by Marie C. Hill, Andrea R. Bendlin, Allan D. Ligon, and Adam Ü
After having to skip our surveys off Saipan last year because of the damage from Typhoon Soudelor, we were happy to return during 7-18 May 2016 to continue our ongoing study of cetaceans in the Marianas. It is good to see and hear that Saipan is recovering. Soudelor was the second strongest typhoon to develop in the northern hemisphere in 2015. On 2 August 2015, it hit Saipan directly and devastated the island. Homes and businesses were destroyed and others were damaged and without power for months.
We had a bit of a slow start to our surveys because the winds and swells were up. Despite the rough conditions, we did find one of our favorite species, rough-toothed dolphins (Steno bredanensis), near Chalan Kanoa Reef, off the west side of Saipan. Their crocodile shaped heads and their mottled bodies make them one of the most unusual looking dolphins alive, and some of the individuals present during this encounter are exceptionally mottled (Figure 1). They look hand-painted. What is also interesting about the Steno we encountered is that four of the five belong to our photo-identification catalog of six individuals. We have seen them together in July 2013 and April 2014 off Aguijan and in July 2013 off Saipan, suggesting that they are resident to this area. The fifth individual was a juvenile that may have been born in 2014.
Other strange looking cetaceans that we encountered during our surveys off Saipan were sperm whales (Physeter macrocephalus) (Figure 2). They are the only cetacean species with their blow hole at the tip of their rostrum and it is canted to the left. This characteristic can make them easily identifiable from a distance because their blow is angled.
We encountered sperm whales on two separate days. Some of the same individuals were present during both sightings. We are able to identify them, primarily from their flukes but in some cases can recognize them from dorsal hump and body characteristics, such as scars. Since 2010, we have encountered sperm whales five times. In addition to our two encounters this year, we have seen sperm whales off Guam and Saipan in 2010 and off Saipan in 2013. After doing some preliminary comparisons with fluke photos taken off Guam and Saipan in 2010 and those we took this year, we found two matches. Both individuals were photographed off Guam 18 February 2010 and during both 2016 sightings (Figure 3). One of the individuals is missing its left fluke. We collected a small tissue (or biopsy) sample from it, as well as five other individuals during our 2016 encounters, for future genetic analyses.
During the sperm whale encounter on 17 May 2016, we deployed a satellite tag on an individual, so that we can learn more about sperm whale movements in this area. Between 17 and 23 May it traveled north and south offshore of Saipan and Tinian’s west sides (Figure 4). On 23 May, it was located approximately 37km WNW of Saipan’s NW tip.
In addition to rough-toothed dolphins and sperm whales, we encountered bottlenose dolphins (Tursiops truncatus) and spinner dolphins (Stenella longirostris) off Saipan. Next, we head to Rota to conduct surveys during 21-25 May.
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, captains, and crew of the Sea Hunter and the Regulator; the CNMI DFW, the CNMI NOAA Fisheries field office, and all of our volunteers during the surveys.