Bycatch species composition over time by tuna purse-seine fishery in the eastern tropical Atlantic Ocean

Within the Ecosystem-based fisheries management framework, we evaluated the changes over time in bycatch species of the European tuna purse-seine fishery operating in the eastern Atlantic Ocean. Bycatch data was collected during two scientific observer programs conducted in the late 1990s and in the late 2000s. Over these two time periods, we compared the temporal trends in bycatch species composition, the probability of occurrence of functional groups per fishing set, the spatio-temporal species richness and the potential impact on several species listed in the red list of the International Union for Conservation of Nature (IUCN). The analyses were performed separately on the two main fishing modes of the fleet, i.e. sets on free-swimming school sets and on fish aggregating devices (FADs). Owing data quality constraints, we did not estimate bycatch rates. Ours results showed that the species composition of sharks caught on FADs decreased over time. The total species richness was higher for FAD sets than for free-swimming school sets (87 vs. 61 species respectively), such difference is common between fishing modes worldwide. For the species catalogued as threatened by the IUCN, in free-swimming schools, 25.5 % of the species caught during first period increased to 30.4 % during second period, while for FAD-fishing the increase was from 28.8 % during first period to 34.9 % in second period. Ours findings suggest that tropical tuna purse-seine fisheries should include ecosystem-based governance of bycatch. Effective tuna management will require a combination of technological improvements for mitigating incidental catch of vulnerable species, best use of byproduct species, regulations in fishing practices and in spatial distribution of fishing effort, and international agreements that, together, can monitor and manage bycatch, reducing the negative fishing effects on the epipelagic ecosystem biodiversity.

[1]  A. Chao.  Nonparametric estimation of the number of classes in a population , 1984 .

[2]  S. J. Cripps,et al.  Defining and estimating global marine fisheries bycatch , 2009 .

[3]  D. Gaertner,et al.  Bycatch of billfishes by the European tuna purse-seine fishery in the Atlantic Ocean , 2002 .

[4]  A. Frid,et al.  Predicting ecological consequences of marine top predator declines. , 2008, Trends in ecology & evolution.

[5]  Robert K. Colwell,et al.  Quantifying biodiversity: procedures and pitfalls in the measurement and comparison of species richness , 2001 .

[6]  R. Olson,et al.  Ecological Metrics of Biomass Removed by Three Methods of Purse‐Seine Fishing for Tunas in the Eastern Tropical Pacific Ocean , 2012, Conservation biology : the journal of the Society for Conservation Biology.

[7]  D. L. Alverson,et al.  By-Catch: Problems and Solutions , 2000 .

[8]  J. Hortal,et al.  Evaluating the performance of species richness estimators: sensitivity to sample grain size. , 2006, The Journal of animal ecology.

[9]  A. Punt,et al.  Ecosystem-based fisheries management requires a change to the selective fishing philosophy , 2010, Proceedings of the National Academy of Sciences.

[10]  S. Garcia.  The ecosystem approach to fisheries : issues, terminology, principles, institutional foundations, implementation and outlook , 2003 .

[11]  Steven A. Murawski,et al.  Definitions of overfishing from an ecosystem perspective , 2000 .

[12]  A. Cosandey-Godin,et al.  Fisheries Bycatch of Sharks : Options for Mitigation , 2011 .

[13]  E. Gilman,et al.  Performance of regional fisheries management organizations: ecosystem‐based governance of bycatch and discards , 2014 .

[14]  Marti J. Anderson,et al.  Multivariate dispersion as a measure of beta diversity. , 2006, Ecology letters.

[15]  Robert K. Colwell,et al.  INTERPOLATING, EXTRAPOLATING, AND COMPARING INCIDENCE-BASED SPECIES ACCUMULATION CURVES , 2004 .

[16]  Marti J. Anderson,et al.  Beta diversity and taxonomic sufficiency: Do higher‐level taxa reflect heterogeneity in species composition? , 2009 .

[17]  D. L. Alverson.  A global assessment of fisheries bycatch and discards , 1994 .

[18]  Emmanuel Chassot,et al.  Bycatch of the European purse seine tuna fishery in the Atlantic Ocean for the 2003-2007 period , 2010 .

[19]  F. Simard,et al.  Reconsidering the Consequences of Selective Fisheries , 2012, Science.

[20]  E. Chassot,et al.  SOME PRELIMINARY RESULTS ON TUNA DISCARDS AND BYCATCH IN THE FRENCH PURSE SEINE FISHERY OF THE EASTERN ATLANTIC OCEAN , 2009 .

[21]  Robert K. Colwell,et al.  Estimating terrestrial biodiversity through extrapolation. , 1994, Philosophical transactions of the Royal Society of London. Series B, Biological sciences.

[22]  Marti J. Anderson,et al.  Distance‐Based Tests for Homogeneity of Multivariate Dispersions , 2006, Biometrics.

[23]  Stephen J. Hall,et al.  Managing by-catch and discards: how much progress are we making and how can we do better? , 2005 .

[24]  Emmanuel Chassot,et al.  Precision in bycatch estimates: the case of tuna purse-seine fisheries in the Indian Ocean , 2012 .

[25]  BY-CATCH AND DISCARDS OF THE EUROPEAN PURSE SEINE TUNA FISHERY IN THE ATLANTIC OCEAN: ESTIMATION AND CHARACTERISTICS FOR 2008 AND 2009 , 2011 .

[26]  James C. Stegen,et al.  PERSPECTIVE Navigating the multiple meanings of b diversity: a roadmap for the practicing ecologist , 2010 .

[27]  M. Hall.  On bycatches , 2004, Reviews in Fish Biology and Fisheries.

[28]  E. Gilman.  Bycatch governance and best practice mitigation technology in global tuna fisheries , 2011 .

[29]  Rebecca L. Lewison,et al.  Understanding impacts of fisheries bycatch on marine megafauna , 2004 .

[30]  L. Kell,et al.  Productivity and susceptibility analysis for species caught in Atlantic tuna fisheries , 2011 .