Microincrement analysis in otoliths of Notothenia rossii fingerlings from the South Shetland Islands to estimate early life history timings and to validate annulus formation

BARRERA ORO, ESTEBAN; LA MESA, MARIO

Hobart

Conferencia; Working Group on Fish Stock Assessment (WG-FSA); 2012

Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR)

Otolith microstructure analysis on blue phase and brown phase fingerlings caught in spring-summer from 2003 to 2010 at Potter Cove, South Shetland Islands, allowed to provide insights on early life history timings and to validate annulus formation. Although it has been reported that N. rossii in the area hatches in spring, our daily ring back counting in otoliths from the capture date showed two periods of larval hatching separated by 5-6 months, one in late summer in February-March and another in winter in July-August. Maximum and minimum ages of pelagic blue phase and demersal brown phase fingerlings were respectively 227 and 240 days, indicating a demersal settlement after about eight months from hatching. The age/length frequency distribution of fish sampled in spring 2010 showed the simultaneous presence of two cohorts, belonging to biological ages 0+ and 1+ that hatched respectively in summer and winter. The estimated growth rate was 0.26-0.31 mm/day, equivalent to that of South Georgia fingerlings and considerably higher than those of other nototheniids within similar size range. Based on early life events associated with the hatching periods, two types of life cycles are hypothesised for South Shetland fingerlings. The pelagic blue phase fingerlings (age group 0+) hatched in July-August (winter cohort), entering in Potter Cove in February-March. The brown phase fingerlings (age group 0+) hatched in February-March (summer cohort), entering in the cove in spring, i.e. from September-October onwards. Finally, early juveniles (age group 1+) hatched in July-August, entering in the cove the following year to spend the second winter inshore.