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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:558643 |
| Date | January 2012 |
| Creators | Wangvoralak, Sansanee |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=185974 |
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