The large-scale deployment of fish aggregation devices alters environmentally-based migratory behavior of skipjack tuna in the Western Pacific Ocean.

Xuefang Wang,Yong Chen,Jie Cao,Liuxiong Xu,Wenjiang Guan,Samuel Truesdell,Jeffrey Buckel

doi:10.1371/journal.pone.0098226

Xuefang Wang, Yong Chen + Show 5 more

Open Access

https://doi.org/10.1371/journal.pone.0098226

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Journal: PloS one	Publication Date: May 21, 2014
Citations: 18	License type: CC BY 4.0

Affiliation: University of Maine, Shanghai Ocean University

Abstract

Fish aggregation devices (FADs) have been used extensively in the tuna purse seine fishery since the 1980s. This long-term modification of natural habitat has generated discussions as to whether FADs impact movement patterns of tuna species. We examined this question using data collected from the skipjack tuna (Katsuwonus pelamis) fishery. We used the longitudinal gravitational center of catch (G) to examine temporal variability in skipjack movement in the Western and Central Pacific Ocean, and related this to El Niño Southern Oscillation (ENSO) events. We found that in most cases G for free-swimming school sets changed with the onset of ENSO events, while G for floating-object-associated school sets remained relatively constant. This suggests that skipjack exhibit distinguishable behavioral strategies in response to ENSO events: they either react by moving long distances or they associate with floating objects. There has been no previous attempt to evaluate the interaction between FADs and the environmentally-determined movement of skipjack; this study shows evidence of an interaction, which should be considered when managing skipjack populations.

Highlights

The tuna purse seine fishery, which accounts for much of the global tuna catch, is divided into two parts: effort that targets freeswimming schools and effort that targets aggregations associated with floating objects
The Gm for free-swimming school sets had a similar pattern to the corresponding monthly southern oscillation index (SOI) (Fig.1) with eastward displacement occurring during El Nino episodes and westward displacement during La Nina episodes
Differences in gravitational catch centers (Gs) by school type Our study reveals an important interaction between the spatial distribution of skipjack catch, fish aggregation devices (FADs) and El Nino Southern Oscillation (ENSO)

Summary

Introduction

The tuna purse seine fishery, which accounts for much of the global tuna catch, is divided into two parts: effort that targets freeswimming schools and effort that targets aggregations associated with floating objects. The attractive nature of floating objects for tuna and tuna-like species greatly increases their catchability, and since the presence of natural floating objects is not always predictable, fishermen often construct and deploy artificial fish aggregation devices (FADs) and have done so since the 1980s [1,2]. This fishing method expanded rapidly during the 1990s, and currently 40% of the global tropical tuna catch comes from purse seine sets on floating objects [3], despite that FAD-associated catches of bigeye (Thunnus obesus) and yellowfin (Thunnus albacares) tuna are comprised mainly of smaller fish [4]. There is still a limited understanding of the potential long-term effects of FADs on tuna stocks and pelagic ecosystems [1,10]

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