S2E07: Fishing For the Future with Dr. Walt Golet

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Welcome to the Podcast!

I'm your host, Katie, and today I'm sitting down with a new friend, Dr. Walt Golet from the University of Maine, who leads the Pelagic Fisheries Lab.

I'm thrilled to have Walt on the show, especially because he's tuning in from the Mid-Atlantic tournament. But before we get into that, I want to set the stage for our listeners. We're here to talk about the Close Kin Mark-Recapture Bluefin Initiative, also known as the Genetics for Giants and Juvies project, a collaboration between Walt's lab and Viking Yachts. This initiative aims to get a more accurate assessment of the Atlantic bluefin tuna population.

As many of you know, Atlantic bluefin tuna have been highly regulated for years, which has led to an incredible recovery of the stock—something we all love to see! However, this success has created a new challenge. We're at risk of entering a regulatory spiral because our current stock assessments may not be as accurate as they need to be. We're catching more fish, which can lead to overages and, in turn, a risk of tighter regulations.

Walt and I are going to discuss how we, as fishermen and members of our communities, can help improve these regulations and ensure the longevity of the bluefin tuna fishery.

The Recipe for a Better Stock Assessment

Walt confirmed that my summary was spot on and offered a great analogy: "It's like being asked to create a meal or a dessert. And if you don't have all the proper ingredients, the product on the other end may or may not resemble what you want it to."

Fisheries stock assessments are incredibly complex. Scientists can only do so much with the data they have. If they're missing key "ingredients," the final assessment may not accurately reflect the true abundance or status of the population.

This brings us to the core of the issue. Our current understanding of bluefin tuna populations is based on methods that, while effective, have their limitations. The Close Kin Mark-Recapture technology is a game-changer. It's a relatively new approach for Atlantic bluefin, but it has been successfully used for other species, including Southern bluefin tuna.

"It's new or maybe novel to the Atlantic bluefin, but it has been used in other systems before and it's been used successfully," Walt said.

Counting Fish vs. Counting Trees

Walt drew a powerful comparison to highlight the challenges of marine research. "Counting fish is like counting trees, except they're invisible, they move around, and they eat each other."

The Atlantic Ocean is the second-largest ocean in the world, and bluefin tuna are highly migratory, capable of swimming from the Bay of Biscay to Cape Cod in just 30 to 40 days. Their ability to move all over the ocean makes management a "really, really tough task."

This is where the Close Kin method shines. Unlike traditional stock assessments that provide a biomass estimate (a weight of spawning fish), the Close Kin method can give us an actual physical number of individuals.

Walt explained, "The idea is that it can actually give us a number... and the uncertainty that surrounds your estimate is also reduced."

When this method was applied to Southern bluefin tuna, the results were an eye-opener: "They found that their biomass estimates through close kin was much higher than the standard assessments." In other words, they had more fish than they thought. This kind of discovery has a massive ripple effect, from management decisions and fishing quotas down to the businesses that support coastal communities.

The Complexities of Stock Mixing

Bluefin tuna populations are incredibly complex. While the International Commission for the Conservation of Atlantic Tunas (ICCAT) currently manages two stocks—Eastern and Western—the reality is much more complicated.

"We believe the complexities in the stock dynamics are much greater," Walt said. "There are probably more than two stocks."

The most significant difference between the two stocks is their size. The Eastern Atlantic stock is estimated to be an order of magnitude larger—10 times bigger—than the Western stock.

Beyond the sheer size difference, there's another fascinating discovery: extensive mixing between the two stocks. Tagging data, as well as otolith chemistry and genetics, have shown that bluefin tuna move freely between the East and West.

"The mixing is actually quite extensive. Very extensive, actually," Walt noted. "We are heavily subsidized, at least right now, we are heavily subsidized by the Eastern Atlantic stock."

What this means is that a high percentage of the fish we catch on the Western Atlantic coast—between 50% and 70%—actually have an Eastern origin signature.

"Five out of every 10 or sometimes seven out of every 10 fish that you're landing actually were spawned in the Eastern Atlantic Ocean or in the Med," Walt explained.

