eremy Miller is awfully proud of himself here at the low intertidal in the Webhannet River (May 11, 2014)Beginning in May 2014 and 2015, we initiated a study in Wells (Webhannet River) and in Portland (Fore River) to examine the interactive effects of tidal height and predator exclusion on the survival and growth of wild and cultured soft-shell clams.

2014 results from Portland and Wells showed that deterring predators increased average clam recruit (juvenile “seed” clams) densities by 23–95X. 2015 results showed that deterring predators resulted in a statistically significant enhancement of recruits (21X more in Wells and 3X more in Portland). Read the results in the 2018 Journal of Shellfish Research article.

Average survival rates of planted clams  from the 2014 experiments are detailed in Figure 2 of this published paper. It was found that 71.0%–77.9% of planted clams survived in units protected from predators, while only  0% to 3.1% percent survived when non protected from predators.

Numerous people from the Wells Reserve, Gulf of Maine Research Institute, Casco Bay Estuary Partnership, the Waynflete School, and AmeriCorps all pitched in to help.  The photos below give a small sampling of the effort this type of project takes.  Kristin Wilson (Wells Reserve) kindly provided the photos except the last one.  You can read the Final Report from 2014 here.  The Final Report from 2015 is here.

Funding for the study in 2014 came from the U.S. Fish & Wildlife Service via the Maine Department of Environmental Protection through a grant written by Beth Bisson (Maine Sea Grant).  Funds were administered through the Casco Bay Estuary Partnership.  In 2015, the study was funded by the University of Maine at Machias and the Downeast Institute.

 

ome of the experimental units had hundreds of wild, 0-year class soft-shell clam recruits.

Some of the experimental units had hundreds of wild, 0-year class soft-shell clam recruits.

ost of the wild clam recruits were associated with experimental units that were protected with Pet screen. In this sample, 7 live hatchery-reared clams (out of 12) survived; however, there were 467 wild clam recruits as well!

Most of the wild clam recruits were associated with experimental units that were protected with Pet screen. In this sample, 7 live hatchery-reared clams (out of 12) survived; however, there were 467 wild clam recruits as well!

This is the size range of the 2014 year class of soft-shell clams (October 10, 2014)

This is the size range of the 2014 year class of soft-shell clams (October 10, 2014)

How can you tell the difference between a hatchery-reared juvenile and a wild juvenile? The cultured clam leaves a distinct disturbance line in both of its valves upon planting in any sediments (this is the clam on top). Wild clams do not have as distinct markings near their hinge (bottom clam).

This is a good comparison of the biomass of clams from a protected vs. an unprotected (control) experimental unit (Wells; October 10, 2014).

his one is a recent settler. It is about 3 mm (one-eighth of an inch) in carapace width.

This green crab is a recent settler (about 3mm).

reen crabs also were found in some of the pots. This one is about 10 mm (about one-half an inch) in carapace width.

Green crabs also were found in some of the pots. This one is about 10 mm (about one-half an inch) in carapace width.

ne data sheet was used for each sample (experimental unit). This is the one that had 467 wild recruits and seven live hatchery clams. The disturbance line allowed us to measure an initial length for each live clam. Only 20 of the 467 wild clams were measured. The 20 were sampled in such a way to provide a representative measure of the average length of the 0-year class clams.

All data was recorded.

ll clams (live and dead) were counted and measured to obtain survival and growth information.

All clams (live and dead) were counted and measured to obtain survival and growth information.

his is a sample from the low intertidal from the Fore River site (near the Waynflete High School playing fields in Portland). In this sample, all 12 hatchery-reared clams survived. The average initial shell length of these 12 clams was 12.0 mm (about one-half an inch), and the average final shell length was 23.4 mm (almost one inch). Growth of clams in experimental units protected with Pet screen vs. protected with a larger aperture flexible netting was depressed by 26% at this study site. A total of 214 wild clams occurred in this experimental unit. The average size of the wild clams was 8.5 mm (about one-third of an inch).

This is a sample from the low intertidal from the Fore River site (near the Waynflete High School playing fields in Portland). In this sample, all 12 hatchery-reared clams survived. The average initial shell length of these 12 clams was 12.0 mm (about one-half an inch), and the average final shell length was 23.4 mm (almost one inch). Growth of clams in experimental units protected with Pet screen vs. protected with a larger aperture flexible netting was depressed by 26% at this study site. A total of 214 wild clams occurred in this experimental unit. The average size of the wild clams was 8.5 mm (about one-third of an inch).

 

Read the Final Report.

 

 

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