Mercury Concentrations in Whale Shark (Rhincodon typus) Embryo Muscle Tissue.

Mercury (Hg) is known to be maternally transferred during embryonic development in sharks; however, Hg concentrations in embryos of filter feeding shark species have not previously been reported. This study measured the total Hg (THg) concentration in muscle tissue of 27 embryos taken from a pregnant whale shark (Rhincodon typus) landed in Taiwan in 1995 and the mean THg concentration compared to the mean muscle THg concentration in embryos from other shark species. The mean (± standard deviation) THg concentration in whale shark embryos was 0.0762 ± 0.0163 µg/g dry weight (0.0224 ± 0.0054 µg/g wet weight). There was no relationship between muscle THg concentration and body length and no significant difference in THg concentration between male and female embryos (p > 0.05). Whale shark embryos have the lowest reported muscle THg concentrations compared to literature values for muscle THg concentrations for embryos from other shark species.

Records of new and rare elasmobranchs from Taiwan.

Five new records of elasmobranchs collected from eastern Taiwan fish markets, Da-xi and Cheng-gong, are presented. Samples were caught by deepsea longliners and bottom trawlers which operate in northeastern waters off Taiwan between 2004 and 2012. These five new species records include the smalltooth sandtiger, Odontaspis ferox (Risso, 1810) (Lamniformes: Odontaspididae), salamander shark, Parmaturus pilosus Garman, 1906 (Carcharhiniformes: Scyliorhinidae), leadhued skate Notoraja tobitukai (Hiyama, 1940) (Rajiformes: Arhynchobatidae), giant skate Dipturus gigas (Ishiyama, 1958) (Rajiformes: Rajidae), and the pelagic stingray Pteroplatytrygon violacea (Bonaparte, 1832) (Myliobatiformes: Dasyatidae), Diagnostic characteristics for each species are given and a key to the genera Parmaturus and Dipturus from Taiwan is presented.

Occurrence of the milk-eye catshark Apristurus nakayai (Carcharhiniformes: Pentanchidae) from the South China Sea.

The milk-eye catshark Apristurus nakayai Iglésias, 2012 was known from three specimens in the southwestern Pacific Ocean. Six specimens were recently collected from the South China Sea. It belongs to the brunneus group, and superficially resembles A. platyrhynchus Tanaka, 1909. Apristurus nakayai differs from A. platyrhynchus by the following characters: iris shiny white when fresh; body brownish black to black; second dorsal-fin insertion above or slightly in front of the anal-fin insertion; denticles absent inside mouth; and maturing at about 400 mm TL in both sexes. The occurrence of Apristurus nakayai from the South China Sea represents the first record in the northern Hemisphere, and a substantial distributional range extension (ca. 4665 km).

Malakichthys formosus, a new species of small seabass (Acropomatiformes: Malakichthyidae) from southwestern Taiwan.

A new species of Malakichthys is described based on six specimens collected from deepwaters off southwestern Taiwan, northwestern Pacific Ocean. The new species, M. formosus sp. nov., exhibits distinct morphological characters, primarily characterized by the absence of chin spines, distinguishing it from other congeners with the exception of M. levis and M. mochizuki. It differs from the two species by having more lateral-line scales, a shorter distance between the snout and dorsal-fin origin, a shallower head, fewer scale rows below the lateral line, and the structure of the first anal-fin pterygiophore. Eight species are now recognized in Malakichthys.

Okamejei picta sp. nov., a new rajid skate from the South China Sea (Rajiformes: Rajidae).

A new species of Okamejei is described based on two adult males collected from deep waters in the South China Sea. The new species, Okamejei picta sp. nov., is readily distinguished from most other congeners in having densely scattered black spots on dorsal disc. Okamejei hollandi and O. mengae is quite similar to the new species by their spot patterns on dorsal disc, but the new species differs from the former by a combination of characters: a yellowish brown dorsal surface densely covered with small, circular to irregular-shaped black spots; blotches on dorsal disc indistinct; posterior ocellus absent; ventral disc white; disc length 45.0-47.7% TL; distance between cloaca to caudal-fin tip 53.6-55.1% TL; trunk centra 31; total basal radials 73-76, morphology of clasper terminal skeleton, and lacking component funnel at the clasper end.

