Trawl fishermen are faced with a dilemma: how to catch as much of the desired species of fish as possible, while limiting the accidental capture of bycatch, which are limited by government quotas and can be a major headache.
A 2018 article in Fish and Fisheries estimated that around 10% of all fish caught worldwide is bycatch. These accidental captures can have negative effects on marine ecosystems and the productivity of fisheries. With large trawl equipment that captures hundreds of tons of fish a day, reducing this number is a difficult task.
This problem has led researchers, fishermen and industry professionals to develop new trawl technology with the hope of reducing bycatch.
Bycatch in the Bering Sea
In the Bering Sea, the main bycatch issue is Chinook salmon, according to Austin Estabrooks, a natural resource analyst with the At-Sea Processors Association. Trawlers looking for Pollock often end up with a net full of these salmon, whose catch is subject to government quotas.
“We are hard-cap limited on the amount of Chinook salmon we are allowed to capture in any given year,” explained Estabrooks. “So, our new technology primarily regards the exclusion of salmon.”
These limits have become more stringent in recent years, with the 2017 implementation of Amendment 110 to the Fishery Management Plan for Groundfish of the Bering Sea and Aleutian Islands Management Area. The amendment reduces the allowable catch of Chinook salmon in years of low Chinook abundance, and penalties for vessels with consistently higher Chinook salmon bycatch relative to other vessels.
Some of the technology already at play for the reduction of bycatch are salmon lights and excluders.
“All of our boats use underwater LED salmon lights,” Estabrooks explained. “We’ve done a lot of investigation and found that salmon are attracted to light and they’re also a lot stronger swimmers than the pollock.”
Alongside these lights are excluder devices, essentially large escape panels in the nets.
“We put the LED lights around these escape panels and have tried to get the salmon to swim towards the lights,” Estabrooks said. He added that vessels usually hope to keep their catches of salmon to less than five per tow, but often bring in closer to double this number.
“When you’ve got more than 50 tons of pollock flowing into the net per hour it’s very difficult to exclude even five salmon,” he said.
One potential means of getting this number down is the introduction of active selection, which could grant captains greater control over how much bycatch they bring in.
“We’re pretty excited about the active excluder work,” he said. “Because that’s going to be the next big step.”
Enter Dr. Craig Rose, the founder and principal scientist for FishNext Research, who has been working on a design for an active excluder. His interest in this idea was sparked more than a decade ago when he was involved in the early phases of development of passive salmon excluders.
“Someone suggested having a device that was essentially a small trawl within a trawl, that would be triggered to open and close,” said Rose. “That’s not the direction that salmon excluders went at the time, but I held it in the back of my mind as a design concept.”
Years later, Rose submitted an application to work on this sort of project, which was funded by the National Oceanic and Atmospheric Administration’s Bycatch Reduction Engineering Program, in partnership with SIMRAD/Kongsberg, a sustainable fishery technology company.
“My project has been to develop a net modification and the equipment to activate the movement to allow fishermen to choose within seconds whether the catch is going into the net or going out of it,” Rose explained.
It works like this: At the push of a button, a netting panel which covers an escape hatch for fish drops to the bottom of the net and forms a ramp leading fish towards that hatch. SIMRAD designed the ability to control the device, while Rose constructed the device itself.
The development process, however, has been slowed by the COVID-19 pandemic. Due to the effects of COVID-19, Rose had to make arrangements to complete the first testing phases of the project remotely. They hired a person to build a model of the device near a testing flume tank in Newfoundland and had the results relayed back to them.
“The process took a lot longer than it would to do that kind of testing when you’re in person,” said Rose.
The pandemic delayed the process by at least a year, according to Estabrooks.
“We initially wanted to do some testing last fall, but we had some pretty strict COVID protocols,” Estabrooks explained. “Companies are still a little bit wary of having anyone on board.”
To develop the new technology, Rose tried several different options. One of the first ideas was to use a drogue to power the netting panel. The concept worked, but according to Rose, it was a complicated contraption which fisherman worried would be likely to malfunction. That’s when he decided on the idea of using a hydrodynamic kite, made of a heavy rubber, which, when adjusted, could cause the escape panel to move up and down.
He got the models working in the Newfoundland flume tank in June 2021. Then, toward the end of July, Rose was able to test his device at sea. After a few hiccups and adjustments on its first two tows, the device was able to function as intended.
“On the third tow, everything went right,” said Rose. “It worked.”
Live Cameras and Bycatch Reduction
Key to this effort is the integration of live camera systems into the trawlers, which allow captains to see when they have travelled into waters teeming with bycatch and activate the selection device accordingly.
“One piece of the history of improving fishing has been giving fishermen a better idea of what’s going on at the net,” said Rose. “Video has been a relatively recent addition to that.”
Mike Hillers, the general manager of SIMRAD Fisheries, followed the development of this type of video technology from its early stages.
