This dataset relates to statistical models of killer whale (Orcinus orca) occurrence in the Bremer Sub-Basin developed from vessel-based and aerial survey data collected between 2015 and 2017. Further information can be found in: Salgado-Kent C, Parnum I, Wellard R, Erbe C, Fouda L. 2017. Habitat preferences and distribution of killer whales (Orcinus orca) in the Bremer Sub-Basin, Australia. Report to the National Environmental Science Programme Marine Biodiversity Hub (CMST 2017-15), 37 p.
Opportunistic, non-systematic vessel surveys were conducted in an area approximately 4,000 sq. km within the Bremer canyon system (centred at 34°44.30'S latitude and 119°35.55'E longitude) between February and April 2015 and 2016. The surveys were undertaken from commercial eco-tourism vessels Cetacean Explorer and Dhu Force (operated by Naturaliste Charters in 2015 and 2016) while these vessels were carrying out normal ecotourism manoeuvres taking tourists to see killer whales. Between March and April 2017, non-systematic vessel surveys were also conducted in the same vicinity aboard a dedicated research vessel Big Dreams chartered by MIRG Australia. Observations were recorded by a minimum of two individuals scanning the area forward to abeam of the vessel on port and starboard sides. Upon sighting a group of killer whales, the GPS position of the vessel, group size and behavioural state were noted. The vessel then switched to closing mode and the group was slowly approached to within 50 m to take photographs and capture more accurate information on group size, group composition (numbers of adults and calves) and predominant behavioural state. Aerial surveys were additionally conducted in March 2017 with a total of 6 flight survey days. A twin-engine over-head wing Cessna 337 aircraft with bubble windows was chartered from Norwest Air Work Pty Ltd to survey pre-determined transects at an altitude of 300 m and a speed of 120 knots (see associated metadata record http://catalogue.aodn.org.au/geonetwork/srv/eng/metadata.show?uuid=7526a44e-dea3-496c-81f4-776d908e2923). The spatial occurrence of killer whale groups over time was modelled as a function of environmental covariates (e.g. seabed depth, seabed slope, mean sea surface temperature) using Generalized Estimation Equations (GEEs) with a log-link function (for Poisson distributed count data).