A blue whale attacks a krill ball from below at Los Coronados Islands, Baja California, Mexico.

In the summer of 1988, Howard Hall captured the first filmed sequence of blue whales feeding on krill underwater. A huge amount of krill had come to the surface near the Los Coronados Islands off Baja California, Mexico, just 15 miles south of San Diego. He filmed massive blue whales in 100-foot visibility as they opened their mouths and swam through layers of krill.

Feeding sardines were pushing some of the krill into tight balls at the surface, making it easier for hundreds of blue sharks to join in the feast. It was a spectacular event that local photographers and filmmakers would not soon forget. It lent an almost mythical quality to krill — for years, on subsequent trips to the open sea, a few serious photographers would look for a telltale patch of red in the great blue background.

A single krill is only about 2 inches in length.
Krill are small shrimplike crustaceans in the order Euphausiacea, with 85 known species worldwide, most of which are found in temperate seas and the Arctic zones. They assemble in huge population masses, with the Antarctic species comprising one of the largest multicellular biomasses on Earth. Scientists estimate the total Antarctic krill population at 125 million tons to 6 billion tons. Krill are a critical food source for a host of animals, including birds, whales, seals, sharks, fish and squid. Like many other marine animals, the blue whale depends largely on krill for survival, while other whales, such as the fin and humpback, supplement their diets with small fish. A blue whale can eat 8,000 pounds of krill in one day during peak consumption.

Krill tend to accumulate in deep canyons, high spots and seamounts, where currents are interrupted and upwelling occurs. At night krill will vertically migrate to shallower surface waters to feed on phytoplankton. Most of the time, however, krill stay beyond human diving depths. Blue whales typically dive to 250 to 600 feet to feed on krill during daylight hours. While working with blue whale researchers, we have watched on the fathometer as blue whales punch though high densities of krill deep below the surface.

Juvenile Pacific sardines feed on a ball of krill at Nine Mile Bank,
San Diego, California.
Krill can occasionally be seen on the surface during the day as they feed in short intervals, but some researchers think this behavior could be related to tides, currents or escape from feeding juvenile fishes and squid.

Krill are especially vulnerable to predation when they go to the surface, and the predators often take advantage. It is a wild scene when marine birds, squid and sardines pound the krill. The whales join in with mouths agape, mowing through hundreds of pounds of krill at a time. During these feeding episodes, the krill begin to jump or dance at the surface as whales approach from below, mouths wide open. At the surface, krill can take on various shapes and looks: individual balls or vast mats or layers that stretch for miles. The krill balls take shape as predators attack them, and they act much like baitfish, continually changing shape to confuse the predators or as many individuals keep trying to get to the center for protection. I have seen krill balls appear like red tornadoes at the surface, spinning wildly and changing shape while small fish and squid attack.

A single blue whale may lazily circle a large krill ball on the surface and make multiple passes to feed. When many whales are present and the competition is high, the aggressive attacks on the krill increase. Mouths come out of the water, and whales cut off other whales to get to the food. Multiple species occasionally join the fray. Humpbacks and blue whales feeding together is not that uncommon off the Northern California coast, and I have photographed blue and fin whales feeding on krill together off Southern California. All three species can occasionally be seen feeding at the same time.

Krill pour into the mouth of a feeding fin whale.
When filming blue whales over the years, film crews have focused on the location of the whales' food source. An underwater sequence of a blue whale feeding on krill is the Holy Grail of filming the blue whale. Production teams may do long shoots of up to 45 days to increase the chances of seeing krill on the surface; about 95 percent of the time the krill are too deep to film. Filming is dangerous when large baleen whales are present. The visibility requirements for success are quite high, and the krill can suddenly reduce visibility to a few feet in seconds. The whales are immense and focused on one thing — food. You can imagine the possibilities.

I have had some unique opportunities to see krill events in the wild. While working on five blue whale shoots for production companies, I have been lucky to witness some great predation situations. The one I remember most clearly was a single minke whale that would go from krill ball to krill ball to eat the sardines feeding on the krill. In 100-foot visibility I could see the event perfectly. The whale stayed about 20 feet away from me and out of good camera range. I couldn't capture it like I really wanted, but that scene is one that I will never forget. Another unforgettable event was watching from our small boat as a group of large Humboldt squid enthusiastically fed on krill with their arms completely out of the water. The krill were so dense at the surface that the squid could use their arms to shovel the krill into their mouths.

A feeding blue whale rolls on its side, exposing its pectoral fin.

Threats to krill populations come mainly from climate change and elevated ocean water temperatures, which can affect productivity and food sources for the krill. Commercial harvesting of krill is growing globally, especially from companies targeting Antarctic krill populations. A major end use of harvested krill is fish farm feed and omega-3 oil for health supplements. The main countries targeting krill have been China, Japan and Norway, but other countries are creating exploratory fisheries, testing for market viability. Some countries, such as the U.S., have regulations against the commercial harvest of krill in its waters. Krill oil and other krill products, however, are abundant in the U.S. market. If the global market expands without strong regulations, it could heavily affect krill populations and the animals that rely on them for sustenance.

Locating krill on the surface is not something that can be planned, predicted or targeted. Protecting krill populations will promote not only the survival of a huge variety of marine life but also preserve krill sightings — one of the ocean realm's great natural events.
Explore More
Watch these videos to learn more about krill.

© Alert Diver — Q1 Winter 2019