BULLETIN OF MARINE SCIENCE, 74(1): 229–235, 2004
FIRST RECORDS OF PACIFIC SLEEPER SHARKS (SOMNIOSUS PACIFICUS BIGELOW AND SCHROEDER, 1944) IN THE SUBTROPICAL WATERS OF EASTERN TAIWAN
John Y. Wang and Shih-Chu Yang
The Pacific sleeper shark (Somniosus pacificus Bigelow and Schroeder, 1944) is a poorly known, very large, deep-sea member of the family Somniosidae (Compagno, 1999). This species is found mainly in cold, temperate to polar waters of both hemispheres (Castro, 1983; Compagno, 1984; Last and Stevens, 1994), but the distribution also extends into the subtropical to tropical regions of the eastern North Pacific Ocean (see Last and Stevens, 1994). Although Pacific sleeper sharks are generally bottom-dwellers of deep water, some individuals may visit shallow waters in high latitudes. In the western North Pacific Ocean, this species has been reported from Sagami Bay (~35oN) and south of Shikoku Island (~32oN), Japan (see Hart, 1973). No specimens have been reported from the subtropical or tropical waters of the western North Pacific Ocean. Data collected from 30 specimens captured from the subtropical waters near the Ching-Shuei Cliffs of Hualien (~24oN) of central eastern Taiwan (Fig. 1) are reported here. The Hualien specimens are compared with previous descriptions of the species and additional information on size dimorphism, parasites, and some stomach contents of these specimens are presented. The fishery cap- turing the Pacific sleeper sharks in Taiwan is also described.
METHODS AND RESULTS
The initial discovery was made in March 1999 when two large, dark brown to black sharks were observed on a truck at the Hualien fishing port. They were photographed and later identified to be of the genus Somniosus. On 18 May 2000, a third specimen was observed at the same fishing port. Some data were recorded and teeth, skin and muscle tissue (for DNA analyses) samples were collected. Partial stomach contents were ob- tained after the animal was butchered for sale. After interviewing fishermen and a fish processor, we collected data and samples from a series of 27 specimens between 19 March and 18 May 2002. The fishermen and fish processor provided additional information about the deep-sea, shark, longline fishery and their catch. DIAGNOSIS (DESCRIPTION/COLOR).—The sleeper sharks captured in the waters of Hualien were very large and matched the description of S. pacificus (Fig. 2). The distance from the tip of the snout to the origin of the first dorsal fin was 45.1–54.7% (mean = 50.0% ± 2.7 [SD]; n = 17) of the total length; this proportion excludes the possibility the present specimens belong to the Greenland shark (S. microcephalus). The shape of the teeth (which numbered 46 and 53 in the upper and lower jaws, respectively, for one specimen) and the dermal denticles resembled the descriptions of S. pacificus in Francis et al. (1988). Two Hualien specimens were examined by J. D. Stevens and M. P. Francis and the precaudal vertebrae (= 29) and spiral valve coils (= 32) of one specimen were counted. Based on the number of precaudal vertebrae and spiral valve coils, the Hualien specimens are consis- tent with, and most likely, S. pacificus and not the recently resurrected species, S. antarcticus (J. D. Stevens, CSIRO Marine Research, Hobart, pers. comm.). However,
Bulletin of Marine Science 229 © 2004 Rosenstiel School of Marine and Atmospheric Science of the University of Miami 230 BULLETIN OF MARINE SCIENCE, VOL. 74, NO. 1, 2004
Figure 1. Map of the capture location of Pacific sleeper sharks in the waters of Hualien, central eastern Taiwan. The broken line represents the 1000 m isobath. examination of these characters on more specimens and results from DNA analyses, which are currently underway, are necessary to confirm the species identity. Reports of the presence of precaudal keels are varied (see Compagno, 1984; Francis et al., 1988; Last and Stevens, 1994). We saw single lateral keels on each side of the caudal peduncle on all 27 Hualien specimens (the lateral keels were barely visible on the small- est specimen). As in previous descriptions, the Hualien specimens were also uniformly dark brown to almost black but no mottling, spotting or stripes were observed as de- scribed for some specimens elsewhere (see Francis et al., 1988). The almost black pig- mentation of these sharks is the result of a slimy, mucous layer that is easily scrubbed off. On the Hualien specimens, the color of the skin under the black mucous layer was uni- formly pale beige to light gray. SIZE AND SEX DATA.