CCAMLR

A revision of the research plan for the Spanish exploratory longline fishery for Dissostichus spp in Divisions 58.4.1 and 58.4.2, submitted to the XXXI-WG-SAM, taking into account the suggestions made by the Working Group is presented. Two methods to estimate the local biomass of the toothfish are proposed, a depletion experiment together with the tag of some specimens using the DeLury model and the tag-recapture estimates using the Simple Petersen model.

To evaluate the potential success in achieving the objectives three study areas with high historical effort have been selected in different SSRUs with four different scenarios related to the extent of the area . The regression coefficients between the CPUE and the cumulative catch seem to be a practical way to stablish the area (10 nautical miles) and the minimum effort (0.3 k/hook) to perform the depletion experiment. Historical recaptures of Spanish tagged toothfish were examined within these areas and Subareas/Division (88.1, 88.2, 58.4.1 and 58.4.2). Results strongly related to the effort made within those areas suggest that the likelihood of achieving the objectives with this research plan is high.             
 

Waters around South Georgia are amongst the most productive in the Southern Ocean, and support internationally important fisheries. However, there is significant inter-annual variability in fish stocks, and some species have failed to recover from historical overfishing. Dispersal and retention of the planktonic stages (eggs and larvae) of marine fish can play a key role in the maintenance of adult stocks. Here we use a numerical modelling approach to examine the influence of oceanographic and life history variability on the dispersal and retention of two species of Antarctic fish: Champsocephalus gunnari (mackerel icefish) and Notothenia rossii (marbled rockcod). Mean retention of N. rossii larvae was predicted to be 5.3%, considerably lower than that of C. gunnari (31.3%), a difference related to the longer planktonic period of the former. Such apparent loss of larvae from local recruitment grounds may contribute to the failure of the N. rossii population to recover from its collapse in the 1970s. However, retention of both species showed high inter-annual variability. Dispersal and retention of C. gunnari were strongly influenced by location of the spawning site, with the greatest contribution to overall retention from spawning sites on the southwest South Georgia shelf. In addition, a consistent feature in C. gunnari was a lack of larval exchange between the proximate South Georgia and Shag Rocks shelves, regions separated by only 240 km. Our findings provide insights into the demographic dynamics and connectivity of C. gunnari and N. rossii populations at South Georgia in relation to prospects for recovery and ongoing responses to environmental variability and change in the region.

We studied the annual distribution, activity and breeding foraging trips of the sibling species of giant petrels, Northern Giant Petrel Macronectes halli and Southern Giant Petrel Macronectes giganteus from the  Crozet Islands (46°25'S; 51°51'E) where the 2 species breed sympatrically and Kerguelen Island (49°19'S; 69°15'E where Northern Giant petrels breed). Distribution and activity data were provided by GLS loggers (Global Location Sensing), and detail of breeding foraging trips were provided by ARGOS PTT. In order to assess differences in bycatch susceptibility, comparisons were made between species, sexes, stages (adult breeding, adult non breeding and juveniles) and sites. Activity patterns were investigated using GLMM and distribution ranges were determined using kernels analysis.

Overall, in adults, all stages remained close to nesting sites, during and outside the breeding season, while juveniles dispersed throughout the southern ocean. In adults, the intersexual differences were higher than interspecific ones, with females showing a greater distribution range than males in both species. Females also spent more time sitting on the water than males, particularly during wintering months. These results have important conservation implications, with males and females facing different kinds of threat in relation to their at-sea behavior. Adults, especially males, are more likely to be threatened by toothfish longline fisheries on shelf area of EEZs, and adult females as well as juveniles, are more likely to overlap with high sea longlining such as tuna fisheries.