Gray whales and their calves have declined

A high number of gray whale strandings in recent years, likely related to climate change and malnutrition, has resulted in declines in this population of marine mammals and fewer calves being produced.

In 2019, scientists began to see more stranded gray whales (Eschrichtius robustus) on beaches across the central coast of California. That raised enough concern that the National Oceanic and Atmospheric Administration declared it an Unusual Mortality Event. “That’s an event where there’s an increased number of mortalities of marine mammals that are thought to be from a common cause,” said Aimee Lang, a research biologist with NOAA’s Southwest Fisheries Science Center.

Many of the whales that were stranded were emaciated. Researchers continued to monitor them the following years and noted the numbers of strandings, while still higher than long-term averages, declined in 2020 and 2021. “We hope that translates to the event starting to wrap up,” Lang said.

A similar mortality event in 1999 and 2000 also resulted in declining whale numbers, but they rebounded by 2015 and 2016. “We know this has happened in the past and the population has rebounded,” Lang said. “We’re hopeful that will happen again.”

NOAA has been conducting gray whale surveys since 1967, typically conducting two surveys every five years. After the COVID-19 pandemic delayed the 2020 survey, the agency conducted the survey this past winter to see how the strandings may have been impacting the whale numbers. They plan to adjust the protocol and conduct a third survey this winter.

Because gray whales migrate so close to shore, counting them isn’t too difficult. Lang and her colleagues were stationed at a field site about 10 miles south of Carmel, California, where they watched the whales from shore. Their trailer was set up with protection from the elements as it can get pretty wet and windy. In teams of two, they scanned the study area by eye, using hand-held binoculars to count them. After the counts are completed, scientists use the count data to estimate the abundance of the population, taking into account the number of whales missed by observers during watches as well as the number of whales migrating at night.

In this most recent survey, they found the population has declined about 38%, from about 27,000 gray whales in 2016 to 16,650 this year. The whales also produced a record low number of calves since 1994, at about 217. That’s down from 383 calves last year. Researchers in Mexico, where the whales migrate, noted that some animals were in poor body condition, suggesting that some females may not have been healthy enough to produce calves this year. “There were some signs it was going to be a low calf year,” she said.

Lang points to climate change as a main issue for the stranding events and declines, especially environmental drivers in the Arctic, where the whales feed in the summer. But, she said, it’s hard to tease apart how much is natural variation and how much is anthropogenic causes.

Despite the low numbers, Lang said she is “cautiously optimistic.” “We have seen these types of events before and the population has rebounded,” she said. Part of that is because gray whales eat lots of diverse prey species and are more adaptable than many other whale species. “I’m hopeful pretty soon here we’ll see stabilization of the numbers and an increase,” she said.