. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 78 CALIFORNIA FISH AND GAME X;i< _II :_. was added. Three drops of this solution were used as a preservative for a 100 ml sample. This latter solution proved advanta- geous in revealing structural detail not visible with the alcohol pre- servative. A 1 ml sample from each collecting vial was examined in a Sedgewick Rafter counting chamber using a Whipple micrometer (APHA, 1971). Veligers appeared continuously in the samples from ea
. California fish and game. Fisheries -- California; Game and game-birds -- California; Fishes -- California; Animal Population Groups; Pêches; Gibier; Poissons. 78 CALIFORNIA FISH AND GAME X;i< _II :_. was added. Three drops of this solution were used as a preservative for a 100 ml sample. This latter solution proved advanta- geous in revealing structural detail not visible with the alcohol pre- servative. A 1 ml sample from each collecting vial was examined in a Sedgewick Rafter counting chamber using a Whipple micrometer (APHA, 1971). Veligers appeared continuously in the samples from early May through mid-September, with the highest count of 419 in- dividuals occurring in mid-July. No veligers appeared in samples taken the remainder of the year, except for a short period from late Decem- ber to mid-January when a small number (less than 10) appeared in the samples (Figure 5). 400 300. 200- 1972 1973 FIGURE 5. Number of straight hinge veligers per 1 ml concentrated sample from weekly plankton tows in the Colorado Lagoon, June 1972—June 1973. It is difficult to distinguish among the species of veligers present in the plankton samples. Basedon comparison with the veligers raised in the laboratory, we judge that the samples in June, July, and August contained Mercenaria mercenaria. In addition, the appearance of large numbers of straight hinge veligers in the plankton during July and August corresponds to an increase in surface temperature above 23 C (73 F). No information is available on bottom temperatures. However, laboratory observations show that this race of Mercenaria mercenaria will spawn spontaneously at 22 C (72 F) and can be induced to spawn from 22-25 C (72-77 F) (see section on spawning). There are four morphologically different veligers, including the Mercenaria type, in the sunnier samples. The winter pelecypod spawn- ing represents a single genus, probably not Mercenaria. We conclude that Mercenaria is among other clams spawning in June, July,
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