Brief presentation of the Portuguese research plan for the improvement of knowledge on pelagic sharks caught in the swordfish fishery in the Indian Ocean

Brief presentation of the Portuguese research plan for the improvement of knowledge on pelagic sharks caught in the swordfish fishery in the Indian Ocean

Year of publication 2013

Product type Document

Edition 1

Synopsis (short abstract) Portuguese longliners targeting swordfish and operating in the Indian Ocean regularly capture elasmobranch fishes as bycatch. Of those, the blue shark (Prioce glauca) and the shortfin mako (Isurus oxyrinchus) constitute the two main shark species captured, even though several other species are also occasiolly captured. IPMA, the Portuguese Sea and Atmospheric Institute, is responsible for the Natiol Data Collection Program, which maintains fishery observers on those vessels to collect data and s amples. Therefore, IPMA has currently the means and opportunity to collect a wide variety of biological samples that are of ultimate importance to the work of the IOCT scientific commission. In this report we present the current Portuguese program research on sharks in the Indian Ocean, and propose the research plans for the near future (over the next 5 years), following IOTC Resolution 13/06.

Meeting Session Number 9

Language English

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Portuguese longliners targeting swordfish and operating in the Indian Ocean regularly capture elasmobranch fishes as bycatch. Of those, the blue shark (Prioce glauca) and the shortfin mako (Isurus oxyrinchus) constitute the two main shark species captured. A recent effort by IPMA (Portuguese Sea and Atmospheric Institute) has been made to recover historical catch data on elasmobranchs captured since the late 1990’s to the present date in that fishery. Nomil CPUEs for these two major sharks were calculated as kg/1000 hooks and standardized with Generalized Linear Models (GLM). Several different modeling techniques were tested and compared, chosen depending on the specific proportion of zeros in the catch data for each species. The models tested included the delta method, tweedie, gamma and lognormal models. Model validation was carried out with residual alysis, and relative indexes of abundance for the two species were calculated. The results presented in this paper update a previous al ysis on the trends of elasmobranch catch rates available from the Portuguese longline fishery operating in the Indian Ocean.

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