46 BULLETIN OF THE BUREAU OF FISHERIES 



data into a single table for the remainder of the Shumagin Island district, finally 

 giving a table of totals for the entire district. 



Still other cases were even more confusing, and our decision to present separate 

 data for a given locality or to include them with those of the next larger including 

 unit has had to rest upon a consideration of such matters as the relative importance 

 of the catches under consideration, the nature of the data supplied, and to a very 

 considerable extent upon our personal local knowledge of the geography and fishing. 



A study of this sort is prunarily a study of abundance. We are concerned to 

 know what changes in the abundance of salmon have taken place, and, so far as they 

 may be discovered, the causes of these changes. We must decide immediately, 

 therefore, what we are to use as a measure of abundance. The best measure un- 

 doubtedly would be one based on the yield per unit of fishing eft'ort, but the intro- 

 duction of new forms of gear, the enlargement and improvement of old forms, the 

 replacement of sailing boats by motor boats, the impossibility of separating in our 

 available data the catch made by different forms of gear, and other similar factors 

 have made it impossible to define a sensible unit of fishing effort. We are forced, 

 therefore, to use the total yield as our chief measure of abundance, although we recog- 

 nize the unsatisfactory features of this procedure. Wherever possible we have given 

 data showing the amount of gear as given m the available records, but we consider 

 the records of gear to be only moderately reliable. The number of traps recorded in 

 many instances includes "dummy" traps, which are driven primarily for the purpose 

 of preempting a trap location and are never really fished. The gill-net records fre- 

 quently include all the gill nets on hand during the season and so give no accurate 

 idea of the actual number fished ; and the aggregate length of the gill nets reported 

 by a single company are given only in certain years. 



In any carefully considered plan for the conservation of a fishery the most 

 important thing is to determine, as accurately as may be, the condition of the re- 

 source. At any time we may wish to know the present condition of the fishery 

 and the prospects for the future, and knowledge of this sort is dependent upon a 

 knowledge of the changes the fishery has undergone in past years. Without a 

 knowledge of the past and present conditions it is impossible to determine whether 

 depletion has occurred or is imminent or what effect regulatory measures that may 

 have been imposed have had. This last is an especially important function of such 

 data, as it is necessary adequately to protect the resources and yet in the interest 

 of true conservation the regulations must not be made so stringent as to reduce 

 the commercial yield below what the resource can provide safely. And, if we can 

 look into the future far enough so that the industry can be advised as to the pros- 

 pects for the next season, a measure of efficiency and stability can be given which 

 will make for the saving of millions of dollars now wasted in outfitting for nms 

 that fail to materialize. Any appreciation of the present situation or any prophecy 

 for a future year must be based upon consideration of the general trend of the 

 fishery, the cyclic fluctuations about that trend (if present), the spawning escape- 

 ments in preceding years, the conditions on the spawning grounds and in the streams 

 and lakes that may have affected the mortality of the broods during their life in 

 fresh water, and such information as may be available on the relative abundance 

 in the preceding year or years of fish of younger age groups derived from the same 

 brood years. 



