Salmon
The 14,000-foot peaks of the Fairweather Range, just west of Glacier Bay, stand poised to catch the moisture-laden storms that blow in from the north Pacific. Once caught, these storms drop their load of snow and rain. The rain percolates down through the trees and moss, joins with other trickles to become streams, and those streams join with others until they return with a rush, back again to the ocean. The snow, if it doesn't melt, is buried, compressed and turned to ice and at a glacier's slow, deliberate pace it, too, returns to the sea. This water, as drenching rainfall, trickling stream, sediment-moving river, and sculpting glacier, is one of the most important factors in defining the Glacier Bay ecosystem. Dependent on the water is another defining component of the Glacier Bay region — the salmon.
Pacific salmon are anadromous, meaning that they are born in freshwater, migrate to the sea, return to freshwater and spawn; and semelparous, meaning that the fish dies after spawning. It is thought that salmon probably became anadromous in the course of adapting to the cycles of ice and water that have dominated their range since the Pleistocene, when they evolved to their present form in the cold, nutrient-poor freshwater of the glaciated north Pacific. Spawned in the cold, oxygenated gravels in upland streams, then feeding and maturing in the rich marine environment, they take full advantage of both worlds.
All of the five species of Pacific salmon found in North America feed and move through Glacier Bay and its surrounding waters. All but chinook salmon are known to spawn in Glacier Bay's streams. Chinook spawn in the large rivers of the Yakutat area, just to the north. Each species of salmon has a different schedule for migrating between freshwater and saltwater and each has different requirements for spawning and rearing.
Chinook salmon (Oncorhynchus tshawytscha), are adapted to long or steep rivers and build size and strength during as many as five years feeding at sea after up to a year in fresh water. A Chinook salmon weighing 145 pounds was caught off the coast of Alaska.
Coho salmon (Oncorhynchus kisutch) have a migration schedule much like that of the Chinook salmon, though it spends less time at sea - usually only 18 months to 2 years. During the year or two that young coho spend in fresh water, researchers have found small, spring-fed streams and tributaries to be very important to them, especially during winter and times of flooding. The presence of riparian vegetation has also been found to be very important. It stabilizes the banks and fallen trees and branches create the pools that young coho need to feed in.
Sockeye salmon (Oncorhynchus nerka) exhibit a greater variety of migration patterns than other salmon and show a wide variety of racial adaptations to specialized spawning and rearing habitat combinations. They generally use a lake rearing habitat during the 1 to 3 years they spend in fresh water. After leaving freshwater they spend from 1 to 4 years feeding at sea before returning to freshwater to spawn.
Chum salmon (Oncorhynchus keta) are second only to Chinook salmon in size and are the most widely distributed of all the Pacific salmon. They spawn in streams of various sizes and the fry migrate directly to the sea soon after emergence. Adults return to their home streams after spending 2 to 5 years feeding in the north Pacific.
Pink salmon (Oncorhynchus gorbuscha) are the smallest and most abundant of all the Pacific salmon species. They also have the shortest and least varied life cycle of all species. Upon emergence from the gravel the pink salmon fry migrate quickly to sea and grow rapidly to 3 to 6 pounds before returning one year later to spawn. Pink salmon generally make relatively short freshwater migrations - usually spawning within a few kilometers of the sea. In some streams they even spawn in the tidally-influenced lower reaches of streams.
Wolf Point Creek, in upper Glacier Bay has been ice free for less than 10 years. Icebergs still float by its mouth and along much of its length. Dryas and alder are just starting to disguise the moonscape of glacial deposits. Here, in the shadow of the glaciers, salmon now make their way up Wolf Point Creek to spawn. In 1993, 2,000 pink salmon, 44 chum salmon, and 19 sockeye salmon were counted spawning in Wolf Point Creek by researchers. As a possible diversification and survival strategy, a small percentage of the spawners in a population stray to spawn in new streams, and that percentage may increase in years of exceptionally large runs, or dry years when spawning habitat is diminished. These fish seem to be finding the streams of upper Glacier Bay.
The existence, species diversity, and abundance of salmon in recently deglaciated steams is dependent on several environmental factors. Primary among them are temperature, sediment loading and stream discharge. No salmon have been found in the cold, turbid meltwater streams that emerge from retreating ice. Clearwater tributaries with warmer summer temperatures support small numbers of salmon, such as those seen in Wolf Point Creek. In more mature streams where stabilizing riparian vegetation and pool and riffle sequences are more developed, and in streams with flow and sediment-buffering lakes within the system, more salmon and a greater diversity of salmon are found. The Berg Bay North stream, draining into the middle reaches of Glacier Bay, with its lake system and maturing spruce forest, supports runs of tens of thousands of pink salmon, thousands of sockeye and hundreds of chum and coho.
Describing life histories, migratory pathways and semelparousity makes the life of Oncorhynchus seem like a tidy, closed, cycling of biomass. In reality it's messy and extravagant, and rather than a closed circle, the salmon weaves its way into the life stories of almost all of the creatures within its range. From its beginning as an egg to the last scraps of flesh from a spawned-out adult, the salmon provides food and nutrients for plants, fish, birds, mammals and man. Thousands of fertilized eggs must be deposited in the redd or nest of the salmon so that one of them might grow, survive and make its way back to spawn again. The rest are the salmons unwitting contribution to the food chain.
