Dr Anthony Bernard1,2, Dr Elodie Heyns-Veale1,2, Dr Denham Parker3, Dr Bruce Mann4, Dr Jade Maggs4,6, Mr Kyle Smith5
1South African Institute for Aquatic Biodiversity (SAIAB), Grahamstown, South Africa, 2Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa, 3Department of Forestry, Fisheries and the Environment, Cape Town, South Africa, 4Oceanographic Research Institute, Durban, South Africa, 5South African National Parks, Sedgefield, South Africa, 6National Institute of Water and Atmospheric Research, Auckland, New Zealand.
Many demersal fish species that inhabit coastal reef ecosystems occupy a broad depth range occurring from the shallow subtidal down to the edge of the continental shelf. While fishing has significantly impacted temperate reef fish populations, past research has suggested that water depth may act as a refuge for targeted species. Utilising data collected with baited remote underwater stereo-video systems for reef associated fisheries targets, we investigated if depth was a refuge from fishing by comparing the assemblage structure, population maturity and total biomass between shallow (10-30 m) and deep (40-80 m) reef habitats from inside and outside of four no-take marine protected areas (MPAs) along South Africa’s south and east coast. In both shallow and deep water habitats the proportion of mature fish and total biomass were significantly greater inside the MPAs, relative to the adjacent areas open to fishing. Within the MPAs, total biomass of fisheries targets was significantly greater on the deeper reefs than the shallow reefs. However, this was not the case outside the MPAs, where biomass was not affected by depth. For many of South Africa’s reef associated fisheries targets, ontogenetic shifts in habitat preference result in larger individuals inhabiting deeper reefs, and this was clearly reflected in the data. Outside of the MPAs, it is possible that fishing, which typically targets the larger individuals, has eroded this ecological pattern. For specific species there were some exceptions where deep reefs open to fishing showed greater than expected abundance of sexually mature individuals, but these cases were restricted to areas isolated from large human populations. In general our results suggest that depth should not be considered a refuge and that deep water MPAs can contribute to the protection of spawner biomass for important fisheries species.
Biography:
My research is focused on understanding the ecology of subtidal reefs within South Africa and the Western Indian Ocean, in particular the role that environmental variability and anthropogenic disturbance play in shaping fish community and population structure.
