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Modelling transport of chokka squid ( L oligo reynaudii ) paralarvae off S outh A frica: reviewing, testing and extending the ‘ W estward T ransport H ypothesis’
Author(s) -
Martins Rodrigo S.,
Roberts Michael J.,
Lett Christophe,
Chang Nicolette,
Moloney Coleen L.,
Camargo Maurício G.,
Vidal Erica A. G.
Publication year - 2014
Publication title -
fisheries oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 80
eISSN - 1365-2419
pISSN - 1054-6006
DOI - 10.1111/fog.12046
Subject(s) - squid , oceanography , upwelling , ridge , diel vertical migration , biology , fishery , productivity , geology , paleontology , macroeconomics , economics
Annual landings of chokka squid ( L oligo reynaudii ), an important fishing resource for South Africa, fluctuate greatly, and are believed to be related to recruitment success. The ‘Westward Transport Hypothesis’ ( WTH ) attributes recruitment strength to variability in transport of newly hatched paralarvae from spawning grounds to the ‘cold ridge’ nursery region some 100–200 km to the west, where oceanographic conditions sustain high productivity. We used an individual‐based model ( IBM ) coupled with a 3‐D hydrodynamic model ( ROMS ) to test the WTH and assessed four factors that might influence successful transport – Release Area, Month, Specific Gravity (body density) and Diel Vertical Migration ( DVM ) – in numerical experiments that estimated successful transport of squid paralarvae to the cold ridge. A multifactor ANOVA was used to identify the primary determinants of transport success in the various experimental simulations. Among these, release area was found to be the most important, implying that adult spawning behaviour (i.e., birth site fidelity) may be more important than paralarval behaviour in determining paralarval transport variability. However, specific gravity and DVM were found to play a role by retaining paralarvae on the shelf and optimizing early transport, respectively. Upwelling events seem to facilitate transport by moving paralarvae higher in the water column and thus exposing them to faster surface currents.