The elimination of unwanted catch in mixed species fisheries is technically challenging given the complexity of fish behaviour within nets. Most approaches to date have employed technologies that modify the nets themselves or use physical sorting grids within the gear. There is currently increasing interest in the use of artificial light to either deter fish from entering the net, or to enhance their escapement from within the net. Here, we evaluated the differences in catch retained in a standard otter trawl, relative to the same gear fitted with a square mesh panel, or a square mesh panel fitted with LEDs. We found that the selectivity of the gear differed depending on water depth. When using a square mesh panel in shallow depths of 29–40 m the unwanted bycatch of whiting and haddock was reduced by 86% and 58% respectively. In deep, darker water (45–95 m), no change in catch was observed in the square-mesh panel treatment, however when LEDs were added to the square-mesh panel, haddock and flatfish catches were reduced by 47% and 25% respectively. These findings demonstrate the potential to improve the performance of bycatch reduction devices through the addition of light devices to enhance selectivity. The results also highlight species-specific and site-specific differences in the performance of bycatch reduction devices, and hence a more adaptive approach to reduce bycatch is probably required to maximize performance.

In 1985, Dashidaira Dam, equipped with a flushing gate, was built on the Kurobe River in Toyama, Japan. Since the dam sediments were first flushed out in December 1991, benthic fish counts have decreased year by year due to repeated flushing of clay-rich dam sediments.

In June 2001, the flushed dam water contained a low oxygen concentration (1 to 2 mg/l) and high concentrations of smectite and vermiculite. To establish the cause of the death of the benthic fish, living flatfish were collected from Toyama Bay in order to examine their gills, which showed tissue damage and chemical changes caused by adherent expandable clays, derived from the flushed dam sediments. For comparison, exposure experiments on rainbow trout were carried out using smectite suspensions. Examination by optical microscopy revealed that the gills had shrunk because of the smectite concentrations. Low oxygen concentrations and large amounts of expanding clays have a significant effect on downstream benthic life.

Beach ecosystems extend from dune to offshore areas along most coasts, and provide essential services that are not provided by any other ecosystem. Indeed, sandy systems contain unique biodiversity and supply nursery and foraging areas for numerous commercially important marine species, such as flatfish. However, these systems are threatened by increasing anthropogenic pressure. Green tides (GT, i.e. accumulations of green opportunistic macroalgae) are a major human-induced threat to marine ecosystems, from inshore to nearshore. This eutrophication process greatly affects both benthic invertebrate communities and flatfish communities, within sheltered and non- or microtidal systems. However, the responses of dynamic open macrotidal sandy systems to eutrophication in the form of macroalgal mats are not yet fully understood. In particular, understanding the effects of GT on two connected biological compartments (infauna and flatfish) within two connected habitats (intertidal and subtidal) is crucial. Here, we set out to assess the influence of several environmental variables, including Ulva biomass, on the variability in infauna and flatfish communities in both the intertidal and the subtidal at four sites impacted or not by GT. In total, 110 biodiversity samples were analysed with classic and novel analytical approaches. Our results demonstrate that the presence of GT specifically impacts intertidal macroinvertebrate communities. However, small effects of GT on subtidal infauna communities, as well as on species-specific flatfish at both intertidal and subtidal, were still detectable. Our findings underline the vulnerability of highly dynamic ecosystems exposed to anthropogenic stress, in particular intertidal sandy shores.

The genus Achirus is made up of demersal fish that have a close relationship with the substrate and exhibit peculiar aspects during their larval stage. The aim of the present study was to determine whether the abundance of Achirus larvae differed among a set of habitats in the estuary of the Formoso River in the State of Pernambuco (north-eastern Brazil). Sampling was performed monthly between April 2009 and March 2010, and comprised horizontal hauls with plankton net during the day and night in mangrove, beach and reef habitats. Fish larvae were sorted, identified, measured and larval stage recorded. Density and body length values were used in a non-parametric analysis of variance for the determination of variations between seasons, habitats and diel periods. A total of 204 larvae were collected, with an average density of 2.1 larvae.100 m−3. Density was greater in the nocturnal samplings, with no differences found between habitats. The larvae occurred in the yolk-sac to post-flexion stage, with pre-flexion the most abundant stage (78%). Size segregation was observed. Larger larvae were captured at night and in the mangrove. The smallest larvae were caught on the reef, with length increasing toward the mangrove. The results indicate that Achirus larvae come from deeper regions near reefs, where spawning probably occurs, and perform ontogenetic migration towards the shallow waters of mangrove, where they settle.

