The Ice Margin and Fjord Communities of the Upper Bay
The glacier-scoured mountainsides and ice-choked fjords of upper Glacier Bay seem an unlikely home for anything. The fjords are deep, sometimes over 150 fathoms (900 feet), cold, silty and covered with a lens of fresh melt water from the glaciers. If the fjords have tidewater glaciers feeding into them, as do Johns Hopkins and Tarr inlets, then they are often packed with chunks of rolling, breaking ice that can quickly open into leads or pack into solid ice, depending on the shifting tides and currents. The surrounding land seems no more hospitable. It is steep, rocky, unstable, barren, and accessible only across icefields and mountain ranges.
In spite of this perception of upper Glacier Bay, a person can sit in a boat off of Margerie Glacier in Tarr Inlet, watching and listening to the cries of thousands of kittiwakes, glaucous-winged gulls, arctic terns and puffins feeding in the cold, silty water, as icebergs break free from the glacier walls around them. In Johns Hopkins Inlet in early to mid June, from a ridge above the inlet, watchers also may see several thousand harbor seals haul out on the icebergs below for pupping and resting. An eagle may observe the entire scene, soaring high above.
Life in the terrestrial environment is much more subtle and dispersed. It's here you find species dependent on the openness, solitude and vast, inaccessible spaces that the land of the upper bay can provide. Wolverine prowl the beaches and open uplands, goats scale near vertical cliffs, and Kittlitz's murrelets, seeking out the most barren and isolated spot they can find, will call a lichen-covered rock a nest. Into it all come the people who want a glimpse of that wildness, hundreds of cruise ship passengers each day, and a much smaller but increasing number of kayakers and hikers.
Black-legged kittiwakes, (Rissa tridactyla), are small, long-lived gulls that range all along the north Pacific from southeastern Alaska to the Siberian and Asian coast. They are colonial nesters, typically found in dense aggregations on steep, coastal cliffs. They can build their nests on the narrowest of ledges, sometimes constructing them so they overhang the ledge by more than half. In Glacier Bay many of the colonies are within sight, if not right at the edge, of the glacier fronts.
Kittiwakes are shallow plunge divers and surface feeders, and so are dependent on prey that lives near the surface or is concentrated at the surface by currents or upwellings. It is the combination of cliffs for nesting and upwellings where food is more abundant that have resulted in the largest and most successful kittiwake colonies being established near the glaciers. It is believed that the introduction of large quantities of freshwater at the glacier face creates a circulation pattern that results in upwelling. Carried in the upwelling are deep-dwelling organisms including many species of amphipods, euphausiids, and fish. When the upwelling brings these organisms up from the deep, salty, dark to the freshwater at the surface they are often killed or stunned by the pressure or salinity change. There, they make easy prey for kittiwakes and other sea birds feeding at the ice front. Myctophids, commonly called lanternfish, are another deep-water species upon which kittiwakes often feed. Small schooling fish such as capelin, herring, and Pacific sandlance also are common prey species. A feeding strategy used by the kittiwakes is to soar back and forth along the ice front until a piece of ice calves off, then to plunge into the turbulent water around the iceberg, seeming sometimes to be crushed by the falling ice, but always emerging, usually with food.
Feeding and sometimes nesting with the kittiwakes at the ice front are several other sea birds: glaucous-winged gulls, arctic terns, horned and tufted puffins, cormorants, and pigeon guillemots. Because most species prefer slightly different nesting substrates, the birds stratify themselves along the cliffs. In the flatter areas near the top, puffins nest in burrows, glaucous-winged gulls build nests on wider ledges at or near the top, and guillemots prefer rocky crevices near the cliff base. The birds share not only nesting and feeding areas but the constant threat of predators as well. Bald eagles have nests in the area and commonly feed on eggs, young and occasionally adults. One summer when the kittiwake colony at Margerie Glacier was being observed carefully, an immature golden eagle was seen preying on the bird colony for most of the summer. Ravens are always around, stealing eggs from all but the more determined gulls. The predator causing the most consternation amongst the birds can be the peregrine falcon. The appearance of a falcon almost always causes the whole colony of kittiwakes to peel off the cliff nests and dive for the water. The falcon will dive on kittiwakes only while they're in the air so if they make it to the water they're safe, but usually one doesn't make it. In contrast to this confusion, the daily appearance of cruise ships and tour boats at the ice front seems to have little effect on most birds' nesting or feeding behavior. In fact, some birds feed in the wake of cruise ships, where turbulence brings food species to the surface.
