Researchers from NOAA Fisheries will soon begin
studying the nighttime behavior of Southern Resident killer whales to better
understand how much time they spend foraging and their use of sound, and to
inform policies that might better protect the whales from vessel noise.
The Southern Resident killer whale population
now numbers 75, its lowest point in close to three decades. NOAA Fisheries is
carrying out an action plan of priority steps to address the three main threats
to the whales: vessel traffic and noise, availability of prey, and chemical
pollution and contaminants.
( See CBB, Aug. 10, 2018, “Agencies Prioritize
West Coast Salmon Stocks For Southern Resident Killer Whale Recovery” http://www.cbbulletin.com/441250.aspx)
Underwater ship noise can disrupt the whales’
use of echolocation, a series of rapid clicks, to detect, track and capture
prey. That limits their foraging opportunities and forces them to expend extra
energy at a time when they can least afford it.
Understanding whether the endangered whales
forage at night, and how they use sound, could help reduce impacts on the
whales. If they forage less at night, for example, that might be a time when
large cargo ships could transit the area with less disturbance.
‘If we can find out when they’re foraging, and
how they are using sound at night, we’ll better understand when protection may
be most important,” said Marla Holt, a research scientist at NOAA Fisheries’
Northwest Fisheries Science Center (NWFSC) and leader of the project.
Fisheries and Oceans Canada is largely funding
the research, with NOAA Fisheries conducting field work and data analysis. This
collaboration is also important to research comparing foraging behavior between
the declining Southern Resident killer whales and the increasing population of
Northern Resident killer whales in British Columbia.
The study will use digital acoustic recording
tags (DTAGs) attached with suction cups to the whales. Scientists will apply
the tags to the whales with long poles. In previous tagging during daytime
hours they typically saw the whales return to normal diving behavior within
minutes. The tags usually remain on the whales for about one or two days until
they fall off on their own.
“This is about as careful as we can be, with
the least impact on the whales, that allows us to get the data that will inform
decisions long-term,” Holt said.
While researchers have extensively studied
Southern Resident behavior during the day, they have limited data on the whales
at night. The DTAGs record sound, and the whales’ movements, which reveal
whether they are actively foraging, and at what times, researchers said.
Shipping traffic through the Salish Sea, the
heart of the whales’ range, has increased in recent years, and is projected to
increase further. Authorities in Canada and the United States are considering
options for managing the shipping traffic to reduce impacts on the killer
whales, which are also protected in Canada.
Killer whale DTAG research at NWFSC