This mixing is most common in smaller fish and seems to decline as the fish get larger. This is a huge logistical challenge for management. A fish caught off Maine could have been spawned off Italy, and in a matter of days, it can cross from U.S. waters into a Canadian fishery.

The Importance of Collaboration

To get the most accurate data, Walt's lab relies on a variety of sources: fishery-dependent data from landings, fishery-independent data from pop-up satellite tags, and surveys that track things like age structure, longevity, and stock structure.

"It's a pretty complex group of data that goes into the assessment," Walt said.

This is where the collaboration between scientists and fishermen becomes so important. Walt's lab collects data from the commercial fishery, including heads from giant tuna. While saving a massive, 110-pound head is a "gnarly, stinky" task for a fisherman, it's a vital contribution.

"The industry goes to great lengths for us to keep heads... we're able to collect that," Walt said. "We work very closely with the industry and we give back everything that we extract from those fish for the sole purpose to make sure that we have the best information available for the fishery and long-term conservation."

As Walt pointed out, the reason he has a research lab is because we have a fishery. And the ultimate goal is to balance the long-term conservation of the stock with providing opportunities for anglers to experience the thrill of catching a giant bluefin tuna.

"There is nothing like catching a giant," Walt concluded, and I couldn't agree more.

A Symbiotic Relationship: Fishermen and Scientists

Walt's opening statement, "I wouldn't be here, my lab wouldn't be here if it weren't for the fishermen," perfectly captures the symbiotic relationship between the two groups. It's a two-way street. Fishermen rely on scientists to provide the data that keeps our fisheries healthy and sustainable, while scientists depend on fishermen to collect the crucial data that fuels their research. This is the core of the Close Kin Mark-Recapture Initiative, a groundbreaking project pushed by Viking Yachts and Walt's lab.

Unlocking a New World of Data from Live Fish

For years, quality data on bluefin tuna has primarily come from dead fish. Obtaining essential information like age, sex, and stock origin meant sacrificing the animal to retrieve samples like ear bones (otoliths). But what about the countless fish that are caught and released? How can we get valuable information from them?

The answer lies in a simple procedure: a fin clip.

"From that finlet, we can get a genetic fingerprint of that animal," Walt explained. This simple tissue sample provides a genetic tag—a permanent and unique identifier for that individual fish. Unlike conventional spaghetti tags that can shed or go unreported, a genetic tag is there for life. If a fish is sampled and released, and then recaptured years later and resampled, we can confirm its identity and track its journey across the ocean.

"The tag is there for life. You can't change your DNA. It's physically impossible and you can't lose it," Walt stated.

More Than Just a Tag: The Power of Genetics

The fin clip provides a wealth of information beyond a simple ID.

• Sex Identification: For the first time, scientists can determine the sex of a bluefin tuna without killing it. This is a massive advancement, as tuna lack external characteristics to differentiate males from females. This has already led to fascinating discoveries, like the observation that male bluefin tuna have consistently outnumbered females in the Northwest Atlantic for nearly 50 years. Understanding these sex ratios is crucial for assessing a population's reproductive health.

• Ageing Without Killing: In the past, ageing a tuna required extracting its otoliths (ear bones), which are laid down with daily and seasonal rings, similar to a tree trunk.1 Now, new techniques like epigenetic aging allow scientists to use DNA from the fin clip to determine a fish's age. This means a single, harmless fin clip can provide age data for a released fish, offering a fuller picture of the population's age structure.

• Genetic Stock Structure: The fin clip can also reveal a fish's population origin—whether it's from the Western or Eastern stock. While otolith chemistry can tell us where a fish was spawned based on environmental signals, genetics provides a deeper understanding of its population relatedness. "The best example I can give you is the Mediterranean Sea and the other spawning ground, the Gulf of Mexico, is different in terms of its chemistry," Walt said.

Both methods are highly accurate, and when they show similar trends, it provides a powerful, redundant verification of the data, which is ideal for scientific certainty.

