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The distribution, abundance and composition of marine fish assemblages are influenced by changes in behaviour and movement associated with the diel cycle. The majority of studies exploring day-night differences have demonstrated that there is a greater abundance and diversity of fishes during diurnal compared with nocturnal hours, and that fish assemblage composition varies with time of day or night. We investigated fine-scale (hourly) diel cycles in the composition and relative abundance of temperate reef fishes using unbaited remote underwater video systems. We observed short crepuscular changeover periods with the hours around dawn and dusk sharing many species, some of which are nocturnal and others diurnal. Diurnal surveys recorded a greater number of individuals (16,990) and species (70) than nocturnal surveys (1053 individuals and 19 species). There was a clear difference between the diurnal assemblage, which was characterized by benthic invertivores, and the nocturnal assemblage composition, which contained zooplanktivores and generalist feeders. Within the diurnal period the hourly temporal variation was relatively homogenous, indicating that standardization of diurnal sampling to a particular time of day may not be necessary. [ABSTRACT FROM AUTHOR]

Cumulative anthropogenic impacts such as overfishing, and climate change are placing marine ecosystems under increasing pressure. This includes the loss or degradation of marine habitats and reductions in fish stocks, with conservation and fisheries management strategies aiming to mitigate, or reverse the effects. Measuring the effectiveness of management actions on fish requires accurate data on the abundance and size of fishes. Diver operated stereo-video systems (stereo-DOVs) have become a widely accepted method for surveying reef fish but have known biases and constraints. A new generation of small and affordable remotely operated vehicles (ROVs) can carry a stereo-video system to collect reef fish data without the need for divers. However, before ROVs are adopted there is a need to understand how they compare to other conventional survey methods. We compared how stereo-DOVs and stereo-ROVs influenced fish behaviour and sampled coral reef fish assemblages inside and outside sanctuary zones in the Ningaloo Marine Park, Northern Western Australia. In general, the numbers of species, individuals and the assemblage composition did not differ significantly between survey techniques and detected consistent patterns in the assemblage composition across locations and inside and outside sanctuary zones. Both methods recorded similar proportions of length measurements (68% and 70% for stereo-DOV and stereo-ROV respectively). Fishes were significantly more wary and exhibited more flight responses towards stereo-DOVs when compared to stereo-ROVs. The use of ROVs has the potential to be a cost-effective method of surveying reef fish while eliminating the health and safety risks involved with SCUBA diving. Given the comparable metrics as well as reduced behavioural bias and logistical advantages of using stereo-ROVs, we recommend stereo-ROVs as a viable alternative to stereo-DOVs surveys. • Fish assemblage composition sampled Stereo-DOVs and stereo-ROV was similar. • Both techniques record similar numbers of species and fish individual. • Fish allowed the Stereo-ROVs to approach them closer than stereo-DOVs. • Stereo-ROV is a cost-effective alternative to stereo-DOVs. • Stereo-ROV can operate deeper, with less health and safety risks then stereo-DOVS. [ABSTRACT FROM AUTHOR]

Marine Protected Areas (MPAs) are a popular conservation strategy aimed at managing anthropogenic pressures and protecting habitats and the diversity of ocean flora and fauna. Robust, cost-effective sampling of fish assemblages is important in understanding the effects of these management strategies on ocean ecosystems. We compared the sampling effectiveness and efficiencies of three commonly used methods of sampling fish assemblages; underwater visual census (UVC), baited remote underwater stereo-video systems (stereo-BRUVs), and diver operated stereo-video (stereo-DOV) and one emerging method (remotely operated vehicle with stereo-video system (stereo-ROV). We assessed the assemblage composition, numbers of species and individuals, and the statistical power to detect hypothetical changes in the number of species and individuals for each method. Stereo-BRUVs sampled a distinctive assemblage compared to all transect-based methods, with more individuals, total species, and predatory fishes from higher trophic groups that are targeted by commercial and recreational fishers. UVC also sampled a distinctive assemblage compared to stereo-ROV and stereo-BRUVs (comparisons with stereo-DOV were not possible due to sampling restrictions). The fish assemblage sampled by UVC consisted of more species and individuals than stereo-ROV and small bodied or cryptic species that were not detected by the video methods. Although stereo-DOV sampled more individuals than stereo-ROV with differences in small schooling species at a few sites, the assemblage composition was broadly comparable. To effectively monitor MPAs a combination of BRUVs, which more effectively sampled fisheries indicator species, and one of the transect based methods should be used. Given the similarities in the assemblages sampled by the stereo-video transect based methods and the advantages associated with health and safety, logistics and field efficiency with remote methods, we recommend stereo-ROV and stereo-BRUVs. • Stereo-BRUVs sampled a distinct assemblage of fishes compared to transect methods. • Stereo-DOV and stereo-ROV sampled similar assemblages and number of species. • UVC sampled a distinct assemblage consisting of more small bodied species. • Stereo-ROV can sample deeper water than diver-based methods. [ABSTRACT FROM AUTHOR]

