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Polar Ecosystems Program

Habitat Use and Seasonal Movements of Adult Bearded Seals in Kotzebue Sound, Alaska

male bearded seal
Figure 1.  A sub-adult male bearded seal, instrumented with an Mk10 SDR.  Photo by John Jansen.
 

Building on relationships and techniques developed during earlier tagging programs that focused on young-of-the-year bearded seals (Erignathus barbatus), NMML researchers, funded by NOAA and the Bureau of Ocean Energy Management (BOEM), contracted with the Kotzebue IRA to support a pilot study in late June and early July 2009 in Kotzebue Sound. This effort resulted in the successful capture and tagging of one adult male and two sub-adult male bearded seals (see AFSC Quarterly Report, Oct.-Dec. 2009). This was the first adult bearded seal ever tagged in Alaska. The seals were instrumented with satellite-linked data recorders (SDRs) and released.

In 2010, the spring field effort was repeated and also expanded to incorporate the North Slope Borough (NSB). Unfortunately, poor sea-ice and capture conditions prevented us from capturing any bearded seals at either Kotzebue Sound or at our two NSB study sites: Peard Bay and Barrow. Based on reports of bearded seals using land for hauling out in the fall, a small field team returned to Barrow in October 2010; however, no seals were captured during this late-season field effort.

With the respective cooperation of the North Slope Borough Wildlife Department and the Kotzebue IRA, springtime field efforts were again mounted in Barrow and Kotzebue in spring 2011. Similar to 2010, no seals were captured in the NSB. However, two females and one male were successfully captured, instrumented with SDRs, and released in Kotzebue Sound (Table 1). Based on their size and dentition, we estimated that one of the females was a yearling (young sub-adult) and the other female and the male were 2-3 years old (sub-adults; see Table 1).

   Table 1.  Deployment information for bearded seals captured and instrumented in Kotzebue Sound, Alaska, in 2009 and 2011.
Season Specimen
Number
Capture
Location
Capture
Time (GMT)
Deployment
(days to date)
Sex Age Weight
(kg)
2009 EB2009_3000 66.3879°N
162.4174°W
6/23/09
00:30
719 M Sub-adult 184
2009 EB2009_3001 66.5617°N
162.6854°W
6/25/09
01:38
729 M Adult 253
2009 EB2009_3002 66.6110°N
162.8948°W
6/26/09
00:30
728 M Sub-adult 197
2011 EB2011_3000 66.6872°N
163.0836°W
6/16/11
20:50
182 F Sub-adult 161
2011 EB2011_3001 66.6431°N
162.6805°W
6/17/11
01:15
181 F Sub-adult
(Yearling)
115
2011 EB2011_3002 66.6438°N
162.9744°W
6/18/11
01:15
180 M Sub-adult 158

Individual bearded seals hauled out on pack ice were slowly approached in small boats, typically causing the seals to enter the water. One or two tangle nets were deployed in the water nearby. These large-mesh (12 in 22 in stretch) twisted-monofilament nets were made of 1 to 3 net panels, each 90 ft long x 24 ft deep. The float line was made of a 3/4-in diameter foam core wrapped in nylon, and the lead line was 1/4-in diameter, light enough to allow a captured seal to reach the surface to breathe. The nets likely were visible to the seals, but some individuals, apparently out of curiosity, approached the nets and became entangled.

Entangled seals were restrained alongside one of the small boats and moved to a nearby ice floe for handling, sampling, and tagging. Captured seals were lightly sedated, removed from the net, measured, and weighed. Samples of their blood and skin were collected to establish baseline blood parameters and for DNA studies. Each seal was then instrumented with two SDRs: a SPOT tag, attached to a rear flipper, and an Mk10 tag glued to the hair on the seal's head (Fig. 1 above).

The SPOT tag relays information on haul-out timing and long-term movements and will transmit for up to 3 years. The Mk10 tag provides the same information, as well as data on the timing and depth of the animal's dives, and will fall off when the seal molts during the following spring. Once the glue on the Mk10 tag had cured, each seal was released back into the water near where it was captured.

The initial movement pattern of the male sub-adult tagged in 2011 was very similar to the patterns displayed by the two sub-adult males tagged in 2009. Shortly after being released, it left Kotzebue Sound and followed the Alaska coastline north, remaining mostly within the relatively ice-free waters 50 nautical miles (nmi) from shore, preferring fairly localized regions between Point Hope and Barrow. In contrast, the two females traveled much farther from the coast, preferring less restricted foraging areas north of 70°N in the central Chukchi Sea.

June 2011 map, figure 2, see caption
2011 June
July 2011 map, figure 2, see caption
2011 July
September 2011 map, figure 2, see caption
2011 August
August 2011 map, figure 2, see caption
2011 September
October 2011 map, figure 2, see caption
2011 October
November 2011 map, figure 2, see caption
2011 November
December 2011 map, figure 2, see caption
2011 December
 
Figure 2.  Maps of the sea-ice distribution and seasonal movements of bearded seals captured and tagged in Kotzebue Sound, Alaska, in June 2009 and 2011:  white triangle=EB2009_3000 (sub-adult male); black triangle=EB2009_3001 (adult male); gray triangle=EB2009_3002 (sub-adult male); gray circle=EB2011_3000 (sub-adult female); white circle=EB2011_3001 (sub-adult female); and black square=EB2011_3002 (sub-adult male).  Click maps to enlarge.

In the fall, all seals began moving south (Fig. 2) with the advancing ice and by December all had passed into the Bering Sea. Similar to the seals tagged in 2009, all seals tagged in 2011 routinely dove to the seafloor. Dive duration appeared to be related to dive and seafloor depth. In autumn, the females occupied areas of deeper water (50-150 m) than the males (approximately 50 m), and their dives were of longer duration (8-16 minutes vs. 6-10 minutes, respectively). In the winter however, when both sexes occupied water less than 50 m deep, dive duration was about 6-10 minutes for all seals.

The patterns in the timing of hauling out were also very similar to seals tagged in 2009. When the females occupied areas with sea ice in July, they hauled out for up to 30 hours, but later in winter and early spring, despite the presence of sea ice, it was rare for either sex to haul out onto the ice. As of this writing, all SDRs continue to function properly, and a field effort is planned in both Kotzebue Sound and the NSB in spring 2012.

By Michael Cameron and Peter Boveng
 

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