From
the Field: Tagging Transient Killer Whales in Southeast Alaska -
Part 1
with Volker Deecke
This past summer, killer whale researcher Volker Deecke travelled to Southeast Alaska for a second consecutive field season to study the hunting behavior of transient killer whales at night, and their impact on endangered Steller sea lions and other marine mammals. Using digital recording tags (DTAGs), which attach to a killer whale with suction cups and remain in place for up to 16 hours, Deecke and his team recorded the whale’s underwater movements. The tags also recorded underwater sound at a very high quality, making it easy to identify a ‘kill’ from the characteristic sounds of feeding killer whales.
Deecke’s research this summer was assisted by Ph.D. students, Filipa Samarra (University of St. Andrews) and Ari Shapiro (Woods Hole Oceanographic Institution), as well as field assistants, Michiru Main and Michael deRoos. The following photos and log entries are taken from Deecke’s log on July 18, 2007, when the team witnessed and recorded two predation events.
11:20 (a.m.)
We left our overnight anchorage at 06:00, heading north in the Charles T, a 60-foot fishing vessel. We were hoping to intercept a group of three transient killer whales that we had followed last night, but at 08:20 we received a report of a sighting of 8-10 killer whales in the vicinity. We arrived less than an hour later, and despite searching the area for two hours we only found a distant group of humpback whales.
13:34
A report came in of 3-4 killer whales heading for the Steller sea lion haul-out at Southwest Brothers Island. This haul-out was monitored continuously for an entire year by a UBC marine mammal research team in 2004/2005.  When we reached the island an hour later, it took us only a few minutes to find the whales. We photographed the left flank and dorsal fin of each whale to identify the individuals present. [They were later identified as adult female T124; her two offspring, T124D (born 1996) and T124E (born 1999); adult female T090; and an unidentified calf.]
19:07
We followed the whales at a distance. After a couple of hours, they encountered a lone Steller sea lion, five nautical miles offshore from the sea lion haulout at Sunset Island. The whales began to follow it at a distance, but in full view of their intended prey. Making no obvious attempt to escape, the sea lion continued to slowly swim in the direction of Sunset Island.
The standoff ended suddenly when the whales moved in for the kill. After ten minutes of intense ramming and tail swipes, the whales moved away to rest as the shaken sea lion continued its slow swim towards Sunset Island. This pattern of attack and rest was repeated several times, helping the killer whales to avoid injury between attacks. They stayed out of reach and allowed the internal injuries they had inflicted on the sea lion to take their toll.
 21:00
The sea lion’s breathing became labored, probably because the persistent ramming had fractured some ribs. Meanwhile, we hoped that the whales were distracted enough to allow us to deploy one of our tags. This time I steered the boat and Mike wielded the tagging pole. We positioned the boat close to the sea lion, in the hope that a whale would surface close enough for Mike to deploy a tag. At the same time, we maintained a safe distance from the attack.
The younger whales moved closer as the sea lion became increasingly debilitated. While they did not participate in the initial attack, we now observed T124E executing a few impressive tail swipes, and even the calf was having a few runs at the sea lion. This was probably an important opportunity for the young transients to learn essential hunting skills without risking injury.
 21:17
Success! I moved the boat to within a few yards of the sea lion, and T124E surfaced less than eight feet from us. Mike deftly applied the tag behind the dorsal fin. The next time the tagged whale surfaced, we photographed it to confirm its identity and to document the tag’s position. The light was fading fast, but the pictures were good enough.
21:48
We can no longer see the sea lion, and assumed the attack was probably successful. This time, there is no need to stay around to look for prey remains – the tag will record the characteristic crunching sounds that indicate a successful attack. We left the whales to their meal, and returned to the Charles T.
This research was funded by:
Feb. 13, 2008 |
