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African Journal of Marine Science

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Do sawfish Pristis spp. represent South Africa’s first local extirpation of marine elasmobranchs in the modern era?

B.I. Everett, G Cliff, S.F.J. Dudley, S.P. Wintner, R.P. van der Elst

Abstract


Largetooth sawfish Pristis pristis and green sawfish P. zijsron were not uncommon in catches made in KwaZulu-Natal (KZN) on the east coast of South Africa in the mid part of the last century but apparently have disappeared from this area. This paper traces the decline in sawfish catches from 1951 and assesses the current population status and local extinction risk, based on historical and current records up to 2012. Records were collected from research surveys, literature, media and museum specimens, and through contacting researchers and conservation managers who have worked in KZN coastal and estuarine areas. A total of 150 green sawfish, 7 largetooth sawfish and 89 unidentified sawfish records were located. Most sawfish (115) were caught during a four-year (1967–1970) gillnetting survey conducted by the Oceanographic Research Institute in the St Lucia estuarine system while 91 were caught in the bather protection nets installed and maintained along the KZN coast by the KwaZulu-Natal Sharks Board. Sawfish ranged from 63 to 533 cm total length (TL). Sawfish caught in the estuarine environments (mean TL 162 cm [SD 72], n = 95) were significantly smaller than those caught in the inshore marine environments (mean TL 310 cm [SD 109], n = 83), confirming the importance of estuaries as pupping and nursery areas. The St Lucia estuarine system, given the high abundance of sawfish, was determined to be the most important nursery area in KZN. The last sawfish encountered in KZN, which was not identified to species level, was caught in the bather protection nets in 1999 and released alive. Extinction probability analysis indicates that sawfish no longer occur in KZN waters. Anthropogenic changes to the St Lucia estuarine system, as well as to other KZN estuaries, gillnetting for bather protection, and illegal fish harvesting, coupled with a non-adaptive life-history style, may have precipitated the disappearance of sawfish from KZN waters.

Keywords: catches, length frequency, local extinction, sex ratios




http://dx.doi.org/10.2989/1814232X.2015.1027269
AJOL African Journals Online