Periodic small-boat surveys were undertaken around the main Hawaiian Islands from February 2000 through February 2005, primarily to collect genetic samples and photo-identify
odontocete cetaceans. A dataset of 529 odontocete sightings exists from these surveys, representing 16 different species. While the dataset is useful to note where certain species have
been seen and document features such as group size and depth preferences, there are a number of biases and limitations of the dataset that must be taken into account for other analyses. There are both inter-annual and seasonal biases in survey effort. While some species are probably resident to the islands and numbers are unlikely to vary seasonally, others may use the area regularly only during certain seasons (e.g., striped dolphins, Risso’s dolphins), and thus are probably underrepresented in the dataset. Information is not available to assess inter-annual variability in any of the species’ use of the area around the main Hawaiian Islands. Survey effort was geographically biased (by region and by depth), and particular depth preferences have been documented for most species of Hawaiian cetaceans. Thus the likelihood of documenting species will depend to a large degree on the water depths surveyed, which varied among islands and among years. Sighting probability varies among species based on dive durations, body size, group size, and surface behavior; it is likely that long-diving and/or cryptic species such as beaked whales, sperm whales, and dwarf and pygmy sperm whales are under-represented in the dataset. Additionally, given the overall low density of cetaceans in Hawaiian waters, and the low sighting rates of some species in particular, a strong small sample size bias exists for areas around Kaua‘i, Ni‘ihau, and O‘ahu; off those areas the small amount of survey coverage relative to sighting rates for some species suggests these species are not likely to have been recorded frequently even if they may use the area on a regular basis.
Citation:
Baird, R.W., D.L. Webster, and D.J. McSweeney. 2005. Biases and Data Limitations of Odontocete Cetacean Sighting Data from Small-Boat Based Surveys Around the Main Hawaiian Islands. Report prepared under Purchase Order No. N62742-05-P-1880 from the NAVFAC Pacific, Pearl Harbor, HI.
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