—The largest Pacific sleeper shark recorded is 440 cm total length, TL, (Froese and Pauly, 2002). Orlov (1999) reported a mature female specimen measur- ing 423 cm TL, but it is believed to grow to at least 700 cm (estimated from film footage of a living shark by Doubilet et al., 1990) and possibly up to 760 cm (see Castro, 1983). The heaviest specimen reported by the shark processor in Hualien was 1280 kg (caught in the spring of 2001), but the TL was not measured. Amongst the 27 Hualien specimens we measured (eight females and 19 males) the longest specimen recorded was a 456 cm TL male weighing 642 kg. However, due to its bent posture, TL was measured along the NOTES 231
Figure 2. A typical female Pacific sleeper shark that was captured by a small, deep-sea, shark long- line fishery off Hualien, central eastern Taiwan on 12 April 2002. This specimen (SCY-02-16) measured 340.0 cm TL and weighed 470 kg. curvature of the body rather than parallel to its longitudinal axis thus inflating the mea- surement. The longest specimen measured parallel to its longitudinal axis was a female that was 418 cm TL and 674 kg. The heaviest shark that we observed was a female weighing 824 kg with a TL of 415 cm. The smallest specimen was a 199 cm TL, 60 kg female (but the fish processor had recorded a 34 kg specimen in 2002). The mean (± SD) TL and weight of the specimens examined (excluding the two that were measured along the curvature of the body) was 358.8 ± 48.8 cm and 510.6 ± 164.7 kg, respectively. This is the largest series reported for this species and is considerably larger than the series reported by Orlov (1999) of 125 specimens captured in the Bering Sea and near the Kurils (mean < 150 cm long and < 30 kg; maximum < 250 cm and < 140 kg). Because of the many differences between this study and Orlov (1999), it is unclear if the observed size difference was due to dissimilar selectivity by the different fishing gear (longline v. trawl), age/size segregation by depth or geographic location, or other factors. The length-mass relationship of the 27 Hualien specimens was: mass (kg) = 2.94 ¥ TL (cm) - 546.8 (r = 0.849). Females were generally heavier than males for any given length indicating that sexual size dimorphism exists in this species. REPRODUCTIVE INFORMATION AND STOMACH CONTENTS.—The internal organs of only a few specimens were examined because the sharks were usually dressed at a different location. Only two females (418 cm TL, 675 kg and 199 cm TL, 60 kg) were examined internally. The larger female had 200–300 small, white, semi-transparent ova of ~1 cm in diameter. Neither fishermen nor the processor had ever seen pregnant females. The clasp- ers of only one male specimen (385.0 cm TL, 586 kg, caught on 18 May 2002) were examined and found to be rigid and calcified, indicating maturity. The outer and inner 232 BULLETIN OF MARINE SCIENCE, VOL. 74, NO. 1, 2004
lengths of the left clasper were 10.0 cm (or 2.6% of TL) and 23.5 cm (or 6.1% of TL), respectively. The Pacific sleeper shark is reported to be a voracious consumer of a wide variety of fishes, squids, crustaceans, other invertebrates, marine mammals, and carrion (see Bright, 1959; Castro, 1983; Compagno, 1984; Crovetto et al., 1992; Yang and Page, 1998; Orlov, 1999). Partial stomach contents of 14 specimens were collected opportunistically when- ever fishermen cut into the stomach to release fluids prior to weighing (the stomachs of the sharks were usually bloated, likely as a result of water filling their stomachs during hauling) and the entire stomach contents of one specimen was collected. We found many beaks of large squids (the largest being an upper beak with a total length of 10 