568 



Fishery Bulletin 101(3) 



50°0'N- 



-50'0'N 



XL 



I I. ll 



12 3 4 5 6 7 



9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 

 Deployment Age in Months 



I r- 



16°0'W 13O0'W 



Figure 1 



Locations where satellite dive recorders (SDRs) were deployed on 25 Steller sea lions in Alaska 

 and Washington between 1994-2000. "Deployment age" is the age of the sea lions when satellite 

 transmitters were attached. 



mid-June as the presumed birth date (Pitcher and Calkins, 

 1981) and pubUshed accounts of mass, standard length, 

 and girth at age (Calkins et al., 1998). Some juveniles 

 before 1996 were chemically immobilized with Telazol'" 

 injected intramuscularly by a dart fired from a pneumatic 

 gun (Loughlin and Spraker, 1989). Those animals were not 

 weighed; therefore exact dosage levels were not determined. 

 However, dosages were most likely between 1.5 and 2.5 mg/ 

 kg. Once a sea lion was immobilized, intramuscular injec- 

 tion of 3-10 cc of Dopram was administered to stimulate 

 respiration and facilitate recovery. After 1996, young sea 

 lions were captured on land with a hoop net and physically 

 restrained. During all years a SLTDR or SDR was glued 

 to the pelage on the animal's back with fast-setting cpoxy 

 resin (Loughlin ot al., 1987), and two plastic cattle ear tags 

 with the same identification numbers were attached, one to 

 each front flipper The instruments were not recovered and 

 were expected to be shed during or before molt. 



Instrument description and programming 



We used 0.5-watt ST-6 SLTDRs (packaged by Wildlife 

 Computers, Redmond, WA), which provide dive depth, 

 dive duration, and transmitter status. Further develop- 



ment by Wildlife Computers resulted in 0.25-watt ST- 10 

 and ST- 16 SDRs which could provide five messages: 1 ) dive 

 depth, 2 ) dive duration, 3 ) transmitter status, 4) proportion 

 of time at depth, and 5) a time line. Messages are sent at 

 prescribed intei-vals; transmission interval at sea is every 

 43 sec and on land it is every 1 min 28 sec. The number 

 of transmissions (and thus messages received) while the 

 sea lion is at sea depends on the length of exposure of the 

 instrument's salt-water switch at the surface. Location 

 data are not sent by the transmitter but are calculated by 

 Service-Argos, Inc. from the received message. Additional 

 information on these instruments and their capabilities 

 can be found in Merrick et al. (1994). The satellite track- 

 ing system (Argos) is described in detail in Fancy et al. 

 (1988) and Stewart et al. (1989). Additional information 

 can be obtained from the manufacturer at their web site 

 (www.wildlifecomputers.com). 



The ST-6 SLTDR stored, summarized, and transmitted 

 dive data as histograms. Individual dives and surface in- 

 tervals were not provided; therefore sampling frequency for 

 measuring dive behavior was not a consideration (e.g. Boyd, 

 1993). Software programming of the SLTDR subdivided 

 each day into four 6-h periods (2100-0300 h, 0300-0900 h, 

 0900-1500 h, and 1500-2100 h local time). Frequency histo- 



