Rhinoptera Bonasus Research Articles

Biomechanical model of batoid (skates and rays) pectoral fins predicts the influence of skeletal structure on fin kinematics: implications for bio-inspired design

Growing interest in the development of bio-inspired autonomous underwater vehicles (AUVs) has motivated research in understanding the mechanisms behind the propulsion systems of marine animals. For example, the locomotive behavior of rays (Batoidea) by movement of the pectoral fins is of particular interest due to their superior performance characteristics over contemporary AUV propulsion systems. To better understand the mechanics of pectoral fin propulsion, this paper introduces a biomechanical model that simulates how batoid skeletal structures function to achieve the swimming locomotion observed in nature. Two rays were studied, Dasyatis sabina (Atlantic ray), and Rhinoptera bonasus (cownose ray). These species were selected because they exhibit very different swimming styles (undulation versus oscillation), but all use primarily their pectoral fins for propulsion (unlike electric rays or guitarfishes). Computerized tomography scans of each species were taken to image the underlying structure, which reveal a complex system of cartilaginous joints and linkages. Data collected from these images were used to quantify the complete skeletal morphometry of each batoid fin. Morphological differences were identified in the internal cartilage arrangement between each species including variations in the orientation of the skeletal elements, or radials, and the joint patterns between them, called the inter-radial joint pattern. These data were used as the primary input into the biomechanical model to couple a given ray skeletal structure with various swimming motions. A key output of the model is an estimation of the uniaxial strain that develops in the skeletal connective tissue in order for the structure to achieve motions observed during swimming. Tensile load tests of this connective tissue were conducted to further investigate the implications of the material strain predictions. The model also demonstrates that changes in the skeletal architecture (e.g., joint positioning) will effect fin deformation characteristics. Ultimately, the results of this study can be used to guide the design of optimally performing bio-inspired AUVs.

Stability Design and Response to Waves by Batoids.

Unsteady flows in the marine environment can affect the stability and locomotor costs of animals. For fish swimming at shallow depths, waves represent a form of unsteady flow. Waves consist of cyclic oscillations, during which the water moves in circular or elliptical orbits. Large gravity waves have the potential to displace fish both cyclically and in the direction of wave celerity for animals floating in the water column or holding station on the bottom. Displacement of a fish can exceed its stability control capability when the size of the wave orbit is equivalent to the size of the fish. Previous research into compensatory behaviors of fishes to waves has focused on pelagic osteichthyan fishes with laterally compressed bodies. However, dorsoventrally compressed batoid rays must also contend with waves. Examination of rays subjected to waves showed differing strategies for stability between pelagic and demersal species. Pelagic cownose rays (Rhinoptera bonasus) would glide through or be transported by waves, maintaining a positive dihedral of the wing-like pectoral fins. Demersal Atlantic stingrays (Dasyatis sabina) and freshwater rays (Potamotrygon motoro) maintained contact with the bottom and performed compensatory fin motions and body postures. The ability to limit displacement due to wave action by the demersal rays was also a function of the bottom texture. The ability of rays to maintain stability due to wave action suggests mechanisms to compensate for the velocity flux of the water impinging on the large projected area of the enlarged pectoral fins of rays.

A biomimetic cownose ray robot fish with oscillating and chordwise twisting flexible pectoral fins

PurposeThe paper aims to develop a cownose ray-inspired robotic fish which can be propelled by oscillating and chordwise twisting pectoral fins.Design/methodology/approachThe bionic pectoral fin which can simultaneously realize the combination of oscillating motion and chordwise twisting motion is designed based on analyzing the movement of cownose ray’s pectoral fins. The structural design and control system construction of the robotic fish are presented. Finally, a series of swimming experiments are carried out to verify the effectiveness of the design for the bionic pectoral fin.FindingsThe experimental results show that the deformation of the bionic pectoral fin can be well close to that of the cownose ray’s. The bionic pectoral fin can produce effective angle of attack, and the thrust generated can propel robotic fish effectively. Furthermore, the tests of swimming performance in the water tank show that the robotic fish can achieve a maximum forward speed of 0.43 m/s (0.94 times of body length per second) and an excellent turning maneuverability with a small radius.Originality/valueThe oscillating and pitching motion can be obtained simultaneously by the active control of chordwise twisting motion of the bionic pectoral fin, which can better imitate the movement of cownose ray’s pectoral fin. The designed bionic pectoral fin can provide an experimental platform for further study of the effect of the spanwise and chordwise flexibility on propulsion performance.

