Distribution, abundance and growth of early stages of the glass squid Galiteuthis glacialis (Cephalopoda: Cranchiidae) captured in Prydz Bay, Antarctica during austral summer

Abstract

We describe the distribution, abundance and growth of the paralarvae and juveniles of the glass squid Galiteuthis glacialis which were collected from tows conducted at 500 m depth in Prydz Bay, Antarctica by using an Isaacs Kidd Midwater Trawl (IKMT). Paralarvae occurred in an area from 57° S to 65°30ʹ S and 57°–66° E. Early juveniles co-occurred with paralarvae at 57°–65°30′ S and 57°37′ E to 64°56′ E. Age of individuals was estimated based on statolith increment counts and ranged from 47 to 85 days with a daily growth rate ranging from 0.13 to 0.25 mm dorsal mantle length (DML)/day (mean 0.18 mm) for paralarvae. The early juveniles had an age of 85–103 days with a slightly faster growth rate ranging from 0.21 to 0.27 mm DML/day (mean 0.24 mm). The presence of paralarve of G. glacialis at the outer continental shelf edge of Prydz Bay during austral summer indicates a spawning site in this area.

Introduction

Cephalopods play an important role in polar marine ecosystems (Xavier et al., 2018). Besides, important commercial cephalopod fisheries exist in seas adjacent to the Antarctic such as around New Zealand and the Falkland Islands (Arkhipkin et al., 2015). Squids are considered as major nutrient vectors and play a key role as transient ‘biological pumps’ linking spatially-distinct marine ecosystems (Arkhipkin, 2013). They prey on crustaceans, fish and other cephalopods, while their predators include fish, other cephalopods, seabirds, seals and whales (Xavier et al., 2018). The Antarctic cephalopod fauna is poorly known and more studies are required to understand its distribution, taxonomy and ecology (Xavier et al., 2018).

Galiteuthis glacialis (Chun, 1906) is a glass squid belonging to the family Cranchiidae distributed throughout the Antarctic Convergence (Rodhouse and Piatkowski, 1995). It is one of the most abundant squid species in the waters around Antarctica (McSweeny, 1971; Rodhouse and Clarke, 1986) and occurs in the diet of wandering albatrosses (Diomedea exulans) and southern elephant seals (Mirounga leonine) (Rodhouse et al., 1987; Rodhouse et al., 1992). An account of the distribution of G. glacialis in a sector of the Southern Ocean ranging from 76° E to 23° W and 15° to 30° E was given by McSweeny (1971) and Rodhouse and Clarke (1986). G. glacialis is the most abundant squid in the Weddell Sea (Piatkowski and Hagen, 1994) and in the Prydz Bay region (Lu and Williams, 1994; Jackson et al., 2002). Knowledge of the early life stages of cephalopod distribution and abundance patterns are useful to determine spawning area and season (Bower et al., 1999).

Age and growth of cranchiids squids Cranchia scabra and Liocranchia reinhardti revealed they are among the fast growing squids in the epipelagic waters of the tropical Atlantic (Arkhipkin, 1996a). Jackson and Lu (1994) conducted preliminary studies on the age and growth of G. glacialis and found statolith increments to be a useful tool for studies on age and growth of this Antarctic squid. The study of statolith microstructure has revealed important aspects of the life history and timing of reproduction of Antarctic squid (Jackson and Lu, 1994). Therefore, here we describe the distribution of early life stages of G. glacialis from the Prydz Bay region of the Indian sector of Southern Ocean and analyse its age and growth based on statolith increment counts.