by Marie Hill, Andrea Bendlin, Adam Ü, and Allan Ligon
After two stormy weeks off Guam, we decided to go to Rota for a week to see what we might find there. In the past, we have had good luck with sightings off Rota so our expectations were high. We are happy to report that Rota not only lived up to, but exceeded our expectations this year!
Our first day off of Rota we encountered Blainville’s beaked whales (Mesoplodon densirostris) and a Bryde’s whale (Balaenoptera edeni) and collected biopsy samples during each encounter. We have seen Blainville’s beaked whales off of Rota before but this was the first time that we collected a tissue sample. Last year we encountered a single adult male. This year’s sighting included a different adult male and three to four sub-adult/female individuals.
The Bryde’s whale was another first for us. We have known that they occur in the Mariana Archipelago from acoustic recordings on our Tinian HARP (High-frequency Acoustic Recording Package) and from shipboard surveys conducted in 2007 and this June, but we haven’t seen them during our small boat surveys that we have been conducting since 2010. Two days after our first Bryde’s whale encounter we had another with a different individual and collected a second biopsy sample. We then had a third encounter on Rota Bank as we transited down to Guam from Rota on September 3, 2015.
While working off Rota we also had multiple bottlenose dolphin (Tursiops truncatus) encounters. During two encounters we had a number of individuals that we know from our photo-identification catalog. We were particularly excited to see one individual that we named “Changey” and have been tracking since 2012. The name was given because this individual acquired an obvious new mark on its fin between 2012 and 2013 and was the first individual to do so in our bottlenose dolphin catalog. “Changey” was first photographed by HDR off Saipan in March 2012. In 2013, we photographed “Changey” off Guam on June 30 and then off Rota on July 9 and 10. We didn’t see “Changey” last year so it was great to see him/her two days in a row this year on September 1 and 2. We haven’t collected a biopsy sample from “Changey”, so his/her gender is undetermined.
During the bottlenose dolphin encounter on September 2 we deployed a satellite tag on an individual that is also in our photo-identification catalog. Our only other encounter with this individual was off of Saipan on July 17, 2013 during which we collected a biopsy sample. We therefore know that this is a male.
The satellite tag is a Wildlife Computers SPLASH10 and will collect information on the location, as well as the diving statistics of this bottlenose dolphin. Since we deployed the tag he has made two round-trips between Rota and Guam and was off Rota Bank on Monday September 07, 2015. So far, his maximum dive depth has been 625 m.
One really interesting thing about bottlenose dolphins in the Marianas is that most of the individuals from which we have collected biopsy samples have some Fraser’s dolphin (Lagenodelphis hosei) genetic material. We have collected another eleven biopsy samples from bottlenose dolphins to investigate this further. Nine of the samples came from an encounter with individuals that we have not seen before. It will be exciting to see how they fit in to the Mariana bottlenose dolphin population.
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.