Animals that live in groups tend to be more protected from predators. That idea might be common sense, but it’s difficult to test for some species, especially for wild populations of fish that live in the ocean.

A new 91̽�� study that leverages historical data has found unique support for the “safety in numbers” hypothesis by showing that Pacific salmon in larger groups have lower risk of being eaten by predators. But for some salmon species, schooling comes at the cost of competition for food, and those fish may trade safety for a meal. The was published June 29 in the journal Science Advances.

“With salmon, most people think of them spawning in freshwater streams, but there’s also this huge amount of time they spend in the ocean feeding and growing,” said lead author , a doctoral student in the UW’s interdisciplinary Quantitative Ecology and Resource Management Program and the School of Aquatic and Fishery Sciences. “One of the reasons why this study is so unique is that we essentially can’t observe these fish at all in their natural ocean environment, and yet we’re able to pull out these really strong results on how grouping affects predation risk and foraging success for individual fish using this incredibly valuable dataset.”

The researchers looked at four species of Pacific salmon — sockeye, chum, coho and pink — drawing on an international fisheries dataset collected for these species from 1956 to 1991. While their individual life histories vary by species, all salmon are born in freshwater streams, then migrate to the ocean to feed and grow before returning to their home streams to lay eggs, spawn and die, continuing the lifecycle for the next generation.

This study relied on analyzing existing historical data in new ways. For more than four decades the UW’s Fisheries Research Institute in partnership with the International North Pacific Fisheries Commission recorded salmon catch data across the North Pacific Ocean as part of managing each species. The study’s authors analyzed catch data from — fishing gear that involves dropping a net and capturing all of the fish in a relatively small volume of water. By looking at numbers of fish caught in one of these nets, the researchers could estimate the size of the schools in which each fish had been swimming.

Additionally, the historical data included careful records of predator wounds on the salmon, plus the stomach contents for a subset of the fish caught. In this way, the researchers could estimate both predator encounters and feeding success for salmon across 45 years, spanning the entirety of the North Pacific Ocean — making this a unique and valuable data set.

“It was serendipitous that these data were available. They suggest that salmon are social during the ocean stage of their life and reveal the benefits and costs of this sociality,” said senior author , an assistant professor in the 91̽��School of Aquatic and Fishery Sciences. “Grouping is very common in marine fish and we think this is largely to help them evade predators, yet there’s actually not much empirical support showing this, especially from wild populations. I think this study is a piece of the foundation that many didn’t realize was missing.”

By looking at the number of fish caught in purse seine nets as a proxy for group size, the researchers then estimated predator risk by considering the fraction of fish in each set that had predator wounds. Fish in larger groups were much less likely to be wounded, across species. For example, with sockeye salmon, an increase in 100 fish in a group cut predation risk in half. Also, wound data showed that fish whose bodies were larger or smaller than others in their group were more likely to be attacked by a predator. This suggests that the salmon’s safety in numbers comes from confusing their predators because visually distinct — larger or smaller — individuals were easier for predators to keep track of.

The researchers also found that for two salmon species — sockeye and chum — fish in larger groups had less food in their stomachs. These fish sometimes sacrificed a meal to remain protected in a group and avoid predators. The team didn’t notice this pattern for pink and coho salmon, however. One possible reason for this, the researchers said, is that sockeye and chum salmon spend a much longer portion of their lives in the ocean, and also tend to travel farther away from their home streams than other species. Spending more time and traveling farther out in the ocean generally means food is harder to find, leading to more competition and less food for fish in larger groups.

The authors hope this paper inspires eventual consideration of group size distributions and the benefits and costs of grouping in current fisheries management models — as well as dusting off other data sets to reveal relevant findings.

“Many of these data sets came at great cost and I think there’s a lot in them still ready to be uncovered,” Berdahl said. “I would hope it also motivates people to think about the ecological implications of collective behavior — in this case, how grouping impacts the food web, both by changing the rate a species is being eaten as well as the rate at which it is consuming others.”

