Cape sardines forced ashore

21 November 2011 - 18:06 By Sapa
subscribe Just R20 for the first month. Support independent journalism by subscribing to our digital news package.
Subscribe now

An extensive and persistent red tide bloom has caused shoals of pilchards to swim into the surf zone around the Cape peninsula.

The fisheries department said the sardine -- known locally as pilchard -- had been observed close to shore in the surf zone in several locations around Cape Town.

"The reason for the sardine mortality and their near-shore distribution around Cape Town is thought to be linked to an extensive and persistent red tide bloom that extends from Walker Bay, around the Cape Peninsula, to St Helena Bay," spokesman Hein Wyngaard said.

The bloom was visible from satellite.

It was caused by the dinoflagellate Gonyaulax polygramma, a non-toxic species that has previously been linked to fish kills elsewhere, because of depletion of oxygen in the water column arising from bloom decay.

This dinoflagellate could attain concentrations of 10-20 million cells per litre and was previously reported from False Bay in March/April 1962 and again in February 2007.

Mortalities of marine life on both occasions were reported.

Dead sardine collected from Hout Bay and off Koeberg had been examined, but neither their stomach contents nor their gills showed any sign of Gonyaulax.

"Given that sardine mortality does not appear to be directly attributable to clogging of the gills, it seems likely that the red tide bloom has 'trapped' sardines in near-shore waters, where they either die due to oxygen depletion and sink to the sea bed, or may be forced into the surf zone and then ashore by predators, such as seals and dolphins," Wyngaard said.

subscribe Just R20 for the first month. Support independent journalism by subscribing to our digital news package.
Subscribe now