The ichthyoplankton of Galway Bay was sampled over the spring and summer of 2007 and 2008 to determine what environmental factors influenced the distribution of larval and early juvenile fish. A total of 549 fish representing 27 taxa were caught. Catches decreased throughout each sampling season, and were generally poor in 2007. Catches were numerically dominated by sprat (Sprattus sprattus), dab (Limanda limanda), sand eel (Hyperoplus immaculatus) and whiting (Merlangius merlangus). Environmental factors driving distribution of fish were modelled using a binomial generalized linear model. The strength and direction of wind in the five days preceding sampling was the only significant environmental factor. Sustained onshore winds increased the probability of encountering larval fish in the areas sampled. The rainfall, tidal state, tow depth and wind conditions during sampling were not significant. Among the parameters measured it appears that onshore winds sufficiently strong to overcome the residual circulation are the main physical driver for the distribution of larval fish in Galway Bay.

In order to assess the effect of feeding deprivation on growth and condition of field-caught newly settled juvenile plaice Pleuronectes platessa, a 3 week starvation experiment was conducted and changes in RNA/DNA ratio, Fulton's K condition index and recent otolith growth were measured. Fed ad libitum and starved fish were analysed after 0, 1, 2, 3, 4, 5, 7, 9, 14, 16 and 22 days of starvation. In parallel, field newly settled juvenile plaice were collected weekly over the settlement period (between April and May 2005) in the adjacent intertidal zone of the Canche estuary (eastern English Channel, France) and fish performances were estimated. After starvation day 4, Fulton's K condition index and RNA/DNA ratio of juvenile plaice significantly differed between treatments while recent otolith growth differed between treatments after day 9 of the experiment procedure. Results indicate that the three biological parameters are sensitive indices and can be used to accurately assess nutritional condition of wild juvenile fish. Values of 0.32 for RNA/DNA, 0.83 mg. mm−3 for Fulton's K index, and 3.99 µm for recent otolith daily growth were defined as critical threshold values below which juvenile plaice can be classified as ‘starving'. When comparing these experimental values with those from field-caught newly settled juvenile plaice, less than 1% of wild individuals can be classified as ‘starving' whatever the index. Our results suggest that feeding conditions throughout the settlement period on the Canche intertidal nursery ground are favourable to juvenile plaice development and survival, and hence to the recruitment success.

This paper presents results of a study conducted on the trawling industrial fishery fleet of Merluccius gayi in south-central Chile, and the resulting interactions with the South American sea lion (Otaria flavescens). This study is based on observations made during September 2004, when incidental sea lion catch in the trawls was 6.3 sea lions/working day (1.2 sea lions/trawl−1). A total of 82 animals were incidentally caught, of which 12 were found dead, and the 70 remaining suffered from internal bleeding and/or fractures as a result of their capture. 83.3% of the fatalities occurred during nocturnal trawls, which comprise 30% of all observed trawls. Possible mechanisms of sea lion take are discussed. This note presents the first records of sea lions incidental by-catch by the trawler fleet along the south-east Pacific coast of Chile.

Bottom trawling is a large-scale fishing activity along the Brazilian coast, but its effects on benthic infauna are still poorly known. This is the first experimental evaluation of benthic responses to bottom trawling along the Brazilian coast. We tested the effects of trawling on macroinfaunal assemblages on the inner continental shelf off Paraná (southern Brazil) by using a sampling design with adjacent trawl and control areas. We hypothesized that if trawl fishing has a negative effect then we should expect lower numbers of species and lower benthic densities after an experimental trawling. Sampling was conducted at adjacent sites within each area to minimize confounding due to spatial variation. Five sites were sampled at a control, and five at an experimental area for infaunal and sedimentological variables. Sampling was carried out just before and one hour after experimental trawling. Multidimensional scaling followed by a PERMANOVA did not show any clear variation tendencies in the structure of the benthic assemblages in the impacted area before and after trawling. However, variance analysis showed a significant and unexpected increase in infaunal total density, in the density of the numerically dominant species (except for the polychaetes Capitella sp. and Loandalia tricuspis) and in species richness in the experimental area. Conversely, no significant variations were recorded in the control area. We suggest that the overall increase in benthic density after a disturbance is correlated with the reworking of the sediment matrix and benefits the suspension-feeders after sediment resuspension.

The ectoparasite community of the blackspot seabream, Pagellus bogaraveo, was studied in different locations in Portuguese waters of the north-east Atlantic Ocean. This is the first study to focus on the ectoparasites of this commercially important sparid fish. Nine ectoparasite species were detected. Gnathia sp., Aega deshaysiana, A. antillensis, Rocinela danmoniensis and Argulus sp. are reported for the first time on this host. Significant differences were detected among the sampling locations, with monogeneans being more prevalent in mainland waters, and crustaceans being more prevalent in the Atlantic islands of Madeira and Azores. Fish from Madeira showed significantly higher infection levels of all ectoparasites, especially crustaceans, and particularly high prevalence of Hatschekia pagellibogneravei. The potential impact of the species detected on captive fish is also discussed, since the blackspot seabream is a promising new species for marine aquaculture.

