Bycatch from the Queensland otter-trawl fishery and the effects of bycatch reduction devices (BRDs)

Project leader: Tony Courtney
Principal investigators: James Haddy, Mark Tonks, Matthew Campbell, Darren Roy, Keith Chilcott, Shane Gaddes, Clive Turnbull, Claire van der Geest, Cassie Rose
Research centres: Southern Fisheries Centre (SFC) and Northern Fisheries Centre (NFC)
Funding body: Fisheries Research & Development Corporation (FRDC)
Dates: July 2000 - June 2007

About this research project

Image of report cover Queensland has the largest trawl fleet in Australia, which in 2007, consisted of 480 licensed vessels. The fishery mainly targets prawns (i.e., king, tiger, banana and endeavour prawns), saucer scallops (Amusium balloti), Moreton Bay bugs (Thenus spp.) and squid (Loligo spp.), but fishers can also retain several other less-commercially important species, known as the "permitted species" which include mantis shrimps (Oratosquilla spp., Belosquilla spp.), cuttlefish (Sepia spp.), octopus (Octopus spp.), Balmain bugs (Ibacus spp.), pipehorses (Solegnathus spp.), barking crayfish (Linuparus trigonus), blue swimmer crabs and three spot crabs (Portunus spp.) and nemipterid fish (i.e., pinkies). In 2005 the fishery landed about 8000 tonnes of product valued at about $100 million (Queensland Fisheries Annual Status Report 2006).

Trawl fisheries like the Queensland fishery produce large amounts of bycatch (see the FAO review by Alverson et al. 1994) which is usually comprised of hundreds of species of small fish and invertebrates, but may also include protected species such as sea turtles and sea snakes. Most bycatch species have no commercial value and although they are returned to the water shortly after being caught, many individuals die as a result of being trawled. The weight of the bycatch is generally significantly greater than the targeted catch of prawns and scallops. Since the introduction of the Trawl Fishery Management Plan [Fisheries (East Coast Trawl) Management Plan 1999] in early 2000, all Queensland otter trawl vessels must have both a turtle excluder device (TED) and a bycatch reduction device (BRD) installed in every trawl net. This research project measured bycatch rates in the fishery and the effects of these devices on the catch rates of prawns, scallop and bycatch.

The project also described the biology and population dynamics of several of the permitted species. Prior to the Trawl Management Plan, fishers were not permitted to retain these species. There is now a need to understand their population dynamics and develop management strategies to sustain them.

The project was funded by the Australian Fisheries Research & Development Corporation (FRDC Project 2000/170) and the Queensland Department of Primary Industries.

The main findings

Project staff obtained measures and sub-samples of bycatch, prawn and scallop catch rates from 1619 individual net trawls over a period of three years from July 2000 to June 2003. These data were obtained from commercial vessels while undertaking their normal fishing operations, and from dedicated research charters that were designed to assess different combinations of TEDs and BRDs. All data were obtained from the main trawl fishing sectors, which include the north Queensland tiger/endeavour prawn fishery, the scallop fishery in central Queensland and the eastern king prawn fishery in southern Queensland. A total of 49.1 tonnes of bycatch was weighed at sea, of which 9.8 tonnes was sub-sampled and processed to species level in the laboratory. Over 1300 taxa were recorded in the bycatch.

Photograph of trawl bycatch with prawns

Photograph of bycatch from the Queensland trawl fishery

Detailed descriptions of the bycatch composition and the effects of TEDs and BRDs on their catch rates are provided in the Project Final Report (see below). Importantly, the project also quantified the effects of the devices on the catch rates of prawns, scallops, Moreton Bay bugs and Balmain bugs.

Bycatch reduction

The most promising finding from the project was obtained from one of the research charters which demonstrated that bycatch rates in the Queensland scallop fishery could be reduced by a mean of 77% by using nets with both TEDs and square mesh codend BRDs, compared to standard nets. Importantly, this reduction was achieved with no reduction in the catch rate of legal size scallops, and with 63% fewer undersize scallops being caught. For these reasons, the researchers recommended that square mesh codend BRDs be made mandatory in the scallop fishery. Note that TEDs are already compulsory in all trawl sectors, but fishers can use less effective BRDs. If all scallop fishers used these devices, it would equate to a reduction in bycatch of over 10,000 tonnes annually in the scallop sector alone, compared to pre-2000 levels (i.e., before TEDs and BRDs were introduced). Because the square mesh codend BRDs caught significantly fewer undersize scallops, they are likely to lower the incidental fishing mortality on these young age classes, thus possibly increasing the exploitable biomass of scallops that can be harvested.

