Cetacean surveys of the southern Marianas: Guam (April 22-27, 2014)

By Marie Hill

Although we didn’t encounter the elusive humpback whales, our surveys off Guam proved to be just as interesting as those off Saipan, Tinian, and Aguijan. During our six survey days we covered 408 km of trackline and had six encounters with four different species (Figure 1).

Figure 1:  Survey tracklines (black lines) and locations of cetacean encounters off Guam. Fa- Feresa attenuata (pygmy killer whale); Pe-Peponocephala electra (melon-headed whale); Sa-Stenella attenuata (pantropical spotted dolphin); Sl-Stenella longirostris (spinner dolphin). Inset: location of Guam within the Mariana Archipelago.

Figure 1: Survey tracklines (black lines) and locations of cetacean encounters off Guam. Fa- Feresa attenuata (pygmy killer whale); Pe-Peponocephala electra (melon-headed whale); Sa-Stenella attenuata (pantropical spotted dolphin); Sl-Stenella longirostris (spinner dolphin). Inset: location of Guam within the Mariana Archipelago.

 

We had a slow start off of Guam without any sightings on our first day out. During our second survey day we encountered a group of pantropical spotted dolphins (Stenella attenuata) (Figure 2). Most of the group appeared to be younger individuals that had not yet acquired many spots, which they tend to do with age.

Figure 2: Pantropical spotted dolphins off Guam (photo credit: Jessica Aschettino).

Figure 2: Pantropical spotted dolphins off Guam (photo credit: Jessica Aschettino).

Once again spinner dolphins (Stenella longirostris) were our most frequently encountered species (3 encounters). During a preliminary scan of the photos, we found that some of the same individuals were photographed over multiple days during these surveys and match individuals within our catalog that were photographed in multiple years since 2010 (Figure 3).

Figure 3: Individual spinner dolphin photographed off Guam in 2010 (in Agat Bay) and during this survey (in Hagatna Bay).  This individual was also photographed in 2013 and on April 25, 2014 (photo credit: Jessica Aschettino and Adam Ü).

Figure 3: Individual spinner dolphin photographed off Guam in 2010 (in Agat Bay) and during this survey (in Hagatna Bay). This individual was also photographed in 2013 and on April 25, 2014 (photo credit: Jessica Aschettino and Adam Ü).

To our pleasant surprise we encountered another group of melon-headed whales (Peponocephala electra) on April 24 (Figure 4). We had been closely tracking our tagged individuals from Saipan/Tinian and were hoping to have another encounter with them. One of the tags (128918) stopped transmitting on April 23 after a tag duration of 4 days. On April 24, the tagged whale 128916 was north of Rota and approximately 82 km north of Guam (Figure 5). As of April 30, tag 128916 was still transmitting making the total tag duration 11 days.

After several hours of staying with the Guam group of melon-headed whales and taking photos we determined that these were definitely different individuals from those that we encountered off of Saipan/Tinian. We were unable to deploy another tag because the group was traveling into the swell and wind. We did however collect eight biopsy samples that will be used to compare with the genetics of the previous group.

Figure 4: Melon-headed whales photographed off Guam (photo credit: Marie Hill).

Figure 4: Melon-headed whales photographed off Guam (photo credit: Marie Hill).

 

Figure 5: Satellite tracks of melon-headed whales tagged on April 19, 2014 near Saipan/Tinian. Tag 128916 continued to transmit as of April 30.

Figure 5: Satellite tracks of melon-headed whales tagged on April 19, 2014 near Saipan/Tinian. Tag 128916 continued to transmit as of April 30.

We had another exciting encounter on April 26 with a group of nine pygmy killer whales (Feresa attenuata) including one young of the year. They were difficult to approach and we were not able to deploy any tags or collect any biopsy samples. After examining the photos we discovered that this was the same group of pygmy killer whales we had encountered off Guam in May 2013, approximately 25 km away. Luckily, we had already collected biopsy samples from three of the individuals in 2013. The calf had not been present in the group we encountered last year.

Figure 6: Pygmy killer whales encountered 1.8km northwest of Cocos Island off Guam with a young of the year pictured in the foreground (photo credit: Jessica Aschettino).

Figure 6: Pygmy killer whales encountered 1.8km northwest of Cocos Island off Guam with a young of the year pictured in the foreground (photo credit: Jessica Aschettino).

We had a productive 15 days on the water and leave here with another species added to our list (melon-headed whales). We may have to wait for next year to find humpback whales, but we will be back next month to continue our surveys of the Marianas. We will travel up the island chain aboard the NOAA Research Vessel Oscar Elton Sette and launch a small boat to investigate the waters around the islands north of Saipan (known as GANI by ancestral Chamorro). Stay tuned….

 All survey operations including satellite tagging, photo-id, and biopsy sampling were conducted under NMFS permit 15240 and CNMI Fish and Game License 02868. Funding was provided by the NOAA Fisheries and the U.S. Pacific Fleet. The satellite tag tracks shown are based on raw transmission data and have not been quality checked. The final products may vary from those shown in the figure above.

 

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