“There were a whole bunch of different ways that cameras were being put on the nets and they weren’t live cameras,” said Hillers, who was involved with the design of the video aspect of the active selection development. “You would have to retrieve the camera, make sure it was in the right direction and then watch video for a couple hours. Live cameras seemed like the way to go.”
Now live cameras are becoming more and more common, though according to Hillers, the technology is more commonly used on large trawlers than smaller boats. Over the years, SIMRAD also introduced color cameras, which can better identify rare fish.
“It’s not for everyone yet but it’s coming along,” said Hillers of the camera technology. “Hopefully over time we can scale it so the cost comes down and then its available to more people.”
“Almost all of our vessels have a live stream video of salmon entering and escaping the nets,” said Estabrooks, whose fleet mainly includes these large sorts of boats. “It allows the captain to halt if he runs into say a lot of herring or ocean perch and avoid catching large quantities of bycatch.”
Hillers said he expects that the video-enabled active selection technology will be presented at the annual Fish Expo event this November, and that they would have deliverable products by April or May of next year.
“It should be fairly significant,” said Hillers, who added that once the technology was in the hands of ship captains, they would likely find innovative ways to use it.
According to Hillers, one of these uses for the technology might be at the set and retrieval portions of the trawl. Bycatch is frequently captured either at these portions of the trawl, so by opening the escape flap at these positions, ship captains could significantly reduce the problem.
Rope Tube and Funnel
Meanwhile, at Alaska Fisheries Science Center, research fisheries biologist Noelle Yochum has been working on a separate new design for exclusion of bycatch: the Rope Tube and Funnel Salmon Excluder.
“Most designs work on the idea that the salmon are flowing back and the salmon would have to become aware of an open area, swim against the flow of the tow and then escape,” Yochum said. “We were thinking about this idea that, when we’re towing at such high speeds, it will be hard for salmon to see this escape area let alone take advantage of it.”
The Rope Tube and Funnel Salmon Excluder design instead features a 360-degree open area to maximize access to escapement. They also worked with a thermodynamics specialist to determine the best method of slowing down water flow in and around escapement areas and experimented with different types of light as a means of luring salmon to the escape.
The technology was tested on a commercial pollock-catcher vessel in 2019 and 2020.
During the 2019 trials (the 2020 data is still being analyzed), the excluder took the desired shape, maintaining an open path to escapement during fishing, turns, and haulback — and salmon escapement rates were high at around 58%.
One potential issue with the Rope Tube and Funnel Salmon Excluder device is pollock escapement.
“That’s a concern because it is a bigger open area,” said Yochum. “You do get loss in other types of excluders but it’s harder to access the escape hatches there.”
With a bigger opening, there is a fear that pollock escapement could be significant.
Yochum recently returned from a research charter aboard a Bering Sea pollock fishing vessel to gather data to further the mechanistic understanding of how excluders work, and to advance the technology and methodology for conducting conservation engineering research.
While the data from the research hasn’t yet been analyzed, Yochum said that anecdotal evidence from the study was encouraging both in terms of salmon escapement and pollock retention.
“The captain didn’t suspect that we were losing very much fish, so that was promising,” said Yochum. “We were catching at similar rates to the boats around us. I thought that was encouraging.”
While she said that there were certainly salmon still being captured, she did see many escape through the excluder device.
Along with testing the device, the team also collected data about a range of factors related to salmon escapement, which, to Yochum, is just as important as the success of her device.
“There’s so much variability, it’s hard for captains to have confidence in [excluders],” said Yochum. “If you can give fishermen more confidence in excluders, they might be more useful.”
She said she hopes that the data collected with give a clearer picture of the efficacy of these devices.
Yochum made sure to stress that the effort had been collaborative.
“The work that I’m doing builds on the work that a lot of fishermen and other researchers have done,” said Yochum. “A lot of great minds have gone into making this project possible.”
Alongside the advances in excluder technology, Estabrooks referenced his hopes to use a satellite system and historical data from Woods Hole Group, an international environmental, scientific and engineering consulting organization headquartered in Falmouth, Massachusetts, to learn where to better deploy trawlers in order to reduce bycatch.
“We just want to correlate those catch events with what the environmental conditions were like and be better able to predict when and where you would encounter salmon or other bycatch,” said Estabrooks. “We want to get from the retroactive to the predictive realm in terms of bycatch.”
Yochum’s team is working on a machine learning artificial intelligence platform for reviewing trawl video footage.
“It’s tedious to go through so much video footage,” said Yochum. “This tool will go through a video and pick out when they suspect there’s a salmon to help expedite the video review.”
Additionally, SIMRAD is working on a new flow sensor, which measures the flow in the mouth of the net rather than in the mesh, which helps captains better rig their equipment. According to Hillers, this technology has been tested on boats in Spain, and will be tested stateside within the coming weeks.
With this forward push in trawl technology, fishermen can hope for increased options to addressing the bycatch problem in the years to come.