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3-1-2007 First Record of a Sleeper in the Western Gulf of Mexico and Comments on Taxonomic Uncertainty Within (Somniosus) George W. Benz Middle Tennessee State University, [email protected]

Eric R. Hoffmayer University of Southern Mississippi

William B. Driggers Mississippi Laboratories

Dan Allen Chevron Gulf of Mexico Business Unit

Lougan E. Bishop Middle Tennessee State University

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Recommended Citation Benz, G. W., Hoffmayer, E. R., Driggers, W. B., Allen, D., Bishop, L. E., Brown, D. A. (2007). First Record of a Sleeper Shark in the Western Gulf of Mexico and Comments on Taxonomic Uncertainty Within Somniosus (Somniosus). Bulletin of Marine Science, 80(2), 343-351. Available at: http://aquila.usm.edu/fac_pubs/2058

This Article is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Faculty Publications by an authorized administrator of The Aquila Digital Community. For more information, please contact [email protected]. Authors George W. Benz, Eric R. Hoffmayer, William B. Driggers, Dan Allen, Lougan E. Bishop, and David A. Brown

This article is available at The Aquila Digital Community: http://aquila.usm.edu/fac_pubs/2058 BULLETIN OF MARINE SCIENCE, 80(2): 343–351, 2007

FIRST RECORD OF A SLEEPER SHARK IN THE WESTERN GULF OF MEXICO AND COMMENTS ON TAXONOMIC UNCERTAINTY WITHIN SOMNIOSUS (SOMNIOSUS)

George W. Benz, Eric R. Hoffmayer, William B. Driggers III, Dan Allen, Lougan E. Bishop, and David A. Brown

Abstract A sleeper shark, Somniosus (Somniosus) sp., is reported from Alaminos Canyon in the western Gulf of Mexico at a depth of about 2647 m based on observations made using a remotely operated vehicle. This is the first record of a sleeper sharkSom ( - niosus, ) from the western Gulf of Mexico and deepest record of any shark from the Gulf of Mexico. Despite claims to the contrary in the literature, no taxonomic character has been identified to date that can be used to unequivocally identify all representatives of Somniosus (Somniosus), and as a result, some records must be considered dubious.

Somniosus Le Sueur, 1818 (Somniosidae, , ) comprises species commonly referred to as sleeper . Knowledge regarding these sharks is limited due to their predominately high-latitude or deep-water occurrence (e.g., see Bigelow and Schroeder, 1948; Compagno, 1984, 1999; Yano et al., 2004) that places them beyond easy reach of planned scientific studies but not beyond incidental col- lections and observations. In addition, close morphologic similarity among some Somniosus spp. (see Yano et al., 2004) has exacerbated confusion regarding the dis- tribution of sleeper sharks. Herein we provide the first report of a sleeper shark from the western Gulf of Mexico and the deepest record of any shark within the Gulf of Mexico. We also review reports of sleeper sharks in waters in close proximity to the Gulf of Mexico and discuss taxonomic uncertainty regarding the identification of Somniosus spp.

Methods and Results

On 6 October 2001, a shark was briefly observed and videotaped with a remote- ly operated vehicle (ROV) during a routine inspection of a deep-water exploration and appraisal well on the Shell-operated prospect, Great White. The well is located (26.108°N latitude, 94.890°W longitude) in Alaminos Canyon at a seafloor depth of 2657 m in the western Gulf of Mexico about 402 km south of Houston, Texas (Fig. 1). The ROV (tethered work-class, 2.29-m high, 3.2-m long, 1.63-m wide, with six pro- pellers driven by two 60-cc hydraulic pumps, Simrad MS 900 sonar, six 250-W lights, surface operator video feed) had been operating in the area for about 4 hrs before the shark was observed. Water temperature in the immediate vicinity of the shark, as recorded by the ROV, was 4.7 °C. The shark was first observed as it slowly swam near the wellhead approximately 10 m above the sea floor. The shark ascended approxi- mately 2 m before leveling off and slowly swimming away from the wellhead and out of view (Fig. 2A–C). The shark was recorded in color on videotape (VHS format) for approximately 24 s. No other fishes were observed during the deep ROV deployment

Bulletin of Marine Science 343 © 2007 Rosenstiel School of Marine and Atmospheric Science of the University of Miami 344 BULLETIN OF MARINE SCIENCE, VOL. 80, NO. 2, 2007

