Calibration of pelagic stereo-BRUVs and scientific longline surveys for sampling sharks

Our understanding of the ecology of sharks and other highly mobile marine species often relies on fishery-dependent data or extractive fishery-independent techniques that can result in catchability and size-selectivity biases. Pelagic Baited Remote Underwater stereo-Video Systems (pelagic stereo-BRUVs) provide a standardized, non-destructive and fishery-independent approach to estimate biodiversity measures of fish assemblages in the water column. However, the performance of this novel method has not yet been assessed relative to other standard sampling techniques. We compared the catch composition, relative abundance and length distribution of fish assemblages sampled using pelagic stereo-BRUVs and conventional scientific longline surveys. In particular, we focused on sharks of the family Carcharhinidae (requiem sharks) to assess the sampling effectiveness of this novel technique along a latitudinal gradient off the coast of Western Australia. We calibrated the sampling effort required for each technique to obtain equivalent samples of the target species and discuss the advantages, limitations and potential use of these methods to study highly mobile species.The proportion of sharks sampled by pelagic stereo-BRUVs and scientific longline surveys was comparable across the latitudinal gradient. Carcharhinus plumbeus was the most abundant species sampled by both the techniques. Longline surveys selected larger individuals of the family Carcharhinidae in comparison with the length distribution data obtained from pelagic stereo-BRUVs. However, the relative abundance estimates (catch per unit of effort) from the pelagic stereo-BRUVs were comparable to those from 5 to 30 longline hooks. Pelagic stereo-BRUVs can be calibrated to standard techniques in order to study the species composition, behaviour, relative abundance and size distribution of highly mobile fish assemblages at broad spatial and temporal scales. This technique offers a non-destructive fishery-independent approach that can be implemented in areas that may be closed to fishing and is suitable for studies on rare or threatened species

Climate-driven impacts of exotic species on marine ecosystems

Aim Temperature is fundamental to the physiological and ecological performance of marine organisms, but its role in modulating the magnitude of ecological impacts by exotic species remains unresolved. Here, we examine the relationship between thermal regimes in the range of origin of marine exotic species and sites of measured impact, after human-induced introduction. We compare this relationship with the magnitude of impact exerted by exotic species on native ecosystems. Location Global. Time period 1977–2017 (meta-analysis). Major taxa studied Marine exotic species. Methods Quantitative impacts of exotic species in marine ecosystems were obtained from a global database. The native range of origin of exotic species was used to estimate the realized thermal niche for each species and compared with the latitude and climatic conditions in recipient sites of recorded impact of exotic species. The difference in median temperatures between recipient sites and the thermal range of origin (i.e., thermal midpoint anomaly) was compared with the magnitude of effect sizes by exotic species on native species, communities and ecosystems. Results Recorded impacts occurred predominantly within the thermal niche of origin of exotic species, albeit with a tendency toward higher latitudes and slightly cooler conditions. The severity of impacts by exotic species on abundance of native taxa displayed a hump-shaped relationship with temperature. Peak impacts were recorded in recipient sites that were 2.2°C cooler than the thermal midpoint of the range of origin of exotic species, and impacts decreased in magnitude toward higher and lower thermal anomalies. Main conclusions Our findings highlight how temperature and climatic context influence ecological impacts by exotic species in marine ecosystems and the implications for existing and novel species interactions under climate change.En prensa5,14

Resilience of seagrass populations to thermal stress does not reflect regional differences in ocean climate

The prevalence of local adaptation and phenotypic plasticity among populations is critical to accurately predicting when and where climate change impacts will occur. Currently, comparisons of thermal performance between populations are untested for most marine species or overlooked by models predicting the thermal sensitivity of species to extirpation. Here we compared the ecological response and recovery of seagrass populations (Posidonia oceanica) to thermal stress throughout a year-long translocation experiment across a 2800-km gradient in ocean climate. Transplants in central and warm-edge locations experienced temperatures > 29°C, representing thermal anomalies > 5°C above long-term maxima for cool-edge populations, 1.5°C for central and < 1°C for warm-edge populations. Cool-edge, central and warm-edge populations differed in thermal performance when grown under common conditions, but patterns contrasted with expectations based on thermal geography. Cool-edge populations did not differ from warm-edge populations under common conditions and performed significantly better than central populations in growth and survival. Our findings reveal that thermal performance does not necessarily reflect the thermal geography of a species. We demonstrate that warm-edge populations can be less sensitive to thermal stress than cooler, central populations suggesting that Mediterranean seagrasses have greater resilience to warming than current paradigms suggest

Climate-driven regime shift of a temperate marine ecosystem.

Ecosystem reconfigurations arising from climate-driven changes in species distributions are expected to have profound ecological, social, and economic implications. Here we reveal a rapid climate-driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. After decades of ocean warming, extreme marine heat waves forced a 100-kilometer range contraction of extensive kelp forests and saw temperate species replaced by seaweeds, invertebrates, corals, and fishes characteristic of subtropical and tropical waters. This community-wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests

An Assessment of Mobile Predator Populations along Shallow and Mesophotic Depth Gradients in the Hawaiian Archipelago.

