Abstract
Skipjack tuna is targeted by various types of fishing gear in coastal countries. Due to itsresilience, it has withstood heavy fishing pressure in the past few decades. Coastal drifting gillnetfleets also mark skipjack as their main target, but it is often overlooked in terms of stock assessment.This study provides new information on an abundance index based on fishery-dependent data from2010 to 2017. Generalized linear models (GLMs) were used to standardize the catch-per-unit-ofeffort(CPUE) using year, quarter, and gross tonnage as the prediction variables. Model goodnessof-fit and model selection were based on the Akaike Information Criterion (AIC), the pseudocoefficient of determination (R2), and model diagnostics with a residual analysis. The finalestimation of the abundance index was calculated by least square means or marginal means. Theresults showed that the index was heavily influenced by the year and quarter, but it did not relateto the vessel’s capacity. While the CPUE series fluctuated greatly, it showed a declining trend overthe years of observation.
Highlights
Skipjack tuna (Katsuwonus pelamis) is commercially valuable and exploited by many coastal countries along the Indian and the Pacific Oceans [1]
In this study we provide new information on an abundance index based on fishery-dependent data, especially from the coastal drifting gillnet fisheries
High standard error (SE) values were found from December to April as a result of a low sample size—less than 100 vessels/month (Figure 1)
Summary
Skipjack tuna (Katsuwonus pelamis) is commercially valuable and exploited by many coastal countries along the Indian and the Pacific Oceans [1]. Since the introduction of fish aggregating devices (FADs), as well as the arrival of industrial purse seiners in the late 1980s, the catch of skipjack in the Indian Ocean has increased substantially [2,3]. The catch of skipjack tuna from Indonesian fleets accounted for 21% of the total catch in the Indian Ocean [4]. The average catch of tunas caught by Indonesian fleets in the Indian Ocean area from 2012 to 2016 was estimated to be around 150,062 tons, where the catch was dominated by skipjack tuna (51.4%), yellowfin tuna (25.9%), bigeye tuna (17.3%), and albacore (5.4%) [4]. Catches of skipjack from Indonesian fleets have declined over the years.
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