*Featured image photo credit: Valerio Sbragaglia

In this episode, Valerio (Postdoctoral fellow, Institut de Ciencias del Mar, Barcelona Spain) takes us on a deep dive of his paper: Sbragaglia, Klamser, et al. 2022: ‘Evolutionary Impact of Size-Selective Harvesting on Shoaling Behavior: Individual-Level Mechanisms and Possible Consequences for Natural and Fishing Mortality.’ We discuss how size-selective fishing practices can have unintended behavioral and ecological consequences for fisheries populations, and how interdisciplinary collaborations – in this case between behavioral ecology and biophysics – can enhance our understanding of complex feedbacks at individual and group levels. Listen to our chat and then read Valerio’s full paper here!

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Fishing for more answers? Email Valerio at valeriosbra@gmail.com.

NATURALIST SELECTIONS IS AN INTERVIEW SERIES PRODUCED BY THE AMERICAN SOCIETY OF NATURALISTS GRADUATE COUNCIL. WE SHOWCASE GRADUATE STUDENT AND POSTDOC AUTHORED WORK IN THE AMERICAN NATURALIST, A PREMIER PEER-REVIEWED JOURNAL FOR ECOLOGY, EVOLUTION, AND ANIMAL BEHAVIOR RESEARCH. CATCH UP ON EXCITING NEW PAPERS YOU MAY HAVE MISSED FROM THE JOURNAL, AND MEET SOME TRULY BRILLIANT EARLY CAREER NATURALISTS!

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Credits

Featured Guest: Valerio Sbragaglia, Institut de Ciències del Mar, Barcelona, Spain

Host, Editor, Producer: Sarah McPeek, University of Virginia, US

Original Music: Daniel Nondorf, University of Virginia, US

Transcript:

You’re listening to Naturalist Selections, a science podcast featuring graduate student and postdoc-authored work in The American Naturalist, produced by the American Society of Naturalists Graduate Council. I’m grad council rep Sarah McPeek and today I’m talking with postdoc first-author Dr. Valerio Sbragaglia! Valerio is currently a postdoctoral researcher at the Institut de Ciències del Mar in Barcelona, Spain. His recent paper is called: “Evolutionary Impact of Size-Selective Harvesting on Shoaling Behavior: Individual-Level Mechanisms and Possible Consequences for Natural and Fishing Mortality.” In this paper, Valerio and his colleagues ask how size selective fishing practices may impact the evolution of shoaling behavior in fisheries populations. They used Dr. Robert Arlinghaus’ lab’s established long-term experimental evolution study on zebrafish, originally established in 2006 by Dr. Robert Arlinghaus in the IFISHMAN group at the Leibniz-Institute of Freshwater Ecology and Inland Fisheries, in Germany. The project was started with funding from the Leibniz-Community Pact of Innovation and Research and was largely the output of hard work by a PhD student Silva Uusi-Heikkilä, who today works in Finland. The lines have been maintained through internal funding by the Leibniz-Institute over the years, and various postdoc projects have been associated with the zebrafish model, including Valerio’s work during his time in the lab. In Valerio’s experiments with the zebrafish, the researchers removed either the largest 75% of fish or the smallest 75% of fish each generation for eight total generations of selection in replicate lines of fish. Several generations after selection stopped, Valerio and colleagues found that fish in the large-harvested lines exhibited increased vigilance while small-harvested lines exhibited decreased vigilance. To dig deeper into the consequences of these behavioral changes, Valerio partnered with two physicists, Pascal Klamser, who shares co-first authorship on the paper, and Pawel Romanczuk. They use fluid movement biophysics to model how these evolved changes in individual vigilance behavior could affect group shoaling behavior and vulnerability to both human fishing gear and non-human predators. Their findings indicate that large-harvested lines may decrease their group shoaling behavior, which may increase their susceptibility to natural predators even while it makes them less vulnerable to mass-fishing practices. These findings contribute to a long list of ways human fishing practices can affect the evolution of fished populations and can have cascading consequences for entire food webs. So without further ado, let’s dive in with Valerio.

Sarah

I’m curious what you think about fishing as a source of predation. Is there some way that it’s fundamentally distinct from, say, predation by another fish species? Is there something unique about that?

Valerio

Yes, I think in a conceptual way, fishing can be compared to a predator because we are acting on mortality of prey or target species, whatever. But I think there is some distinctions that make fishing quite interesting from an evolutionary perspective. So first of all, we have many fishing gears around the world, passive and active fishing gears. A passive fishing gear could be a trapper net, a net that you leave at the sea bottom and wait, then the fish moving around just get trapped into the net. That’s a passive capture. And then there are other gears, such as active fishing gears such as a trolling net, is an active fishing gear because it pushes the fishes and then tries to capture them. Another very interesting active fishing gear is something that I work with in my previous papers is spearfishing, which is a unique kind of fishing predation, let’s say, because humans are underwater with a visual contact with the prey and a spear gun or a pole spear. So they can really select the prey according to a double behavioral interaction, the spear fisher and the fish.

Sarah

Yes.

Valerio

And this can occur on a commercial and recreational basis. So it’s a very complex selection environment if you want, because there are many gears used for different purposes. What accommodates all of them is that if in a natural context, usually larger fish have lower mortality rates than smaller fish in a fishing context, either for commercial or recreational purposes, fishers are selectively search for larger fish. They have more commercial value usually. And then for recreational purposes, a big fish is a trophy fish. So that’s, I think, is the main difference between fishing mortality and natural mortality. It’s size selection. And this is what we simulated in our experiment.

Sarah

Yeah. Are you a fisherman yourself?

Valerio

Yes, I am a recreational spear fisherman.

Sarah

Oh, wow. Cool.

Valerio

When I have time, I would say.

Sarah

Do you think that because of the work you do, you’re more conscious about what size of fish you go after when you’re spearfishing?

Valerio

Yeah. We are working a lot with stakeholders and recreational fishers in order to communicate this important message. That’s quite an interesting topic at the moment because many recreational fishers, in particular spear fishers, have the belief that harvesting larger fish is the most sustainable way to practice recreational spear fishing. They say, okay, these big guys have already spawned. So we just select them and we leave the small ones. We allow the small ones to reproduce, to breed. But then the scientific community is showing that that’s not always the case. We are engaged with NGOs and other stakeholders to communicate this message to the community. It’s very hard because it’s a very deep belief which is governing their behavior.

Sarah

Yeah. I guess there would be the assumption that the larger fish would be the older ones. They’ve already reproduced. They’re kind of on their way out anyway. But we know that it’s the larger, older fish who contribute disproportionately to the reproduction in the population. So you’re really removing the fittest members of the group.

Valerio

Yes. And also, if you look at the regulation of fishing, there are minimum size limits, but not larger size limits, in particular in my context here in the Southern Europe and the Mediterranean Sea. So they are right. They never got the message that you need to save the big ones. I mean, it’s a very interesting topic to dig in.

Sarah

Absolutely. When you select on size, you’re selecting on all of these other traits that you aren’t intending to carry along with you. And in this paper, you specifically looked at social behavior. I’m really curious what gave you the idea to dig into that particular aspect of behavior specifically? Because I wouldn’t have naively suspected that there would be a link.

Valerio

Yeah, you are right. Size is a very simple but complex trade. So it adds so many complexities into that. And so the experiment was inspired by a paper published in Science in 2002 by Conover and Munch which selected on Menidia menidia. It’s a small marine fish.

Sarah

Yeah.

Valerio

Similar experiment, large and small selection.And we got this idea basic