The development of small hydropower dams is widespread throughout Brazil and elsewhere in the world, vastly overshadowing large hydropower projects. The proliferation of these smaller dams is a response to growing energy and security needs. Their expansion, however, threatens many of the remaining free-flowing rivers and biodiverse tropical regions of the world— interrupting the migrations of freshwater fishes, on which millions of peoples’ livelihoods depend.

A new 91̽�� published Jan. 11 in Nature Sustainability quantifies these tradeoffs between hydroelectric generation capacity and the impacts on river connectivity for thousands of current and projected future dams across Brazil. The findings confirm that small hydropower plants are far more responsible for river fragmentation than their larger counterparts due to their prevalence and distribution. 

“The cumulative impacts of many small hydropower dams have long been ignored; instead, focus has been on them in isolation, resulting in claims that their impacts are small,” said co-author , a 91̽��professor of aquatic and fishery sciences. 

This study was led by , a recent doctoral graduate in the 91̽��School of Aquatic and Fishery Sciences who is now a postdoctoral researcher at Florida International University.

Dams constrain the movement of migratory fish along river networks and isolate critical habitats, such as spawning and feeding grounds, which may contribute to local extinctions, population declines and collapses of fishery stocks. This makes migratory fish species some of the most vulnerable organisms to hydropower development in the tropics. 

The authors emphasize that many of the migratory fish species impacted by fragmentation are of high ecological and socioeconomic importance, and that some communities may feel the impacts more than others. For example, some small hydropower dams have been linked to the decline of fish stocks that are relied on heavily by Brazil’s Indigenous groups, because fish are no longer reliably migrating through their historic range. 

Another concern cited by the authors is that small hydropower dams greatly outnumber large hydropower dams, but their combined energy output is much less. In Brazil, small hydropower plants only account for only 7% of total generation capacity even though they represent more than 85% of hydropower plants in the country. 

The collective impacts of Brazil’s rapidly growing small hydropower development on river fragmentation and migratory fish species is extensive, and shows no signs of lessening as the planned construction of new dams continue, the study explains. It is projected that river fragmentation will increase by 21% in the future, and two-thirds of the 191 migratory species assessed in the study occupy river basins that will experience greater connectivity losses. The authors advocate for improved strategic planning of hydropower development with environmentally informed criteria to minimize the potential adverse ecological effects.

“We were motivated by the hope that society could be smarter about new dam constructions in the future,” said Olden. “The study demonstrates that with careful planning, Brazil can meet future energy production needs with only modest impacts on river fragmentation and migratory fishes.”

This research was funded by a H. Mason Keeler Endowed Professorship from the 91̽��School of Aquatic and Fishery Sciences, the CNPq/Science Without Borders Fellowship, the Rufford Foundation and National Geographic Society. Mathis Messager, who recently earned a master’s at the 91̽��School of Aquatic and Fishery Sciences and is now at McGill University, is also a co-author.

For more information, contact Olden, at olden@uw.edu.

The Columbia River is home to one of the West Coast’s most important Chinook salmon runs. Through late spring and early summer, mature fish return from the sea and begin their arduous journey upriver to spawn. In recent years, these fish have faced an additional challenge: hungry California sea lions.

A new 91̽�� and NOAA Fisheries study found that sea lions have the largest negative effect on early-arriving endangered Chinook salmon in the lower Columbia River. The  were published Oct. 19 in the Journal of Applied Ecology.

Opportunistic sea lions have learned that by swimming as far as 145 miles upriver, they can easily feast on migrating salmon, including those hindered by the Bonneville Dam.

“We investigated whether mortality rates varied depending on the specific threatened Chinook salmon population, determined by when they arrive in the river,” said lead author , a doctoral student at the 91̽��School of Aquatic and Fishery Sciences. “We found that, based on their individual return timing and the abundance of sea lions in the river when they return, individual populations experience different levels of sea lion-associated mortality.”

Researchers learned that the earliest arriving populations of Chinook salmon experienced an additional 20% mortality over previous years, and the later arriving populations experienced an additional 10%. This increase in mortality was associated with increased sea lion abundance at those times of year in the period of 2013 to 2015 compared to the period of 2010 to 2012.

The numbers of California sea lions are highest at the mouth of the Columbia in early spring, before they depart for their breeding grounds in southern California. The researchers also discovered that the earliest arriving salmon migrate through the lower Columbia River more slowly than those arriving later in the season, thereby increasing their exposure to predation.

