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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).

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.

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.

Overfishing is the primary cause of marine defaunation, yet declines in and increasing extinction risks of individual species are difficult to measure, particularly for the largest predators found in the high seas1-3. Here we calculate two well-established indicators to track progress towards Aichi Biodiversity Targets and Sustainable Development Goals4,5: the Living Planet Index (a measure of changes in abundance aggregated from 57 abundance time-series datasets for 18 oceanic shark and ray species) and the Red List Index (a measure of change in extinction risk calculated for all 31 oceanic species of sharks and rays). We find that, since 1970, the global abundance of oceanic sharks and rays has declined by 71% owing to an 18-fold increase in relative fishing pressure. This depletion has increased the global extinction risk to the point at which three-quarters of the species comprising this functionally important assemblage are threatened with extinction. Strict prohibitions and precautionary science-based catch limits are urgently needed to avert population collapse6,7, avoid the disruption of ecological functions and promote species recovery8,9.

The catch of Japanese butterfish, Psenopsis anomala in Taiwan is greater than those of any other nation; however, the biology, particularly the age and growth, of this economically important fish species is little known. This study describes the age and growth of P. anomala based on 734 specimens (340 females, 363 males, 31 unsexed) caught by trawl fishery in the north-eastern waters off Taiwan from March 2007 to July 2008. The age of specimens was estimated by counting the growth annuli in sagittal otoliths. The periodicity of annulus deposition on otolith was estimated to be one year with opaque zone deposited between July and August based on marginal increment analysis. The maximum age for both sexes was estimated to be ~4. The female portion of the population was dominated by the 3+ age class, while the male portion was dominated by the 2∞ age class. The parameters of the von Bertalanffy growth function with standard error estimated based on the observed length at age using a non-linear method are as follows: L∞ = 25.47 ± 0.65 cm, k = 0.30 ± 0.03 year−1, and t0 = −1.84 ± 0.16 year for females (n = 350), and L∞ = 22.39 ± 0.45 cm, k = 0.46 ± 0.04 year−1, and t0 = −1.38 ± 0.13 year for males (n = 378). The growth performances of P. anomala reported from different geographic regions were compared, and the potential influences of sample size distribution on the estimated growth parameters were further discussed.

Simple Summary In this study, we integrate Megachasma pelagios records from the three oceans, refine previous results, add more individual data, solve the problem of uncertain body size estimations, and provide additional information on the horizontal and vertical distributions. A checklist of over 250 M. pelagios is integrated in this study based on numerous public sources, published papers, personal communication, and unreleased information, especially the catch records from Taiwanese waters. The conversion equations among different length measurements are provided. In addition, the spatial–temporal movement of M. pelagios is inferred from the integrated data, and the results may provide important information on the vertical and geographic migration behavior of the mysterious species. Abstract 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.

A Bayesian population modelling tool integrating separable virtual population analysis, per‐recruit models and age‐structured demographic analysis was developed for the bigeye thresher Alopias superciliosus (Lowe) population in an area subset of the western North Pacific. The mortality rates for years 1989–2016 were estimated, various biological reference points and associated risks of decline were also estimated, and alternative harvest strategies for the stock were evaluated. Estimates of the posterior mean of fishing mortality for bigeye thresher shark suggest fishing pressure has been high in recent years (2011–2016). The estimated population growth rate (λ) (without fishing) obtained from age‐structured demographic model was relatively low (λ = 1.01 per year; 95% confidence intervals of 1.00 and 1.03 per year). Risk analyses revealed that only low levels of fishing pressure (10% of the current fishing pressure) over a wide range of ages could maintain a relatively low risk of population decline for bigeye threshers. Sensitivity testing indicated that the model is robust to prior specification. The developed framework could be used as an assessment tool to evaluate the risk of decline for other widely distributed pelagic shark species where insufficient catch and effort data are available.

