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April-June 2006
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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.

Shipboard observations:

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 approached 180°W. 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 after deployment.

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.
Species No. observed Species Age Class Sex SPOT Only SPLASH Only SPLASH & SPOT
Bearded seals  20 Ribbon Pup M 3    
Ribbon seals 158 F 2    
Ringed seals   0 Adult M 1    
Spotted seals 380 F   2 2
Steller sea lions   4 Spotted Pup M 6    
Unknown pinnipeds 197 F   1  
 Total 759 Yearling F     1

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

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