How You Can Participate: Genetics for Giants and Juvies

Viking Yachts is a key partner in this project, which is playfully named "Genetics for Giants and Juvies." They're helping to get the word out to the fishing community.

Participating is easy and completely free. You can sign up using a simple Google form . The lab will ship you a free kit with 15 vials and a small pair of scissors. All you have to do is catch a bluefin, take a small piece of the finlet—about the size of the head of a pushpin—and place it in the vial. The fixative is a simple salt solution, so it's not dangerous. You'll also be asked to provide some basic information like approximate length, weight, and a general location.

The lab even covers the return shipping! Your samples are crucial, and every single one is valuable, regardless of how often you fish.

Get your sample kit here!

You can also donate to the cause here.

This initiative is a way for fishermen to have a direct voice in the science and management of their beloved fishery. As Walt said, "The beauty of Close Kin is that the onus is on the industry to now say or show us that in fact, this is going on."

The Future of Bluefin Management

The initial pilot project for Close Kin has been completed, and the results are promising. While Walt cautioned that international negotiations are complex, he confirmed that the data shows a significant change in the outlook of the bluefin stock's abundance.

"Everybody on our end is buying into Close Kin," Walt said, "from the industry folks... to the scientists... to the assessment community, to the managers."

This new method, which narrows the uncertainty window in stock assessments, is a revolutionary way to provide estimates of stock abundance. It gives the scientific community much higher confidence in their data and provides the fishing community with a powerful tool to ensure a sustainable future for the fishery.

From Uncertainty to Opportunity

The current system of fisheries management operates with a precautionary approach, where a "cloud of uncertainty" surrounds population estimates. This often leads managers to be conservative, potentially closing fisheries early, lowering daily retention limits, or changing fishing categories. As Walt noted, this has a significant ripple effect, impacting not just large corporations but also individual charter boat operators and family-run businesses that rely on the ability to provide a fish for their clients to take home.

The Close Kin initiative is a game-changer because it narrows that uncertainty window. The data it provides gives managers and scientists much higher confidence in their stock assessments, which could lead to more stable and potentially increased quotas.

The Allure of Catching and Releasing

For many, fishing is about the thrill of the fight and the experience on the water. However, as Walt points out, for many charter clients, there's also the desire to bring home a fish. "Bluefin taste really good," he said, and being able to take home a 40-inch fish is a "great day" that makes the trip worthwhile. This shared experience fosters a deeper connection to the ocean and creates a sense of loyalty to the sport and the charter captains who provide the opportunity.

This is where the Close Kin project truly shines. By taking a simple fin clip, anglers can contribute to the long-term health of the fishery without having to harvest the fish. It's a way to give back and become a part of the science.

The Power of Data: Every Fish Tells a Story

Walt emphasized that every single fish, whether it's a giant or a juvenile, contributes to the overall dataset. The program is designed to be as simple and accessible as possible. If you catch a fish you have to release, just take a small fin clip and record whatever information you can, even if it's just a rough estimate of size and location.

"Do what you can," Walt said. "If you've got eight fish on and you are only able to sample one, I don't care. That's fine."

The program is a game changer because it allows scientists to collect data from the recreational fishing community, which is geographically widespread and has a high number of releases. The commercial fishing industry has been an incredible partner, but the angling community holds the key to filling crucial data gaps. This includes sampling fish at different times of the year to understand seasonal changes in the population's size, condition, and movements.

The Deep Dive into Close Kin Matching

The term "Close Kin" refers to the core of the project's genetic analysis. By taking DNA from adult and juvenile fish, as well as from larvae collected during specialized research cruises, scientists can create a vast family tree.

• Parent-Offspring Pairs (POP): Scientists match the DNA of larvae to adult fish to identify "Parent-Offspring Pairs." This allows them to track which adult fish are successfully reproducing.

• Sibling Pairs: The data can also reveal sibling pairs, which helps to estimate the overall population size.

