New research published in the journal Ecology finds that a wide-variety of fish and wildlife are professional surfers. But don’t expect to see these animals in the next remake of Point Break, they don’t surf waves of water; they surf waves of food, and it may be their only way to make a good living.A grizzly bear catches the “red wave” by arriving at this tributary stream just as salmon begin to spawn. In a few weeks this salmon run will subside, but the bear can move to other streams with later runs, surfing the wave.
Species ranging from tiny fig wasps to grizzly bears meet their seasonal energy demands by tracking waves of food that propagate across landscapes. In each instance, the food source is ephemerally available at any single location, but the timing of availability varies among locations, creating a wave that lasts for much longer than its component parts.
For example, bears move across watersheds to surf waves of salmon, which allows them to feed on tasty fish for much longer than the 3-5 weeks that they are available in a single stream. Deer, geese, and other herbivores surf waves of plant green-up, moving vast distances to track early stages of growth that offer nutritious foraging. The list goes on, but the message is the same – many commercially and culturally important fauna surf resource waves to make a living off of fleeting food supplies. If the waves were to subside, or if consumers were to lose their ability to surf them, there could be big trouble. Indeed, recent work shows that when drought diminishes the green wave in Yellowstone National Park (USA), migratory elk experience substantial declines in fitness (pregnancy rates plummeted).
Despite their ubiquity and importance, resource waves are rarely accounted for in conservation. Ecosystem-based management typically assumes that the total abundance of food is what matters to fish and wildlife. However, when food sources are ephemeral, animals may be constrained as much by time as they are by food abundance.
A mathematical simulation found that in many scenarios, the degree to which food sources shifted across the landscape (i.e. generated a resource wave) mattered more to animals than total food abundance. In other words, adding more food only helped animals if they had time to eat it. This emphasizes that we should think beyond abundance when managing harvest, permitting resource development, or prioritizing areas for conservation.
For example, when scientists evaluate the effects of a mining proposal in a salmon-bearing watershed, they typically place heavy emphasis on the total number of fish under the footprint. If bears made the rules, they would likely worry less about total counts of fish and more about timing. Salmon populations with unique spawning dates contribute disproportionately to the resource wave. Specifically, early-spawning salmon tend to occur as small populations in tiny spring-fed streams. These fish make up an unimpressive fraction of the total salmon run by numbers, but comprise a substantial fraction of a bear’s seasonal food supply because they are the only salmon available for the first month of the season (plus they’re the easiest to catch). Conservation planning would often not place value on small streams, yet they may be critical to the duration of the salmon resource wave, and thus the energy budgets of bears.
Resource waves are also changing the way we think about landscape connectivity. It turns out that many animal migrations surf resources waves. The seasonal migrations of mule deer, zebra, and several species of geese are timed to track the green wave and follow the emergence of young grasses. These wide-ranging migrants need more than just a path connecting their winter and summer range – they need a path that follows the green wave and provides quality foraging while they travel. Nobody wants to go on a road trip without snacks.
— Jonny Armstrong, Department of Fisheries and Wildlife, Oregon State University.