mainland streams with headwaters in Canada was 

 obtained from the Canadian government by the U. S. 

 Fish and Wildlife Service. 



U. S. Federal Power Commission. The report, Water 

 Power of Southeastern Alaska, 1947, published with 

 the cooperation of the U. S. Forest Service, provides 

 discharge rates and stream drainage areas, and other 

 information about a number of important salmon 

 streams. 168 p. 



U. S. Forest Service. Data on stream characteristics 

 and salmon escapements are available on several 

 streams in records of studies conducted by this agency 

 on the effects of logging on the physical makeup of 

 streams. 



U. S. Geological Survey. Aerial photographs from 

 this agency are the primary source for measurements 

 of stream distances and areas and for valley features 

 not visible from the ground. These photographs, 

 which are of most of the streams in Southeastern 

 Alaska, were made by the U. S. Navy (Patrol Squad- 

 ron Four) in 1948. 



Local residents. Another source is the descriptive in- 

 formation on several major streams provided by local 

 residents. 



LIMITATIONS OF DATA 



Escapement estimates obtained by visual means 

 are often limited in accuracy because fish are not seen 

 in turbid water, under overhanging stream banks, or 

 in areas inaccessible to observers. Actual count: 

 throughout the duration of the salmon run past a count- 

 ing weir or tower are relatively accurate estimates of 

 total escapement. However, it is not economically 

 feasible to establish a weir on each stream, and escape- 

 ment surveys are the only source of information for a 

 large part of the area which must be covered. The 

 value of the catalog as a history of the salmon escape- 

 ments can be realized only if its limitations are fully 

 known. 



Escapement Estimates 



Escapement estimates do not indicate the actual 

 total escapement. At no time are all the salmon in the 

 stream simultaneously since the spawning run extends 

 over a period of weeks. Therefore, each escapement 

 estimate is an index of the relative abundance at the 

 time of survey. 



The maximum estimate determined by survey 

 methods at about the peak of the run is used as an esti- 

 mate of the relative abundance of the total escape- 

 ment. Reliable indices of relative abundance from 

 year to year can be made only if the surveys are com- 

 parable. Evaluation of the following factors is 



necessary to determine the accuracy of the escapement 

 estimates. 



Observers. --The escapement records are 

 from many different observers. Variability in 

 estimating the number of salmon in a given area by 

 different observers should be considered in judging 

 the accuracy of the data. In general, with more 

 observers variability increases. 



Survey systems. --Different survey systems 

 have been used by the various agencies. Reliability 

 of the escapement estimates varies with the systems 

 used. 



Survey systems that employ standard count- 

 ing techniques over standard distances are the most 

 reliable method now available for comparison of 

 abundance between years, particularly when streams 

 can be only partially covered. Standard survey 

 distances in comparatively long streams were not 

 widely used prior to 1949. 



Survey systems requiring periodic visits 

 to each stream during the spawning period are more 

 reliable for estimates of peak abundance than systems 

 requiring only one or two visits. The peak period of 

 abundance in a salmon stream is usually relatively 

 short, and one or two visits may miss the peak. 



Type of survey . — Two basic methods for cov- 

 ering the streams during escapement surveys are being 

 used. 



The oldest method is the ground survey in 

 which the observer follows the stream course on foot 

 or in a skiff with an outboard motor. Most parts of 

 the stream can be closely observed by this type of 

 survey. 



The newer method is aerial survey. This is 

 a fast, economical means of covering a large number 

 of streams in a short period of time over stream dis- 

 tances greater than is possible on the ground. This 

 method requires experienced personnel familiar with 

 ground surveys as well. 



Aerial surveys are best suited for large 

 rivers and streams where ground coverage is limited 

 usually to the lower portion of the stream near the 

 banks. Ground surveys are more reliable than aerial 

 surveys on small streams that offer poor visibility from 

 the air. 



Observation conditions. --Weather is an 

 extremely important factor in the reliability of 

 escapement estimates. During flooding, ground 

 surveys can be made only with great difficulty. Visi- 

 bility is also greatly reduced because of turbid water. 

 Any estimate made during years that had heavy rains of 