This is where it gets nerdy. A single female bluefin tuna can lay up to 15 million eggs in a single season. Of these, 99.999% will not survive. By sampling larvae and matching them to adults, scientists can understand which individuals are the most successful spawners and why. Some parents might produce higher-quality eggs, while others might spawn in areas that are more favorable for larval survival. This information is critical for understanding the health and resilience of the entire population.

As Walt enthusiastically put it, "It works. It's not as though we're in an area where it's an unknown... We have proof of concept. It works."

The initial pilot project has been so successful that it has already produced 118 Parent-Offspring pairs from over 3,000 larvae and more than 8,000 adults. This is a monumental achievement that has the potential to revolutionize how we manage bluefin tuna.

To get involved and contribute to this groundbreaking project, please visit the links in the podcast description. Your samples will help provide a clear picture of the bluefin population, ensuring a sustainable future for these incredible fish and the communities that depend on them.

The Journey of a Scientist

Walt shared a relatable anecdote about his students' summer projects, where the initial plans often fall apart. He explained that this is the reality of science, where failure is a learning opportunity that leads to breakthroughs. The Close Kin project is a perfect example of this. It's the culmination of work from a large, diverse group of people—geneticists, mathematicians, managers, and scientists—all collaborating to make a revolutionary concept a reality.

"To have it all come together and work for everybody is, in my opinion, pretty amazing," he said.

How Fish Navigate a "Featureless Medium"

One of the most profound mysteries of the ocean is how highly migratory fish like bluefin tuna, marlin, and sharks navigate vast, seemingly featureless stretches of water.

• No GPS: Unlike terrestrial animals that use landmarks like mountains and rivers, fish are in a three-dimensional, ever-moving fluid with limited visibility. A tuna's visibility is often no more than 40 feet.

• A Tiny Brain: Walt highlighted the staggering fact that a giant 800-pound bluefin tuna has a brain about the size of his thumbnail. Yet, this tiny brain allows it to travel from the Gulf of Maine to the Straits of Gibraltar with incredible precision.

• Pineal Window: While we don't have all the answers, scientists have a few theories. Walt mentioned the pineal window, a clear, non-pigmented spot on a tuna's head that allows light to reach the pineal gland. It's theorized that this might help the fish track changes in day duration, which is a predictable cue for seasonality, unlike water temperature.

• Not All Cues Are Reliable: As Walt explained, temperature is a poor navigational cue because it changes both horizontally (in fronts) and vertically (in the thermocline). Light, however, is a consistent and reliable signal.

This ability to navigate is one of the most amazing aspects of animal behavior, and it’s something scientists are still working to fully understand.

On the Ground at the Mid-Atlantic Tournament

Walt was live from the Mid-Atlantic tournament, where he and his team were collecting valuable data despite challenging weather conditions. Hurricane Erin was bearing down on the coast, but the boats were still out there, braving the elements.

Tournaments are crucial for scientific research because they act as a funnel point, concentrating a large number of fish in one location. This makes it possible for scientists to collect data that would be nearly impossible to gather otherwise. Walt's team was collecting samples for several ongoing projects:

• Billfish Aging: They are working with a bomb radiocarbon specialist to confirm the age and longevity of blue marlin, swordfish, and white marlin. They have found that blue marlins can live for over 20 years.

• Fin Sampling for Billfish: Building on the success of the Close Kin project for bluefin, they are launching a similar initiative for billfish. This will allow them to collect genetic samples and age information from the majority of billfish that are released.

• Dietary Studies: In a past project, Walt's lab sampled billfish and tuna stomachs to answer a question about the importance of chub mackerel as a prey species. This was a direct request from a fisheries council, and they were able to provide a robust, data-backed answer.

A Final Thank You and Call to Action

Walt concluded by expressing immense gratitude to the fishing community. "Everything from the Close Kin project would not be possible" without their collaboration. He encouraged anyone with questions or curiosity to reach out to him or his lab via email or their social media platforms. He wants people to feel welcome to ask questions, share data, and get involved.

The entire conversation underscored a powerful message: the future of our fisheries depends on an ongoing partnership between science and the fishing community. By working together, we can ensure the health and longevity of these incredible species.

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