Population structure and growth of the squid Todarodes sagittatus (Cephalopoda: Ommastrephidae) in north-west African waters

Abstract

The population structure of the European flying squid Todarodes sagittatus was studied using data of about 5000 squid caught in waters off the western Sahara between 1969 and 1997. The bulk of the population consisted of winter-spawned squid, which occurred as juveniles of 80–120 mm mantle length (ML) over the slope in spring, and as immature squid of 160–180 mm ML both on the shelf and slope in summer. In autumn, the squid attained 220–280 mm ML, matured, and shifted to the slope, where the spawning was supposed to occur in winter. Age and growth of T. sagittatus was studied using statolith ageing techniques. Assuming daily production of putative growth increments within statoliths, as well as sizes and proportions of immature and maturing females, the lifespan of the west Saharan populations of T. sagittatus lasts ∼1 y. Todarodes sagittatus is a fast growing squid at juvenile and immature ontogenetic phases. Early maturation (at ages 220–230 d in males and 250–260 d in females, respectively) and subsequent decrease of somatic growth rates caused rather small modal sizes of mature squid (250–300 mm ML) compared with those of their northern counterparts (350–420 mm ML). Both hatching dates and seasonality in occurrence of mature females shows that in waters off the western Sahara T. sagittatus spawns throughout the year with a well-pronounced winter peak.

Variation in age, growth and maturity in the Australian arrow squid Nototodarus gouldi over time and space-what is the pattern?

“…Similarly, populations of Loligo pealeii off northeastern North America show geographic differences in body size with cooler northern waters having larger individuals than warmer southern waters, at least during some seasonal periods (Hatfield & Cadrin 2002). Similar trends in cooler zone, bigger, slower-growing squid vs warmer zone, smaller, faster-growing squid have also been observed in Todarodes sagittatus populations from the north Atlantic (Rosenberg et al 1981) compared to tropical Africa (Arkhipkin et al 1999). Arkhipkin (1996) also found geographical differences in size and growth rates in different populations of Illex coindetii in tropical waters off western Africa.…”

Growth strategies in the squidLoligo vulgarisfrom Portuguese waters

“…Cephalopod growth is generally described as continuous and non-asymptotic (Jackson & Moltschaniwskyj 2002). Nonetheless, the growth of many ommastrephid squid species has been modelled using Gompertz or logistic models (Todarodes sagitattus , Arkhipkin et al 1999; Todaropsis eblanae , Arkhipkin & Laptikhovsky 2000;Illex coindetii , Arkhipkin et al 2000;Illex illecebrosus, Hendrickson 2004; Dosidicus gigas , Markaida et al 2004), which suggests an inflexion in growth at some point. It seems that the power model best fits most Loligo size-at-age data (e.g.…”

Temporal variation in dwarf sperm whale (Kogia sima) habitat use and group size off Great Abaco Island, the Bahamas

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