An Unintended Consequence

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An Unintended Consequence
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By Sonia Fernandez, UC Santa Barbara

Life on Earth is all about strategies for survival, with every organism developing behaviors and bodies that maximize chances of staying alive and reproducing while minimizing the likelihood of being injured or eaten.

Fish are one such example. For millions of years, many species have evolved a safety-in-numbers strategy that confuses predators and ensures the survival of the maximum number of individuals as they move about in the ocean. According to scientists at UC Santa Barbara, the Santa Fe Institute and the University of Washington, however, thanks to modern industrial fishing practices and technologies, schooling behavior may become less common.

“The findings from our model suggest that industrial fishing can decrease the tendency of fish to form large groups,” said UCSB graduate student researcher Ana Sofia Guerra, lead author of a paper published in the journal Proceedings of the Royal Society B. This change in behavior has implications for both the fish and their predators, including humans.

Ana Guerra
Ana Sofia Guerra

“People have been studying fisheries science for centuries,” added marine ecologist and paper co-author Douglas McCauley, an associate professor of ecology, evolution and marine biology at UC Santa Barbara. “But we’ve never considered: Could modern fishing technology be killing schooling behavior?”

Indeed, the capacity to extract large amounts of fish from the ocean has grown in the past several decades, with ships and fleets able to access and fish from even remote areas of the ocean. Purse-seining and trawling both involve deploying enormous nets that target large groups of fish. Drones and spotter planes increase the efficiency of these mass-capture methods.

“One of the reasons schooling behavior exists is to avoid a predator attack, but by developing technology that can capture entire schools, we have turned the tables on that strategy,” Guerra said. 

To better understand this effect, Guerra and McCauley, along with colleagues Albert Kao from the Santa Fe Institute and Andrew M. Berdahl from the University of Washington, constructed an evolutionary fission-fusion model to simulate the behavior of individual schooling fish faced with different levels of predation, both natural and human. The model describes changes in fishes’ preference to form large schools while subjected to different levels of human fishing pressure and natural predation.

Douglas McCauley
Douglas McCauley

The results show that the larger the prevalence of mass-capture practices relative to natural predation, the more individual fish preferences shift toward smaller group sizes.

“Suddenly the sardine in a big school is a lot more vulnerable to a human predator than one that prefers smaller schools or a solitary lifestyle,” Guerra said. Collectively, this change in preference will result in smaller groups and more solitary individuals.

In fact, this change could have several impacts, according to the researchers. For one thing, natural predators that rely on these fish also have evolved hunting methods based on the fishes’ tendencies to travel in large groups.

“We are not the only predators who have figured out how to exploit schooling fish,” Guerra said. Seabirds and pelagic predators often coordinate their attacks. Humpback whales corral herring using ‘bubble nets’ before swooping in, although their ability to exploit schools is not as effective or expansive as that of humans. “By altering schooling behavior, we could actually impact marine predators that rely on schooling fish,” she said.

It’s a socioeconomic issue, too. Foragefish, which include anchovies, herring and sardines, are a large segment of the global fishing industry, valued at $16.9 billion. The economy and efficiency of their capture makes them the basis of thousands of livelihoods. Changes in their schooling behavior might require more time, effort and resources to catch them, which puts the fisheries in a vulnerable position.

Is it reversible? Yes, but only after a lag that would allow the fish to evolve their preferences similar to those observed in the absence of fishing, according to the paper.

“If you wanted to reverse the effects of fishing on a fish population’s tendency to school, you would have to reduce fishing to a much lower level than what it took to cause the effect in the first place,” Guerra said.

Especially worrying is their finding that it is difficult to see these impacts on schooling until it is too late — data is incomplete at best. For example, data from purse-seining operations will focus on large schools and ignore the smaller schools. “If what happens in these models is actually playing out in the ocean, it means we may keep catching fish schools, thinking everything is fine,” McCauley said. “Until we catch the last school. And discover that everything is not fine.”

This wouldn’t be the first time large-scale fishing has introduced evolutionary pressures into fish populations. For instance, the practice of selecting for the largest individuals, has, generation over generation, produced smaller adults in some species.

“Because we consistently harvest the largest fish in the population, it has become an advantage for them to be smaller — they are less of a target and therefore more likely to survive and reproduce,” Guerra explained. “With intense fishing pressure, it is also advantageous to reproduce earlier at a smaller size.” This phenomenon has already occurred with salmon in the Atlantic and Pacific Oceans, in Europe and North America.

This research is an investigation into the area of the behavioral consequences of targeting large schools, a rather underexplored area of fishery science. Most research assumes that fish behaviors do not change.

“Fishery science sometimes tends to treat fish as just numbers on an accounting sheet,” McCauley said. “Our work reminds us that fish are not just numbers. They are living animals with behavior.

“We know from many contexts that hunted animals can shift behavior slowly to evade capture — this seems to be possible for fish as well,” he continued. “Our models suggest fishing could very easily be changing fish behavior in ways that affect both fish and fishers.”

