Seasonal Distribution of Tuna and Non-tuna Species Associated With Drifting Fish Aggregating Devices (DFADs) in the Western Indian Ocean Using Fishery-Independent Data

Blanca Orúe,Hilario Murua,Jon Lopez,Gala Moreno,Josu Santiago,Lourdes Ramos,Maria Grazia Pennino

doi:10.3389/fmars.2020.00441

Abstract

Man-made floating objects in the surface of tropical oceans, also called drifting fish aggregating devices (DFADs), attract tens of marine species, including tunas and non-tuna species. In the Indian Ocean, around 80% of the sets currently made by the EU purse-seine fleet are on DFADs. Due to the importance and value of this fishery, understanding the habitat characteristics and dynamics of pelagic species aggregated under DFADs is key to improve fishery management and fishing practices. This study implements Bayesian hierarchical spatial models to investigate tuna and non-tuna species seasonal distribution, based on fisheries-independent data derived from fishers’ echo-sounder buoys, environmental information (Sea Surface Temperature, Chlorophyll, Salinity, Eddie Kinetic Energy, Oxygen concentration, Sea Surface Height, Velocity and Heading) and DFAD variables (DFAD identification, days at sea). Results highlighted group-specific spatial distributions and habitat preferences, finding higher probability of tuna presence in warmer waters, with higher sea surface height and low eddy kinetic energy values. In contrast, highest probabilities of non-tuna species were found in colder and productive waters. Days at sea were relevant for both groups, with higher probabilities at objects with higher soak time. Our results also showed species-specific temporal distributions, suggesting that both tuna and non-tuna species may have different habitat preferences depending on the monsoon period. The new findings provided by this study will contribute to the understanding of the ecology and behavior of target and non-target species and their sustainable management.

Highlights

Pelagic ecosystems are highly dynamic environments in time and space (Kaplan et al, 2010; Dueri and Maury, 2013), accounting for 99% of the biosphere volume (Angel, 1993) and supplying more than 80% of the fish consumed by humans (Pauly et al, 2002)
The species-specific temporal distributions found in this study suggest that both tuna and non-tuna species associated with drifting fish aggregating devices (DFADs) may have different habitat preferences depending on the monsoon period
The Bayesian Hierarchical Spatial Models (B-HSMs) used in this study provides a description of the seasonal distribution of tuna and non-tuna species associated to DFADs in the Indian Ocean using large-scale, non-invasive sampling, and identifies the suitable and preferential areas of these species’ groups

Summary

Introduction

Pelagic ecosystems are highly dynamic environments in time and space (Kaplan et al, 2010; Dueri and Maury, 2013), accounting for 99% of the biosphere volume (Angel, 1993) and supplying more than 80% of the fish consumed by humans (Pauly et al, 2002). In the Indian Ocean, more than 80% of the total sets of purse seiners in recent years have been on man-made drifting fish aggregating devices (DFADs) (Báez et al, 2018). Studies on detailed distribution patterns of pelagic species are scarce in the Indian Ocean Those studies have been carried out using fishery-dependent data, such as catch logbooks (Chen et al, 2005; Lee et al, 2005; Rajapaksha et al, 2013; Potier et al, 2014; Arrizabalaga et al, 2015; Druon et al, 2017) or observers data onboard commercial vessels (Sequeira et al, 2012; LezamaOchoa et al, 2016; Coelho et al, 2017) and have not necessarily been focused on purse seine information

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