FISHERY BULLETIN: VOL. 81, NO. 2 



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FIGURE 1. — Harbor seal study area of Netarts and Tillamook Bays on the northern Oregon coast. 



served abundances between years. 

 To examine movements, 12 harbor seals were cap- 

 tured in August and October 1978, using a modified 

 gill net (Brown 1981), and tagged with numbered 

 plastic cattle tags and radio transmitters (Telonics 

 Inc., Mesa, Ariz. 3 ). The plastic tags were placed in the 

 webbing of each hind flipper of all harbor seals, and 

 radio tags were attached by an anklet to a hind 

 appendage of 1 1 seals. Each transmitter package (84 

 g) was operated on a discrete frequency between 148 

 and 149 MHz, allowing identification of individual 

 animals. Movements of tagged harbor seals were 

 documented by identification of plastic tags and by 

 reception of radio signals from seals carrying 

 transmitters. Radio signals could be received only 

 when tagged animals were out of the water. All haul- 

 out sites in Netarts and Tillamook Bays were check- 

 ed visually and by radio for tagged harbor seals 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



292 



during a minimum of seven low tides per month, from 

 August 1978 through June 1979. An additional 36 

 harbor seals were tagged and released at Netarts and 

 Tillamook Bays in 1979, 1980, and 1981. Movements 

 of these harbor seals were not monitored on a regu- 

 lar basis. 



Harbor seals preying on chum salmon near the 

 mouth of Whiskey Creek were observed during 

 daylight hours from a 4 m high blind using binoculars 

 and a spotting scope. The observation area included 

 the lower 25 m of the creek and a semicircular area 

 centered at the creek mouth and extending out onto 

 the bay at a radius of about 200 m. Whiskey Creek 

 enters Netarts Bay in its shallow upper reaches so 

 that low tides prevent chum salmon from returning to 

 the hatchery. Only when the rising tide has flooded 

 this area can chum salmon approach and enter the 

 creek. Harbor seals use this area only when the tide is 

 high enough to allow them deepwater access or 

 averaged over all observation periods, about 2.5 h 

 before and after the peak of each high tide. 



