Research plan for the Spanish exploratory longline fishery for Dissostichus spp. in Divisions 58.4.1 and 58.4.2: preliminary results of stage 1 (2012/13 season)

Abstract

During the 2012/13 season Spain started the approved multi-year research survey in Divisions 58.4.1 and 58.4.2 in order to obtain information to better understand the population dynamics of both species of Dissostichus in areas off the Antarctic continent close to the Ross Sea and Banzare Bank, and to implement the use both local depletion and tag-recapture methods in areas described so as to estimate local abundance. The research plan, as it was stated in the proposal, takes several years to be completed. It has started in the SSRUs closest to the Ross Sea, 58.4.1H and G, during the 2012/13 season. In order to fix the protocols and ascertain the viability and suitability of the study, it was establish the return to the same areas the two-three subsequent years along with the movement to new places and westwards to SSRUs 58.4.1D, C, B and 58.4.2E is expected.

The vessel Tronio has started the research plan after the exploratory fishing season in the Subarea 88.1, using the Spanish bottom longline system. A total of 42 research sets were performed within the SSRUs 58.4.1H and 58.4.1G. Two depletion experiments were completed and three prospecting-phase clusters of sets did not reach the established threshold to start the depletion. A prospective estimation of the local biomass (BLOC) of the two localized areas where the depletion experiments were performed is done and regarding the maximal and minimal biomass for the SSRUs (BSSRU) considering areas with high and low densities. This study will be reviewed and completed the upcoming years with the new data obtained revisiting the same areas as well as with the tag-recapture data in order to estimate the local abundance using two different approaches, depletion and tag-recapture methods. A summary of the activities and results from the survey is also presented related to the sampling scheme, collected samples and species.