Selective fishing pressure on more highly valued marine living resources is one of the key factors proposed to explain changes occurring in fish communities and associated landings of commercial fisheries. The aim of this paper is to establish the nature of changes in the landings of French fishing fleets operating in the Bay of Biscay in the period 1973-2002, and whether these changes could be related to the relative economic attractiveness of different fish species. The analysis focuses on trends observed in the landings of all commercial fish species over the last three decades. It is based on data of annual quantities landed and ex-vessel prices compiled from official French landings records, and on bio-geographical descriptors of these species derived from published data. Using simple index numbers and multivariate analysis, we examined changes in total landings in terms of their volume and value, as well as changes in their composition. We show that the composition of landings significantly changed over the study period, with an increase in the proportion of pelagic species, of lower economic value. The average ex-vessel price of production by the fleets tended to decrease from the late 1980s; partly due to a cross-species drop in prices, occurring mainly after 1993, but also to the increased proportion of low-priced species in the landings. This caused a significant drop in the total gross value of production in the second half of the study period.

Hatchery produced pearl oyster spat are generally transferred to the ocean on spat collectors which may, or may not, be covered with fine mesh to prevent spat loss. This study examined the effectiveness of mesh bag covers on culture units for spat of the blacklip pearl oyster, Pinctada margaritifera. It assessed spat retention and growth in culture units without mesh bags (REMOVE) and in those where mesh bags were replaced weekly (REPLACE), washed weekly (WASH) or left unwashed (NO WASH) for the duration of the six-week experiment. Culture units in the REPLACE treatment had the greatest number of spat at the end of the experiment and 41% more spat than in the REMOVE treatment. Grading of the spat from each treatment at the end of the experiment showed that the REPLACE treatment had the highest number of spat in large and medium size classes with mean (± SE) dorso-ventral height of 23.9 ± 0.5 mm and 17.4 ± 0.5 mm, respectively. Mean wet weight of the mesh bags at the end of the experiment differed between treatments with bags from the WASH and NO WASH treatments having significantly greater mean wet weights than those from the REPLACE treatment. The results show that the presence of a mesh bag around spat culture units may improve retention of spat by between 18–41%. However, protective mesh bags may foul quickly and, to maximise retention and spat growth, weekly replacement of mesh bags should be undertaken.

The degree to which larvae of the invasive American slipper limpet (Crepidula fornicata) and the Japanese oyster (Crassostrea gigas) may compete for food was examined during 2003 in the laboratory. Larval microalgae uptake, growth and mortality were compared for larvae fed each of six species of unicellular algae, ranging in length from 2 to 10 µm. Tested diets included the two flagellates Tetraselmis chui (Prasinophyceae) and Isochrysis affinis galbana (T-ISO, Haptophyceae), one member of the Chlorophyceae (Nannochloris atomus), and three diatom species (Chaetoceros calcitrans forma pumilum, Chaetoceros gracilis, Skeletonema marinoï). We found that the limpet larvae ingested phytoplankton over a wider range of cell sizes and ate at higher rates on each diet than did the oyster larvae. For example, oyster larvae consumed 2216 cells h−1 of N. atomus, while limpet larvae consumed the same phytoplankton cells at approximately twice that rate, 5159 cells h−1, on the same diet. Larvae of both species grew more quickly on a mixture of flagellates than on any of the diatom alone (12 versus 7 µm d−1 for oyster larvae and 41 versus 28 µm d−1 for limpet larvae). Our results suggest that in the Bay of Mount Saint-Michel (France, Western Channel), where larvae of both species co-exist in the summer, intensive grazing by limpet larvae can potentially deplete phytoplankton concentrations to cause competition with oyster larvae, particularly for smaller sized phytoplankton species.

Sampling efficiency (p), estimated from the Zippin depletion model and the percentage of fish obtained during first runs (single-pass electrofishing), which is also named relative abundance (C1), calculated as the ratio of C1 to estimated density for a site (Ce), were analysed in five contiguous sites in a small lowland stream in Poland over 23 years. The sampled reach was unregulated during the first decade of the study period, but regulated by weirs and sluices in the latter 13 years. The sites were populated with 17 fish species during this period. Sampling efficiency p calculated for all species did not differ significantly between the five sites in any given year, between benthic and non-benthic species, or between the natural and regulated periods. Differences in p were only observed between some species. C1 differed significantly between large and small species and, except for roach, was not dependent on the number of runs. Results indicate a high stability of both sampling indices in this small stream, despite changes in channel morphology after regulation: information which could be useful for future sampling research in streams.

