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Cownose Ray (Rhinoptera Bonasus) Predation Relative to Bivalve Ontogeny Robert Fisher, Garrett Call, and Dean Grubbs

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Cownose Ray (Rhinoptera Bonasus) Predation Relative to Bivalve Ontogeny Robert Fisher, Garrett Call, and Dean Grubbs Florida State University Libraries Faculty Publications FSU Coastal and Marine Laboratory 2011 Cownose Ray (Rhinoptera Bonasus) Predation Relative to Bivalve Ontogeny Robert Fisher, Garrett Call, and Dean Grubbs Follow this and additional works at the FSU Digital Library. For more information, please contact [email protected] Journal of S/11'1/jish Research. Vol. 30. o. I. 187 196.2011. COWNOSE RAY (RHINOPTERA BONASUS) PR EDATION RELATIVE TO BIVALVE 0 TOGENY ROBERT A. FISHER,' * GARRETT C. CA LL 1 AND R. DEAN GRUBBS2 1 Virginia Institllfe of Marine Science. College of William and Mary, PO Box 1346. Gloucester Point, VA 23062: 2Fiorida State University Coastal and Marine Labor(ltory . 36 18 Hll')' 98. St. Teresa. FL 32358 ABSTRACT The purpose of this ｾｉｕ､Ｉ＠ was to determine the ability of the cownose ray. Rhiuoptera houasus (Mitchill. 1815). 10 manipulate oysters and ｣ｬ｡ｭｾＮ＠ to test for relative prey preference. and to investigate whclher susceptibility to cownosc ray predation changes wi1h bivalve omogeny. We investigated patterns of preda1ion forcaplivc aduh and young-of-yearcownose rays on 4 species of bivalves, including Crassostrea 1•irgiuica (Gmelin, 1791 ). Cm.uostrea ariakeusis (Fuji ta. 1913). ;\-lercenaria mercenaria (Linnaeus. 1758). and My a areuaria Linnaeus, 1758. In oyster (C. ｬ ｩｲｾＺｩ ｵｩ ｣ｴｴＩ＠ irials, predation probabilities by adull rays were highest at shel l heights of30 70 rnrn and shell depth s of8 22 mm. The ra tes of preda ti on by adult rays in trials in which sa me­ size oysters were used were higher than rates in most comingled trials. Adult rays showed no differences in predation between nati ve oysters (C. virginim) and nonnative oysters (C. ariakensis; P > 0.05). Adult rays selected hard-and soft-shell clams (Manly­ Chcsson index M. merrenaria. a = 0.736 ± 0.002. elcctivity = 0.473 ± 0.007: M. arenaria. a = 0.742 ± 0.003. elcctivity = 0.485 ± 0.013) over oysters (C. 1•irginira. a = 0.263 ± 0.002. clcctivity = - 0.473 ± 0.007: a = 0.257 ± 0.003. elcctivit)' = 0.485 ± 0.003). In young-of-year feeding trials. oysters with a shell height of 10-35 mm and a shell depth of3- 12 mm had the highest probabili1y of predation. a ative oyster and hard clam peak force or load crush tests resulted in forces of200-1.500 and 400 1.400 1 across shell depths of 10-35 mm and 21 34 mm. respectively. before valve failure. The results of th is study indicate that cownose ray predation on shellfish is limited by shell size and is likely related to ray jaw gape and bite force. KEl' WORDS: Durophagy. cownose ray. prey selection. predation risk. Rhinnptera. bivalve mollusc I TROOUCI'IO has been documented (Gray ct al. 1997). and studies have shown the general absence of oysters in the diets of rhinoptcrid The cownosc ray. Rhinoptem honasus (Mitchill. 1815), is and myli obatid rays (Smith & Mcrrincr 1985. Collins et al. a member of the order Myliobatiformcs. which includes 10 2007) even when associated with oyster beds (Gray et al. 1997). families of stingra ys. Cownosc rays (Rhinoptcridae) include at The ability of cownose rays to feed on large oysters is also least 7 species (Compagno 2005) of coastal pelagic rays that questionable a a result of the gape limitations of these rays often travel in large schools. R. /)onttsus is the onl y species that (Summers 2000. Sasko et al. 2006) and the force required to occurs along the cast coast of the United States. and is crush Eastern oysters (Bishop & Peterson 2006). However. distributed from southern cw England to Brazil and through­ Peterson ct a!. (2001 ). report that cownose ra ys in orth out the Gulf of Mexico. Cownosc rays undergo long seasonal Carolina arc capable of depleting dense patches of weaker migrations similar to those exhibited by most coastal sharks shelled bay scallops (Argopecten irradians (Lamarck. 1819)). (Smith & Merriner 1987, Grusha 2005). In spring. they migrate Oyster restoration and commercial grow-out efforts in Virgi nia north. reaching the Outer Banks of North Carolina by April have undoubtedly experienced setbacks because of cownosc and subsequently the Chesapeake Bay in early May (Smith & rays consuming deployed oyster on experimental reefs and Mcrriner 1987). Cownose rays arc abundant in the Chesapeake commercial grounds. In 2004 and 2006. 1.2 million and 775.500 Bay and its tributaries throughout the summer. occurring at oysters were seeded for reef restoration in Virginia. respectively. salinities as low as 8 (practical salinity scale) and temperatures Wesson (2009) reported that 95% were c;llen by cownose rays. from 15-29°C (Smith & Merriner 1987). By early October. most Of the 9 species of batoids that inhabit the Chesapeake Bay cownosc rays have vacated the Chesapeake Bay to begin their during summer months, only 2 species the cownose ray and the southerly migration to wintering areas primarily oli the Atlan­ bullnose ray (M_rliobatisj'remim•illii Lcscur. 