Many marine fish populations have declined due to the individual or cumulative impacts of increasing water temperatures, ocean acidification, overfishing and other human-induced impacts such as land run-off, dredging and habitat alteration. Some solutions may be offered by ecosystem-based fisheries and conservation management. However, understanding their effectiveness relies on the availability of good quality data on the size distributions and abundance of fish populations and assemblages, collected at appropriate temporal and spatial scales. Since the early 2000s, baited remote underwater video systems (BRUVs) have become a popular tool for collecting data on fish assemblages across a range of depths and habitats. In Australia, this technique has been adopted by many different agencies and institutions, creating a unique opportunity to compile a continental-scale synthesis of fish data using a standardised sampling technique. Key Australian researchers and managers were invited to contribute to a synthesis workshop on baited underwater video in Albany, Western Australia between the 4th and 8th of February 2018. Data from 19,939 BRUVs deployments, collected between 2000 and 2017 around Australia, were compiled using GlobalArchive (globalarchive.org). The workshop identified and prioritised several key research themes that would contribute to the conservation and sustainable management of focal species and broad assemblages. Our goal is to describe where and when the data were collected, the type of equipment used and how the imagery was analysed. We also discuss the types of questions that can be addressed by analysing these standardised datasets and the potential benefits to conservation and fisheries management. [ABSTRACT FROM AUTHOR]

Abstract: Baited remote underwater video systems are becoming a widely adopted tool for sampling fish assemblages. One of the outstanding knowledge gaps associated with this technique is the effect of different quantities of bait on the fish assemblages sampled. We investigated how different quantities of bait (0g, 200g, 1000g or 2000g of crushed pilchards, Sardinops sagax) influenced the relative abundance and species richness of a temperate, Western Australian reef fish assemblage sampled with baited remote underwater stereo-video systems (stereo-BRUVs). The presence of bait significantly increased the relative abundance and numbers of fish species sampled, with few differences between the three quantities of bait. Trends in fork length were identified between bait quantities for some species. For example, juvenile stage Coris auricularis (a protogynous labrid) were significantly larger in the unbaited treatment, whereas males of the same species were significantly smaller at unbaited treatments. This pattern was interpreted as being the result of intraspecific competition and the dominance of larger males in the presence of bait. When bait was present, fish were significantly closer to the stereo-BRUVs. However, there was again no difference between the three baited treatments. At this location in temperate Western Australia, stereo-BRUVs with 200g of bait are as effective at sampling the temperate reef fish assemblage as stereo-BRUVs set with greater quantities of bait. In our study, the numbers of high trophic level species recorded were low. In areas with abundant high trophic level fishes, such as tropical reef systems, greater quantities of bait may be required to prevent it being quickly depleted by intense feeding. [Copyright &y& Elsevier]

El Niño Southern Oscillation (ENSO) events have impacted the marine environment of the Galapagos, causing massive die-offs of corals and megafauna, and benthic habitat shifts. With ENSO events predicted to intensify under climate change scenarios it is important for managers to have an evidence-based understanding of how these events may affect fish assemblages in the Galapagos. We assess the abundance and size fluctuations of benthic and mid-water shore fishes during the 2015–16 "Godzilla" ENSO using data from baited remote underwater stereo-video surveys collected on four occasions over 2015–16. We found significant differences in the assemblage structure between the pre-El Niño, El Niño onset, El Niño receding, and La Niña onset sampling periods. Mackerels (i.e. Trachurus murphyi and Decapterus spp.) had a ∼480% greater relative biomass, 229% greater relative abundance, and 20.6% greater size during La Niña onset compared to El Niño. With the onset of La Niña we observed a severalfold increase in the abundance of mid-water species including large Carangids, medium-size Scombrids, elasmobranchs (i.e. Sphyrna lewini , Carcharhinus galapagensis) and several other bentho-pelagic taxa. We also found evidence of seasonal abundance fluctuations across years, independent of seasonal effects, in Scarids, Haemulids, Labrids, Chaetodontids, and Carangids. Although the 2015–16 ENSO appears to have had a lesser impact on the Tropical Eastern Pacific than past El Niño events, it was linked to changes in the abundance of several species of key ecological and economic importance. This information furthers our understanding of the influence of large-scale climatic events on fish populations and improves our ability to predict how these populations may change under future climate scenarios. • Significant changes in Galapagos fish assemblage structure linked to 2015–16 ENSO. • Mackerels displayed marked fluctuations in size and abundance during ENSO. • Changes in other fish taxa including carangids, scombrids, and elasmobranchs. • ENSO impacts Galapagos fish species of key ecological and economic importance. • Important implications with projected ENSO intensification due to climate change. [ABSTRACT FROM AUTHOR]

We compared and contrasted fish assemblage data sampled by baited remote underwater stereo-video systems (stereo-BRUVs) and stereo-video remotely operated vehicles (stereo-ROVs) from subsea pipelines, reef and soft sediment habitats. Stereo-BRUVs sampled greater fish diversity across all three habitats, with the stereo-ROV sampling ~46% of the same species on pipeline and reef habitats. Larger differences existed in soft sediment habitats, with stereo-BRUVs recording ~65% more species than the stereo-ROV, the majority of which were generalist carnivores. These differences were likely due to the bait used with stereo-BRUVs attracting fish from a large and unknown area. Fish may have also avoided the moving stereo-ROV, an effect possibly magnified in open soft sediment habitats. As a result of these biases, we recommend stereo-ROVs for assessing fish communities on pipelines due to their ability to capture fish in-situ and within a defined sampling area, but caution is needed over soft sediment habitats for ecological comparisons. • Stereo-BRUVs and Stereo-ROV sampled different compositions of fish on and off the pipeline. • Stereo-ROV may under-sample fish in open sandy habitats. • Stereo-BRUVs may over-sample fine-scale habitat associations due to bait attraction. • Stereo-ROV samples fish-habitat associations in greater detail. • Stereo-ROV is a more suitable tool for sampling fish on pipeline and fine-scale structures. [ABSTRACT FROM AUTHOR]