A Closing Bound for Beach Seining: The Largest Seine a Standard Hauling Team Can Close, and the Haul Rate Longer Seines Require

A beach seine traps fish in a pocket between the net and the shore, and the fish leave the way they came in: around the ends, through the gap that stays open until the haul is nearly finished. This paper originates a closing bound for that process. The seine is modelled as a semicircle against a straight beach, both ends are hauled toward each other at a speed limited by the hauling team's strength working against water drag on the net, and every fish is assumed to head straight for the nearer end at an effective speed of 0.25 m/s for the whole closing time, which makes the computed escape fraction an upper bound. Against a stated design bound of one fish in five escaping (a fraction of 0.20), the largest seine a standard team of two haulers per end, pulling 400 N per end, can close in time is 25 m: at 25 m the model's escape fraction is 0.1677, and at 30 m it has already risen to 0.2471. For longer seines the paper inverts the calculation and gives the minimum haul rate. The required haul speed turns out to be almost independent of length — 0.768 m/s at 40 m of seine and only 0.821 m/s at 200 m — but the force needed to haul that fast against a longer net grows in proportion to length, from 615 N per end (4 haulers) at 40 m to 1,615 N per end (9 haulers) at 100 m and 3,283 N per end (17 haulers) at 200 m. The bound is sensitive to fish speed: the limiting length is 40 m if the fish's sustained speed is 0.3 m/s and only 10 m if it is 0.8 m/s. The practical reading is that closing speed is bought with hauling force, not technique, and that long seines cannot be saved by hauling harder at any realistic team size — they stand or fall on keeping fish from making for the ends at all. The study is simulated, not measured.