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

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
Pages1
Number of pages1
Publication statusPublished - 2017
EventAnnual Meeting of the Asia-Oceania-Geosciences-Society (AOGS) - Singapore, Singapore
Duration: 6 Aug 201711 Aug 2017
Conference number: 14
http://www.asiaoceania.org/aogs2017/

Conference

ConferenceAnnual Meeting of the Asia-Oceania-Geosciences-Society (AOGS)
Abbreviated titleAOGS
CountrySingapore
CitySingapore
Period6/08/1711/08/17
Internet address

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catchability
benthic boundary layer
crab
fishing
Acoustic Doppler Current Profiler
upwelling
conductivity
catch statistics
stratified flow
mesoscale eddy
bait
internal wave
in situ
speed
eddy
advection
stratification
acoustics
plume
water column

Cite this

SPENCER, D., LEMCKERT, C., Lee, S. Y., & Brown, I. W. (2017). In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina). 1. Abstract from Annual Meeting of the Asia-Oceania-Geosciences-Society (AOGS), Singapore, Singapore.
SPENCER, David ; LEMCKERT, Charles ; Lee, S. Y. ; Brown, I. W. / In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina). Abstract from Annual Meeting of the Asia-Oceania-Geosciences-Society (AOGS), Singapore, Singapore.1 p.
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SPENCER, D, LEMCKERT, C, Lee, SY & Brown, IW 2017, 'In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina)' Annual Meeting of the Asia-Oceania-Geosciences-Society (AOGS), Singapore, Singapore, 6/08/17 - 11/08/17, pp. 1.

In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina). / SPENCER, David; LEMCKERT, Charles; Lee, S. Y.; Brown, I. W.

2017. 1 Abstract from Annual Meeting of the Asia-Oceania-Geosciences-Society (AOGS), Singapore, Singapore.

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

TY - CONF

T1 - In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina)

AU - SPENCER, David

AU - LEMCKERT, Charles

AU - Lee, S. Y.

AU - Brown, I. W.

PY - 2017

Y1 - 2017

N2 - 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.

AB - 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.

KW - spanner crabs

KW - coastal processes

KW - Physical oceanography

KW - Bottom boundary layer

M3 - Abstract

SP - 1

ER -

SPENCER D, LEMCKERT C, Lee SY, Brown IW. In situ observations of the shelf bottom boundary layer and implications for the catchability of spanner crabs (Ranina ranina). 2017. Abstract from Annual Meeting of the Asia-Oceania-Geosciences-Society (AOGS), Singapore, Singapore.