Abstract

Historically, the Cownose Ray (Rhinoptera bonasus) was considered the only Rhinopterid residing in the northern Gulf of Mexico (GOM); however, recent studies have confirmed the presence of the Brazilian Cownose Ray (R. brasiliensis) throughout this region. As the two species are externally indistinguishable, the confirmation of R. brasiliensis confounds previous life history studies of R. bonasus in the GOM. Neither Rhinopterid is managed by state or federal fisheries programs; however, the new interest in sport fishing for cownose, and its frequent use as bait by recreational anglers and commercial fishers, has put more pressure on their populations. In order to maintain these populations, it is vital that the life history of both species is fully investigated. To date, 209 R. bonasus (118 males and 74 females) ranging in size from 346-930 mm disc width and 67 R. brasiliensis (44 males and 23 females) ranging in size from 444-1030 mm disc width have been collected. Here we show initial results for reproductive timing and seasonality, and gestation periods for both species. Analyses indicate a gestation period of 11-12 months with R. bonasus females pupping in June and R. brasiliensis females pupping in June and July. The smallest mature R. bonasus observed were: 659 and 678 mm disc width; while R. brasiliensis were 741 and 705 mm disc width, females and males respectively. Defining the life history for these two species is this first step toward developing a fisheries management plan and ultimately ensuring the future sustainability of these batoids.

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