Oceanographic Surveys of Traitors Cove 

 Revillagigedo Island, Alaska 



By 



DOUGLAS R. McLAIN, Physical Oceanographer 



Bureau of Commercial Fisheries Biological Laboratory 

 Box 155, Auke Bay, Alaska 99821 



ABSTRACT 



Traitors Cove is a small fiordlike estuary in southeastern Alaska. It is divided 

 into two basins by a narrow constriction, where a reversing tidal falls forms. Four 

 oceanographic surveys of the estuary between 1963 and 1965 showed that this tidal 

 falls creates a region of strong turbulence and destroys the stratification of the water 

 near it. Surface currents in the estuary are predominantly seaward on ebb tide and 

 toward the head of the estuary on flood tide. 



INTRODUCTION 



Pink salmon ( Oncorhynchus gorbuscha ) and 

 chum salmon (O. keta) spawn in the gravels of 

 nnany of the streams of southeastern Alaska. 

 In the spring, the juvenile fish emerge from 

 the gravel and soon migrate downstream to 

 salt water. Their first few weeks in saltwater 

 are a critical period in their life cycles. 

 Probably a large portion of the total ocean 

 mortality of these fish takes place during this 

 period. 



Relatively little is knownof the oceanography 

 of the salt-water areas in southeastern Alaska 

 where this mortality occurs. This paper de- 

 scribes a study of water temperature, chem- 

 istry, and surface currents of such an area-- 

 Traitors Cove estuary near Ketchikan. Powers 

 (1963) made a similar study of Little Port 

 Walter estuary, Baranof Island, southeastern 

 Alaska. Both estuaries are the sites of salnnon 

 research facilities of the Bureau of Commer- 

 cial Fisheries. 



Traitors Cove estuary (fig. 1) penetrates 

 Revillagigedo Island, near Ketchikan. It is 

 divided into two basins, Inner Bay and Outer 

 Bay, by a narrow constriction which has a sill 

 depth of 1 or 2 m. below mean low water. 

 Because of the large range of the tides in the 

 region and the limited capacity of the con- 

 striction, a reversing tidal falls forms at the 

 constriction. Tidal currents are strong near 

 the constriction. Inner Bay is about 5.9 km. 

 long and 0.7 km. wide and has a maximum 

 depth of 46 m. Several streanns enter Inner 

 Bay; the largest, Traitors River, empties into 

 the head of this bay (fig. 1). Outer Bay is about 

 6.5 km. long and 1.3 km. wide and has a 

 maximum depth of 130 m. Margareta Creek is 



the largest of several streams that enter this 

 bay. Outer Bay is freely connected to Behm 

 Canal over a sill 55 m. deep. Behm Canal is a 

 large deepwater body connected to the Pacific 

 Ocean through Clarence Strait and Dixon En- 

 trance. 



Traitors Cove lies in a maritime climate 

 and receives large amounts of precipitation 

 and runoff. Annual precipitation at Ketchikan, 

 40 km. south of Traitors Cove, is about 390 cm. 

 (U.S. Weather Bureau, 1965); watersheds trib- 

 utary to Traitors Cove probably receive similar 

 amounts. Because discharge records for 

 Traitors River are available only since June 

 1964, I include records from Fish Creek, a 

 stream about 40 km. southeast of Traitors 

 Cove which has suitable records. Discharge 

 data for these two streams for the 10-day 

 periods immediately before each survey of the 

 estuary are shown in table 1. 



Table 1. — Discharge of Traitors Mver and Fish 

 Creek, Revillagigedo Island, Alaslca. Data 

 from U.S. Geological Survey (1963, 1964-, 

 1965) 



