In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina)

David SPENCER, Charles LEMCKERT, S. Y. Lee, I. W. Brown

Research output: Contribution to conference (non-published works)Abstract


Catchability is a key parameter used for stock management of fisheries. Factors which influence catchability are largely associated with fishing methods and species abundance; however, physical oceanographic drivers have also been linked to fluctuations in spanner crab catches. Current speed and direction play an important role for passive fishing, as bait scent plumes undergo advection and dispersion before they reach the target species downstream of the trap. Previous studies demonstrate the number of spanner crabs caught is proportional to the magnitude of the current and crabs approach baited nets from the opposite direction of the current flow. The work presented here was aimed at further exploring the dynamic nature of the Bottom Boundary Layer (BBL) and processes attributed to BBL current speed and direction.
Using a Nortek Vector Acoustic Doppler Velocimeter (ADV) anchored to the seabed and spanner crab catch data, results indicate fluctuations in current speed are the most influential for catch rates. Increasing or decreasing current speed had a significant impact by respectively improving or declining catches during the fishing day. A Nortek Aquadopp Acoustic Doppler Current Profiler (ADCP) and Conductivity Temperature Depth (CTD) profiles were used to provide insight into processes linked to changes in current speed. CTD profiles illustrated days with strong stratification at the bottom boundary layer typical of upwelling and an entirely mixed water column characteristic of a mesoscale eddy, while ADCP profiles illustrated stratified flow and a potential internal wave propagating along the coast. Overall, in situ observations of shelf hydrodynamics provide valuable insight into the complex nature of BBL dynamics and the importance of different processes impacting current speed/direction, which in turn affect spanner crab catches. Results from this study prompt the need to investigate the effect large scale processes (upwelling and eddies) have on spanner crab catch rates.
Original languageEnglish
Number of pages1
Publication statusPublished - 2017
Externally publishedYes
EventAnnual Meeting of the Asia-Oceania-Geosciences-Society (AOGS) - Singapore, Singapore
Duration: 6 Aug 201711 Aug 2017
Conference number: 14


ConferenceAnnual Meeting of the Asia-Oceania-Geosciences-Society (AOGS)
Abbreviated titleAOGS
Internet address


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