The effects of an unexpected pause for marine soundscapes in Alaska
- by Michelle Fournet, PhD, May 26, 2020
In yet another casualty of the Covid-19 pandemic, Earth Day parades and Science Marches were cancelled this year as people globally were instructed to stay home. In this monumental moment, humans are experiencing an unprecedented change in how they interact with their loved ones, their communities, their professions, and yes, their ecosystems. All of this in an effort to reduce the devastation associated with the spread of a virus for which we have no vaccine, no cure, and are only beginning to understand. Unprecedented doesn’t confer the gravity of the global situation; but in Southeast Alaska the seals don’t know that.
In Alaska’s Inside Passage, harbor seals are gearing up for their early summer breeding season; humpback whales are just starting to migrate into the waterways of their historic foraging grounds; and in Glacier Bay National Park, NPS researcher Chris Gabriele recently heard a soft ‘crunch’ echo through the hydrophone moored underwater outside her office — the sound of a killer whale, eating something. Traditionally, late April marks the arrival of the first cruise ships of the season into Southeast Alaska. For decades, marine mammals have started their own summer seasons under the alternating roar or distant din of marine tourism. This year, however, no cruise ships are scheduled to come into port until at least July, under a mandate released by the Centers for Disease Control and Prevention. This means also no whale watching, no kayak tours, no glacier tours, or no helicopter rides, and no charter fishing. The economic ramifications of the Covid-19 pandemic are dire, and no intentional experiment could justify such massive social consequences, but despite the devastation to humans, the ocean is quieter as a result of our absence.
This protracted pause in ocean noise is certainly the first of its kind, and may represent the first time in decades that seals and whales have been granted unadulterated access to a quiet ocean. Humpback whales in Alaska alter their calling behavior when vessel noise inundates the soundscape by calling louder and calling less. While the implications of these behavior shifts are unknown, it is likely that these adaptations increase humpback whale resilience to noise to some degree. This doesn’t appear to be the case for seals, however.
New research led by Dr. Leanna Matthews and Dr. Susan Parks of Syracuse University in collaboration with CCB indicates that during the early summer breeding season male harbor seals, who rely on sound to attract mates and defend territories, may not be able to compensate for vessel noise. On a breeding ground, Glacier Bay harbor seals weren’t able to call louder than the noise associated with passing cruise ships and tour vessels, and as a result they likely couldn’t be heard by potential mates. The inability to communicate this critical message means that breeding gets harder. Except… not this year.
So, what does it all mean? We don’t know for sure, but we can safely predict that ambient noise levels in Southeast Alaska this year will be lower than they have been in recent decades, and as a result, seals and whales should have an easier time hearing each other. Will this mean more pups will be born? Hard to say, but it’s possible. Will whales have an easier time finding prey? Maybe. The truth is, we don’t know. But you can rest assured knowing that this summer in Southeast Alaska, we’ll be listening.