humpback whale


By Sean Nealon, OSU news editor

NEWPORT, Ore. – New research partly funded by Oregon Sea Grant is beginning to unravel the times of year and locations where whales are at greatest danger of getting entangled in crab gear on the Oregon coast.

“We’ve been able to geographically locate some areas where the risk of entanglement for whales is higher,” said Solene Derville, a postdoctoral fellow at Oregon State University’s Marine Mammal Institute. “We’ve also discovered that risk varies with time. It’s a very dynamic thing. And it varies with responses to ocean conditions.”

The research, which was published in the journal Biological Conservation and conducted in collaboration with the Oregon Department of Fish and Wildlife (ODFW), is important because it provides better tools to manage fisheries, the researchers said.

The study focused on the Dungeness crab fishery, the most economically important in Oregon. Commercial Dungeness crab pot gear is one of the most frequently identified gear types involved in entanglements along the West Coast of the United States, according to the National Oceanic and Atmospheric Administration (NOAA).

Researchers looked at rorqual whales, which include humpback, fin and blue whales, along the entire Oregon coast. Humpback whales are most frequently reported as entangled with Dungeness crab gear on the West Coast. To a lesser extent, endangered blue and fin whales are also at risk of entanglement, although neither species have been confirmed entangled in any Oregon fishing gear, the researchers note.

The scientists drew on past work that estimated rorqual whale density, including via monthly helicopter flights along the coastline. That work was conducted by the lab of Leigh Torres, who is an author of the new paper and a marine mammals specialist with Oregon Sea Grant and the OSU Extension Service.

In the new study, Torres and other researchers predicted monthly whale densities in Oregon based on variation in ocean and climate conditions for 2011-20. The team then overlaid these maps with data on Dungeness crab fishing locations to determine where and when whales were most at risk of entanglement with crab gear.

Among their findings:

  • Entanglement exposure was higher on average in nearshore waters (less than about 240 feet deep) off Astoria, off Garibaldi, north of Newport, north of Charleston, north of Port Orford and at the southern border of Oregon waters.
  • Exposure peaked in April, when whales were predicted to occur in greater numbers and closer to shore due to the onset of the upwelling season. Upwelling is the process where deeper, cooler water is pushed toward the surface where it encounters light to support productivity and aggregations of krill that whales feed on.
  • Exposure remained constant until the end of the crab season in nearshore waters and decreased past these depths.
  • Exposure was lower during the marine heatwave from 2014-16 when fishing was more active near shore and whales were predicted to be less abundant.
  • Exposure was higher before (2011-13) and after (2017-20) the heatwave, which corresponds with stronger upwelling periods.

Fluctuations in climate and ocean conditions, such as the upwelling events and marine heat waves, appear to be the main drivers of entanglement risk to whales in Dungeness crab fishing gear, the researchers concluded. When this information is combined with time of year and location data, the researchers believe that their findings can help fishery managers make decisions.

“Although there can be inherent tension between commercial fishing and whale entanglements, no one wants to catch a whale, and we all want a thriving, sustainable Dungeness crab fishery,” Torres said. “We feel our findings are an important step toward simultaneously achieving both these goals and relieving any tension.”

“The more knowledge we have about when and where whales are, and how that overlaps with the fishery distribution, the better,” said Troy Buell, a state fishery management program leader for ODFW and an author of the paper. “It helps us design more targeted management measures that are most effective for the whales, while having the least amount of impact on the fishery.”

In 2020, ODFW adopted regulations for the commercial Dungeness crab fishery to address whale entanglement concerns. Several key provisions of those rules end after the current Dungeness crab season. ODFW will take into account findings from the new paper to evaluate their effectiveness. By fall 2023, it will recommend continuing or adjusting the regulations for future seasons, said Kelly Corbett, ODFW’s commercial crab project leader and an author of the paper.

Entanglement in fishing gear presents a major threat to whales because it can drown individuals; cause long-term injuries that limit their ability to eat, travel and reproduce; and potentially affect their abundance. Entanglement is a pressing concern for whales off the West Coast of the United States, where documented entanglements have risen sharply during the past decade.

During an eight-year period ending in 2021, an average of about 35 entanglements were reported annually in West Coast waters of the United States, according to NOAA data. That is roughly three times more than the average from the previous eight years. Scientists agree that these counts likely represent only a small fraction of the actual number of entanglements since some may never be observed or reported.

Craig Hayslip of the Marine Mammal Institute is also an author of the paper. The research was funded by NOAA, the Oregon Dungeness Crab Commission, the Marine Mammal Institute, ODFW and Oregon Sea Grant.