Clarification on the Fecundity ofRhinoptera bonasus(Mitchill)

Abstract Accurate fecundity estimates are necessary for the proper assessment of fish stocks. Despite all recent investigations of the reproductive biology of Rhinoptera bonasus (Cownose Ray) indicating a maximum fecundity of 2 embryos per brood, maximum fecundity estimates of 6 per brood persist. All reports of 6 embryos per brood seem to stem from a single account. It is the purpose of this paper to present evidence indicating that the report of 6 embryos is based upon a misidentification in the field, and that maximum fecundity estimates for the Cownose Ray are therefore up to six-fold higher than actually observed.

Characterization of Bycatch in the Cannonball Jellyfish Fishery in the Coastal Waters off Georgia

AbstractStudies have been conducted in Georgia to examine bycatch in many fisheries, but none has focused on the trawl fishery for cannonball jellyfish Stomolophus meleagris. Although this fishery is relatively new, it presently ranks in the top three by weight (kg) in Georgia, along with the food shrimp and blue crab Callinectes sapidus fisheries. The purpose of this study was to characterize and quantify the finfish and invertebrate bycatch species in the cannonball jellyfish trawl fishery in Georgia. Between December 2005 and December 2012, observers accompanied commercial fishers utilizing trawl gear to target cannonball jellyfish in the coastal waters off Georgia; a total of 133 tows were sampled. Observed tow duration ranged from 0.15 to 1.22 h, averaging 0.55 h/tow. During the study period, 1,488 finfish and 150 invertebrates were collected, and 13 individuals representing four species of concern were present in the bycatch. The most numerous species were the Harvestfish Peprilus paru (n = 677), Cownose Ray Rhinoptera bonasus (n = 185), Atlantic Bumper Chloroscombrus chrysurus (n = 179), Butterfish Peprilus triacanthus (n = 175), and blue crab (n = 114). The estimated numbers of captured cannonball jellyfish and bycatch varied monthly and yielded an overall cannonball jellyfish : bycatch ratio of 291:1. Results suggest that bycatch in the cannonball jellyfish fishery is nominal in comparison with other Georgia trawl fisheries (e.g., shrimp trawl fishery) and is dominated by a few species that are known to associate with jellyfish. Information gained in the present study provides fishery managers with the knowledge necessary to better understand the impacts of Georgia's commercial cannonball jellyfish trawl fishery on other species.Received September 3, 2014; accepted March 10, 2015

Preservation Effects on Stable Isotope Values of Archived Elasmobranch Fin Tissue: Comparisons between Frozen and Ethanol‐Stored Samples

AbstractElasmobranch fin tissue has been sampled and archived for decades to support genetics research. However, these collections have the potential to provide additional information on the trophic ecology of and habitat use by elasmobranch species. The use of fin tissue is especially attractive considering the threatened status of many elasmobranchs and the call for limiting mortalities. Yet, the use of fin samples for stable isotope analysis requires either that (1) storage methods do not alter tissue isotope values or (2) any alterations in isotope composition that occur during storage are predictable. In this study, paired fin tissues sampled from Smalltooth Sawfish Pristis pectinata and cownose rays Rhinoptera spp. were stored frozen and in ethanol and were subsequently analyzed for carbon (δ13C) and nitrogen (δ15N) isotope ratios. Fin δ13C and δ15N values were highly correlated between treatments for both taxa (r2 ≥ 0.80). For Smalltooth Sawfish, ethanol storage significantly increased fin δ13C values by 0.5 ± 0.1‰ (mean ± SE) and decreased fin δ15N values by 0.1 ± 0.1‰ relative to frozen samples; differences were similar for cownose rays (δ13C: 0.2 ± 0.2‰; δ15N: 0.2 ± 0.1‰) but were not significant. A range of approximately 3‰ for δ13C between treatments could have effects on data interpretation, suggesting the use of regressions for ethanol correction of δ13C values, although trends were comparable between frozen and ethanol‐preserved samples without correction. Given the low variability in δ15N values, a correction is not warranted. For endangered species such as the Smalltooth Sawfish, stable isotope analysis of ethanol‐archived fin samples can provide important information regarding habitat use and trophic ecology, with potential significance for conservation and management strategies. The general uniformity in isotope ratio shifts observed for archived samples between the two taxa suggests that these findings can be generalized across elasmobranch species.Received March 27, 2014; accepted July 30, 2014

