REPRODUCTIVE CYCLE OF THE SOFT-SHELL CLAM, 

 MY A ARENARIA, AT SKAGIT BAY, WASHINGTON 



Russell G. Porte r^ 



ABSTRACT 



The annual reproductive cycle of the soft-shell clam, Mya arenaria L., was studied at Skagit Bay in 

 northern Puget Sound. Wash. Spawning occurred from late May to early September in both 1971 and 

 1972 with peak spawning in July and June respectively. Small clams (less than 60 mm in length) had a 

 spawning peak that coincided with other size classes although the spawning period was shorter in 

 duration. The single yearly spawning period at Skagit Bay corresponds with east coast populations in 

 Canada and Maine. 



The soft^ shell clam, Mya arenaria L., is found on 

 virtually all coastlines in the northern hemi- 

 sphere (Hanks, 1963) and is still extending its 

 range as evidenced by its recent movement into 

 the Black Sea (Zambriborshch, Marchenko, and 

 Telegin, 1968; Ivanov, 1969). On the North 

 American continent, it is native to the east coast 

 from which it reportedly was accidentally intro- 

 duced into San Francisco Bay, Calif., about 1874 

 (Fitch, 1953). However, there is some evidence 

 from Indian middens that the soft^shell clam is 

 also native to the west coast (Craig, 1927). Its 

 range on the west coast presently extends from 

 California to Alaska (Morris, 1966). 



The reproductive cycle of the softr-shell clam 

 has been described from a variety of locations on 

 the east coast, but no data have been presented 

 for west coast populations except for one brief 

 note from Oregon (Edmondson, 1920). The first 

 detailed study on the histology of the gonad of 

 Mya arenaria was conducted by Coe and Turner 

 (1938) in New England. They found that spawn- 

 ing occurred in the summer. At Martha's Vine- 

 yard in Massachusetts spawning was found to 

 occur over a 6-mo period from spring through 

 early fall (Deevey, 1948). In northern Mas- 

 sachusetts, spawning occurs in late summer and 

 early fall (Ropes and Stickney, 1965), while in 

 New Jersey, spawning takes place in the spring 

 (Belding, 1930; Nelson and Perkins, 1931). Two 

 spawnings per year (spring and fall) have been 

 reported for the Chesapeake Bay in Maryland 

 (Pfitzenmeyer, 1962, 1965) and for Narragansett 

 Bay, R.I. (Landers, 1954). Ropes and Stickney 



(1965) have tabulated the results of most east 

 coast studies for easy comparison. 



This paper describes the annual reproductive 

 cycle for a soft^shell clam population from Puget 

 Sound, Wash. Skagit Bay was selected as the 

 study area since it has a potential for commercial 

 operations, a commercial soft-shell clam fishery 

 is in the beginning stages, and it appears to be 

 the area with the greatest abundance of 

 soft-shell clams in Puget Sound. 



DESCRIPTION OF AREA 



Skagit Bay, Wash., is located in northern Puget 

 Sound 60 miles north of Seattle. The Skagit River, 

 which has an average discharge of 16,560 ft^/s 

 (U.S. Department of Interior, 1971:190),^ empties 

 into the end of the bay via the South Fork and at 

 the northern entrance of the bay via the North 

 Fork. The northern side of the bay is made up of a 

 large broad mud flat approximately 13 square 

 miles in area. The study area was located on the 

 mud flat off Fir Island between Hall Slough and 

 Browns Slough. 



The mean tide range at Skagit Bay is 6.5 feet, 

 and the diurnal range 10 feet. The soft^shell clam 

 beds are located at a tidal level of approximately 

 + 3.5 feet. 



Water temperatures and salinities in the vicini- 

 ty of Skagit Bay may vary widely on both an 

 annual and a diurnal basis due to river discharge 

 and tidal effects. During 1971, surface tempera- 

 tures at Strawberry Point varied from 4.79° to 

 15.68°C, while salinities ranged from 2.54 to 

 24.53/^0. The maximum recorded daily variation 



'Washington Cooperative Fishery Unit. University of Washing- 

 ton, Seattle. WA 9819.S. 



Manuscript accepted December 197.'?. 

 FISHERY BULLETIN: VOL. 72. NO. y. 1974 



648 



^Thirty-year period — maximum recorded flow: 144,000 ff/s, 

 minimum recorded flow: 2,740 ft^/s. 



