Shoou-Jeng Joung

The whale shark, Rhincodon typus, is a livebearer : 300 embryos found in one 'megamamma' supreme

Shoou-Jeng Joung’, Che-Tsung Chen’, Eugenie Clark’, Senzo Uchida3 & William Y.P. Huang4 I Department of Fishery Science, National Taiwan Ocean University, 2 Pei-Ning Road, Keelung 20224, Taiwan, Republic of China ’ Department of Zoology, University of Maryland, College Park, MD 20742, U.S.A. .’ Okinawa Expo Aquarium, Motobu-Cho, Okinawa Prefecture, Japan 4 R.O.C. Game Fish Association, Taipei, Taiwan, Republic of China

Demographic analysis of the pelagic thresher shark, Alopias pelagicus, in the north-western Pacific using a stochastic stage-based model

Thepelagicthreshershark,Alopiaspelagicus,likemostlargesharksproducesalownumberofoffspring(two embryos per litter). However, there is no accurate information on its population status. To improve the accuracy of population simulations, a stochastic stage-based birth-flow model was constructed to assess the stock status of the pelagic thresherinthenorth-westernPacific. Basedonthebestbiologicalinformationavailable, itslifehistorywasrepresentedas four stages: neonates, juveniles, subadults, and adults. Results indicated that, without mortality from fishing, the stock would clearly increase (mean annual population growth rate (l) ¼1.058 year � 1 , 95% CI ¼1.014-1.102 year � 1 ). When current fishing mortality was taken into account, a decrease in population was indicated (l ¼0.979 year � 1 , 95% CI ¼ 0.921-1.030year � 1 ) with a projected reduction of 34.3% over 20 years. These results suggest that the stock is overexploited. Simulations using various management measures showed that the population will remain steady under these protection options. However, this species is extremely vulnerable to overexploitation and is especially sensitive at the juvenile and adult stages, implying that nursery closures or size limit management measures are urgently needed to ensure the sustainable utilisation of the stock.

Fisheries, management and conservation of the whale shark Rhincodon typus in Taiwan

The Taiwanese government introduced a catch-and-report system for the whale shark Rhincodon typus in 2001, and in the following year limited the total allowable catch (TAC) to 80 individuals. This limit was reduced over the following years, reaching a low of 30 individuals in 2007. In November 2007, a comprehensive ban on R. typus fishing came into effect and protection measures were adopted for the species. This study measured and recorded the total length (L(T) ), body mass and sex of 810 R. typus, using fisheries and other released data for the period 1995-2008. The mean L(T) of individuals caught from June to October was smaller than that for individuals caught from November to May. Mean annual catches in set nets were higher in south-western Taiwan than in other regions of Taiwan. The sex ratio showed that males were caught more frequently than females in Taiwanese waters, indicating sex segregation. For the first time, the stock structure, conservation and management regulation of R. typus in the north-west Pacific Ocean have been reviewed. The results provide a useful resource for future assessment of the possible development of R. typus ecotourism in Taiwan.

Reproduction of the blacktip sawtail catshark,Galeus sauteri, in the waters off northeastern Taiwan

The reproductive biology of blacktip sawtail catsharks,Galeus sauteri, in northeastern Taiwan waters was investigated. Male catsharks possessed paired testes producing spermatozoa, which were then stored in the epididymides all year round. No spermatophores were observed in the lower ductus deferens. Only the right ovary was functional in females, oogonia being formed in the ovarian cortex and then developing into mature ova. Ova exceeding 17 mm in diameter were ovulated. Pregnant individuals contained one eggcase only, in each side of the uterus. No hatched embryos were observed in such eggcases. The size at which 50% of blacktip sawtail catshark specimens were mature was 410–420 mm and 350–360 mm for females and males, respectively. The species does not have a well-defined reproductive season.

The first record, tagging and release of a neonatal whale shark Rhincodon typus in Taiwan

On 27 October 2013, a Rhincodon typus was apparently chased by a group of Caranx ignobilis into nearshore waters near Green Island (Ludao), east of Taiwan. A fisherman brought it back to port where it was kept in a small sea pen until release. The R. typus was 78 cm total length, and was tagged and released on 29 October 2013.

