|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)
Tagging of Pacific Pelagics (TOPP)
The aim of this program was to generate a detailed understanding of how marine animals from several trophic levels use distinct oceanic regions in the North Pacific. These included the Continental Shelf System stretching from Baja California to the Aleutians, the pelagic realm of the Sub-arctic and the Sub-tropical Transition Zones and Central and Alaska Gyres, and complex current systems, including the California Current and the Alaska Coastal Current. The project, which would identify migration routes and critical habitats and link behaviour and distribution to oceanographic processes, would employ advanced electronic tags, whose use had already changed our perception of the distribution of some key species. Elephant seals, for example, which had been regarded as essentially coastal animals in 1990, were now known to range over the whole North Pacific and to show striking differences in distribution between the two sexes.
A workshop in Monterey in November 2001, which had been funded by the Sloan and Packard Foundations, had identified a list of 15-20 species for potential investigation. These species, which included cephalopods, sharks, teleost fish, birds and marine mammals, were thought to make extensive movements, could be readily tagged and would catch the imagination when trying to educate the public about the nature and complexity of the ocean (outreach was a key component of the project). It would, however, not be possible to work with all the identified species and the project would concentrate initially on several foundation species, which included the northern elephant seal, bluefin tuna, one or more species of turtle, squid and albatross. Detailed planning for the project was now under way with further funding from the Sloan and Packard Foundations.
The project would use available electronic tags, or new tags that could be field-tested in 2002; the target species had been partly selected on their ability to carry these tags without difficulty. Archival tags, which could be implanted or attached externally, and pop-up tags, which were towed by the fish until release, both incorporated light sensors, which were sufficiently sensitive to detect dawn and dusk at depths of 200-300 m in relatively clear water. From these measurements it was possible to determine geographical location (latitude rather less accurately than longitude) with sufficient precision for the proposed aims. There had been technical problems with the first generation of archival tags for use on large pelagic species, but these had been relatively minor and had now reportedly been solved by the respective manufacturers. In once case the light stalk had proved to be too fragile, leading to ingress of water; in the other, the pressure sensor had not been robust enough to withstand the pressures to which the fish subjected them. Field tests of the replacement tags were now needed. Pop-up tags that could transmit data via the Argos satellite system were now quite well proven and both manufacturers had recently made a number of improvements to solve the problems of premature release and fish mortality. The rate of data transmission via Argos was low, but no alternative was available in the short-term. Standard GPS tags for use with marine mammals had high power consumption, but it was hoped to use a new tag currently under development in the UK, which would record a rapid ‘snapshot’ of the GPS satellites each time the animal surfaced, but would not process the data.
A key technical issue would be to merge the data obtained from electronic tags on individual animals with oceanographic data (physical and biological) obtained from in situ instruments, or by satellite. Models would be needed to predict the depth distribution of physical quantities from surface measurements (e.g. SST from SeaWifs data), although this problem could be solved by using diving animals to record depth profiles, a technique already used with sea birds and marine mammals. Elephant seals, for example, could be tagged with a simple GPS receiver to provide geographical location and an archival tag to record temperature, depth and other factors; data obtained in this way had been entered in the World Ocean Database. Problems were, however, envisaged as a consequence of having to collect information on a variety of spatial or temporal scales. It was known, for example, from the "winds to whales" project that whales appeared in Monterey Bay following wind-driven upwelling, the onset of primary production and the consequent large increase in the local numbers of krill. This was a general phenomenon and the behaviour of crab-eater seals in the Antarctic, for example, followed a similar pattern. Krill surveys were time consuming, however, and whilst it was easy to describe the behaviour of individual seals it was difficult to obtain an integrated picture of the local densities of their prey to which the seals were responding. LIDAR might offer a solution in some circumstances.
Discussion focused on a number of issues including rates of satellite data transmission, tag attachment, rewards for the recovery of archival tags (currently $1000 for Atlantic bluefin tuna), low frequency acoustic location, prey visualisation, passive listening devices and the effects of floating objects on tuna behaviour and migration. Ed Urban asked about the feasibility of easing the limitations on data transmission by increasing the bandwidth of the Argos system. In reply, David Farmer listed the alternative satellite systems and explained that Orbcomm, which was used to track vehicles and other items, had a transmitter that was generally too large for use with animals. The system was, however, suitable for retrieving oceanographic data and Geoff Arnold reported that CEFAS was routinely using Orbcomm to recover data from buoys on the European continental shelf. Iridium, which had a smaller transmitter and should be practical for animal telemetry, was not yet fully in operation, following financial difficulties in recent years. David Farmer made several suggestions including long-range, low-frequency acoustic location using fixed RAFOS transmitters (range 1000 km) and miniaturised receivers; low light level cameras fitted to diving marine mammals to record prey and feeding events; and passive identification of sound-producing fish. The last technique had great scope, as evidenced by the University of Rhode Island’s archive of fish sounds, which had recently been digitised. Fred Grassle suggested that MBARI’s Neptune test site would provide a good location at which to test passive detection and also drew attention to a map of ocean fronts (reference needed). This would provide a good guide to the location of floating objects (FADs) which, as François Gerlotto pointed out, were known to attract tuna and possibly alter their migration routes. Behaviour also changed when individual tuna aggregated to form schools and for this reason Dan Costa suggested that a proximity detector would be a useful sensor to add to electronic tags designed for use with schooling pelagic species. Ron O’Dor suggested that it might be possible to measure school cohesion using Vemco VR2 receivers and compatible acoustic tags.