“This information on how different populations are affected by sea-lion associated mortality is key because recovery of endangered Chinook salmon requires multiple of the individual populations to be healthy,” said Sorel.

California sea lions have seen their numbers rebound along much of the U.S. West Coast since the passage of the Marine Mammal Protection Act of 1972, which protects them from being killed, captured and harassed. The increased presence of sea lions is now at odds with the endangered salmon populations on which they feed, putting managers in a difficult position.

Researchers are concerned that something must be done quickly as these hunting behaviors are learned, and the problem could continue to grow exponentially. In August, the National Marine Fisheries Service for Washington, Idaho, Oregon and several Pacific Northwest tribes to capture and euthanize both problematic California and Steller sea lions within a larger area of the lower Columbia and Willamette Rivers. Previously, only California sea lions could be killed in these rivers if managers deemed them a threat to salmon.

This complicated decision was enacted after non-lethal methods, such relocation and hazing, to limit the impact sea lions have on salmon — plus some targeted lethal removal — were met with limited success.

“This is often a challenging management problem as both sea lions and salmon are of strong interest to the public, and both are protected under federal statutes,” said Sorel. “Management must consider multiple social values and operate within existing legal frameworks.”

Continued monitoring will help to reduce the remaining uncertainty about the effects of sea lions on salmon and the expected outcomes of alternative management actions.

Other co-authors are and A. Michelle Wargo Rub of NOAA Fisheries Northwest Fisheries Science Center; of NOAA Fisheries Alaska Fisheries Science Center; and , leader of the U.S. Geological Survey Washington Cooperative Fish and Wildlife Research Unit and 91̽��associate professor. This research was funded by the National Marine Fisheries Service West Coast Protected Resource Division.

For more information, contact Sorel at marks6@uw.edu and Converse at sconver@uw.edu.

A cooler full of fish might not be the only thing anglers bring back from a trip to the lake. Unknowingly, they may also be transporting small aquatic “hitchhikers” that attach themselves to boats, motors ― and even fishing gear ―  when moving between bodies of water.

Considerable research shows that aquatic invasive species can completely transform ecosystems by introducing disease, out-competing and eating native species, altering food webs, changing physical habitat, devastating water-delivery systems and damaging economies. Furthermore, once established, eradication of nuisance species is near impossible, and management can be extremely difficult and costly.

Although preventative measures have been enacted to reduce their introduction and spread, such as mandatory watercraft inspections, educational programs and even dogs trained in sniffing out invasive species, these aquatic stowaways still manage to find their way into new water bodies around the country.

One of the many challenges is identifying how these species spread through human movement. A new 91̽�� study uses passive data from a fishing technology company to model the movement of anglers and predict where aquatic invasives may be spreading. The were published Sept. 2 in the journal NeoBiota. 

“Focusing on anglers allows us to look at a population that uses a wide range of gear on the water; therefore, they have the potential to move a very wide range of species,” said Rachel Fricke, a graduate student at the 91̽��School of Aquatic and Fishery Sciences. Fricke’s research on invasive species is a continuation of her undergraduate capstone project which she also completed at the school.

The researchers used data provided by ReelSonar, the Seattle-based developer of the pocket-sized fish finder . The iBobber syncs with an angler’s smart device and collects multiple pertinent data points, including fishing location. To date, over five million locations have been recorded from around the world.

“In the past, ecologists have done an incredible job extracting big datasets from the web without necessarily working with the organizations who collected the data in the first place,” said co-author , a professor of aquatic and fishery science. “This is to be expected, but I believe that real creativity in the future will come from more authentic collaborations where both ideas and products are co-generated.”

Previous studies relied on optional online forms, requiring anglers to log fishing trips from each location they visited. With ReelSonar’s passive data, these points are generated automatically, offering researchers an exciting opportunity to further understand where people are moving and when.

The authors specifically looked at location data in the United States and narrowed it down to identify individual trips made by anglers. By quantifying geographic patterns of fishing activities and assessing how these patterns change seasonally, the authors explored angler behavior (fishing frequency and distance traveled) between sites.

“We were predominantly interested in where people were fishing and the amount of time between their trips to different lakes,” said Fricke. “The length of time determines the types of species anglers unintentionally move, as each species has very different survival rates out of the water.”

