Locomotion of infaunal bivalve mollusks primarily consists of vertical movements related to burrowing; horizontal movements have only been reported for a few species. Here, we characterize hard clam walking: active horizontal locomotion of adults (up to 118 mm shell length, SL) of the commercially important species, Mercenaria mercenaria, at the sediment surface—a behavior only briefly noted in the literature. We opportunistically observed walking over a 10-yr period, at 9 different sites in the Peconic Bays, New York, USA, and tested several hypotheses for the underlying cause of this behavior through quantitative field sampling and reproductive analyses. Hard clam walking was exhibited by males and females at equal frequency, predominantly during June/July and October, when clams were in peak spawning condition. Extensive walking behavior appears to be cued by a minimum population density; we suggest it may be mediated by unidentified pheromone(s), infaunal pressure waves and/or other unidentified factors. There was no directionality exhibited by walking clams, but individuals in an area of extensive walking were highly aggregated and walking clams were significantly more likely to move toward a member of the opposite sex. Thus, we conclude that hard clam walking serves to aggregate mature individuals prior to spawning, thereby facilitating greater fertilization success. In the process of investigating this behavior, however, we apparently oversampled one population and reduced clam densities below the estimated minimum threshold density and, in so doing, suppressed extensive walking for a period of >3 years running. This not only reinforces the importance of detailed field investigations of species biology and ecology, even for those that are considered to be well studied, but also highlights the need for greater awareness of the potential for research activities to affect focal species behavior.

In our ongoing bay scallop restoration efforts in eastern Long Island, NY, United States, we have planted millions of hatchery-reared juveniles to serve as broodstock when they mature. These plantings have driven the resurgence of larval recruitment, benthic population sizes, and commercial fishery landings over a 12-year period. In this article, we detail an attempt to track the contribution of our restoration efforts to population rebuilding using planted "skunks," an uncommon color morph, by looking for increased skunk frequencies in subsequent wild cohorts. Although we saw higher skunk frequencies among large juveniles in natural populations in the first 3 years after extensive skunk plantings, supporting use of uncommon color morphs as a passive tracer, this conclusion was not supported when examined over a 12-year period, as no strong correlations were seen between skunk frequencies at different life stages (adult broodstock, small and large F1 juveniles, F1 adults) for respective cohorts. Potential reasons for poor correlation between skunk frequencies and restoration efforts include lower than expected production of skunk offspring, dilution of out-planted contribution to growing natural populations, interannual variability in skunk frequencies that may have obscured the expected skunk signal, and/or differentially higher mortality of skunks at postset and larger juvenile stages. In the latter case, skunks experienced higher overwinter mortality, most likely due to predation, in 9 of 11 years. This led us to suspend skunk plantings after 3 years. Nevertheless, commercial fishermen perceived skunks to be "our" scallops, helping raise the profile of and support for our restoration efforts. Implications for Practice• Tracking the success of restoration efforts is critically important for fostering the support of different user groups; however, many of these approaches (e.g. genetic markers, intensive surveys) are expensive or infeasible. • We utilized a phenotypic marker as an additional, low cost means of supporting strong correlations that we had previously established between overall numbers of planted bay scallop broodstock and both natural recruitment and commercial fishery landings. The present effort ultimately proved unsuccessful over the long term, but may provide guidance for future efforts with other species. • Despite our lack of success on an operational level, the perception of increased abundance of uncommon color morphs by fishermen has raised support for restoration efforts.