Journal article

Investigating connectivity between two sardine stocks off South Africa using a high-resolution IBM: Retention and transport success of sardine eggs


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Publication Details

Author list: McGrath AM, Hermes JC, Moloney CL, Roy C, Cambon G, Herbette S, van der Lingen CD

Publisher: Wiley: 12 months

Publication year: 2020

Journal: Fisheries Oceanography

Volume number: 29

Start page: 137

End page: 151

Total number of pages: 15

ISSN: 1054-6006

eISSN: 1365-2419


Abstract

This study applied a previously used Lagrangian individual-based model (IBM) for sardine in the Southern Benguela to an improved and more robust hydrodynamic model to investigate whether a more representative spatial coverage, greater hori-zontal and vertical resolution, more realistic winds and improved representation of mesoscale features such as eddies and filaments would give different results for transport and retention of early life stages. Despite major differences between the old and new hydrodynamic models, overall the IBM results were quite similar to the previous southern Benguela sardine IBM study. This surprising result indicates that it is the macroscale circulation features resolved by the two hydrodynamic models that are controlling transport and retention of sardine early life stages. The contribu-tion of transient mesoscale features such as eddies and filaments appears to be less important when transport patterns are averaged over the 21-year-long experiment. Another aim of this study was to better estimate the contribution of south coast spawning to west coast sardine recruitment. This was possible because of an east-ward extension of the geographical domain of the new hydrodynamic model which provided a more realistic representation of the south coast spawning ground. Three main spawning and nursery area systems, similar to those identified in the previ-ous sardine IBM, were identified: west coast and west coast (WC-WC), south coast and west coast (SC-WC), and south coast and south coast (SC-SC). Spawning area proved to be an important determinant of modelled retention and transport success, with spawning depth also playing an important role on the west coast. The main dif-ference observed from the previous study was an increase in the average percent-age of particles released on the south coast and transported to the west coast (P0, 17.4%). This indicates more connectivity between the southern and western sardine stocks than previously thought and is therefore important for fishery management. Standardized anomalies from the modelled retention/transport were compared with recruitment estimates from stock assessment models but there was no correlation between the two sets of anomalies. However, a significant correlation was observed between the modelled retention/transport anomalies for the west coast and total cumulative upwelling anomalies for the Southern Benguela (r = −0.67, p < .001).


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Last updated on 2020-18-03 at 09:24