April Scrapbook

a sea lion necropsy, grazing geese, and other fascinations

In mid-April, I had the privilege of observing a necropsy of a subadult male sea lion that had recently died. The carcass lay near the end of a rocky point. I was fascinated not only to see the big beast close-up but also to watch the well-organized NOAA necropsy team in action (lead veterinarian Kate Savage). The animal had no perceptible wounds, but it was very thin and its stomach held nothing more than a stone, a small clam, and a cluster of round worms. Was it unable to feed, for some reason, or could it not find enough food? The lab reports might identify some ailment but we may never know why the big fellow came to lie on the rocks.

Several days later, I went back out to see if the remains were still there. The carcass had washed up on a high tide nearly to the trees. The bones had been picked quite clean, except for the flippers, which were still covered with skin. Two immature eagles tugged at stringy tissues but could nip off only tiny morsels—hardly worth fighting for. Despite the poor rewards to be had, the trees held several other eagles that were keeping a close eye on the bones. As often happens at carcasses, the intestines had not been eaten, even though the bones were picked bare. What makes that body part undesirable?

The next day, I went to Eagle Beach. Circling a bunch of grazing geese in the meadow (so as not to disturb them) and arriving at the berm near the mouth of the river, I saw a group of fourteen snow geese, resting on a sand bar and wondered if the solo bird that had been around in previous weeks had finally found some friends of its own kind. Walking the beach past the day-use area, I noted that some irresponsible person had dumped an eight-cylinder engine from the highway lookout down onto the upper beach. What are the prospects of getting that big piece of junk out of there?!

As I returned to my car, I saw a very dark bird perched at the top of a small spruce. A merlin! Merlins of the Pacific race are charcoal-black on wings and back, and the chest streaks are thick and dark. This bird looked very burly and husky. Checking a bird guide, I found out that merlins are a bit bigger than kestrels in linear dimensions but considerably heavier. Merlins typically prey on small birds, which seemed rather scarce that day. This sighting was my good prize for the day (my other ‘prize’ was a five-gallon bucket full of trash from the beach).

The following day, I went out on the Boy Scout/Crow Point trail with two friends. Good weather, this time, in contrast to a few days before, when stiff, cold winds had us hiding the trees and sent the ducks and geese into shelter well up the river. On this day, however, the waterfowl were spread out over the sand bars near the mouth of the river. Eagles stood at the edges of the sand bars exposed by the dropping tide. One of them was attended by two or three quick and daring crows that darted in to snatch bits from the big bird’s prey. Six snow geese, heads down, grubbed up food from the meadow soils while several Canada geese stood watch. Later, more snow geese flew in, gliding elegantly on black-tipped wings, bringing the total back to fourteen.

Some sea lions, large and small, cruised along the southern end of the beach, tightly packed together. They were soon joined by another group. The whole gang dithered back and forth but did not appear to be foraging. We wondered if the second group had brought word of a pod of transient killer whales somewhere not far away.

The sands were full of animal track: shorebirds of two sizes (although we saw none of the makers), geese, gulls, ravens, a mystery critter. The wrack line from the last high tide was a very thin line of small debris. We could see that a crow had marched along the line for some distance, no doubt looking for things edible.

The goose-flat meadow was empty of geese, so we strolled across it, looking for signs of emerging green shoots. A sharp whistle brought us bolt-upright and looking toward some trees, where three marmots stood on a small rise. There is presumably a colony of beach marmots nearby, perhaps under tree roots in a sand bank.

Songs of ruby-crowned kinglets and robins entertained out ears, filling out a good early-spring walk.

Winter wildlife extravaganza

in Juneau’s Auke Bay

During late November and early December, 2015, Auke Bay harbor put on a wildlife spectacular, drawing photographers, reporters, and just plain gawkers (such as me). Hordes of young-of-the-year herring, mixed with a few capelin and sand lance, milled around the docks and boats. The banquet of small fish also drew many predators, who put on a good show for observers.

