By Marc Donadieu
Because Cook Inlet beluga whales are an endangered species that is genetically distinct with a geographically isolated population, researchers have been actively studying its environment, feeding patterns and behavior patterns. Researchers are looking for clues to determine why the Cook Inlet beluga population continues to decline and if this detrimental trend can be reversed.
Cook Inlet belugas were listed as an endangered species in 2008 due to the effects of subsistence hunting in previous decades. According to the National Marine Fisheries Service (NMFS) webpage on beluga whales, “Subsistence harvest is the only factor that can be identified as influencing the decline of the Cook Inlet population from 1994-1998, when 67 whales per year were harvested, prompting the ‘depleted’ designation under the MMPA [Marine Mammal Protection Act]; the lack of recovery of the population was a factor that contributed to the endangered listing.”
The beluga whale subsistence hunt ceased in 2004 after population levels became perilously low. Since then, population numbers have continued to plummet. The results of the June 2014 Abundance Survey, which is conducted every other year, is due by February 2015 after all of the aerial video footage is reviewed. The survey will provide valuable data about the current number of Cook Inlet belugas and whether they show signs of recovery or not. The current number of belugas based on a 2012 count is estimated to be 312. The population is believed to have been as high as 1,300 whales.
Because researchers are not currently allowed to work with live Cook Inlet belugas to take samples and measurements, researchers must rely on bone, teeth, tissue and organ samples obtained from belugas that died from being stranded or died from other reasons. Taking samples from a dead beluga and conducting a variety of tests yields valuable information.
Biologist Lori Quakenbush and wildlife technician Mark Nelson, both with the Alaska Department of Fish and Game in Fairbanks, have been conducting research by analyzing past and current feeding data. Each researcher has taken a different scientific approach to obtain data about what beluga whales are eating and what they ate in the past.
The current results from their ongoing research will be published in the spring in the biannual Marine Fishery Review, which will be a special issue dedicated to beluga whale research. The review is published by the NMFS, which is part of the National Oceanic and Atmospheric Administration.
Quakenbush’s research involves examining stomachs taken from dead belugas that have washed up or that have died while stranded.
“We’ve been collecting diet information from stomach contents from all five stocks of belugas that occur in Alaska,” said Quakenbush. “It’s been a question about data from other studies back to as early as the 1950s to current stomachs that have been collected.”
Once the beluga stomach has been obtained onsite, it is shipped to a lab in Fairbanks. “We get them in coolers, sometimes fish boxes,” Quakenbush said. “They basically put the stomach in a couple of plastic bags and they tie it up, freeze it, and ship it. We receive the stomach, sort through it, rinse things out, pull out hard parts, and identify them at the lowest taxonomic level we can. Belugas eat invertebrates and vertebrates, so we’ve got lots of species to look out for with prey items.”
The process for inspecting stomach contents involves a number of steps depending on the stomach’s condition and what is found in it. After thawing, the goal is to preserve and identify whatever is found by placing the contents in a sieve with water running through.
Quakenbush is looking for otoliths (ear bones) to identify the fish species it came from. If the fish are whole, they are weighed and measured. Worn fish parts are hard to identify, and parts of invertebrates can be challenging to identify definitively.
An adult beluga’s stomach can be rather large, especially if it is engorged with fish. “We had one stomach that was filled with 12 coho salmon,” Quakenbush said. “It weighed 27.8 kilograms, which is 61 pounds. Those silver salmon were not little salmon. Belugas swallow their prey whole. They do not chew anything. If it’s a big salmon, they’re swallowing a big salmon whole. They swallow them head first, and they line up in the stomach. It looks like you opened a can of sardines.”
The study of beluga stomach contents has given researchers a better understanding of its eating habits. Quakenbush said, “Knowing what animals eat when is a really important part of understanding why they’re where they are and where they go and what is important for them, and what parts of Alaska they are in at different times of the year.”
A beluga whale’s diet contains quite a variety that is partly determined by the seasonal migration of fish species. Cook Inlet belugas are known to eat four out of five species of Alaska salmon. Red salmon haven’t been found in stomachs, but there is no reason to believe belugas don’t eat them.
Other species on the beluga menu include Pacific cod, walleyed pollock, eulachon (hooligan), yellowfin sole, starry flounder, the occasional anadromous Dolly Varden, and a freshwater long nosed sucker was found once. As far as invertebrates go, belugas eat shrimp, polychaetes (marine worms) and arthropods, which are variety sea creatures with an exoskeleton, body segments and jointed limbs.
One of the real mysteries of beluga eating habits that researchers are attempting to uncover is its winter eating habits.
“We don’t know much about what they eat in the winter,” Quakenbush said. “That’s certainly a data gap we would like to know more about. For some of these belugas in places like Bristol Bay and maybe Cook Inlet, they may not need to feed much in the winter. They can bulk up on salmon all summer long. The bigger animals can actually be fine without eating much in the winter. Maybe some of the smaller animals, the sub-adults or the ones that are no longer nursing, about to wean and go on their own, they have to eat more in the winter. Those are things we would like to know more about.”
The challenges of Alaska winters, like ice in Cook Inlet, make it difficult for researchers to obtain data.
“It’s a tough time of year to get any information,” Quakenbush said. “Animals aren’t seen when they’re stranded or we can’t get to them. It’s the ice or other things. We have very few samples from belugas in winter. I think the ice has a lot to do with it and day lengths. There are a lot less people out looking.”
“The animals are farther away from shore in winter,” Quakenbush said. “Cook Inlet belugas, from radio telemetry, are out more in the middle of Cook Inlet and not as much up in the arms. It’s hard to see belugas if you’ve got chunks of ice floating. They look similar.”
Quakenbush’s colleague, Mark Nelson, is looking at whether the isotopes that come from diet have changed in the belugas over time.
“Certainly there are fewer Cook Inlet belugas than there were in the past, and one of the things you ask when a population isn’t doing well is, ‘Is there enough food?’” said Quakenbush. “We’re trying to understand whether something about the diet changed over the time period that population numbers have changed. He [Nelson] has found the change on the trophic level [food chain].”
The next article will explain how Mark Nelson used stable isotope analysis to examine a change in the beluga whale’s diet by examining their skulls and teeth with samples from as early as the 1960s to the present.