Distribution and abundance of Sepioidea off South Africa

Abstract

The distribution and abundance of six species of Sepia and one of Rossia were studied during six west coast and three south coast bottom trawl surveys off South Africa. The two most common species on both coasts were Sepia australis and S. hieronis. Both were most abundant on the northern West Coast (Orange River and Port Nolloth areas) and were sparsely distributed over the rest of the region. The depths of greatest abundance were 60–190 m (S. australis and 110–250 m (S. hieronis. The highest biomass indices were recorded on the West Coast (S. australis — 5 250 tons in August 1988; S. hieronis — 1 070 tons in February 1988). The former species also peaked in May 1988 on the South Coast (803 tons). The environmental factors most influential in the distribution of the two species were bottom oxygen concentration and temperature. Both Sepia australis and S. hieronis are tolerant of very low levels of oxygen and S. australis is abundant in oxygen-depleted areas on the West Coast, where the best catches are associated with oxygen concentrations between 1,5 and 3.5 mℓ·ℓ⁻¹. The two species were most abundant at relatively low temperatures: on the West Coast catches peaked when the temperatures were about 9°C. Of the remaining five species, four (S. officinalis vermiculata, S. papillata, S. simoniana and S. typica) are usually found in shallow water (<100 m), mainly on the South Coast. Rossia enigmatica, a sepiolid, is most abundant in 400–500 m of water, generally on the West Coast.