Determining when and where to fish: Linking scallop spawning, settlement, size and condition to collaborative spatial harvest and industry in-season management strategies

Commercial scallop (Pecten fumatus) fisheries were overfished in southeast Australia from their inception in the 1920s right up until the late 1980s, when there were no productive scallop grounds left in the region. Because of this historical overfishing, current management of the harvest faces the significant challenge of trying to rebuild the stock and recruitment. The present study, undertaken by University of Tasmania’s Institute for Marine and Antarctic Studies, was developed to critically examine spatial harvest strategies employed in the southeast Australian commercial scallop fisheries, which aim to buffer against recruitment variation to increase both production and continuity between seasons. As part of the Commonwealth Bass Strait Central Zone Scallop Fishery (BSCZSF) harvest strategy and the Tasmanian Scallop Fishery (TSF) Management Plan, pre-season surveys determine areas to be opened/or closed during the upcoming season. Known areas with >20% discard rate are closed to fishing, regardless of scallop quality and potential for opening during the season. A detailed characterization of morphometric relationships across different locations would permit greater confidence in the use of the relationships that exist between various measurements used. Additionally, scallops in the areas opened can be unsuitable for harvest due to poor condition when the season opens. This means the areas are opened then rapidly closed to fishing again, causing disruption to fishing/processing businesses, and marketing problems. Delayed opening while scallops gain condition can also prevent the total catch being taken because there is a fixed, pre-determined finish date. The fixed finish dates have been established to protect settling scallop spat, which traditionally occurs between September and December following spawning between August and October. The problem with poor condition at the start of the season has arisen because scallops are increasingly reaching spawning condition between December and February, particularly in the BSCZSF. As well as potentially putting settling scallops at risk through impacts upon opening the fishery, this late development is also contributing to difficulty in providing well-conditioned scallops throughout the season. This study aimed to better define timing of scallop spawning based on gonad condition, and hence potential settlement of recruits across the different populations/beds of the fishery and determine any differences in spawning potential among scallop beds/locations. Additionally, this project aimed to define differences in spawning potential between scallops ranging from 80 to 90 mm shell length (SL) and assess the size limits used to define a bed as commercially viable across the three southeast Australian jurisdictions. Furthering our understanding of growth rate in several fishing locations across all three jurisdictions may also allow better management of individual beds and in addition to scallop condition will be used to inform current season openings and closings. An overall aim was to also provide information that will allow the jurisdictions greater capacity to work together to facilitate effective management for the fishery as a whole.