exploited by the fishery in the Falkland Islands Interim Conservation and ... This paper reviews present knowledge of the life history of Loligo gahi and examines ...
Journal of Cephalopod Biology (1991), 2(1): 41
BIOLOGY AND FISHERY OF THE PATAGONIAN SQUID LOLIGO GAHI (DORBIGNY, 1835): A REVIEW OF CURRENT KNOWLEDGE1 Emma M.C. Hatfield and Paul G. Rodhouse Marine Life Sciences Division, British Antarctic Survey Natural Environment Research Council High Cross, Madingley Road, Cambridge CB3 OET, Cambs., U.K.
Abstract The loliginid squid Loligo gahi (d’Orbigny, 1835) is one of the two major squid species exploited by the fishery in the Falkland Islands Interim Conservation and Management Zone (FICZ). The commercial fishery is regulated by the Fishery Department of the Falkland Islands Government. There are two fishing seasons in each year, from February to June and August to October. The two seasons arise as a result of the presence of two, or possibly more, spawning groups within the population. The species is annual and appears to conform to the general loliginid life history pattern. The young squid hatch in shallow water then migrate away from the spawning grounds, moving down the continental shelf and slope as they feed and mature. The mature adults then move back up the continental shelf to spawn in shallow water after which they die. Growth data for L. gahi are restricted to the time when the species is available to the commercial fishery. Squid from each spawning group recruit into the fishery at an age of about 6 months and are fished during the second half of their life cycle. The eggs and major spawning grounds have yet to be found. Key words: Population biology - Growth - Maturation - Mortality - Fishery
Introduction Loligo gahi is found off the Pacific and Atlantic coasts of South America from southern Peru to Argentina. It is a neritic species occurring from the surface to depths of about 600 m, and like many other teuthoid squid (Boyle, 1983) it is semelparous and has a maximum life span of about one year. L. gahi was first described in 1835 but until the development of an international fishery the only information available has been taxonomic or descriptive (Castellanos and Menni, 1968; Castellanos and Cazzaniga, 1979; Brakoniecki, 1984). Roper, et al., (1984) collated the then available information on the species and emphasized that the systematics, biology and fisheries of the species are poorly known. The fishery for L. galu started to develop in 1982 on the Patagonian Shelf around the Falkland Islands and in coastal waters from 42° to 48°S (Csirke, 1987). Data have since become available from the fishery for the analysis of the life history and growth of the species. Present knowledge of the biology of L. gahi is derived from data mainly from the fishery within the Falkland Island Interim Conservation and Management Zone (FICZ) which was established in 1986 (Anon., 1989). Growth studies on L. gahi are restricted to post-recruits, the latter part of the species life cycle, because most resented at the Symposium on the Biology and Fishery of Commercially Important Squid, August 2nd and 3rd, 1990, Hotyrood, Conception Bay, Newfoundland.
Hatfield & Rodhouse: Biology and fishery ofLoligo gahi
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Journal of Cephalopod Biology, (1991), 2(1):
data are taken from the commercial fishery. No information is available on the early life history stages or the location of the major spawning grounds. This paper reviews present knowledge of the life history of Loligo gahi and examines the commercial fishery that has developed on the Patagonian Shelf around the Falkland Islands.
Population Biology The population of Loligo gahi within the FTCZ appears to consist of at least two spawning groups (Patterson, 1988) with two distinct seasons of hatching from the egg (Hatfield, submitted). The two hatching periods overlap to some extent and biochemical genetic studies on the FICZ population have shown that the two spawning groups are not genetically distinct (Carvalho and Pitcher, 1989). Some male L. gahi live for more than one year (Hatfield, submitted) which provides further opportunity for interbreeding between spawning groups. Female L. gahi do not appear to live for more than one year and presumably die after spawning as spent females are never caught. L gahi has not been cultured under laboratory conditions so there is no information on the duration from spawning to hatching in this species. The egg stage would experience ambient temperatures of about 6°C (1st spawning group) in inter and about 9°C (2nd spawning group) in summer.
By comparing hatching times with other species of loliginid squid (McGowan, 1954;
Mangold-Wirz, 1963; Fields, 1965; McMahon and Summers, 1971) an egg stage of approximately 70 days for the summer spawners and 60 days for the winter spawners can be estimated. Loligo gahi seems to have a similar life cycle to other loliginid species (see Fields, 1965; Holme, 1974; Summers, 1968,1969, 1971; Vovk, 1978; Hixon, et al., 1981; Hixon, 1983; Worms, 1983; see also reviews in Boyle, 1983). In shallow waters (
