The relative importance of shallow and deep shelf spawning habitats for the South African chokka squid (Loligo reynaudii)

Abstract

Roberts, M. J., Downey, N. J., and Sauer, W. H. 2012. The relative importance of shallow and deep shelf spawning habitats for the South African chokka squid (Loligo reynaudii). – ICES Journal of Marine Science, 69: 563–571. It is well known that the spawning grounds of chokka squid Loligo reynaudii lie along the shallow inshore regions of South Africa's south coast. However, egg masses have been found in deeper water on the Agulhas Bank, and hydroacoustic targets deemed to be large aggregations of spawning squid have been identified. The aim of this study was to investigate the extent, depth range, and importance of deep spawning. Trawl data collected during demersal research surveys between Port Nolloth on the west and Port Alfred on the south coast were examined for egg capsules. No spawning was found on the west coast. Data showed that chokka squid preferred the eastern Agulhas Bank for spawning. Spawning occurred not only inshore but also on the mid-shelf extending to depths of 270 m near the shelf edge. Squid egg biomass markedly decreased beyond 70 m, suggesting delineation between the inshore and offshore spawning grounds. Total egg biomass calculations for depths shallower and deeper than 70 m indicated the coastal area to be strongly favoured, i.e. 82 vs. 18%. These results contest the commonly accepted notion that L. reynaudii is an inshore spawner and redefine the spawning grounds to extend across the shelf.

The São Paulo shelf (SE Brazil) as a nursery ground for Doryteuthis plei (Blainville, 1823) (Cephalopoda, Loliginidae) paralarvae: a Lagrangian particle-tracking Individual-Based Model approach

“…This was preliminarily addressed to a limited degree in the present study by dividing the shelf into two broad release subareas, but this is unlikely to reasonably capture the variability of transport trajectories within the shelf. For instance, larval transport IBM studies of chokka squid (Loligo reynaudii d'Orbigny, 1839) paralarvae off the South African eastern coast, where the location of the spawning grounds is well known (Sauer et al, 1992;Roberts et al, 2012) showed that the release areas were the most important explanatory variable in the models (Martins, 2009;Martins et al, 2010a). Furthermore, dispersal and retention patterns changed cross shore, with the former being important for paralarvae released on the mid-shelf and the latter important for those released inshore.…”

Life cycle of chokka-squidLoligo reynaudiiin South African waters

“…Spawning in the deep was confirmed, mapped and quantified as comprising 18% of total spawning. Experimentation has demonstrated the viability of this spawning through the production of healthy hatchlings (Oosthuizen and Roberts 2009;Roberts et al 2012 Figure 3). This regional pattern of morphological divergence occurred despite high gene flow.…”

An assessment of the current status of the chokka squid fishery in South Africa and an evaluation of alternative allocation strategies

“…The most important region for both spawning and fishing is over the Agulhas Bank between Plettenberg Bay and Algoa Bay [7,8] (Fig. 1).…”

“…In about 1984, it was realised that catching and exporting of squid could be a lucrative business and this led to the establishment of the commercial squid jig fishery which developed rapidly from 1985 onwards driven by high demand and good catches [13,14]. Effort was initially concentrated inshore on the spawning aggregations at depths of no more than 40 m, but advancement in technology and upgrading of vessels allowed fishing to move offshore onto the feeding grounds, thus enabling catches to be made throughout the year [8].…”