The narrow-barred Spanish mackerel Scomberomorus commerson is an economically essential species; however, few studies have investigated its demographic structure in the northwestern Pacific, which includes Taiwan’s waters. This study examined the growth parameters, age composition, mortality, and sex ratio of S. commerson catches by examining sagittal otoliths and other biological data collected in a 3-year project from June 2018 to June 2021. The transverse sections of sagittal otoliths exhibited alternating translucent and opaque zones, in annual cycles, and this observation was validated by otolith edge analysis. Opaque zones began to form in October; the growth peaked in December and lasted until March. Growth parameters were estimated for female (L∞ = 144.1 cm fork length [FL], k = 0.39 y−1, to = −0.85 y) and male (L∞ = 136.0 cm FL, k = 0.32 y−1, to = −1.49 y) specimens. The maximum recorded FL, body weight, and age were 159.0 cm, 27 kg, and 9.2 y for female and 135.0 cm, 17.8 kg, and 7.2 y for male specimens. Rapid growth was observed for both sexes, with FL reaching 66.8 ± 14.2 cm in female specimens and 70.1 ± 11.0 cm in male specimens during the first year of life. An age–length key based on the direct otolith aging and FL dataset (N = 646) was used to estimate the age composition of 3-year catches measured at landing (N = 16,133). The results verified that the S. commerson currently caught in the central Taiwan Strait are mainly young fish aged 1+ to 2+ y. The estimated fishing mortality (0.27 y−1) and exploitation rate (0.30) suggested that overfishing was not occurring in this stock. The findings of this study have helped clarify the population dynamics of the S. commerson in the Taiwan Strait, and the biological parameters reported herein can aid the management and conservation to ensure the sustainability of this species in this region.

The blue shark (Prionace glauca) is the most frequently captured shark in pelagic oceanic fisheries, especially pelagic longlines targeting swordfish and/or tunas. As part of cooperative scientific efforts for fisheries and biological data collection, information from fishery observers, scientific projects and surveys, and from recreational fisheries from several nations in the Atlantic and Indian Oceans was compiled. Data sets included information on location, size and sex, in a total of 478,220 blue shark records collected between 1966 and 2014. Sizes ranged from 36 to 394 cm fork length. Considerable variability was observed in the size distribution by region and season in both oceans. Larger blue sharks tend to occur in equatorial and tropical regions, and smaller specimens in higher latitudes in temperate waters. Differences in sex ratios were also detected spatially and seasonally. Nursery areas in the Atlantic seem to occur in the temperate south-east off South Africa and Namibia, in the south-west off southern Brazil and Uruguay, and in the north-east off the Iberian Peninsula and the Azores. Parturition may occur in the tropical north-east off West Africa. In the Indian Ocean, nursery areas also seem to occur in temperate waters, especially in the southwest Indian Ocean off South Africa, and in the south-east off south-western Australia. The distributional patterns presented in this study provide a better understanding of how blue sharks segregate by size and sex, spatially and temporally, and improve the scientific advice to help adopt more informed and efficient management and conservation measures for this cosmopolitan species., Sí

The 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 ...

Overfishing is the primary cause of marine defaunation, yet declines in and increasing extinction risks of individual species are difficult to measure, particularly for the largest predators found in the high seas

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.

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

Full stock assessment of sharks is usually hindered by a lack of long time-series catch and effort data. In these circumstances, demographic and per-recruit analyses may provide alternate approaches to describe population status because these methods can be applied to estimate biological reference points (BRPs) for shark stocks. However, the appropriate level of BRPs for sharks is difficult to determine, given the expected low reproductive rates. To determine which BRPs are most appropriate for the CITES-listed species&mdash, bigeye thresher shark, Alopias superciliosus, a stochastic demographic model with Monte Carlo simulations and per-recruit models were used to estimate BRPs in this study. The results indicated that conventional fishing mortality-based BRPs (FBRPs) derived from per-recruit models may result in a clear population decline. Our analyses also demonstrated that the bigeye thresher population in the Northwest Pacific will stabilize only if demographic-based FBRP is implemented. The FBRP estimated based on the stochastic demographic model was 0.079&ndash, 0.139 y&minus, 1, which was equivalent to SPR = 50&ndash, 70%. The findings strongly suggested that more conservative threshold FBRPs should be implemented to ensure sustainable utilization of the bigeye thresher stock. The present study provides new and strategically important information on the population dynamics of the bigeye thresher in the Northwest Pacific, which can be used to help fishery managers to adopt more efficient management measures for this stock. It is also suggested that this approach can be applied to other shark species with limited catch and effort data.

