ENSO drives lateral separation of FAD-associated skipjack and bigeye tuna in the Western Tropical Pacific

Abstract

14Incidental capture of juvenile bigeye tuna in fish aggregating device (FAD)-associated 15 purse seine fisheries targeting skipjack tuna have contributed significantly to the degradation of 16 bigeye stocks in the Western Tropical Pacific (WTP) Ocean. One way to reduce this incidental 17 catch is to simply limit purse seine fishing effort; however, skipjack tuna stocks are healthy and 18 economically important to many small island nations in the region. Here we assess whether there 19 is sufficient lateral separation of skipjack and bigeye within FAD-associated purse seine fisheries 20 in the WTP to allow limiting bigeye catch while maintaining a robust skipjack fishery. Based on 21 monthly 5°-longitude-by-5°-latitude catch and effort data, FAD-associated bigeye and skipjack 22 catch per unit effort (CPUE) covary tightly throughout the WTP, such that lateral separation 23 between the two species is generally small. There are, however, significant variations in the 24 amount of separation over both space and time. Waters within the Party to the Nauru Agreement 25 exclusive economic zones (EEZs) belonging to Palau, Solomon Islands, and Tuvalu regularly 26 exhibit some of the smallest bigeye-to-skipjack catch ratios, especially during El Niño. In 27 contrast, waters within Kiribati's Phoenix Islands EEZ regularly exhibit some of the largest 28 bigeye-to-skipjack catch ratios, which are particularly high during La Niña. In general, El Niño 29 lowers bigeye-to-skipjack catch ratios east of 170°E, while La Niña lowers bigeye-to-skipjack 30 catch ratios west of 170°E. These ENSO-driven variations in separability are larger and more 31 widespread than those driven by seasonality, due to larger associated variations in environmental 32 conditions. Sea surface height anomalies may be particularly useful for demarcating the different 33 environments preferred by skipjack and bigeye throughout the WTP. Sea surface temperatures, 34 temperatures at 100 m, and thermocline depths may also help distinguish between the two 35 species' preferred habitats in many areas. These analyses can help better inform the complex 3 36 decisions made by both fishers during operations and fisheries managers during creation of 37 effective, dynamic policies to preserve bigeye stocks in the WTP. They also show that climate 38 variability can have substantial effects on the spatial distributions of top pelagic predators and 39 their interactions with one another. 40 1 Introduction 41 The Western and Central Pacific Ocean (WCPO) accounts for more than 60% of total 42 global tuna catch [1]. Tuna and other highly migratory species in this region are managed by the 43 Western and Central Pacific Fisheries Commission (WCPFC), which is one of five tuna Regional 44 Fishing Management Organizations in operation around the world. The most commonly fished 45 tuna species in the WCPO are skipjack (Katsuwonus pelamis), yellowfin (Thunnus albacares), 46 bigeye (Thunnus obesus), and albacore tuna (Thunnus alalunga) [2]. Though these sought-after 47 tuna species...

Analysis and simulation of three tropical cyclones with different paths in the Arabian Sea

“…Several studies have highlighted the warming of eastern North Indian Ocean (NIO) waters as a key factor in storm formation in the NIO region (Bay of Bengal and AS), particularly during the La Niña phase of ENSO (Leung and Leung, 2002;Lin et al, 2020). Additionally, research suggests a higher occurrence of TCs during the negative or neutral phase of ENSO and the positive phase of IOD (Mahala et al, 2015).…”