A Waiting Rule for Newly Anchored Fish Aggregating Devices: How Long a New Device Must Stand Before Fishing It, with a Mooring Scope and Anchor Table

A fish aggregating device, a moored raft or buoy under which fish gather, does not fish at full strength on the day it is anchored. This paper models the build-up of the aggregation as an approach to a settled level with a time constant of 7 days, a stated assumption informed qualitatively by published accounts of aggregation behaviour, and turns that curve into a waiting rule. A new device reaches 50 percent of its settled catch rate after 4.85 days, 80 percent after 11.27 days, 90 percent after 16.12 days, and 95 percent after 20.97 days. The recommended rule is therefore to let a new device stand for about 16 days before fishing it in earnest if 90 percent of the settled rate is wanted, or about 21 days for 95 percent. Fishing every day from day 1 at a settled rate of 40 kg per day, taken as a stated assumption, returns a mean of only 41.2 percent of the settled rate across the first week and a cumulative shortfall of 22.8 percent across the first 28 days, not because waiting creates fish, but because early effort is spent at low rates. Alongside the waiting rule, the paper originates a mooring scope rule in which the required scope ratio grows with surface current, from 1.312 at 0.5 knots to 1.95 at 2.0 knots, and tabulates rode length and concrete anchor mass by depth and current: at 200 m depth and 1.0 knots the rode is 300.0 m and the computed minimum concrete anchor is 187.3 kg in air, rising to 915.9 kg at 2.0 knots. The study is simulated, not measured, and the anchor figures are steady-current minima that exclude wave and storm loading.