Last week, we had the opportunity to observe one of the most exciting humpback whale behaviors in Southeast Alaska - lunge-feeding! Lunge-feeding is a cooperative foraging strategy that occurs when a group of whales works together to corral prey and herd it towards the surface. The water surface acts as a barrier to trap the prey. Once the prey - fish such as herring or pilchard - are pushed towards the surface, the whales lunge up out of the water with their mouths open and engulf thousands of gallons of water and prey. It is truly one of nature's wonders to witness and we are fortunate that it occurs fairly regularly in Southeast Alaska during the summer.
When whales lunge-feed, they often perform another behavior called bubble-net feeding. This occurs when whales blow bubbles out of their blowholes underwater and form a net of bubbles to trap the prey. During our observations last week, the water was choppy so we couldn't see a bubble ring at the surface but it is possible that the whales were bubble-net feeding.
About 10 whales were lung-feeding together when we first saw the group. There were also a few individual whales in the area feeding on their own. After a few minutes, these individual whales joined the group and the group size grew to about 15 whales. It was neat to see this changing group dynamic over the course of the hour that we observed the whales.
We also observed a calf in the group. The calf, being too unexperienced to participate in the lunge-feeding, remained at the surface while its mom and the rest of the group dove. He/she would splash at the surface, performing some tail slaps, and then join the group when it surfaced.
The typical dive time of the group was about 5 minutes, so we could predict when the group would surface. It was more difficult, however, to predict where the group would surface. For this, we looked to the birds. Over 100 seagulls were flying around at the surface, waiting for the whales to push the fish towards the surface so they could also get a meal. By watching the direction and area where the seagulls were flying, we could position the boat in the area where the whales surfaced. This helped us to obtain photos of the whales' flukes, which are important in identifying individual whales.