26 research outputs found
Effectiveness of five personal shark-bite deterrents for surfers
The number of shark-human interactions and shark bites per capita has been increasing since the 1980s, leading to a rise in measures developed to mitigate the risk of shark bites. Yet many of the products commercially available for personal protection have not been scientifically tested, potentially providing an exaggerated sense of security to the people using them. We tested five personal shark deterrents developed for surfers (Shark Shield Pty Ltd [Ocean Guardian] Freedom+ Surf, Rpela, SharkBanz bracelet, SharkBanz surf leash, and Chillax Wax) by comparing the percentage of baits taken, distance to the bait, number of passes, and whether a shark reaction could be observed. We did a total of 297 successful trials at the Neptune Islands Group Marine Park in South Australia, during which 44 different white sharks (Carcharodon carcharias) interacted with the bait, making a total of 1413 passes. The effectiveness of the deterrents was variable, with the Freedom+ Surf affecting shark behaviour the most and reducing the percentage of bait taken from 96% (relative to the control board) to 40%. The mean distance of sharks to the board increased from 1.6 ± 0.1 m (control board) to 2.6 ± 0.1 m when the Freedom Surf+ was active. The other deterrents had limited or no measureable effect on white shark behavour. Based on our power analyses, the smallest effect size that could be reliably detected was âŒ15%, which for the first time provides information about the effect size that a deterrent study like ours can reliably detect. Our study shows that deterrents based on similar principlesâoverwhelming a sharkâs electroreceptors (the ampullae of Lorenzini) with electrical pulsesâdiffer in their efficacy, reinforcing the need to test each product independently. Our results will allow private and government agencies and the public to make informed decisions about the use and suitability of these five products
A field and video-annotation guide for baited remote underwater stereo-video surveys of demersal fish assemblages
Researchers TL, BG, JW, NB and JM were supported by the Marine Biodiversity Hub through funding from the Australian Government's National Environmental Science Program. Data validation scripts and GlobalArchive.org were supported by the Australian Research Data Commons, the Gorgon-Barrow Island Gorgon Barrow Island Net Conservation Benefits Fund, administered by the Government of Western Australia and the BHP/UWA Biodiversity and Societal Benefits of Restricted Access Areas collaboration.1. Baited remote underwater stereo-video systems (stereo-BRUVs) are a popular tool to sample demersal fish assemblages and gather data on their relative abundance and body-size structure in a robust, cost-effective, and non-invasive manner. Given the rapid uptake of the method, subtle differences have emerged in the way stereo-BRUVs are deployed and how the resulting imagery are annotated. These disparities limit the interoperability of datasets obtained across studies, preventing broad-scale insights into the dynamics of ecological systems. 2. We provide the first globally accepted guide for using stereo-BRUVs to survey demersal fish assemblages and associated benthic habitats. 3. Information on stereo-BRUV design, camera settings, field operations, and image annotation are outlined. Additionally, we provide links to protocols for data validation, archiving, and sharing. 4. Globally, the use of stereo-BRUVs is spreading rapidly. We provide a standardised protocol that will reduce methodological variation among researchers and encourage the use of Findable, Accessible, Interoperable, and Reproducible (FAIR) workflows to increase the ability to synthesise global datasets and answer a broad suite of ecological questions.Publisher PDFPeer reviewe
What are we missing? Advantages of more than one viewpoint to estimate fish assemblages using baited video
Published by the Royal Society under the terms of the Creative Commons
Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted
use, provided the original author and source are credited.Counting errors can bias assessments of species abundance
and richness, which can affect assessments of stock structure,
population structure and monitoring programmes. Many
methods for studying ecology use fixed viewpoints (e.g. camera
traps, underwater video), but there is little known about
how this biases the data obtained. In the marine realm, most
studies using baited underwater video, a common method for
monitoring fish and nekton, have previously only assessed
fishes using a single bait-facing viewpoint. To investigate
the biases stemming from using fixed viewpoints, we added
cameras to cover 360° views around the units. We found
similar species richness for all observed viewpoints but the
bait-facing viewpoint recorded the highest fish abundance.
Sightings of infrequently seen and shy species increased with
the additional cameras and the extra viewpoints allowed the
abundance estimates of highly abundant schooling species to
be up to 60% higher. We specifically recommend the use of
additional cameras for studies focusing on shyer species or
those particularly interested in increasing the sensitivity of the
method by avoiding saturation in highly abundant species.
Studies may also benefit from using additional cameras to focus
observation on the downstream viewpoint.Funding for this project was provided by the Holsworth Wildlife Endowment Fund and DEWNR