Other co-authors are , a 91̽��professor of aquatic and fishery sciences, and , previously a research scientist at the 91̽��School of Aquatic and Fishery Sciences. This research was funded by the Fisheries Research Institute and the H. Mason Keeler Endowed Professorship at the UW.

For more information, contact Polyakov at polyakov@uw.edu, Quinn at tquinn@uw.edu and Berdahl at berdahl@uw.edu.

91̽�� astrobiologist has created software that simulates multiple aspects of planetary evolution across billions of years, with an eye toward finding and studying potentially habitable worlds.

Barnes, a 91̽��assistant professor of astrobiology, astronomy and data science, released the first version of VPLanet, his virtual planet simulator, in August. He and his co-authors described it in a accepted for publication in the Publications of the Astronomical Society of the Pacific.

“It links different physical processes together in a coherent manner,” he said, “so that effects or phenomena that occur in some part of a planetary system are tracked throughout the entire system. And ultimately the hope is, of course, to determine if a planet is able to support life or not.”

VPLanet’s mission is three-fold, Barnes and co-authors write. The software can:

• simulate newly discovered exoplanets to assess their potential to possess surface liquid water, which is a key to life on Earth and indicates the world is a viable target in the search for life beyond Earth
• model diverse planetary and star systems regardless of potential habitability, to learn about their properties and history, and
• enable transparent and open science that contributes to the search for life in the universe

The first version includes modules for the internal and magnetic evolution of terrestrial planets, climate, atmospheric escape, tidal forces, orbital evolution, rotational effects, stellar evolution, planets orbiting binary stars and the gravitational perturbations from passing stars.

It’s designed for easy growth. Fellow researchers can write new physical modules “and almost plug and play them right in,” Barnes said. VPLanet can also be used to complement more sophisticated tools such as machine learning algorithms.

An important part of the process, he said, is validation, or checking physics models against actual previous observations or past results, to confirm that they are working properly as the system expands.

“Then we basically connect the modules in a central area in the code that can model all members of a planetary system for its entire history,” Barnes said.

And though the search for potentially habitable planets is of central importance, VPLanet can be used for more general inquiries about planetary systems.

“We observe planets today, but they are billions of years old,” he said. This is a tool that allows us to ask: ‘How do various properties of a planetary system evolve over time?’”

The project’s history dates back almost a decade to a Seattle meeting of astronomers called “Revisiting the Habitable Zone” convened by , principal investigator of the UW-based , with Barnes. The habitable zone is the swath of space around a star that allows for orbiting rocky planets to be temperate enough to have liquid water at their surface, giving life a chance.

They recognized at the time, Barnes said, that knowing if a planet is within its star’s habitable zone simply isn’t enough information: “So from this meeting we identified a whole host of physical processes that can impact a planet’s ability to support and retain water.”

Barnes discussed VPLanet and presented a tutorial on its use at the recent AbSciCon19 worldwide astrobiology conference, held in Seattle.

The research was done through the Virtual Planetary Laboratory and the source code is available .

Barnes’s other faculty co-authors are astronomy professor ; , professor of atmospheric sciences; and research scientist . Other 91̽��co-authors are doctoral students , , and ; and undergraduate researchers Caitlyn Wilhelm, Benjamin Guyer and Diego McDonald.

Other co-authors are of the Carnegie Institution for Science; of the Flatiron Institute, of the Max Planck Institute for Astronomy in Heidelberg, Germany, of the University of Bern, of the NASA Goddard Space Flight Center and of Weber State University.

The research was funded by a grant from the NASA Astrobiology Program’s Virtual Planetary Laboratory team, as part of the research coordination network, or NExSS.

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For more information, contact Barnes at 206-543-8979 or rkb9@uw.edu.

Grant numbers

VPL under cooperative agreement #NNA13AA93A

NASA grants #NNX15AN35G, #13-13-NA17 0024, and #80NSSC18K0829

NASA Earth and Space Science Fellowship Program grant #80NSSC17K0482

Hansen Creek, a small stream in southwest Alaska, is hard to pick out on a map. It’s just over a mile long and about 4 inches deep. Crossing from one bank to the other takes about five big steps.

