The Maine (USA) aquaculture industry has grown considerably in recent decades, and with it the farming of the American oyster (Crassostrea virginica). Due to a combination of overharvesting, industrial development, and environmental change in the Gulf of Maine, wild populations of American oysters in Maine have been considered functionally extinct since the early 1900s. However, anecdotal evidence indicates that oysters are becoming more prevalent in the intertidal zone outside of culture operations. Still, very little is known about American oyster population dynamics in Maine estuaries. We sought to determine if adult oysters are spawning in two estuaries - the New Meadows and the Sheepscot.
Between May and September of 2024, we conducted sampling of adult oysters in the New Meadows and Sheepscot river estuaries. Fifteen individuals were collected monthly at each site. Sampling was opportunistic in that we obtained oysters from different sources in each estuary, but selective in that we aimed for oysters of a consistent size within an estuary. For each individual we measured wet weight (whole, meat-only, and shell-only) and shell dimensions (height, width, and depth), before preserving and processing tissue for histological analysis of reproductive tissue. In the New Meadows River, oysters (shell height 49-112 mm, average 78.10 mm) were collected from a Limited Purpose Aquaculture permitted site managed by a community-based collaboration working on local oyster restoration. In the Sheepscot River, oysters (shell height 77-146 mm, average 112.3 mm) were collected from a bottom culture oyster lease in June and then held in floating bags nearby. Sondes were deployed for the duration of sampling in the New Meadows and Sheepscot River estuaries to collect continuous data for water temperature, salinity, chlorophyll and turbidity.
Results will focus on characterizing the environmental parameters of the two estuaries, a preliminary analysis summarizing the presence and absence of reproductive tissue and possibly the timing of a spawning event, as well as relating reproduction to environmental parameters. To our knowledge, this study is the first to examine the presence of reproduction in American oysters in Maine estuaries through histology sampling.