What fish want

What do fish want? I thought I would try to focus on a seasonally-appropriate question, but also one that I spend a lot of time these days pondering. You might think that it would be simple to figure out what motivates a fish—after all, they probably aren’t influenced by the complex emotions that drive people. But unfortunately, we can’t just ask them (I have often wished for just one hour as a fish—I would learn… and publish… so much!).

In general, animal behavior is driven by a balance between the drive to maintain/gain energy stores, survive, and ultimately reproduce. So when asking why a fish chooses to inhabit a particular area of the river, we start by looking at the environmental factors (such as water temperature and shelter from potential predators) that might be influencing its behavior. In my research, I’m interested in what environmental factors are influencing juvenile steelhead behavior surrounding coolwater refugia (areas that are cooler than the main river, often because of an incoming cold creek). What causes fish to use coolwater refuges? And when the river is really hot, what causes fish to leave the refuge? In asking these questions, I’m hoping to gain an understanding of when these refugia areas are most important to fish.

Juvenile steelhead being measured

A heat image of a coolwater refugia area on the Klamath River (Image from U.S. Bureau of Rec)

Taking a step back… many rivers are getting hotter, both because of climate change (influence of higher air temperatures), and land use practices such as logging and agriculture. Logging the riparian area next to a stream reduces shading,  causing the water to heat up. Irrigation can lead to hotter water temperatures if water is diverted into shallow, slow-flowing irrigation ditches, then returned to the river. The Klamath River in northern California, where I do my research, can reach 80°F in the summer, which feels like bathwater. On cool mornings I would sometimes even get into the water to warm up.

Salmon are a coldwater fish, and prefer a temperature range of about 10-18°C (50-65°F). This means that during the summer, when the river temperatures reach 80°F, they are under serious thermal stress—the high temperatures increase their metabolism, so they struggle to maintain weight. As a result, fish will seek out areas in the river that are cooler, such as areas where tributaries flow into the river (i.e. thermal refugia). You can sometimes see hundreds of juvenile salmon packed into small coolwater refuges. However, fish sometimes leave the coolwater areas, even when the river is hot. Why? This question forms the root of my research.

Juvenile steelhead in a coolwater refugia area

I’m hypothesizing that it’s a trade-off between water temperature and the need to find sufficient food. While the fish gain a thermal benefit by hanging out in the cooler water, the high densities of fish suggest that there may be competition for food, forcing fish to leave for brief periods in search of prey.

To put this dilemma in a human perspective, imagine that it's 120°F outside, and you are in a nice air-conditioned house… with no food. You have the choice to go out and pick some food from the garden, or just stay inside and feel hungry. It’s a trade-off! At what point do you decide to leave? Now imagine that your body temperature changes to that of the outside temperature—so as soon as you walk out the door, your temperature begins to rise. This is what happens for fish, since they are poikilotherms—cold-blooded animals that do not stay in a temperature-constant environment, so their internal temperature varies over a wide range. While they are adapted to function over a certain range of temperatures, water temperatures may be rising more quickly than fish can adapt, leaving them with a shrinking amount of available habitat.

In order to understand when and where coolwater refugia are most important, we need to figure out what specific environmental factors are driving fish’s decisions to enter and leave refugia. To do this, I conducted behavioral field studies on juvenile steelhead at coolwater refugia sites on the Klamath River for the past 3 summers. I put radio tags into steelhead (see video below), and was able to track their movement and body temperature (pretty cool!) over time. So far, I’ve found some interesting effects of water temperature dynamics on the likelihood of fish using thermal refugia… stay tuned! (And to learn more about how I’m researching this, visit my website!)

Put in a larger (non-fishy) context, refugia habitats such as this will become increasingly important as the climate continues to change. Whether it’s a range shift upwards onto mountaintops for a high altitude terrestrial species, or a fish seeking out cooler water, understanding how animals use refugia and when they are crucial to their survival will be an important aspect of preserving some species.

And now, if you’ve made it this far, enjoy the holidays! I, for one, will be enjoying a taste of the fruits of my labor.

A river running free

Last week I went on a hike along the Elwha River in Olympic National Park, Washington. Not only was I excited to get out and hike (which happens far too infrequently these days), but I wanted to see the Elwha now that it’s a completely free flowing river again. The largest dam removal in the world just took place on the Elwha—the two dams that were located 5 and 13 miles upstream of the Strait of Juan de Fuca are now almost completely gone.

