This study investigated aspects of the biology of Sarpa salpa,
such as reproduction, age and growth, and mortality, which are
necessary for an assessment of the status of this species off the
KwaZulu-Natal (KZN) Coast.
The importance of S. salpa to the shore-based fishery in KZN was
evaluated using Natal Parks Board shore patrol data. These data
were validated by analysing preliminary results of an independent
shore-angling survey along the KZN Coast. Despite differences
in the catch composition and catch rates between the two
analyses, both data sources highlighted the importance of S.
salpa to the shore-based fishery in KZN. Shore-based catches
were markedly seasonal coinciding with the breeding season of the
species. The species in KZN is targeted primarily to provide a
supplementary source of animal protein.
An investigation of the reproductive biology of S. salpa
indicated a protracted spawning period for the species. Size at
50 percent maturity for combined sexes was attained at 145 mm
fork length. The sex ratio in shore-based catches was 1:1.6 in
favour of males. A frequency distribution by size indicated that
males dominated the smaller size classes while females dominated
the larger size classes. Detailed histological examination of
gonadal development showed that S. salpa has the potential for
protandrous sex change.
An age and growth study based on the examination of whole
otoliths indicated that S. salpa was relatively fast-growing and
a maximum age of six years was recorded for the species. One
opaque band was laid down per year. This was validated by
marginal increment analysis and by an oxytetracycline labelling
experiment using captive fish. Growth in S. salpa was described
by a Von Bertalanffy growth function:
Lage (mm FL) = 224mm(1 -e-o.55 year-1(age+o.51years))
The natural mortality rate (M = 0.6 year-1) was derived using
Pauly's equation and the current fishing mortality (F) rate was
estimated at 0.8 year-1. The current status of S. salpa in the
shore-based fishery was assessed by determining the effects of
F and age-at-capture on the yield- and spawner biomass-per-recruit.
Current levels of fishing pressure on S. salpa appeared
to be appropriate for utilisation of the stock off the KZN South
Coast. In terms of management, S. salpa appears to be in no need
of any restrictive measures at present. / Thesis (M.Sc.)-University of Natal, Durban, 1995.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5143 |
| Date | January 1995 |
| Creators | Van Der Walt, Bryan Anthony. |
| Contributors | Govender, Anesh., Beckley, Lynnath E. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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