A quantitative assessment of continuous versus structured methods for the detection of marine mammals and seabirds via opportunistic shipboard surveys

Abstract

Marine monitoring efforts are increasingly supported by opportunistic shipboard surveys. However, opportunistic survey methods often require adaptation to suit the vessel and the operations being conducted onboard. Whilst best-practice techniques for surveying marine wildlife on vessels of opportunity are yet to be established, testing and development of alternative methods can provide means for capturing ecological information in otherwise under-surveyed areas. Explicitly, survey methods can be improved while baseline ecological data for new regions are gathered simultaneously. Herein, we tested different survey approaches on a vessel of opportunity in a remote offshore area where little is known about the community composition of top-order marine vertebrate predators: western and south-western Tasmania, Australia. We found that continuous surveys provide greater species counts than structured "snapshot" surveys over the course of a voyage, but that structured surveys can be more practical when managing factors such as observer fatigue. Moreover, we provide a baseline dataset on the marine vertebrate community encountered in western and south-western Tasmania. This information will be critically important for industry and conservation management objectives, and is key to our understanding of the offshore ecosystem around Tasmania.

Figure 1

Marine mammals observed from the RV Investigator during the IN2023_V02 voyage. Panel A depicts all sightings—with each species described by the colours in the legend below. This colour key extends into panel B and C which depict pinniped and cetacean sightings, respectively. For panels B and C, a white boundary depicts the Tasmanian coastline. A GEBCO_2022 Bathymetric product is displayed under data. This figure was created with GlobalMapper (version 24.1, see: https://www.bluemarblegeo.com/global-mapper/).

Figure 2

Elevation map of study area (west and south-west Tasmania) with ship tracks (4193 nautical miles) shown in cream, continuous survey effort shown in black, structured survey effort shown in orange, and marine national parks shown in red. A separate legend for bathymetry (depth, GEBCO_2022) is shown to the right of the figure. This figure was created with GlobalMapper (version 24.1, see: https://www.bluemarblegeo.com/global-mapper/).