Dynamic modeling of a flexible oscillating pectoral fin for robotic fish

Purpose– The paper aims to present a dynamic model of flexible oscillating pectoral fin for further study on its propulsion mechanism.Design/methodology/approach– The chordwise and spanwise motions of cow-nosed ray’s pectoral fin are first analyzed based on the mechanism of active/passive flexible deformation. The kinematic model of oscillating pectoral fin is established by introducing the flexible deformation. Then, the dynamic model of the oscillating pectoral fin is developed based on the quasi-steady blade element theory. A series of hydrodynamic experiments on the oscillating pectoral fin are carried out to investigate the influences of motion parameters on the propulsion performance of the oscillating pectoral fin.Findings– The experimental results are consistent with that obtained through analytical calculation within a certain range, which indicates that the developed dynamic model in this paper is applicable to describe the dynamic characteristics of the oscillating pectoral fin approximately. The experimental results show that the average thrust of an oscillating pectoral fin increases with the increasing oscillating amplitude and frequency. However, the relationship between the average thrust and the oscillating frequency is nonlinear. Moreover, the experimental results show that there is an optimal phase difference at which the oscillating pectoral fin achieves the maximum average thrust.Originality/value– The developed dynamic model provides the theoretical basis for further research on propulsion mechanism of oscillating pectoral fins. It can also be used in the design of the bionic pectoral fins.

A genetic technique to identify the diet of cownose rays, Rhinoptera bonasus: analysis of shellfish prey items from North Carolina and Virginia

Cownose rays are implicated in the consumption of commercially important shellfish on the U.S. East Coast. We tested this assumption by developing a molecular technique for species identification from cownose ray gut contents. Digestive tracts sampled from 33 rays in Pamlico Sound, NC and Chesapeake Bay, VA contained pieces of partially-digested tissue, well-digested tissue, fluid, and minute shell fragments which made visual identification to the species level nearly impossible. We sequenced the cytochrome oxidase subunit I (COI) for seven locally acquired bivalve species, chosen for their commercial and ecological importance in NC and VA. Sequences were used to design species-specific primers for each bivalve species to amplify polymerase chain reaction (PCR) products. We designed primers such that PCR products were sufficiently different in size to be distinguishable from one another when resolved on an agarose gel, and multiplexing of several species in one reaction was possible. Digestive tract sample testing revealed that cownose rays in Chesapeake Bay ate stout tagelus and soft shell clams. There was no evidence of the rays in the study consuming commercially important oysters, hard clams, and bay scallops. Further sampling over an extended period of time and additional locations is required to confirm these results. Our diagnostic tests could easily be expanded to elucidate the impact of cownose ray predation on prey populations.

Reproductive variations in cownose rays (Rhinoptera bonasus) from Chesapeake Bay

The cownose ray, Rhinoptera bonasus, a K-selected species in Chesapeake Bay is subject to an unregulated fishery with no management plan in place. Understanding the reproductive potential for cownose ray is important for successful conservation and management. This study marks the first observation of multiple embryos and right uterus functionality. Eight instances of multiple embryos in cownose rays are reported; two sets of twin live births from captive rays and six separate in utero multiple embryos discovered during necropsy of fishery-dependent and -independent samples. All multiple embryos were in the left uterus. Live births in captivity were confirmed as two sets of twins through direct sequencing of a portion of the mitochondrial DNA and analysis of nuclear microsatellite loci from the newborn pups and putative mothers. In addition, first- and third- quarter term embryos were removed from the right uterus of two female rays during necropsy, marking the first reports of gestation in the right oviduct of cownose rays. The recovery of a three-quarter term albinistic cownose ray embryo through necropsy is also reported.