cm), the remains of large teleosts and elasmobranchs, large pieces of cetacean flesh (including a dorsal fin and flukes), fishing nets, and other trash. The lower beaks of at least five differ- ent kinds of squids and the bodies of the diamond squid (Thysanoteuthis rhombus) and possibly an Onychoteuthis sp. were found (the identities of most squid species require closer examination of the beaks and comparison with a reference collection). The teleost species consumed included: mahi-mahi (Coryphaena hippurus); wahoo (Acanthocybium solandri); bonito (Sarda orientalis); sickle pomfret (Taractichthys steindachneri); spot- ted moonfish (Mene maculata); cutlassfish (Trichiuridae); an unidentified conger eel; green bones that we believe belong to a Belonidae species; kawakawa (Euthynnus affinis); and mackerel (Scomber spp.). However, the last two prey species were likely bait used in the longline fishery. The elasmobranchs consumed could not be identified from the di- gested material observed. Remains of what appeared to be a large jellyfish were also found. Unlike previous findings of the diet of the Pacific sleeper shark (e.g., Gotshall and Jow, 1965; and Yang and Page, 1998), most of the fish species from the stomachs of the Hualien specimens were not bottom, but mid-water or epipelagic species. The Pacific sleeper shark may have strategies to ambush prey. However, due to the very sluggish disposition of this species, at least some of these fast-swimming prey species were most likely consumed as carrion. PARASITES.—The eyes of Pacific sleeper sharks are commonly infected with the ecto- parasitic copepod Ommatokoita elongata (Benz et al., 1998). Copepod parasites fitting the description of O. elongata were also found attached to the eyes of nine of the 27 Hualien specimens. Five had O. elongata attached to both eyes and four had the parasite on only one eye (ovisacs were also present on several parasites). Due to the working environment and the condition of the specimens (e.g., the eyes were frequently covered by tissues that had distended as a result of rapid depressurization), we did not examine the eyes in detail for the presence of larvae or signs of previous infections. However, on the cornea of one shark, we found two small opacities that appeared to be the previous attachment sites of O. elongata. Another ectoparasitic copepod species, Dinemoura ferox (Ho et al., 2003), was found on the skin of four of 18 specimens examined with the heaviest infection being eleven parasites on one shark. After these parasites were re- moved, the points of attachment revealed a slimy scarred area of the skin with no black mucous layer. Within the gills of four specimens examined, an unidentified species of monogenean (Polyopisthocotylea) was found. The spiral valves of 11 sharks that were examined all contained unidentified tapeworms (Cestoda). Nematodes resembling Anisakis sp. were also found in the stomachs of four of seven sharks examined. On three speci- mens, there were round to oval crater scars (2.5–3.0 cm in diameter along the major axis) NOTES 233 that resembled wounds attributable to cookie-cutter sharks (Isistius brasiliensis and I. plutodus). FISHERY AND MARKET.—All the Pacific sleeper sharks reported in this paper were cap- tured in a small, localized fishery where only three small (< 20 t and < 10 m long) coastal fishing boats are involved. Bottom-set longlines are deployed in canyons surrounding deep (about 500–1000 m deep) underwater seamounts in a small region near the Ching- Shuei Cliffs of Hualien where Pacific sleeper sharks appear to concentrate. Fishermen claim that smaller and fewer Pacific sleeper sharks are found in the shallower depth range used by the fishery. Longlines are usually hauled after 24 hrs to check for catches, re- baited, and set again (usually in the same location), weather permitting. In the past, dol- phin blubber and meat were used to bait the 36 hooks of each longline (the distance between hooks is about 55 m; 30 fathoms). Because cetaceans are now legally protected in Taiwan, scombrids (e.g., Euthynnus affinnis, Scomber spp.) about 