PHOTOGRAPHIC DEVICE FOR ACCURATELY MEASURING 



FISH 



INTRODUCTION 



The photographic measuring device 

 described in this paper was developed to aid 

 the work of the International North Pacific Fish- 

 eries Commission. One of the objectives of 

 the Commission is to devise a suitable method 

 of identifying the various races of Pacific sal- 

 mon so that North American stocks can be 

 differentiated from the Asian stocks. Work to 

 date has shown generally that the differences 

 between the races of salmon are extremely 

 slight. For this reason and others closely re- 

 lated, many aspects of the body characteristics 

 of salmon are being investigated. Among these 

 investigations are bone studies, blood studies, 

 parasite studies, and morphological studies, 

 since one or a combination of these may provide 

 the data needed to characterize the various 

 races (International North Pacific Fisheries 

 Commission, 1955). 



In the morphological studies, consider- 

 able work is being done on the determination 

 of body proportions and measurements. The 

 taking of accurate measurements, however, 

 from a three-dimensional object such as a fish 

 is difficult. In addition, methods now in use 

 have an indeterminate error due to bias of op- 

 erators. The problem at hand was to develop a 

 method of taking these measurements by means 

 of photography. 



The advantages of photography over 

 present methods of measurement are: 



1 . Tlie pictures of the fish would form per- 

 manent records from which measurements 

 could be checked and rechecked. 



2. When fish were needed for measurements 

 that were not contemplated in an original study, 

 these measurements could be taken by the biolo- 

 gist from the many pictures of the fish that 

 would have accumulated over the years instead 

 of his having to wait till the season arrived and 

 then obtaining measurements from only one 

 year's sample. 



3. In interpretation of visual characteristics, 

 such as net marks and scale counts, pictures 

 could be analyzed in the laboratory by experts 



in such analyses. 



4. Photography and its associated tools 

 would lend themselves readily to automation, 

 thus tending to minimize human errors and bias 

 of operators . 



Because of the potential value of a photo- 

 graphic measuring machine and the need it would 

 fill, the development of such a machine was 

 undertaken. Many factors had to be considered 

 in order to develop a machine that would be use- 

 ful to U. S. Fish and Wildlife Service field 

 personnel under the variety of conditions under 

 which they must work. Some personnel work on 

 board motor vessels on the high seas, where 

 storms frequently cause an unstable footing for 

 a measuring machine. Others work in canneries, 

 where lighting conditions may make the use of 

 photography difficult. Still others work on spawn- 

 ing grounds, where portability is important, 

 since the base camp may be some distance from 

 the spawning sites. Yet, despite these difficulties, 

 there must be no sacrifice in the accuracy of the 

 measurements . 



The objective of this investigation, tliere- 

 fore, was to design a machine that would meet 

 the following qualifications: 



1. Give measurements accurate to within 

 + 0.05 cm. 



2 . Be fully portable . 



3. Incorporate as many automatic features 

 as is possible. 



4. Be capable of rapid use in the field. 



5. Be rugged. 



6. Be not overly expensive . 



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