Stock enhancement is a method for replenishing depleted wild finfish populations by supplementing them with hatchery-raised fish. In Taiwan, silver sea bream (Rhabdosargus sarba) is a predominant commercial species involved in stock enhancement projects. Although management agencies conduct stock enhancement projects, there are a lot of private releases without records. Stock enhancement is performed by the private aquaculture sector without accurate genetic records, potentially leading to unintended consequences for wild populations. We analyzed the genetics of 459 wild and 701 hatchery-reared specimens from nine batches produced by various hatcheries. Wild and hatchery-reared samples could be considered two separate clades by using a set of stable and informative microsatellite markers including type I (from gene introns and 3&prime, UTR) and type II markers (randomly picked up from genome). Type I microsatellite markers could more sensitively reflect the loss of genetic diversity more than type II markers in the domestication process. All specimens were considered native by using mtDNA COI and microsatellites. The genetic composition of the wild population is relatively simple, and the estimated low contribution rate of the hatchery stock (1.3&ndash, 10.9%, 6&ndash, 50/459) indicated a weak but significant genetic effect of stock enhancement. Therefore, establishing standards for the stock enhancement of silver sea bream for more effective supplementation of wild populations is imperative.

The narrow-barred Spanish mackerel (Scomberomorus commerson) is an economically important fish species in Taiwan. Nevertheless, its reproductive biology in the region is poorly understood. This study provides the first information on the reproductive biology of this species in the central Taiwan Strait. In total, 1031 specimens were collected from January 2016 through August 2017, and the sex ratio (0.55) was significantly different from 0.5 (p = 0.0016). On the basis of progressive changes in ovary size, ovary histology, oocyte diameter, and gonadosomatic index, the spawning season was estimated to extend from March through August, peaking between March and May. The fecundity (F) and batch F (BF) were estimated to range from 193,212 to 9,810,450 and 91,117 to 2,077,581 eggs per fish, respectively. The relationships of F and BF to fork length (FL) were estimated as follows: F = 0.0247FL4.005 (r2 = 0.57, n = 110, p = 1.05 × 10−10) and BF = 0.00071FL3.999 (r2 = 0.514, n = 41, p = 0.0000149). Based on a logistic model, sizes at 50% of maturity were 68.0 and 68.4 cm in FL for female and male specimens, respectively. Hydrated and postovulatory oocytes were collected from March through June, suggesting that the Taiwan Strait is a spawning ground for S. commerson. The proportion of reproductively active female fish with postovulatory oocytes during the spawning season was 0.15, indicating that spawning occurs every 6.5 days on average. The parameters measured in this study, which provide useful information about S. commerson, can facilitate management, conservation, and sustainable fishing of this species in the region.

The diet and feeding habits of the whitespotted bamboo shark (Chiloscyllium plagiosum) were described using stomach content analysis and stable isotope analysis based on 327 and 78 specimens, respectively, that were collected in northern Taiwanese waters from October 2013 to March 2015. The index of relative importance indicated that both females and males mainly fed on Demospongiae, unidentified organisms, Annelida, and crustaceans. Juveniles ( 65 cm in TL) fed more on teleost fishes. Similar standardized diet breadths ( B a ) were found for sharks caught by different fishing gear and for sharks at different maturity stages; however, seasonal variation in B a was noted. These results suggest that the whitespotted bamboo shark is a prey specialist. No significant differences in prey composition among fishing gear, sexes, maturity stages, or seasons were found by the multi-variate statistical analysis. Permutational multi-variate analysis of variance and a global test also indicated that there were no significant differences in diets between the maturity stages and sexes. The stable isotope analysis indicated that the mean values of δ 15 N and δ 13 C for the females and males were similar, suggesting the existence of high overlap in terms of feeding for both sexes. A multi-variate analysis of variance indicated that significant differences were found for the mean values of δ 13 C and δ 15 N among the different seasons, maturity stages and season–maturity stage interactions. These results suggested that an ontogenetic shift in the diet of C. plagiosum may occur when the fish approach the size of maturity.

