Distribution and density of six large whale species in the New York Bight from monthly aerial surveys 2017 to 2020

Abstract

This multi-year study investigated the density and distribution of six large whale species in the New York Bight (NYB): the blue whale (Balaenoptera musculus), fin whale (B. physalus), humpback whale (Megaptera novaeangliae), North Atlantic right whale (Eubalaena glacialis), sei whale (B. borealis), and sperm whale (Physeter macrocephalus). During 36 line-transect aerial surveys conducted systematically nearshore out to 120 nm from March 2017 to February 2020, 318 total sightings of these species were recorded. Sighting rates varied by season and distance from shore. The combined density of the six species, uncorrected for detectability on the survey line (g[0]), was 1.7 individuals/1,000 km2, and average annual abundance was estimated to be 76 whales (CV = 21.2%) in the NYB survey area. When species-specific corrections for trackline detectability bias were applied, the overall density estimate increased to 6.3 individuals/1,000 km2 and 272 average annual abundance. Sightings were characterized within four habitat distribution zones based on depth or distance from shore out to 250 nm. Humpback and fin whales occurred in greater numbers than the other four species and were recorded in all years, in all four seasons, at minimum at least once in each month, and from nearshore to offshore in all habitat zones. Right whales were seen in all seasons except summer and occurred mainly in the shelf zone. Sperm whales were seen in all seasons and in all months except May and November, mainly in offshore waters in the plain. Blue whales were seen in fall and winter in offshore waters, and sei whales in spring on the shelf and slope. All large whales were most frequently sighted in the shelf zone with similar albeit lower numbers seen in the slope and plain habitat. Large whale sighting rates were highest during summer, followed by spring. Results from these surveys provide valuable data on the year-round occurrence of large whales, including blue and sei whales which have rarely been recorded in Atlantic seaboard waters west of Cape Cod, and provide a basis for management and conservation efforts in the NYB. These data can inform assessments of current measures to protect large whales from anthropogenic threats like fishing, shipping, and offshore wind development in the NYB, as well as evaluations of specific potential impacts of such activities (e.g., site-specific take estimates and noise exposures).