Characteristics of bycatch of porcupine crabs, Neolithodes grimaldii (Milne-Edwards and Bouvier, 1894) from deepwater turbot gillnets in the northwest Atlantic

Abstract

Abstract Porcupine crabs, Neolithodes grimaldii (Milne-Edwards and Bouvier, 1894), are caught as bycatch in deepwater gillnets targeting turbot (Reinhardtius hippoglossoides) off Newfoundland and Labrador and in Davis Strait in the northwest Atlantic. Biological information was obtained through measurement and examination of samples from gillnets vessels. Carapace length (CL) of the samples ranged from 57 mm to 180 mm with a mean CL of 128 mm. The size of male crabs was larger than that of female in the samples measured. The weight of the crab was similar for both males and females of the same carapace length. Bycatch rates of the crab and catch rates of turbot were analyzed from log books returned from the vessels. Bycatch rates of the crab ranged from 0 to 2800 kg/fleet of 50 nets (mean 297 ± 18.5 kg/fleet, N = 256). Crab bycatch rates (kg/fleet) increased with the duration the nets were soaked in water, but daily rates (kg/(fleet day)) were relatively steady (mean 50.4 ± 6.4 kg/(fleet day), N = 166). Greater bycatch rates were recorded in areas north of 59°N and in water depths greater than 1200 m. The average bycatch rate in relation to turbot catch increased with water depth with a mean rate of 19.8 kg of crabs for every 100 kg of turbot (N = 176, S.E. 4.8). It is estimated that a total of 767,000 kg of porcupine crab was caught and discarded by gillnet vessels fishing in Canadian waters in Northwest Atlantic Fisheries Organisation (NAFO) Areas 0, 2, and 3 in 1996, during which a total turbot landing from gillnets from the same areas was around 3,872,000 kg.