GEOSTATISTICAL ESTIMATION OF BLUE CRAB CALLINECTES SAPIDUS ABUNDANCE IN CHESAPEAKE BAY AT LOCAL SCALES

Abstract

Increases in the sizes of container ships due to the expansion of the Panama Canal has increased the need for dredging activities in the Chesapeake Bay. Placement of dredged material in the Bay is restricted to winter months owing to concerns for threatened and endangered species. Placement of dredged material in the lower Chesapeake Bay in Wolf Trap Alternate Open Water Placement Site (WTAPS) overlaps with overwintering locations for mature female blue crab. To estimate the potential magnitude of winter mortality in WTAPS and WTAPS Northern Extension (WTAPSNE) resulting from placement of dredged material, a range of geostatistical tools (e.g., inverse distance weighting and kriging) were used to map the distribution and estimate the abundance of blue crab in Chesapeake Bay, WTAPS, and WTAPSNE (i.e., small-scale estimation) from 1990–2020 using data from the winter dredge survey. These analyses indicated that a low proportion of the age-1+ female blue crab population occurs within WTAPS and WTAPSNE (<1.18% and <1.5% respectively). Variability of abundance estimates was high when female age-1+ abundance was less than 150 million in the Chesapeake Bay. Therefore, we suggest the Port limit placement of dredged materials in WTAPS and WTAPSNE when female age-1+ abundance is less than 150 million; we recommend the Port not undertake placement activities when the stock is declared overfished (i.e., when female age-1+ abundance is less than 72.5 million).