Effects of climate variability on the distribution and fishing conditions of yellowfin tuna (Thunnus albacares) in the western Indian Ocean

Kuo-Wei Lan,Ming-An Lee,Karen Evans

doi:10.1007/s10584-012-0637-8

Kuo-Wei Lan, Ming-An Lee + Show 1 more

Open Access

https://doi.org/10.1007/s10584-012-0637-8

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Abstract

Variations in the abundance and distribution of pelagic tuna populations have been associated with large-scale climate indices such as the Southern Oscillation Index in the Pacific Ocean and the North Atlantic Oscillation in the Atlantic Ocean. Similarly to the Pacific and Atlantic, variability in the distribution and catch rates of tuna species have also been observed in association with the Indian Ocean Dipole (IOD), a basin-scale pattern of sea surface and subsurface temperatures that affect climate in the Indian Ocean. The environmental processes associated with the IOD that drive variability in tuna populations, however, are largely unexplored. To better understand these processes, we investigated longline catch rates of yellowfin tuna and their distributions in the western Indian Ocean in relation to IOD events, sea surface water temperatures (SST) and estimates of net primary productivity (NPP). Catch per unit effort (CPUE) was observed to be negatively correlated to the IOD with a periodicity centred around 4 years. During positive IOD events, SSTs were relatively higher, NPP was lower, CPUE decreased and catch distributions were restricted to the northern and western margins of the western Indian Ocean. During negative IOD events, lower SSTs and higher NPP were associated with increasing CPUE, particularly in the Arabian Sea and seas surrounding Madagascar, and catches expanded into central regions of the western Indian Ocean. These findings provide preliminary insights into some of the key environmental features driving the distribution of yellowfin tuna in the western Indian Ocean and associated variability in fisheries catches.

Highlights

Climatic oscillations, anomalies, and changes clearly affect many ecological processes in marine ecosystems, affecting the population abundances and distributions of many species (Sharp 1992; Stenseth et al 2004; Tian et al 2008)
Given that most of the variability in Catch per unit effort (CPUE) occurred in the region of 30°N–25°S, 40°E–80°E, we restricted further investigations of relationships between the Dipole Modular Index (DMI) and yellowfin tuna catch rates to this region
Wavelet analysis identified a significant negative correlation between standardized CPUE and the DMI with periodicities centred around 4 years (Fig. 3b), suggesting that during positive Indian Ocean Dipole (IOD) events standardized CPUE is reduced and during negative IOD events standardized CPUE increases

Summary

Introduction

Anomalies, and changes clearly affect many ecological processes in marine ecosystems, affecting the population abundances and distributions of many species (Sharp 1992; Stenseth et al 2004; Tian et al 2008). The distribution of warm water species of tuna such as yellowfin (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis) expands into central and eastern regions of the Pacific, increasing their exposure to fisheries in this region. The depth at which yellowfin tuna have access to abundant food compresses with the shallowing of the thermocline in the west, resulting in increased vulnerability of this species to surface fisheries in this region (Lehodey et al 1997, 1998; Lehodey 2004). During La Niña, the opposite occurs with stronger trade winds pushing the warm pool region to the west and deepening the thermocline, while the PEQD increases resulting in a shallower thermocline in the central and eastern Pacific. Distributions of yellowfin and skipjack tuna are pushed further to the west and the vertical habitat of yellowfin tuna is expanded, reducing the vulnerability of the species to surface fisheries in the region (Lehodey et al 1997, 1998; Lehodey 2004)

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