A new NOAA Fisheries assessment shows that the population of gray whales that migrate along the West Coast of North America has been declining for the past two years. Since its peak in 2015 and 2016, the population has decreased by 38%, and researchers are still looking into the causes.
An accompanying report explains that this year, since counts began in 1994, the population also gave birth to the fewest calves ever.
The population of whales in the eastern North Pacific has fluctuated in the past, but the 38 percent drop from a peak of around 27,000 whales in 2016 to 16,650 this year is comparable.According to scientists at the Southwest Fisheries Science Center, it requires ongoing, careful observation. Gray whale population surveys in the eastern North Pacific are typically carried out over a two-year period. However, from late December to mid-February 2023, NOAA Fisheries will add a third year to this survey to count gray whales that pass along the Central California Coast.
Dr. David Weller, Director of the Marine Mammal and Turtle Division at the science center, stated that “given the continuing decline in numbers since 2016, we need to be closely monitoring the population to help understand what may be driving the trend.” “We want to keep track of the population change because we have seen it over time.”
In 2019, a rise in gray whale strandings prompted NOAA Fisheries to declare a population-wide Unusual Mortality Event, sparking an investigation into the likely causes. Numerous potential contributors have been identified by the ongoing investigation. According to new research that came out earlier this year, these changes include ecological changes in the Arctic that affect the seafloor and the amphipods and other invertebrates that live in and above the sediment and in the water column and that gray whales eat every summer.
According to Dr. Sue Ellen Moore, a University of Washington researcher who is in charge of the UME team analyzing ecological influences, some gray whales may have had difficulty locating food during those changes. She pointed out that because gray whales consume a wide range of prey, there may be a variety of factors influencing how, when, and where they find food.
Some of the roughly 600 dead whales that were discovered between 2019 and 2022 did not appear to be malnourished, though many did. It was evident that some stranded whales had passed away from other causes, such as being struck by ships or being eaten by killer whales. After an initial peak in 2019, the number of strandings began to decline. This suggests that most of the gray whale population decline probably happened in the years right after the UME was declared.
According to Deborah Fauquier, Veterinary Medical Officer in NOAA Fisheries’ Marine Mammal Health and Stranding Response Program, who oversees the UME investigation, “there is no one thing that we can point to that explains all of the strandings.” We are still trying to figure out what all of the factors, which seem to be many, are.
Population Represents Changing Ocean Conditions
The annual visible migration of gray whales along the West Coast is well known. The population has experienced significant fluctuations in the past, including a similar decline of about 40% between the late 1980s and the early 1990s. Later, the population increased to a brand new high. The eastern Pacific Ocean’s gray whales have completely recovered from the era of commercial whaling, and in 1994 they were taken off the endangered species list.
In 1999 and 2000, when the population fell by about 25%, an earlier Unusual Mortality Event was declared due to a similar spike in strandings. It then re-climbed to a peak in 2015 or 2016. Scientists rely on the 2015-2016 estimate even though Table 1 in the report includes a higher estimate for 2014-2015 because that number was less accurate.
The majority of gray whales travel between lagoons in Baja Mexico during the winter, where they feed their young calves, and feeding grounds in the Arctic during the summer. The more than 10,000-mile roundtrip they make every year exposes them to a variety of stressors. Additionally, a small group of gray whales spend the summer feeding near and along the coast of the Pacific Northwest.
According to biologist Dr. Tomo Eguchi, the lead author of the new NOAA Fisheries reports on the whale population abundance and calf production, the population has probably always fluctuated in response to changes in its environment without having any lasting effects. He noted that the population had previously recovered from low counts numerous times. “We have a cautious amount of optimism that it will proceed similarly this time. Monitoring will be done to see if and when they recover. ”
Calves are fewer as well.
Researchers from NOAA Fisheries keep tabs on the population size of gray whales by counting whales traveling south toward Mexico. Every spring, when mothers and calves migrate north from lagoons in Baja California, where some whales give birth, they count the mothers and calves to keep track of calf production. The total number of calves born this year, according to the most recent count that ended in May, was around 217. This figure, which was the lowest since the counts began in 1994, was down from 383 calves the previous year.
The number of calves born each year has changed over time, just like the gray whale population as a whole. Before increasing, low calf counts were observed for stretches of three to four years. In two of the previous three instances of low calf production, population declines and unusual mortality events have coexisted. The conclusion of the report on calf numbers is that this shows that the same things that affect gray whales’ ability to stay alive are probably also things that affect their ability to have babies.
Aerial photos of gray whales in Mexican lagoons revealed declines in many adult whales’ body conditions, highlighting that connection. Scientists say that depending on how old the whales were, this lower body condition may have caused them to reproduce later, have fewer calves, or live less long.
Teams will start the subsequent count in December by aiming binoculars at whales passing through Granite Canyon, just south of Monterey Bay in California, as they migrate south. Dr. Aimee Lang, a coauthor of the new reports, said: “What we hope to see in the next few years is that the abundance stabilizes and then starts to show signs of increase.” “We will keep a close eye on things.”