Towed-float satellite telemetry tracks large-scale movement and habitat connectivity of myliobatid stingrays

Batoids are important mesopredators whose high mobility and extensive migrations can link seemingly distant food webs in coastal ecosystems. Despite this recognition, our knowledge of the movement patterns of many species is limited due to the logistical challenge of tracking these animals on multiple scales. Smart Positioning or Temperature (SPOT) satellite-linked transmitters allow for precise, multi-scale tracking of species that regularly use surface waters. To date, SPOTs have been predominantly used on sharks, with only a single application to a batoid. Given the epipelagic nature of myliobatid stingrays, we examined the potential for towed-float SPOT transmitters to monitor large-scale movements of two representative species: the Cownose Ray (Rhinoptera bonasus; n = 15) and Spotted Eagle Ray (Aetobatus narinari; n = 9). Tracking data identified several consistent outmigration patterns of Cownose Rays along the Mississippi-Alabama shelf and seasonal variation in movement rates along barrier island habitats. We also documented sex-related differences in movement rates and habitat use of Spotted Eagle Rays along the Bermuda platform, where males exhibited significantly higher movement rates than females and more transient behavior between inshore lagoons and outer coral reefs. Both Cownose and Spotted Eagle Rays were shown to exhibit connectivity among several habitat types along continental shelves in their respective locales, demonstrating future challenges to the management of these species over large spatial scales. While reductions in tag size and improved tethering techniques would undoubtedly broaden the applicability of towed-float satellite telemetry to other species and sizes, our work highlights the strong potential for this technology to provide insights into the spatial ecology and habitat use of myliobatid rays.

Ontogenetic testicular development and spermatogenesis in rays: the Cownose Ray, Rhinoptera bonasus, as a model

An understanding of testicular anatomy, development, and seasonality has implications for studies of morphology, behavior, physiology, and bioenergetics of males. Ontogenetic testicular development and spermatogenesis is essentially unknown for chondrichthyans. We examined embryo, juvenile, and adult male Cownose Rays (Rhinoptera bonasus) during development and throughout the annual reproductive cycle. Spermatogonia and Sertoli cells originated from germ cells and somatic cells, respectively, in the embryonic testicular germinal epithelium. In embryos and small juveniles, discrete regions of spermatocyst production appeared within a series of papillae that projected from the dorsal surface of each testis. Because these papillary germinal zones appeared to proliferate through ontogeny, we hypothesize that (1) the germinal zones of juvenile and adult testes are derived from embryonic testicular papillae that form from the germinal epithelium and (2) the papillae become the dorso-central portion of the distinct testicular lobes that form at maturation due to increased spermatocyst production. Our observations indicate that testicular development and the process of spermatogenesis began during embryonic development and increased in scale through ontogeny until maturation, when distinct testicular lobes formed and began enlarging or shrinking based on the annual reproductive cycle. Gonadosomatic indices peaked corresponding to seasonal increased sperm production between January and April, just prior to the April–June mating period. In all life stages, spermatocysts had efferent ducts associated with them from their formation through all stages of development. Year-round presence in the Charlotte Harbor estuarine system, Florida made R. bonasus a good model for beginning to understand ontogenetic gonad development and spermatogenesis in chondrichthyans, especially viviparous rays.

