Saucer Scallop monitoring
Background to the fishery
Ballot’s Saucer Scallop (Ylistrum balloti) is an important commercially harvested species inhabiting sandy substrates up to 100m deep, particularly around central and southern Queensland. Scallops are targeted in the East Coast Otter Trawl Fishery, along with a range of prawn and bug species.
The saucer scallop was formerly the state’s most valuable commercially-fished species. In 1993, annual landings peaked at just under 2000 tonnes (meat weight), with an approximate value of $30 million. In recent years, landings have dropped to less than 546 tonnes of scallop meat, dipping to 134 tonnes as the fishery has hit historical lows.
In 2014, we conducted a quantitative stock assessment in response to concerns raised by the trawl industry about decreasing catch rate. The assessment revealed that in 2015 spawning stock estimates were potentially 5–6% of 1977 levels. This assessment resulted in the fishery being classed as overfished. Ballot’s Saucer Scallop is classified as depleted in the most recent Status of Australian Fish Stocks (SAFS) report. Urgent management changes were introduced in January 2017 to prevent further declines in scallop stocks.
How are saucer scallops monitored?
We have surveyed high scallop catch areas between 1997–2006 and 2017– 2019 to investigate the recruitment and abundance of saucer scallops in central and southern Queensland.
Between two to four commercial trawl operators are chartered to survey this large area and contribute their vessels and fishery expertise, while accommodating our scientists for up to 14 nights.
The survey is run around September to October in up to 18 areas (strata), intending to trawl more than 300 sites in open commercial fishing areas and Scallop Replenishment Areas (SRAs). Biological data on blue swimmer crabs (Portunus armatus), Moreton Bay bugs (Thenus sp.) and species of conservation interest (SOCI (PDF, 1.6MB)), such as sea snakes and pipefish, are also collected.
Site distribution is based on the commercial catch and effort from the fishery for those areas. Surveying of the randomised sites consists of a one-nautical mile or 20-minute tow using common East coast commercial prawn trawl gear in different net configurations of 3–5 nets, throughout the history of the survey.
Prawn-sized nets are used for the survey to target very small, pre-recruitment sized scallops (less than 15mm), as well as large adult scallops.
Prior to 2006, the survey was conducted from offshore Yeppoon to Hervey Bay with the majority of the fishery occurring in these areas. In 2017, the survey restarted with trawled strata moved as far south as Noosa to reflect the southern movement of the fishery’s major harvest.
To help standardise catch rates and test the performance of each vessel, side-by-side trawls are completed on the first evening. This testing allows different gear configurations to be compared. Each vessel then conducts as many shots as possible at randomly allocated unique locations to collect information on the catch. The data from all survey sites is able to be compared due to this first night of calibrating.
Due to the length of time that the survey has been running for and the changing dynamics of the fishery due to catch rates and management decisions, the results of the survey have been presented in many forms. All 1997–2006 survey data is presented in the Scallop Survey Results (1997-2006) report.
The results update for 2017–2019 survey data is available in the Scallop Survey Results update (2019) – includes comparison to 2017 and 2018. These results are displayed in a different format due to the current management needs, however a report on the entire scope of ‘Improving the Natural Mortality rate estimates of the Queensland Saucer Scallop Fishery’ is due in late 2020.