|SCOR Working Group 118: New Technologies for Observing Marine Life|
Terms of Reference
Working Group Members
Funding provided by
the SLOAN Foundation's
Census of Marine Life
2001 Working Group Meeting
(27 October 2001, Mar del Plata, Argentina)
Pacific Ocean Salmon Tracking (POST)
This project aimed to investigate the migrations of Pacific salmon, using archival tags in the open ocean and acoustic tags on the narrow continental shelf from California to Alaska. Smolts would be tagged internally with surgically implanted acoustic tags, a well-tried technology. The plan was to install ~25 lines of acoustic receivers across the shelf at strategic points, and also to instrument all west-coast rivers from Sacramento northwards. A total of 600-700 receivers was envisaged. The technical requirement was for autonomous units with lithium batteries providing a 3-5 year life. Each unit would comprise a low power memory board with serial ports, a hydrophone and acoustic receiver for detecting acoustic tags, a modem for acoustic telemetry and an acoustic transponder for relocation, as well as sensors to measure temperature, salinity, depth, wave height and current speed (low power ADCP?). A tilt sensor could be useful for initial deployment. The instruments would be encapsulated in resin inside a low-profile cast iron, or concrete mount that would not readily be trawled up. A research vessel would recover data every few months. Acoustic receivers were readily available at low cost, but information was needed on acoustic modems.
A number of points were made in discussion. David Farmer suggested that it would be more efficient to use transponding acoustic tags instead of continuously transmitting ‘pingers’, although Dan Costa thought that it might be difficult to motivate the manufacturer to develop these. Geoff Arnold pointed out that transponding acoustic tags had been in use for fish tracking in Europe since 1970 and that electronic circuits for high-frequency tags (76 – 300 kHz) had been published by both CEFAS and the University of Aberdeen in the UK (Annex D). Cynthia Decker asked if the use of transmitting arrays could create difficulties with public relations and Ken Foote emphasised that it would be necessary to demonstrate that there would be no interference with marine mammals. David Welch pointed out that, with the system he had proposed, acoustic transmission would be limited to data recovery when a research vessel would be alongside the acoustic unit. At all other times, when unattended, the acoustic unit would only be listening. Low power tag transmissions were not regarded as significant sources of noise for marine mammals. In relation to data retrieval, David Farmer commented that many acoustic modems were available and that experts at WHOI would be well placed to advise. Fred Grassle commented that ROVs had been successfully used to recover seabed instruments during oil rig surveys and might offer a cheaper more effective solution than an acoustic modem. Another alternative would be to use a communication pod that came to the surface on command. Other technical issues included: the use of oil-immersed lead-acid batteries (with a pressure-venting membrane), which could provide ballast as well as a lot of power; risks of siltation (avoidable by choice of substrate) and bio-fouling (low at 40 m depth); acoustic releases to recover ADCPs; and speed of sound measurements to determine salinity over long periods.