Precautionary measures for a new fishery on Martialia hyadesi (Cephalopoda, Ommastrephidae) in the Scotia Sea: an ecological approach
In anticipation of the development of a new fishery for the ommastrephid squid Martialia hyadesi in the Scotia Sea, this paper presents a revision of annual consumption of the species by higher predators and provides a brief review of information about the life cycle and distribution of the species obtained from research fishing and commercial catches. This species is eaten by seals, whales and seabirds, the latter being the most reliable source of consumption data because comprehensive sampling can be carried out during their breeding seasons. A conservative estimate for total annual consumption of M. hyadesi by higher predators in the Scotia Sea is 245 000 tonnes, with an upper estimate of 550 000 tonnes if less reliable data are included. M. hyadesi spawns between autumn and mid-summer with peak hatching in winter/spring. Its life span has not been established. Data from the CCAMLR Convention Area suggest that M. hyadesi may live for two years, but this may vary. In common with other ommastrephids, the species is probably semelparous. It is proposed that the timing and catches of the fishery should be highly conservative and set taking into account the timing of breeding and consumption rates of the most sensitive of the dependent species. Most Antarctic predators which have been studied consume relatively small and immature specimens of M. hyadesi. Fishing for M. hyadesi after the chick-rearing period of the most sensitive predator (grey-headed albatross) would minimise competition locally and ensure that the fishery only exploited the stock after escapement from most higher predator species. It would also allow seabird predation of the stock to be monitored prior to the fishing season as a way of assessing numbers of pre-recruits. Closing the fishery before recruitment of the next generation of squid would ensure availability of prey to higher predators during the following chick-rearing period. Preliminary data from a squid jigger which undertook research fishing around South Georgia in June 1996 provided the basis for determining realistic potential catch rates.