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Life History

Softshell clams (Mya arenaria) are a clam species endemic to the East coast of North America but have been introduced to a large portion of the Northern Hemisphere. Softshell clams were reintroduced to California in the 1870s and can now be found from southern California to southcentral Alaska. Paleontological evidence suggests that softshell clams were native to the west coast of North America but went extinct during the Pleistocene epoch due to glaciation. Their reintroduction to the west coast has allowed them to successfully recolonize their historic native habitat.
Softshell clams inhabit upper to mid tidal zones in marine and estuary environments. They are typically found in sand-silt substrate and do very well in mudflats but they can also be found in a more coarse substrate. Softshell clams can spawn twice a year, once in late fall and again in late spring. The sperm and egg fertilize externally and after 6-12 hours the egg will hatch and undergo three planktonic larval stages before it metamorphosizes and settles out as a juvenile clam. The process from fertilized egg to juvenile clam can occur in 1-3 weeks. 
Anecdotal evidence from local harvesters indicates softshell clam populations have been increasing in Southcentral Alaska, while other populations of native clams have experienced significant decline.



APMI has developed techniques for producing softshell clams for enhancement and study of life history. APMI is exploring the optimal substrate to determine the optimal outplanting substrate. In the spring of 2021, a habitat suitability study was conducted across several transects within known softshell clam harvest areas. Habitats during these collections were evaluated for sediment composition and total softshell clams observed within each sediment type and depth. A total of 220 softshell clams were collected as broodstock during this effort. These clams were held at the Alutiiq Pride Marine Institute (APMI) in a downwell tank system at 12°C, and were successfully spawned in early July 2021 using heated water to 17°C and the addition of Chatocerous spp. and Isochrysis spp. as feed. An estimated 5 million eggs at 𝑥̅ 70 µm were counted, yielding approximately (2.7 million larva for setting by day 17 (235 microns)). Estimated setting success was 50% and the water was maintained at 19°C to accelerate l growth. Clams at 𝑥̅ 10 mm and 14 months of age were placed in varying substrates and settlement and survival rates were both evaluated as a method to determine preferred habitat for outplanting. APMI hopes to utilize the methodologies developed in this study to further softshell clam enhancement for shellfish harvesters. We believe that Softshell clam enhancement can be used as an adaptation strategy for mitigating tradition shellfish harvest loss and increase food security across Southcentral Alaska.

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