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At-haulback mortality of elasmobranchs caught on the Portuguese longline swordfish fishery in the Indian Ocean

Year of publication 2013

Product type Meeting

Category Meeting document

Edition 1

Statutory body / Meeting title Indian Ocean Tuna Commission (IOTC)

Meeting symbol IOTC-2011-WPEB07-31

Meeting Session Number 7

Language English

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    Brief presentation of the Portuguese research plan for the improvement of knowledge on pelagic sharks caught in the swordfish fishery in the Indian Ocean 2013
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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, 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.
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    An updated overview of the swordfish catches by the Portuguese pelagic longline fishery in the Indian Ocean between 1998-2012: catch, effort, CPUE and catch-at-size 2013
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    The Portuguese longline fishery targeting swordfish in the Indian Ocean started in the late 1990’s, targeting mainly swordfish. A recent effort by Portuguese Marine and Atmosphere Institute (IPMA) has been made aiming the collection of historical catch data on this fishery since the late 1990’s to the present date. This working document reports an updated overview of the Portuguese swordfish fishery, including alyses on the catches, effort, catch-at-size and CPUE trends for the period 1998-2012. The trends in the swordfish catch-at-size were alyzed annually, and compared between months and regions of operation of the fishery. Nomil annual CPUEs were calculated as kg/1000 hooks, and were standardized with Generalized Linear Models (GLMs) using year, quarter, location and swordfish/blue shark ratio as explatory variables. Three different modeling approaches were used and compared, including tweedie, gamma and lognormal models, and model validation was carried out with a residual alysis. A sensitivity alysis to the influence of the ratio factor in the models was carried out. The results presented in this paper update a previous alysis on the trends of swordfish catches available from the Portuguese longline fishery operating in the Indian Ocean.
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