Beaked whales: is absence evidence?

There's not much evidence of significant impacts on beaked whales from Navy sonar activity in Hawaii, but does that mean there aren't such impacts?

Not necessarily, according to a new paper.

The beaked whales most commonly implicated are Cuvier’s (Ziphius cavirostris) and Blainville’s (Mesoplodon densirostris) beaked whales. For more information see here. And here.

(Image: A juvenile Blainville's beaked whale off Hawai'i in 2008 with suction-cup attached time-depth recorder. The suction device stayed attached about two hours, providing information about dive depth and other behavior. Credit: Robin Baird .)

Meghan Faerber, of the University of Wales in Great Britain, and Robin Baird, of Cascadia Research Collective in Olympia, Washington, asked the question:

“Does a lack of observed beaked whale strandings in military exercise areas mean no impacts have occurred? A comparison of stranding and detection probabilities in the Canary and main Hawaiian Islands.”

They point out that strandings of beaked whales during naval activity are more common in the Canaries than in Hawai'i. But they caution that it doesn't mean there aren't impacts in the Hawaiian Islands. They cite an old dictum: “The absence of evidence (of an impact) is not evidence of absence.”

There have been 11 documented mass strandings in the Canaries, six of which are associated with Naval exercises.

Meanwhile, “The Hawaiian Islands experience regular naval exercises and contain resident beaked whale populations. Only nine beaked whale strandings have been documented in the Hawaiian Islands through 2007 , and no mass strandings have been reported.”

Since there does seem to be a link between naval sonar and whale strandings elsewhere, the authors are unwilling to assume that there would be no link in the islands. Rather, it's possible, they say, that the impacts are being missed due to unique factors in Hawai'i.

They argue that beaked whale habitat may be farther from shore in the Hawaiian Islands, that reefs and scavenging sharks, as well as current patterns, may prevent injured whales from appearing on the shore in Hawai'i,

Their point: “It cannot be concluded that the lack of mass strandings in Hawai‘i is evidence of no impact.”

Which of course puts the Navy in a difficult position of attempting to address an assertion for which there is little evidence.

© Jan TenBruggencate 2010