-Fish larvae were collected monthly between March and September 1997 in the Mira and Guadiana estuaries (southern Portugal). Hydrological parameters were registered and zooplankton samples were obtained simultaneously. Densities of fish larvae (ind·100 m -3 ) were calculated from 211 samples and larval nutritional condition measured as RNA/DNA ratios were obtained for 346 individuals, using a fluorimetric method for nucleic acid quantification. Correlating variables were further studied using multiple regression analysis in order to assess the relative importance of abiotic and biotic factors affecting within-year trends in abundance and nutritional condition of estuarine fish larvae. Results indicated that: 1) the abundance of fish larvae seems conditioned by temperature and predation; and 2) their nutritional condition is dependent on temperature and prey availability. Temperature is an important variable structuring estuaries and therefore conditions the behaviour and physiology of fish larvae. Furthermore, the co-occurrence of predators and larvae might be related to similar feeding patterns or comensalism. Whenever feeding conditions are suitable, they usually determine enhanced growth and nutritional condition. However, predation seems to control this latter relationship through its effect on larval mortality. © 2000 Éditions scientifiques et médicales Elsevier SAS Fish larvae / distribution / RNA/DNA ratios / nutritional condition

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Most studies of factors affecting catching efficiency and selectivity in longlining have focused on various gear parameters (mainline and snood material, hook design and size, rigging) and on the bait (type and size), and few studies have investigated how catch rates are affected by the way the gear is operated during fishing. We carried out fishing experiments to study the effects of setting time, setting direction (relative to the current direction) and soak time on catch rates of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus). Lines set before dawn and lines set across the current gave higher catch rates of haddock than lines set after dawn and in the same direction as the current, respectively. Similar effects were not found for cod, and these differences between haddock and cod were explained by differences in behaviour and interspecific competition for the available baits. Soak time was not found to significantly affect the catch rates of either species, indicating that other factors have a more pronounced effect on longline catch rates and may therefore mask the effect of soak time.

Diel and seasonal changes in nutritional condition of the anadromous twaite shad Alosa fallax fallax (Lacépède, 1803) larvae Esteves E, Pina T, Andrade JP. Diel and seasonal changes in nutritional condition of the anadromous twaite shad Alosa fallax fallax (Lacépède, 1803) larvae.Abstract -In this work we aim to study: (i) the diel and seasonal changes in nutritional condition, herein RNA ⁄ DNA ratios, of twaite shad (Alosa fallax fallax) larvae and (ii) the influence of environmental and biological covariates on those changes. Samples were collected in the River Mira (Portugal) from February 1998 to July 2000. The RNA ⁄ DNA ratios were significantly lower than average during dawn and dusk hours. This pattern can be attributed to: the absence of better-fit specimens escaping the net; a nightly increase in the RNA content in response to circadian rhythm; and ⁄ or nucleic acids of prey items remaining in the gut of larvae during daylight. Thus, the time of day is important when examining RNA ⁄ DNA ratios of twaite shad. Generalised additive model of seasonal data showed that water temperature, freshwater pulses and ⁄ or turbidity largely contribute to create adequate environments. These might enhance the nutritional condition of twaite shad larvae during the period that they remain in the upper reaches of River Mira.