Fisheries stock assessments commonly ignore space when assessing the status of small pelagic fish species like herring, anchovy, and sardines, because including multiple areas adds a large of number of parameters to the models. Results from a new simulation framework based on herring in Haida Gwaii, British Columbia, now suggest that stock assessment estimates of spawning fish is improved when the models matched the true underlying changes in fish across areas, and therefore that future stock assessments should always include spatial structure when the fish population can be assigned to subpopulations. The work by SAFS director André Punt and 20 coauthors appears in the journal Fisheries Research.
Tracking the pulse of the Earth’s fresh waters
To detect floods and protect fish and other stream critters, warning systems are needed that track river flow. But while these stream gage monitoring systems have been restored to historical levels in the U.S., they are declining globally. A new study highlights trends in stream gage numbers, and pinpoints areas in the U.S. that need additional monitoring because of a combination of floods, droughts, and risk to biodiversity. The paper by Albert Ruhi (SESYNC), SAFS MS student Matthis Messager, and SAFS professor Julian Olden, appears in Nature Sustainability.
Predators amplify fluctuations in the numbers of small schooling fish
Forage fish are small and densely schooling fish like herring and sardines, that hang out in the open water and become the perfect food for predatory fish, marine mammals, and birds. One key feature of their population numbers is that they have dramatic boom and bust cycles because of ocean conditions, fishing, and highly variable recruitment (numbers of baby fish produced each year). Now, new research shows that increased predation exacerbates the bust part of these cycles, and decreased predation allows for recovery. In addition, variability in predation and ocean conditions has a larger effect than the influence of fishing on forage fish populations, highlighting the key role that natural predators play in regulating the abundance of forage fish. The new paper was written by SAFS postdoc Nis Jacobsen and SAFS professor Tim Essington and appears in the journal Fish and Fisheries.
New study reveals why some fisheries are formally assessed and others are not
Catch limits are set for fisheries in the U.S. based on formal fisheries stock assessments: complex models that seek to explain all the available data and make forecasts, similar to the methods used for weather forecasts. However, because there is a shortage of both data and trained scientists, not all fisheries can be assessed every year. A new study finds that assessments are conducted on 59% of fisheries within fisheries management plans, but only 13% of fisheries outside management plans. Since assessments are more common for large-volume and high-priced fisheries, though, almost all (77-100%) of the catch in the regions examined came from assessed fisheries. Projections of the rate at which fisheries are assessed for the first time, suggest that continued but slower increases in the proportion assessed should be expected in the future, unless funding for training of stock assessment scientists is increased. The new work was conducted by Philipp Neubauer, SAFS research scientist Michael Melnychuk, and NOAA scientists James Thorson, Rick Methot and Kristan Blackhart, and appears in the journal PLoS One.
Freshwater critters rely much less on food originating on land than previously thought
Zooplankton, the living tiny animals in water, are an important component of freshwater food webs, sustaining many freshwater fisheries. It has long been thought that a substantial portion of zooplankton diets come originally from land-based ecosystems, for example from nutrients leaching out of plant matter falling into the water, rather than being based entirely from freshwater sources. Now, a bias has been demonstrated in a key hydrogen-based method used to estimate the land portion of zooplankton diets. This method relies in the ratio of different isotopes of hydrogen that contain either one neutron (1H) or two neutrons (2H, called deuterium), and land-based plants preferentially get rid of the lighter 1H when they transpire water. Most analyses of diet using tracers like these are based on the axiom that “you are what you eat”. However, stable isotope analyses using deuterium are more correctly based on the axiom that “you are what you eat, and drink and swim in”. A critical part of the calculation is an assumption that only 16% of hydrogen in zooplankton cells comes from water, but the new study shows that actually 27% of hydrogen in zooplankton cells comes from water. The net effect of the improved estimates of this critical parameter is that the estimated contribution of land-based matter in zooplankton diets drops from nearly one-third to near-zero. The new paper was authored by three University of Washington professors: Michael Brett from Civil and Environmental Engineering, and Gordon Holtgrieve and Daniel Schindler from the School of Aquatic and Fishery Sciences, and is published in the journal Ecology.
Where were the salmon going, and how many should we catch?
