Population assessment of tropical tuna based on their associative behavior around floating objects.

M Capello,J L Deneubourg,L Dagorn,K M Schaefer,K N Holland,M Robert

doi:10.1038/srep36415

Abstract

Estimating the abundance of pelagic fish species is a challenging task, due to their vast and remote habitat. Despite the development of satellite, archival and acoustic tagging techniques that allow the tracking of marine animals in their natural environments, these technologies have so far been underutilized in developing abundance estimations. We developed a new method for estimating the abundance of tropical tuna that employs these technologies and exploits the aggregative behavior of tuna around floating objects (FADs). We provided estimates of abundance indices based on a simulated set of tagged fish and studied the sensitivity of our method to different association dynamics, FAD numbers, population sizes and heterogeneities of the FAD-array. Taking the case study of yellowfin tuna (Thunnus albacares) acoustically-tagged in Hawaii, we implemented our approach on field data and derived for the first time the ratio between the associated and the total population. With more extensive and long-term monitoring of FAD-associated tunas and good estimates of the numbers of fish at FADs, our method could provide fisheries-independent estimates of populations of tropical tuna. The same approach can be applied to obtain population assessments for any marine and terrestrial species that display associative behavior and from which behavioral data have been acquired using acoustic, archival or satellite tags.

Highlights

As growth rates and migration patterns[27,28,29,30,31]
Different species of tropical tunas, such as skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna are known to associate with natural or man-made floating objects, usually called Fish Aggregating Devices (FADs) and fishers have been exploiting this associative behavior for years[41]
This natural phenomenon has been exploited by purse seine tuna fisheries, which deploy a large number of drifting FADs to increase their chances to locate and catch tropical tuna[42]

Summary

Introduction

As growth rates and migration patterns[27,28,29,30,31]. they allowed unprecedented sampling of subpopulations of animals, these approaches suffer possible bias when applied to pelagic fish species. The recent introduction of animal remote tracking technologies through satellite, archival and acoustic tagging allows unprecedented opportunities for gaining knowledge of the spatial and behavioral ecology of different species in their natural habitats Thanks to this technology, marine scientists can gain more insights about movements and behavior of large pelagic fish (e.g. refs 35–38). Different species of tropical tunas, such as skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares) and bigeye (Thunnus obesus) tuna are known to associate with natural or man-made floating objects, usually called Fish Aggregating Devices (FADs) and fishers have been exploiting this associative behavior for years[41] In recent decades, this natural phenomenon has been exploited by purse seine tuna fisheries, which deploy a large number of drifting FADs to increase their chances to locate and catch tropical tuna[42]. We demonstrate, through modeling and data analysis, that knowledge of tropical tuna behavior around FADs and quantification of individual residence times around floating objects can provide a new path for direct estimates of populations of tropical tuna

Methods

Results

Conclusion