Figure 1. Location (×) in western Gulf of Mexico where a sleeper shark, Somniosus (Somniosus) sp. (Somniosidae, Squaliformes), was observed by a remotely operated vehicle on 6 October 2001 as it swam about 10 m above the sea floor in water 2657-m deep. when the shark was observed. Prior to that dive, 11 similar ROV deployments, with a total bottom time of 134 hrs, had been conducted without a shark sighting. Image quality of the recorded encounter was compromised by back-scattered light from settling particles of marine snow and sporadic image washout created by the ROV’s lights. For dissemination and review, the videotaped encounter was converted into a digital media file using standard techniques, a process that probably reduced image quality. Efforts to enhance the resolution of the digital media file were -un successful, and unfortunately, the original VHS record of the encounter was sub- sequently lost. In reviewing the encounter, morphologic features of the shark were examined from various digital images captured from the movie media. There was a noticeable reduction in image resolution on the captured images in comparison to that of the streaming movie file. Attempts to enhance image resolution without otherwise altering the images were partially successful using Adobe® Photoshop® 7.0 (Adobe® Systems Inc., San Jose, CA). The streaming digital file of the encounter has been deposited as a voucher in the Florida Museum of Natural History (UF 162795). The encountered shark was identified as Somniosus (Somniosus) sp. based on its length and a suite of taxonomic features (in accordance with information in Yano et al., 2004; Compagno et al., 2005). The total length of the shark was estimated to be 2.4 m, based on its relative comparison to a 1.8-m long rectangular panel on the wellhead’s blow-out preventer (Fig. 2A). The shark (Fig. 2A–C) was heavy-set, seemingly cylindrical in cross-section, and torpedo shaped. It lacked an anal fin and possessed a short snout, which was moderately broad and rounded in dorsoventral view, a moderately broad head, small precaudal fins, low first and second dorsal fins, paddle-shaped pectoral fins, first dorsal fin posterior to pectoral fins and anterior to pelvic fins, pelvic fins not larger than dorsal fins, short caudal peduncle, and a broad epibatic caudal fin with subterminal dorsal lobe and wide ventral lobe. The pelvic fins were at times visible; however, no claspers were observed. No spine was noticed on any fin, no spiracle was observed, no caudal keel was observed, and no teeth were seen; however, poor image quality prevented a robust search for these and other small features. Likewise, the shark’s eyes and gill slits were not clearly visible. The dorsum of the shark appeared mostly dark; however, the snout, ventral surface of the head, and abdomen appeared whitish or mottled under bright illumination from the ROV (Fig. 2B). Our morphologic measurements were considered compromised BENZ ET AL.: SLEEPER SHARK IN GULF OF MEXICO 345

Figure 2. Still images of Somniosus (Somniosus) sp. taken from digital media file of shark en- counter on 6 October, 2001 at a deep-water (2657 m) petroleum prospect site in western Gulf of Mexico. (A) Shark swimming (ca. 2647-m deep) in front of blow-out preventer, marine riser, and wellhead area. Note that length of open rectangular superstructure of blow-out preventer imme- diately behind shark measured 1.8-m long and was used to estimate shark as 2.4-m total length. (B) Shark swimming at angle toward ROV. Note bright reflection of ROV lights from shark and shark’s mottled appearance. (C) Shark swimming at angle away from ROV. Note torpedo-shaped body of shark and size and location of fins.

by poor image quality and inappropriate body perspective (e.g., see Fig. 2A–C), hence these data are not reported.

Discussion

In their recent review and most authoritative taxonomic treatment of the sleeper sharks, Yano et al. (2004) considered Somniosus to comprise two subgenera and five species: subgenus Rhinoscymnus containing Somniosus (R.) rostratus (Risso, 1827) and S. (R.) longus (Tanaka, 1912) and subgenus Somniosus containing S. (S.) micro- cephalus (Bloch and Schnieder, 1801), S. (S.) pacificus Bigelow and Schroeder, 1944, and S. (S.) antarcticus Whitley, 1939. Regarding Somniosus (Somniosus) , Yano et al. (2004) advanced nine diagnostic characters (listed in Table 1). However, significant differences regarding these characters exist between information provid- ed in the species identification key of Yano et al. (2004) and the often more detailed data elsewhere in that publication. Furthermore, detailed data contained in Yano et al. (2004) denote considerable overlap among S. microcephalus, S. pacificus, and S. antarcticus regarding the nine aforementioned characters (Table 1). Thus, while data presented by Yano et al. (2004) may allow some individuals to be identified to species, the high degree of interspecific character state overlap indicates that unequivocal identification will be impossible for many Somniosus (Somniosus) individuals. In ad- dition, interpretation of the intraspecific variation exhibited for the aforementioned 346 BULLETIN OF MARINE SCIENCE, VOL. 80, NO. 2, 2007 – – – – – – – – – – – – 4 (n) 4 (n) 4 (n) 1 (n) 0.034 In addition, data 0.44–0.5 1 0.62–1.57 0.119–0.24 S. pacificus (de Astarloa et al., 1999) (de 2 ) individuals. 2 2 2 – – – – – – – – – – – – – – – – – Somniosus 0.889 0.465 0.185 ( S. pacificus (Moreno and Pol, 1992) Somniosus

