National Marine Mammal Laboratory (NMML)
Polar Ecosystems Program
Ice Seal Operations
NMML researchers, were joined by two Alaska Native seal hunters and a wildlife
scientist from the Vyatka Agricultural Academy in Kirov city, Russia, to
conduct research on the four species of ice breeding seals (i.e., bearded,
spotted, ribbon, and ringed seals) that are known to occupy the eastern region
of the Bering Sea in spring and summer. The field work conducted aboard the
University of Washington research vessel Thomas G. Thompson consisted of
shipboard observations for pinnipeds and the capture and instrumentation
of ribbon and spotted seals with satellite-linked dive and location recorders.
Whenever the Thompson was within 300 m of sea ice and moving,
between the hours of 08:00 and 20:00 (Aleutian Daylight Time), observers
were posted on the bridge to record the presence of seals. Information
on the species, group size, and distance from the ship’s track
line (as calculated using angle measurements from inclinometers and
reticle binoculars), were recorded along with sea ice type and concentration,
weather, and visibility. Where possible, the age, sex, and molt stage
of animals was also recorded.
In all, 759 individual seals (Table 1) were observed during 52 hours
and 10 minutes of survey effort covering 925.8 nautical miles (nmi)
of survey line. The number of ribbon seals observed increased as we
On 26-27 April 2006 we surveyed an area (near 58°30'N, 171°18'W)
with very high numbers of seals (e.g., 10-20 seals observed/nmi). (See
map below.) We did not encounter high numbers of seals when we returned
to the same area on 28 April.
Captures and instrumentation:
Capturing individual seals and fitting them with Satellite-Linked Data Recorders
(SDRs) was the primary objective of the ice seal project. SDRs allow seals
to be tracked, and transmit collected data via satellite for later analyses.
Two types of SDRs were used:
SPLASH tag – This tag provides information on the movements, dive, and
haul-out behaviors of the instrumented seal. It is attached to the seal’s
fur using epoxy and will fall off when the seal molts, which is likely to occur
sometime in June. As such, SPLASH data will only be available for 1-2 months
SPOT tag – This tag only provides information on the movements and haul-out
behavior of the instrumented animal. It does not provide dive data, and the
transmission frequency is restricted to once each week to conserve battery
life. SPOT tags are much smaller and lighter than SPLASH tags and are attached
to a cattle ear tag, which is then affixed to the inter-digital webbing of
one of the seal’s hind flippers. As such, SPOT tags do not fall off with
the molt and are programmed to transmit for at least 18 months before exhausting
the battery. Because the seal’s hind flippers are nearly always submerged
while the seal is at sea, these tags are best suited for studying haul-out
behavior and long-term movements between haul-out locations.
|Table 1. Number of seals
observed during surveys.
|| Table 2. Number of
seals instrumented with different SDR types.
||SPLASH & SPOT
While conducting shipboard observations, whenever a seal was seen in a location
favorable for capture (e.g., with a pup, in the middle of a large floe, on
the edge of an ice finger), the Thompson was stopped to launch three Mark-III
Zodiac inflatable rafts. Directed by an observer on the Thompson's bridge,
the three Zodiacs surrounded the seal; researchers jumped onto the
floe and, using long-handled nets, captured the seal. After physically
restraining the seal, the SPLASH and/or SPOT tag(s) were attached,
a tissue sample for DNA analysis was taken from the rear flipper, any scat
or urine present on the floe was collected, and the seal’s length
and girth were measured before releasing it.
Overall, 10 ribbon seals (5 adults, 5 pups), and 8 spotted seals (1
yearling, 7 pups), were captured and instrumented (Table 2) at different
locations throughout the study area. Shortly after deployment, all
instruments were transmitting as expected. Researchers from NMML will continue
to monitor the seals’ daily
movements and dive behavior.
By Michael Cameron