Ongoing research by NOAA’s Northwest Fisheries Science Center continues to look more deeply into the effects of boat noise on Puget Sound orcas. The research team, led by Marla Holt, had previously found that orca calls increase in volume in step with background boat noise: for each decibel of added background noise, their calls also got a decibel louder. In their latest round of research, the team is trying to determine whether the background noise is diminishing their foraging success due to masking (drowning out) some of the critical group communication, and whether calling louder makes the animals use more energy.
A 20% population decline among the Southern Resident orcas during the late 1990’s has been attributed to a combination of fewer salmon, toxins, and vessel noise. According to a recent article on National Geographic.com, Holt, who will present the team’s preliminary findings in October at the Biennial Conference on the Biology of Marine Mammal in Quebec, said that their research indicates killer whale communication is particularly important during hunting. What’s more, previous studies in birds had suggested that the animals consume more oxygen to raise their voices above ambient noise, making their metabolic rates spike and burning up stored energy, Holt said, adding that it’s possible the same phenomenon could be occurring with killer whales, although it’s too early to know for sure.
NOAA’s recovery efforts for the orcas include new regulations that will keep whale-watching vessels 200 yards from orcas, as well as efforts to reduce toxin pollution and to restore salmon runs. Longtime orca researcher Ken Balcomb feels it all comes down to the decline in salmon: “If you deny them the food, [there’s] basically no point in worrying about other factors,” Balcomb said. He calls the whale-watching limits “feel-good thing,” adding that “my observations over 35 years [are] that [whales] don’t really get disturbed by anything, much less vessels.” Holt acknowledges the limits of the new regs, saying that “a lot of people would argue, Why focus on these vessel regulations? But it’s one thing we can do immediately.” It appears to AEI that the question is not really whether the boat noise disturbs the orcas, but whether it may drown out parts of their foraging communication, making it more difficult for them to find and eat the few salmon that do remain available to them. And, given their tenuous situation, if they are forced to use more energy to call during hunting, their overall health is likely to be at least somewhat affected. Moreso, each time that a particular foraging attempt is aborted due to a noise intrusion, a larger bit of the daily energy budget has gone to waste. Time will tell whether the new boat limits actually lower the received sound levels for foraging whales; if so, it’s a step in the right direction.