The age and growth of Kwangtung skate, Dipturus kwangtungensis, in the waters off northern Taiwan were estimated from 422 specimens collected between July 2006 and July 2008 at the Tashi fishing market in north-eastern Taiwan. The sexes-combined relationship between total length (TL) and centrum diameter (D) was estimated as follows: TL = 14.11D0.888 (N = 411, r2 = 0.94, P L∞) = 96.7 cm TL, growth coefficient (kG) = 0.144 year−1 and constant (t0) = 5.45 year (N = 364, P

The Yellowfin Tuna Thunnus albacares is one of the major fish species caught around subsurface fish aggregation devices (FADs) in the waters southwest of Taiwan. However, how it interacts with other organisms around FADs is poorly known. In this study, the diet and feeding habits of juvenile Yellowfin Tuna were estimated from the analysis of stomach contents from 1,477 specimens with FLs ranging from 24 to 108 cm and stable isotope analysis (202 specimens) collected around FADs in the waters southwest of Taiwan. The analysis of stomach contents indicated that juvenile Yellowfin Tuna with FL < 50 cm mainly feed on larval purpleback flying squid Sthenoteuthis oualaniensis, larval shrimps, and zooplanktonic organisms such as amphipods. Yellowfin Tuna with FL of ∼50 cm switch their diet to teleost fishes such as Japanese Barracudina Lestrolepis japonica, Skinnycheek Lanternfish Benthosema pterotum, and fishes in the families Exocoetidae and Scombridae. Stable isotope analysis indicated that the δ15N v...

Most demographic models explicitly track the dynamics of a single sex. However, single-sex models may lead to rather poor results when vital rates and other demographic parameters differ between the sexes. Consequently, the population may not be optimally managed if management measures are based on a single-sex model, which suggests the need for two-sex models. The consequences of ignoring sexual dimorphism and mating mechanisms when proposed management strategies are based on single-sex demographic models are illustrated for shortfin mako shark, Isurus oxyrinchus, in the Northwest Pacific Ocean. Analyses based on single-sex models would underestimate the probability of decline risk. The findings imply that management decisions should be based on sex-specific models to better achieve management goals. The mating mechanism principally affects the proportion of breeding females, which has a large impact on the perceived population growth rate. Which mating function best describes the dynamics of shortfin mako populations is still unknown. More research is needed to avoid making inaccurate management decisions, such as genetic paternity studies to clarify the mating mechanism for this species.

Most demographic models are single sex, and assume both sexes have the same vital rates. However, many species, including the shortfin mako shark, are sexually dimorphic in vital rates, which suggests the need for two-sex models. In this study, a two-sex stage-structured matrix model was constructed to estimate shortfin mako shark demography and population dynamics. Monte Carlo simulations were used to evaluate the impact of uncertainties on the estimate of population growth rate. The number of shortfin mako sharks is found to be dropping under current conditions, but will stabilize if size-limit management is implemented. The simulations indicated that population growth rate estimates are mainly influenced by the uncertainty related to survival rate and fecundity. The effects of uncertainty regarding the age at maturity and longevity were found to be relatively minor. Future research should focus on obtaining estimates of natural mortality and reproductive traits for this species to improve the accuracy of demographic estimates.

