Bycatch diversity and variation in a tropical Australian penaeid fishery; the implications for monitoring

The composition of teleost and elasmobranch bycatch in two tropical Austral ian penaeid prawn fisheries was examined using scientific surveys. These co vered the major fishing grounds in February and October 1997. On average 82 % of the bycatch was teleosts and elasmobranchs, resulting in a high propor tion of the bycatch which is unlikely to survive capture. The bycatch is hi ghly diverse (over 350 species of teleosts and elasmobranchs) and dominated by species which occur rarely (75% of species occurred in < 10% of trawls) and in low abundance (< 10n h(-1)) and biomass (< 1 kg h(-1)). Eight famil ies, including 83 species had to be included to account for 66% of the byca tch weight. Overall the general catch characteristics (e.g. total bycatch weight, catch rate of teleosts and elasmobranchs), bycatch composition and individual sp ecies abundances showed significant variation among the regions and between February and October. The variation due to regional differences was much g reater than between the two times of year. The inclusion of covariates (dep th, acoustic measures of seabed roughness and hardness, commercial prawn ca tch and commercial fishing effort) explained some of the observed variation but there was still significant regional variation present. The primary im plication of the results is the clear need for future monitoring strategies to be stratified with respect to region. Monitoring from a single region o r time is unlikely to be representative of the fishery. (C) 2001 Elsevier S cience B.V All rights reserved.