Flatfishes represent an important resource in Portuguese fisheries. Although flatfish landings represent a low percentage of total fish weight landed, their importance is higher when commercial value is considered (11%). Official data on flatfish landings from 1992 to 2005 for all landing ports in Portugal were analysed, together with vessel characteristics, in order to detect patterns in flatfish fisheries. Fleet characteristics were heterogeneous, but most of the vessels were multi-gear. Three landing profiles were identified in the flatfish fishery, and the target species of these métiers showed variation in space and in time. Small vessels caught species that occur in coastal areas, mainly soles, bastard sole, flounder, turbot and brill, and usually also presented high landings of octopuses, cuttlefish and rays. Megrims and spotted flounder were caught with others species, like small pelagic fishes and seabreams by coastal trawlers. For this fleet component, catches of flatfish were usually bycatch. Generalized Linear Models (GLM) were used to analyse flatfish landings (LPUE, landings per unit effort and landings in terms of value) between 1992 and 2005 and to evaluate their relationships with several variables. The main effects in the models included year, month, landing port, vessel length class and total landings (kg). The models explained between 15% and 60% of the variability of the LPUE, and 46% to 82% of the variability of landing value, for the flatfish groups considered, with the most important factors being landing port, vessel length class, month, total landing (kg) and landing port: vessel length interaction. These results suggest high spatial and temporal variability. The results of this study may have implications for fishery management, because the LPUE was highest during the important periods of flatfish life cycles, like the spawning season. This fishing pattern has a negative impact on the stocks because of increased fishing pressure during a sensitive period for these species. The adoption of spatial and temporal closures should be implemented.

The extent to which host biology, ecology and phylogeny determine the diversity of macroparasite assemblages has been investigated in recent years in several taxa, including fish. However, consensus has not been reached probably as a result of data being collected from different sources, different temporal scales or host and parasite biogeography and phylogeny having greater influence than expected. The present study evaluates the relative importance of 27 biological, ecological and phylogenetic characteristics of 14 flatfish species on the diversity of their ecto- and endoparasite assemblages, comprising a total of 53 taxa. Redundancy analyses were applied to the mean abundance of each parasite taxa infecting each host and to the richness, taxonomic distinctness and variance in taxonomic distinctness calculated for each assemblage within each host. Only a few host characteristics contributed significantly to the observed patterns: host distribution was more important in determining the type and mean abundance of ectoparasites present in an assemblage, whereas diversity of these assemblages were mainly related to the host's maximum size. Endoparasite mean abundance and diversity were mostly influenced by the number of food items ingested and by the presence of Crustacea and Polychaeta in the diet. However, the sympatric occurrence of related hosts also played an important role in the diversity values found in macroparasite assemblages. Results showed that a host characteristic has different importance according to the host-parasite relationship being examined, suggesting an important role for host-parasite co-evolution on the diversity of extant macroparasite assemblages.

Common sole, Solea solea and Senegalese sole, S. senegalensis, were collected between January 2003 and June 2005 from commercial fishing vessels operating with gill-nets and bottom trawls along the Portuguese coast, to examine diet, age and growth and reproduction. Soles fed mainly on crustaceans, polychaetes and bivalves. Feeding activity was highest in summer, for males and for the largest individuals. Significant differences were found between the proportion of prey items according to season, sex and size-class. Common sole presented a wider dietary breadth compared to Senegalese sole. Dietary overlap between the two species was higher for the winter period and for females. Age of soles was determined from sagittae otoliths readings. The length of fish analysed varied between 187 mm and 462 mm (oldest fish 9 years), for S. solea, and between 199 mm and 472 mm (oldest fish 8 years), for S. senegalensis. The von Bertalanffy growth equation coefficients differed between sexes. For both species, the asymptotic length L∞ and growth coefficient k obtained for females were higher compared to those estimated for males. The highest values of the gonadosomatic index were obtained for the winter period, when the highest proportion of individuals at spawning stage was recorded.

Macroparasites are generally aggregated within their hosts with infection and aggregation levels resulting from a continuous arms race between maintaining high mating probability and host mortality low for which host and environmentally related factors contribute to some extent. Here, infection and aggregation patterns of the macroendoparasites infecting the flatfish Citharus linguatula, Arnoglossus laterna, Lepidorhombus boscii, Scophthalmus rhombus and Platichthys flesus in 3 areas along the Portuguese coast were analysed. Of the 21 macroendoparasite species found only 1 infected all hosts and most were host or area exclusive. For each host-parasite system, values of the indices varied between areas and macroendoparasites were not always aggregated; in fact, some macroendoparasites were generally uniformly distributed, which can be related to specific density-dependent regulation mechanisms. No general pattern was found for infection or aggregation levels of the 3 species infecting more than 2 hosts along the Portuguese coast, i.e. Lecithochirium rufoviride, Nybelinia lingualis and Anisakis simplex s.l., suggesting that regulation mechanisms are not species specific but are locally determined, with host ecology playing a significant role.

Ecological information on the polychaete community may improve habitat descriptions and distribution models of commercially important species that are polychaete-feeders. This study reports on the first new observations in nearly three decades on the polychaete assemblages in the south-eastern Bering Sea. This information was used in an exploratory assessment of the association between polychaete assemblages and environmental variables that define the benthic habitat. The spatial association between polychaete assemblages and groundfish predators was also explored for insight into whether prey assemblages influence predator distribution. Canonical correspondence analysis indicates that surficial sediment is the most important factor in organizing polychaete assemblages, over other common environmental variables such as depth and temperature. Co-correspondence analysis of the distributions of groundfish species and polychaete families does not indicate that predators are associated with specific prey families. Families that are most frequent in stomach contents of some of the fish in the analysis, mainly Maldanidae and Nephtyidae, are widely distributed across the Bering Sea shelf in diverse sediment types, as are the principal polychaete-feeders in the eastern Bering Sea such as Alaska plaice (Pleuronectes quadrituberculatus) and northern rock sole (Lepidopsetta polyxystra).

