Use of remote underwater video to record littoral habitat use by fish within a temporarily closed South African estuary

Littoral zones within estuaries represent important nursery areas for many species of marine fish but often consist of a mosaic of small habitat patches that are fragmented throughout the estuarine landscape. Fish within small shallow patches of reef, bare sand and reed beds were examined using remote underwater video within the temporarily closed East Kleinemonde Estuary during July and August 2009. A total of 45, hour long deployments were conducted in which seven taxa from five feeding guilds were identified. The omnivorous sparid Rhabdosargus holubi was present most often across all habitat types and was observed in 25 of the 45 deployments, while small shoaling zooplanktivores such as the clupeid Gilchristella aestuaria and atherinid Atherina breviceps were found in the highest abundances. While no significant differences in total fish abundance were recorded between the three habitat types, the composition of the assemblages were found to differ. Zooplanktivores had a higher affinity to reed habitats and the detritivores were more common in reef and bare sand. Passive remote underwater camera footage also allowed for behavioural observations under natural conditions. Distinct behavioural patterns associated with the different habitats were observed. Fish generally displayed rapid swimming behaviour over sand while slow meandering behaviour was common in both reef and reed habitats. This indicates that the value of various habitat patches within nursery grounds is not necessarily indicated only by fish abundance or assemblage composition but also by how these habitats are utilised. Results from this study suggest that remote underwater cameras provide a useful tool to study fish within shallow nursery habitats.