The influence of seasonal environmental changes on ontogenetic migrations of the squid Loligo gahi on the Falkland shelf

Abstract

The Patagonian longfin squid Loligo gahi undertakes horizontal ontogenetic migrations on the Falkland shelf: juveniles move from spawning grounds located in shallow, inshore waters (20–50 m depths) to feeding grounds near the shelf edge (200–350 m depths). Immature squid feed and grow in these offshore feeding grounds and, upon maturation, migrate back to inshore waters to spawn. The possible influence of environmental factors on L. gahi migrations was investigated using data from oceanographic transects, crossing the region of known L. gahi occurrence. They were made from the inshore waters of East Falkland eastwards to depths of 1250 m on a monthly basis from 1999 to 2001. Four main water types were found in the region: Shelf, Sub‐Antarctic Superficial and Antarctic Intermediate water masses, and Transient Zone waters. The inshore spawning grounds occur in the Shelf Water mass, whereas the feeding squid (medium‐sized immature and maturing individuals) were associated with the Transient Zone. The 5.5°C isotherm appeared to mark the limit of squid distribution into deeper waters in all seasons. Seasonal changes in water mass characteristics and location were found to be important for seasonal changes in L. gahi migrations on the Falkland shelf.

Squid as nutrient vectors linking Southwest Atlantic marine ecosystems

“…Inshore spawning and nursery grounds are located in shelf waters at depths of 10-50 m. Upon growth, small immature D. gahi (5-7 cm mantle length, ML) migrate offshore to their feeding grounds located on the outer shelf at depths 130-250 m. Offshore feeding grounds are occupied by the Transient Zone that is a mixture between shelf and Sub-Antarctic waters of the Falkland Current (Arkhipkin et al, 2004). Feeding period lasts several months.…”

Seasonal movements of veined squidLoligo forbesiin Scottish (UK) waters

“…The authors suggest that recruitment (therefore smaller squid) appears to be associated with low temperature in L. forbesi from the English Channel. Arkhipkin et al (2004) however, suggests that, in summer, immature L. gahi prefer warmer waters. Nevertheless, Loligo forbesi is the most cold water Loligo species and it has been reported that juveniles and post-larval stages are highly sensitive to temperature (Challier et al 2005).…”

“…Some maps also reveal two distinct abundance peaks, either in different coasts or one further south than the other. This could suggest that two cohorts or microcohorts exist (see Collins et al 1997Collins et al , 1999Pierce et al 2005), with different migratory behaviour -as Arkhipkin et al (2004) discussed for the migratory squid L. gahi. However, these two abundance peaks are not visible in all years.…”

“…In some years, high squid abundance appears in offshore grounds one month earlier or later than usual, but otherwise the pattern described above is rather consistent between years. Arkhipkin and Middleton (2002) discussed possible distinct migratory behaviour around the Falkland waters between two different cohorts of L. gahi: when one cohort is in offshore areas to feed the other is in inshore waters to spawn and this arrangement changes when the maturity season of the offshore cohort arrives (Arkhipkin et al 2004). In the present study, since L. forbesi is present close to the coast all year around, and very few squid are recorded offshore in spring and summer, it is possible that one cohort is resident in inshore waters.…”

Marine effect of introduced salmonids: Prey consumption by exotic steelhead and anadromous brown trout in the Patagonian Continental Shelf

“…Common hake Merlucious hubbsi alone consume 8 3 10 9 kg of amphipods and euphausiids in this region (Prenski and Angelescu 1993). The continental Patagonian longfin squid stock has been estimated at 3 3 10 7 kg (Arkhipkin et al 2004 ; Table 3); seabirds consume nearly half of this stock (1.4 3 10 7 kg), potentially reducing squid densities around colonies. No biomass estimates are currently available for silversides, but regarding their restricted distribution to coastal waters (first 5 km from the coast), their abundance should be lower than the other prey considered, making this prey a candidate for potential competition and localized depletion.…”