Modelling transport of chokka squid (Loligo reynaudii) paralarvae off South Africa: reviewing, testing and extending the `Westward Transport Hypothesis'

Authored by Christophe Lett, Coleen L Moloney, Rodrigo S Martins, Michael J Roberts, Nicolette Chang, Mauricio G Camargo, Erica A G Vidal

Date Published: 2014

DOI: 10.1111/fog.12046

Sponsors: Brazilian Ministry of Education (CAPES) Brazilian National Council for Scientific and Technological Development (CNPq)

Platforms: Ichthyop

Model Documentation: Other Narrative

Model Code URLs: Model code not found

Abstract

Annual landings of chokka squid (Loligo 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 100-200km 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.
Tags
Life-cycle Agulhas-bank Fish larvae Vulgaris-reynaudii Spawning grounds Yolk utilization Nursery areas Opalescens cephalopoda Swimming behavior Eastern cape