Environmental associations of cownose ray (Rhinoptera bonasus) seasonal presence along the U.S. Atlantic Coast

Abstract

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.

Intraocular Pressures of Aquarium-Housed Cownose Rays (Rhinoptera Bonasus) With Normal and Abnormal Ophthalmic Exams

“…This species spends its life underwater in either pelagic or benthic regions of the water column. 1 There are currently no instruments to measure IOP underwater, making it impossible to evaluate this species' IOP in situ . The overall effect of removing cownose rays from the water to measure IOP remains unclear, but with limited tonometer technology, measurement out of water is currently the only practical option.…”

Recent expansion of the Atlantic cownose ray (Rhinoptera bonasus) into Bermudian waters

“…However, since those conditions do not last for long periods, it is possible rays simply move to warmer waters in the North Lagoon, similar to the pattern observed in the northern Gulf of Mexico (9,24), or are resident, as reported in parts of south Florida (25,26). Along the Atlantic coast of the U.S., northward migration cues for females and males depend on different factors: sea surface temperature for females, and day of year for males (22). While all collections of cownose rays in Bermuda to date are of females, the acquisition of small, immature rays (e.g., CNR-3) suggests pupping may have recently occurred here.…”

“…Based on thermal conditions alone, cownose rays can likely reside in Bermuda for extended periods. Outmigration of cownose rays along the Atlantic coast (i.e., southbound departure from the Chesapeake Bay in fall) is triggered by changes in thermal conditions; in particular, as temperatures fall below 20 • C (22,23). In Bermuda, wintertime temperatures can approach 15 • C within shallow inshore bays (1), which could force rays to become migratory.…”

The influence of light on elasmobranch behavior and physiology: a review

“…An influence of photoperiods on movement has also been inferred based on broad scale trends in shark abundances, such as daily aggregations (Brunnschweiler and Barnett, 2013;Nosal et al, 2014), rate of movement (Cartamil et al, 2003), and bycatch rates (Niella et al, 2021b). Seasonal behaviors associated with solar and lunar photoperiods include aggregation (Grubbs et al, 2007;Nosal et al, 2014;Kajiura and Tellman, 2016;Ayres et al, 2021;Niella et al, 2021a), migration (Kessel et al, 2014;Bangley et al, 2021), site fidelity (Vaudo and Lowe, 2006;Grubbs et al, 2007;Kneebone et al, 2012;Dudgeon et al, 2013;Nosal et al, 2014), residency (Kneebone et al, 2012;Kessel et al, 2014), and diving (Andrews et al, 2009).…”