The authors were also interested in the routes people were using to travel between fishing locations.

What they found was the vast majority of road distances traveled are over small spatial scales. Most anglers are staying near urban areas, but fishing multiple different lakes or rivers in a small radius over a short amount of time. The authors then focused on “invasion hubs,” water bodies that have many linkages via human movement to other nearby water bodies. The timeframe of these movements, which was mostly two days or fewer, fell well within the out-of-water survival threshold for the six invasive species identified in the study.

“Boiled down, people are moving a lot and they’re moving quickly from one place to the next, which has the potential to move a number of different invasive species,” said Fricke. “I don’t think we need to change the preventative measures that we use in light of this data, but it does enable us to better locate those preventative measures in space and time.”

Identifying highly trafficked roads near invasion hubs can be valuable from a management perspective and can help influence where roadside inspection stations and educational signage are placed. 

“If we see points in these data where invasion hubs exist and where resources are not being allocated, this gives managers the opportunity to identify and implement required boat cleaning and boat inspection stations in those locations,” said Fricke. “This kind of data offers a ripe opportunity to reassess where we’re enacting preventative measures and to be more strategic about where we do that.”

Other co-authors are Spencer Wood and Dustin Martin of ReelSonar. This research was funded by the Gordon and Betty Moore Foundation, the Alfred P. Sloan Foundation, and the Edward Allen Power, W.F. Thompson and Mary Gates Endowment scholarships.

Plastic pollution is an increasingly present threat to marine life and one which can potentially impact your dinner table. 

Oysters, and other economically valuable shellfish, filter their food from the water where they may also inadvertently capture tiny microplastics. The ingestion and accumulation of these microplastics can have detrimental effects on their health and may be passed to other animals, including humans, through the food chain.

In a recent interdisciplinary study, 91̽�� researchers at the School of Aquatic and Fishery Sciences, Department of Chemistry and Department of Materials Science and Engineering used advanced methodologies to accurately identify and catalog microplastics in Pacific oysters from the Salish Sea. They have discovered that the abundance of tiny microplastic contaminants in these oysters is much lower than previously thought. The were published in January in the journal Science of the Total Environment.

“Until now, not a lot of chemical analysis has been done on microplastics in oysters,” said co-author , a 91̽��doctoral student in chemistry. “The microplastics that chemists have looked at in previous studies are slightly bigger and easy to visually recognize, but with oysters, the microplastics are much smaller and harder to identify.”

In their study, the team sampled wild Pacific oysters harvested from Washington’s state parks throughout the Salish Sea. Using standard processing methods, the oysters’ tissue is dissolved and the remaining solution is passed through a filter. The filter collects all of the possible microplastic particles.

“Observation of filters is the method researchers have typically used, so if we had stopped there, we would have thought all the oysters had microplastics because small particles were present in most of the filters,” said lead author , a 91̽��postdoctoral researcher at the School of Aquatic and Fishery Sciences.  

Martinelli’s initial observations under a dissecting microscope revealed what were thought to be high numbers of microplastics left behind in the testing filters, but when Phan further analyzed those filters with three advanced chemical identification techniques, they realized that most of what was left in the filters was not actually plastic.

“When we’re characterizing plastics, or any polymers in chemistry in general, we have to use multiple techniques, and not every technique will give you a full picture. It’s half a picture or just part of the picture,” said Phan. “When you put all those pictures and characterizations together, you can have a more complete understanding of what the composition or identities of these particles are.”

During their analyses, the team realized that many of the particles were, in fact, shell fragments, minerals, salts and even fibers from the testing filters themselves. In the end, they found that only about 2% of the particles distilled from the oysters could be confirmed as plastics. 

“Most people so far have not used the combination of techniques or instruments that we used,” said Martinelli. “It’s really easy to stop at the first part and say, ‘Oh, there’s a lot of particles here. They look like plastic. They must be plastic.’ But when you actually go deeper into the chemical composition, they might not be.”

The number of plastic particles that the team found was relatively low compared to the total number of particles analyzed; however, they stress that while it appears Pacific oysters are not accumulating large amounts of plastic, they could not identify 40% of the particles observed due to technical limitations. The researchers also acknowledge that while using a combination of instruments is the most complete way to analyze these particles, access to the equipment, elevated costs and the extremely time-consuming nature of the work are limiting factors for widespread use.

