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An overview of the hooking mortality of elasmobranchs caught ina swordfish pelagic longline fishery in the Atlantic Ocean

Published online by Cambridge University Press:  21 November 2012

Rui Coelho ,
Joana Fernandez-Carvalho ,
Pedro G. Lino  and
Miguel N. Santos
Rui Coelho*
Affiliation:
Instituto Português do Mar e da Atmosfera, I.P. (IPMA), Avenida 5 de Outubro s/n, 8700-305 Olhão, Portugal Centro de Ciências do Mar (CCMAR), Universidade do Algarve, Campus de Gambelas FCT Ed.7, 8005-170 Faro, Portugal
Joana Fernandez-Carvalho
Affiliation:
Instituto Português do Mar e da Atmosfera, I.P. (IPMA), Avenida 5 de Outubro s/n, 8700-305 Olhão, Portugal
Pedro G. Lino
Affiliation:
Instituto Português do Mar e da Atmosfera, I.P. (IPMA), Avenida 5 de Outubro s/n, 8700-305 Olhão, Portugal
Miguel N. Santos
Affiliation:
Instituto Português do Mar e da Atmosfera, I.P. (IPMA), Avenida 5 de Outubro s/n, 8700-305 Olhão, Portugal
*
a Corresponding author: [email protected]
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Abstract

Hooking (or “at-haulback”) fishing mortality was analysed in elasmobranchs captured byPortuguese longliners targeting swordfish in the Atlantic Ocean. Information was collectedby on-board fishery observers who monitored 834 longline fishing sets between August 2008and December 2011, and recorded information on 36 067 elasmobranch specimens from 21different taxa. The hooking mortality proportions were species-specific, with some specieshaving relatively high percentages of live specimens at time of haulback (e.g., blueshark, crocodile shark, pelagic stingray, manta, devil and eagle rays), while others hadhigher percentages of dead specimens (e.g., smooth hammerhead, silky shark, bigeyethresher). For the most captured species (Prionace glauca, Pseudocarchariaskamoharai, Isurus oxyrinchus and Alopias superciliosus),logistic generalized linear models (GLMs) were carried out to compare the mortality ratesbetween sexes, specimen sizes and the regions of operation of the fleet. The sex-specificproportions of hooking mortality were significantly different for blue and crocodilesharks, with the males of both species having higher proportions of hooking mortality thanthe females. Specimen size was significant for predicting the hooking mortality for blueand shortfin mako sharks: in both cases, the larger specimens had lower odds of dying dueto the fishing process. There were differences in the hooking mortality depending on theregion of operation of the fleet, but those differences were also species-specific. Forblue and crocodile sharks, the hooking mortality was higher in the Equatorial and southernAtlantic areas (when compared to the NE Atlantic region), while the opposite was observedfor the shortfin mako, with lower mortality rates in the NE tropical area compared withthe other regions. The results presented in this paper can be integrated into futureecological risk assessment analysis for pelagic elasmobranchs. Furthermore, the newinformation can be used to evaluate the impact of recent recommendations prohibiting theretention of some vulnerable elasmobranch species.

Keywords

Hooking mortalitypelagic longline fisheriesbycatchdiscardssharksraysAtlantic Ocean
Type
Research Article
Information
Aquatic Living Resources , Volume 25 , Issue 4 , October 2012 , pp. 311 - 319
Copyright
© EDP Sciences, IFREMER, IRD 2012

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