Sexual segregation in ontogenetic migrations by the squid Loligo gahi around the Falkland Islands
Intra-annual variations in length-frequency composition and sex ratio in Loligo gahi were studied at different depths in three areas of the main fishery region, using data collected both on research cruises and by scientific observers placed on commercial vessels during 1997–2000. Approximately half a million squid were analysed. It was found that small immature squid (<100 mm ML) tended to occur at shallow depths (<100 m), with males and females in almost equal numbers. Larger squid (>100–110 mm ML) in the feeding grounds were segregated by sex and by depth, with females occurring deeper (250–300 m) than males (170–250 m). The feeding grounds were deeper in the northern areas (200–350 m) than in the south (150–250 m). At the start of the spawning period males emigrated from their shallower feeding grounds first, and then for a short time (several weeks) these grounds were occupied by mature females emigrating from their deeper feeding grounds to spawn in shallow waters. In the shallow spawning grounds (30–100 m), the sex ratio reached equality in the middle of the spawning period with a prevalence of spawning females by the end of the period. The fishing fleet operates mainly in the feeding grounds, at varying depths according to season, and therefore targets the sexes differentially.
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Document Type: Research Article
Publication date: 2002-07-01
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