Figure 7.- -An intertidal spawning area at low tide. 



apparent that efforts to trap free-swimming 

 fry in the intertidal zone would not yield 

 quantitative data. Fry move in and out of the 

 area with the tides, and probably an inter- 

 mingling of fry from adjacent streams occurs. 

 In 1957 therefore emphasis was on developing 

 methods of measuring abundance of larvae 

 while they were still in the gravel — an approach 

 that has an advantage over continuous trapping 

 because it is necessary to sample an area only 

 once before fry emerge. Once sampling tech- 

 niques are worked out, this method should make 

 it possible to sample many more streams than 

 with traps or other devices that are dependent 

 on capturing fry as they emerge from the 

 gravel. Of course, there is a continual mor- 

 tality of fry during the time between gravel 

 excavations and fry emergence, and caution 

 must be taken when combining estimates de- 

 rived by the two methods. 



along regularly spaced transects. The tech- 

 nique consisted of turning over the gravel with 

 a shovel or spading fork while proceeding 

 across and then along the stream and observ- 

 ing the numbers of fry and dead eggs un- 

 covered. The absence of eggs or fry defined 

 the seaward limits of the spawning area. The 

 area thus defined was mapped, and the total 

 area of intertidal spawning computed. 



The average density of fry in the gravel was 

 determined as follows: A metal sampling 

 device suitable for use in rapid stream cur- 

 rents and rugged enough to withstand repeated 

 use was developed. It consisted of a 3-foot 

 square metal frame with two opposite sides of 

 sheet metal and two of plastic screen (fig. 8). 

 The sides were 2 feet high, which was about 

 the maximum depth of water at which gravel 

 would be excavated. 



The limits of spawning areas in the intertidal 

 zone were delineated by digging systematically 



The total intertidal spawning area of a stream 

 was divided into sections 96 feet long. Each 



