Abstract
Instruments are often deployed at depth for weeks to years for a variety of marine applications. In many cases, divers can be deployed to retrieve instruments, but divers are constrained by depth limitations and safety concerns. Acoustic release technology can also be employed but can add considerable expense and acoustic releases will at times fail. Here, we report a simple method that utilizes a commercially available mooring hook integrated with a mini remotely operated vehicle to attach lines to instruments deployed on the sea floor, which can then be winched to the surface. The mooring hook apparatus was tested in a pool setting and then used to retrieve acoustic telemetry receiver bases (50 kg) or fish traps (30–50 kg) from the northern Gulf of Mexico continental shelf at depths between 28 and 80 m. During 2013–2019, 539 retrievals (100% success rate) were made of receiver bases (n = 239) and traps (n = 300) on 30 sea days using this approach. This method could easily be applied to other types of instruments, or recovery and salvage of objects that are too deep for standard diving operations.
Highlights
Marine research often requires deployment and retrieval of scientific instruments at depth, including on the seafloor
Receiver bases were constructed of poly vinyl chloride (PVC) pipes embedded in 40 kg of concrete (Fig 4a and 4e)
Four stainless steel eye hooks were embedded in the concrete and two nylon ropes (450-kg lifting strength) were each tied to an eye bolt, extended 1.5 m up the PVC pole where they were secured with 2 50-kg cable ties, and tied to an eye bolt on the opposite side of the pole
Summary
Marine research often requires deployment and retrieval of scientific instruments at depth, including on the seafloor. Instruments may require long soak times and rely on being tethered to surface floats for later retrieval [1], [2], [3], or require Self-Contained Underwater Breathing Apparatus (SCUBA) divers or other approaches to retrieve equipment [4]. Attaching instruments to surface buoys for long durations (months to years) can be problematic as boat traffic can displace equipment or sever mooring lines [5], [6], and theft of equipment can occur [1], [5], [6]. SCUBA can be a cost-effective means to conduct underwater research [7], [4], but there are associated risks for diver health due to myriad effects, such as barotrauma, decompression illness, pulmonary edema, or toxic effects of increased partial pressure of gases [7], [8]. Conventional SCUBA is limited to depths
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