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Sail380 Nov 24, 2020 12:40 PM
An Unintended Consequence

To bad the sardines and anchovies never evolved and learned how to escape the whales. Have you ever seen how many they gulp up at one time?

PitMix Nov 24, 2020 04:04 PM
An Unintended Consequence

Somehow the sardines and whales coexisted for thousands of years without wiping each other out. Then the clever monkeys came along with their vacuum ships and are taking both of them out. But go ahead, focus on the whales.

biguglystick Nov 23, 2020 11:00 AM
An Unintended Consequence

Industrial fishing needs to END now. As a child, I remember growing up on our beaches and seeing shells everywhere... no more. Our oceans are sterile of life and gutted. It won't take long before there is more plastic in the ocean than fish. GO VEGAN for the planet.

PitMix Nov 24, 2020 07:27 AM
An Unintended Consequence

BigUgly, what do you think of that recent article that vegans are more subject to bone fractures as they age?

CoastWatch Nov 23, 2020 08:29 AM
An Unintended Consequence

China, Japan and India have done more damage to the environment, particularly oceans, then any other countries- They just continue and don't care.

haskelslocal Nov 23, 2020 07:55 AM
An Unintended Consequence

Amazing the sophistication and complexity that goes into a study such as this. Interesting that the outcome is always the same; it stops at inability for prediction. However, the anecdotal reality is obvious for humans are decimating the oceans and depleting every resource it holds. We know this. Why do these types of studies stop at fancy and fall into the attempt at policy vortex? What's going to need to happen is similar to how the diamond industry runs, or that of pharma drugs. Make resources artificially scarce, reduce distribution points (we do not need fish at every grocery store just rotting away in waste) and protect industry fishermen by reducing the haul in exchange for higher wages. The exploitation and hording of "all the money" occurs at wholesale and needs to stop.

PitMix Nov 23, 2020 07:39 AM
An Unintended Consequence

Fisheries are doomed no matter what happens. The Japanese vacuumed up all of the fish in the Gulf of California and the Chinese are doing the same off of the territorial limits near the Galapagos. Also in the Southeast Asian seas. They have already had to switch to lesser quality fish for commercial purposes. Too many people, too much pollution, not enough smarts.

PitMix Nov 24, 2020 07:32 AM
An Unintended Consequence

Kohn1, they fished out the abalone so switched to urchins. The rockfish were nearly gone until they put quotas on them and created sanctuaries. The Pacific sardine industry collapsed. "Some of the species most threatened by overfishing currently include Atlantic Halibut, the Monkfish, all sharks, and Blue Fin Tuna. Other animals not usually associated with the seafood industry are also affected, with inadvertent by-catches claiming loggerhead turtles, sharks, dolphins and whales." Houston, some of us think we might have a problem.

biguglystick Nov 23, 2020 11:02 AM
An Unintended Consequence

Sorry, Kohn, but as someone who has been an ocean dweller all my life, PITMIX is correct. Just because you made a living fishing doesn't negate this scientific study. Money seems to be the ruler of all. I care about our ocean life. Wish industry fishing would die down.

kohn1 Nov 23, 2020 08:46 AM
An Unintended Consequence

PITMIX. In my humble opinion the first mistake would be to base an opinion on scholarly articles. I was a commercial fisherman for a good chunk of my life and have seen a lot of these kinds of theories come & go. This article has no empirical proof.

PitMix Nov 23, 2020 07:41 AM
An Unintended Consequence

And your learned scientific opinion is based on what scholarly articles? I assume you have a long and storied career studying the fisheries?

a-1606113071 Nov 22, 2020 10:31 PM
An Unintended Consequence

Very interesting article. We have romanticised fisheries and fishermen in a way we do not do for other hunters, killers of wildlife. Good for the fish to adapt other survival mechanisms. Perhaps there can be further extrapolation into the effect of human density, packing humans into smaller and smaller living spaces, along with efforts to reduce the possession or at least usage of cars?

PitMix Nov 23, 2020 07:37 AM
An Unintended Consequence

Is the fisheries the last industry that does not have to put any effort into maintaining the source of their production, much like the logging and fur trapping industries in the 1800s? They may well be going the way of the buffalo hunters who killed their livelihoods out of existence in a few short years.

a-1606106377 Nov 22, 2020 08:39 PM
An Unintended Consequence

Adaptation leads to survival; those that by serendipity or purpose avoid death and destruction will propagate and replace those that cannot. It will be interesting how this will translate to other species impacted by human predation.

Basicinfo805 Nov 22, 2020 03:02 PM
An Unintended Consequence

Long list of assumptions went into that model I'll tell you that.

Alexblue Nov 23, 2020 08:40 AM
An Unintended Consequence

Why would you hold back on a complete explanation as to the flaws in their premise? How can you be so selfish as to withhold you insights from the world at large?

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