FISHERY Bl'LLETlN: VOL. ,S3. NO. .S 



The Candlestick Point site has a sandy substratum 

 and is adjacent to a broad expanse of mud flat. 

 Temperatures and salinities at this site reflect those 

 of the central San Francisco Bay (Conomos 1979). 

 Clams were collected high on the sandy beach front 

 0.6 m above Mean Lower Low Water (MLLW) in the 

 areas exposed as the tide begins to recede. 



Burlingame Lagoon is separated from San Fran- 

 cisco Bay by a levee with a narrow channel connect- 

 ing to the open body of the Bay (Fig. 1). Salinity and 

 temperature can vary dramatically with heavy rains 

 (8 to 12 ppt) (pers. obs.). The area has a heavy clay- 

 mud substratum. The collecting site was 0.6 m above 

 MLLW. 



The Foster City site was selected because it 

 reflects conditions more closely associated with the 

 south bay (Conomos 1979). The substratum is sandy- 

 mud with rocks and cobble intermixed. The area juts 

 into the bay and is exposed to wave action and 

 temperatures and salinities characteristic of the bay 

 waters (Conomos 1979). It is adjacent to outflow 

 from the tidal channel that winds through Foster 

 City. The collecting site was 0.24 m above MLLW. 



The Point Isabel site is on the mud banks of a nar- 

 row (4 m wide) tidal channel that bisects the Point 

 Isabel promontory. The substratum is clay-mud with 

 rock and debris intermixed. Clams were collected 

 from 0.15 to 0.46 m above MLLW. 



The depths of the collection sites (relative to 

 MLLW) at the four locations were dictated by the 

 presence of M. arenaria at each site. Mya arenaria 

 signals its presence by distinct siphon holes at the 

 surface of the substratum. After an initial excavation 

 of each collection site to a depth of 10 cm, it became 

 obvious that clams were present only in the specific 

 areas clearly marked by their siphon holes. There- 

 after only these areas were sampled. 



Temperature and salinity were recorded with a 

 field hydrometer (marked at ppt) and thermometer 

 at each' site each month, beginning in October 1979 

 and continuing through November 1980. 



Collecting Methods 



A gardener's hand rake and careful hand digging 

 was used for excavating the deep-dwelling M. 

 arenaria. At least 25 clams were collected from each 

 of the four sites each month for 1 yr (with the follow- 

 ing exceptions: 4 October- Foster City, 12 collected; 

 3 November- Foster City, 20 collected; 25 Decem- 

 ber- Foster City, 24 collected; 2 November- Candle- 

 stick Point, 20 collected; 24 September- Point 

 Isabel, 20 collected; 3 November- Burlingame, 7 col- 

 lected). A total of 1,625 clams were examined in this 



study. Clams were collected, placed in a Thermos* 

 jug of cool bay water, and returned to the laboratory. 



Processing Methods 



Analysis of gonadal stage was made by micro- 

 scopical examination of histological preparations 

 (Ropes and Stickney 1965). The presence and devel- 

 opment of gametes was used to infer the spawning 

 stage or readiness of the clam. Specimens were 

 measured for shell length to the nearest 0.1 mm. The 

 anterior one-third of the visceral mass (Ropes and 

 Stickney 1965) was removed, labeled, and placed in 

 Bouin's seawater fixative. During dissection, tissues 

 were submerged in cool seawater to prevent drying 

 or osmotic changes. The time between collection and 

 preservation was under 3 h to prevent any gonadal 

 changes. 



The tissues were subjected to standard histological 

 procedures (dehydrated in alcohol and embedded in 

 paraffin). Embedded tissues were thin sectioned (5 ^A) 

 on a rotary microtome. Sections were mounted on 

 glass slides, stained with Harris' hematoxylin and 

 eosin, and examined using standard light micro- 

 scopy. 



Each slide of gonadal tissue was studied to deter- 

 mine the presence of male or female gametes and the 

 condition of the gonadal tissues. This allowed clams 

 to be placed into one of the five classes of spawning 

 readiness (inactive, active, ripe, partially spawned, 

 spent) employed and described by Ropes and Stick- 

 ney (1965) for M. arenaria. 



Categories of Spawning Readiness 

 (adapted from Ropes and Stickney 1965) 



Female Gonads 



INACTIVE PHASE. -Ropes and Stickney (1965) 

 used the term "inactive" to describe this phase. 

 Brousseau (1978) preferred the term "indifferent" 

 because cellular activity is continuing although no 

 gametogenic activity is obvious. The term "inactive" 

 is employed here and refers to individuals which are 

 not seen to be producing gametes whether due to 

 seasonal (quiescence or immaturity. Thus in this 

 research which presents pooled male and female 

 datii, the "inactive phase" may contain sexually un- 

 differentiated individuals along with inactive animals 

 clearly recognizable as male and female. 



Females in the inactive phase exhibit small oocytes 



^Reference to trade names does not imply endorsement hy the Na- 

 tional Marino P^i.shories Service, NOAA. 



404 



