Four-Month Survey Tracking West Coast Marine Mammals Finds Some Shifting North

NOAA Fisheries scientists have completed a 4-month, roughly 4,500-nautical-mile, survey of marine mammals and seabirds off the U.S. West Coast. They collected a trove of some of the most thorough data and biological samples ever on West Coast whales, dolphins, and other marine mammals.

Researchers also saw immense schools of dolphins, an unusual number of sei whales, and rare seabirds. Scientists said several marine mammal species appear to have shifted north along the coast compared to earlier surveys. That change may reflect their response to marine heatwaves and other ecosystem changes that have become common off the West Coast in the last decade.

"We're definitely seeing things farther north," said Jeff Moore, chief scientist of the marine mammal survey led by NOAA Fisheries' Southwest Fisheries Science Center. He said the survey spotted striped dolphins off the Oregon and Washington coasts, beyond their more typical range in California's warmer waters. The species may be following their preferred water temperatures and prey.

Details from the survey help inform marine mammal stock assessments required by the Marine Mammal Protection Act and decisions on fishing seasons and areas. We also use the data collected by surveys to help assess the risk fisheries and other activities may pose to the protected species. Expanding the number and types of platforms these observations are taken from will ultimately lead to greater efficiencies in how we conduct these surveys.

Revisiting Transects

The survey recorded more than 1,354 groups of cetaceans (dolphins, whales, and porpoises) representing at least 24 species off the West Coast. It also recorded more than 30,000 birds from 91 species. The abundance and diversity of species reflect the high productivity of the California Current Ecosystem fed by the wind-driven upwelling of nutrients from the deep ocean along the coast.

The number and diversity of cetaceans follow the continuing rebound of many species from near-extinction in the whaling era. Humpback, blue, and fin whale populations have been trending upwards in recent decades. These species are reclaiming their prominence as some of the largest predators in the marine food web.

The Science Center conducts a marine mammal survey roughly every 5 years; the last survey occurred 6 years ago in 2018. For this most recent survey, NOAA Fisheries contracted with the research ship R/V Bold Horizon. It follows patterns known as transects off the West Coast to detect trends in the number and distribution of species compared to prior surveys.

"That long-term record makes the results much more powerful because we get a high-resolution snapshot of what is happening now; at the same time, we can see how things are changing," Moore said. The survey also took advantage of new technologies to collect even more data, such as:

• Autonomous underwater gliders
• Drifting acoustic recorders
• Uncrewed aerial systems or "drones"
• Environmental DNA sampling

Aerial Perspective

The last leg of the survey included the first authorization within NOAA Fisheries to fly a drone beyond sight of the pilot from a research vessel. This allowed the documentation of cetacean groups up to 2 miles from the ship. "In addition to capturing spectacular images and video of cetaceans and other marine wildlife, this effort provided verified information on the size and composition of marine mammal groups to help calibrate group size estimates made by the visual observer team," said Trevor Joyce, lead investigator and pilot.

Frames extracted from aerial videos helped measure the body condition and health status of large whales including blue, fin, Sei, and sperm whales. Additionally, the drone helped the research vessel track whales while underwater between surfacings. This improved the success rate for collecting skin and blubber samples used in genomics and tissue culture.

Ears in the Water

While a visual team surveyed marine mammals during daylight hours, drifting recorders listened for marine mammals passing by around the clock. Scientists deployed 27 drifting acoustic recorders in the California Current over the course of the survey. The recorders are suspended 100 meters below a surface buoy that relays its location by GPS.

The 27 buoys traveled nearly 2,000 nautical miles, exceeding the length of the entire West Coast. They recorded marine mammal calls, echolocation, and other underwater sounds. The passive acoustic method helps estimate the density of deep-diving beaked whales the survey might otherwise miss because they remain underwater for long periods, surfacing only rarely.

"These animals are often shy and don't spend much time at the surface," said Cory Hom-Weaver, who led the acoustic research during the survey. "But as they are diving and foraging, they use sound to echolocate, which makes passive acoustics a perfect platform for understanding their ecology."

eDNA Reveals Species Diversity

Scientists also collected 139 water samples for environmental DNA, which is the genetic traces of different species swimming through offshore waters. eDNA offers an increasingly powerful method of assessing the range of species in different waters at different times.

"Several of these samples were taken in the absence of a visual sighting of a marine mammal to see if the samples could help us characterize the diversity of whales and dolphins in the California Current even if we couldn't actually see the animals," said Brittany Hancock-Hanser, who co-led the eDNA research during the survey.

Scientists can also go back to archived water samples later to answer future questions about as-yet-undiscovered species that may be represented in the eDNA evidence.

The science team will now return to the lab to process their extensive sighting and other data to pin down numbers, trends, and distributions of species across the California Current Ecosystem. "We have a lot of work to do to fully understand everything this data has to tell us and that is what we will be focused on in the coming months," Moore said.

The survey is funded by NOAA Fisheries with support from the Inflation Reduction Act and in partnership with the Bureau of Ocean Energy Management. This critical work supports our science-based mission to gather data that informs decision-making as marine resources adapt to rapidly changing oceans.

Public link

Please use the above public link if you want to share this noodl on another website.