School of Aquatic and Fishery Sciences

Pacific salmon hatcheries aim to supplement declining wild populations and support commercial and recreational fisheries. However, there are also risks associated with hatcheries because the captive and wild environments are inherently different. It is important to understand these risks in order to maximize the success of hatcheries. Inbreeding, which occurs when related individuals interbreed, is one risk that may inadvertently be higher in hatcheries due to space limitations and other factors. Inbred fish may have reduced fitness and survival compared to non-inbred fish. We quantified inbreeding and its effect on key fitness traits across four generations in two hatchery populations of adult Chinook salmon that were derived from the same source. We utilized recent advancements in DNA sequencing technology, which provide much more precise estimates of inbreeding and its potential effects on fitness. Our results indicate that inbreeding may not be severe in salmon hatcheries, even small ones, provided that appropriate management practices are followed. However, we documented an influence of inbreeding on the phenology of adult spawners, which could have biological implications for individual fitness and population productivity. Our findings provide a better understanding of changes that may occur in hatchery salmon and will further inform research on “best” hatchery practices to minimize potential risks.

Article: Waters CD, Hard JJ, Fast DE, Knudsen CM, Bosch WJ, Naish KA. 2020. Genomic and phenotypic effects of inbreeding across two different hatchery management regimes in Chinook salmon. Molecular Ecology https://doi.org/10.1111/mec.15356

The next time you eat sashimi, nigiri or other forms of raw fish, consider doing a quick check for worms.

A new study led by the University of Washington finds dramatic increases in the abundance of a worm that can be transmitted to humans who eat raw or undercooked seafood. Its 283-fold increase in abundance since the 1970s could have implications for the health of humans and marine mammals, which both can inadvertently eat the worm.

Thousands of papers have looked at the abundance of this parasitic worm, known as Anisakis or “herring worm,” in particular places and at particular times. But this is the first study to combine the results of those papers to investigate how the global abundance of these worms has changed through time. The findings were published March 19 in the journal Global Change Biology.

“This study harnesses the power of many studies together to show a global picture of change over a nearly four-decade period,” said corresponding author Chelsea Wood, an assistant professor in the UW School of Aquatic and Fishery Sciences. “It’s interesting because it shows how risks to both humans and marine mammals are changing over time. That’s important to know from a public health standpoint, and for understanding what’s going on with marine mammal populations that aren’t thriving.”

Despite their name, herring worms can be found in a variety of marine fish and squid species. When people eat live herring worms, the parasite can invade the intestinal wall and cause symptoms that mimic those of food poisoning, such as nausea, vomiting and diarrhea. In most cases, the worm dies after a few days and the symptoms disappear. This disease, called anisakiasis or anisakidosis, is rarely diagnosed because most people assume they merely suffered a bad case of food poisoning, Wood explained.

After the worms hatch in the ocean, they first infect small crustaceans, such as bottom-dwelling shrimp or copepods. When small fish eat the infected crustaceans, the worms then transfer to their bodies, and this continues as larger fish eat smaller infected fish.

Humans and marine mammals become infected when they eat a fish that contains worms. The worms can’t reproduce or live for more than a few days in a human’s intestine, but they can persist and reproduce in marine mammals.

Seafood processors and sushi chefs are well-practiced at spotting the worms in fish and picking them out before they reach customers in grocery stores, seafood markets or sushi bars, Wood explained. The worms can be up to 2 centimeters in length, or about the size of a U.S. 5-cent nickel.

“At every stage of seafood processing and sushi preparation, people are good at finding worms and removing them from fish,” Wood said.

Some worms can make it past these screening steps. Still, Wood — who studies a range of marine parasites — said she enjoys eating sushi regularly. For sushi consumers who remain concerned about these worms, she recommends cutting each piece in half and looking for worms before eating it.

For the analysis, the study’s authors searched the published literature archived online for all mentions of Anisakis worms, as well as another parasitic worm called Pseudoterranova, or “cod worm.” They whittled down the studies based on set criteria, ultimately keeping only those studies that presented estimates of the abundance of each worm in fish at a given point in time. While Anisakis worms increased 283-fold over the study period of 1978 to 2015, Pseudoterranova worms did not change in abundance.

Although the health risks of these marine worms are fairly low for humans, scientists think they may be having a big impact on marine mammals such as dolphins, whales and seals. The worms actually reproduce in the intestines of these animals and are released into the ocean via the marine mammals’ feces. While scientists don’t yet know the physiological impacts of these parasites on marine mammals, the parasites can live in the mammals’ bodies for years, which could have detrimental effects, Wood said.

“One of the important implications of this study is that now we know there is this massive, rising health risk to marine mammals,” Wood said. “It’s not often considered that parasites might be the reason that some marine mammal populations are failing to bounce back. I hope this study encourages people to look at intestinal parasites as a potential cap on the population growth of endangered and threatened marine mammals.”

The authors aren’t sure what caused the large increase of Anisakis worms over the past several decades, but climate change, more nutrients from fertilizers and runoff, and an increase in marine mammal populations over the same period could all be potential reasons, they said.

Marine mammals have been protected under the Marine Mammal Protection Act since 1972, which has allowed many populations of seals, sea lions, whales and dolphins to grow. Because the worms reproduce inside marine mammals — and their rise occurred over the same time period as the mammals’ increase — this is the most plausible hypothesis, Wood said.

“It’s possible that the recovery of some marine mammal populations has allowed recovery of their Anisakis parasites.” Wood said. “So, the increase in parasitic worms actually could be a good thing, a sign that the ecosystem is doing well. But, ironically, if one marine mammal population increases in response to protection and its Anisakis parasites profit from that increase, it could put other, more vulnearble marine mammal populations at risk of increased infection, and that could make it even more difficult for these endangered populations to recover.”

Other co-authors are Evan Fiorenza, who completed the work as a UW graduate student; Catrin Wendt, a graduate student in the UW School of Aquatic and Fishery Sciences; Katie Dobkowski of Bates College; Teri King of Washington Sea Grant; Marguerite Pappaioanou and Peter Rabinowitz of the UW School of Public Health’s Department of Environmental and Occupational Health Sciences; and Jameal Samhouri of NOAA’s Northwest Fisheries Science Center.

This study was funded by Washington Sea Grant, the National Science Foundation, the Alfred P. Sloan Foundation and the University of Washington.

For more information, contact Wood at chelwood@uw.edu.

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 University of Washington 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 Ecological Applications and the Journal of Shellfish Research.

“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 Laura Spencer, 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 Yaamini Venkataraman, 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 $150 million a year and provides over 2,700 jobs. 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 Puget Sound Restoration Fund; Micah Horwith, who completed the work with Washington Department of Natural Resources but now works at Washington State Department of Ecology; and Steven Roberts, a UW professor of aquatic and fishery sciences.

This research was funded by the National Science Foundation Grant, the University of Washington 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.

This release was written by Dan DiNicola of the School of Aquatic and Fishery Sciences.