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Buoy gear - a potential for bycatch reduction in the small-scale swordfish fisheries: a Florida experience and Indian Ocean perspective









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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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    Exploratory analysis of the relationship between swordfish capture and environmental features in the southwest Indian Ocean 2013
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    Oceanic circulation plays a major in the distribution of nutrients and oceanic structures such as fronts and eddies may become hotspots of biological activity through concentration and enrichment processes. Oceanic structures generally attract forage fish and cephalopods and may therefore be targeted by marine top-predators. The link between swordfish (Xiphias gladius) captures and environmental structures is poorly documented in the southwest Indian Ocean despite the growing need of the local f ishery from Reunion Island for such information. In this study we used a set of temporal (date, moon phase), geographic (longitude, latitude, distance to coast, bathymetry) and environmental covariates (sea surface temperature, chlorophyll-a concentration, sea level anomalies, index of convergence) to explain variations in swordfish catch per unit of effort (CPUE) throughout 2012. Univariate alyses show strong seasol and latitudil patterns in swordfish occurence. We also found that higher swordf ish CPUE are associated with shelf-break areas and sea mounts, as well as dymic environmental structures, even though these relationships explain only a small fraction of swordfish CPUE variations. Chlorophyll-a fronts and dymic convergent structures as identified by finite-size Lyapunov exponents might attract swordfish.
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    Standardized CPUE series for blue and shortfin mako sharks caught by the Portuguese pelagic longline fishery in the Indian Ocean, between 1999 and 2012 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. 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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