Peeps and chirps

One of my favorite parts of summer is sleeping with the windows wide open – and, if there’s a pond or a marshy spot nearby, drifting off to the peeps and chirps of frogs calling to one another.

The global chorus of frogs, however, is getting quieter – amphibian populations are declining around the world due to many factors, including habitat loss, climate change, and disease. The deadliest disease amphibians face is chytridiomycosis, an infection caused by a type of fungus called Batrachochytrium dendrobatidis, or Bd for short.

Bd infections can devastate amphibian populations and even drive them to extinction, though some locations and species seem to be resistant to the fungus. Scientists believe that environmental differences in temperature, altitude, and moisture influence the ability of some amphibians to survive infection, or avoid it altogether. New research reported in the journal Freshwater Biology suggests that the presence of predators might play a role as well.

Scientists exposed a group of wood frog tadpoles to ‘predator cues’ – in other words, they added the excretions of predacious beetle larvae that had been fed a diet of tadpoles to the tanks containing the experimental tadpoles, signaling to the tadpoles the presence of a predator. Another group of tadpoles were kept under similar conditions, but not exposed to predator cues. The researchers also added Bd, the fungus responsible for chytridiomycosis, to some of the tanks.

The two groups of tadpoles exposed to Bd – those that experienced predator cues and those that didn’t – had equal rates of Bd infection; about thirty percent of the tadpoles were infected with Bd. The infected tadpoles in the predator-present group, however, had less than half as many fungal spores in their bodies as the tadpoles that weren’t exposed to predator cues.

The scientists suspect that the stress-inducing predator cues primed the tadpoles’ immune systems, allowing them to lower their Bd infection loads. “This is an important result,” the researchers note, “because virulence is often associated with Bd pathogen load.” In other words, lower infection loads could translate to higher survival rates.

Amphibian decline is a complex, worldwide problem, but studies on chytridiomycosis and the fungus that causes it move us closer to a solution – and a world in which nocturnal frog choirs continue to sing.

An adult wood frog showing off inflated vocal sacs.

(Image by Dave Huth via Flickr/Creative Commons license)

Salmon eggs

Over 100 years ago, in 1910, workers began construction on the first of two hydroelectric dams that would eventually be built on the Elwha River, on Washington State’s Olympic Peninsula. Before the dams were built (the lowest just five miles from the river’s outlet on the Strait of Juan de Fuca), the Elwha was home to robust populations of several species of Pacific salmon. After the dams were built, most of the river was cut off from the ocean – salmon could no longer migrate back to freshwater to spawn, reproduce, and nourish the streams where they were born.

Last August, three years after the largest dam-removal project ever conducted in the U.S. began, the last section of the uppermost dam was demolished, and just weeks later, salmon were back in the upper Elwha.

Scientists anticipate that salmon will continue to follow their migrations upstream and recolonize the upper Elwha River; as they do so, some will encounter a mysterious population of fish living in Lake Sutherland, a small lake connected to the Elwha River by a creek that comes in above the location where the lower dam used to be.

Those mysterious fish are Oncorhynchus nerka, also known as sockeye salmon or kokanee. Sockeye salmon and kokanee are distinct populations of the same species that tend to either migrate to the ocean and return to freshwater streams to spawn, a trait scientists call ‘anadromy’ (sockeye salmon), or spend their entire lives in freshwater (kokanee). The population of Oncorhynchus nerka in Lake Sutherland was landlocked by the Elwha Dam for a hundred years, but researchers were not sure whether their ancestors were sockeye salmon trapped above the dam when it was built, or kokanee that might never have migrated to the ocean and back at all.

Now, a team of scientists believes they have the answer, and they came to their conclusion based on a humble clue – the size of the eggs the Lake Sutherland Oncorhynchus nerka produce.

As the researchers recently reported in the journal Ecological Research, they compared the Lake Sutherland fish eggs to eggs produced by several populations of sockeye salmon and kokanee from Alaska, Washington, British Columbia, and New Zealand. Kokanee eggs tend to be smaller than those of sockeye salmon (just as kokanee adults tend to be smaller than sockeye salmon adults). The Lake Sutherland fish themselves were typically about a foot long, the same size as the adults of the kokanee populations and half as big as the sockeye salmon adults.

Their eggs, however, were much larger than the kokanee eggs – and well within the range of the sockeye salmon eggs. The growth of the adult fish in Lake Sutherland appears to have been limited by their inability to access the ocean, and, based on the size of their eggs, it’s likely that the Oncorhynchus nerka in Lake Sutherland are descendants of sockeye salmon.

The scientists note that this has “immediate relevance to the restoration” of salmon in the Elwha River, because “it would mean that other traits linked to anadromy might also remain in the population, facilitating the resumption of anadromy in this population.”

