Effect of marine climate and baitfish availability on the tuna baitboat fishery CPUE OFF northwestern Mexico

Tunas caught by the baitboat fleet are one of the most sustainable products of the high seas. We analyzed catches of the baitboat fleet operating off northwestern Mexico from 1978 to 2013. We assessed the relationship between the standardized tuna catch and the Multivariate El Niño Index (MEI), the Pacific Decadal Oscillation (PDO), and landings of the two main species (Pacific sardine, Sardinops sagax, and northern anchovy, Engraulix mordax) used as baitfish in the Northeastern Pacific Ocean tuna fishery. Results showed a strong correlation between yellowfin tuna (Thunnus albacares) catches and sardine landings, and an inverse correlation between yellowfin tuna catches and both MEI and PDO. Yellowfin tunas are more abundant during colder-than-normal conditions. We hypothesized that, when the sardine population is more vulnerable to the small-pelagic fishery in the Gulf of California, environmentally ideal conditions, as well as baitfish (sardine) availability, resulted in high yellowfin tuna landings. The opposite behavior was observed for the standardized catch of skipjack tuna (Katsuwonus pelamis): a strong correlation with anchovy landings and a positive correlation with both MEI and PDO suggested that there is an alternation between tuna and small pelagic species.