[MARMAM] Publication on dolphin bycatch from North-Western Australia

Simon Allen S.Allen at murdoch.edu.au
Wed Apr 9 23:46:56 PDT 2014

G'day MARMAM folks,

We're pleased to announce the online publication of the following research article in PLoS ONE last week:

Allen SJ, Tyne JA, Kobryn HT, Bejder L, Pollock KH and Loneragan, NR (2014). Patterns of Dolphin Bycatch in a North-Western Australian Trawl Fishery. PLoS ONE 9(4): e93178. doi:10.1371/journal.pone.0093178


The bycatch of small cetaceans in commercial fisheries is a global wildlife management problem. We used data from skippers’ logbooks and independent observers to assess common bottlenose dolphin (Tursiops truncatus) bycatch patterns between 2003 and 2009 in the Pilbara Trawl Fishery, Western Australia. Both datasets indicated that dolphins were caught in all fishery areas, across all depths and throughout the year. Over the entire datasets, observer reported bycatch rates (n = 52 dolphins in 4,124 trawls, or 12.6 dolphins/1,000 trawls) were ca. double those reported by skippers (n = 180 dolphins in 27,904 trawls, or 6.5 dolphins/1,000 trawls). Generalised Linear Models based on observer data, which better explained the variation in dolphin bycatch, indicated that the most significant predictors of dolphin catch were: (1) vessel - one trawl vessel caught significantly more dolphins than three others assessed; (2) time of day – the lowest dolphin bycatch rates were between 00:00 and 05:59; and (3) whether nets included bycatch reduction devices (BRDs) - the rate was reduced by ca. 45%, from 18.8 to 10.3 dolphins/1,000 trawls, after their introduction. These results indicated that differences among vessels (or skippers’ trawling techniques) and dolphin behavior (a diurnal pattern) influenced the rates of dolphin capture; and that spatial or seasonal adjustments to trawling effort would be unlikely to significantly reduce dolphin bycatch. Recent skipper’s logbook data show that dolphin bycatch rates have not declined since those reported in 2006, when BRDs were introduced across the fishery. Modified BRDs, with top-opening escape hatches from which dolphins might escape to the surface, may be a more effective means of further reducing dolphin bycatch. The vulnerability of this dolphin population to trawling-related mortality cannot be assessed in the absence of an ongoing observer program and without information on trawler-associated dolphin community size, broader dolphin population size and connectivity with adjacent populations.

If interested, you can download the PDF at http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0093178

Kind regards, Simon

Simon Allen
Research Associate and PhD candidate
Murdoch University Cetacean Research Unit
School of Veterinary and Life Sciences
Murdoch University
WA 6150 Australia

ph: +61(8) 9360 2823
mob: +61(0) 416 083 653
email: S.Allen at murdoch.edu.au
web: http://mucru.org/group-members/simon-allen/

"The opposite for courage is not cowardice, it is conformity. Even a dead fish can go with the flow" (Jim Hightower)
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