Four New Records of Cartilaginous Fishes from Taiwan

In this paper, four new records of cartilaginous fishes from Taiwan and its adjacent waters are presented. They are Centrophorus squamosus (Bonnaterre, 1788), Centroscyllium kamoharai Abe, 1966, and Scymnodon squamulosus (Gunther, 1877) of Squaliformes, and Bathyraja trachouros (Ishiyama, 1958) of Rajiformes. Keys and diagnostic characteristics of each species are given.

Distribution Pattern, Age, and Growth of Blue Sharks in the South Atlantic Ocean

AbstractThe distribution pattern and the age and growth of Blue Sharks Prionace glauca were described based on 44,092 and 785 specimens, respectively, that were collected by scientific observers onboard Taiwanese longline fleets in the South Atlantic Ocean between December 2004 and December 2013. Size segregation was found, and the mean length of Blue Sharks was significantly larger in the equatorial–tropical area (0–15°S) than in the subtropical–temperate area (south of 15°S) during all seasons. Males predominated in both areas and during all seasons; the exceptions were seasons 2 (April–June) and 3 (July–September) in the equatorial–tropical area and season 2 in the subtropical–temperate area. The sex ratio increased with shark size in the equatorial–tropical area but decreased with size in the subtropical–temperate area. Growth band pairs (including translucent and opaque bands) were counted on images photographed from X-ray films of vertebrae from the caudal peduncle region. The centrum edge analysis ...

Estimates of life history parameters of the oceanic whitetip shark, Carcharhinus longimanus, in the Western North Pacific Ocean

ABSTRACT The age, growth and reproduction of the oceanic whitetip shark, Carcharhinus longimanus, in the western North Pacific Ocean were estimated based on 188 specimens (89 females and 99 males) collected before the prohibition of retaining on board for commercial use by the Western and Central Pacific Fisheries Commission (from November 2002 to January 2006) at the Nanfanao fish market in north-eastern Taiwan. The relationship between body weight (W) and total length (TL) for both sexes combined was estimated as follows: (n = 188, P < 0.01). The relationship between TL and the pre-caudal vertebral centrum radius (R) for sexes-combined data was described using the following equation: TL = 29.98 + 20.99R (n = 112, P < 0.05). The opaque bands in pre-caudal vertebrae are formed once annually between June and September based on a marginal increment ratio analysis. The maximum number of growth band pairs was 12 for both sexes in this study. The two-parameter von Bertalanffy growth function best fits the length-at-age data, and the growth parameters (sexes combined) were estimated as follows: asymptotic length (L∞) = 309.4 cm TL and growth coefficient (k) = 0.085/yr with the size at birth set as 64 cm TL (n = 112, P < 0.01). The litter size was 10–11, and the size at birth was at least 64 cm TL. The sizes at first and 50% maturity were 190 cm and 193.4 ± 0.97 cm TL for females and 172 cm and 194.4 ± 6.57 cm TL for males. These corresponded to 8.5 yr and 8.8 yr for females and 6.8 yr and 8.9 yr for males.

The Occurrence of Two Lanternsharks of the Genus Etmopterus (Squalidae) in Taiwan

Two forms of the lanternshark,Etmopterus, reported from Taiwan waters under the nameEtmopterus lucifer were reexamined.E. lucifer sensu Teng (1959), Chen (1963) and Shen and Ting (1972) does not conform to the original description ofE. lucifer Jordan et Snyder, 1902. One form described by Shen and Ting (1972) conformsto E. splendidus Yano, 1988, whereas another form reported by Teng (1959) and Chen (1963) agrees well withE. molleri (Whitley, 1939). These were identified based on a combination of the following characters: shape and length of the flank and caudal markings, position of the posterior end of flank markings, shape of the upper teeth, distributional patterns of dermal denticles on the second dorsal fin and preoral area, and length of the caudal peduncle.

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.