Yet this stream is home to one of the most dense sockeye salmon runs in Alaska’s Bristol Bay region. Each summer, about 11,000 fish on average return to this stream, furiously beating their way up the shallow creek to spawn and eventually die.

For the past 20 years, dozens of 91̽�� researchers have walked this creek every day during spawning season, counting live salmon and recording information about the fish that died — for a salmon, death is inevitable here, either after spawning or in the paws of a brown bear. After counting a dead fish, researchers throw it on shore to remove the carcass and not double-count it the next day. The data collection is part of a long-term study looking at how bear predation affects sockeye salmon in this region.

When this effort began in the mid-1990s, , a professor in the 91̽��School of Aquatic and Fishery Sciences, decided that everyone should throw sockeye carcasses to the left side of the stream — facing downstream. They might as well be consistent, he thought, and who knows — maybe someday they could see whether the tossed carcasses had an effect on that side of the stream.

Twenty years later, Quinn and colleagues have found that two decades of carcasses — nearly 600,000 pounds of fish — tossed to the left side of Hansen Creek did have a noticeable effect: White spruce trees on that side of the stream grew faster than their counterparts on the other side.

What’s more, nitrogen derived from salmon was found in high concentration in the needles of the spruce trees on the side of the tossed carcasses.

Essentially, as they report in a published October 23 in the journal Ecology, the sockeye carcasses were fertilizing the trees.

“Tossing the carcasses to the left side started out just as a convenience to keep from counting the same fish twice. I thought at some point in the future, it would be kind of cool to see it if had an effect,” said Quinn, the paper’s lead author who has taught and led research projects in the UW’s for 25 years.

The researchers were able to tell that the fertilized trees grew faster by taking a deep slice out of the trunks, called a tree core, from white spruce on both sides of the stream. They examined the growth rings during the 20-year study period (1997 to 2016) as well as for the 20-year span before the study began (1977 to 1996), looking at the spacing of the rings each year. The first 20 years served as a control for the field experiment, because during that period the trees on both sides were growing under similar densities of salmon carcasses.

By 2016, the trees on the salmon-enriched side were not noticeably taller, the authors found, even though they grew faster over the 20-year study period. This is because those trees started out shorter and were growing more slowly before the study began than their counterparts on the other side.

The salmon didn’t turn these spruce into towering giants, but instead gave a boost to vegetation on the slower-growing side of the stream. Numerous factors such as soil chemistry, temperature and light all contribute to tree growth over many years.

“This study demonstrates the importance of salmon carcasses for the growth of trees, yet within the context of an area where the trees are growing very slowly, and where climate and other factors also play a part in their growth,” Quinn said.

Over the 20-year study period, close to 200 undergraduate and graduate students, professors, staff and visiting scientists walked Hansen Creek, which drains into Lake Aleknagik, and other remote streams in the Bristol Bay region. They traveled in groups in case they came upon bears, which catch fish in the streams and often eat just part of the carcass.

At the start of the spawning season in July, it is common to see up to several thousand sockeye swarming the mouth of the creek, their ruby-red bodies jostling in water less than 2 inches deep.

“At some point they just go for it,” Quinn said. “They are basically swimming over what’s little more than wet rocks, powering through the mouth of the stream and up the creek.”

Data on sockeye numbers, behavior and predation by bears collected by Quinn and his colleagues for decades are unique — long-term datasets of this detail for sockeye salmon don’t exist anywhere else. Many papers have resulted from these valuable data, Quinn said, and this new study is no exception.

“This study contributes to our understanding of the role of salmon in the ecosystem, but it also illustrates the importance of patient, careful, long-term research, and the educational benefits that result from such research in a university,” Quinn said.

Other co-authors are James Helfield and Andrew Bunn of Western Washington University, Catherine Austin of the 91̽��School of Aquatic and Fishery Sciences and Rachel Hovel of the University of Maine. Helfield and Hovel both earned their doctoral degrees at the UW.

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For more information, contact Quinn at tquinn@uw.edu.

Related paper: ““

Planets orbiting “short-period” binary stars, or stars locked in close orbital embrace, can be ejected off into space as a consequence of their host stars’ evolution, according to new research from the 91̽��.

