded information on 36 067 elasmobranch specimens from 21 different taxa. The hooking mortality proportions were species-specific, with some species having relatively high percentages of live specimens at time of haulback (e.g., blue shark, crocodile shark, pelagic stingray, manta, devil and eagle rays), while others had higher percentages of dead specimens (e.g., smooth hammerhead, silky shark, bigeye thresher). For the most captured species (Prionace glauca, Pseudocarcharias kamoharai, Isurus oxyrinchus and Alopias superciliosus), logistic generalized linear models (GLMs) were carried out to compare the mortality rates between sexes, specimen sizes and the regions of operation of the fleet. The sex-specific proportions of hooking mortality were significantly different for blue and crocodile sharks, with the males of both species having higher proportions of hooking mortality than the females. Specimen size was significant for predicting the hooking mortality for blue and shortfin mako sharks: in both cases, the larger specimens had lower odds of dying due to the fishing process. There were differences in the hooking mortality depending on the region of operation of the fleet, but those differences were also species-specific. For blue and crocodile sharks, the hooking mortality was higher in the Equatorial and southern Atlantic areas (when compared to the NE Atlantic region), while the opposite was observed for the shortfin mako, with lower mortality rates in the NE tropical area compared with the other regions. The results presented in this paper can be integrated into future ecological risk assessment analysis for pelagic elasmobranchs. Furthermore, the new information can be used to evaluate the impact of recent recommendations prohibiting the retention of some vulnerable elasmobranch species.

Otolith shape analyses were conducted on three different species of Mullidae (Mullus barbatus barbatus, M. b. ponticus and M. surmuletus). The otolith shape was described by 19 harmonics from elliptic Fourier descriptors. In a first step, their comparison through canonical discriminant analyses (CDA) was run for all fish with right otoliths, left otoliths and both otoliths pooled. The latter possibility had a higher discriminating power and allowed much more visually explicit results. This implied that the two otoliths were not similar as often claimed, and had each their specific information. In a second step, the CDA demonstrated strong spatial discrimination of local populations from various areas within the Mediterranean basin, i.e. NW Mediterranean, Aegean Sea and Black Sea, and between sites within each area. The percentage of well classified individuals of M. barbatus in predefined groups varied between 78 to 100% depending on sites, and even reached 100% for each site for M. surmuletus. These spatial patterns were most likely linked to differences in environmental conditions between areas and sites, such as effects of strong river runoffs and differences in depths and/or habitat types. In a third step, CDA also evidenced ontogenetic discriminations of mullet populations that could be linked (i) to influence of diet of fish of various sizes and (ii) to changes in physiological conditions according to the stage of development of the fish.

In this study, we compared the size selectivity of a T90 codend (netting turned by 90 degrees) with that of a standard codend made of similar netting. Sea trials were conducted in a Norway lobster directed fishery in the Kattegat-Skagerrak area, where there is a need for improved selectivity because of a severe discard problem. The codends were tested by fishing simultaneously with them in a twin trawl rig. Codend covers mounted with Minisamplers were used, which made it possible to catch individuals escaping during towing and haul-back separately. Herein we proposed a model to assess the sequential selection during towing and haul back. This model takes into account the parameter Ctow, which can be interpreted as the proportion of fish that comes into contact with the codend meshes during towing and, thereby, has a chance of escape. Compared to the standard codend, the T90 codend retained fewer Norway lobster both below and above the legal minimum landing size (40 mm, cephalothorax length), thereby causing a reduction of commercial catch. The difference was mainly due to a significantly higher escape rate during towing for the T90 codend. For plaice below minimum landing size (27 cm), the retention was slightly but significantly higher for the T90 codend compared to the standard codend. A model developed for both codends showed that not all plaice are able to attempt escapement during the towing process. For cod, the results indicated an increased L50 (the length at which 50% of this species is caught) for the T90 codend, but the effect was not statistically significant, probably due to the limited number of cod retained during the sea trials. The results demonstrated that, for all three species, a significant proportion did escape during haul-back in both codends.

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.

