Research in Queensland is focused on maximising the commercial and ecological health of one of northern Australia’s iconic species, the Giant Mud Crab.
By Brad Collis
Giant Mud Crabs (Scylla serrata) are biologically very complex, says Dr Julie Robins, who leads research into the species as a principal scientist at the Queensland Department of Agriculture and Fisheries.
To unravel some of these complexities, FRDC is funding two projects aimed at learning more about the biology of Giant Mud Crabs (2019-062) and evaluating the efficacy of escape vents for bycatch entering Giant Mud Crab pots (2021-119). The research team is seeing flow-on benefits through close working relationships with commercial and recreational fishers with information gathered from these fishers being used to progress both projects.
Responding to industry concerns
The review of the Giant Mud Crab pot escape vent specifications was instigated following concerns from commercial crabbers raised via FRDC’s Queensland Research Advisory Committee.
Queensland introduced regulations making the use of escape vents in crab pots mandatory for commercial crabbers, in September 2022. Based on existing crab pot escape vent specifications and findings from earlier studies undertaken in Northern Territory and Queensland, three different sizes and shapes were authorised.
Julie says that while the regulations give crabbers different vent options, feedback from industry indicated the need for further research, especially into regional variations in Giant Mud Crab morphometrics, i.e., the differences in their size and shape in relation to the pots and vent options available. Additionally, this information will also contribute to the larger Giant Mud Crab biology project (2019-062).The Giant Mud Crab pot escape vent project is also providing an opportunity for researchers to consider more broadly, the issues of bycatch and entanglement in crabbing gear. For example, there are risks associated with marine turtles interacting with float lines, vent funnels, or entering crab pots. Identifying these risks for marine turtles will help crab fishers develop and implement risk mitigation strategies.
Industry collaboration
Researchers have been able to tap into the networks they have established with commercial crabbers and recreational fishers (as part of the crab biology project) to evaluate the performance of Giant Mud Crab pot vents. These networks extend along the Queensland east coast and Gulf of Carpentaria, so researchers can undertake sampling onboard crab boats as well as run trials on their own research craft, across a broad geographical area.
Fishers within these networks have also asked researchers to evaluate alternative design options for the placement of vents in pots. The current regulations specify that escape vents must be attached to the bottom ring of the crab pot. Some fishers would prefer the escape vents higher up in the pot when being deployed on soft mud.
Julie says the escape vents project will provide the fishery with information for developing a risk mitigation strategy, covering both undersized crabs and bycatch issues.
Female Giant Mud Crabs are being tagged as part of research into spawning patterns. Photo: Queensland Department of Agriculture and Fisheries
“We’ve spent a lot of time out on the water measuring in our own trials, where we control how the fishing gear is used, and out with commercial fishers operating under commercial conditions where pots vary greatly.
“We have covered as much of the Queensland coastline as possible, from Moreton Bay to Hinchinbrook Island and in the Gulf, to get that regional variation in crab morphometrics – and to test how or if, legal-size Giant Mud Crabs are escaping.
“We’ve also then had to assess if varying vent sizes makes a difference in different locations. We’re confident that the larger regulated escape vents reduce the number of sub-legal Giant Mud Crabs in pots, with minimal impact on legal Giant Mud Crab catch in most regions. But as the research to date shows, the answers are not black and white.”
Trials are testing the effectiveness of Giant Mud Crab pot vents to cater for the regional differences in the size and shape. Photo: Queensland Department of Agriculture and Fisheries.
Escape vents are allowing undersized crabs and fin fish to get away, reducing bycatch in pots. Photo: Queensland Department of Agriculture and Fisheries.
Reach-out to rec fishers
The escape vent research project (2021-119) has further cemented the relationship between researchers and the recreational fishing community.
“The escape vents are only regulated for the commercial sector but given the significant size of the recreational crab fishing community, it’s important that they also understand prevailing crab fishing requirements,” Julie points out. “So, we’re exploring ways to encourage the recreational sector to voluntarily use pots with escape vents.”
A recent Queensland Department of Agriculture and Fisheries social media campaign offered recreational crabbers free Giant Mud Crab escape vents in return for participating in a crab tagging program that is part of the larger crab biology research.
The tagging is designed to learn more about when and where female Giant Mud Crabs are spawning. “There are anecdotal reports about female Giant Mud Crabs going ‘offshore’ to spawn, but we really don’t understand the seasonality, how far ‘offshore’ they go, or whether most survive this migration to return to the same or different estuary,” says Julie.
FRDC research portfolio manager Adrianne Laird oversees both crab projects, which she says aim to fill knowledge gaps so the industry can continue to develop sustainably and profitably. “They are both about maximising commercial and ecological outcomes.”
Adrianne expects that the Giant Mud Crab research being undertaken in Queensland will be of value to similar fisheries in northern New South Wales, the Northern Territory and the north-west of Western Australia.
“There is so much variability in Giant Mud Crab populations that there is no ‘one size fits all’ approach to these issues. The Queensland research will provide a solid basis for other jurisdictions to tweak their own management responses to the same issues.”
Industry players have been pivotal in driving this mud crab research and participating in the projects with the researchers.
“Commercial crabbers know they have to address issues like bycatch or undersized catch for their long-term sustainability," explains Adrianne. “It’s these sorts of projects that fit together the puzzle pieces that are so important to a fisheries’ long-term viability.”
The escape vents project (2021-119) is scheduled to submit a draft report on its findings to FRDC midway through this year. The findings will also inform any future revisions of the Harvest Strategy for the Queensland Mud Crab Fishery.
Related projects
- 2021-119: Improving bycatch reduction strategies and escape vents in Queensland Mud Crab fisheries
- 2019-062: Knowledge to improve the assessment and management of Giant Mud Crabs (Scylla serrata) in Queensland
This relates to R&D Plan Outcome 1 & 3
