Listening for Whales in the Mariana Islands: The 2018 Cetacean Survey in Pictures

In 2018, NOAA Fisheries' Pacific Islands Fisheries Science Center sailed the Mariana Archipelago Cetacean Survey (MACS) aboard the NOAA Ship Oscar Elton Sette. Its main job was to deploy and recover drifting acoustic recorders, whose recordings let scientists estimate the density and numbers of beaked whales and other cetaceans. Alongside, observers ran visual surveys (counting groups, taking identification photos and biopsy samples, attaching satellite tags) and the ship towed a hydrophone array to hear animals along a systematic survey grid.

The survey's greeting, Håfa adai ("half a day"), means "hello" in Chamorro, the native language of Guam. All photographs were taken under NOAA Fisheries research permits, and the U.S. Navy's Pacific Fleet Environmental Readiness Office helped fund the survey through a long-term marine species research partnership with NOAA in the Marianas.

Two ways to listen

Drifting Acoustic Spar Buoy Recorders (DASBRs) float free for weeks with a recorder, two hydrophones and satellite tracking, recording any whales and dolphins they pass while drifting with the currents, until the team picks them up.

How a Drifting Acoustic Spar Buoy Recorder is built. NOAA Fisheries.

High-frequency Acoustic Recording Packages (HARPs) sit on the seafloor for a year or more. They record a very wide range of frequencies, so every vocal species in the area is heard. Each year the team recovers the HARPs off Saipan and Tinian, collects the recordings and puts them back.

Refurbishing a HARP before it goes back on the seafloor. NOAA Fisheries.

Along the island chain

Farallon de Medinilla. For years military training nearby had kept NOAA's Cetacean Research Program from surveying the waters close to this small island. In 2018 the team was given two days. A small boat circled the whole island and out to a shoal in about an hour, and from the ship further offshore they saw spinner dolphins, spotted dolphins and short-finned pilot whales.

The Oscar Elton Sette off Farallon de Medinilla, seen from the small boat. NOAA Fisheries.

The observer team surveying close inshore. NOAA Fisheries.

Anatahan. Pilot whales were a priority. The program had many identification photos from the southern islands but none from the north, so a group seen midway up the chain, about 23 km (13 nmi) offshore of Anatahan, may help show how the population moves. The team launched the small boat to photograph and sample them.

Short-finned pilot whales off Anatahan. NOAA Fisheries.

Pagan. The acoustics team set a HARP near Pagan Island, where only one had been placed before. It would listen on the bottom for two years, showing which species pass without anyone having to survey there.

Deploying a HARP near Pagan Island. NOAA Fisheries.

Tinian and Saipan. Two more HARPs came up from the seafloor near these islands after more than a year of recording.

Recovering a HARP off Tinian and Saipan. NOAA Fisheries.

Drifting recorders

The team deployed seven drifting recorders along the west side of the archipelago. The first one recovered had recorded 12 days of sound while drifting from Guam to the West Mariana Ridge.

Deploying a drifting recorder. NOAA Fisheries.

The first drifting recorder recovered on the survey. NOAA Fisheries.

A towed array of hydrophones, 300 meters behind the ship, listened in real time and gave bearings to calling animals, guiding the visual team toward them. Towing an oil-filled array at 10 knots is hard on it, so the cable and sensors were watched constantly and repaired as needed.

Tending the towed hydrophone array. NOAA Fisheries.

What they saw

• Bryde's whales (pronounced "broo-dess"), one of the few baleen whales expected in tropical waters in summer. Photos confirmed the species, and sonobuoys recorded their calls. In one encounter three approached the ship, and two were biopsied.
• Striped dolphins, a first for the program, which had surveyed the Marianas since 2010.
• Rough-toothed dolphins, at the southern end of the West Mariana Ridge.
• Melon-headed whales, riding the bow wave. They travel in groups of hundreds, which makes identifying individuals hard, but at least one had been photographed in 2015, about 175 nmi east, near Sarigan Island.

A Bryde’s whale takes a breath. NOAA Fisheries.

Striped dolphins, seen for the first time in the program’s Marianas surveys. NOAA Fisheries.

Rough-toothed dolphins near the West Mariana Ridge. NOAA Fisheries.

Melon-headed whales come to ride the bow wave. NOAA Fisheries.

Life aboard also meant weekly safety drills, abandon-ship among them, and, in the last days, packing and cleaning before the team went home.

Sources

• NOAA Fisheries, "Photo Journal: Whales and Dolphins in the Marianas"; rewritten in hubnx's own words. Photographs: NOAA Fisheries, taken under NMFS research permits.