The survival of the highly endangered, anadromous fish species North Sea houting (Coregonus oxyrinchus) depends on the correct timing of downstream dispersal during its early ontogenetic stages. To date, however, no studies have investigated the ontogenetic differentiation of swimming performance and behaviour, including the potential of habitat complexity to influence dispersal rates. By testing larval and juvenile North Sea houting in a laboratory, we examined (1) swimming performance measured as maximum swimming performance (Umax) and routine swimming speed (Uroutine) and (2) the potential of habitat complexity (i.e., cover providing shade) to influence dispersal behaviour in an indoor stream channel. The Umax and the Uroutine were 9.4 and 4.6cm s-1, respectively, in the larvae [body length (BL) s-1: 7.3 and 3.5, respectively], and 25.2 and 16.3 cm s-1 in the juveniles (BL s-1: 7.0 and 5.2, respectively). We compared laboratory swimming performance data with water speeds in North Sea houting spawning areas in the Danish River Vidaa. Results showed that the water speeds present in 95% and 85% of the water column caused downstream displacement of larvae and juveniles, respectively. However, areas with slow-flowing water near river banks and river beds could function as nursery habitats. Stream channel experiments showed that cover providing shade caused delayed dispersal in both larvae and juveniles, but the larvae dispersed later and spent less time under cover than the juveniles, a finding that implies ontogenetic effects. Finally, the larvae refused to cross an upstream-positioned cover, a behaviour that was not observed in the juveniles. Therefore, habitat complexity may have the potential to influence dispersal behaviour in both larval and juvenile North Sea houting. Overall, we provided the first evidence of ontogenetic differentiation in the North Sea houting. These findings will be valuable for the development and dissemination of science-based conservation strategies.

Although many studies have been made on fish community changes in reservoirs, the diversity of situations means that general models are still difficult to construct. In order to be useful to managers, the information gathered in these studies must cover the regional taxonomic peculiarities. The inclusion of ecological strategies allows the detection of general patterns of fish community change. In the present study, multivariate analyses and non-parametric tests were used in order to detect relationships between ecological traits of 39 fish species and pelagic fish assemblages. We used gillnet captures of fish made in the Sinnamary River before filling of the Petit-Saut Reservoir and in the reservoir 8 years after closure of the dam and published data on fish species diet, life history parameters and morphology. Significant relationships were detected between fish assemblages and every ecological trait, which would have allowed the forecast of the type of species able to colonize the Petit-Saut Reservoir. Provided that the general characteristics of a river before damming are taken into account, it seems that feeding strategies can be used to predict future fish population and species changes on a general basis. Conversely, the lack of published data prevents definitive conclusions from being drawn concerning life-history and swimming strategies.

The knowledge of how fish survive and grow at different temperatures, and how these traits vary between life stages, is essential to evaluate the effects of climate change on wild fish and implement effective strategies in aquaculture. These issues are addressed in this study through a series of experiments that evaluate the effect of temperature (23–34 °C) on the embryos and larvae of clown loach, Chromobotia macracanthus. This species is endemic to the rivers of Sumatra and Borneo, highly praised on the ornamental fish market, and has been reproduced in captivity recently. No embryo survived a 24-h exposure to 34 °C until the age of 3 days after hatching (dah); mortality was high at 32 °C at 2 and 3 dah, whereas it was low and similar from 1 to 4 dah at 23–29 °C (<10%). Yolk absorption was proportional to water temperature (Q10°C of 1.69 in the 23–32 °C range), but fish reared at cold temperatures were larger than others at the start of exogenous feeding (5.7 vs. 5.5 mm TL, at 23 and 32 °C, respectively). The survival of larvae fed Artemia nauplii ad libitum was high at 23–32 °C (80–100%), but almost null at 34 °C. Growth models at different temperatures were produced from weekly measurements in two experiments, and tested by comparing their predictions with the results of a third experiment. Throughout the larval stage, the optimal temperature for growth (T°opt) was close to 29 °C, and departures from T°opt resulted in substantial growth penalties (–30% SGR for –5.1 °C and  + 3.1 °C). High survival, fast growth (0.7 mm day-1) and limited size dispersal at T°opt are encouraging perspectives for the aquaculture of clown loach. From an ecological perspective, the species has an atypical thermal biology, as it is less thermophilic than other tropical fishes, but more stenothermal than temperate fishes exhibiting similar values of T°opt , both traits being of particular concern in the context of global warming.

The present study investigates vertical distribution of fish size in three 12 m  ×  12 m wide and 14 m deep sea cages stocked with Atlantic salmon of average weight from 3.5 to 3.7 kg, at commercial densities between 15.6 to 16.2 kg m-3, in Norway. For each cage, individual fish weight were estimated by three 0.6 m  ×  0.6 m measuring frames as fish swam through. The frames were positioned at 3, 6 and 9 m depth. Recordings were carried out over five days per cage in succession, and during relatively stable environmental conditions in late autumn 2010. In all cages, measured fish were 15−25% smaller at 3 m compared to the average weights at 6 and 9 m depth. Largest average weight difference between depths within one cage was 0.995 kg. The average weight at 6 and 9 m was higher at night-time compared to daytime. Fish at the lower end of the weight spectrum were predominantly registered at 3 m, while fish at the higher end of the spectrum were mostly registered at the greater depths. Fish of average size were well represented at all three depths. The fact that smaller fish swam shallower may be ascribed to natural behavioural traits and introduce an important consideration in representative sampling within commercial sea cages. In biomass estimations and sea lice counts size-dependent vertical stratification needs to be accounted for.

