SHELLFISH RESOURCES OF NORTHWEST COAST. 7 



An estimated census of the clams was taken in 1917. In the most 

 densel}' populated areas, from 25 to 30 claims per square yard were 

 often taken, with the number frequently reaching 50. From the 

 point of maximum yield in bed the number was reduced to few or 

 none per square yard as the shore line was approached. Local resi- 

 dents who had observed the clam beds in the Siuslaw River for 

 many years believed in 1917 that there was no appreciable reduction 

 in the abundance of clams from season to season. It is the author's 

 opinion, after viewing the beds at intervals for nearly two years 

 that, although certain areas which in past years were systematically 

 worked over and exhausted have not restocked themselves, the clams 

 are holding their own fairly well. 



Sudden catastrophies have occurred, however, and may occur again 

 to inhibit the natural development of the clams in the Siuslaw 

 River. The North Fork, a tributary of the Siuslaw River, flows 

 into the latter about 1^' miles above Florence, near the upper end of 

 the clam beds.. During December, 1917, and January, 1918, ex- 

 cessively hard rains filled all of the mountain streams tributary 

 to the Siuslaw River and for nearly tAvo months this river and the 

 North Fork were overflowing their banks. An immense amount 

 of silt was carried down the streams and deposited over the clam 

 beds. During that time the clams were continuously under this 

 flow of fresh water, and when next observed, late in January, 1918, 

 it was found that large numbers of the young clams, which in the 

 preceding December had measured from 10 to 25 millimeters in 

 length, had perished. Medium-sized and large clams were unin- 

 jured, but the small ones situated near the surface could not maintain 

 themselves. Their appearance was similar to that assumed by other 

 clams of the same species killed in fresh water during experimental 

 investigations. This destruction resulted in a noticeable reduction 

 of half-grown clams in the beds in the following summer. Although 

 heavy rains are characteristic in western Oregon during the winter 

 months, rarely are floods of so long duration as they were in De- 

 cember, 1917, and January, 1918, and similar destruction of young 

 clams probably seldom occurs. 



That Mya arenaria spawns in late August and during September 

 on the Oregon coast is well established. In the early part of Sep- 

 tember, 1917, an examination of the ovaries and spermaries of the 

 species was made at Florence. The clams were found to be in spawn- 

 ing condition with mature ova and very active sperm. These observa- 

 tions were verified during the corresponding season of 1918. That 

 spawning does not occur at other seasons of the year was also demon- 

 strated by repeated microscopic examinations of the gonads of the 

 species during nearly every month of the year. 



Portions of the clam beds of the Siuslaw River were, in 1917, 

 well covered v.-ith eel grass which gave support to the glochidia, as 

 was apparent by turning over the upper layers of mud in which 

 the eel grass Avas rooted. Here during late November and early 

 December, 1917. were to be foimd large numbers of j^oung clams 

 from 10 to 25 millimeters in length in the surface of the ooze beneath 

 patches of the eel grass. Spawning in late August or September, 

 apparently young clams may reach a length of 25 millimeters by 

 December if conditions are favorable. 



