Stock separation and life history of Argyrozona argyrozona (Pisces: Sparidae) on the South African east coast

Abstract

Fishery independent biomass surveys and commercial linefish catch returns were used to elucidate the spatial patterns of carpenter Argyrozona argyrozona distributed along the South African continental shelf. Two distinct areas of abundance were determined, one on the central and the other on the eastern Agulhas Bank. Tagging studies revealed little exchange between them. Nurseries were identified in Algoa Bay on the eastern Agulhas Bank and on the central Agulhas Bank (CAB). Early juveniles (<100mm total length) on the CAB were found offshore in the vicinity of the Alphard Bank. They were found to move inshore with growth and then back offshore as they approached maturity. Juveniles in Algoa Bay dispersed both eastwards and westwards with growth. Otolith readability and growth rates varied between regions, with fish from the Eastern Cape (Port Elizabeth and Port Alfred combined) having the lowest average percentage error (4.82 vs 5.33 and 7.03) and the slowest growth rates. Size-at-50% maturity (L₅₀) varied regionally, female fish in the Eastern Cape maturing at a smaller size (L₅₀ = 206mm fork length) than in the Tsitsikamma National Park (L₅₀ = 292mm) or the CAB (L₅₀ = 267mm). Mass-at-length varied between regions, with carpenter in the Park having the highest mass-at-length and those in the Eastern Cape having the lowest. Based on the distribution of carpenter, variability in otolith readability, mass-at-length, variation in growth and size-at-maturity, it is concluded that carpenter exist as two separate stocks and should be managed accordingly.

Keywords: age and growth, age-at-maturity, life history, size-at-maturity, stock separation

African Journal of Marine Science 2005, 27(3): 585–595