As suspension feeders, oysters pull in water and the particles present in it when they inhale. Particles are then sorted in and out of the animal through their gills. Previous experiments have shown that when oysters are given microfibers or microbeads, they expel the majority of them either immediately or after a few hours. The hypothesis is that oysters’ gill anatomy and physiology might be the reason why the team did not see large amounts of plastic accumulation in their samples.

“A lot of this has to do with how the oysters process water through their gills and how they get rid of particles,” said Martinelli. “It doesn’t mean microplastics are not in the water, it means that the animals are better at expelling them.” 

In agreement with this, it has been suggested that suspension-feeding bivalves like oysters might not be good indicators of pollution in estuaries because they naturally expel microplastics instead of ingesting them, which is good news for consumers that like eating oysters.

Other co-authors are , a 91̽��professor of materials science and engineering, and , a 91̽��assistant professor of aquatic and fishery sciences.

This research was supported by NOAA-SK and the Royal Research Fund awarded to Padilla-Gamiño. Part of this work was conducted at the Molecular Analysis Facility, a National Nanotechnology Coordinated Infrastructure site at the 91̽�� supported in part by the National Science Foundation, the 91̽��, the Molecular Engineering & Sciences Institute and the Clean Energy Institute, and the Washington Research Foundation.

For more information, contact Martinelli at julimar@uw.edu and Phan at samphan@uw.edu.

Grant number:  NNCI-1542101 (NSF)

As oceans absorb more carbon dioxide, they are becoming increasingly acidic and shifting the delicate balance that supports marine life. How species will cope with ocean acidification and the other consequences of global climate change is still very much unknown and could have sweeping consequences.

Researchers from the 91̽�� School of Aquatic and Fishery Sciences have discovered that ocean acidification impacts the ability of some oysters to pass down “memories” of environmental trauma to their offspring.

The two papers were published in December in and the .

“Warming and acidifying oceans negatively influence many marine species. However, some species that live in extreme environments, such as the intertidal, may be more resilient than others to these changes,” said , one of the two lead authors and a graduate student in aquatic and fishery sciences. “Some species may even be able to pass on memories of harsh conditions to their offspring, making them more capable of surviving in similarly harsh environments.”

Researchers studied two species of ecologically and commercially valuable oysters found throughout Puget Sound: the Olympia oyster and the Pacific oyster. Although oyster larvae are sensitive to acidifying oceans, adult oysters commonly occur in intertidal areas and estuaries where they must endure constantly fluctuating water conditions.

It is this hardiness that has researchers hopeful that oysters can withstand an increasingly acidic ocean. If their resilience to stressors can be passed down to their offspring, it could promote an increased tolerance among the future population.

In Spencer’s study, Olympia oysters were exposed to a combination of elevated temperatures and acidified conditions during winter months, mimicking what might happen under climate change. The higher water temperatures caused the oysters to spawn earlier; however, these effects were canceled out when combined with acidified conditions. Researchers then reared and transplanted the exposed oysters’ offspring to four estuaries in Puget Sound. They observed that the offspring whose parents were exposed to acidified conditions in the lab had higher survival rates in two of the four bays.

“We found that Olympia oyster adults were relatively resilient to acidification and warming when exposed during the winter,” said Spencer. “Most interestingly, we found evidence that adult exposure to acidified conditions can benefit offspring by improving survival.”

This carryover effect demonstrates that the experiences of oyster parents have a direct impact on how their offspring perform, and juvenile oysters may be more resilient in certain environments when their parents have been pre-conditioned by similar stressors.

In the other study, adult Pacific oysters were similarly exposed to acidified conditions in the lab. The oysters were then placed back in ambient water to recover before spawning. Researchers observed that the embryonic and larval offspring of female oysters exposed to these experimental conditions experienced poorer survival than a similar control group.

“The conditions one generation of Pacific oysters experience can affect how their children perform,” said lead author , a graduate student in aquatic and fishery sciences. “Even if oysters are not in stressful conditions when they reproduce, their previous stressful experiences can impact their offspring.”

These two contrasting results are both encouraging and concerning to Washington’s shellfish industry, which generates nearly . While one study revealed that juvenile Olympia oysters benefited and experienced a survival advantage due to parental exposure to acidified conditions, the other study showed the embryonic and larval survival of Pacific oysters decreased with parental exposure. The authors believe these differing results could be species-specific or because the experiments focused on different life stages of oysters.

