Kwang-Ming Liu

Age, Growth, and Reproduction of the Pelagic Thresher Shark, Alopias pelagicus in the Northwestern Pacific

Age, growth, and reproduction of Alopias pelagicus are described based on 831 specimens (508 females and 323 males) collected from September 1993 to August 1995 in waters off northeastern Taiwan. Alopias pelagicus embryos are oophagous. Five developmental stages (two encapsulated and three posthatching) are recognized. The number of embryos per litter is two, and size at birth is between 158 cm and 190 cm total length (TL). The sex ratio of embryos is 1:1. Total length at maturity is 282-292 cm for females and 267276 cm for males, which corresponds to age of 8.0-9.2 yr and 7.0-8.0 yr, respectively. Gestation period could not be determined from present data because females were in various stages of pregnancy throughout the year. Based on marginal increment analysis and verified by length-frequency analysis, annuli in precaudal vertebrae form once a year and numbered up to 16 and 14 for females and males, respectively. However, extrapolating the growth rates for the largest sharks would yield maximum ages of 28.5 yr and 17.5 yr for females and males, respectively. The von Bertalanffy growth equations in PCL were estimated as Lt = 197.2(1 e-0.085(t+7.67)) for females, and L, = 182.2(1 e-0118(t+5.48)) for males.

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.

Reproductive biology of whitespotted bamboo shark Chiloscyllium plagiosum in northern waters off Taiwan

In total, 491 whitespotted bamboo sharks were collected from northern Taiwanese waters from February 2002 to February 2003. The sex ratio of the specimens was 0.65, total length (TL) ranged from 35.3–85 cm, and weight ranged 124–2580 g. The mean size at first maturity was estimated to be 64.9 and 65.6 cm TL for females and males, respectively, based on the relationship between mature percentage and TL. The ovulation season was estimated as March to May based on gonadosomatic index (GSI) variations and captive observation. The monthly changes in GSI of males suggested that the mating season was from December to January. The inconsistency between mating and ovulation seasons suggested that females have sperm storage and delayed fertilization. One or two eggs were deposited every 6 or 7 days on average. Deposition of eggs extended for 2 months, and fecundity was 8±3.8 eggs. Thirteen of 48 eggs deposited in 2003 were hatched and the hatching rate was 0.27. The hatching period was 107±9.3 days with accumulated water temperature ranging from 2372–2835°C.

Reproductive biology of the common ponyfish Leiognathus equulus in the south-western waters off Taiwan

Reproductive biology of the common ponyfish Leiognathus equulus was described based on 958 specimens caught by otter trawlers in the south-western waters off Taiwan and landed at Tungkang and Linuan fishing ports from March 2000 to February 2001. Macroscopic appearance of the ovary, gonad-somatic index, oocyte diameter frequency distribution, and histological examination suggested that the spawning season of the common ponyfish in south-western Taiwan waters is from May to August. Eight stages of oocyte development were determined based on histological examination, and ovarian development can be divided as immature, early maturing, late maturing, mature and spent stages. The sex ratio of 0.52 was not significantly different from 0.5 using χ2 test. but females were overwhelmingly more when fork length (FL) was greater than 170 mm. The relations between fecundity (F), batch fecundity (BF), and body weight (BW) were estimated to be F=−5328+1.2946 BW (n=132, P<0.05) and BF=−11.26+0.2748 BW (n=25, P<0.05), respectively. Mean fecundity and mean batch fecundity (±standard error) were estimated to be 129 955±79 343 and 28 160±14 698, respectively. Sizes at 50% maturity estimated from the Logistic model were 162 mm FL and 158 mm FL for females and males, respectively.

Estimating Finite Rate of Population Increase for Sharks Based on Vital Parameters.

The vital parameter data for 62 stocks, covering 38 species, collected from the literature, including parameters of age, growth, and reproduction, were log-transformed and analyzed using multivariate analyses. Three groups were identified and empirical equations were developed for each to describe the relationships between the predicted finite rates of population increase (λ’) and the vital parameters, maximum age (Tmax), age at maturity (Tm), annual fecundity (f/Rc)), size at birth (Lb), size at maturity (Lm), and asymptotic length (L∞). Group (1) included species with slow growth rates (0.034 yr-1 < k < 0.103 yr-1) and extended longevity (26 yr < Tmax < 81 yr), e.g., shortfin mako Isurus oxyrinchus, dusky shark Carcharhinus obscurus, etc.; Group (2) included species with fast growth rates (0.103 yr-1 < k < 0.358 yr-1) and short longevity (9 yr < Tmax < 26 yr), e.g., starspotted smoothhound Mustelus manazo, gray smoothhound M. californicus, etc.; Group (3) included late maturing species (Lm/L∞ ≧ 0.75) with moderate longevity (Tmax < 29 yr), e.g., pelagic thresher Alopias pelagicus, sevengill shark Notorynchus cepedianus. The empirical equation for all data pooled was also developed. The λ’ values estimated by these empirical equations showed good agreement with those calculated using conventional demographic analysis. The predictability was further validated by an independent data set of three species. The empirical equations developed in this study not only reduce the uncertainties in estimation but also account for the difference in life history among groups. This method therefore provides an efficient and effective approach to the implementation of precautionary shark management measures.

Evaluating the impacts of uncertainty on the estimation of biological reference points for the shortfin mako shark, Isurus oxyrinchus, in the north-western Pacific Ocean

Biological reference points (BRPs) are commonly used to assess the harvest level and stock status of marine fish populations. However, BRP estimates may be influenced by uncertainties about life-history parameters and fishing practices. The shortfin mako shark, Isurus oxyrinchus, is one of the most important by-catch species for tuna longline fisheries; however, its stock status remains poorly understood. To understand its population dynamics, the present study examined fishery statistics data and biological measurements of the shortfin mako in the north-western Pacific, and evaluated the impact of uncertainties associated with various sources of uncertainty, by using a simulation approach. The simulations indicated that BRPs are especially sensitive to changes in weight–length relationship and the growth parameters. Failure to take this into account may lead to inaccurate estimates and have serious consequences for management decision-making. To improve the accuracy of BRP estimates, biological measurements and life-history parameters should be updated regularly to account for changes in size composition and population structure. Further research could focus on increasing the sex-ratio sample size, updating the weight–length relationship and growth equations, incorporating ageing error into BRP calculations and determining BRPs by using appropriate levels of spawning-potential ratio.

Virtual population analysis of the big eye Priacanthus macracanthus in the waters off northeastern Taiwan

Abstract A length–frequency data set including 9548 specimens of the big eye, Priacanthus macracanthus , from the waters off northeastern Taiwan during the period from 1994 to 1997 was analyzed. Six age classes were identified from a length–frequency analysis and dominant age classes were 3 + , and 4 + . Instantaneous total mortality ( Z ) was estimated to be 0.88, 1.36, 1.97 and 1.56/yr for 1994–1997, respectively. Natural mortality ( M ) estimated from Paulys equation ranged from 0.326 to 0.373/yr. Age-specific abundance estimated from virtual population analysis indicated that the abundance of 2 + peaked in 1995, 3 + in 1996, 4 + in 1997, and 5 + and 6 + in 1994. The abundance of the 1989–1994 year–class indicated that the big eye stock experienced the highest mortality during the period of ages 4 and 5. Abundance of the big eye stock (for 2 + to 6 + ) increased from 1994 to 1995 and decreased thereafter. Similar patterns of abundance, catch and catch per unit of effort suggested that the big eye stock might fluctuate periodically.

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.