Spontaneous swimming activity of O-group common sole (Solea solea) was evaluated using a video-tracking system under laboratory conditions. An experiment was conducted during two consecutive days on individuals sampled in June, July, September and November (2004) in a coastal nursery ground (Pertuis Charentais, Bay of Biscay, France). The measured behavioural variables were: distance travelled and frequency of occurrence of burying, swimming and immobility. O-group sole showed a relatively clear circadian activity in line with the artificial light conditions (day, twilight and night). Swimming activity of O-group sole decreased drastically from June to July, thereafter remaining at a very low level in September and November. Such important changes reflect the transition between the exploratory behaviour of the post-colonization period and a well established sedentary behaviour remaining until the onset of winter. These results highlight the potential limitation in habitat use capacities of O-group sole once settled in coastal nursery grounds.

Over the last few years, several aspects of Senegalese sole (Solea senegalensis) culture have been developed and optimised but the dietary lipid level for optimal growth has never been determined. Hence, five isonitrogenous diets (56 % dietary protein) with increasing dietary lipid levels (4, 8, 12, 16 and 20 % DM) were fed to satiation to triplicate groups of twenty fish (mean initial weight 10 g). Fifteen tanks were randomly assigned one of the five diets. Feed was distributed using automatic feeders, and fish were fed over a 16-week period. At the end of the experiment the fish fed on diets containing the two lowest dietary lipid levels (4 and 8 %) showed a 3-fold body-weight increase with a significantly higher daily growth index than fish fed higher lipid levels (1·2 v. 0·8). Moreover, these fish displayed a significantly lower dry feed intake (12 g/kg per d) and feed conversion ratio (1·0) compared with fish fed higher lipids levels (16–19 g/kg per d; feed conversion ratio 2·0). Low dietary lipid levels ( < 12 %) significantly improved nutrient retention and gain and hence growth, without major effects on whole-body composition. Despite the slight alteration in n-3 PUFA muscle content in the fish fed low-fat-diets, this fish fed low dietary lipid still remains a rich n-3 PUFA product and generally maintained its nutritional value. These results evidenced a low lipid tolerance of Senegalese sole juveniles and suggest a maximal dietary inclusion level of 8 % lipids for both optimal growth and nutrient utilisation without compromising flesh quality.

Sand sole, Solea lascaris, were collected along the Portuguese coast, between October 2002 and July 2003, to examine feeding habits, age and growth and sexual cycle. The most important prey items were Mysidacea, Amphipoda and Polychaeta. Differences in diet according to season and length size were found: Amphipoda were very important in diet during winter, while Echinodermata were consumed mostly in summer; smaller individuals feed on Amphipoda while larger feed on Decapoda. Age of S. lascaris was determined from sagittae otoliths. The length of fish analysed ranged from 61 mm to 340 mm. The von Bertalanffy growth equation parameters differed significantly between sexes (L∞ = 342.3 mm, k = 0.50, t0 = −0.87 and L∞ = 264.5 mm, k = 0.82, t0 = 0.13, females and males, respectively). The highest values of the gonadosomatic index were obtained in winter and spring, when the highest proportion of individuals at spawning stage was recorded.

Tidal embayments in the Bay of Biscay (France) host nursery grounds where common sole, Solea solea, is the most abundant flatfish species. This study aimed to appraise the way those habitats function as nurseries through juvenile sole's responses in somatic growth and condition (Fulton's K) during their first year of occupancy. Field data, two yearly trawling series, taken monthly, were compared with a 6-month-long mesocosm experiment involving reared fish of the same wild origin. Growth rates were compared with predicted maximum growth according to an experimentally established model in relation to temperature. In the field, 0-group sole total length (TL) averaged 130 mm from September onwards in 1999 and 2000. Mean growth rates were 0.7–0.9 mm day−1 in summer and ≤ 0.1 mm day−1 in autumn, when the model predicted 1.4 and 0.9 mm day−1, respectively. In the mesocosm, the growth rates were 0.9 and 0.4 mm day−1 for the same seasons and for stocking densities (300 fish 1000 m−2) about 10 times higher than usually recorded in the field. Wild sole remained in medium condition (K ca. 1 g cm−3) during the entire growing season, whereas they attained a higher K after being released into the mesocosm (1.2–1.3 g cm−3). During the mesocosm experiment, growth was shown to be primarily temperature-controlled: fish reached 150–160 mm (TL) in November. From this investigation, it can be concluded that sole's responses in condition and growth are altered over the whole growing season on nursery grounds. The situation is exacerbated in autumn when the sum of abiotic constraints increases as the competitive biomass does. This indicates impairment of the nursery functioning which, in the context of fish habitat conservation, emphasises the particular vulnerability of embayments to the addition of any further constraint.