Marianas Cetacean Surveys 2013: Guam Summary (June 22-July 1)

by Marie Hill, Allan Ligon, Adam Ü, and Mark Deakos

This is our fourth year conducting cetacean surveys aboard small boats (7.6 – 12.2 m) around the southern Mariana Islands of Guam, Rota, Saipan, Tinian, and Aguijan (Figure 1).  We are continuing to collect individual photo-identifications, biopsy samples, and acoustic recordings (when possible) of the cetacean species that we encounter.  We have also added another element of satellite tagging to the project.  We are using Wildlife Computers SPOT5 location-only satellite tags.  The data that we collect is being used to reveal the occurrence and distribution, stock structure, movements, and vocal characteristics of cetaceans within the study area.

Figure 1: The Commonwealth of the Northern Mariana Islands Exclusive Economic Zone (CNMI EEZ; outer grey line within the red box) and the survey area within the southern Mariana Islands.

This year off of Guam, we conducted 10 days of surveys using two different vessels (5 surveys aboard each).  The first was a 9.4 m Bertram Sport Fisherman with flying bridge and twin diesel inboard engines (Lucky Strike) and the other was a 7.6 m Pro-Line with a 4‐stroke outboard engine (Pro-Line 25).  During the 10 days of effort we covered 1087 km of trackline (Figure 2).  Our surveys were primarily focused on the west side of the island because of predominant winds from the east.

Figure 2: Guam survey tracklines (22 June – 01 July, 2013). Lucky Strike departed from Hagåtña Boat Basin and the Pro-Line 25 departed from Apra Harbor.

We have had an exciting start to this year’s surveys.  Not only have we added false killer whales (Pseudorca crassidens) (Figure 3) as a new species to our list of encounters, but we have successfully deployed three satellite tags on short-finned pilot whales (Globicephala macrorhynchus) from three separate groups.

Figure 3: False killer whale (Pseudorca crassidens) encountered off the west side of Guam approximately 8 km from shore (photo credit: Adam Ü, collected under NMFS permit 15240).

Two of the groups of short-finned pilot whales had individuals that we have photographed in previous years and are a part of our photo-identification catalog.  We currently have 129 individuals in our catalog.  The first whale that we tagged (PTT 128884) was a member of a group of approximately 30 individuals including a male who has the most distinctive fin of all (Figure 4).  We have seen this male and some of his other group members off Rota in September 2011 and off Guam in May 2012.  The tagged individual was also photographed off Rota in 2011.

Figure 4: Male pilot whale within our photo-identification catalog seen three years in a row (MIGm-000057; “Chop-Top”) (photo credit: Erik Norris and Marie Hill, collected under NMFS permit 14097 in 2011 and 15240 in 2012).

The second tagged individual (PTT 128885) (Figure 5) was in a group of four.  They were approximately 1.2 km from the first group and were traveling slowly in the same direction.  Their dive behavior was very different from the others though.  They were making longer duration dives (18-20 min) while the first group dove for approximately 5-8 min at a time.  All four individuals were photographed off of Tinian in September 2011 and one was photographed by another research group in March 2012 off of Guam.  During these encounters with the short-finned pilot whales, a small group of bottlenose dolphins (approximately 8-10) were close by and between the groups and traveling in the same direction.  Three individuals approached the boat to bow ride.  Two of these individuals were photographed last year (one off of Guam and the other off of Saipan).

Figure 5: Short-finned pilot whale satellite tagged (PTT 128885) off of Guam on June 30, 2013 (photo credit: Marie Hill, collected under NMFS permit 15240).

A third short-finned pilot whale was satellite tagged on July 1 and was a member of a group of 17 individuals that have not been photographed by us before.  None of the most obviously marked individuals could be found within our existing catalog.  Although all three tagged animals were encountered in close proximity in both time and space (a maximum of one day and 20 km), they moved to very different locations in the few days after they were tagged (Figure 6).

Figure 6: Tracklines of satellite tagged short-finned pilot whales (128884, 128885, 128886) showing the most recently recorded transmission locations (July 3, 2013 @ 02:07 GMT).

In addition to false killer whales and short-finned pilot whales we encountered spinner dolphins (Stenella longirostris), pantropical spotted dolphins (Stenella attenuata), bottlenose dolphins (Tursiops truncatus), and pygmy killer whales (Feresa attenuata) (Figure 7).  The pygmy killer whales (Figure 8) were another exciting encounter because we have only seen them here once before and this was the first time that we have been able to approach them for photos and biopsy sampling.  Across all encounters we collected just under 5400 photos and 21 biopsy samples.  Our next stop is Rota.  We are excited and hope for continued success!

Figure 7: Locations of cetacean sightings around Guam (n = 11). Fa-Feresa attenuata (pygmy killer whales), Gm-Globicephala macrorhynchus (short-finned pilot whale), Pc- Pseudorca crassidens (false killer whale), Sa-Stenella attenuata (pantropical spotted dolphin), Sl-Stenella longirostris (spinner dolphin), Tt-Tursiops truncatus (bottlenose dolphin).

Figure 8: Pygmy killer whales (Feresa attenuata) off of Guam (photo credit: Adam Ü, collected under NMFS permit 15240).