Transkei coastal fisheries resources. Special Publication number 3

A survey of the invertebrate subtidal and estuarine resources on the Transkei coast was undertaken in April 1993 by the Oceanographic Research Institute in association with the University of Transkei (UNITRA). This survey examined the stocks of abalone, rock lobsters, mud crabs, oysters, subtidal mussels, and sand and mud prawns. During the latter half of 1993, the Zoology Department of UNITRA examined shellfish resources in the intertidal zone along the coast. Information on past and current levels of utilisation of all resources was collated and, where possible, survey and biological data were combined to make preliminary assessments of the potential for sustainable utilisation

Moon, tidal and diel influences on catch composition of fishes in the surf zone of Pontal do Sul beach, Paran\ue1

Fishes were sampled by beach seine during the day and night at the high and low sygygy tides, on a sandy beach at the southeast coast of Brazil. The quantitative results appear to indicate a larger concentration of fish in the surf zone of this beach, in low tides at the start and end of the day. Only eight from the 17 most abundant taxa, appeared to have been influenced singly or in combination by the factors of the moon, day, night and tide

Size matters: competition within populations of the limpet Patella depressa

Competitive interactions within and between size-classes of the limpet Patella depressa Pennant were investigated in central Portugal. Experimental enclosures of 25 x 25 cm containing marked limpets were set up at mid-tidal level on the shore. Twelve treatments with different combination of densities and size-classes were assigned to the plots, with three replicates of each. Mortality was recorded every 15 days and length was measured monthly during the approximately 6 months of the experiment. 2. At the end of the experiment limpets were collected for determination of length, height, dry weight, sex and gonad development. The availability of food was assessed indirectly by determination of chlorophyll concentration with spectrophotometric analysis of rock chips. Reduced density treatments showed very low mortality and substantially increased growth. Both size-classes of limpets showed increased mortality and reduced growth in increased density treatments. This effect was, however, more marked for large than small limpets when caged separately.3. Although both size-classes could negatively affect each other, the effect of large limpets on small was greater than the reverse. Large limpets are superior competitors that may modulate the abundance of small limpets on the shore. It is unlikely, however, that they will totally exclude small limpets due to intensity of competition within the large size-class. Niche differentiation and high recruitment at low shore levels are other possible factors that can contribute to reduce competition between the size-classes.<br/