Bram Setyadji

Developing data- and capacity-limited stock assessment methods for sustainable neritic tuna fisheries

Name: Bram Setyadji
Primary Supervisor: Matthew Spencer
Year: 3
Discipline: Earth, Ocean, and Ecological Sciences
Presentation type: 6 Minute talk
Project Title: Developing data- and capacity-limited stock assessment methods for sustainable neritic tuna fisheries

Abstract:

Catch-per-unit-of-effort (CPUE) as index of abundance can serve as a valuable indicator of trends in stock biomass, particularly for calibrating the stock assessment. However, obtaining a reliable index becomes challenging in fisheries interacted with fish aggregating devices (FADs), as effort is no longer easily defined. FADs are designed to maintain catchability, thereby violating the assumption that CPUE is proportional to stocks size. To address this, a simple alternative approach is proposed that estimates stock abundance using the ratio of catches between target and reference species. The catch-ratio estimator performs well when its assumptions are met, and including multiple reference species can improve estimation accuracy. In this case, yellowfin tuna, particularly when combined with skipjack tuna, appears to be a suitable predictor for eastern little tuna. However, further research is needed before this method can be applied in formal stock assessments.

Keywords: Catch-per-unit-of-effort, data-limited fisheries, purse seine fisheries, stock assessment.