372 Mercury levels in four species of sharks from consumed in limited amounts, and fish containing greater than 1.5 the Atlantic coast of Florida ppm of total mercury should not be consumed. The 1991 health advi- Douglas H. Adams sory regarding sharks in Florida Florida Marine Research Institute waters was derived from a limited Florida Department of Environmental Protection number of samples taken from re- 1220 Prospect Ave., Suite 285 tail sources and from studies that Melbourne, Florida 32901 E-mail address: [email protected] lacked important information re- garding species, capture location, sex, and size of sharks examined. Robert H. McMichael Jr. Increased landings of sharks in Florida Marine Research Institute Florida for human consumption Florida Department of Environmental Protection 1 100 Eighth Ave. SE (Brown, in press; FDEP ) has St. Petersburg, Florida 33701 prompted the need for more de- tailed information regarding mer- cury levels in Florida shark species. Consequently, we report here analyses of total mercury levels in Florida’s commercial and recre- methylmercury and has been rec- the muscle tissue of three carcha- ational shark landings represent a ommended as the standard for rhinids (bull shark, Carcharhinus significant portion of the total U.S. regulatory monitoring (Bloom, leucas; blacktip shark, C. limbatus; Atlantic shark landings (NMFS, 1992). Elevated mercury concentra- and Atlantic sharpnose shark, Rhizo- 1993). Shark landings have in- tions in fish have been a growing prionodon terraenovae) and one creased significantly during the concern among resource manage- sphyrnid (bonnethead shark, Sphyr- past decade because human con- ment agencies. Apex predators, par- na tiburo) from the east-central coast sumption of shark meat has become ticularly long-lived species such as of Florida. increasingly acceptable and be- billfishes (Förstner and Wittman, cause, in Asian markets, the de- 1981; Barber and Whaling, 1983; mand for shark fins is very high— Kai et al., 1987), tunas (Miller et Materials and methods as are the prices paid for them al., 1972), mackerels (Meaburn, (NMFS, 1993; Brown, in press). The 1978), and sharks (Forrester et al., Sample collection and mercury east-central coast of Florida is an 1972; Walker, 1976; Lyle, 1986; Vas, analysis important area for commercial and 1991; Hueter et al., 1995, and oth- recreational shark fishing, and a ers) have been reported to accumu- Sharks were collected during the wide array of shark species, includ- late relatively high levels of mercury. Florida Department of Environ- ing those examined in this study, In May 1991, the Florida Depart- mental Protection, Florida Marine are landed in this region (Trent et ment of Health and Rehabilitative Research Institute’s Fisheries-In- al., 1997; FDEP1). Services (FHRS) released a health dependent Monitoring Program in Mercury, a toxic metallic ele- advisory urging limited consump- the Indian River Lagoon system ment, has been shown to bioac- tion of all shark species from and adjacent coastal waters or from cumulate in fish tissue, and there- Florida waters.2 Owing to mercury commercial gillnet or longline fish- fore, fish can represent a major di- concentrations in excess of U.S. eries operating in the nearshore etary source of mercury to humans Food and Drug Administration and (Phillips and Buhler, 1978; Turner State of Florida standards, FHRS et al., 1980; Lyle, 1986). Methyl- recommended “adults should eat 1 FDEP (Florida Department of Environ- mercury is the most toxic form of shark no more than once a week; mental Protection) Marine Fisheries In- formation System, Fisheries Assessment mercury for humans to consume children and women of childbear- Section, 100 Eighth Ave. SE, St. Peters- (Meaburn, 1978; NMFS, 1993) and ing age should eat shark no more burg, FL 33701. essentially all mercury found in fish than once a month.” State of Florida 2 FHRS (Florida Department of Health and Rehabilitative Services). 1991. Health muscle tissue (>95%) is in the guidelines recommended that fish Advisory for Marine Fish. 1317 Winewood monomethyl form (CH3Hg)(Grieb containing less than 0.5 ppm of to- Blvd., Tallahassee, FL 32399, 3 p. et al., 1990; Bloom, 1992). There- tal mercury should represent no fore, the measurement of total mer- dietary risk, fish containing 0.5 to Manuscript accepted 20 May 1998. cury provides an approximation of 1.5 ppm of total mercury should be Fish. Bull. 97:372–379 (1999). NOTE Adams and McMichael: Mercury level in four species of sharks from the Atlantic coast 373 and offshore waters of east-central Florida. All bull sures included analysis of laboratory blanks, dupli- sharks were collected from estuarine nursery habi- cate or triplicate tissue samples, and standard fish tats within the Indian River Lagoon system from Oak tissue reference material (DORM-1, obtained from Hill, Florida (approximately 28°52'N), south to the the National Research Council of Canada) for each