A new record of the rare Bigeye Sand Tiger shark Odontaspis noronhai Maul, 1955 (Lamniformes: Odontaspididae) from the northwestern Pacific, with notes on dentition.

In the Pacific Ocean, the rare Bigeye Sand Tiger shark Odontaspis noronhai has only been recorded twice, once from its central and once from its eastern part. Here we report the first record of this species from the northwestern Pacific. This specimen measuring 312 cm total length (TL) was captured off northeastern Taiwan (2525N, 12410E) from a depth of 100 m (in waters over 2100 m deep) in mid-December 2019, and was retrieved on 27 December 2019 when landed in port. Photo of the fresh specimen along with morphometric and meristic data and DNA information are provided herein. Dentition of the specimen is different from all other specimens by having two cusplets on at least one side of cusps on most of the teeth (vs. only one cusplet per side), and lower total tooth count (29/29 vs. 3438/3746). This record documents an extended distribution (about 7864 km westward from the central Pacific Ocean), and provides strong evidence for the wide distribution and mesopelagic characteristic of this poorly known species.

Redescription of the longnose houndshark Iago garricki (Carcharhiniformes: Triakidae), based on specimens recently collected from the South China Sea.

The longnose houndshark, Iago garricki Fourmanoir & Rivaton 1979, was described based on five specimens collected from Vanuatu. Five additional specimens were recently collected from the waters off Dongsha Atoll, South China Sea. A redescription of this species is provided based on the holotype, non-types collected near the type locality and off Dongsha Atoll. The species is characterized by eye length larger than gill slit height; first dorsal-fin origin not reaching a vertical line through pectoral-fin base; head length 20.2-22.2% TL; preoral length 7.2-8.3% TL; upper labial furrow 2.2-3.4% TL; lateral teeth with 1-3 small cusplets on lateral side basally; diplospondylous centra 53-61; precaudal centra 94-102; and total centra 149-157. The specimens collected from the South China Sea represent the northernmost distributional record of this species.

Vulnerability Assessment of Pelagic Sharks in the Western North Pacific by Using an Integrated Ecological Risk Assessment.

The vulnerability of 11 pelagic shark species caught by the Taiwanese coastal and offshore longline fisheries in the western North Pacific were assessed by an ecological risk assessment (ERA) and 10 of the 11 species was assessed by using an integrated ERA developed in this study. The intrinsic rate of population growth was used to estimate the productivity of sharks, and the susceptibility of sharks was estimated by the multiplication of the catchability, selectivity, and post-capture mortality. Three indices namely, the IUCN Red List category, the body weight variation trend, and the inflection point of population growth curve coupled with ERA were used to conduct an integrated ERA. The results indicated that the scalloped hammerhead is at the highest risk (group 1), followed by the silky shark, and the spinner shark at high risk (group 2). The bigeye thresher, and sandbar shark fall in group 3, the smooth hammerhead falls in group 4, and the shortfin mako, pelagic thresher, oceanic whitetip, and dusky shark fall in group 5. Rigorous management measures for the species in groups 1 and 2, setting total allowable catch quota for group 3, and consistent monitoring schemes for groups 4 and 5 are recommended.

Spatial-Temporal Distribution of Megamouth Shark, Megachasma pelagios, Inferred from over 250 Individuals Recorded in the Three Oceans.

The megamouth shark (Megachasma pelagios) is one of the rarest shark species in the three oceans, and its biological and fishery information is still very limited. A total of 261 landing/stranding records were examined, including 132 females, 87 males, and 42 sex unknown individuals, to provide the most detailed information on global megamouth shark records, and the spatial-temporal distribution of M. pelagios was inferenced from these records. The vertical distribution of M. pelagios ranged 0-1203 m in depth, and immature individuals were mostly found in the waters shallower than 200 m. Mature individuals are not only able to dive deeper, but also move to higher latitude waters. The majority of M. pelagios are found in the western North Pacific Ocean (>5° N). The Indian and Atlantic Oceans are the potential nursery areas for this species, immature individuals are mainly found in Indonesia and Philippine waters. Large individuals tend to move towards higher latitude waters (>15° N) for foraging and growth from April to August. Sexual segregation of M. pelagios is found, females tend to move to higher latitude waters (>30° N) in the western North Pacific Ocean, but males may move across the North Pacific Ocean.