Age, growth and mortality of the goldlined seabream, Rhabdosargus sarba, were estimated based on 593 and 6516 specimens that were collected in waters off southwestern Taiwan from September 2015 to August 2016, and April 2015 to December 2017, respectively. The body weight (BW) and total length (TL) relationship (all data-pooled) was expressed as: BW = 0.01511 TL3.0346 (r2 = 0.95; n = 593). Growth rings (identified as opaque and translucent zones) were counted on 447 sectioned sagittal otoliths using a microscope under transmitted light and were counted up to 8 (42.0 cm TL) for both sexes. Edge analysis indicated that growth rings in otoliths were deposited once per year, and the opaque zone was formed in December. The von Bertanlanffy growth function (VBGF) best fit the observed length at age data for R. sarba. The growth parameters (±standard error) of VBGF for R. sarba (all data-pooled) were estimated as: L∞ = 53.94 ± 3.71 cm TL, k = 0.217 ± 0.033 yr-1, t0 = –0.182 ± 0.167 yr (n = 447). Total mortality estimated from a length converted catch curve was 0.655 yr-1, age-specific natural mortality and fishing mortality were estimated as 0.789–0.293 yr-1 and 0.109–0.365 yr-1, respectively. The exploitation rate was estimated to be 0.440.

Whale shark, the largest fish in the world, has been concerned by many environmental groups and has been included on the CITES Appendix II list since 2002. Taiwan has taken a series management measures on whale shark since 2000 including catch quota and size limit and has banned fishing since 2008 for effective management and conservation of this species. Some countries that fished for whale sharks have developed their ecotourism as an alternative income earner. However, this alternative utilization has never been evaluated in Taiwan. Hence this study is to examine the feasibility of whale shark ecotourism in Taiwan. Based on averaged catch per unit effort (CPUE), Pingtung (PT) and Penghu (PH) were identified as the highest potential hot-spots for ecotourism development. March to June was identified to be the best season for this activity based on occurrence of whale sharks in Taiwan waters. PH and PT had the highest CPUE, adequately shallow sea depth, accessible transportation, lodging and dining facilities, and other established tourism activities adding to its suitability. Questionnaires for tourists visiting and set net operators in PT and PH demonstrated that the majority welcomed whale shark ecotourism. In order to successfully develop this highly lucrative activity, the participation and collaboration between stakeholders, government and non-governmental organizations should be achieved.

Summary An increase in yellowfin tuna (Thunnus albacares) catch by danish seine fisheries around the subsurface fish aggregating devices (FADs) in southern Taiwan waters has been a concern of local government and environmental groups. However, the attraction mechanism of aggregating tunas at the subsurface FADs is still poorly understood. The objective of this study is to examine the fine-scale vertical and horizontal movements of juvenile yellowfin tunas around a subsurface FAD. In total, 53 tunas (35–81 cm fork length) were tagged with ultrasonic telemetry tags and released at a subsurface FAD in the waters off Shiao-Liu-Chiu Island, southwestern Taiwan from October 2008 to December 2009. These tunas stayed at the subsurface FAD for up to 31 days, with daytime vertical movement depths averaging 60–80 m at a maximum depth of 250 m. At night, the tuna gathered at a shallow depth of 40 m. The mean depth of vertical movement in the daytime is significantly different from that of the nighttime (P