Feeding comparisons of four batoids (Elasmobranchii) in coastal waters of southern Brazil

Food partitioning between species is a common strategy for avoiding resource competition which allows the coexistence of two or more species in the same place. In order to evaluate the feeding of four species of batoids regularly caught by artisanal fisheries in southern Brazil, the present study aimed to analyse and compare the diet of the four batoid species. The Chola guitarfish,Rhinobatos percellens, had a specialized diet, consisting predominantly of blue crabsCallinectessp., followed by teleost fish. The Lesser guitarfishZapteryx brevirostrisalso had a very specialized diet, consuming mainly on Polychaeta, followed by Caridea shrimp. The Cownose ray,Rhinoptera bonasus, fed mainly on Ophiuroidea, followed by Gastropoda and Bivalvia. Finally, the Rio skateRioraja agassizi, fed on teleost fish, Gammaridae, Caridea shrimp and Dendrobranchiata shrimp. An analysis of similarity showed significant differences among species in their diet. The trophic levels of the batoids in this study are <4.0, placing them in intermediate trophic levels. The analysis of the diets indicates that feeding differs substantially among the four species, suggesting a partitioning of food resources available in the environment.

Records of Himantura granulata (Dasyatidae) and Rhinoptera jayakari (Rhinopteridae) from the Red Sea

The occurrences of two species of rays of the families Dasyatidae and Rhinopteridae are confirmed for the central and southern Red Sea, respectively. The Oman Cownose Ray, Rhinoptera jayakari, is reported as a new record from the Red Sea on the basis of two males collected at Jizan, southern Saudi Arabia. An adult individual of the Mangrove Whipray, Himantura granulata, previously only reported from the Gulf of Aqaba was observed and photographed in a shallow lagoon off Al Lith, Saudi Arabia, also confirming its presence in the Red Sea.

Distribution extension of Glyphobothrium zwerneri Williams & Campbell, 1977 (Tetraphyllidea: Serendipeidae) from the cownose ray Rhinoptera bonasus (Mitchill, 1815) (Myliobatiformes: Myliobatidae) from Campeche, México

The collection of four specimens of Glyphobothrium zwerneri extends the geographic distribution of the species from the original locality (Chesapeake Bay, Virginia, U.S.A.) to at least Ciudad del Carmen, Campeche, México, at the southern limit of the Gulf of Mexico. The species is a parasite of Rhinoptera bonasus, a stingray that is thought to migrate within a wide range, suggesting that conservation efforts should be consistent within the stingray’s range, just as is necessary for birds and other species that migrate.

Behavioral responses of batoid elasmobranchs to prey-simulating electric fields are correlated to peripheral sensory morphology and ecology

Electrosensory pore number, distribution, and sensitivity to prey-simulating electric fields have been described for many shark species. Electrosensory systems in batoids have received much less attention. Pore number and distribution have yet to be correlated to differences in sensitivity. However, pore number, pore distribution and sensitivity have been linked to behavior, diet, and morphology and follow species-specific trends. We report here that cownose rays have a greater number of pores than the yellow stingray, most of which are concentrated on the anterior ventral surface for both species. However, yellow stingrays have a broader arrangement of pores on both their dorsal and ventral surfaces than the cownose rays. Yellow stingrays demonstrated a median behavioral sensitivity to weak electric fields of 22nVcm−1 and are among the most highly sensitive batoids studied to date. Cownose rays are less sensitive than all other elasmobranch species with a median sensitivity of 107nVcm−1. As reported in previous studies, a higher pore number did not result in greater sensitivity. Cownose rays are benthopelagic schooling rays and may benefit from reduced sensitivity to bioelectric fields when they are surrounded by the bioelectric fields of conspecifics. Yellow stingrays, on the other hand, are typically solitary and bury in the substrate. A greater number of pores on their dorsal surface might improve detection of predators above them. Also, increased sensitivity and a broader distribution of pores may be beneficial as small prey items move past a buried ray.