The effects of osmolality and accidental urine contamination on spermatozoa velocity and motility were studied, combined with an examination of the biological characteristics of stripped and testicular sperm. Analysis of Northern pike sperm showed higher ionic concentrations of Na+ (123 ± 9 mM), Cl- (127 ± 7 mM), and K+ (35 ± 5 mM) in the seminal fluid of testicular sperm (TS), than in that of stripped sperm (SS): Na+ (116 ± 9 mM), Cl− (116 ± 7 mM) and K+ (25 ± 4 mM). Highest osmolality of seminal fluid was observed in TS with a value of 358 ± 77 mOsmol kg−1 compared with 273 ± 21 mOsmol kg−1 for SS and 68 ± 36 mOsmol kg−1 for urine. A significantly higher spermatozoa concentration was observed in TS (34 ± 5 × 109 ml−1) than in SS (23 ± 4 × 109 ml−1). Spermatozoa concentration per male and per kg body weight was 22 ± 17 × 109 for TS and 18 ± 2 × 109 for SS, respectively. Both TS and SS showed significantly higher spermatozoa velocities and motilities after dilution in urine than after dillusion in distilled water during the activity period. In conclusion, the results obtained from the present study provide information on northern pike sperm physiology that be used to improve sperm management efficiency for this species.

This study aims to evaluate the health status of Bizerta lagoon using a sentinel species, the Neogastropod Murex trunculus. Trace metal concentrations (Cd, Cu and Zn) in the foot and digestive gland, and biomarkers such as acetylcholinesterase (AChE), catalase (CAT) and glutathione transferase (GST) activities in the digestive gland, were determined in samples collected at four sites at different periods of the year. One site, in the North of the lagoon, is influenced by urban and industrial waste waters. Another, to the south, is located at the outfall of Ichkeul Lake. A third site is one that may be impacted by eutrophication processes, and the last, in the center of lagoon, is considered as less polluted. Temperature and salinity were simultaneously measured during the mollusc samplings. They varied greatly, from 13.5 °C and 30 psu in February to much higher values in summer-autumn: 30.7 °C and 37 psu. Metal concentrations were always higher in the digestive gland than in the foot. In the digestive gland, the lowest Cd and Cu concentrations were found in the center of the lagoon (mean ± standard deviation: 9.35 ± 0.78 µg Cd g−1 and 84.5 ± 15.3 µg Cu g−1) and no significant Zn variations were noted (682± 38 µg g−1) between sites. Metal concentrations in both types of tissue were higher in winter than in summer. AChE varied significantly among sites with high activities for individuals in the center of lagoon (15.4 ± 0.3 nmol min−1 mg-1 protein), whereas GST were low (12.2 ± 0.8 nmol min−1 mg−1 protein); CAT activities were low in this site 8.7 ± 0.5 µmol min-1 mg-1 protein. Season also had an influence on biomarkers, with low AChE in winter and rather low CAT and GST in summer. Principal component analysis showed that the center of lagoon can be considered as a reference site, whereas high chemical and biochemical responses were found in M. trunculus from other sites; particularly at the site which may be subject to eutrophication.

The present paper analyzes data collected between 2001 and 2002 on 81 reef fish species targeted by fishers at 5 sites in the Kingdom of Tonga (South Pacific). We first ranked the sites with respect to fishing pressure using two independent methods: (i) Tongan demography and reef surfaces available for fishing, and (ii) the differential effects of fishing on the whole set of 81 species grouped by their life history traits (LHT). We then focused on Parrotfish (Scaridae), which are heavily targeted in coral reef fisheries. We used the identified gradient of fishing pressure to study the effect of fishing on the community structure and test the hypothesis of “shifting dominance” amongst the 20 Scarid species present in the surveys. In addition to the classical effect of decreasing fish size in a family strongly targeted by fishers, the shifting dominance phenomenon includes a decrease in the abundance of the large-bodied and highly targeted species, favouring their replacement by smaller-bodied species from the same family, which are less impacted by fishing. In a context of interspecific competition amongst Scarids, the stress of fishing appears as a factor favouring the replacement of species with large maximum size, and LHT promoting low resilience, by smaller species with the opposite attributes. The discussion focuses on the various processes that can explain the shifting dominance phenomenon. The total density of resilient species, which increased along the gradient of increasing fishing pressure, can be used as an indicator of the over-exploitation of fish communities for reef fisheries management.