In common with most squid fisheries, the Falkland Islands fisheries for <i>Illex argentinus </i>and <i>Loligo gahi </i>are characterised by unpredictable, inter-annual variations in distribution and abundance. In recent years, much research effort has been directed at understanding the influences of physical oceanographic variability, such as sea surface temperature, on the recruitment, distribution and abundance of these species. This study considers the influence of predation and food availability on the recruitment, distribution and abundance of these species. Cannibalism (defined as intraspecific predation) is a feature of cephalopod feeding biology and impacts on natural mortality and population dynamics. The research provides the first comprehensive account of cannibalism in two commercially exploited squid species in the southwest Atlantic. The diets of <i>I.</i><i> argentinus </i>and <i>L. gahi </i>were examined over a wide spatial area and over several years and results showed that this behaviour is related to population density and the availability of food. This study also quantified cannibalism in <i>I.</i><i> argentinus </i>and <i>L. gahi </i>as a major source of natural mortality and has assessed the impact on the population dynamics of these species. This links between food availability at the base of the food chain and the distribution and abundance of <i>I.</i><i> argentinus </i>and <i>L. gahi </i>were examined using satellite-derived chlorophyll-<i>a</i> data imaged by Sea-viewing Wide Field-of-view Sensor (SeaWiFS). Results showed that phytoplankton biomass appeared to be related to <i>I.</i><i> argentinus </i>biomass during the period of the fishery. The addition of information on food availability using SeaWiFS technology may improve current forecasting models for <i>I.</i><i> argentinus </i>and <i>L. gahi. </i>Within season estimates of the natural mortality due to cannibalism may be used to make real-time modifications to the target escapement of the <i>I.</i><i> argentinus </i>and <i>L. gahi </i>fishery populations.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:605669 |
| Date | January 2004 |
| Creators | Johnston, Nadine Marie |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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