School of Aquatic and Fishery Sciences

Black swan events are highly improbable events that nevertheless occur, and drive risk estimation in stock market collapses, earthquake frequency, and deaths from the largest wars. But how often do animal populations exhibit surprisingly large booms and busts? A new study finds strong evidence for black swan events in about 4% of animal populations, typically driven by climate, severe winters, predators and parasites. Of particular note, 86% of the black swan events were declines in animal populations, which implies that we need to increase the probability of sudden declines when predicting extinction risk in animal populations, and not rely on predictions coming from a normal distribution. The research appears in the Proceedings of the National Academy of Sciences USA and was conducted by SAFS postdoc Sean Anderson and Prof. Trevor Branch, together with Andrew Cooper and Nicholas Dulvy from Simon Fraser University. More recently, follow-up work in response to a rebuttal acknowledges the important role of immigration and emigration in black swan events, and points out that either population die-offs are more common or that emigration is more rapid than immigration.

The natural pattern of river flows, with frequent flood events, has been substantially altered worldwide through dams and other forms of water diversion for human uses. A new modeling study now shows that changing historical flow patterns results in simplified interactions between plant species in and around rivers, and the replacement of large riverside trees with shrubs. These changes to plant species are influenced by the loss of frequent floods, increased droughts, and a river flow pattern that is more stable than is normal. The new work in Nature Ecology & Evolution was coauthored by SAFS professor Julian Olden.

Native oysters are important players in many nearshore ocean ecosystems, but their numbers are declining worldwide. Restoration success depends on how well oysters survive when transplanted to new habitats. In a new experiment, native Olympia oysters were transplanted among oyster regions in Puget Sound in a reciprocal fashion to see how this affected their survival, growth, and reproduction. There were substantial differences in each small population of Olympia oysters within Puget Sound, providing information on which source population would be best suited for broad-scale oyster restoration in the region. The work by SAFS Masters student Jake Heare, researcher Brent Vadopalas, and Prof. Steven Roberts, together with Brady Blake of the Washington Department of Fish and Wildlife and Jonathan Davis of the Puget Sound Restoration Fund, appears in the journal Marine Ecology.

Fish catch limits are set based on the results of complex fisheries stock assessment models, which are somewhat like weather forecast models, but for fish populations. An examination of historical assessments of Australian fisheries has determined that there is considerable uncertainty in estimates of fish biomass, with a 95% chance that stock assessment estimates of spawning biomass are within half to double of the best estimates. These results are similar to those found in a previous analysis of U.S. west coast fisheries, implying that managers need to take into account this model uncertainty when setting catch limits. The research by SAFS director André Punt and graduate student Kristin Privitera-Johnson, and their many coauthors, appears in the journal Fisheries Research.

Endangered whooping cranes form long-term monogamous bonds, but it has not previously been known when these pair bonds first form. New data now reveals that 62% of breeding pairs actually form more than a full year before breeding, and 28% of breeding pairs begin to “date” more than two years before breeding starts. These findings suggest there are substantial benefits to partnering in addition to breeding, perhaps to support each other when competing with other birds or to increase partner familiarity. The new paper by Claire Teitelbaum, University of Georgia, SAFS professor Sarah Converse, and Thomas Mueller from Goethe University, Germany appears in the journal Animal Behavior.

The Tonle Sap Lake in Cambodia is a seasonal wetland that floods every year during the rainy season. New research examining the isotope ratios in carbon, sulfur, and nitrogen in fish, shows that fish species benefit greatly from this flooding because it expands their access to new and different types of food contained in the newly flooded areas. The resulting highly diverse assemblage of fish species are the basis of a productive fishery that is a major provider of food in the region, which will be impacted in uncertain ways by the planned construction of more than 200 dams in the greater Mekong River Basin that feeds Tonle Sap Lake. The research by SAFS postdoc Thomas Pool, Prof. Gordon Holtgrieve, and their coauthors, appears in the journal Ecosphere.

Chinook salmon on the Snake and Columbia rivers face challenges, notably navigating through hydropower systems, during their migration from freshwater to the ocean; these experiences may change their survival in the ocean. A recent laboratory experiment compared Chinook salmon that were barged through five or seven dams (experiencing cooler temperatures) to those that swim through the hydropower system (experiencing warmer temperatures). Barged salmon survived better in the experiments although it was not possible to tell whether this was because they experienced cooler temperatures or other conditions related to their seasonal migration timing. The research by SAFS researcher Jennifer Gosselin and Prof. Jim Anderson was published in the Transactions of the American Fisheries Society.

A new series of laboratory experiments on Chinook salmon reveals the effect of warmer freshwater on the time from egg hatching to emergence from gravel as fry. Warmer water resulted in fry emerging two and a half months earlier than those exposed to cooler water, after accounting for genetic differences among eggs produced by different combinations of parental fish. The newly emerged fry were also less developed on emergence when exposed to warm water. The new research was conducted as part of a MS degree in SAFS by Abby Fuhrman and other researchers at the Northwest Fisheries Science Center and US Forest Service, and SAFS professor Graham Young. It was published in the journal Ecology of Freshwater Fish.