Articles | Volume 42
29 Aug 2016
 | 29 Aug 2016

Relationships between tuna catch and variable frequency oceanographic conditions

Franklin Isaac Ormaza-González, Alejandra Mora-Cervetto, and Raquel María Bermúdez-Martínez

Abstract. Skipjack (Katsuwunus pelamis), yellow fin (Thunnus albacares) and albacore (Thunnus alulunga) tunas landed in the Eastern Pacific Ocean (EPO) countries and Ecuador were correlated to the Indexes Oceanic El Niño (ONI) and Multivariate Enso Index (MEI). The temporal series 1983–2012, and 1977–1999 (warm Pacific Decadal Oscillation, PDO), and 2000–2012 (cold PDO) were analyzed. Linear correlation showed that at least 11 % of the total landings were associated with the MEI, with a slightly negative gradient from cold to warm conditions. When non-linear regression (n  =  6), the R2 was higher up to 0.304 (MEI, r =  0.551). The correlation shows high spread from −0.5 to +0.5 for both MEI/ONI; the highest landings occurred at 0.34–0.45; both indexes suggested that at extreme values < −1.0 and > 1.1 total landings tend to decrease. Landings were associated up to 21.9 % (MEI) in 2000–2012, 1983–1999 rendered lower R2 (< 0.09); i.e., during cold PDO periods there was a higher association between landings and oceanographic conditions. For the non-linear regression (n  =  6) a R2 of 0.374 (MEI) and 0.408 (ONI) were registered, for the 2000–2012, a higher R2 was observed in 1983–1999, 0.443 and 0.711 for MEI and ONI respectively, suggesting that is better to analyze split series (1983–1999, 2000–2012) than as a whole (1983–2012), due to noise produced by the transition from hot to cold PDOs. The highest landings were in the range −0.2 to 0.5 for MEI/ONI. The linear regression of skipjack landings in Ecuador gave an R2 of 0.140 (MEI) and 0.066 (ONI) and the non-linear were 0.440 and 0.183 respectively. Total landings in the EPO associated to oceanographic events of high and low frequencies could be used somehow as predictors of the high El Niño o La Niña. There is a clear evidence that tuna fish biomass are at higher levels when the PDO is on cold phase (2000–2030) and vice versa on warm phase (1980–1999). The analysis of the skipjack catch per unit effort (CPUE) on floating aggregating devices (FADs) suggests higher CPUE on FADs (around 20 mt set−1) when oceanographic indexes ONI/MEI are below −0.5. Findings of this work suggest that fishing and management of commercial fish must be analyzed under the light of oceanographic conditions.

Short summary
This Paper endeavors to find or understand the relationships between tuna landings and dramatic events as El Niño in the Central Eastern Pacific and visualize the impact of long term oscillations, like the Pacific decadal Oscillation (PDO). Here for the first time tuna landing, fish efforts and the El Niño indexes (ONI and MEI) are correlated to find how the later affect the tuna fishery. Special attention has been put on tuna landings in Ecuador.