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This study describes the proximate composition (moisture, lipid, protein and ash content) and energetic value of 39 species (27 teleosts, 3 sharks, 7 rays and 2 squids) that are known as key prey or potential prey of top predators on the Patagonian continental shelf. Specimens were collected in the SW Atlantic Ocean in the area 39 to 51°S, 55 to 65°W. Fifty-two catches were performed at a depth range of 73 to 370 m: 27 catches in autumn and 25 in summer. A multivariate correspondence analysis showed an association between species identity and certain biochemical variables (main dimension = 83% of variance explained). Sharks and some demersal-pelagic teleosts were associated with lipids (9 to 18% wet mass). Teleosts constituted a higher source of protein (9-28% wet mass) than elasmobranches. Rays were nutritionally poor, with the lowest lipid contents (2 to 10%) and energy values (3 to 7 kJ g -1 wet mass), in agreement with the general biochemical characteristics of benthic fishes. Demersal-benthic and demersal-pelagic species did not change in their nutritional values with increasing size. However, demersal-benthic species increased seasonally in protein content from 11-16% in summer to 10-19% in autumn. The energetic value of teleosts from the SW Atlantic Ocean was not different from those of the Pacific or Indian Southern Ocean, but was higher than the energetic value of teleosts from the Northern Hemisphere. This study contributes to the understanding of the biochemical composition and energetic value of prey species over the seasons and their relevance as potential prey for top predators.

Loggerhead turtles Caretta caretta use a wide variety of foraging strategies, and some populations forage in sub-optimal habitats. Different foraging strategies may not be equivalent in terms of fitness and may result in differences in adult body size and clutch size among populations. Accordingly, we tested whether differences in clutch size among rookeries in the Mediterranean Sea are related to differential use of foraging grounds of contrasting productivity. Stable isotope ratios of carbon and nitrogen of turtle hatchlings from 8 Mediterranean rookeries were used to characterise the foraging grounds of their mothers. Clutch size was also studied in each rookery to assess reproductive output linked to foraging ground productivity. According to stable isotope ratios, most of the females nesting in the considered rookeries foraged in the southern Ionian Sea. The highly productive Adriatic/northern Ionian Sea region was mainly used by females nesting in western Greece. The explanation for these patterns might be linked to water circulation patterns and drifting trajectories followed during developmental migrations, which might determine individual knowledge on the location of productive foraging patches. Average clutch size in each rookery was positively correlated to the proportion of females accessing highly productive areas such as the Adriatic/northern Ionian Sea. This has a strong influence on reproductive output, and hence females using the most productive foraging grounds had the largest clutch sizes.

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