Conservation challenges for Patagonian squid populations after sudden range expansion of predatory Argentine squid

Alexander Arkhipkin (1), Tomasz Zawadowski (1), Zhanna Shcherbich (1), Andreas Winter (1)

1 Fisheries Department, Bypass Road, Stanley, FIQQ 1ZZ, Falkland Islands,

Patagonian shelf and slope waters of the Southwest Atlantic are inhabited by two abundant and commonly allopatric squids. Argentine shortfin squid Illex argentinus is associated mainly with temperate waters of the Patagonian Shelf, with the highest concentrations observed to the north-west of the Falkland Islands. Adult I. argentinus attain 800-1000 g in body mass. Patagonian longfin squid Doryteuthis gahi is associated with the transient zone between temperate shelf waters and Sub-Antarctic waters of the Falkland Current. This much smaller squid (adult body mass of 60-100 g) are most abundant to the south-east of the Islands. Both squid are important commercial stocks targeted by jigging (I. argentinus) and trawling (D. gahi) fishing fleets. In April-May 2015, dense aggregations of I. argentinus emerged unexpectedly in the nursery and feeding grounds of D. gahi. They quickly dispersed commercial aggregations of D. gahi, causing an earlier closure of the fishery. Stomach analysis of I. argentinus in the nursery grounds showed that they mainly preyed upon small D. gahi that should recruit to the next fishing season starting in August 2015. Subsequently, the following season showed very low recruitment and had to be closed a month early. Possible ecological consequences of such a profound impact of sudden appearance of predatory I. argentinus onto recruitment and stock size of D. gahi are discussed. A suite of conservation measures is considered to preserve the D. gahi stocks and regulate its fishery in case of I. argentinus range expansion in future.