Therefore, each escapement estimate is an index 

 of the relative abundance at the time of survey. 



The maximum estimate determined by sur- 

 vey methods- at about the peak of the run is used as 

 an estimate of the relative abundance of the total 

 escapement. Reliable indices of relative abundance 

 from year to year can be made only if the surveys 

 are comparable. Evaluation of the following factors 

 is necessary to determine the accuracy of the es- 

 capement 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, variability 

 increases with more observers. 



Survey systems. — Different survey systems 

 have been used by the various agencies. Reliability 

 of the escapement estimates varies with the systems 

 used. 



Observation conditions. — Weather is an 

 extremely Important factor in the reliability of 

 escapement estimates. During flooding, ground sur- 

 veys can be made only with great difficulty. Visibil- 

 ity is also greatly reduced because of turbid water. 

 Any estimate made during years that had heavy rains 

 of long duration during the peaks of spawning runs is 

 not comparable with an estimate made during normal 

 water levels. 



Streams in which lntertidal spawning pre- 

 dominates may present difficult observation condi- 

 tions at high tide. Spawning salmon in the inter- 

 tidal zone behave differently when the spawning 

 areas are flooded by the high tide. 



Aerial observations vary with the different 

 types of aircraft used. Observations made from 

 small light planes capable of following winding 

 stream courses are more reliable than those made 

 from larger planes which must fly at considerable 

 height above the stream and generally at greater 

 speeds. 



Survey systems that use 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. 



Physical Observations 



Observations of the characteristics of each 

 stream by different observers have been recorded 

 with varying degrees of accuracy. Many details of 

 stream descriptions are dependent upon the individ- 

 ual observer's ability and knowledge. 



Many stream dimensions are merely esti- 

 mates. Instruments for measurement were usually 

 not available to observers, and pacing and esti- 

 mating were used. 



Most basic stream distances have been taken 

 from aerial photographs and are relatively accurate. 

 However, some errors may have occurred where ref- 

 erence points were difficult to identify. Drainage 

 estimates were based on compensating polar planim- 

 eter measurements of valley areas, but occasion- 

 ally drainage divides were difficult to distinguish 

 and the areas given are only approximate. 



EXPLANATION OF CATALOG FORMAT 



Further descriptions of the data such as esti- 

 mates of timing, temperature ranges, and spawning 

 facilities are included under these specific headings 

 in the explanation of the catalog format that follows: 



Stream Designations 



Stream name . — This appears in the center 

 of the first line of the heading. Recorded names or 

 common local names are used when available. Other- 

 wise unnamed streams of importance are given 

 descriptive names corresponding to location or other 

 distinguishing features. Some streams have identical 

 names; they are retained without change because of 