Now that the dams on the Elwha River have come down, several species of salmon will once again be able to migrate upstream to spawn – and some Oncorhynchus nerka may finally be able to make it downstream to the ocean, before returning to freshwater to start the cycle anew.

The Elwha Dam in October 2011, about a month after the removal project began. 

(Image by Sam Beebe via Flickr/Creative Commons license)

Turtle footage

In several of the video clips, a loggerhead sea turtle, shell studded with barnacles and matted with an undulating crop of green algae, is flanked by an entourage of fish, apparently eating the bounty of food growing on the turtle’s shell or perhaps using the large turtles for cover (adult loggerhead sea turtles are typically about three feet long).

In another clip, a turtle, evidently in response to the shadowy presence of a shark, flips over so its shell is facing the threat and swims away.

These and other natural loggerhead sea turtle behaviors were captured on video by a remotely operated vehicle, or ROV, deployed off the coast of New Jersey, Delaware, and Maryland, by a group of researchers from the Coonamessett Farm Foundation and the Woods Hole Laboratory of the Northeast Fisheries Science Center, both based in Massachusetts. They recently published their findings in the Journal of Experimental Marine Biology and Ecology – and, as the scientists note in their paper, the “study represents the first example of an ROV for tracking sea turtles.”

The scientists spotted the turtles from a boat, focusing on areas where loggerhead sea turtles have been active in the past; when they found one, they launched their ROV, tethered to the boat, and followed the turtle wherever it went. Over their 10 research trips (during which they recorded footage of 70 turtles), the researchers found that they could maneuver the ROV to within about three to five yards of the turtle without disturbing it.

From that vantage point, the scientists were able to observe a number of apparently natural behaviors which would have been difficult to capture by other means, such as human divers, cameras attached to turtle shells, and tracking tags implanted into turtles, all of which have been used to study sea turtles in the past. “[T]he ROV add[s] a new technique that complements existing technologies while overcoming several of the limitations,” the researchers write.

ROVs appear to be a new and useful tool for scientists attempting to understand how loggerhead sea turtles behave in their natural environment, and how they interact with each other and other animals.

Loggerhead sea turtles are typically about three feet long and weigh about 250 pounds.

(Image by Richard Ling via Flickr/Creative Commons license)

Vanishing glaciers

The sky was cloudless, a spotless expanse of endless blue, and not a single breath of wind rippled the water of Bowman Lake, a long and slender finger of water nestled between two ridges in the northwestern corner of Glacier National Park.

After growing up on the east coast, nine years ago this summer I visited the American West for the first time, and I understood why Montana is nicknamed “Big Sky Country.” I spent eight weeks at the University of Montana’s Flathead Lake Biological Station, where my fellow students and I dove into our field ecology classes, exploring the mountains and lakes of northwestern Montana along the way.

We visited Glacier National Park on several of our field trips, and one day in particular sticks in my mind – the lake was a perfect mirror for the mountains and the sky, and it was too beautiful for us to leave without taking out our cameras.

The sky and surrounding ridges reflected in Bowman Lake, along with several other photographers, in mid-summer 2006.

(Image by Emily Benson)

The majestic scenery of Glacier National Park, however, is changing – scientists estimate that by 2030, all of the park’s glaciers will be gone, melted under the force of global climate change. As the National Park Service notes, “the park’s glacially fed streams provide a constant flow of cold water throughout the summer season, maintaining necessary water levels and regulating stream temperature for fish and other aquatic species. Plant and animal species throughout the park rely on this flow.”

One of those animal species is the western glacier stonefly, an aquatic insect that, in the past, has only been found in alpine streams in Glacier National Park.

Recently, a group of scientists (including one of the professors that I studied with during my summer in Montana) surveyed all of the locations where the western glacier stonefly has been found in the past, as well as some similar habitats, in order to determine whether their distribution is shrinking along with the glaciers in the park.

The researchers detected western glacier stoneflies in only one of the six streams where they’ve been found before; they also found the stoneflies in two new alpine sites within the park, as well as one site about 335 miles away in Grand Teton National Park.

The scientists note that further study on the “status, distribution, and vulnerability” of the western glacier stonefly is warranted, but the results they’ve already gathered “suggest that an extremely restricted historical distribution of [the western glacier stonefly] in [Glacier National Park] has been further reduced over the past several decades by an upstream retreat to higher, cooler sites as water temperatures increased and glacial masses decreased.”

At some point, the western glacier stonefly will run out of mountain as the population searches for higher and higher sanctuaries, and, left with no place to go, it may face extinction. Glacier National Park is still beautiful today, but it isn’t the same park that I visited nine years ago. In nine more years, will there still be a place within the park’s borders where the western glacier stonefly can feel at home?

An adult western glacier stonefly.

(Image by Joe Giersch/USGS)