Assigning shark fin origin using species distribution models needs a reality check.

Vincent Raoult,Tommaso Giarrizzo,Luís Fernando Rodrigues Filho,Michael I Grant,Leonardo Manir Feitosa,Jorge Luiz S Nunes,Matias Braccini,Andrew Chin,Diego Cardeñosa,Luís Fernando Carvalho Costa,Colin A Simpfendorfer,John Carlson,Ana Paula Barbosa Martins,Jane E Williamson,João Bráullio L Sales,Tobey Curtis

doi:10.1098/rsbl.2020.0907

Abstract

[Extract] The conservation and management of shark populations have become urgent issues to ensure the future health of our oceans [1]. There are many drivers of the decline of shark populations, with the demand for shark fins being one of the more important [2]. Understanding fin origin can help identify regions for improved management, and hence has been the focus of recent research (e.g. Fields et al. [3], Cardenosa et al. [4]). In a recent Biology Letters article, Van Houtan et al. [5] contributed to this work using data on species composition of shark fins at four markets and species distribution models (SDMs) to predict the probability of fin origin. Their purpose was to address knowledge gaps in source and trade routes of shark products, which currently limit the effective allocation of management resources. While the broad concept behind their paper is novel, we disagree with the results and conclusions owing to flaws in methodology and interpretation.

Highlights

From the IUCN red list of threatened species (a) Isurus oxyrinchus (b) Carcharhinus amblyrhynchos (c) Sphyrna tudes (d) Sphyrna mokarran heterogeneous [6] because of the patchy nature of target species and spatially explicit management arrangements
An example of the dissonance caused by excluding fishing activity is northwestern Australia, where Van Houtan et al [5] indicate a high probability of shark fin origin for many species, despite the area being closed to commercial shark fishing since 1993, and no operational fisheries to support suggested catch [7]
The paper’s use of DNA data from some markets may be misleading since it assumed that all markets contributed to the global fin trade

Summary

Introduction

From the IUCN red list of threatened species (a) Isurus oxyrinchus (b) Carcharhinus amblyrhynchos (c) Sphyrna tudes (d) Sphyrna mokarran heterogeneous [6] because of the patchy nature of target species and spatially explicit management arrangements (e.g. marine protected areas, shark sanctuaries, catch and effort limits). The fact that the size of a nation’s exclusive economic zone accounted for more of the variation in Van Houtan et al.’s [5] estimate of a nation’s contribution to the fin trade (r2 = 0.48) than its elasmobranch catch as reported to FAO (r2 = 0.20) underlines this erroneous assumption.

Results

Conclusion