By Marie C. Hill, Andrea R. Bendlin, Allan D. Ligon, Adam Ü, and Karlina Merkens
After spending five windy days working off Rota (21-25 May 2016) where we encountered spinner dolphins, spotted dolphins and a Mesoplodont beaked whale, we flew to Guam to finish off our Marianas survey effort (28 May -5 June). We were greeted with incredibly calm conditions and a new species for us off Guam! Our first two encounters were with dwarf sperm whales (Kogia sima), some of which we actually re-sighted six days later. We’ve encountered a dwarf sperm whale off Saipan in 2011 but have not seen any others until now. The dwarf sperm whale is a very cryptic species that is difficult to find (unless conditions are very calm) and difficult to approach (they are very shy of boats). This year’s encounters were particularly exciting because we collected a biopsy sample, as well as acoustic recordings! It’s exciting because dwarf sperm whales have rarely been biopsy sampled, and there has been only one other acoustic recording of visually-confirmed dwarf sperm whales in the wild! In order to collect the recordings, we used a free floating hydrophone and recorder attached to a buoy and flag. We call it the CARB (Compact Acoustic Recording Buoy). At one point during our fourth dwarf sperm whale encounter a mom-calf pair swam directly toward, then passed by the CARB (Figure 1). The acoustic recordings are of excellent quality and match up well with the only other recording of this species, which came from the Bahamas. They will go a long way toward helping us understand and monitor Kogia species.
While surveying off Guam we also encountered the dwarf sperm whale’s much larger cousin, the sperm whale (Physeter macrocephalus). The group of nine individuals included a newborn calf (Figure 2).
During the sperm whale encounter we collected three biopsy samples (for genetic studies) and deployed a satellite tag (ID 141723) on an individual (to look at movements and spatial use). The tag (ID 141712) that we deployed on a sperm whale off Saipan on 17 May was still transmitting on 10 June. These tags are the first ones that we have deployed on sperm whales in the Marianas. The tracks of the two individuals have come close but have not overlapped (Figure 3). The sperm whale with tag 141712 spent several weeks north of Saipan and went as far north as Guguan. On 10 June, it was just southwest of Farallón de Medinilla. Our Guam sperm whale, tagged on 31 May, spent several days off the west side of Guam and then traveled north. It was approximately 50 miles west of Saipan on 10 June.
Another first for us this year was the deployment of a satellite tag on a pantropical spotted dolphin (Stenella attenuata) off Guam. People sometimes mistake spotted dolphins and spinner dolphins (Stenella longirostris) because they are similar in size and color. Two features of spotted dolphins that make them easy to distinguish from spinner dolphins is the white tip of the rostrum and presence of spots on the bodies of adults (both features become more pronounced as individuals age) (Figure 4).
The spotted dolphin that we tagged has moved up and down the west side of Guam and even went out to 11-Mile Reef (Figure 5). On 10 June, it was just south of Agat Bay.
Finally! We found short-finned pilot whales again! We didn’t encounter them during our 2015 small-boat surveys. While working off Guam this year we had four sightings of short-finned pilot whales, during which we re-sighted individuals between days. Most of the individuals are in our photo-identification catalog. Some of these individuals have not been seen together before. One of our favorites also showed up on the last day of our surveys (5 June). “Chop Top” (Figure 6) is an adult male that we first photographed off Rota in 2011. We last saw him in 2013 off Guam and were worried we wouldn’t see him again.
During three of our four short-finned pilot whale encounters we deployed six satellite tags. Since tagging, some of the individuals have stayed in close proximity to one another while others have split up, come together and split up again (Figure 7). By having tags out on multiple individuals we can get a better idea of the spatial use of the population of short-finned pilot whales that we encounter off the southernmost islands in the Marianas. We’re hoping that one of these tags breaks the previous record for longest duration (235 days).
All survey operations including satellite tagging, photo-id, and biopsy sampling are conducted under NMFS permit 15240. Funding was provided by the NOAA Fisheries and the Commander U.S. Pacific Fleet. We would like to thank the vessel owners and captains of the Asakaze and Ten27, the Guam NOAA Fisheries field office, and all of our volunteers during the surveys.