Short Communication

An investigation of the effect of temporal variation in growth rate of Umbrina robinsoni on biological reference point estimates calculated using per-recruit models

  • K Hutchings
  • MH Griffiths
  • SJ Lamberth


The effect of temporal variation in growth rate on per-recruit model outputs was investigated by comparing biological reference points obtained using growth curves derived for Umbrina robinsoni populations from False Bay, on the south coast of South Africa, sampled 10 years apart (1991–1993 and 2001–2003), and applying the two different age–length keys to length frequency data collected over the period 1991–1993 (n = 1 389) for the estimation of total mortality (Z), fishing mortality (F)and spawner biomass per recruit (SB/R). The SB/R and yield per-recruit (Y/R) curves constructed using biological data collected during the two different time periods were very similar, with target and threshold reference points differing only moderately (11%). This suggests that for long-lived species, the frequency of age and growth studies can be at least the lifespan of a cohort if they are to be assessed with a per-recruit approach. The use of the more recent length-at-age data, however, resulted in lower estimates of F (0.61 y–1 vs 1.05 y–1) and a slightly higher spawner biomass per-recruit ratio (19.5% vs 14.5%) for the earlier period. The reduced estimate of F when using the more recent dataset was likely due to a bias towards older fish caused by small sample size, the philopatric nature of U. robinsoni, and possible recruitment collapse. This highlights the importance of having a large, representative sample of length-at-age data for construction of age–length keys.

Keywords: growth rate variation, management, Sciaenidae, slender baardman, stock assessment

African Journal of Marine Science 2010, 32(3): 633–636

Author Biographies

K Hutchings
Department of Zoology and Marine Biology Research Centre, University of Cape Town, Rondebosch 7700, South Africa
MH Griffiths
Ministry of Fisheries, PO Box 1020, Wellington, New Zealand
SJ Lamberth
Branch Fisheries, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Rogge Bay 8012, South Africa; and South African Institute for Aquatic Biodiversity, Private Bag 1015, Grahamstown 6140, South Africa

Journal Identifiers

eISSN: 1814-2338
print ISSN: 1814-232X