) species identification by Yano et al. (2004) and available 0.03 0.822 0.474 0.202 0.029 16 (n) 18 (n) 22 (n) 23 (n) 23 (n) 0.744–0.9 0.45–0.531 0.17–0.237 Somniosus 0.663–0.971 0.452–0.496 0.187–0.217 0.025–0.035 0.022–0.039 0.026–0.032 0.024–0.036 S. antarcticus ( (Yano et al., 2004) (Yano Somniosus ; sample size (n) and other data from or calculated from cited sources. Note that while the 0.211 0.732 0.484 0.037 0.034 29 (n) 25 (n) 29 (n) 29 (n) 29 (n) 0.034–0.04 S. pacificus 0.649–0.815 0.614–0.985 0.466–0.502 0.442–0.526 0.194–0.228 0.151–0.242 0.028–0.042 0.031–0.037 0.027–0.041 (Yano et al., 2004) (Yano S. pacificus

1.025 0.401 0.185 0.042 0.035 33 (n) 37 (n) 37 (n) 38 (n) 38 (n) 0.17–0.2 0.03–0.04 0.03–0.055 0.931–1.119 0.855–1.259 0.378–0.424 0.355–0.459 0.151–0.225 0.036–0.048 0.028–0.045 S. microcephalus (Yano et al., 2004) (Yano prebranchial length: to first dorsal fin origin/ total length (TL): TL: to first gill slit/ fin/ precaudal length: fin/ precaudal length: Table Table 1. Taxonomic data among for overlap considerable denote data nine the for range characters overall the and corresponding range data considered SD regarding 1 two ± additional mean diagnostic records the species, of among for different are (2004) al. et Yano of data character mean species and indicate that none of the nine diagnostic characters can be used unequivocally to identify all Astarloa et al. (1999) do not allow robust species identification of the reported sharks. from the reports of Moreno and Pol (1992) de Character 1. Interdorsal space/ mean mean ± 1 SD range overall range 2. Distance from snout tip mean mean ± 1 SD range overall range 3. Distance from snout tip mean mean ± 1 SD range overall range 4. Height of first dorsal mean mean ± 1 SD range overall range 5. Height of second dorsal mean mean ± 1 SD range overall range BENZ ET AL.: SLEEPER SHARK IN GULF OF MEXICO 347 – – – – – – – – – – – – – – – – S. pacificus (de Astarloa et al., 1999) (de 2 2 – – – – – – – – – – – – – – – 56 S. pacificus (Moreno and Pol, 1992)

54.2 30.1 37.3 8 (n) 8 (n) 38.58 11 (n) 11 12 (n) 49–59 36–41 30–31 36–38 51.1–57.3 29.7–30.5 36.3–38.3 37.27–39.89 S. antarcticus (Yano et al., 2004) (Yano 54.9 29.0 37.4 34.05 35 (n) 19 (n) 16 (n) 16 (n) 46–63 32–37 28–30 35–39 36–38.8 51.1–58.7 28.3–29.7 S. pacificus 32.74–35.36 (Yano et al., 2004) (Yano

