Three weeks ago, on Jan. 18, the California Department of Fish and Wildlife opened the commercial Dungeness crab fishery from the Sonoma/Mendocino county line to the U.S./Mexico border. There was a stipulation, however, that the number of traps needed to be reduced by 50% to lower the probability of any whale entanglement.

This decision was achieved through considerable coordination with affected fishers, businesses and environmental organizations and after soliciting input from the California Dungeness Crab Fishing Gear Working Group, which expressed broad support for this management decision.

Whale entanglements are harmful to all parties involved, occasionally causing injury or death to the whale, and almost always causing damage or loss to the fishing equipment. It was an increase in whale entanglements in recent years that led NOAA Fisheries to classify the California Dungeness crab fishery as a category II fishery, defined as one responsible for killing between 1 and 50% of the highest number of animals that can be removed from the population without causing decline.

Dungeness crabs were named after Dungeness, Washington, a small community on the Strait of Juan de Fuca, where they were first harvested commercially. The U.S. commercial Dungeness crab fishery began in San Francisco in 1848, (before Washington became a state) and has been regulated in the state of California since 1895. Washington, Oregon and Washington are all involved in the Dungeness crab fishery.

This is an important fishery and has generated about $57 million on average for each year for past decade, although the numbers can vary widely from year to year. The 2013 catch reached 15,700 tons, worth $81.8 million, but this dropped to just 1,550 tons in 2015 bringing only $17 million. The good news is that despite years of variable catch rates, the West Coast’s population of Dungeness crabs seems to be doing just fine. NOAA scientists reported in 2020 that the number of legal-sized male Dungeness crabs has been stable or increasing in recent decades.

Crabs are commercially caught using cylindrical crab traps or pots. The metal frame of the pot is wrapped in netting with one or more small openings which allow the crabs to crawl inside. They can get in, often to go after some bait, typically a fish carcass, but rarely can they get back out again. Pots are usually dropped to the ocean floor in water depths ranging from about 60 to 300 feet. Each pot is attached to a line with a buoy that floats on the surface. The size and shape of the pots and the length of the attached buoy line are tightly regulated to minimize the trap’s impact on the environment and other wildlife.

In order to reduce the chances of marine mammals entangling the lines attached to the traps, for example, the line between the trap and the surface buoy must be taut. The line to the buoys at the surface must be as short as possible and no longer than 24 feet in water less than 210 feet deep, and no longer than 36 feet in water deeper than 210 feet.

The traps then “soak,” or sit in the water for a period of time ranging from a few hours to a few days, giving the crabs time to enter the trap before the crabbers pull them up. Crabbers are able to soak their traps for up to 64 hours before the season opens, but they can’t pull up their traps until the official start date.

There are also restrictions on what crabbers can keep — only males that don’t have a soft shell (which happens when the crabs molt) and have a shell diameter of at least 6.25 inches. Soft shell crabs, undersized crabs, and female crabs are separated out and thrown back to continue living. There’s no limit to the number of crabs fishers can catch as long as every trap has a $5 buoy tag from the California Department of Fish and Wildlife.

Crabbers, whale conservationists and Department of Fish and Wildlife all want to avoid whale entanglements as much as possible, which is why the opening of the commercial season has often been delayed when there are large numbers of whales along the coast. In order to support the crab fishery and reduce whale entanglements, crabbers and fishers came together in 2015 and created the California Dungeness Crab Fishing Gear Working Group.

One of the group’s primary goals is to come up with innovative crab trap technology that doesn’t require dangling ropes. But the gear must go through a series of tests before it can be authorized for use. And getting the crabbers to adapt or change out their gear for something new presents challenges.

The possible approaches for reducing whale entanglements are of two flavors, those which focus on the fishing gear itself, and those that involve the timing, area and size or scale of fishing.

Considerable attention and creativity has been focused recently on ways to modify the system of crab pots, lines and floats in order to achieve the objective of fewer entanglements. There are a handful of these which include:

• A high-tech approach where there are no buoys at the surface but an acoustic signal from a fishing boat releases a buoy that then surfaces with a rope attached to the seafloor trap which can then be pulled up. These are still being tested and show promise but are expensive, have problems with release failures and involve time-consuming trap resetting. Anything that spends significant time in seawater and has moving parts is going to have issues over time.

• Galvanic-timed releases where lines are submerged for set period of time until pots are ready to be recovered. These are inexpensive and can keep lines out of the water column for an extended period of time.

• Removing half of the top of trap which allows crabs to crawl out so fishers are incentivized to stay with their traps rather than leaving them with their ropes and buoys in the water for extended periods of time.

• Using rope with a lower breaking strength or weak links in the lines so that a whale impact creates a certain strain, the line breaks and the whale isn’t entangled.

• Experiments with either colored line or emitting acoustic signals that whales might avoid haven’t proven effective.

Christopher Free, a researcher at UC Santa Barbara has recently reported on running computer models that indicate simpler strategies such as reducing the number of traps and basically gear reduction, would be more effective way of reducing entanglement, with a 30% reduction in trap numbers as the optimal course of action. They agree that rope-less gear would be the silver bullet solution to this problem; if there are no ropes, then whales can’t get tangled. As described earlier, this technology does exist, but it presents significant challenges, important ones being high costs, failure of release mechanism and more time spent locating and recovering the traps.

Free has several explanations for these findings. Reducing the amount of gear directly addresses the problem: the number of lines in the water for whales to get entangled in. Dynamic closures merely move these lines around, so a regional closure might just move traps into an area that’s actually riskier for whales. There can also be a long delay between when a whale gets entangled and when it’s spotted. The animal could have dragged the gear for several weeks and hundreds of miles, meaning nobody can be sure where and when the whale got ensnared.

Static strategies are cheap and predictable and don’t rely on surveys or monitoring efforts which can be inconsistent, irregular and expensive. They require no costly equipment, and don’t introduce any uncertainty into the fishing season or fishing grounds. The Dungeness crab fishery is characterized by intense fishing effort early on. The abundance of crabs means that fishermen can still make good catches in those early weeks even with fewer traps. Indeed, most of the catch is landed early in the season.

Gary Griggs is a Distinguished Professor of Earth and Planetary Sciences at UC Santa Cruz. He can be reached at griggs@ucsc.edu. For past Ocean Backyard columns, visit https://seymourcenter.ucsc.edu/ouroceanbackyard.