Glines Canyon Dam before removal

Glines Canyon Dam as of 11/6/12

 I hiked through the mossy dripping rainforest up above where the dams had been, imagining (or, let’s be honest, hoping) that I would come across Bigfoot around the next bend and make my millions. The ecosystem there is incredibly verdant — temperate rainforest that gets approximately 150 inches of rain annually—with towering Douglas firs, dripping alders and Bigleaf maples, and plenty of mushrooms pushing their way up through the mossy ground. I kept my eye out for Oyster mushrooms, but no luck. I also stopped frequently to scour the turbid water for salmon, since both Chinook and Pink salmon, as well as steelhead, have already been sighted upriver of the lower dam! (Granted, it would be surprising to find them above the upper dam, which is not yet completely gone… but as with Bigfoot, one can hope).

Olympic National Park forest

... Bigfoot?

 While I am a firm believer in ecological restoration, there are not many restoration stories that have brought tears to my eyes, but hearing that salmon are already returning to parts of the Elwha that have been inaccessible to them for the past century did literally make me tear up. It’s also a nice example of how dam removal can be successful. A few months ago, my friend asked me, “Is dam removal good?” A great question! She had been at a party and gotten into a discussion about dam removal. As a scientist and someone generally in favor of ecological restoration, she felt intuitively that dam removal is a good thing, but when asked why, she wasn’t sure. What really are the benefits of taking out dams? To emphasize the importance of this question, you should know that there are about 75,000 larger dams (over 6ft) in the U.S., and an estimated 2 million total. However, most of these were built with only a 50-year useful life-span, and the number of “high hazard dams” in need of either reinforcement or removal is rising sharply.

Map of major dams in the U.S.

 One of the many exciting aspects of dam removal (and one close to my heart) is the benefit to anadromous fish, such as salmon. (Anadromous fish begin life in freshwater, travel to the ocean to grow, and return to the river to spawn). Salmon rely on large amounts of high quality river habitat for spawning, juvenile rearing, and migration. Large dams without fish ladders are impassible to salmon, cutting off enormous amounts of good river habitat. And the habitat that’s left is often lower quality, in terms of temperature (too hot) and sediment composition. Dams block sediment, meaning that lots of fine sediment that naturally flows downriver is blocked behind dams. The result is that you get huge sediment build-ups behind dams (there are 5 billion tons of sediment behind the Glen Canyon Dam!). The downstream impacts of this sediment blockage include a coarsening of the riverbed sediment (since all the fine sediment is trapped upstream), which decreases the amount of good spawning habitat for salmon. In addition to the impacts on salmon, the lack of natural sediment flow has caused substantial beach erosion, since this sediment is what beaches are made of (California beaches are being reduced by ~2.8 million cubic meters of sand per year). 

Towards the end of my hike along the Elwha, I made my way down to the large rocky expanse where the upper reservoir used to be. It was sobering to stand on the bank of what is now a flowing river, and realize that only a year and a half ago, I would have been deep underwater. The floodplain hasn’t reconnected with the river yet, but with the river’s natural flow regime restored, this should happen in time. (Dams drastically alter a river’s flow regime—the pattern of water flow over time—usually by homogenizing it, so that the water flow doesn’t change much throughout the year.) One of the less widely known benefits of dam removal is the restoration of the flow regime. The animals and plants along a river evolve to take advantage of that particular river’s flow regime. For example, cottonwoods time the release of their seeds with floods, to aid in dispersal, and aquatic insects such as caddisflies synchronize their metamorphosis (from aquatic insect to terrestrial adult) with the average timing of flood season. When flow regimes change drastically over a short time period, as happens when a dam goes up, it can be hard for these species to adapt.

Glines Canyon reservoir bed from the air

On my hike, standing in the Glines Canyon reservoir bed looking downstream

As I’m reminded daily through conversations with my husband, there’s a lot of controversy surrounding dam removal. I’ve seen my share of this during my summers doing research on the Klamath River, where the 4 lowest dams are scheduled to come out in 2020. Many people want to keep dams because they are a symbol of progress (at least, the Greatest Generation feels this way), and because they like boating and fishing in the reservoirs. However, since many of America’s dams are old, it’s worth considering the fact that it may be more beneficial (ecologically and economically) to remove than to restore them.

A sign from near where I work on the Klamath River

Another sign from near where I lived...

There’s a lot more to learn about dam removal, but I hope I’ve given you a few good points to fall back on if you find yourself defending its benefits at a party. And if you haven’t seen it yet, you really need to watch this spectacular video of another Washington state dam removal, the Condit dam on the White Salmon River.