This metadata record describes cetacean line-transect distance sampling dataset collected during the 2021 TEMPO (Trends in Euphausiids off Mawson, Predators, and Oceanography) voyage onboard the RV Investigator. The primary goal of TEMPO was to collect data to estimate krill biomass with a view to update the precautionary catch limit for krill in CCAMLR’s Division 58.4.2-East. The survey was also designed to improve our understanding on the connectivity of the krill population, and overlap between krill and predators. The survey consisted of six major acoustic line-transects to estimate krill biomass and to observe swarm behaviour across ecological and density gradients within the survey area south of 62°S between 55° and 80° E, and a single fine-scale krill box acoustic survey off the Mawson coast. Comprehensive oceanographic (CTDS, XBTs ARGSO floats) and biological (plankton) sampling were also conducted to understand the habitat environment of krill and its predators. Predator observation was undertaken throughout the voyage to improve our understanding on the connectivity of the krill population, and overlap of distribution between krill and predators. The information gathered contributes to the design of tractable and sustainable long-term monitoring plan and to evaluate spatial management of the krill fishery.
A team of four dedicated cetacean observers (with contributions from other experienced staff onboard) undertook formal line transect distance sampling when conditions allowed. Two observers were on effort during line transect effort; they were stationed in protective boxes on the forward Deck 05 of the RV Investigator. A data entry person was situated on the bridge; sighting, effort and weather data were logged using PAMGUARD (Pamguard Development Team 2021). The two observers scanned port and starboard, respectively, from abeam (~90° from the ship’s heading) through to around ~10° beyond the trackline on the other side. (i.e., this is single platform sighting data, sensu Burt et al. 2014). They searched using a combination of naked eye, Fujinon 7 x 50 FMTRC-SX binoculars and Fujinon 25 x 150 MT binoculars. Radial distances were estimated using the reticles of the 7 x 50 binoculars, or were estimated when detections were too close, or if the horizon was not available. Reticle information can be used to estimate radial distance to the observation using the methods outlined in Kinzey et al. (2000) and Kinzey and Gerrodette (2001). On Deck 05, average observer eye-height was ~18.4 m above the water line; the average observer eye-height on the bridge was ~20.7m. The observers maintained line transect search effort during daylight hours, with a sea state ≤ 6, and with reasonable visibility. For shorter periods of poorer visibility (or ship operations which slowed the vessel considerably or altered travel direction) they maintained ‘visual search’ effort on Deck 05, or moved to the bridge to undertake ‘bridge only’ searching during extended periods of poor weather and/or ship operations.
A total of 3612 km of line transect distance sampling effort for cetaceans was achieved both within the TEMPO survey area and during the transit periods, in addition to 153 km of informal sighting effort from Deck 05, and another 1115 km of bridge only effort. This combined effort yielding 621 sightings of approximately 1609 animals. The most prevalent species observed was humpback whales, followed by fin whales.
Sightings may include non-cetacean species like seabirds and pinnipeds, but as these were not the target taxa for this observation process, consistent recording of sighting for these should not be assumed.
References
Burt, M. L., Borchers, D. L., Jenkins, K. J., and Marques, T. A. (2014). Using mark-recapture distance sampling methods on line transect surveys. Methods in Ecology and Evolution, 5(11), 1180-1191. doi:10.1111/2041-210x.12294
Kinzey D, Olson P, Gerrodette T. 2000. Marine mammal data collection procedures on research ship line-transect surveys by the Southwest Fisheries Science Center. Southwest Fisheries Science Center, Administrative Report LJ-00-08.
Kinzey, D., and Gerrodette, T. (2001). Conversion factors for binocular reticles. Marine Mammal Science, 17, 353-361.
Pamguard Development Team (2021). Pamguard. Version 2.02.01, Available at: http://www.pamguard.org/.