Background The whale shark, Rhincodon typus, was utilized extensively in Taiwan before 1996. A quota management measure was put in place in 2002, and the whale shark fishery was completely banned in 2008. Biological studies including age and growth, and migration/ movement have been conducted. However, the feeding ecology of whale sharks in different life history stages and sexes in Taiwan waters (Northwest Pacific Ocean) is still unknown. Approach The stable isotope technique was used to analyze the tissue of whale sharks to understanding their feeding ecology. The ´13C value can be used to indicate the foraging habitat of fish, and the ´15N value can be used to estimate the relative position of the consumer in the ecosystem. The specimens (tissue) were taken from individuals entangled in set nets during the period 2008 – 2013 in Taiwan. Results In total, 66 tissue samples from 42 males and 24 females, ranging from 2.84 to 11.90 m TL (total length) were used in stable isotope analysis. Among these specimens 50 and 16 were from the eastern and western waters off Taiwan, respectively. The value of ´13C was from –13.68 to –18.42%, and the value of ´15N was from 5.17 to 13.01%. There was a positive relationship between ´13C and ´15N, and both ´13C and ´15N increased with body size. No gender or geographic difference was found in this study, but the range of stable isotope values of whale shark tissue was wider in eastern Taiwan waters. Conclusions In this study, ontogenetic changes in the diet of whale sharks were found. More specimens are needed to examine the differences in stable isotope values among different genders, seasons, and regions. The results derived from this study can provide useful information on the husbandry of whale sharks, which can help ecotourism operators become more knowledgeable about the ecology of whale sharks. In addition, the results can also be used as an important reference for ecosystem-based management in the future. Future work should focus on discussion on the habitat partition, utilization, and adaption in various marine environments for whale sharks.

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.

The dramatic decline in annual yield of the Japanese butterfish, Psenopsis anomala, in southwestern Taiwan over the past decade suggests that this stock might have been overexploited. However, its fishery biology and stock status is poorly understood. This study therefore provides the first information on P. anomala reproductive biology based on 983 specimens collected by small trawlers in southwestern Taiwan waters between February 1999 and February 2000. The sex ratio, 0.44 (431/983), differed significantly from 0.5 and females predominated in fork length above 180 mm. The relationships between body weight (BW) and fork length (FL) were estimated as BW = 1.62 A— 10−4 A— FL2.637 (r2 = 0.74; n = 430, P 

The sharpspine skate Okamejei acutispina is one of the most abundant bycatch species of trawl fishing in the waters of northeastern Taiwan. However, its life history parameters, which are essential for stock assessment and management, are still poorly understood. The objective of this study was to estimate important parameters for this species, including age, growth, age at maturity and mortality. Age estimates were derived from 652 specimens (356 females and 296 males, 9.5–33.8 cm in disc width) using vertebral band counts and verified by length-frequency analysis of 1443 specimens (768 females, 675 males) collected between October 2004 and December 2007 in waters off northeastern Taiwan. The sexes-combined relationship between body weight (W) and disc width (DW) was W = 0.0193 × DW 3.0144 ( n = 1399, p DW ∞ ) = 32.4 (31.3–34.0) cm DW, growth coefficient ( k ) = 0.367 (0.315–0.426) yr −1 for females; and DW ∞ = 28.8 (27.6–30.3) cm DW, k = 0.365 (0.311–0.424) yr −1 for males. Age at maturity was estimated to be 7.2 and 6.8 yrs for females and males, respectively, while longevity was estimated to be 13.2 and 13.3 yrs, respectively. Length-frequency analysis produced similar results, supporting the vertebral aging estimates. Total mortality was estimated to be 0.85 and 0.86 yr −1 , while natural mortality was 0.32 and 0.32 yr −1 for females and males, respectively. Our study indicates that it is likely that the sharpspine skate is at the margin of optimal exploitation and therefore close monitoring and seasonal closure management of trawl fishing are recommended to ensure sustainable utilization of this stock.

