Article/Figures Provided By: Katie Sweeney (NMFS/AKFSC/NMML)
In 1963, NOAA Fisheries’ Marine Mammal Laboratory (MML) began to use the mark-recapture method of shear-sampling northern fur seal pups to estimate pup abundance. Presently, these surveys are conducted every two years on St. Paul and St. George Island (Pribilof Islands, Alaska). These trips require up to 22 people to be stationed on the islands for up to three weeks and the presence of scientists on the rookery creates disturbance (authorized by a Federal permits: NMFS/MMPA 14327 and IACUC ANW2013-3). With the help of the UAS Program Office, MML has been collaborating with NOAA’s Aircraft Operations Center (AOC), National Environmental Satellite Data and Information Service (NESDIS), Mystic Aquarium, Aerial Imaging Solutions, and GeoThinkTank (Figure 1) to work on developing a UAS-based approach for conducting northern fur seal abundance surveys.
MML has successfully implemented unoccupied aircraft systems (UAS; i.e., drones) to supplement annual Steller sea lion abundance surveys since 2014. Given the size and relatively more distinct coloration from their background, using a high-resolution mirrorless camera has worked well for capturing images of Steller sea lions (Figure 2). The challenge with developing a similar approach for northern fur seals has been deciphering small black fur seal pups from the black boulder substrate common in the Pribilof Islands—northern fur seals are much harder to count in images!
We have a few objectives for our project to get us closer to our goal: (1) assess a heavy-lift hexacopter with longer flight times and ability to carry heavier payloads, (2) evaluate imaging capabilities of a thermal sensor for northern fur seals, and (3) conduct an on-the-ground assessment of the feasibility of multi-spectral imaging for distinguishing northern fur seals from their background.
In August of 2018 during the shear-sampling surveys on St. George Island, we were able to test the APH-28 hexacopter (Figure 3) (Aerial Imaging Solutions) mounted with the FLIR DUO Pro R thermal sensor and conduct aerial surveys of a small rookery (Figure 4). We completed redundant surveys of this rookery with this thermal sensor and also with a high-resolution mirrorless digital camera. We will soon count northern fur seals from these two sets of imagery and be able to compare the counts to our traditional ground-survey estimates.
During this same trip, we worked with GeoThinkTank to collect spectral measurements using a handheld spectroradiometer (loaned by NESDIS) of northern fur seals (pups, adult females, and a deceased adult male) and the substrate (rocks, grass, driftwood, etc.) (Figure 5). Collecting measurements like these is a normal procedure for plants and other substrate (e.g., for calibrating satellite imagery), but as far as we know, has never been done for wildlife.
Collecting these spectral measurements in the field in Alaska was made easier by our preliminary trip to Mystic Aquarium in May of 2018. Mystic Aquarium allowed us the opportunity to collect more measurements of northern fur seals (from animals far more cooperative than those we encounter in the wild) and in a more controlled environment to help us streamline our methods for the harsher field conditions in Alaska (Figure 6). These spectral measurements will be used to model a virtual northern fur seal rookery environment to run various aerial survey simulations. This will allow scientists to test various bands beyond the typical four bands customary to off-the-shelf multi-spectral UAS sensors. If optimal bands are identified and multi-spectral imaging is found to be effective, this will guide our next steps towards developing a custom UAS-mounted sensor.
Assessing optimal imaging capabilities will guide sensor selection and further development of an observing system. Once we have a handle on the best sensor payload option, we can explore which UAS platforms would be most effective for abundance surveys, and eventually replace and improve upon the current traditional survey method.