The findings help explain why astronomers have detected few — which orbit stars that in turn orbit each other — despite observing thousands of short-term binary stars, or ones with orbital periods of 10 days or less.

It also means that such binary star systems are a poor place to aim future ground- and space-based telescopes to look for habitable planets and life beyond Earth.

There are several different types of , such as and binaries, named for the ways astronomers are able to observe them. In a accepted for publication in , lead author , a 91̽��astronomy doctoral student, studies binaries, or those where the orbital plane is so near the line of sight, both stars are seen to cross in front of each other. Fleming will present the paper at the Division on Dynamical Astronomy conference April 15-19.

When eclipsing binaries orbit each other closely, within about 10 days or less, Fleming and co-authors wondered, do tides — the gravitational forces each exerts on the other — have “dynamical consequences” to the star system?

“That’s actually what we found” using computer simulations, Fleming said. “Tidal forces transport from the stellar rotations to the orbits. They slow down the stellar rotations, expanding the orbital period.”

This transfer of angular momentum causes the orbits not only to enlarge but also to circularize, morphing from being eccentric, or football-shaped, to perfect circles. And over very long time scales, the spins of the two stars also become synchronized, as the moon is with the Earth, with each forever showing the same face to the other.

The expanding stellar orbit “engulfs planets that were originally safe, and then they are no longer safe — and they get thrown out of the system,” said , 91̽��assistant professor of astronomy and a co-author on the paper. And the ejection of one planet in this way can perturb the orbits of other orbiting worlds in a sort of cascading effect, ultimately sending them out of the system as well.

Making things even more difficult for circumbinary planets is what astronomers call a “region of instability” created by the competing gravitational pulls of the two stars.

“There’s a region that you just can’t cross — if you go in there, you get ejected from the system,” Fleming said. “We’ve confirmed this in simulations, and many others have studied the region as well.”

This is called the “dynamical stability limit.” It moves outward as the stellar orbit increases, enveloping planets and making their orbits unstable, and ultimately tossing them from the system.

Another intriguing characteristic of such binary systems, detected by others over the years, Fleming said, is that planets tend to orbit just outside this stability limit, to “pile up” there. How planets get to the region is not fully known; they may form there, or they may migrate inward from farther out in the system.

Applying their model to known short-period binary star systems, Fleming and co-authors found that this stellar-tidal evolution of binary stars removes at least one planet in 87 percent of multiplanet circumbinary systems, and often more. And even this is likely a conservative estimate; Barnes said the number may be as high as 99 percent.

The researchers have dubbed the process the Stellar Tidal Evolution Ejection of Planets, or STEEP. Future detections — “or non-detections” — of circumbinary around short-period binary stars, the authors write, will “will provide the best indirect observational test of the STEEP process.

The shortest-period binary star system around which a circumbinary planet has been discovered was , with a period of about 7.45 days. The co-authors suggest that future studies looking to find and study possibly habitable planets around short-term binary stars should focus on those with longer orbital periods than about 7.5 days.

Fleming and Barnes’ co-authors are 91̽��astronomy professor , post-doctoral researcher and undergraduate student David E. Graham. This work used storage and networking infrastructure provided by the Hyak supercomputer system at the UW, funded by the UW’s Student Technology Fee.

The research was funded by the NASA Astrobiology Institute through the UW-based . Fleming is supported by funding from the NASA Space Science Fellowship Program.

As for habitability and the search for life, Fleming said planets orbiting short-term eclipsing binaries might otherwise be attractive targets for closer study, with their edge-on angle showing eclipses, and more, to the distant viewer.

“But this mechanism tends to kill them,” he added. “So, it’s not a good place to look.”

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For more information, contact Fleming at dflemin3@uw.edu, or Barnes at 206-543-8979 or rory@astro.washington.edu.

Grant numbers: NSF IGERT DGE-1258485 fellowship; NASA Earth and Space Science Fellowship Program # 80NSSC17K0482; Virtual Planetary Laboratory, under Cooperative Agreement # NNA13AA93A, NNX14AK26G.