Adult salmon are well known to return to the lake or stream where they hatched, to spawn another generation of salmon. In many places, fisheries catch them in the ocean on the way back to spawning, but before it is possible to assign them to a particular population from a stream or lake. A new model now shows a way forward to disentangling catches that come from multiple salmon populations, using genetics and analysis of scales. The new method combines recent DNA samples with historical DNA obtained from fish scales stored for decades in archives, to assign catches to their natal regions, supplementing more extensive data collected from fish scales that are used to estimate the number of years each salmon spent in freshwater and the ocean. The model is applied to sockeye salmon catches in Bristol Bay, Alaska, which hosts the world’s most largest salmon fishery, but is threatened by a massive proposed mine. The model finds that salmon spending more years at sea before returning, are also more likely to be caught in the fishery, and that there are sometimes large interception rates of salmon heading for one river system but that are caught near the mouth of another river system. The new run reconstruction model estimates large differences in the run sizes of some populations that were formerly thought to be caught in higher or lower numbers. The results will feed back into management estimates of maximum sustainable catch for each Bristol Bay fishing district. A paper describing the method appears in the Canadian Journal of Fisheries and Aquatic Sciences, and is authored by former SAFS graduate students Curry Cunningham and Matt Smith, and SAFS professors Trevor Branch, Lisa Seeb, Jim Seeb, and Ray Hilborn, together with Tyler Dann of the Alaska Department of Fish and Game.
Career advice for scientists from Prof. Tom Quinn
In a retrospective look back on his career, SAFS professor Tom Quinn reflects on the experiences that have shaped his outlook and his philosophy on science, teaching, and mentoring. His experiences have included driving past defunct vulture-topped nuclear reactors, and waking up with bear prints on the outside of the window above his bed in his cabin in Alaska, together with many years working in the field on the long-term studies (since the 1950s) at the University of Washington’s Bristol Bay field program focused on salmon. The field site and the salmon runs themselves, which are the largest sockeye salmon runs in the world, are now threatened by the planned development of a massive mine in the region. Prof Quinn advocates specializing in a topic (such as salmon and trout), and then using that topic to explore broader implications for ecology, behavior, and evolution. He highlights the virtues of long-term field programs, because “there is no such thing as an average year” (Don Rogers), while admitting the frustrations of looking for continued funding when funders are always seeking the new and exciting instead of supporting long-running programs. Ironically, he points out that the two worst things an ecologist can do are to start a long-term field program (because the costs and risks are high but the rewards take a long time to materialize), and to stop one (because of their immense value once underway). Prof Quinn has received numerous teaching and mentoring awards, and highlights that faculty “should be willing to give their best ideas away to their graduate students” (Ronald Merrill), and be aware that different students appreciate different mentoring styles. The full paper is available at the ICES Journal of Marine Science.
Improving genetic methods that estimate migration rates
Estimates of migration are important for understanding and managing natural populations. A statistic known as FST is often used as a measure of the amount of genetic difference expected for a given population size and migration rate. Equations that translate FST into estimates of migration exist but the underlying ideal assumptions often do not apply. Now a new model has been used to test which factors affect FST in a real life example based on Atlantic cod. Results showed that knowledge of the effective population size and biology of the population of interest is sufficient to use theoretical equations to translate FST into a starting point for estimates of migration. The research was authored by Ingrid Spies of the QERM program at the University of Washington, and among the coauthors were SAFS professors Lorenz Hauser and Andre Punt. It was published in the Proceedings of the National Academy of Sciences, USA
Seabirds like hanging out in river plumes
When large rivers discharge their water into the sea, this creates a plume of freshwater that is highly variable. A new study that attached tiny satellite tags to seabirds now shows that both shearwaters and murres prefer to forage in plumes created by the massive Columbia River. In particular, they prefer the boundary areas between freshwater and sea water, since this area is where zooplankton and prey fish species are most concentrated. The seabirds shift where they forage as the plume area expands and contracts in size, and moves north and south of the mouth of the Columbia River. The new paper by SAFS PhD student Elizabeth Phillips, SAFS professor John Horne, and their coauthors, appears in Marine Ecology Progress Series.
Massive new map of genetic variation in rainbow trout and steelhead
Genetic techniques are capable of finding the entire sequence (“genome”) of DNA letters (“base pairs”), and have recently been applied to completely sequence 61 unrelated rainbow trout and steelhead individuals. The study found that one in every 64 letters varied across the rainbow trout examined (with variability in more than 30 million locations), and that there were more than 4 million locations where the individual DNA letters differ substantially. These places of variability are known as single nucleotide polymorphisms (SNPs) to can be used to allocate individual fish to their birth populations, identify genetic variation underlying fitness traits, and characterize genes. The vast new SNP database will be a key resource for future genetic analyses, and was authored by a collaboration between US and Norwegian scientists including SAFS professor Kerry Naish. The paper was published in Frontiers in Genetics.