1824)- ha ve grinding tic coast of Florida (Grusha 2005). plates and jaw musculature potentiall y capable of manipulating Cownosc rays are durophagous (feeding on hard-shelled and crushing oysters and hard clams (Mercenaria mercenaria prey) predators. feeding on molluscs as well as crustaceans and (Linnaeus. 1758)). Although the bullnose rays may be capable of benthic polychaetes. Collins ct al. (2007) reported that cownose manipulating and crushing adult oysters and hard clams. they arc rays from Charlotte Harbor on the Gulf coast of Florida fed relatively uncommon in Virginia waters. are generally solitary, primarily on small crustaceans (cumacca ns) and sedentary and arc therefore unlikely to be major predators on bivalves in polychactcs, but most earlier studies reported that the dominant this region. Cownose rays. in contrast. arc ex tremely abundant in prey arc small. weak-shelled bivalves (e.g .. Smith & Mcrriner the Chesapeake Bay. The reports of cownose ray predation on 1985. Blaylock 1993). Concern over predation on commercial commercial bivalves coupled wi th questionable claims of dra­ bivalve resources have been raised by fishe ry and aquaculture matic increa es in the cownose ray population coastwide (Myer operation for many years and in several regions of the world. et al. 2007) have spurred interest in developing a commercial However. little evidence of actual predation on these re ources fishery for cownosc rays or at least identifying nonlethal de­ terrents for keeping cownosc rays from commercial beds. •corresponding author. E-mail: rlishcr(a vims.cdu Cownose rays use several behaviors in feeding on bcnlhic DOl : 10.2983/035.030.0 126 prey. Cown ose rays excavate invertebrate prey from the substrate 187 188 FtSII ER ET 1\1 .. by using vigorou o cillati ons of the pectoral fins and ｢ｾ＠ jelling Iarine Science in Gloucester Point. VA. We held adult rays and water taken in through the spiracles during ｲ･ｾｰｩｮｴｬｩｯｮ＠ from the performed predation trials in an aboveground. oblong fiber­ mouth to separate prey funher from sediment (Schwal'li' 1967. ｧｬ｡ｳｾ＠ tank (3 X 4.2 m) with sand filter recircula 1ion . Water depth Sasko 2000). Inertial suction feeding moves prey from the was maintained <II 0.6 m. We held YOY ra y predation trials in sediment imo the mouth. Anterior expansion:> of the pectontl 1.2 X 2.4-m recirculating tanks wi th a water depth of 0.6 m. flns form two mobile cephalic lobes in cownose rays. These lobes aid in the creation of feedin g depressions in the substrate as they arc rhythmically but asynchronously ex tended ventra lly. Feeding trials were conducted no more than once per day. and retracted during feeding (Sasko et al. 2006). The lobe · may ｃ ｯｷｮｯｾ･＠ ra)s were maintained in a less than atiated. but not al o ｾ･ｲｶ･＠ in increasing sucti on :.trength b) surrounding iden­ stancd. condition. Daily ration for clasmobranch . including tified prey. thereby creating a confined vacuum against the batoid:.. range. from 0.3 4.3% of body weight per cla y substrate (Fisher. pers. obs.). When not actively feedin g. these (Wetherbee & Cones 2004). The state of hunger. or mainte­ lobes arc retracted and held ti ght against the body to im:reasc nance level. was achieved by feeding rays approximately 3% of hydrodynamic efficiency. their cumulative body weight per day in live oysters (average The j;tws of cownose ra ys also arc modi lied for durophagy. meal weights from va rious s i1.e oysters were calculated) and The jaws of sharks and rays consist of -1 primary canilages: 2 in freshly killed and dismembered blue crabs. The total weight of the upper jaw and 2 in the lower jaw. The symphyses that biv<tlves (meat) consumed in most trials in this tudy did not loosely connect the two ides of the mandible (lower jaw) and of exceed Ｎ ｾＮＰ Ｅ＠ of the total body weight of the cowno:.c rays. the palatoquadratc (upper jaw) arc fused in the rhinopterid and Supplemental posttrial feeding occurred daily when estimated closely related myli obatid ntys (Summers 2000). Hyperdevel­ consumption by the rays ｷ｡ ｾ＠ less than 3%. oped mandibular adductor and coracomandibular muscles in When not feeding. rays schooled coumerclockwi sc around the jaws (Gonzitlez- ls(tis 2003). highly calcilied jaws. and hard. the holding tank. keeping close proximity to each other. Upon pavemcntlike tooth plates enable cownose rays to Iced on prey initiating each feeding trial. the ray typically made a si ngle with hard shells. The tooth plates are interlocked. distributing ··investigatory"· pass over the shclllish. and then routi nel y began bite force across the whole jaw rather than on a single point preying on the shellfish upon their second pass.
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