Beluga Notebook--Beluga By the Numbers, Part Two

Many folks familiar with my volunteer work as a Cook Inlet beluga whale monitor usually ask me two questions: “How many beluga whales do you see?” and “How many beluga whales are there?” 

In a previous blog entry, I addressed the first question.  In this blog entry, I address the second.

The latest stock assessment estimated the abundance of Cook Inlet beluga whales at 328 whales in 2016, down from an estimate of 340 whales just two years earlier.  To place these two numbers into context, the best available historic abundance estimate is 1,293 beluga whales obtained from 1979 surveys.  Within two decades, in 1998, this estimate stood at 347 beluga whales.  While the large reduction was attributed to an unsustainable harvest by Alaska Native hunters in the 1990s, the numbers have not rebounded as expected after the cessation of hunting.  In fact, the decline continues.

While the estimates of abundance in the accompanying figure show year-to-year fluctuatations, the trend is definitely downward. So when asked how many beluga there are in Cook Inlet perhaps the best response is "328 whales, but they continue to decline rather than increase which is why I and others are doing monitoring."  Hopefully, we are not witnessing a gradual countdown to beluga whales' extirpation (local extinction).

Whenever I discuss wildlife abundance estimates, I recall a conversation I had in 1988 with an official from the California Department of Fish and Game's Marine Resources Division.  "It's not like counting cattle on a hillside to get an estimate of herd size.  In the marine enviromnent you have a great deal of uncertainty.  Many different factors contribute to this uncertainty."  We see this with beluga abundance estimates.  How one counts a thing is as important as how many of a thing one counts.  Numbers play the role of indicating whether things are getting better or worse.  They motivate us to stop keeping score and start refereeing.

One of the earliest estimates of beluga whale abundance in Cook Inlet comes from a 1972 University of Alaska, Fairbanks Institute of Marine Science Report R72-23, A Review of the Oceanography and Marine Resources of the Northern Gulf of Alaska, one chapter of which discusses marine mammals. The section reports that "aerial surveys of Cook Inlet ...made in 1963 and 1964, indicated a summer population of 300 to 400 animals." This statement, if not examined critically, could lead to the conclusion that with a point estimate of abundance of 328 whales today, the population has remained relatively stable of 60 years.    The conclusion is erroneous. 

As noted in the National Marine Fisheries Service Cook Inlet Beluga Whale Recovery Plan (December 2016) "aerial surveys in the 1960s, 1970s and early 1980s counted belugas in the Cook Inlet but only a few of these had sufficient coverage to estimate the population size...The survey in 1979 resulted in an estimate of 1,293 whales using a correction factor of 2.7 developed to account for submerged whales ....This is the best available estimate of historical beluga abundance in Cook Inlet, and represents the maximum observed size of this population."

The trend in abundance estimates since 1993 is shown graphically in figure 2, which is from the Marine Mammal Commission 2018 Cook Inlet Beluga Stock Assessment.  At certain points, the number of beluga whales got the stock declared "depleted" under the Marine Mammal Protection Act and "endangered" under the Endangered Species Act.  In the future, the stock may be "downlisted" from "endangered" to "threatened" when the abundance estimate equals or exceeds to 520 individuals.  "Delisting" from "threatened" to "recovered" may occur then the population reaches 780 individuals.  Other criterial will have to be satisified as well.  The number alone will not suffice.

We have a long way to go to acheiving either number.  As a monitor, I make a small contribution to achieving the goal--a topic that will be covered in a future blog entry.