Coastal and oceanographic influences on the Queensland (Australia) east coast saucer scallop (Amusium balloti) fishery

A benthic trawl fishery for saucer scallops (Amusium balloti) has been operating on the southern Queensland east coast (22-27 degrees S) since the 1970s. During this period annual landings have varied between ~300 t and 2000... [ view full abstract ]

A benthic trawl fishery for saucer scallops (Amusium balloti) has been operating on the southern Queensland east coast (22-27 degrees S) since the 1970s. During this period annual landings have varied between ~300 t and 2000 t (meat weight). In order to explain this variation and develop catch forecasting tools, we examined relationships between annual indices of scallop abundance, based on logbook catch rates in November from 1988-2013 (~26 years), and coastal and physical oceanographic parameters [freshwater flow, sea water temperature, sea level height, eddy kinetic energy (EKE), Chlorophyll-a (Chl-a) and the Southern Oscillation Index (SOI)]. The fishery is located west of and adjacent to the mesoscale cyclonic lee eddy, the Capricorn Eddy, which is the dominant physical oceanographic feature of the region. Estimates of sea water temperature, sea level height and EKE were derived from the numerical hindcast Bluelink ReAnalysis (BRAN 3.5) dataset which is based on the Bluelink ocean model covering the period 1993-2012. Chl-a data were obtained from the Australian Bureau of Meteorology eReefs Data Access-Thredds data server for 2002 to 2013. The Chl-a data were obtained via the MODIS Aqua satellite and have been adjusted using an inversion algorithm which gives much more accurate measures for coastal regions. Simple Pearson correlation coefficients (r) were used to examine relationships between scallop catch rates and the coastal and oceanographic variables. Lags of zero to 24 months were applied to each variable. The largest significant correlation of 0.85 was found between November catch rates and Chl-a concentration five months prior (in June). Scallop catch rates double as Chl-a increases from about 3 to 5 mg per cubic m. A number of significant correlations were obtained with physical properties of the Eddy, including a marked decline in catch rates with increasing bottom water temperature anomaly at the Eddy three months prior (in August). No significant correlations were obtained with the SOI. Although the biological mechanisms underlying the correlations remain speculative, the relationships may help explain variation in landings and are now being incorporated in stock assessment models of the fishery.