by Marie Hill, Allan Ligon, Adam Ü, and Amanda Bradford
The Pacific Islands Fisheries Science Center’s Cetacean Research Program returned to Saipan in the Marianas during February-March 2015 to look for humpback whales (Megaptera novaeangliae). We have known that they occur there during winter/spring months (December-April) from accounts by local fisherman and dive operators, from a sighting at Marpi Reef during a 2007 shipboard survey of the Guam/CNMI EEZ, and from recordings from our passive acoustic devices on the seafloor off Saipan and Tinian. We surveyed in the waters off Saipan, Tinian, and Guam in February 2010 and again in April 2014, but didn’t find any humpbacks.
We didn’t know exactly what to expect this time except for the rough sea conditions that typically occur during winter months in the Marianas. We started out by looking for humpback whale blows from an elevated shore station on the west side of Saipan (Figure 1).
We had heard previous accounts of humpbacks swimming relatively close to shore outside of the lagoon and outer reef off the west side of the island. While we were initially setting up our shore station, we spotted a breaching whale several miles offshore. We knew then that we were in luck, and our timing was right! We found humpbacks every day we went out on the water for a small-boat survey (Figure 2).
It quickly became clear to us that the place to be was on Chalan Kanoa (CK) Reef (a.k.a. Double Reef or 6-Mile Reef) due to its relatively easy access from the harbor and regular whale presence. All but two of our humpback whale sightings were over CK Reef (Figure 3). Unfortunately, we were unable to effectively survey other areas around Saipan/Tinian due to the poor sea conditions.
During the eight days that we were on the water, we saw four mom/calf pairs (Figure 4). We saw two of the four pairs over multiple days and collected biopsy samples from three of the moms.
The presence of moms with small calves suggests that the waters off western Saipan and likely adjacent areas may be a breeding area for humpback whales. Research on humpbacks in the North Pacific has demonstrated that these whales feed during the summer off the coasts of California, Oregon, Washington, Alaska, Canada, and Russia. During the fall and winter, they travel as far as 3,000 miles south to mate and calve in warmer waters. The known North Pacific breeding grounds are off Mexico, the Hawaiian Islands, the southern islands of Japan, and the northern islands of the Philippines. Exactly where our humpbacks came from is a mystery. We hope that genetic analyses from the biopsy samples we collected will help to inform us.
In addition to the mom/calf pairs, we confirmed with photographs that there were four other non-calf individuals on the reef, bringing the total number of documented whales to 12. There may have been more than 12 whales using the area, but because of difficult whale behavior (e.g., long dive times, fast travel) and rough sea conditions, we weren’t able to get close enough to take photos of every whale sighted. Only two individuals showed their flukes (Figure 5), which are used as primary identifiers for individual humpback whales. These individuals could possibly be matched to humpbacks within existing photo-identification catalogs from other parts of the Pacific.
Although humpbacks were our primary focus, we were also hoping to see other cetacean species. Because the sea conditions were so poor (mostly Beaufort sea states 5-6 and 6-8 ft swells), we had little chance of seeing anything except large whales unless other species came to us. We got lucky and had a single bottlenose dolphin (Tursiops truncatus) approach our boat to bow ride for a few minutes while we were following a humpback mom/calf pair. Several days later, we saw a group of six pygmy killer whales (Feresa attenuata) that were swimming around and along with two adult humpback whales that appeared to be socializing. Unfortunately, we were unable to collect any individual catalog-ID photos or biopsy samples from either the bottlenose dolphin or pygmy killer whales because of the conditions and our focus on the humpbacks. However, we did collect a fourth biopsy sample from one of the humpbacks with the pygmy killer whales.
As if finding humpback whales wasn’t good enough, we were incredibly lucky to see two different juvenile whale sharks (Rhincodon typus) a couple days apart (Figure 6). This was a lifetime first for most of us! The whale shark is the largest living fish and can grow to 40 ft. in length. We found that whale sharks are easier to work with than whales. They were very interested in our vessel and swam closely around it, providing us with the opportunity to record some close-up footage from our pole-mounted video camera. We could have spent hours with them, but remembering that we are whale biologists we had to break away.
This research was conducted under NMFS permit 15240 and CNMI DFW license no. 03086-2015 issued to PIFSC CRP. Funding was provided by PIFSC and U.S. Pacific Fleet. We would like to thank those individuals and organizations that provided us logistical support, including Mike Trianni (PIFSC CNMI), Eric Cruz (PIFSC Guam), Steve McKagan (PIRO CNMI), Erik Norris (PIFSC JIMAR), the CNMI DFW, Sam Markos, Ben Sablan, Fred Guzman, and Aesha Sablan (owner, captains, and crew of the Sea Hunter), and the Hyatt Regency.