A physiological analysis of color vision in batoid elasmobranchs

The potential for color vision in elasmobranchs has been studied in detail; however, a high degree of variation exists among the group. Evidence for ultraviolet (UV) vision is lacking, despite the presence of UV vision in every other vertebrate class. An integrative physiological approach was used to investigate color and ultraviolet vision in cownose rays and yellow stingrays, two batoids that inhabit different spectral environments. Both species had peaks in UV, short, medium, and long wavelength spectral regions in dark-, light-, and chromatic-adapted electroretinograms. Although no UV cones were found with microspectrophotometric analysis, both rays had multiple cone visual pigments with λ max at 470 and 551 nm in cownose rays (Rhinoptera bonasus) and 475, 533, and 562 nm in yellow stingrays (Urobatis jamaicensis). The same analysis demonstrated that both species had rod λ max at 500 and 499 nm, respectively. The lens and cornea of cownose rays maximally transmitted wavelengths greater than 350 nm and greater than 376 nm in yellow stingrays. These results support the potential for color vision in these species and future investigations should reveal the extent to which color discrimination is significant in a behavioral context.

The morphology of the cephalic lobes and anterior pectoral fins in six species of batoids

Many benthic batoids utilize their pectoral fins for both undulatory locomotion and feeding. Certain derived, pelagic species of batoids possess cephalic lobes, which evolved from the anterior pectoral fins. These species utilize the pectoral fins for oscillatory locomotion while the cephalic lobes are used for feeding. The goal of this article was to compare the morphology of the cephalic lobes and anterior pectoral fins in species that possess and lack cephalic lobes. The skeletal elements (radials) of the cephalic lobes more closely resembled the radials in the pectoral fin of undulatory species. Second moment of area (I), calculated from cephalic lobe radial cross sections, and the number of joints revealed greater flexibility and resistance to bending in multiple directions as compared to pectoral fin radials of oscillatory species. The cephalic lobe musculature was more complex than the anterior pectoral fin musculature, with an additional muscle on the dorsal side, with fiber angles running obliquely to the radials. In Rhinoptera bonasus, a muscle presumably used to help elevate the cephalic lobes is described. Electrosensory pores were found on the cephalic lobes (except Mobula japonica) and anterior pectoral fins of undulatory swimmers, but absent from the anterior pectoral fins of oscillatory swimmers. Pore distributions were fairly uniform except in R. bonasus, which had higher pore numbers at the edges of the cephalic lobes. Overall, the cephalic lobes are unique in their anatomy but are more similar to the anterior pectoral fins of undulatory swimmers, having more flexibility and maneuverability compared to pectoral fins of oscillatory swimmers. The maneuverable cephalic lobes taking on the role of feeding may have allowed the switch to oscillatory locomotion and hence, a more pelagic lifestyle.

A Retrospective Study of Disease in Elasmobranchs

This report reviews diseases of 1546 elasmobranchs representing at least 60 species submitted to Northwest ZooPath from 1994 to 2010. Cownose rays (Rhinoptera bonasus) (78), southern rays (Dasyatis americana) (75), dusky smooth-hounds (Mustelus canis) (74), bonnethead sharks (Sphyrna tiburo) (66), and bamboo sharks (Hemiscylliidae) (56) were the most commonly submitted species. Infectious/inflammatory disease was most common (33.5%) followed by nutritional (11.9%, mostly emaciation), traumatic (11.3%), cardiovascular (5.5%, mostly shock), and toxin-associated disease (3.7%). Bacterial infections (518/1546, 15%) included sepsis (136/518, 26%), dermatitis (7%), branchitis (6%), and enteritis (4%). Fungal infections (10/1546, 0.6%) included dermatitis (30%), hepatitis (30%), and branchitis (20%). Viral or suspected viral infections or disease processes (15/1546, 1%) included papillomatosis (47%), herpesvirus (20%), and adenovirus (7%). Parasitic infections (137/1546, 9%) included nematodiasis (36/137, 26%), ciliate infections (23%), trematodiasis (20%), coccidiosis (6%), myxozoanosis (5%), amoebiasis (4%), cestodiasis (1%), and flagellate infections (1%). Inflammation of unknown cause (401/1546, 26%) included enteritis (55/401, 14%), branchitis (9%), encephalitis (9%), and dermatitis (7%). Traumatic diseases (174/1546, 11.3%) included skin trauma (103/174, 60%), stress/maladaptation (9%), and gut trauma (7%). Toxicoses (57/1546, 4%) included toxic gill disease (16/57, 26%), gas bubble disease (19%), fenbendazole (7%), ammonia (7%), chlorine (5%), and chloramine (3%). Species trends included visceral nematodiasis in black-nosed sharks (Carcharhinus acronotus) (55%); sepsis in dusky smooth-hounds (41%), blue-spotted stingrays (36%), southern rays (36%), and wobeggong sharks (Orectolobus spp) (69%); emaciation in bamboo (33%) and bonnethead (32%) sharks and freshwater stingrays (Potamotrygon motoro) (32%); and trauma in bonnethead sharks (30%).

