US Navy


Marine Species Monitoring

Small vessel visual surveys in the Mariana Islands Range Complex

Introduction & Objectives

The Pacific Islands Fisheries Science Center (PIFSC) Cetacean Research Program (CRP) has conducted research on cetaceans in the Mariana Archipelago since 2010 in cooperation with U.S. Navy Pacific Feet. The effort included summer and winter small-boat surveys off the southernmost islands (Saipan, Tinian, Aguijan, Rota, and Guam), development of photo-identification catalogs, and analysis of collected tissue samples and satellite telemetry tag data. Beginning in 2015, winter surveys were conducted specifically targeting humpback whales.  The goal of these efforts is to collect the data necessary to conduct population assessments for cetaceans within the Mariana Archipelago, including the determination of their occurrence, population structure and abundance, movements, distribution, and habitat use. In addition, these data may be used to evaluate the potential exposure of cetaceans to human-caused stressors within the waters surrounding the Mariana Archipelago including U.S. Navy operations (e.g., sonar, use of explosives), fisheries interactions, and dolphin tourism.

Technical Approach

PIFSC CRP conducted non-systematic visual surveys for cetaceans in the waters off the southernmost islands of the Mariana Archipelago (Saipan, Tinian, Aguijan, Rota, and Guam) aboard small vessels during 2010–February 2018.  All cetacean groups encountered were approached for species confirmation, group size estimates, photo-identification, biopsy sampling/sloughed skin collection, and acoustic recording when possible. In 2013, LIMPET configuration satellite tagging was implemented to investigate movements and spatial use of individuals of some species. Additional data collected during each sighting included the location (latitude/longitude), behavior, and estimates of calf (neonates and young of the year) numbers. Survey conditions (e.g., Beaufort sea state, swell height) and effort status were recorded regularly as conditions changed. A handheld Global Positioning System (GPS) automatically recorded the vessel’s track at 1-minute intervals.

In 2015, PIFSC CRP began conducting small-boat surveys targeting humpback whales off Saipan in February–March when the whales were expected to be present based known presence from December–April. The field procedures were the same as described above; however shallow water (≤ 200 m) areas were targeted based on known humpback whale habitat preferences in other wintering areas.

Progress & Results

Across all summer and winter small vessel survey efforts, PIFSC CRP conducted 245 days of non-systematic surveys for cetaceans off the southernmost islands of the Mariana Archipelago (Saipan, Tinian, Aguijan, Rota, and Guam) between 2010 and February 2018 and completed 22,488 km of on-effort trackline. There were 330 groups (excluding within-day re-sights) identified to 14 species including (in order of frequency of occurrence) spinner dolphin (Stenella longirostris), pantropical spotted dolphin (Stenella attenuata), bottlenose dolphin (Tursiops truncatus), short-finned pilot whale (Globicephala macrorhynchus), rough-toothed dolphin (Steno bredanensis), false killer whale (Pseudorca crassidens), sperm whale (Physeter macrocephalus), dwarf sperm whale (Kogia sima), pygmy killer whale (Feresa attenuata), Bryde's whale (Balaenoptera edeni), melon-headed whale (Peponocephala electra), Blainville's beaked whale (Mesoplodon densirostris), and Cuvier's beaked whale (Ziphius cavirostris). A total of 122,871 photos and 402 biopsy samples were collected, 39 satellite tags were successfully deployed, and 9 single-species acoustic recordings were made. The cumulative number of species discovered during PIFSC small-boat surveys steadily increased before leveling out after a survey distance of 17,206 km.

Humpback whales were encountered in February–March 2015–2018 when targeted surveys were conducted off Saipan.  During these 31 days of survey, there were 39 encounters with humpback whales.  These resulted in the creation of a photo-identification catalog with 43 non-calf humpback whales.  Comparison of the photo-id catalog against catalogs from collaborators in other regions and genetic analysis of biopsy samples determined that humpback whales present in the Mariana Islands belong to the Western North Pacific distinct population segment. 



Found: a missing breeding ground for endangered western North Pacific humpback whales in the Mariana Archipelago

Short‐finned pilot whales (Globicephala macrorhynchus) of the Mariana Archipelago: Individual affiliations, movements, and spatial use

Clicks of dwarf sperm whales (Kogia sima)