Abstract
North American Black Terns ( Chlidonias niger ) breed primarily in the Prairie Pothole region of southern Canada and the northern United States, winter in Central and South American waters, and often migrate through the northern Gulf of Mexico (nGoM). This species has exhibited long-term population declines and is exposed to a myriad of anthropogenic threats in the nGoM, including oil spills, with an estimated 800–1,000 injured during the Deepwater Horizon oil spill, yet historical studies of Black Terns' use of the nGoM are sparse, with inconsistent spatial and temporal coverage. Using vessel-based observations collected from 2017 to 2019, we characterize Black Tern spatial and temporal occurrence in marine waters of the nGoM. We develop 2 separate habitat models: one describing spatial and temporal aspects of Black Terns occurrence and the other describing the relative density when present. In 10 months of survey effort, January–October, we observed Black Terns in 7 (Mar–May and Jul–Oct), predominantly on the continental shelf at <200 m depth. Relative densities were greatest in the fall, coinciding with Black Terns' southward migration. Spatial distribution and habitat models suggest an association with river mouths or ports, as well as cool, productive waters, frequently associated near the outflow of the Mississippi River and just off the coast from Corpus Christi, Texas. The enhanced understanding of Black Terns in the nGoM could inform the preparation for, and response to, future oiling events or provide insight into potential interactions with the installation of offshore wind farms and aquaculture.
North American black terns ( Chlidonias niger ) breed primarily in the Prairie Pothole region of southern Canada and the northern United States, winter in Central and South American waters, and often migrate through the northern Gulf of Mexico (nGoM). This species has shown long-term population declines and is exposed to a myriad of anthropogenic threats in the nGoM, including oil spills, with an estimated 800–1,000 individuals injured in the Deepwater Horizon oil spill, but historical studies of black tern use of the nGoM are sparse, with inconsistent spatial and temporal coverage. Using vessel-based observations collected from 2017 to 2019, we characterize the spatial and temporal occurrence of black terns in marine waters of the nGoM. We developed two distinct habitat models: one describing spatial and temporal aspects of black tern occurrence and one describing relative density when present. Over the 10 months of surveys, from January to October, we observed black terns in seven months (March to May and July to October), primarily on the continental shelf at <200 m depth. Relative densities were highest in autumn, coinciding with black tern migration southward. Spatial distribution and habitat patterns suggest an association with river mouths or harbors, as well as fresh, productive waters, frequently associated near the mouth of the Mississippi River and just offshore Corpus Christi, Texas. A better understanding of black terns in the nGoM could inform preparedness and response to future oil spills or provide insight into potential interactions with offshore wind farms and aquaculture.