Ecology, reproduction and life histories of Southern Ocean and Antarctic squids
A project undertaken at the University of Tasmania and supervised by George Jackson
Squids are an important component of many marine ecosystems, from the tropics to the poles. They are characterised by rapid growth, short life spans, early maturity and rapid population turnover. They have been described as ‘weeds of the seas’ and living ‘life in the fast lane’ (Jackson & O’Dor 2002). In the Southern Ocean ecosystem, squids play an important role as both predators and prey of marine mammals, fish and birds (Cherel 1999, Jackson et al. 1998, 2000). It has been estimated that the annual consumption of squids by sperm whales alone, exceeds 100 million tonnes, which is equal to the entire catch of all fisheries of all species combined, and probably equates to half the biomass of humanity (Clarke 1983). The biomass of squids in the world ocean therefore, would greatly exceed the biomass of all humans on the earth. It is indeed surprising that for such an important group of organisms, so little is known. For example, no photos have ever been taken of giant squid alive, and another large species that is 9 m long is now known from ROV photos to inhabit all deep oceans, but an adult specimen has never been collected (Vecchione 2001, O’Dor 2003).
In the Southern Ocean, squids are probably only second in importance to krill. Furthermore, worldwide, squids are likely to be increasing in numbers due to removal of their fish predators and competitors. For example, it has been estimated that the documented increase in tuna catch of 2 million tonnes has resulted in an extra 20 million tonnes of squid in the world ocean (Caddy & Rodhouse 1998). Furthermore, the latest research has shown that 90% of the large predatory fish have been removed by industrialised fishing (Myers & Worm 2003). It is therefore likely that this dramatic decline in predators has resulted in a concomitant expansion (?explosion) in squid populations.
A major breakthrough in our understanding of squid life histories has been the discovery of the laying down of daily increments in the small balance ‘bones’ or statoliths in the back of the squid head (Jackson 1994, Jackson & O’Dor 2002). Every day an increment is laid down in the statoliths, so that in cross section under a microscope, they look like annual bands in a tree trunk. These unique ‘calendars’ have revealed, age, lifespan, hatch date, growth rate and age-at-maturity of individual squid. We now know that squids mostly live less than 1 yr, with many tropical species having life spans less than 200 d (Jackson 1994, Jackson 2004).
The general aims of this project are therefore:
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