Comparative study of skipjack tuna &lt;em&gt;Katsuwonus pelamis&lt;/em&gt; (Scombridae) fishery stocks from the South Atlantic and western Indian oceans

Lol I Dahlet,Nicola Downey-Breedt,Warwick H.H Sauer,Maria A Gasalla,Gabriel Arce

doi:10.3989/scimar.04804.22c

Abstract

The skipjack tuna, Katsuwonus pelamis, inhabits tropical and subtropical oceans the world over, and contributes substantially to total tuna catches. Both fishing pressure and anthropic influences affect skipjack populations, impacting on economic returns and investment. The present study analyses and compares spatial time series of catch and catch per unit effort (CPUE), of pole-and-line fishing of skipjack tuna from Brazil, South Africa and the Maldives. Both regional and inter-regional analyses were conducted for the period 1970-2014 in order to ultimately investigate potential associations between these fisheries, climatic conditions and the El Niño Southern Oscillation (ENSO). Correlation tests and spatial mapping tools were used. From 2004 to 2011, South African skipjack catches correlated positively with Brazilian ones and negatively with Maldivians. CPUEs from the Brazilian and Maldivian skipjack fisheries showed a significant positive correlation in the period 1982-1993. Yearly catches from all regions were strongly associated with the Northern Oscillation Index (p < 0.001), an ENSO index. This study reflects an effort to articulate an inter-regional appraisal of skipjack pole-and-line fisheries embedded in the context of a globally changing climate, in the face of which emerging economies are the most vulnerable. Evidence of common patterns influencing these fisheries should encourage international South-South cooperative management and understanding of the resource.

Highlights

Temporal and spatial fluctuations in the abundance of oceanic pelagic populations spread geographically around the globe are common (Cushing 1975). The causes of these fluctuations may be exogenous or endogenous to the organism (Ricker 1954). This scenario applies to some tuna stocks, including the skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758), known as bonito-listrado in Brazil, katunkel, or ocean bonito in South Africa, and godhaa or kadumas skipjack in the Maldives
The non-linear regression explained 40% of the yearly catch distribution pattern, suggesting that higher catches are associated with a Northern Oscillation Index (NOI) of –1 and 0.5, while lower catches are associated with neutral years (NOI around 0)
The common increasing trend may be linked to the overall development of the fisheries, and influenced by the considerable fluctuation of catch data (c.f. the low R2 found for the linear regression of BR catch time series), which can camouflage the status of the stocks (ICCAT 2014b)

Summary

Introduction

Temporal and spatial fluctuations in the abundance of oceanic pelagic populations spread geographically around the globe are common (Cushing 1975). The causes of these fluctuations may be exogenous (environmental or anthropogenic) or endogenous to the organism (e.g. ontogenetic drivers) (Ricker 1954). This scenario applies to some tuna stocks, including the skipjack tuna, Katsuwonus pelamis (Linnaeus, 1758), known as bonito-listrado in Brazil, katunkel, or ocean bonito in South Africa, and godhaa (bigger) or kadumas (smaller) skipjack in the Maldives. Off South Africa, skipjack catches are 1000 to 10000 times lower than those from Brazil and the Maldives, and the highest catches were recorded in 2012

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