From
the Field: Tagging Transient Killer Whales in Southeast Alaska
 Part II: Night-time Follow and Tag Recovery
with Volker Deecke
The following photos and log entries are excerpted
from Deecke’s
log on July 18 and 19, 2007, when the team tracked a group of killer
whales to recover a digital recording tag (DTAG). The data retrieved
from the DTAG will provide valuable information on the underwater
and nocturnal hunting behavior of transient killer whales in Southeast
Alaska.
July 18 2007 Tonight we deployed one
of our digital recording tags on T124E, a juvenile transient killer
whale, to record its underwater movements and any sounds it makes
or hears. Attached to T124E’s back with four suction cups,
this non-invasive tag will transmit the whale’s location
every time it surfaces. Ari Shapiro, programmed
the tag to release around 2:30 p.m. tomorrow and float to the surface
for retrieval.
 In the meantime, our job is to follow the tagged whale through a
labyrinth of fjords, channels and inlets to make sure we don’t
lose the expensive tag or its precious data. Losing the tag would
also jeopardize several other research projects conducted by colleagues
around the world, who all depend on the few existing DTAGs to collect
their data.
21:17
As the light fades, we follow the whales at a distance
of one nautical mile so as not to affect their behavior. The group
has only moved a few miles since we deployed the tag, presumably
socializing after attacking a sea lion and feeding on the carcass (see Part
I).
23:30
While the rest of us sleep, team
members Ari Shapiro and Michiru Main work the VHF receiver to track
the tagged whale. They are not receiving a regular signal, presumably
because the tag is quite far back on the tail stock and the antenna
doesn’t break
the surface every time T124E comes up for air. This is bad news;
it is almost dark and the odds of losing the group are rapidly
increasing. I’m hoping that the whales will head for the
harbor seal nurseries of Tracy and Endicott Arm, dead-end fjords
where the floating tag will be relatively easy to spot.
July 19
01:47
The
inevitable has happened: Ari and Michi have received no VHF signals
for over 20 minutes. It seems like we’ve lost the
whales. Tomorrow we will split up and send the Charles T up
Stephens Passage in case the whales continued north, while we search
the seal nurseries in Tracy and Endicott Arm. We head for an anchorage
at the entrance to Tracy and Endicott Arm to get some rest.
 04:00
It is daylight by the time we finally drop anchor. We take turns
looking for the whales with binoculars and scanning for radio signals
using a portable antenna. Twice during my half-hour watch I hear
faint radio signals from the tagged whale, although it is impossible
to determine their direction. We will resume the search this afternoon
after the tag has released from the whale. Once it floats to the
surface, the radio transmitter transmits continuously, making the
tag much easier to locate.
12:36
The tag should be releasing from
the whale within an hour or two, and we begin what is best described
as an “over-gadgeted
Easter egg hunt”. We send the Charles T north to
search Stephens Passage and the adjacent inlets, while we board
the skiff to search the fjords of Tracy and Endicott Arms.
16:12
After a few false starts, the radio antenna finally picks up clear,
continuous signals from the direction of Endicott Arm. We radio
the Charles T and instruct them to call off the search
of Stephens Passage.
 Four miles up Endicott Arm, the direction of the radio signal
suddenly changes from southeasterly to due south. However, radio
tracking in fjords like Endicott Arm can be deceiving – the
steep sides of the inlet reflect the radio signal and mask
the transmitter’s true direction. We head further up the
arm past Sumdum Island to try to get a clearer direction, and one
mile past the island we get a clear signal from our original direction.
It seems that the last signal we picked up was indeed a reflection.
The strength of the signal has increased, suggesting that we are
getting closer to the tag.
17:45
Two miles further, the direction on the next scan changes completely
and we receive a clear and strong signal from behind us and to
the north. What is going on? Did the island block the signal? Have
we been chasing echoes for the last two scans? Whatever happened,
we must be getting very close. Mike now scans continuously while
I steer the boat in the direction of the strongest signal.
Less than five minutes later we spot the tag floating just off
the north shore of Endicott Arm. Mike scoops up the tag with a
dip net and we check the tag for bits of sloughed skin that sometimes
stuck to the suction cups, but find none. These would have been
valuable for genetic analyses.
We have retrieved the tag and its data, but the whales have somehow
eluded us. Endicott Arm is only three miles wide at its widest,
and with the clear visibility and calm sea conditions I don’t
think we could have missed them on their way out of the fjord.
The mystery is solved when the Charles T spots the whales
at the entrance to Endicott Arm at 7:00 p.m., heading for Tracy Arm.
While we were looking for them off the south shore of Sumdum Island,
the only island in the fjord, they must have headed east along
its north shore and snuck past us that way. Once again, Sumdum
Island lives up to its name!
This research was funded by:
March 25, 2008 |