You can usually smell and hear an active salmon stream before you see it. The sickly sweet smell of decaying salmon flesh mixes with the smell of wet, crushed grass. Gulls shriek, eagles squabble, ravens croak, bears splash, and behind it all are the constant, skittery splashes of hundreds of salmon making their way up the stream, often so shallow that the males' humped backs stick out of the water.
At the mouth of the stream, where the fresh water mixes with the ocean, the sea-bright salmon that are going to spawn in the stream begin gathering. It is here that the salmon begin to change from sleek, silvery, ocean feeders to humpbacked, hook-jawed, mottled spawners. The gathering salmon are easy prey for the seals, sea lions and eagles that gather, too, to gorge themselves on the rich flesh of the salmon. Even after the predators are satiated, most of the thousands or tens of thousands of salmon remain to make their determined way up the stream to the place where they were born.
Once in the stream the salmon are even more vulnerable. Bears, both black and brown, actually seek out and defend the best of the fishing sites along the stream and many different fishing techniques are used and taught by sows to their cubs. Wolves, where their range overlaps with salmon, are sometimes seen feeding at salmon streams. Most birds and small mammals aren't big enough to catch and carry off a live salmon but do very well scavenging off carcasses left by the larger predators. Once the salmon have spawned and died, their carcasses are available to anything able to carry them off. Sometimes, when there are lots of carcasses available, the larger animals will eat only the more nutritious parts, leaving the rest of the fish for the other scavengers.
Eagles carry fish off to their nests where the discarded bones and bits feed smaller animals and fertilize the forest. River otters and mink carry them to pungent feeding mounds in the forest or in the beach fringe. Even bears will often take a hard won fish off into the woods, away from the fracas along the stream, to eat in peace. In these ways the salmon's influence reaches far beyond the bounds of the streams. Scientists are finding that up to fifty percent of the biomass in juvenile salmon, stream invertebratesm and even streamside vegetation is derived from salmon carcasses.
Black bears (Ursus americanus) are generally found throughout the forested mainland and the southern islands of southeast Alaska. Brown bears (Ursus arctos) are found on the mainland and on the three northern islands of southeastern Alaska, including the Glacier Bay area. In areas where their ranges overlap black bears generally keep out of the way of the larger, more powerful, brown bears. Both brown and black bears evolved from a dog-like carnivore into an omnivore with the canine teeth of a wolf and the grinding molars of a pig or a human. Their stomachs are still those of a carnivore and can digest only high quality vegetation such as berries, shoots, and tender roots.
After emerging from dens in the spring, both brown and black bears forage on newly emerging shoots and tender roots, on beaches, salt marshes and south-facing open slopes. In mid-July most bears move to the salmon streams. Comparing the body weight and the size of the home ranges of coastal and interior brown bears gives an idea of how important salmon are to the coastal brown bear. Coastal bears grow larger because of their protein-rich diet of fish and their home ranges are much smaller because of the abundance and concentration of fish in spawning streams. Researchers have found bear densities as high as 1 bear per square mile on salmon-rich, Admiralty and Chichagof islands in southeast Alaska. By comparison, brown bears in Alaska's sub-arctic use up to 300 square miles. In mid-September many bears have left the spawning streams and begun moving up to the subalpine meadows and avalanche slopes, where they feed extensively on berries before denning up in late October.
The story doesn't end with the death of the spawned out salmon. Each female salmon has left behind thousands of eggs — ranging from 1200 eggs in pink salmon to 17,000 eggs in a large Chinook salmon. Often, eggs laid by one fish are disturbed by another fish digging a redd for their eggs. These drifting eggs become food for many different birds and fish.
Back in the early 1920's it was decided that the anadromous Dolly Varden char were serious predators on salmon eggs and young, and a bounty program was established — each tail was worth five cents. After running the bounty program for 20 years the U.S. Bureau of Fisheries discovered that most of the tails turned in for the bounty came from rainbow trout and salmon, the very species they were trying to protect. Moreover, studies were showing that Dolly Varden may actually benefit salmon in many ways. For example, by eating the drifting eggs, which quickly die and often develop fungal infections, Dolly Varden protect healthy, buried eggs from possible infection.
The eggs that remain undisturbed and healthy in the streambed gravels overwinter there and hatch in late winter. The fry remain in the gravel until they have absorbed their yolk sac, then emerge into the current in the spring. The juvenile pink and chum salmon make their way immediately to the sea, while the coho, Chinook and sockeye juveniles spend from one to three years feeding and being fed upon, in freshwater streams, ponds, sloughs and sometimes salt marshes. Whether they spend 3 days or 3 years in freshwater, during this time they are particularly susceptible to predation by red-breasted mergansers, great blue herons, Dolly Varden char, bald eagles, gulls, and many other species of birds, small mammals, and fish. If they make it through the gauntlet of freshwater predators to the sea, they find more predators waiting for them there — not the least of which is man.
Logging, mining, urban development, water pollution, and overfishing are all threats that have taken their toll on salmon populations to the south of us, in California, Washington, Oregon and British Columbia. Many of the huge wild stocks on the major rivers, and in many of the smaller rivers and streams, of the Pacific coast south of British Columbia have been reduced or are gone. While salmon in the Glacier Bay area face some of those same threats, stocks presently appear to be healthy. With the goal of protecting these beautiful and marvelously adapted fish, researchers continue to monitor local stocks and learn more of their role in the Glacier Bay ecosystem.