50.6 34.7 42.8 30.85 25 (n) 33 (n) 12 (n) 12 (n) 45–57 29–34 31–36 41–44 47.6–53.6 33.2–36.2 41.9–43.7 29.76–31.94 S. microcephalus (Yano et al., 2004) (Yano of Moreno and Por (1992) were calculated from reported means ratio components corresponding to three measured specimens. S. pacificus vertebrae: lower jaw: turns: vertebrae: Note that beyond the considerable species overlap denoted by the overall range data, 31.73% of sampled sharks would be expected to exhibit a value outside the mean ± 1 SD range SD 1 ± mean the outside value a exhibit to expected be would sharks sampled of 31.73% data, range overall the by denoted overlap species considerable the beyond that Note ratios for Tabled Table 1. Continued. Table Character 6. Number of tooth rows mean mean ± 1 SD range overall range 7. Number of spiral valve mean mean ± 1 SD range overall range 8. Number of precaudal mean mean ± 1 SD range overall range number of Total 9. mean mean ± 1 SD range overall range 1 1996). on a character by basis (assuming normal model; Zar, 2 348 BULLETIN OF MARINE SCIENCE, VOL. 80, NO. 2, 2007 diagnostic characters is muddied because no information exists regarding possible covariance between characters. Thus, we consider it currently impossible to identify all Somniosus (Somniosus) individuals based on morphology and propose that results of molecular analyses may be necessary to test the validity and establish the iden- tity of Somniosus (Somniosus) spp. such that morphologic differences among spe- cies might be ascertained. However, given the possibility that Somniosus (Somniosus) spp. may coexist in some regions, it is crucial that sharks used for such morphologic studies be assigned to species using molecular, rather than geographic or morpho- logic data. Here it is important to consider that without a robust means of assigning species identity, Yano et al. (2004) apparently grouped sharks for analysis based on geographic data. Such being the case, some of the intraspecific variation reported by Yano et al. (2004) may represent interspecific variation caused by species lumping. Despite the fact that their data supported no decisive characteristic to identify all Somniosus (Somniosus) individuals to the level of species, Yano et al. (2004) con- cluded that S. microcephalus occurs only in the and North Atlantic Oceans, S. pacificus occurs only in the North Pacific Ocean from the Bering Sea to Baja Cali- fornia and Japan (but see Benz et al., 2004 for a record of a beach-cast specimen re- ported as S. pacificus in the Chukchi Sea above the Arctic Circle), and S. antarcticus occurs only in the Southern Hemisphere. In adopting this view, Yano et al. (2004) considered several reports of S. pacificus in the Southern Hemisphere (e.g., Peque- ño et al., 1991; de Astarloa et al., 1999) and allocated them to S. antarcticus based on what we feel was uncompelling morphologic evidence (e.g., see Table 1). In light of the taxonomic uncertainty discussed above, we feel it premature to assign Som- niosus (Somniosus) individuals to a particular species in geographic regions where these sharks are poorly known (e.g., central and South Atlantic Ocean, South Pacific Ocean, Indian Ocean). Furthermore, one could argue that technically, only the type species of Somniosus (Somniosus), i.e., S. microcephalus, can defend its species status (this defense based on the principal of taxonomic priority). This is the first report of a sleeper shark from well within the Gulf of Mexico (see Compagno, 1984, 2002; McEachran and Fechhelm, 1998, 2005; Yano et al., 2004; Compagno et al., 2005). The closest geographic records forSomniosus to that report- ed here are contained in several reports of sharks captured near Cuba. Somniosus rostratus was reported by Espinosa (1987) and Moreno and Pol (1988; as reported in Moreno and Pol, 1992) based on specimens caught in the Straits of Florida north of Havana and Pinar del Rio (Santa Lucia), Cuba. Somniosus pacificus was reported by Moreno and Pol (1992) based on specimens caught east of the Yucatán Channel in the Bahía de Corrientes (off southwestern Cuba). Comparison of data presented by Moreno and Pol (1992) to that presented by Yano et al. (2004) illustrates that the Somniosus (Somniosus) specimens captured off Cuba are not reliably assignable to a particular species (Table 1). Beyond the Cuban reports, the next closest geographic records of a Somniosus sp. to the Gulf of Mexico are from the western North Atlantic Ocean (Herdendorf and Berra, 1995; Kohler et al., 1998). Herdendorf and Berra (1995) reported S. micro- cephalus in deep water, 370 km east of Savannah, Georgia, from a videotaped ROV encounter. Their taxonomic assignment, based on an expert’s review of the video- tape, seems to have been heavily influenced by observation that the, “first dorsal fin was characteristically located midway between the pectoral and pelvic fins” (Herd- endorf and Berra, 1995; p 951). However, we feel this ratio is not reliable regarding the BENZ ET AL.: SLEEPER SHARK IN GULF OF MEXICO 349

Table 2. Ranges for the ratio between the distance from the tip of snout to the middle of first dorsal fin and distance to the midpoint between the pectoral and pelvic fins for Somniosus (Somniosus) spp., each calculated using proportional dimension data in Yano et al. (2004).1 Note that a shark with a first dorsal fin located midway between the pectoral and pelvic fins (as mentionedby Herdendorf and Berra, 1995) would have a ratio of 1.