Why are there so many young herring in the harbor this year? There are possibly several reasons, suggests Michelle Ridgway (Oceanus Alaska). It may have been a good spawning season in spring. The sunny spring, plus an El Niño, warmed the harbor waters, even at considerable depths, and all the spring run-off from the soggy land brought in nutrients. Those conditions produced a fine bloom of phytoplankton, which led to good body condition and burgeoning populations of zooplankton. For example, Ridgway has noticed extended reproduction of little shrimp-like crustaceans called mysids, extra-large fat globules in copepods, an abundance of amphipods not far from the surface, and an unusual influx of ‘sea butterflies’ (molluscs that fly through the water). That made excellent foraging for baby herring. In addition, young herring may seek protection from the massive maws of humpback whales by moving into shallower bays and harbors, with docks and boats, where the whales are less likely to forage intensively.

Herring and other so-called forage fishes often form densely packed balls, especially when predators are lurking about. When a predator dives through the ball of fish, the survivors scatter in all directions, but not far and only briefly, before returning to the tight cluster. Researches have called this behavior ‘the geometry of the selfish herd’: each fish trying to put as many other little fish as possible between itself and predators. The result is a tight ball of nervous, jittery fish.

The baby herring in the harbor had every reason to be jittery. The millions of small fish were being attacked on all sides by throngs of predators. They may have eluded most of the whales in the confines of the harbor, but other predators took advantage of the great aggregation.

A gang of Steller’s sea lions cruised rapidly back and forth, diving continually, probably after pollock that were gorging on the herring. The pollock drove the little fish toward the surface. The sea gulls knew this, of course, and hung about, just waiting for the fleeing fish to get close to the surface where the gulls could nab them. Indeed, the fish were caught ‘between the devil and the deep’ (the gulls and the aquatic predators respectively).

Several harbor seals were there, some with well-grown pups. They did their share of fish-driving too, but usually not near the sea lions. I watched one seal surface-swimming slowly along, on its back, in a most relaxed fashion. It may have been looking down into the depths, for eventually its head went down, followed by the plump body, into a mob of fish.

Scattered Pacific loons and little clusters of common mergansers foraged away from the biggest crowds of predators. Marbled murrelets in snazzy winter plumage could be observed at close range; they were much less skittish than in the breeding season.

The most amazing sight was the huge flock of common murres—many hundreds of them. They rafted up just beyond the last float and split off occasional smaller bunches that moved in among the inner floats. They, and everybody else except the gulls, avoided the sea lions that charged to and fro. I had never seen so many murres before, except at the St Lazaria nesting colony on the outer coast. The murres talked to each other constantly, except when they were diving.

murres-in-Auke-Bay-Jos
Photo by Jos Bakker

That huge concentration of murres was arguably the most unusual happening in the harbor. All the other predators visit the area rather regularly to feast on small fish that spend the winter there. Although murres nest on the outer coast, they tend to move closer to shore in winter, congregating where prey is abundant. But we don’t customarily see the murres in such numbers in Auke Bay harbor. Furthermore, over near Glacier Bay, good observers reported uncountably huge numbers of murres moving about.

The throngs of murres may be a sign of bad news, however, according to John Moran (NOAA). A mysterious oceanic anomaly in the Gulf of Alaska called the Warm Blob (because water temperatures are as much as five degrees (F) above average) created nutrient-poor conditions that greatly reduced productivity and thus decreased the abundance of fishes that feed on plankton, or at least caused them to move to deeper waters where diving birds can’t get them. The Blob developed in 2013 and its effects have contributed to reduced nesting success and great mortality of some marine birds in the Gulf. The poor food supply may have been one factor that drove the murres we’ve seen in Auke Bay out of their usual foraging areas in search of better feeding conditions.

All those baby herring in the harbor seem to offer a ready banquet but, in fact, those little fellows have very little fat because they put their energy into growing as fast as they can. On a gram-for-gram basis, they are much less rewarding than capelin or adult herring, for example, and even less than krill, according to data of Moran and colleagues. So a murre or any other predator would need a lot of them in order to survive—and that’s certainly what was available in the harbor.

Humpback whales were reported to pass by the harbor upon occasion, but there are other spots where they might find better foraging. Seymour Canal is a good place for foraging on krill, for example, and adult herring (far more nutritious than the young ones) from all over Lynn Canal winter in deep, dense schools northward of Tee Harbor. When a whale dives deep through such a school of herring, some of the fish try to escape up shallower water, but there the sea lions can get them. Sea lions themselves may attract the attention of transient killer whales; a few years ago, Moran watched killer whales take down five sea lions (plus two probable kills) in five days. But in Auke Bay harbor, the foraging sea lions were quite safe from the killers.

