Low-cost device for retrieval of moorings deployed with underwater remote release systems

Underwater acoustic and timed-release systems are commonly deployed with sensors and other equipment for ecological and oceanographic research in aquatic environments. These systems allow equipment deployed at depth to be remotely released from their moorings for retrieval. However, a current limitation is that most systems do not incorporate mechanisms for retrieval of the mooring anchor and attachments (e.g. shackles, cable). Herein we provide a detailed description and evaluation of a 'retrieval pod' that can be attached directly to remotely released underwater devices to facilitate mooring retrieval. The system was tested using acoustic release telemetry receivers under field conditions in a large estuary in the Northern Territory, Australia. Six receivers fitted with pods were retrieved from the field after two consecutive 6-month deployments (12 retrievals in total) with no failed mooring retrievals. Although our tests were confined to shallow depths (<8m), it should be straightforward to modify the system for use in deeper water by increasing the spool capacity. The retrieval pods are reusable, require minimal construction skills and can be assembled from basic equipment available at most hardware or boating stores, making them a convenient and low-cost option for the retrieval of moorings deployed with remote release systems.