It’s no secret that human activities affect fish, particularly those that must migrate to reproduce. Years of building dams and polluting rivers in some regions have left fish such as salmon struggling to return to their home streams and give birth to the next generation.

A new 91̽�� study points to yet another human factor that is hampering the ability of fish to reproduce: the timing of our fishing seasons. The paper, last month in the journal Fish and Fisheries, is one of only a handful of studies that considers how the timing of fishing efforts might disproportionately target certain fish and change the life history patterns of entire populations.

“The more you think about it, the more pervasive you realize it is,” said senior author , a 91̽��professor of aquatic and fishery sciences. “The real purpose of this essay is to raise the profile of this neglected issue.”

The authors build the case for more attention on timing by outlining examples of how fishing seasons have altered a population’s makeup — specifically, its diversity and productivity.

Fishing regulations, the patterns and habits of people who fish, and even weather can increase fishing efforts at certain times, putting more pressure on fish during a short period. For salmon in particular, migration and spawning are timed so that both parents and offspring have the highest chance for survival. Fishing that targets only early or late-arriving fish can, over many generations, reduce the numbers moving and spawning at the time that is most favorable for them biologically, the researchers explain.

This may also affect the ability of fish to adapt to climate change. If colder stream water necessary for spawning turns up later each autumn due to climate change, fish must “choose” between being fished or being fried — when they otherwise would adapt to changes and swim upstream whenever water temperatures proved adequate.

“We are reducing the ability of fish to find good environmental conditions,” said lead author , a 91̽��doctoral student in aquatic and fishery sciences. “We’re perhaps also reducing the ability of fish to adapt to climate change.”

Salmon return from the ocean to the streams in which they were born to spawn at predictable times throughout the year. The migration and spawning timing vary over the years for each salmonid species, but factors such as daylight hours and water temperature are natural markers that drive when salmon will start their journey home.

Commercial and tribal fishing seasons are built around salmon’s reproductive timing; regulations vary, but in general, fishing can occur in the ocean and rivers starting on a specific day as salmon migrate home to spawn. The season ends on a predetermined date, or when a certain number of fish are caught.

For example, if a fishery opens on Aug. 1, salmon that return to their natal streams before that date are home free. In contrast, fish migrating on the first of the month or after can face an incredible amount of fishing pressure, especially if the weather is favorable and the conditions good for harvesting.

When this pattern repeats year after year, a population can evolve to migrate earlier or later because parents that migrate early tend to have kids that migrate early, too. But those changes also affect their ability to survive; migrating earlier in the summer means spawning in warmer water, which isn’t favorable for egg survival. Returning too late also decreases chances for survival.

“By disrupting this long-evolved distribution of timing, you can reduce the reproductive output of adults or the survival of their offspring,” Tillotson said. “This paper is serving as a call to attention for researchers.”

While salmonid species were the focus of this study, the findings could be applied to other fish that have equally complex migration and breeding behaviors. Fishing seasons often are set around periods when breeding adults congregate in a specific location, which also puts undue pressure on fish during an important period of their lives.

Fishing season dates should reflect the biology of fish, recognize the importance of timing, and be responsive to changes, the authors say. The goal of management, in addition to making sure enough fish spawn, should be ensuring those that do reflect the diversity of the total population. This, the researchers said, is key for giving salmon and other fish the best chance to adapt in a changing world.

They hope other scientists and fisheries managers will apply these findings to their own data and respective fish populations, and ultimately devise fishing regulations that will be viable for the future.

“We would like to think creatively about how to integrate climate-driven processes with fishing to be more protective of the populations, and more sustainable in fishing practices in the long run,” Quinn said.

The study was funded by a fellowship from the 91̽��’s IGERT Program on Ocean Change and the Achievement Rewards for College Scientists Foundation.

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For more information, contact Tillotson at mdt3@uw.edu and Quinn at tquinn@uw.edu.

Even fish look forward to retirement.

After making an exhausting migration from river to ocean and back to river — often multiple years in a row — one species of Alaskan trout decides to call it quits and retire from migrating once they are big enough to survive off their fat reserves.

