Virginia Institute of Marine Science
Identifying the mechanistic drivers of migration can be crucial in shaping conservation and management policies. The cownose ray (Rhinoptera bonasus) is a relatively poorly understood elasmobranch species that occurs along the U.S. Atlantic coast and undergoes large-scale seasonal migrations. To better understand the drivers and timing of cownose ray seasonal migration in order to inform potential management measures, we analyzed telemetry detections of 51 mature cownose rays (38 female, 13 male) tagged with acoustic transmitters in the Maryland and Virginia portions of Chesapeake Bay. Detections within their summer habitat in Chesapeake Bay and winter habitat in the vicinity of Cape Canaveral, Florida, were matched with publicly available sea surface temperature (SST) data recorded by data buoys near the areas of tag detections and with local photoperiod and day of year. These variables were used in boosted regression tree models of ray presence (all rays combined, females only, and males only) in each seasonal habitat. Models were developed for presence during the entire summer and winter season, and for the time periods of arrival and departure from both summer and winter habitats. Seasonal presence in both summer and winter habitats was associated with distinct temperature, photoperiod, and date ranges, with temperature as the most influential variable in seasonal models. In models of arrival and departure periods, southward migration (departure from Chesapeake Bay and arrival off Cape Canaveral) was strongly associated with SST for all rays and arrival in the Chesapeake Bay region after northward migration was most strongly associated with day of year. The most influential variable during the period of northward departure from Cape Canaveral differed between males (day of year) and females (SST). This suggests that mature female northward migration may be driven by temperature while male northward migration may be driven by endogenous cues. These findings provide detailed information on the timing of cownose ray arrival at, presence in, and departure from seasonal habitats and provide potential justification for including the species in cross-taxa comparative studies on migratory behavior.
elasmobranch; migration; photoperiod; sea surface temperature
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Bangley, Charles W.; Edwards, Michelle L.; Mueller, Claire; Fisher, Robert A.; and et al, Environmental associations of cownose ray (Rhinoptera bonasus) seasonal presence along the U.S. Atlantic Coast (2021). Ecosphere, 12(9), e03743.