Profile and consumption risk assessment of trace elements in megamouth sharks (Megachasma pelagios) captured from the Pacific Ocean to the east of Taiwan.

Focusing on 27 rare filter-feeding megamouth sharks (Megachasma pelagios) captured as a by-catch of drift gillnet fishery in the Pacific Ocean to the east of Taiwan, this study analyzes the concentrations of 24 elements in their muscle, discusses the bioaccumulation of each element and the correlation between different elements, and assesses the potential health risks of consuming megamouth shark muscle. Among the 24 elements, mean concentrations of Ga, Ag, Li, Bi, Hg, Co, and Cd were relatively low ranging from 10-3 to 10-1 mg/kg, those of Pb, Ba, Mn, Ni, As, Cr, B, Sr, Cu, and Zn ranged from 10-1-101 mg/kg, and those of Fe, Ca, Al, K, Mg, Ti, and Na were relatively high ranging from 101 to 103 mg/kg. The toxic element content index was most significantly correlated with the concentration of Cu. Hence, this study recommends that the concentration of Cu could be used as an indicator of metal accumulation in megamouth shark muscle. The log bioconcentration factor (BCF) ranged from less than 0 to 7.85 in shark muscle. For elements with a concentration of less than 100 µg/L in seawater, the log BCF was inversely proportional to their concentration in seawater. According to the correlation analysis, the accumulation of elements in muscle of megamouth sharks is primarily affected by the concentrations of dissolved elements in seawater, except that the accumulation of Hg, As, Cu, Ti, Al, and Fe appears to be mainly affected by feeding behaviors. The assessment of the health risk of consuming megamouth shark muscle showed that its total hazard index was greater than 1. This suggests that the long-term or high-frequency consumption of megamouth shark muscle may cause health hazards due to the accumulation of trace elements, particularly those with a large contribution of health risk, including As, Hg, and Cu.

Somniosus (Rhinoscymnus) cheni sp. nov., A New Species of Sleeper Shark (Squaliformes: Somniosidae) from Eastern Taiwan, with Aspects of Embryo Biology.

A new species of sleeper shark is described based on a 134.0 cm total length pregnant female collected from off Hualien, eastern Taiwan. The species belongs to a small species group (subgenus Rhinoscymnus) and can be distinguished from its congeners in having a smaller second dorsal fin, smaller eyes, more rows of teeth in the upper jaw and fewer in the lower jaw, and a different body proportion. Moreover, the specimen had 33 embryos, which is substantially more than the two other small species in the subgenus. Information on embryo biology are also provided.

Genetic diversity and connectivity of the megamouth shark (Megachasma pelagios).

The megamouth shark (Megachasma pelagios) was described as a new species in 1983. Since then, only ca. 100 individuals have been observed or caught. Its horizontal migration, dispersal, and connectivity patterns are still unknown due to its rarity. Two genetic markers were used in this study to reveal its genetic diversity and connectivity pattern. This approach provides a proxy to indirectly measure gene flow between populations. Tissues from 27 megamouth sharks caught by drift nets off the Hualien coast (eastern Taiwan) were collected from 2013 to 2015. With two additional tissue samples from megamouths caught in Baja California, Mexico, and sequences obtained from GenBank, we were able to perform the first population genetic analyses of the megamouth shark. The mtDNA cox1 gene and a microsatellite (Loc 6) were sequenced and analyzed. Our results showed that there is no genetic structure in the megamouth shark, suggesting a possible panmictic population. Based on occurrence data, we also suggest that the Kuroshio region, including the Philippines, Taiwan, and Japan, may act as a passageway for megamouth sharks to reach their feeding grounds from April to August. Our results provide insights into the dispersal and connectivity of megamouth sharks. Future studies should focus on collecting more samples and conducting satellite tagging to better understand the global migration and connectivity pattern of the megamouth shark.