Estimating the frequency and extent of bloodworm digging in Maine from aerial photography

Abstract

The extent and frequency of bloodworm digging in northeast North America has never been investigated, making bloodworm fishery management difficult and an assessment of ecological impact impossible. We examined the spatial and temporal patterns of bloodworm digging by surveying 13 mudflats in mid-coast Maine using monthly aerial photography. We used ArcGIS to “georeference” spatial information into the photographs, allowing us to quantify the area of the mudflat disturbed by digging. Of the 122 ha of flats we monitored, almost 48% was dug in 2006, and 24% was dug in 2007, corresponding to 57.9 ha and 24.8 ha, respectively. Individual flats in this study were dug as much as 155% and as little as 0% annually, but rarely were they dug more than once a year as studies assessing the impact of digging on soft-sediment communities have assumed. Digging activity peaked in early spring with a smaller peak in August. On average, 3% of the visual evidence of digging faded each month. Except for those erased by winter storms and ice scour, no dug strip faded before 5 months of age, therefore flats could be monitored every 4–5 months for an accurate estimate of digging activity. Our results allow us, for the first time, to estimate the impact of digging on the bloodworm resource and to design realistic experiments to measure the impact of digging on the soft-sediment community and non-target species.