Stephen T. Tettelbach

Reproduction of hatchery-reared and transplanted wild bay scallops, Argopecten irradians irradians, relative to natural populations

Efforts to restore bay scallop populations in the United States throughtransplantation of wild stock and reseeding of hatchery-reared individuals haveincreased due to declines in natural populations, yet little is known of thecomparative spawning patterns and relative reproductive investment of thesedifferent groups. In this study, spawning patterns of wild scallops from asource population in Northwest Harbor, New York and of scallops transplanted toa distant site in the same embayment (Flanders Bay) were similar.Hatchery-reared scallops held in pearl nets in Hallock Bay, New York showed thesame temporal spawning pattern and level of reproductive investment as scallopsfrom adjacent wild populations and wild scallops held in pearl nets. We suggestthat hatchery-reared scallops may be equally valuable as potential broodstockfor reseeding operations as wild scallops of the same size, provided thatappropriate conditioning and rearing practices are maintained. Both wild andhatchery-reared scallops may be transplanted a short period (i.e. 2–4weeks) prior to expected spawning to provide a source of potential broodstockinareas where natural population densities are low.

Hard clam walking: Active horizontal locomotion of adult Mercenaria mercenaria at the sediment surface and behavioral suppression after extensive sampling

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.