Title : Nonlinear soak-time dynamics and efficiency optimum in tropical mud crab pento (trap) fisheries
Abstract:
Soak duration is a critical operational variable in baited crab gears, but its contribution to catch efficiency in tropical small-scale systems remains insufficiently quantified across diel periods. Field trials were conducted from August to October 2025 in Indragiri Hilir, Indonesia, using six standardized pento gears over 21 fishing trips and five immersion durations of 4, 6, 8, 10 and 13 h. Catch performance was evaluated using total catch, catch per unit effort and time-standardized catch per unit effort, and a nonlinear catch-duration model was fitted separately for day and night operations. Mean catch increased from 4 to 10 h and declined at 13 h, producing a consistent hump-shaped response. The highest catch per haul occurred at 10 h during both night (4.33 ± 1.06 individuals) and day (4.24 ± 1.45 individuals). Total observed catch was higher at night (225 individuals) than during the day (194 individuals), while estimated optimal durations were 9.57 h at night and 10.18 h during the day. Model fit was modest, indicating that environmental and behavioural variability also influenced catches. This study provides an early quantitative estimate of the operational duration that maximizes catch performance in a tropical mangrove pento fishery and offers practical guidance for improving the efficiency of small-scale mud crab harvesting.
Keywords: Diel period; Mud crab; Nonlinear model; Soak time; Traditional traps.
