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Abstract
Baited underwater video techniques are increasingly being utilised for assessing and monitoring demersal fishes because they are: 1) non extractive, 2) can be used to sample across multiple habitats and depths, 3) are cost effective, 4) sample a broader range of species than many other techniques, 5) and with greater statistical power. However, an examination of the literature demonstrates that a range of different bait types are being used. The use of different types of bait can create an additional source of variability in sampling programs. Coral reef fish assemblages at the Houtman Abrolhos Islands, Western Australia, were sampled using baited remote underwater stereo-video systems. One-hour stereo-video recordings were collected for four different bait treatments (pilchards, cat food, falafel mix and no bait (control)) from sites inside and outside a targeted fishery closure (TFC). In total, 5209 individuals from 132 fish species belonging to 41 families were recorded. There were significant differences in the fish assemblage structure and composition between baited and non-baited treatments (P<0.001), while no difference was observed with species richness. Samples baited with cat food and pilchards contained similar ingredients and were found to record similar components of the fish assemblage. There were no significant differences in the fish assemblages in areas open or closed to fishing, regardless of the bait used. Investigation of five targeted species indicated that the response to different types of bait was species-specific. For example, the relative abundance of Pagrus auratus was found to increase in areas protected from fishing, but only in samples baited with pilchards and cat food. The results indicate that the use of bait in conjunction with stereo-BRUVs is advantageous. On balance, the use of pilchards as a standardised bait for stereo-BRUVs deployments is justified for use along the mid-west coast of Western Australia.
Highlights
Fish assemblages have been recognised as sensitive indicators of habitat degradation, ecosystem productivity and overall environmental change [1]
A total of 5209 individuals from 132 fish species belonging to 41 families were recorded by 108 stereo-Baited remote underwater video systems (BRUVs) deployments taken from four sites inside and four sites outside the Targeted Fishery Closure (TFC)
Assemblage Composition The significant differences in the assemblage composition between the types of bait was driven by increases in the relative abundance of fish in baited compared to non-baited stereoBRUVs, regardless of the type of bait
Summary
Fish assemblages have been recognised as sensitive indicators of habitat degradation, ecosystem productivity and overall environmental change [1]. Stereo-BRUV systems record species attracted to the bait, and species that are present in the field of view by chance, attracted to the stereo-BRUVs structure, or to the behaviour of other fishes [2]. Both BRUVs and stereo-BRUVs have been demonstrated to be robust sampling tools for investigating spatial and temporal patterns in reef fish assemblages [2,6,7,8,9,10,11]. The use of bait as an attractant in BRUVs studies continues to raise questions regarding bias and selectivity [2]
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