Nevertheless, determining how and why some species, such as the Olympia oyster, tolerate ocean acidification and warming helps inform where to focus conservation resources and how to improve growing methods, said Spencer.

“We needed to broaden our understanding of environmental memory when thinking about how oysters or other organisms will persist in the face of climate change,” explained Venkataraman. “The aquaculture industry is part of the fiber of Washington, and understanding how oysters will respond to changes in their environment, like more acidic water conditions, across multiple generations is crucial to sustaining the industry.”

This recent research shows that as the world’s oceans warm and become more acidic due to climate change, species tolerance or sensitivity can’t be defined by looking solely at one generation of oysters.

Additional co-authors are Ryan Crim and Stuart Ryan with the ; Micah Horwith, who completed the work with but now works at Washington State Department of Ecology; and , a 91̽��professor of aquatic and fishery sciences.

This research was funded by the National Science Foundation Grant, the 91̽�� Hall Conservation Genetics Research Fund, the National Science Foundation Graduate Research Fellowship Program, the National Shellfisheries Association Melbourne R. Carriker Student Research Grant, Washington State Department of Natural Resources and Washington Sea Grant.

For more information, contact Spencer at lhs3@uw.edu and Venkataraman at yaaminiv@uw.edu.

A population of humpback whales in the South Atlantic has rebounded from the brink of extinction.

Intense pressure from the whaling industry in the 20^th century saw the western South Atlantic population of humpbacks diminish to only 450 whales. It is estimated that 25,000 whales were caught over approximately 12 years in the early 1900s.

Protections were put in place in the 1960s as scientists noticed worldwide that populations were declining. In the mid-1980s, the International Whaling Commission issued a moratorium on all commercial whaling, offering further safeguards for the struggling population.

A new study co-authored by , and from the 91̽��’s School of Aquatic and Fishery Sciences shows the western South Atlantic humpback (Megaptera novaeangliae) population has grown to 25,000. Researchers believe this new estimate is now close to pre-whaling numbers.

The were published Oct. 16 in the journal Royal Society Open Science.

“We were surprised to learn that the population was recovering more quickly than past studies had suggested,” said Best, a 91̽��doctoral student.

The study follows a previous assessment conducted by the International Whaling Commission between 2006 and 2015. Those findings indicated the population had only recovered to about 30% of its pre-exploitation numbers. Since that assessment was completed, new data has come to light, providing more accurate information on catches — including struck-and-lost rates — and genetics and life-history.

“Accounting for pre-modern whaling and struck-and-lost rates where whales were shot or harpooned but escaped and later died, made us realize the population was more productive than we previously believed,” said Adams, a 91̽��doctoral student who helped construct the new model.

By incorporating detailed records from the whaling industry at the outset of commercial exploitation, researchers have a good idea of the size of the original population. Current population estimates are made from a combination of air- and ship-based surveys, along with advanced modeling techniques.

The model built for this study provides scientists with a more comprehensive look at the recovery and current status of the humpback population. The authors anticipate it can be used to determine population recovery in other species in more detail as well.

“We believe that transparency in science is important,” said Adams. “The software we wrote for this project is available to the public and anyone can reproduce our findings.”

Lead author of the UW’s Joint Institute for the Study of the Atmosphere and Ocean stressed the importance of incorporating complete and accurate information when conducting these assessments, and providing population assessments without biases. These findings come as good news, he said, providing an example of how an endangered species can come back from near extinction.

“Wildlife populations can recover from exploitation if proper management is applied,” said Zerbini, who completed this work at the NOAA Alaska Fisheries Science Center’s Marine Mammal Laboratory.

The study also looks at how the revival of South Atlantic humpbacks may have ecosystem-wide impacts. Whales compete with other predators, like penguins and seals, for krill as their primary food source. Krill populations may further be impacted by warming waters due to climate change, compressing their range closer to the poles.

“Long-term monitoring of populations is needed to understand how environmental changes affect animal populations,” said Zerbini.

Other co-authors are of Alaska Fisheries Science Center and of the British Antarctic Survey.

This research was funded by the Pew Bertarelli Ocean Legacy Project, the U.S. National Marine Fisheries Service-National Oceanic and Atmospheric Administration, the British Antarctic Survey and the 91̽��.

For more information, contact Zerbini at alex.zerbini@noaa.gov, Best at jkbest@uw.edu and Adams at adamsgd@uw.edu.