Albrecht Götz

Optimal BRUVs (baited remote underwater video system) survey design for reef fish monitoring in the Stilbaai Marine Protected Area

Marine protected areas (MPAs) play an important role in coastal conservation, but there is presently no uniformly applied methodology for monitoring the efficacy of coastal fish protection. Whereas underwater visual census and controlled angling surveys have been used, their skilled-labour requirements and environmental impact have prevented their nation-wide application in South Africa. We used a baited remote underwater video system (BRUVs) to provide the first survey of reef fishes in the Stilbaai MPA (SMPA), and assessed the deployment time and sample size requirements of BRUVs for reef fish monitoring. Thirty-eight species, including 13 chondrichthyans, were recorded in one-hour deployments across 29 sites in the 11.3 km2 no-take zone of the SMPA, in depths ranging from 5 to 41 m. Bait was limited to sardine Sardinops sagax homogenate, but the species recorded by BRUVs comprised several feeding guilds, including herbivores. Optimal deployment time was 49 min, but 60 min is recommended as a conservative and practical standard. Over a five-year period, annual BRUVs sample sizes required to detect increases in abundance of 0.1 y−1 with 80% power would be 28 deployments for abundant species and 129 for rare species. Detection of decreases of equivalent magnitude will require more samples.

The effects of barotrauma on five species of South African line-caught fish

Management measures for South African line-caught fish include output controls such as closed seasons, bag and size limits and no-take moratoria. The main condition for these measures to be effective is that undesirable catches can be successfully released. However, most of the line-caught fish species are susceptible to barotrauma, a condition caused in physoclists by the rapid reduction of hydrostatic pressure during the ascent to the surface during capture. We investigated the effects of barotrauma on five commercially important species: roman Chrysoblephus laticeps, silver kob Argyrosomus inodorus, hottentot Pachymetopon blochii, santer Cheimerius nufar and carpenter Argyrozona argyrozona. A classification of the external signs of barotrauma was developed and internal and external signs of barotrauma were examined in relation to fishing depth and fish size, and compared between species. Immediate post-release mortality was investigated during a catch-and-release experiment. Medium-term survival of C. laticeps (~1 d) was examined by returning fish to depth in cages and subsequent monitoring on SCUBA. Our results indicate that most of the fish experience barotrauma even when caught at relatively shallow depths. External signs include extension of the inflated, everted stomach through the mouth, distended eyes, protrusion of the hind-gut and other organs through the cloaca, and gas bubbles in the dermal tissue between the fin rays. The absence of any obvious external signs of barotrauma can be misleading as dissections of such fish revealed ruptures of the swimbladder and other internal injuries consistent with barotrauma. Our results indicate that there might be significant post-release mortality, a factor that needs to be taken into account during stock assessment predictions and during the implementation of catch restrictions.

Baited remote underwater video system (BRUVs) survey of chondrichthyan diversity in False Bay, South Africa

Global declines in chondrichthyan populations necessitate evidence‑based planning for their conservation. False Bay, in south‑west South Africa, has a high diversity of marine biota, with Atlantic and Indian Ocean influences, but its chondrichthyan fauna is poorly described ecologically. False Bay has a long fishing history and supports various harvesting methods, including shark‑directed fishing. This is the first baited remote underwater video system (BRUVs) survey of the relative abundance, diversity and seasonal distribution of chondrichthyans in False Bay. Nineteen species from 11 families were recorded across 185 sites at between 4 and 49 m depth. Diversity was greatest in summer, on reefs and in shallow water. Endemic scyliorhinids, especially Haploblepharus edwardsii, dominated everywhere, in summer and winter. Habitat and season were key predictors of species composition, and a significant interaction between depth and season indicated migration patterns for Mustelus mustelus. By avoiding the selectivity associated with catch records, BRUVs data are superior to fishery‑dependent catch‑per‑unit‑effort data to monitor chondrichthyan diversity and abundance. Baited remote underwater video systems access greater depths and more habitats than previously surveyed in False Bay and avoid taxonomic lumping typical of catch records in the region, making them more efficient than other methods of surveying chondrichthyan diversity.

First survey of fishes in the Betty's Bay Marine Protected Area along South Africa's temperate south-west coast

This first survey of fish in the Bettys Bay Marine Protected Area (MPA), on the south coast of South Africa, was conducted using baited remote underwater video systems (BRUVs). A total of 58 deployments recorded 42 species in 20 km2, including reef, kelp and sand habitats in protected and exploited zones, at between 5 and 40 m depth. Chondrichthyans accounted for 28% of diversity. Teleost diversity was dominated by Sparidae, Cheilodactylidae, Sciaenidae and Ariidae. Diversity (H′) was highest in kelp and lowest over sand. Species composition differed among habitat and depths, but protection had no effect. Among four commercial species, only Pachymetopon blochii responded positively to protection. The apparent failure of protection may attest to poor compliance, but an investigation into fish size might show an effect. Many species were detected at the western extreme of their range. Diversity in Bettys Bay was predictably lower than in the more eastward Stilbaai MPA, but also lower than in the westward Table Mountain National Park MPA. Fish diversity did not follow a linear increase eastwards from Cape Point. Bettys Bay includes the most easterly protected kelp forests and contains seven species not recorded in the other two areas, and is therefore an important element in the MPA network.