This is the first time such a “retirement” pattern has been seen in fish that make this river-to-ocean migration, according to published in July in the journal Ecology.

, a common and abundant trout in Southwest Alaska’s rivers, live mainly in freshwater streams, but travel to the ocean in the summer months to feed and grow. This migration pattern, called anadromy, is seen in salmon and steelhead as well as some cutthroat and bull trout.

For the Dolly Varden, going to the ocean is risky yet necessary business. The sea offers a banquet feast when compared with poor food sources in their home streams, but the ocean is also a dangerous place with many predators.

The study shows that Dolly Varden, once they reach about 12 inches in length, can retire permanently from going to sea. They rely on digestive organs that can and a unique relationship with sockeye salmon.

“As far as we know, no one has ever seen  a population of large-bodied fish come back to freshwater and just park there for the rest of their lives,” said lead author , a postdoctoral researcher at the National Oceanic and Atmospheric Administration who completed this work as a 91̽��doctoral student.

Dolly Varden trout, perhaps the lesser-known cousin of Alaska’s famous sockeye salmon, are abundant in the relatively untouched Alec and Chignik rivers of the Alaska Peninsula. Every summer, sockeye also spawn by the hundreds of thousands here, and an excess of salmon eggs is left floating in the rivers or collecting in clusters along the bank.

These eggs become a short-lived nutritious meal for other species, namely Dolly Varden trout.

Dolly Varden binge on the eggs for about a month, doubling or quadrupling the size of their stomach and intestines to accommodate the feast. Then, once the salmon spawning ends, Dolly Varden shrink their guts and survive for the next year off their reserves in cool water because there is little else to eat in the rivers.

Small Dolly Varden will migrate out to the ocean in early summer to eat even more, trying to get big enough to stay in the river next season — and for the remainder of their lives.

“Small fish gain enough to make this risk worthwhile because they can pack on a good deal of growth in a summer at sea,” said senior author , a 91̽��professor of aquatic and fishery sciences. “However, fish that are already big will only grow a bit more, and there are still predators that can eat them. So, in this case the big fish retire from anadromy at a certain age and stay in the river, waiting for the ocean to come to them — in the form of the eggs released by the salmon.”

The researchers observed this pattern by looking at the ear bone, called an otolith, of more than 300 Dolly Varden fish. When cross-sectioned, otoliths show a growth ring for each year of life, providing the age of the fish. Otoliths also record natural variation in water chemistry. Marine water has a higher concentration of the element strontium, so a spike in strontium on a fish’s otolith means it migrated to the ocean that year.

In this pristine Alaska watershed, Dolly Varden retirement plans depend on a healthy sockeye salmon run. If low numbers of sockeye return to spawn one year, that could force the Dolly Varden to migrate to sea again for food. Likewise, Dolly Varden rely on cool rivers in the winter and spring to slow down their metabolism and conserve energy. If rivers warm under climate change, it could prevent the fish from living off their reserves all year.

In both cases, they would be forced to seek a new feeding pattern.

“This population is clearly on the edge between two extremes, and their life history patterns could shift to complete residency or anadromy depending on climate change and the health of the other species they interact with,” Bond said.

Other Pacific trout, including sea-run cutthroat and bull trout, which are listed as threatened in Washington, might also retire given the right ecological circumstances. More studies are needed to know whether this is happening, though it’s likely the trout wouldn’t have access to the same abundance of salmon eggs, researchers said, because the spawning activity in Washington’s rivers is much less than in Alaska.

The research took place as part of the UW’s long-tenured , where scientists are studying a range of issues including population genetics, migration patterns and the relationship between salmon and bears. The program is the world’s longest-running effort to monitor salmon and their ecosystems.

This study was funded by the Gordon and Betty Moore Foundation, the National Science Foundation, the U.S. Army Corps of Engineers, and the H. Mason Keeler and other endowments at the UW. The paper’s other co-author is Jessica Miller of Oregon State University.

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For more information, contact Bond at 206-860-3428 and 831-706-1274 or morgan.bond@noaa.gov and Quinn at 206-543-9042 or tquinn@uw.edu.