Age, Growth, and Reproductive Biology of Cownose Rays in Chesapeake Bay

AbstractThe Cownose Ray Rhinoptera bonasus is an opportunistic predator of benthic invertebrates and has had a long history of negative interactions with commercial shellfish industries. Most recently, Cownose Rays have been implicated in negatively affecting the recovery of bay scallop Argopecten irradians stocks in North Carolina and oyster restoration and commercial aquaculture efforts in Chesapeake Bay. A mitigation attempt to decrease predation on shellfish has resulted in an unregulated fishery for Cownose Rays. Cownose Ray life history suggests that they are highly susceptible to overexploitation. We determined age, growth, and size at maturity for Cownose Rays collected in Chesapeake Bay. In total, 694 rays were used for the study: 246 males ranging in size from 30.0 to 98.0 cm disc width (DW) and 448 females ranging from 30.0 to 110.5 cm DW. The oldest individual observed was a female (107 cm DW) estimated at age 21. Our data suggested that Cownose Rays grow considerably faster during the first few years than has been previously reported, thus producing higher estimates of the growth coefficient k. The best‐fit growth models (three‐parameter von Bertalanffy models) estimated k‐values of 0.2741 for males and 0.1931 for females. The large sample size and inclusion of many older animals (n = 119 rays over age 10) resulted in theoretical maximum size estimates that matched the observed sizes well. The median size at 50% maturity was 85–86 cm DW for males and females (corresponding to ages of ∼6–7 for males and ∼7–8 for females). Fecundity in Cownose Rays was typically one embryo per mature female, with a gestation period of 11–12 months. Our study confirms that the Cownose Ray is a K‐selected species with late maturity, long gestation, and low reproductive potential, indicating that it could be highly susceptible to overexploitation.Received February 28, 2013; accepted June 3, 2013

Reproductive Biology of the Cownose Ray in the Charlotte Harbor Estuarine System, Florida

AbstractThe Cownose Ray Rhinoptera bonasus is an abundant species in the western Atlantic Ocean, including the Gulf of Mexico, but its reproductive biology is not completely known because of the difficulty of obtaining year‐round samples in large portions of its range where the species is migratory. To address this knowledge gap, Cownose Rays were studied in a subtropical estuarine system where rays are available year‐round. Size at maturity and reproductive cyclicity were assessed using 140 females and 151 males. For females, the size at 50% maturity was 701 mm disk width (DW) based on ovary length and weight, maximum follicle diameter, and mating wounds and scars; the size at 100% maturity was 712 mm DW. For males, the size at 50% maturity was 681 mm DW based on clasper morphology, testis length and weight, and epididymis width; the size at 100% maturity was 712 mm DW. Overall testis size (length and weight) and mean testis lobe diameter peaked up to 2 months prior to ovary size and maximum follicle diameter, indicating that males were preparing to inseminate females during the entire parturition and mating period. Mating behaviors and fresh mating wounds were observed mostly between April and June. Ovulation peaked in May, and parturition occurred primarily in March and April after an 11–12 month, single‐embryo gestation period, suggesting that females are synchronous in Charlotte Harbor. Size at birth was 202–383 mm DW. Concurrent vitellogenesis and gestation indicated a clearly defined annual reproductive cycle that may be completed within the estuary. Understanding reproductive life history in wide‐ranging species such as the Cownose Ray is useful in the short term for making sound management decisions and for future comparison as the effects of global climate change are realized.Received September 30, 2012; accepted March 21, 2013