The analysis of both the digestive gland and the muscle tissue of Lolliguncula brevis showed that fatty acid and stable isotope signatures of the predator changed with time to reflect the signatures found for prey species fed in the experiment. Both short-term (digestive gland) and long-term effects (muscle) of the diet could be established through the analysis of these metabolically different tissues and the present study proved that these methods are viable for the use in reconstructing diets of squid species in the wild. Using this combination of techniques it was possible to identify seasonal and regional differences in the diet of L. forbesi. Ontogenetic differences in feeding could be established with bigger squid taking more varied prey and switching from a predominantly benthic to more pelagic diet. It was furthermore possible to distinguish between squid feeding in coastal and offshore waters respectively. Through the application of either fatty acid or stable isotope analysis to tissues of Todarodes sagittatus, Illex coindetii and Illex argentinus it was possible to determine short-term and long-term trends in the diet and formulate hypotheses as to which ecosystem mainly contributed to the diet. The diet of T. sagittatus was influenced by both benthic and pelagic prey species. Fatty acid profiles indicated a shift from small planktonic prey taken by small squid to a more piscivorous feeding in bigger squid. Similarities found for fatty acid signatures of deepwater fish and T. sagittatus suggest that this species spends part of its life cycle in deeper waters. Fatty acid signatures of I. coindetii indicated an omnivorous diet for this species determined by prey availability in two regions subject to different hydrographical conditions. Stable isotope signatures of I. argentinus indicated a diurnal feeding rhythm and regional differences in feeding in this highly migratory species point towards differences in migration routes from spawning to feeding grounds.

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The aims of this study are to improve the understanding of the life cycle biology of L. forbesii and examine the ecological importance of this squid in the marine ecosystem. The life history study was based on two years of sampling during July 2006-June 2008 and, for the first time in this study area, made use of age data based on reading growth increments in statoliths. The statolith increment analysis suggests that the life-span of L. forbesii may be longer than one year, and hatching apparently occurred throughout the year. Two modes in size at maturity and a single mode in age at maturity suggest differences in growth rates between males and females as well as the existence of alternative growth strategies. The approach to statistical modeling was based on GAMs and revealed that growth and maturation of L. forbesii were influenced by both internal and external factors, in which their effect was sex-specific. This study provides evidence that males continue to invest energy for somatic growth, including growth in length, as they mature, while females invest more energy in growing reproductive tissue. A new study of squid diet, based on data from 2006-07 showed that clupeid fish were less important in the squid diet compared to a previous study in 1990-92, while the importance of gobies had increased. Modelling results revealed the influence of squid (predator) size, season and region on variation in diet and prey size of L. forbesii. The observed changes in the diet of L. forbesii over time may be related to changes in fish abundance. The results from the ecosystem model constructed using Ecopath with Ecosim suggest that squids have both direct negative impacts on their prey and indirect negative impact on other predators. The results from simulation suggest that increasing squid fishing intensity could impact most groups in the system, not only groups with direct trophic relationships with squid as prey or predators.