30–50 cm long are now used more often than dolphins. The fishery usually operates between late February to June with peak catches occur- ring in March, April, and May. Daily catches per boat can be up to three Pacific sleeper sharks and about eight sixgill sharks (Hexanchus spp.). Although we examined 27 sleeper sharks, the total catch of this species in 2002 was 92 individuals (as of 12 June). If this species grows as slowly as the closely related Greenland shark, Somniosus microceph- alus (growth rate based on recapture of tagged sharks; Hansen, 1963) and pregnant fe- males are rare (Compagno, 1984), then this species may not be able to sustain even mod- est levels of exploitation. The number of sharks that can be taken without depleting the species in this area needs to be evaluated. The flesh of the Pacific sleeper shark has been reported to contain an inebriating toxin (Tinker, 1978), but it is consumed fresh in Taiwan. The muscle of Pacific sleeper and sixgill sharks is similar consistency to that of the prized whale shark (Rhincodon typus), which is known in Taiwan as ‘tofu’ shark because of its soft, white flesh. With recent reductions in, and regulation of, whale shark catches in Taiwan, the market for the flesh of Pacific sleeper and sixgill sharks has developed as a replacement for, or mimic of, the whale shark meat. The flesh of these three species is rather bland and tasteless. The de- mand for their flesh appears to be driven by status and curiosity seekers and scientifically unsubstantiated or misleading information about the nutritional or medicinal values of sharks. Although Pacific sleeper sharks have not been reported previously from the waters of Taiwan (Shen, 1993) or any other subtropical region of the western Pacific Ocean (Castro, 1983; Compagno, 1984; Last and Stevens, 1994; Carpenter and Niem, 1998), this species does not appear to be uncommon in, or a vagrant of, the deep waters of Hualien. The lack of records from Taiwan (and other subtropical) waters is likely due to the lack of fishing effort in depths where the species is found. The distribution of Pacific sleeper sharks may extend to other subtropical (and possibly tropical) waters once fishing effort in deep wa- ter increases in these regions. Even though the Hualien fishery has operated for about 10 yrs, this very large species has escaped detection in Taiwan because the fishery is small, seasonal (catches peaking for only about two months), and highly localized. Animals are also processed very quickly for the fresh meat market (freezing apparently reduces the palatability of the meat). The Hualien fishery provides an excellent opportunity to study the biology of this poorly known species. 234 BULLETIN OF MARINE SCIENCE, VOL. 74, NO. 1, 2004
ACKNOWLEDGEMENTS
We are very grateful to the Hualien processors R.-S. Chen, J.-L. Tsai and employees and fisher- men for allowing us to collect data and samples and providing additional information about the sharks and their fishery. Without their help, our information would have been very limited. We would also like to thank: J.D. Stevens and M.P. Francis for examining two of our sharks during a recent visit to Hualien, confirming our identification and for comments that improved this paper; J.-S. Ho for identifying the parasites found on the sharks; and two anonymous reviewers.
LITERATURE CITED
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Shen, S. -C. (ed.). 1993. Fishes of Taiwan. Dept. Zoology, National Taiwan Univ., Taipei. 960 p. (In Chinese). Tinker, S. W. 1978. Fishes of Hawaii: a handbook of the marine fishes of Hawaii and the central Pacific Ocean. Hawaiian Service Inc., Honolulu. 568 p. Yang, M. -S. and B. N. Page. 1998. Diet of Pacific sleeper shark, Somniosus pacificus, in the Gulf of Alaska. Fish. Bull. U.S. 97: 406–409.
DATE SUBMITTED: November 27, 2002. DATE ACCEPTED: September 8, 2003.
ADDRESSES: (J.Y.W.) National Museum of Marine Biology & Aquarium, 2 Houwan Road, Checheng, Pingtung County, 944, Taiwan and FormosaCetus Research & Conservation Group, 310-7250 Yonge St., Thornhill, Ontario, Canada, L4J-7X1. E-mail: