Dogbreath
Well-Known Member
Lots of us wish there were more Transients chewing on Seals but according to the research done this past summer Transients know exactly what they want when feeding on Furballs.
From http://www.marinemammal.org/2008/matkin.php
A Feast of Fur Seals
Studying killer whale predation in the Pribilof Islands
This past summer, a research team headed by veteran killer whale researcher Craig Matkin ventured to the Pribilof Islands, a cluster of five tiny islands in the heart of the Bering Sea that hosts the largest population of northern fur seals in the world. The team’s goal was to investigate whether predation by mammal-eating transient killer whales is having an effect on the already-declining numbers of fur seals in the Pribilofs.
Northern fur seals at St. Paul Island
“Since the 1920s there have been reports of killer whales attacking fur seals in the Pribilofs, but nobody had looked at it that closely,” Matkin says. “We had no idea of when or how often it happens, or how serious an effect it has on the population.”
Living aboard a 45-foot research boat for five-and-a-half weeks, the research team logged 35 research days between July 5 and August 13. With the help of a land-based sightings network set up by local biologists Bruce Robson and Phil Zavidil, Matkin and his research partner, John Durban, tallied a total of 22 kills or harassments of fur seals, 10 of which were certain kills.
“We identified 28 individual killer whales right away, and resighted them in various groups during the study,” Matkin recalls. “We also tagged a couple of whales with satellite tags to track their movements, and we found a real pattern in the way they behaved.”
Killer whale leaps on top of a fur seal during the initial stage of the attack
Matkin and team found that the killer whales typically rested offshore during the day, as far as 15-20 nautical miles from St. Paul Island, the largest of the Pribilof Islands, and would return to the island to forage between midnight and 4 a.m. Most of the 22 predation events observed by the researchers lasted up to half and hour, and occurred late at night or very early in the morning.
Disappearing act
“The interesting thing, and what we didn’t expect, is that it was quite lively until July 21, and after that most of the killer whales just left, even the tagged ones,” Matkin says. “It was amazing.”
The sudden disappearance of the killer whales, though perplexing, might be explained by the seasonal changes in their prey. Body condition (including body fat) of male and female fur seals likely declines after they arrive on land to breed, making fur seals less nutritious in late July and August. Matkin suspects that the fur seals’ deteriorating body condition in late summer may make them less appealing prey to killer whales. “Apparently, the killer whales come back in late September when the newborn pups take to the water for the first time,” he notes.
Killer whales move in on a fur seal (left) that has been knocked unconscious by slaps of the whales' tails
Further research
Matkin remarks that St. Paul provided him and his colleagues with a “wonderful natural laboratory” in which they could observe predation occurring within a limited area. The researchers collected excellent data on short-term movement, from which they hope to determine predation rates and the potential impact of killer whales on fur seal populations during the summer.
“We made good progress in understanding how many killer whales were around and when predation was occurring,” Matkin says. “We also discovered something we didn’t expect at all: that the animals leave in the middle of the summer. Now we need to find out what happens during the earlier and later parts of the season in order to get a full picture of predation rates.”
To this end, Matkin is analyzing samples of killer whale blubber, which contains the unique lipid-fatty acid signatures of prey consumed up to 1.5 months earlier. Thus, the blubber samples obtained in mid July should reflect what the whales were eating in early June.
Another part of the research involves recording the killer whales’ vocalizations with underwater microphones. Matkin will compare his own field data, which documents the time and location of 22 kills, with concurrent recordings of each event made from remote autonomous recorders placed on the sea floor and recovered by Kelly Newman, a graduate student at the University of Alaska Fairbanks.
Killer whale with a chunk of fur seal meat after sharing the carcass between three whales
“Transient killer whales vocalize loudly after kills,” Matkin notes. “If we can consistently identify the number of kills just by listening, we can tally them remotely. This would allow us to study the whales year-round, not just in the summer when the seas are calm enough for field work.”
November 4, 2008
From http://www.marinemammal.org/2008/matkin.php
A Feast of Fur Seals
Studying killer whale predation in the Pribilof Islands
This past summer, a research team headed by veteran killer whale researcher Craig Matkin ventured to the Pribilof Islands, a cluster of five tiny islands in the heart of the Bering Sea that hosts the largest population of northern fur seals in the world. The team’s goal was to investigate whether predation by mammal-eating transient killer whales is having an effect on the already-declining numbers of fur seals in the Pribilofs.
Northern fur seals at St. Paul Island
“Since the 1920s there have been reports of killer whales attacking fur seals in the Pribilofs, but nobody had looked at it that closely,” Matkin says. “We had no idea of when or how often it happens, or how serious an effect it has on the population.”
Living aboard a 45-foot research boat for five-and-a-half weeks, the research team logged 35 research days between July 5 and August 13. With the help of a land-based sightings network set up by local biologists Bruce Robson and Phil Zavidil, Matkin and his research partner, John Durban, tallied a total of 22 kills or harassments of fur seals, 10 of which were certain kills.
“We identified 28 individual killer whales right away, and resighted them in various groups during the study,” Matkin recalls. “We also tagged a couple of whales with satellite tags to track their movements, and we found a real pattern in the way they behaved.”
Killer whale leaps on top of a fur seal during the initial stage of the attack
Matkin and team found that the killer whales typically rested offshore during the day, as far as 15-20 nautical miles from St. Paul Island, the largest of the Pribilof Islands, and would return to the island to forage between midnight and 4 a.m. Most of the 22 predation events observed by the researchers lasted up to half and hour, and occurred late at night or very early in the morning.
Disappearing act
“The interesting thing, and what we didn’t expect, is that it was quite lively until July 21, and after that most of the killer whales just left, even the tagged ones,” Matkin says. “It was amazing.”
The sudden disappearance of the killer whales, though perplexing, might be explained by the seasonal changes in their prey. Body condition (including body fat) of male and female fur seals likely declines after they arrive on land to breed, making fur seals less nutritious in late July and August. Matkin suspects that the fur seals’ deteriorating body condition in late summer may make them less appealing prey to killer whales. “Apparently, the killer whales come back in late September when the newborn pups take to the water for the first time,” he notes.
Further research
Matkin remarks that St. Paul provided him and his colleagues with a “wonderful natural laboratory” in which they could observe predation occurring within a limited area. The researchers collected excellent data on short-term movement, from which they hope to determine predation rates and the potential impact of killer whales on fur seal populations during the summer.
“We made good progress in understanding how many killer whales were around and when predation was occurring,” Matkin says. “We also discovered something we didn’t expect at all: that the animals leave in the middle of the summer. Now we need to find out what happens during the earlier and later parts of the season in order to get a full picture of predation rates.”
To this end, Matkin is analyzing samples of killer whale blubber, which contains the unique lipid-fatty acid signatures of prey consumed up to 1.5 months earlier. Thus, the blubber samples obtained in mid July should reflect what the whales were eating in early June.
Another part of the research involves recording the killer whales’ vocalizations with underwater microphones. Matkin will compare his own field data, which documents the time and location of 22 kills, with concurrent recordings of each event made from remote autonomous recorders placed on the sea floor and recovered by Kelly Newman, a graduate student at the University of Alaska Fairbanks.
Killer whale with a chunk of fur seal meat after sharing the carcass between three whales
“Transient killer whales vocalize loudly after kills,” Matkin notes. “If we can consistently identify the number of kills just by listening, we can tally them remotely. This would allow us to study the whales year-round, not just in the summer when the seas are calm enough for field work.”
November 4, 2008