Ratio S. microcephalus S. pacificus S. antarcticus maximum range2 0.71–1.6 0.86–1.45 0.8–1.52 minimum range3 1.01–1.13 1.11–1.13 1.01–1.22 1 Calculated as follows (Roman numerals correspond to Arabic numeral designations for specific proportional dimension data defined in figure 1 and presented in table 1 of Yano et al., 2004; Arabic numeral is mathematically operational): ratio = (XIV + XXXIV) / (X + XXXXIV + XX)/2 2 Maximum range calculated using minimum to minimum and maximum to maximum range values for low range and high range (respectively) ratio components 3 Minimum range calculated using minimum to maximum and maximum to minimum range values for low range and high range (respectively) ratio components identification ofSomniosus (Somniosus) species, based on calculations of the ratio of the distance to the first dorsal fin and the midpoint between the pectoral and pelvic fins for S. microcephalus, S. pacificus, and S. antarcticus that we made using data in Yano et al. (2004) (Table 2). Kohler et al. (1998) documented several S. microcephalus captures along and just outside of the 200-m isobath east of Delaware Bay (to avoid confusion, it should be noted that the legend for figure 154 in Kohler et al. (1998) was an error and should have referred to the smooth hammerhead, Sphyrna zygaena (L., 1758); P. A. Turner, National Marine Service, Narragansett, pers. comm.). The present report is also one of the deepest records for any shark species, the deepest reliable report for any shark within the Gulf of Mexico, and the deepest re- cord for a representative of Somniosus (Somniosus). The deepest reliable record of any shark is a report of an unidentified “” observed at a depth of 4050 m in the eastern Atlantic Ocean (Houot, 1958). Only a few shark species have been reli- ably reported from depths > 3000 m (see Clark and Kristof, 1990, 1991; Herdendorf and Berra, 1995; Priede et al., 2006), and it is generally thought that sharks are largely confined to ocean depths < 2000 m (Priede et al., 2006). Shark species that have been reliably reported from depths below 2000 m are all representatives of Squaliformes (, , , and Somniosidae) and (Hexanchidae) (see Clark and Kristof, 1990, 1991; Herdendorf and Berra, 1995; Priede et al., 2006). Sleeper sharks (Somniosidae) are the largest sharks and one of the most species rich and possibly globally abundant groups of sharks inhabiting waters below 1500 m (Isaacs and Schwartzlose, 1975; Herdendorf and Berra, 1995; Compagno et al., 2005; Priede et al., 2006). Regarding Somniosus (Somniosus) species, the greatest reported depths of occurrence for S. pacificus are 1920 m (Clark and Kristof, 1990) and 2009 m (Dayton and Hessler, 1972). Yano et al. (2004) reported S. antarcticus present at depths over 1000 m but shallower than 2000 m. The maximum reported depth for S. microcephalus is 2200 m (Herdendorf and Berra, 1995). But given the taxonomic uncertainty discussed above, these species-specific depth records must be considered tentative.

Acknowledgments

We thank M. Weaver (Shell) for relaying information regarding the shark encounter, V. Mullen for translating some literature, D. Johnson and J. Franks for information and com- ments used in an earlier manuscript, G. Skomal for comments influencing the final manu- 350 BULLETIN OF MARINE SCIENCE, VOL. 80, NO. 2, 2007 script, G. Burgess and R. Robins for accessioning the voucher in the Florida Museum of Natu- ral History, and our respective companies, agency, and universities for general support.

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Date Submitted: 19 June, 2006. Date Accepted: 29 November, 2006.

Addresses: (G.W.B.) Department of Biology, P.O. Box 60, Middle Tennessee State University, Murfreesboro, Tennessee 37132. (E.R.H.) Center for Fisheries Research and Development, Gulf Coast Research Laboratory, University of Southern Mississippi, 703 East Beach Drive, Ocean Springs, Mississippi 39564. (W.B.D.) National Marine Fisheries Service, Southeast Fisheries Science Center, Mississippi Laboratories, P.O. Drawer 1207, Pascagoula, Mississippi 39568. (D.A.) Chevron Gulf of Mexico Business Unit, 241 Highway 1085, Madisonville, Louisiana 70447. (L.E.B.) Department of Biology, Middle Tennessee State University. Present Address: 1070 West Main Street, Hendersonville, Tennessee 37075. (D.A.B.) Shell EP Europe, Schep- ersmaat 2, Postbus 28000, 9400 HH, Assen, The Netherlands. Corresponding Author: (G.W.B) E-mail: .