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Friday, April 19, 2024

Study by UC Davis scientists highlights overlooked threats to California whales

The study, led by graduate students at UC Davis, looks at gaps in policy geared toward ending human-caused whale mortality


By SONORA SLATER — science@theaggie.org


Whales face a multitude of human-caused threats — from entanglement in crab traps, to marine debris, to increased noise pollution. The Ocean Protection Council plans to mitigate these threats in such a way as to achieve a zero-mortality rate for human-caused whale fatalities along the California coastline in the next 10 years.

In order to assist in realistically achieving this goal, a group of scientists from UC Davis, as part of the Sustainable Oceans project, looked into the main threats currently facing whales and the existing policy targeting some of the sources of whale mortality, according to a recent press release

Their study, published in early April in the journal Marine Policy, found that while some of these threats have been met with relevant policy responses — including through regulation of the crab fishing industry and speed limits on boats in certain areas off the California coast — other factors in whale mortality such as nutritional stress and access to prey should also be considered in policy. 

Helen Killeen, a Ph.D. candidate in ecology at UC Davis and a co-author on the paper, talked about why considering a wider array of factors is important in reaching this goal. 

“If as a state we’re saying we’re going to bring whale mortality down to zero, but we’re only going to do those two things, it’s really important to have an answer to the question, do we think those are the only two things that lead to whale deaths caused by human action?” Killeen said.

Co-leading author Eliza Oldach, a Ph.D. candidate in ecology at UC Davis, said that some of these “fuzzier” causes of mortality, while harder to pin down, are important to consider. 

“While we have policy in place for some of the bigger, more acute, more obvious sources of whale mortality, what’s actually killing whales is an overlapping network of all of these different sources,” Oldach said. 

Priya Shukla, one of the co-authors on the paper and a Ph.D. candidate in ecology at UC Davis, gave an example of acute versus broader stressors. 

“One of the key examples are things like pollutants,” Shukla said. “You can trace where waste is coming from, or with sound, most of that is coming from boats. But then you get things like climate change, which is a lot tougher. […] There’s no specific ship or specific factory that is putting waste in the ocean that is causing these things, [so] it’s a lot more challenging to create policy to target that.” 

Killeen gave another example of overlapping issues: the Dungeness crab fishing industry, and its connection to whale entanglement. 

According to Killeen, when people fish for crab, they drop a big metal cage over the side of their boat and let it sink to the bottom. It is attached to a long rope with a buoy at the top, so that when fishing crew return to collect the cage once it’s full of crabs, they can find it and pull it up. However, while the cages are in the water, the rope stretches through the whole water column. 

“Whales will sometimes swim through [the area] and the ropes will get wrapped around the fins or wrapped around their body cavity,” Kileen said. “If they’re unable to get the rope off of them it can result in really terrible damage to their bodies or even just additional levels of stress that aggravates other problems like preexisting disease or trouble finding food. So it either makes life harder for them, or it results in fatalities.” 

However, according to Killeen, while Dungeness crab fishermen are often pointed to as the problem, in reality the issue is much more nuanced. 

“In 2014 to 2016 there was this warm blob in the ocean,” Killeen said. “The coastal ocean off the coast of California became warmer during that time period, and that impacted the distribution of prey that whales feed on, forcing the whales closer to shore.”

After a surge in entanglements, the state was forced to temporarily shut down the Dungeness crab fishery, at great economic cost to the fishermen.  

In the paper, the authors mention several programs that they believe to be addressing whale mortality in a promising and holistic way — one of which is the Risk Assessment and Mitigation Program (RAMP). 

RAMP, according to Killeen, uses physical data about the state of the ocean to make predictions about how risky it will be for crab fishermen to drop their cages in the water at particular times and places. 

“When the model-predicted risk level gets too high, the state will say, we’re going to shut down the crab fishery in several weeks,” Killeen said. “We think that there are going to be too many whales close to shore, because that’s where the prey is going to be. And they can give [the fishermen] several weeks heads-up, which allows them to more efficiently allocate their effort and resources and saves them money in the long run.” 

Shukla said that their study sees this as one example of a solution that takes interdisciplinary needs into account. 

“If you bring in this panel of people to think about whales and also crabbing and also climate change and also pollution, you’re going to have a lot of head-butting at first because people are going to have different priorities,” Shukla said. “But the idea is that through conversation we can […] create solutions that are beneficial enough that at the end of the day, everybody’s interests are served.” 

This idea of framing research around policy and management solutions at all is somewhat novel, according to Shukla. Typically, academics are trained to use their own observations to drive question-asking. However, the Sustainable Oceans project “puts the policy focus on the front end of the research,” according to their website, which is part of why this study developed in the way it did. 

“The idea often in academic environments is just to advance knowledge, but with this paper, we’re synthesizing knowledge to develop a new idea, and I think that’s actually really key,” Shukla said. “By looking at what policies already exist and just tweaking them a little bit […] we’ll actually be able to make some really dynamic changes. We don’t need to come up with something brand new, we just need to update what we already have.” 


Written by: Sonora Slater — science@theaggie.org  



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