AbstractThe primary objective of this thesis was to better understand the population biology and fishery of southern calamary, Sepioteuthis australis, in Gulf St. Vincent, South Australia, which accounts for over 40% of the total reported Australian catch, to facilitate management of this important natural resource. Towards this end, population structure was determined across the species range, and patterns of distribution, abundance, growth, reproductive biology and recruitment were described at several localities within Gulf St. Vincent.
Three genetic types were found across southern Australasia, comprising two parental taxa that seemed to mate at random where they co-existed to form infertile hybrids. In Gulf St. Vincent, there was one genetic type with no evidence of population substructuring. This meant that the subsequent biological studies were focussed on a single stock.
Southern calamary were ubiquitous throughout Gulf St. Vincent, but were unevenly dispersed with respect to size, age and sexual maturity. Newly-hatched individuals and mature adults dominated waters of <10 m in depth, whilst deeper, offshore waters were occupied by juveniles and sub-adults. The abundance of adults varied in a sequential, systematic way that conformed to an anti-clockwise progression around the gulf, being most abundant in the south east in summer,in the north in the following autumn, and in the south-west by winter.
The growth and longevity of 910 individuals were determined from estimates of age derived from counts of microincrements in statoliths. Males grew faster and attained a larger maximum size than females. Growth varied with season of hatch and amongst localities. The maximum age was 284 days, suggesting that southern calamary were most likely an annual species. This also indicated that location-specific spawning aggregations that form at the same time in each year,consist of a single generation of individuals. Spawning activity reflected the abundance of mature adults, and thus also varied spatially and temporally around the gulf. It was hypothesised that the environmental influence here was the requirement for clear water to facilitate mating.
The resulting year-round spawning might be a bet-hedging mechanism that reduces the risk of recruitment failure.
|Date of Award||Aug 2002|
|Supervisor||Charles Webb (Supervisor)|