In Amazonian fisheries, the silver arowana, Osteoglossum bicirrhosum (Cuvier 1829) is heavily exploited for human consumption as an adult, and for the aquarium trade as a small juvenile (yolk sac juvenile mainly). The periodicity of annuli formation on otoliths and growth variability of the silver arowana were studied in different river river-basins of the Peruvian Amazon between 2006 and 2009. Transverse stained sections of 606 individual otoliths were analysed from four different river-basins, the Amazonas, Ucayali, Napo and Putumayo, of which 554 could be interpreted. These belonged to 274 females ranging from 15 to 91 cm (standard length) and 280 males ranging from 30 to 91 cm. In addition, yolk sac juveniles of known age were collected to improve growth modelling. Monthly proportions of stained otolith edges validated the formation of a single annulus per year in two different river-basins with lagged hydrological cycles: the Amazonas-Ucayali and the Putumayo. Stained growth mark counts resulted in a longevity estimate of at least 16 years for the silver arowana in the Peruvian Amazon. This fish grew quickly during the first two years, and asymptotic growth was reached after four to five years, except in the Putumayo where it was reached slightly earlier. Results showed no significant growth dimorphism between sexes within basins, but indicated significant growth differences among river basins. Silver arowanas measured, on average, between 38 and 40 cm at the end of their first year. Length-at-age differences among river basins increased with age to reach over 14 cm (and >3 kg) after 7 years between the faster and slower growing populations (Amazonas and Putumayo, respectively). The growth differences observed emphasize the need for further investigation on the population structure of this species as, although these differences might merely be phenotypic responses to contrasted environmental conditions, they could alternatively reflect the existence of several populations with distinct genetic and life history characteristics. The consequences of such differences would be very important for the management and conservation of this fragile and extensively exploited species.

Virtual population analysis requires information on the fishing mortality rate (or abundance) for one age group from each cohort. In many cases available data are insufficient to estimate these rates for every age group and structural assumptions must be imposed to reduce the number of effective parameters. Past assessments of western Atlantic bluefin tuna (Thunnus thynnus) have reduced the number of parameters by assuming pre-specified values for the ratios of the fishing mortality rates on adjacent age groups. More recent bluefin tuna assessments have estimated terminal fishing mortality rates (F) on each age with a constraint that restricts change from one year to the next. We explore the implications of these methods of estimating terminal-year F through retrospective analyses of the 2006 bluefin tuna assessment and through stochastic simulations. The use of pre-specified ratios for F created strong retrospective biases and may have led to overly optimistic projections. Constraining annual changes in the terminal-year F appeared to mute retrospective patterns and resulted in abundance projections less prone to spurious initial leaps. Simulation results indicate that the constraint improves estimation, particularly with moderate to low interannual changes in selectivity.

Among other applications, self-feeding has been used to study food preferences in fish allowing them to choose between feeders with different food content. Preference tests assume that (i) trigger actuations are motivated by appetite, (ii) fish can learn which feeder contains which food and discriminate between feeders solely on the basis of their content, and (iii) in groups of fish, the triggering preferences is representative for the individuals of the group. We studied individual triggering behaviour in four groups of 14 Atlantic cod (length of 34  ±  2 cm, weight of 424  ±  102 g, mean  ±  SE, water temperature comprised between 7–8 °C) that were first given the choice between two self-feeders with identical content (Period 1 of 14 days) and subsequently with one feeder full and the other empty (Period 2 of 14 days) . In all four groups, one or two individuals performed the majority of the actuations, and in three groups the high triggering fish was a female high-ranked for size and growth rate. Cod displayed a preference for one of the two feeders despite their identical content. When the preferred feeder was emptied, the preference switched after one to eight days but both feeders were still actuated throughout the experiment. In conclusion, the assumption that actuation frequency reflects food preference and is representative for the individuals of the group may not be true, at least for Atlantic cod. If aiming at determining preferences representative for the whole population multiple representative fish should be kept isolated in separate tanks, with self-feeders containing each food option, on each tank.