Similar positive effects from a square mesh codend BRD were obtained during a research charter in the deepwater eastern king prawn fishery, where bycatch rates were reduced by a mean of 29% due to the TED and square mesh codend with no reduction in the catch rate of the target species, eastern king prawns. The reason square mesh is so effective at reducing bycatch is because, unlike normal diamond mesh nets, square mesh remains open, thus allowing many of the small byatch fish and invertebrates to escape by passing through the net.

The permitted species

Research on the permitted species resulted in an improved understanding of the biology and population dynamics of these species. For example, minimum legal sizes were derived and recommended for barking crayfish, three spot crabs and Balmain bugs. The project provided the first descriptions of the growth rates and reproductive biology of pinkies (i.e., Nemipterus theordorei and N. aurifilum) and provided a clearer understanding of the distribution of pipehorses. It also provided a clearer understanding of the mantis shrimp catches of Moreton Bay and their reproductive biology. Further information on the population dynamics of the permitted species and recommendations for their management are provided in the Project Final Report .

Complete Project Final Report ( PDF, 6.2mB) Large file warning!

If you are unable to download the Final Report in its entirety, you have the option to download individual sections or chapters of the Report, below.

Sections 1-4. Objectives, Non-technical Summary, Background and Need ( PDF, 53kB)
Chapter 5. Effects of the Radial Escape Section BRD in the shallow water eastern king prawn fishery ( PDF, 371kB)
Chapter 6. Effects of the Radial Escape Section BRD in the north Queensland tiger/endeavour prawn fishery ( PDF, 461kB)
Chapter 7. Effects of square mesh codends in the Queensland scallop fishery ( PDF, 670kB)
Chapter 8. Diver whiting bycatch in Hervey Bay ( PDF, 302kB)
Chapter 9. BRDs in the deepwater eastern king prawn fishery( PDF, 516kB)
Chapter 10. Measuring the effects of BRDs used by fishers ( PDF, 361kB)
Chapter 11. Elasmobranch (i.e., sharks and rays) bycatch in the Queensland trawl fishery ( PDF, 167kB)
Chapter 12. Literature review of the permitted species ( PDF, 296kB)
Chapter 13. Biology of barking crayfish (Linuparus trigonus)( PDF, 442kB)
Chapter 14. Biology and minimum legal size of three spot crabs (Portunus sanguinolentus)( PDF, 257kB)
Chapter 15. Biology of mantis shrimps (Oratosquilla spp.) in Moreton Bay ( PDF, 829kB)
Chapter 16. Pipehorse (Solegnathus cf. hardwickii) distribution and faunal associations ( PDF, 425kB)
Chapter 17. Biology of Balmain bugs (Ibacuc spp.) ( PDF, 456kB)
Chapter 18. Biology of pinkies (Nemipterus spp.) ( PDF, 302kB)
Sections 19-25. Benefits and adoption, Further development, Planned outcomes, Conclusion, Acknowledgements, Intellectual Property and Staff ( PDF, 158kB)
Appendix 1. List of bycatch species in the shallow water eastern king prawn fishery ( PDF, 393kB)
Appendix 2. List of bycatch species in the north Queensland tiger/endeavour prawn fishery ( PDF, 459kB)
Appendix 3. List of bycatch species in the scallop fishery ( PDF, 439kB)
Appendix 4. List of bycatch species from Hervey Bay ( PDF, 170kB)
Appendix 5. List of bycatch in the deepwater eastern king prawn fishery ( PDF, 366kB)
Appendix 6. Bycatch species from the 2000 scallop fishery Long-Term Monitoring survey ( PDF, 300kB)
Appendix 7. List of pipehorses caught during the project ( PDF, 203kB)
Appendix 8. Age estimates of Nemipterids ( PDF, 194kB)

References

Alverson, D.L., Freeberg, M.H., Murawski and Pope, J.G., 1994. A global assessment of fisheries bycatch and discards. FAO Fish. Tech. Pap. 339. FAO, Rome, 233pp.

Courtney, A. J., Tonks, M. J., Campbell, M. J., Roy, D. P, Gaddes, S. W., Kyne, P.M. and O'Neill, M. F. (2006) Quantifying the effects of bycatch reduction devices in Queensland's (Australia) shallow water eastern king prawn Penaeus plebejus trawl fishery. Fisheries Research 80 :136-147 ( PDF, 503kB)

Queensland Fisheries Annual Status Report 2006. Queensland Department of Primary Industries and Fisheries. 331 pages.