#FieldWorkWin: Signing off from Saipan

By Marie Hill, Amanda Bradford, Allan Ligon, and Adam Ü

We recently concluded a series of small-boat surveys for whales and dolphins (aka cetaceans) off Saipan in the Mariana Archipelago. Our primary target species was the endangered western North Pacific humpback whale.  Between February 11-22, we were able to survey on 6 days.  We were not able to survey as much as we would have liked due to rough sea conditions and stormy weather.  Despite this challenge, we had 13 encounters with a total of 25 individual humpback whales (including 2 calves), more than twice the number of individuals we photo-identified in each of our two previous field seasons (2015 and 2016).

Survey tracks (gray lines) and cetacean encounter locations during our small-boat surveys off Saipan (February 11-22, 2017)

We collected biopsy samples from 11 whales (that we will use for genetic analyses) and fluke images from 19 whales (that we will use for comparing to other North Pacific humpback whale photo-identification catalogs).  Most of the whales that we encountered this year are new to us. However, three individuals were seen in previous years and are in our photo-identification catalog.  One is a male that we photographed and biopsy sampled in 2015. Another is a female that we photographed and biopsy sampled last year.  She was with a calf in 2016 but not this year. The third was an individual of unknown sex that was first seen in 2007 during a shipboard survey in the Marianas conducted by the U.S. Navy. We collected a biopsy sample of this whale and will now be able to determine its sex.  This is the second humpback that we have matched to the 2007 survey.

A male humpback whale photographed off the west side of Saipan in 2015 and 2017. Photos: NOAA Fisheries/Marie Hill

One of our humpback whale encounters was particularly interesting because it was with a very active competitive group of five whales.  Breeding humpback whales are known to form competitive groups where males compete with each other for access to females.  One of the whales repeatedly lunged out of the water with his mouth full of water and slapped his “chin” on the surface creating a big splash. He was letting the other males know that he meant business!

A male member of a competitive group of breeding humpback whales displays to other males in the group. Photos: NOAA Fisheries/Amanda Bradford

During our short-finned pilot whale encounter on our first day of surveys, we deployed a satellite tag on an individual that we last reported off the east side of the island of Pagan.  We thought that the tag had come off the animal because we had not received any transmission for a 4 day period. On February 27, we started receiving signals again! The whale was 120 nautical miles southeast of its previous location and appeared to be following the Marianas Trench south.  Over the following week the tagged whale continued to move south going back and forth across the Mariana Trench until the tag stopped transmitting on March 10th.  Preliminary matching to our photo-identification catalog revealed that this group of short-finned pilot whales is new to us.  We have seen some groups of individuals multiple times over the years that regularly use the waters around the southernmost islands of the Mariana Archipelago (Guam, Rota, Saipan, Tinian, and Aguijan), but other groups may only be occasional visitors to these islands.

Track from a satellite tag deployed on a short-finned pilot whale at Marpi Reef (about 10 nautical miles north of Saipan) on February 11, 2017.

All photos taken with research permits (NMFS and CNMI DFW).  Funding was provided by U.S. Navy Commander, U.S. Pacific Fleet and PIFSC.  We would like to thank those individuals and organizations that provided logistical support, including Mike Trianni (PIFSC CNMI); Steve McKagan (PIRO CNMI); the CNMI DFW; Sam Markos, Benigno Sablan, Benigno Sablan Jr., Ymanuel Sablan, Aisha Sablan, and Claire Sablan (owner, captains, and crew of the Sea Hunter); and the Hyatt Regency.