Large-bodied coral reef roving predators (sharks, jacks, snappers) are largely considered to be depleted around human population centers. In the Hawaiian Archipelago, supporting evidence is primarily derived from underwater visual censuses in shallow waters (=30?m). However, while many roving predators are present or potentially more abundant in deeper strata (30-100?m+), distributional information remains sparse. To partially fill that knowledge gap, we conducted surveys in the remote Northwestern Hawaiian Islands (NWHI) and populated Main Hawaiian Islands (MHI) from 2012-2014 using baited remote underwater stereo-video. Surveys between 0-100?m found considerable roving predator community dissimilarities between regions, marked conspicuous changes in species abundances with increasing depth, and largely corroborated patterns documented during shallow water underwater visual censuses, with up to an order of magnitude more jacks and five times more sharks sampled in the NWHI compared to the MHI. Additionally, several species were significantly more abundant and larger in mesophotic versus shallow depths, which remains particularly suggestive of deep-water refugia effects in the MHI. Stereo-video extends the depth range of current roving predator surveys in a more robust manner than was previously available, and appears to be well-suited for large-scale roving predator work in the Hawaiian Archipelago

Development and validation of a mid-water baited stereo-video technique for investigating pelagic fish assemblages

Understanding the abundance, demographics and composition of pelagic fish communities has historically relied on fisheries catch data or destructive fishery-independent methods. Here, we test and validate the use of a pelagic stereo-Baited Remote Underwater Video system (BRUVs) as a non-destructive, fishery-independent approach to study pelagic fish assemblages. We investigated whether differences in the vertical composition of fish assemblages could be detected with pelagic stereo-BRUVs by sampling at different depths in the water column. The effects of soak time and replication on the precision and cost of sampling were explored to allow for the optimization and standardization of future pelagic stereo-BRUVs studies. Pelagic stereo-BRUVs effectively identified 43 fish taxa from 18 different families in the mid-water, 5 and 20 m below the surface, in the Ningaloo Marine Park (Western Australia). The fish assemblages sampled at the two mid-water depths were significantly different demonstrating that this method could be used to investigate the vertical distribution and diel migration patterns of both pelagic and demersal fishes.Precision estimates under different sampling regimes showed that a soak time of 120 min and a sample size of at least 8 replicates per treatment would be optimal for sampling using pelagic stereo-BRUVs in tropical or warm-temperate areas. In order to account for the spatial and temporal variability of the system and to facilitate future comparisons across studies using this method, we encourage maximizing replication given the resources available while standardizing the soak time. Pelagic stereo-BRUVs may provide a useful, non-destructive method to improve our understanding on the ecology and behavior of fishes in pelagic ecosystems

Effects of a spatial closure on highly mobile fish species: an assessment using pelagic stereo-BRUVs

The effects of a spatial area closure on pelagic fish assemblages within the Houtman Abrolhos Islands were assessed using mid-water pelagic stereo-BRUVs. The spatial area closure within the Easter group of the Houtman Abrolhos Islands was found to have no significant effect on the species composition and relative abundance of pelagic fish assemblages. The most abundant demersal target species recorded was pink snapper (Chrysophrys auratus) and, individuals measured within the spatial closure were significantly larger than those sampled in the area open to fishing. This spatial area closure is of moderate size (22.3 km2), but the spatial management of highly mobile species may require larger area closures than those for reef-associated species. The monitoring of pelagic species both in large and small spatial area closures is required in order to better understand how mobile species respond to this management strategy. Some species were only recorded in relatively low numbers using pelagic stereo-BRUVs. Moreover, some of the highly mobile pelagic fish species, such as tunas, mackerel and some shark species have proven difficult to measure, as these species were observed furthest from the camera systems. While pelagic stereo-BRUVs are an effective fishery-independent approach to monitor spatial fishing closures, improving the power of replicates by pooling individual deployments, and increasing the attraction rate of pelagic fish to the stereo-cameras, will enhance their performance in future studies

The Use of Stationary Underwater Video for Sampling Sharks

This pioneering book, written by experts in shark biology, examines technologies such as autonomous vehicle tracking, underwater video approaches, molecular genetics techniques, and accelerometry, among many others

Performance of bycatch reduction devices varies for chondrichthyan, reptile, and cetacean mitigation in demersal fish trawls: Assimilating subsurface interactions and unaccounted mortality

To improve bycatch mitigation of chondrichthyans, reptiles and cetaceans for a tropical demersal fish-trawl fishery, species-specific responses to bycatch reduction devices (BRDs) were investigated using both in situ subsurface and onboard observations. There are few, if any, studies that have determined mitigation performances of BRDs from subsurface interactions for these species, as most are rarely encountered and thus require substantial levels of observer coverage for robust assessments. This study combined in-net and onboard (774 day trawls and 1320 day trawl hours of subsurface observer coverage) electronic monitoring on all fish-trawl vessels (n = 3) to compare bycatch mitigation performances among nine megafauna groups, based on escape rates and interaction durations for three BRDs over 6 months (June to December 2012). Overall, 26.9% of day trawls had no megafauna interactions and 38.3% of the 1826 interactions escaped, with most in rapid time (91.4% in ≤ 5 min). The upward inclined exclusion grid significantly improved the escape proportions for most chondrichthyans by 20–30%. All BRDs were highly effective in reducing reptile (turtles and seasnakes) bycatch, but irrelevant for the few sawfish (n = 13) that readily entangled in the anterior of the net. Cetacean (bottlenose dolphins only) interactions with BRDs were very rare (n = 7) despite high levels of attendance and depredation during trawling. Loss of targeted teleosts through the BRD hatch was rare (1.3% of day trawls). This relatively cost-effective method of electronic monitoring achieved very high levels of subsurface observer coverage (60% of day trawls or 56% of day trawl hours), and provided evidence that the subsurface expulsion of megafauna in poor condition is negligible. Furthermore, this study provides species-specific improvements toward bycatch mitigation strategies for demersal fish trawling

Santana-Garcon_etal_MEE-rawdata

Abundance and length data sampled using pelagic stereo-BRUVs and scientific longline surveys along a latitudinal gradient off the coast of Western Australia