Tagging studies have shown that kittiwakes will travel some distance from their colony to feed. Researchers have found tagged birds from the Margerie Glacier colony feeding at tidal rips in Sitakaday Narrows in lower Glacier Bay and South Inian Pass in Cross Sound, over 100 miles away.
Kittiwake populations in other areas of the north Pacific have been declining for the last 20 years and the situation has worsened in the last ten years. In Glacier Bay, kittiwake numbers have remained relatively stable in spite of drastic fluctuations in reproductive success. In 1991 and 1992 less than ten percent of the nests at Margerie Glacier produced young. During the relatively warm summer of 1993, 47 percent of the nests produced young. In 1994 and again in 1995 there was an apparent nesting failure. It is thought by researchers at Glacier Bay and elsewhere that food limitations are the reason for the decline in reproductive success. It's not known why food might be more limiting in some years but it is hypothesized that summer temperatures might have an effect on the availability of prey at the surface.
Harbor seals, (Phoca vitulina ) are the gray, splotchy, "earless" seal, familiar to coastal residents throughout the northern hemisphere. In the North Pacific the seals are predators on bottom fish and invertebrates such as cod, flounder and shrimp, and small schooling fish such as herring, smelt, capelin, and Pacific sandlance. Seals also are found in groups feeding on salmon schooling at the mouths of spawning streams.
Seals spend 35 to 45 percent of their day resting while hauled out of the water. This increases to more than 50 percent of the day, during the pupping and molting seasons. Safe haulouts are very important to the seals; most harbor seals use relatively protected areas on reefs and isolated beaches. During the last 100-150 years, changes in the ice conditions in the upper inlets of Glacier Bay have created a predator-free refuge on the floating ice for local populations of pupping, mating and molting harbor seals. They use only the inlets with tidewater glaciers active enough to fill the inlet and keep it full of ice in spite of the flushing action of the tides and currents. In the last decade, Muir Inlet, the large inlet in the east side of Glacier Bay, has been lost as a major pupping area because of the grounding of Muir Glacier and subsequent lack of floating ice.
There are several behaviors of the Glacier Bay seals that indicate they pupped on terrestrial beaches in the distant past. First, seals hauled out on the ice react strongly to disturbances more than 200 meters away. Second, the mothers and newly born pups show little ability to maintain contact with each other should they be forced off their iceberg. These behaviors are much more appropriate for a beach than for the shifting, predator-free ice pack of upper Glacier Bay. Because of the tenuousness of the mother-pup bond during the first day after the birth, the inability of the pair to easily find each other amongst the ice, and the ease with which they're distressed, observers have realized how important it is not to disturb them during this time. Even without human disturbance there are many pups that are seperated from their mothers and quickly die. During the pupping season, from about late May to mid or late June, Johns Hopkins Inlet is closed to boat traffic. While choked with ice the inlet also seems to be unusable by killer whales, one of the few known marine predators of seals. Though bald eagles don't seem to prey on the healthy pups, as many as 12 have been seen feeding in the inlet on seal afterbirth.
During 3 days of the 1996 pupping season, observers counted approximately 4,800 seals in Johns Hopkins Inlet, and 1,200 of those were pups. This is the highest number of seals counted since this monitoring program began in 1992.
Researchers are now realizing that during the seal's molt, in late summer, the upper bay is again used as a major haulout. The seals metabolism slows and they get lethargic and unable to spend as much time in the water feeding.
Another animal aggregation that comes to the nearly predator-free waters of the upper bay at a vulnerable time are molting Canada geese. They seek out the quiet, protected inlets, such as Wachusetts, Adams and Hugh Miller, to use during the time they're flightless. Geese are "synchronous molters", meaning their worn feathers are pushed out of the follicles by new feathers all at the same time. Geese tend to be heavy relative to their wing surfaces - they have high "wing loading". The loss of only a few flight feathers would seriously compromise their flying ability, and so evolution has favored being grounded for a "quick overhaul" rather than a longer period of difficult flying.
