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243 posts in Publications

Fishing reduces the abundance of fish parasites with complex life cycles

Fishing removes parasite species that rely on multiple hosts, according to a comparison of fish parasites on three fished islands and three unfished islands in the central Pacific. The new research also finds that the positive relationship between parasite diversity and fish diversity is eliminated on fished islands. However, it remains an open question whether the impacts of fishing on parasite species increase or decrease disease in host fish. 

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With warming, polar bears spend less time in their maternal dens

In recent years (2009-2015) polar bears in Baffin Bay come on to land about one month earlier than they did in the 1990s, largely owing to early sea ice breakup. This has reduced the duration of maternity denning by approximately 27 days. Maternity dens are now at higher elevations than they were in the 1990s as pregnant bears seek places with deep snow. 

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Faster method of dealing with uncertainty in fisheries assessments

Complex computer models are used to estimate sustainable catches in fisheries, by finding the best values for dozens or hundreds of variables so that the models explain data such as trends in abundance and the number of fish at each age and length. Traditionally, software packages are used for this kind of model fitting, most commonly a package called AD Model Builder (ADMB), but more recently a package called Template Model Builder (TMB). 

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Some differences between sexes in coho salmon are not linked to sex-determining DNA

A section of DNA in each species determines sex, and it is usually assumed that the many differences between sexes are due to DNA variability in this section. However, fresh evidence suggests that other parts of the genome also contribute to differences between sexes in many species from humans to fruit flies. A new study examines what parts of the DNA result in males and females reaching sexual maturity at different ages in coho salmon, and what influences their growth rates at young ages, finding that indeed there is some sex-specific control over these traits that comes from DNA outside of the sex-determining section of DNA. 

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Deciding how to best save toads from a deadly fungal disease

The deadly fungal disease Bd (Batrachochytrium dendrobatidis) is a major cause of the wave of recent extinctions of frogs and toads, but it is difficult to decide how to best save amphibian populations from its ravages. Now a new framework has been developed that helps managers decide which actions are the most beneficial. A combination of a model of multiple boreal toad breeding sites, and expert judgment, was used to assess 35 possible actions that either preserve habitat, reduce Bd prevalence, or reintroduce boreal toads to areas where they no longer exist. 

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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. 

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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). 

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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. 

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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. 

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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. 

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