The phenotypic shell shape variation of Mactra isabelleana was tested using the geometric morphometric method. Four localities were sampled along the Río de la Plata estuary and the coast of Buenos Aires province. Principal component analysis and canonical variates analysis of the first principal components were performed to reveal the shell variation and differences among localities, respectively. The specimens from different microhabitats mostly overlapped, although differences in shape were observed in the development of the umbo, the enlargement of the dorsoventral axes and the elongation of the posterior end. The ecological and physical parameters that could influence shell shape variation are discussed.

Oyster population reproductive capacity and dynamics are controlled at the most basic level by the observed sex-ratios. Since oysters are sequential, protandric hermaphrodites the population sex-ratio is related to the demographics (shell length, age, and biomass). Oysters were collected from June through to August 2008 at twelve bars in the James, Rappahannock and Great Wicomico Rivers, Virginia, USA. Bars were aggregated into five groups on the basis of similar age–length relationships. Sex-ratios (fraction female), age–length, and biomass–length relationships were determined for each group. The fraction female increased within increasing shell length, age, and biomass at all sites. Simultaneous hermaphrodites were rarely observed. Group specific differences in shell length (SL, mm) and age (yr) for the timing of the protandric shift were observed with the earliest shift from male to female occurring at ~60 mm SL and ~1.6 yr. The proportion of females observed in the larger or older individuals was at least 70–80%. Sex-ratios from summer 2008 were used to develop sex–length, sex–age, and sex–biomass keys that were applied to autumn-survey data from 2006, 2007, 2008 and 2009. In these years, sex-ratios by shell length and age were strongly biased towards males while the sex-ratio by biomass was strongly biased towards females. Disease mortality compounds natural and fishing mortality resulting in age/size specific cropping yielding truncated population demographics and an earlier protandric shift in populations on the extremes of the range examined. Regardless of location, market (>76 mm SL) oysters are predominantly female.

Protandric oysters generate a relatively uniform reproductive potential over a wide range of environmental conditions that impose variations in growth rate and life span. Sex-at-length keys applied to survey data show that the female fraction routinely fell between 0.4 and 0.5, regardless of location in the salinity gradient. About 70% of population biomass is female over the same salinity range. Due to the necessary local modulation of the rate of male-to-female conversion to limit the influence of varying growth and life span over the salinity gradient, the number of males always exceeds by a small amount the number of females; thus improving the likelihood of a female having neighbouring males, a necessity for an immobile broadcast spawner. However, oysters at the extremes of the estuarine gradient all yielded populations with divergent sex-ratios. One consequence of reduced generation time brought about by increased mortality from disease should be selection favouring the switch from male to female at smaller size, if disease mortality is strongly female-biased. The site with the longest record of high mortality manifests such an increase. Sites up coastal rivers, putative refuges from disease, harbour animals with the slowest male-to-female conversion rates. Arguably these animals are most similar to the ancestral oyster pre-disease. Marketed animals range from 62% to 69% female. The principal influence of the fishery, and of oyster disease, would seem to be a reduction in lifetime egg production. Dermo disease may have reduced lifetime fecundity of females by nearly a factor of four.

Age structure and hatchling dates of the squid Illex argentinus collected by bottom-trawl fishery in southern Brazilian waters were assessed by the analysis of statolith growth increments. Catches occurred between 2001 and 2002, from 23° to 32°S at depths of 100–700 m. Squid from juvenile to post-spawning stages were collected year round, with age estimated from 98 to 320 days and mantle lengths ranging from 112 to 376 mm. Duration of life cycle events based on statolith growth zones revealed that squids can spend about 14% of their lifespan as paralarva (~30 days), 70% as juvenile (~130 days), leaving maturity and spawning condition to the terminal 10–20% (~30–60 days). The results suggest that, unlike estimates available for Patagonian populations, a general 0.5 year lifespan is predicted for I. argentinus off Brazil. The wide range of size-at-ages implied that catches of shortfin squid off southern Brazil probably include squid hatched throughout the year. Mature and spawning squid caught in summer months hatched in winter and spring, while winter catches revealed mature-spawning individuals hatched both in summer/autumn (~6 months of age) and winter/spring periods (~10–11 months of age). It has been argued that such groups may combine both squid resident of Brazilian outer shelf and slope (22°–34°S) with a six months' lifespan and migrating squid originated from the northern Patagonian shelf (~42°S) with 10–11 months' lifespan.

Based on the samples collected in Chinese scientific surveys off the Costa Rica Dome from July to August in 2009, statolith microstructure of the jumbo flying squid, Dosidicus gigas, was analysed for studying their age, growth and population structure. Three typical growth zones (postnuclear, dark and peripheral zones), abnormal increments (checks) and aberrant microstructure (additional centre and additional rings) were found in the statoliths examined. Squid sizes ranged from 205 to 429 mm dorsal mantle length (ML) with ages no more than 10 months for females and 8 months for males. Back-calculated hatching dates were from November 2008 to April 2009. Growth in ML was best described by a linear function for both the sexes, while growth in body weight was best quantified by an exponential function for females and a power curve for males. The maximum absolute daily growth rates and instantaneous growth rate in ML were reached during 181–210 and 151–180 days for females and males, respectively. The Costa Rica Dome and its adjacent waters were considered as a potential spawning ground because of presence of not only high proportion of mature squid but also rhynchoteuthion paralarvae, and high primary productivity from the strong upwelling. This study suggests that D. gigas have complicated intra-specific population structure and large spatial variability in the key life history parameters.