Atlantic herring (Clupea harengus)in the offshore regions of the Gulf of Maine migrate each fall fromtheir feeding grounds to the northern portion of Georges Bank tospawn.The Northeast Fisheries Science Center’s (NEFSC) herringacoustic survey has taken advantage of this behavior by conductingsystematic surveys of the pre-spawning fish each year since 1999.Multi-frequency acoustic and midwater trawl data were collectedalong 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 temporaldistribution) of Atlantic herring during these surveys and regressiontrees were used to examine the aggregation characteristics. Thepositional variables of distance to spawning grounds and verticallocation in the water column were the primary characteristics fordescribing pre-spawning aggregations. Secondary to these were thetemporal variables of diel and survey timing, and the morphological characteristicof aggregation area. Lower numbers of aggregations were observedclose to the herring spawning grounds but with higher acoustic energythan larger numbers of aggregations observed further from the spawninggrounds but smaller in size and lower in acoustic energy. Most aggregationswere in the lower portion of the water column, but those that werein the upper portion of the water column had higher acoustic energy.Consistently throughout the decade, 90% or more of herring aggregationswere located within 40 nautical miles of their spawning grounds.The regression tree method provided valuable insight to the dataseries where it highlighted spatial and temporal patterns and wasan effective way to quantitatively summarize relationships.

A lightweight sorting grid was developed to reduce bycatch in the Danish small-meshedtrawl 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 poutwith 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 estimatedrelease of between 88.4 and 100% of the total number of haddock (Melanogrammusaeglefinus) and whiting (Merlangius merlangus) entering thetrawl. However, bycatch reductions were not significantly different between day and nightor between grid orientations, indicating that the grid rejection of haddock and whiting isnot 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 lengthdependent. Consequently, loss of target species would vary with the size structure of thepopulation fished. Although results were not statistically significant, length-basedanalyses 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 encounterprocess for Norway pout.

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.

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.

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.

Inter- and intraspecific crossbreeding experiments were conducted to evaluate the aquaculture potential of hybrids in the genus Dicentrarchus, focusing on fertilisation and hatching success. The experimental design consisted of 24 controlled crosses in which individual and pooled fertilisations were made between wild D. labrax individuals (8 dams and 5 sires originating from West Mediterranean and Atlantic populations) and wild D. punctatus (6 sires). Three experiments were successively performed: (1) dams from the Mediterranean population, individually considered to have good egg quality, (2) dams from Mediterranean population, individually considered to have poor egg quality and (3) crossbreeding using pooled eggs from the Atlantic population. In each case, batches of these eggs were fertilized by sperm from males of the two species. Sperm cell quality (concentration and motility) was verified before experimentation in all cases and equal numbers of sperm cells from each male were used to individually (without inter-sire competition) fertilise egg batches. Through the repeated artificial crosses between female common sea bass Dicentrarchus labrax (Linnaeus 1758) and male spotted sea bass D. punctatus (Block 1792), these experiments showed that no post-zygotic reproductive barriers exist to interspecific hybridisation between these two species when using D. labrax as dams and D. punctatus as sires. Phenotypically, the F1 hybrids were easily recognisable: they inherited the characteristic black spots of D. punctatus. Furthermore, embryo survival was significantly higher in interspecific crosses compared with intraspecific controls, showing increased fitness for this trait (increased performance at early life stage). Then, the experimental breeding design validates the observation that West Mediterranean and Atlantic common sea bass populations are different. Indeed, the inter-population crosses (between West Mediterranean dams and Atlantic sires) also revealed increased fitness at early life stages in comparison with the progeny of intra-Atlantic population crosses. However, these individuals were still smaller than their interspecific counterparts. The ability to produce viable F1 hybrids will have significant implications for the practical improvement of sea bass aquaculture.

Sex ratios in farmed European sea bass are highly biased towards males (75 to 95%), which is problematic for aquaculture. In this mini-review, we re-analyse fisheries literature data about sex ratios in wild sea bass from 13 population samples, representing altogether 4889 individuals covering the major part of the distribution range of the species. We find that as a whole, the sex ratio of wild populations is biased towards females (59.4% females, p < 0.001), but that the sex ratio of the younger fish (<30 cm total length) is balanced (52.0% females, p = 0.15), while the sex ratio of the older fish is heavily biased towards females (69.5% females, p < 0.01). Possible causes of these differences (differential longevity, biased sampling) are discussed. When age-group sex ratios are available (three population samples out of 13), significant variation between age groups appears, part of which is most likely of environmental origin. This study shows that the excess of males in culture is not a characteristic of the species, but rather a consequence of the environments used in culture, interacting with a complex system where both environmental and genetic influences govern sex determination in sea bass.

Pinctada margaritifera mollusc is cultivated in French Polynesia for the production of black pearls. For this study, the colour of juvenile samples (48 days old) was investigated in the visible range spectra (430–700 nm) using spectrophotometry. A first measurement was done with the soft parts still inside the shell (entire animal). Then, the soft parts were removed in order to do a second measurement on the growing edge of the shell. Comparison of the two measurements shows that the estimation of the living animal colour with unaided eye is strongly influenced by the colour of the soft parts. The use of the International Commission on Illumination (ISI) chromaticity diagram shows that at this growth stage, the shells are “white”; i.e. present no absorptions to the visible part. Multivariate statistical analyses based on the intensities of 6 wavelengths show that the shell colour is less variable than the colours of the entire animals. Wavelength intensities of the shells are similar, so no colour trend is visible. On the other hand, the colours of the entire animals are darker, and more variable. At this growth stage, the shell colour is not predictable for a potential selection of receiver or donor.