Eagles were notably scarce in Auke Bay harbor during this extravaganza, although they are known to feed on murres (we saw the evidence in Berners Bay one spring). Perhaps the eagles sought out the adult herring to the north.

A little squad of goldeneye ducks quietly kept to themselves along a rocky shore of the harbor. Seemingly uninterested in the shimmering mass of herring, they may have been looking for molluscs.

Thanks to John Moran of the NOAA lab and Michelle Ridgway of Oceanus Alaska for extensive discussion, not all of which could be packed into this essay.

Cruisin’ to Berners Bay

in search of an annual wildlife congregation

Every year, Juneau Audubon offers several spring cruises to Berners Bay, not far north of town. There is always a hope that the cruise might happen to arrive in the bay during the time when the hooligan (=eulachon=candlefish=salvation fish) are running. this is hard to do, because the hooligan spawning run is short, only a week or two, and the timing varies from year to year—and it may be getting earlier than it was a few years ago.

When the hooligan come in, they mill about in the bay for a while, and that’s when the marine mammals enjoy a feast. Whales pass through, and seals hang out on a reef near Slate Cove. Steller’s sea lions stock up on the fatty little fish before heading out to their outer-coast rookeries for pupping and mating. On the rookeries, males don’t feed for several weeks, being busy defending harems and mating; females give birth and nurse the newborns, which costs them a lot of energy—so putting on some fat ahead of all that activity is essential. Years ago, when we studied the predators at hooligan runs, we counted over two hundred sea lions in the bay on some days, making a racket and leaving hooligan-grease slicks on the water.

Hooligan spawn in the lower reaches of the glacial rivers that enter the bay, and sometimes the seals and sea lions follow their prey up-river. It was quite a sight to watch a big bull sea lion humping hastily over the sand bars to reach deeper river waters and the up-running spawners.

thayers-gull-with-eulachon-by-bob-armstrong
A Thayer’s Gull with eulachon. Photo by Bob Armstrong

Birds come to the spawning run in droves. White clouds of over forty thousand gulls would be calling, chasing, pirating fish from each other, loafing on the sands. Eagles lined the river banks—we estimated that there could be a thousand or so. Local ravens and crows scavenged hooligan that were stranded by out-going tides and stashed their prey in the grass or fed them to chicks in the nest. Even dabbling ducks, such as mallards, chowed down moribund hooligan.

In some years, herring also spawn in the bay about the same time as the hooligan run. Herring spawn on the seaweeds along the rocky shores and attract hordes of egg-eating scoters and gulls, along with eagles interested in the fish themselves.

It was all very exciting! But, as a naturalist aboard the cruises this year, I had to tell folks to imagine all that predatory excitement. It seemed as if the hooligan run was over, although gulls still hung out along the edges of the river mouths. We heard rumors that the herring were in, and getting ready to spawn, but it didn’t seem to be happening just yet.

While it was a bit disappointing, perhaps, to miss the big show, I suspect that the folks on board were not unhappy at all. We saw a fine display of “pec-slapping” by humpback whales: whacking the water with powerful slaps of their long pectoral fins. The pectoral fins of humpbacks are longer, relative to body size, than those of other whales. Those mighty pecs are reportedly used to herd small fish, in fighting off attacks by orcas, and in making a swimming whale very maneuverable. They may also be used as some kind of display (still to be studied), and male humpbacks sometimes use them as props for their headstand posture while they sing during the mating season in winter.

Near Tee Harbor we chanced upon several orcas (=killer whales), splashing about and moving along the shores. There were several orcas, including one quite small one, mostly foraging independently, not in a close bunch. I guessed that these were likely to be the fish-eating ‘resident’ sort of orcas, probably after spring king salmon. Orcas had recently been seen near downtown in Gastineau Channel too, and we wondered what had lured them there.

We were treated to the delightful presence of several Dall’s porpoises, rushing hither and thither, sometimes riding our bow waves. A picturesque little flight of swans headed north, against a backdrop of the Chilkats. And I have not even mentioned the pigeon guillemots, marbled murrelets, loons, Arctic terns, scoters of two species, and clusters of Bonaparte’s gulls dipping down to the water surface to snatch some tiny prey.

Altogether, very satisfactory wildlife viewing, and fine days on the water!