Evaluation of the Morrison soft turtle excluder device: prawn and bycatch variation in Moreton Bay, Queensland

Abstract

The present study assesses the effects of a Morrison soft turtle excluder device (TED) upon catch rates of commercial prawn, fish and non-commercial bycatch species at an essentially oceanic site and an estuarine site. Effects of the TED upon catch rates were highly variable. Reductions in prawn catch ( Penaeus plebejus, Penaeus esculentus, Metapenaeus bennettae) in the TED-equipped net varied between no significant reduction to a 29% reduction, by weight, depending on location and season. Reductions in prawn catch could not be attributed to the loss of prawns by species or solely to the selective loss of prawns on the basis of size. Fish catches ( Sillago sp., Platycephalus sp., suggrundus sp.) were highly variable and showed no significant difference between control and TED-equipped nets. Catches of marketable sand crabs ( Portunus pelagicus) were reduced by more than 50% in the TED-equipped net. Large bycatch animals, such as shovelnose rays ( Rhinobatus batillum), sand rays ( Amphotistius kuhlii) and turtles ( Caretta caretta), were caught occasionally in the control net but were absent from the TED-equipped net. Non-commercial bycatch, composed of fish and crustaceans, was reduced by up to 32% by weight in the TED-equipped net. Results from this study suggest that it is difficult to predict accurately the effect of the Morrison soft TED upon catches of prawns and bycatch for all trawl locations and seasons.