Filename
AEBR-325-Novel-Technologies-For-Inshore-Fisheries-Dolphin-Capture-Risk-Mitigation-4441-2023.pdf
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AEBR-325-Novel-Technologies-For-Inshore-Fisheries-Dolphin-Capture-Risk-Mitigation-4441-2023.pdf (7.8 MB)
Abstract
New Zealand’s Hector’s dolphins are an endangered species. A key threat to their survival is entanglement in fishing gear, including trawl nets. In this study, we report on a field trial where underwater microphones (hydrophones) were fitted to trawling equipment and the echolocation clicks naturally produced by Hector’s dolphins were localised to determine how the dolphins interacted with the trawling equipment as it moved through the water. The hydrophones were protected within custom-built cages to withstand the physical stress associated with being attached to fishing equipment that is dragged along the seabed. The field trial was conducted off the coast of Timaru, New Zealand, in September and October 2022. While the hydrophones recorded dolphin sound underwater, a Fisheries New Zealand observer on the boat also looked out for dolphins.
The protective cages around the hydrophones proved effective and we were able to successfully localise dolphins. Dolphins were localised moving towards the mouth of the fishing net from various approach angles, and, on several occasions, we were able to successfully distinguish multiple dolphins each moving along different paths. Even though we only analysed a subset of the acoustic data from each trawl, dolphin clicks were detected acoustically during trawls on more occasions than the observer on the fishing boat was able to see dolphins. Unfortunately silt from the seabed entered some of the connections between the hydrophones and the acoustic recorder, which resulted in corrupted data on some days, but overall the field trial was successful.
This study showed that listening for the presence of dolphins can be more effective than looking for dolphins from a boat. We suggest that a combination of listening and looking for dolphins would be the most effective way to detect dolphins that might be near the fishing net. In the long term, the listening system described here could be developed into a real-time warning system that alerts the fishing vessel master when dolphins are close to the fishing net. If the vessel master is aware of the dolphins, they could avoid activities that result in high-risk of entanglement, such as sharp turns or drawing in the net at the end of the trawl. Dolphin detection could also help with targeted use of devices that encourage the dolphins to move away from the high-risk areas—such devices emit noise and should be used as little as possible to minimise noise pollution and disturbance to the dolphins.
Document date
Monday, 11 December 2023
Document type
V 1.3
File format
Adobe PDF
File size
7.8 MB
Reference number
325
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Uploaded from
AEBR-325-Novel-Technologies-For-Inshore-Fisheries-Dolphin-Capture-Risk-Mitigation-4441-2023.pdf
Uploaded date
Monday, 11 December 2023
Search tags
AEBR:
325;
ISBN:
978-1-991120-52-6;
ISSN:
1179-6480;
AUTHOR:
Warren, V.E.;
Delarue, J.J.-Y.;
McEachern, J.;
Martin, S.B.;
McPherson, C.R.;
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