Robert Service, a Canadian poet of the early 19th century, wrote of the popularity of the "Ice Worm Cocktail" amongst the hard-drinking miners of the Yukon gold rush. The cocktail was probably straight out of Service's imagination, but the ice worm, a relative of the earthworm, actually exists. It was discovered at Muir Glacier in upper Glacier Bay in the 1880s. An ice worm might easily be passed over as a piece of dirt or debris on the glacier surface, but a closer look would show a segmented worm, one to three centimeters long. Ice worms live by day deep in tiny cracks in the ice, and at dusk move up to feed in areas on the surface of the ice where pollens and algae collect in meltwater rivulets.
The beaches of the upper bay are relatively small and intermittent, but they're still important travel corridors and feeding areas for the exclusive guild of terrestrial animals that make a hard and meager living in the upper bay. Here amongst the dryas mats and willow fringes you might find the tracks of a wide-ranging and solitary wolverine. You might find the well-picked bones of a mountain goat that left the relative safety of the cliffs for a quick, salty, bite of seaweed or beach grass. You might poke open a wolf scat and find mostly mud with a little vole hair or ptarmigan feather mixed in. If you' re on a beach already claimed by a pair of oystercatchers or arctic terns you'll be harassed loudly and unmercifully until you retreat. At a different spot you might find a semi-palmated plover nest that had been abandoned when people camped too close. If you're in just the right place at just the right time and are watching carefully, you might see a just-fledged Kittlitz's murrelet on its first flight, from it's nest in the glaciated uplands, down to the sea.
Wolverines (Gulo gulo) are the largest and most solitary of the terrestrial members of the mustelid or weasel family. They prefer the wild, open areas of upper Glacier Bay and can travel many as 40 miles of its uplands and beaches each day in search of carrion, or prey such as marmot and ptarmigan. Their large teeth and powerful jaws make them well adapted for crushing bone and eating frozen meat. Home range sizes are vast, with males patrolling up to 240 square miles, encompassing four or five smaller home territories of the female. It is only once a year during the summer breeding season that male and female wolverines interact. Wolverines have a delayed implantation reproductive strategy that allows females to become pregnant months after mating. This occurs if and when food supplies and their physical condition are such that they can successfully raise kits. One to three blind and helpless kits are born in snow caves or deep dens, generally in late winter. They grow rapidly, are weaned at about 8 weeks of age, and leave their mother at about five or six months, to forage on their own.
Of all the species found in upper Glacier Bay there is probably none tied so closely to Alaska's coastal glaciers as the Kittlitz's Murrelet (Brachyramphus brevirostris). They nest only on barren uplands in the vicinity of glaciers or glacial cirques and feed among glacially-silted freshwater plumes that discharge into the sea. Only fourteen of the nests have been found and they have been nothing more that an indentation in the gravel or lichen in which one egg is laid. Little to nothing is known of the incubation or fledging time of the chick. It is thought that the first flight the chick makes has to get it all the way to the sea. There it will feed for four or five years until it is sexually mature. Then it flies back up to the barren, glacial uplands to nest.
Glacier Bay is home to at least one fourth of the estimated total population of 18,300 Kittlitz's murrelets. Because murrelets don't breed until they are four or five years old, it is assumed that almost one-third of the population is composed of non-breeding subadults, making it likely that there are less than 7,000 breeding pairs of Kittlitz's murrelets left in the world. Scientists have identified several short-term threats to the murrelet population. Kittlitz's murrelets are considered very vulnerable to oil pollution in the marine environment; an estimated three percent of the world's total population were killed during the Exxon Valdez oil spill. In areas where gill-nets are used for commercial fishing there is significant gill-net mortality of Kittlitz's murrelets. Less obvious, but possibly more detrimental in the long term, are changes in the abundance and distribution of forage fish such as capelin, sandlance, herring and juvenile pollock. This could result from alterations in the food web of the North Pacific ecosystem, perhaps caused by overfishing, or from natural oscillations in the physical and biological environment of the Gulf of Alaska. Scientists believe the biggest long-term threat to Kittlitz's murrelets is the gradual retreat of coastal glaciers. During the last few decades the southernmost population of Kittlitz's murrelet, in the vicinity of LeConte Glacier, has already apparently disappeared.