Ft. Pierce Inlet area (approximately 27°28'N). All group of ten shark samples analyzed (EPA, 1991; blacktip, sharpnose, and bonnethead sharks were Frick3; Booeshahgi et al.4). All mercury levels are collected in nearshore and offshore waters from reported as parts per million (ppm) wet weight. northern Cape Canaveral, Florida (approximately ° 28 55'N), south to the Sebastian Inlet/Wabasso, Data analyses Florida, area (approximately 27°45'N). Samples were collected from 1992 to 1995. Data regarding size and total mercury for each spe- Sharks were placed directly on ice and returned to cies were tested for normality by using the Kolmo- the laboratory, where species, precaudal length gorov-Smirnov test with Lilliefors’ correction (Fox et (PCL), and sex were recorded. Stage of maturity was al., 1994) and for homoscedasticity by using the Fmax- determined by examination of internal and external test (Sokal and Rohlf, 1981) or by computing the reproductive organs, as well as by comparison of Spearman rank correlation between the absolute shark size with estimates of size at birth or matu- values of the residuals and the observed value of the rity from previous studies (Parsons, 1983, 1993; dependent variable (Fox et al., 1994). Linear regres- Branstetter and Stiles, 1987; Castro, 1996). Individu- sions were used to describe relationships between als were classified as neonates on the basis of un- shark size and total mercury concentration. Mercury healed or healing umbilical scars (Castro, 1993). To data were log transformed to meet homoscedascity allow for comparisons with other studies, total length requirements. We used a t-test or Mann-Whitney (TL), fork length (FL), and other morphometrics were rank sum test, as appropriate, to test for significant also recorded according to Compagno (1984). With differences in total mercury levels and sizes between the exception of embryos, all sharks sampled were males and females for each species. considered to be within the size range landed in Florida recreational or commercial fisheries. Axial muscle tissue samples were removed from the left Results dorsal area anterior to the origin of the first dorsal fin. White muscle tissue taken from this region is Bull shark, Carcharhinus leucas representative of the portion of shark used for hu- man consumption. Tissue samples were immediately Eighty-three percent of 53 neonate and juvenile bull placed in sterile polypropylene vials, sealed, and fro- sharks (552–1075 mm PCL) tested from the Indian zen at –20°C until analyzed. Before analysis, tissue River Lagoon region had total mercury levels that samples were digested by using standard procedures were greater than or equal to the 0.5-ppm threshold (EPA, 1991; Frick3) to convert all mercury in the level (x =0.77 ppm; median=0.74 ppm; range 0.24– sample to Hg+2. The mercury in each digested sample 1.7 ppm) (Table 1). There was no significant differ- was reduced to atomic mercury by reaction with ex- ence between lengths of males (x =735 mm PCL) and cess stannous chloride. This atomic mercury was females (x =754.6 mm PCL; t-test, P>0.5) nor was purged from solution in a gas-liquid separator and there a significant difference between mean total swept into an atomic absorption spectrometer for mercury levels between males and females (x =0.76 detection and quantification following standardized ppm for both sexes; Mann-Whitney rank sum test, procedures (EPA, 1991; Booeshahgi et al.4) at the P>0.05). Ranges of total mercury for both sexes were Florida Department of Environmental Protection’s also similar. Division of Technical Services by using cold vapor There was a significant positive correlation be- atomic absorption spectrometry. Quality control mea- tween total mercury level and bull shark length (both sexes combined) (P<0.001; Fig. 1). Total mercury lev- els in juvenile bull sharks increased as individuals 3 Frick, T. 1996. Digestion of fish tissue samples for total mer- grew larger, although some small sharks contained cury analysis. Florida Department of Environmental Protec- tion, Division of Technical Services, 2600 Blair Stone Road, levels as high as those in larger sharks. Tallahassee, FL 32399. Report MT-015-1. 4 Booeshahgi, F., M. Witt, and K. Cano. 1995. Analysis of to- Blacktip shark, Carcharhinus limbatus tal mercury in tissue by cold vapor atomic absorption. Florida Department of Environmental Protection, Division of Techni- cal Services, 2600 Blair Stone Road, Tallahassee, FL Total mercury levels for 21 juvenile and adult black- 32399. Report MT-010-1. tip sharks examined ranged from 0.16 to 2.3 ppm 374 Fishery Bulletin 97(2), 1999 Figure 1 Figure 2 Relation between ln total mercury level (ppm) and Relation between ln total mercury level (ppm) and precaudal length (mm) for juvenile bull sharks, precaudal length (mm) for juvenile and adult Carcharhinus leucas, from the Atlantic coast of blacktip sharks, Carcharhinus limbatus, from the Florida. Atlantic coast of Florida.