Conservation of ecologically related species and understanding the discard composition of fisheries are major concerns for marine ecosystem conservation. However, high sea longline fisheries data are insufficient because of difficulties in deploying observers for data collection. Observer data collected from 77 trips on Taiwanese large-scale longline fishing vessels in the Indian Ocean from June 2004 to March 2008 were used to estimate the scale of the bycatch. At least 40 species were recorded. Albacore, bigeye, yellowfin, and southern bluefin tuna were the major species recorded and comprised over 73.30% of the total retained catch. Major bycatch species were swordfish, blue shark, sailfish, pomfret, and escolar. The average discard rate was 14.09%, ranging from 3.20% for the yellowfin tuna fleet to 18.09% for the bigeye tuna fleet. In total, 0.80% of the catch of the albacore, 4.74% of the bigeye, and 2.32% of the yellowfin tuna were discarded. There were significant differences among seasons and areas for the discard rates of the bigeye and yellowfin tuna. The discard rates of the bigeye and southern bluefin tuna were positively correlated to the catch per unit effort. The depredation percentage of tuna by cetaceans was from 0.7% to 12.3% of total discards for the different fleets. The high discard and cetacean depredation rates showed that major possible reasons for discards are depredation by cetaceans, economic factors, and quota limitations. Regarding other species, 61 seabirds and 84 sea turtles were a part of the bycatch. The major species were Indian Yellow-nosed Albatross in the southern Indian Ocean and Olive Ridley turtles in tropical areas. The estimated annual incidental catch numbers were 715 to 311 seabirds and 1856 to 1127 sea turtles from 2004 to 2007. For conservation, this discard information could be used to assess tuna stocks. Mitigation measures, including the live release of small-sized fish, and the use of bird-scaring lines and circle hooks, are required to minimize the bycatch.

The age and growth of the blue shark Prionace glauca in the central South Pacific is described based on 267 specimens that were collected by scientific observers on board Taiwanese large-scale tuna longline fleets between May 2009 and May 2011. Growth band pairs (identified as translucent and opaque bands) were counted on images photographed from X-ray films of the vertebrae from the caudal peduncle region. The marginal increment ratio and centrum edge analysis indicated that a growth band pair was formed on the vertebral centrum once per year. The band pairs after the birthmark were counted from 2 to 11 for females and from 2 to 15 for males. The bias corrected Akaike information criterion indicated that the von Bertalanffy growth function (VBGF) best fitted the observed total length (TL)-at-age data. The parameters of sex-specific VBGF were estimated as follows: for females, theoretical maximum length (L∞) mean±s.d.=330.4±46.6cm TL, growth coefficient k=0.164±0.057year–1 and theoretical age at length 0 (t0)=–1.29±0.78 years; for males, L∞=376.6±32.6cm TL, k=0.128±0.022year–1 and t0=–1.48±0.54 years. The longevities were estimated to be at least 16.8 and 21.6 years for females and males respectively.

The shortfin mako shark (Isurus oxyrinchus) is a cosmopolitan species abundant in the Northwest Pacific. Some aspects of its biological information have been well documented yet its population dynamics is poorly known. The objective of this study is to assess the population status of the shortfin mako in the Northwest Pacific. The whole weights of 68,943 female and 64,338 male shortfin mako landed at Nanfangao and Chengkung fish markets, eastern Taiwan from 1990 to 2004 were converted to total length and the age for each individual was estimated based on the sex-specific von Bertalanffy growth equation. Total mortality obtained with length-converted catch curves ranged from 0.175 yr−1 to 0.272 yr−1 for females and from 0.196 yr−1 to 0.286 yr−1 for males. Natural mortality estimated from Peterson and Wroblewski's equation were 0.077–0.244 yr−1 for females and 0.091–0.203 yr−1 for males. Based on virtual population analysis, the highest fishing mortality occurred in ages 6–10 years for females and 7–12 years for males. Increases of fishing mortality in ages 3–5 years for females and 3–6 years for males since 1996 indicated that the young shortfin mako experienced higher fishing pressure in recent years. Both deterministic and stochastic simulations showed that annual spawning potential ratio (SPR) of shortfin mako was lower than the biological reference point (BRP) of SPR 35% and had a decreasing trend since 2000. Current fishing mortality (0.066 yr−1) was greater than the BRP of F30% (0.052 yr−1), F35% (0.045 yr−1), F40% (0.04 yr−1) and F0.1 (0.063 yr−1) suggesting that this stock might have been overexploited. Therefore, to ensure sustainable utilization, a management measure of 32% reduction of current fishing effort was suggested for the shortfin mako stock in the Northwest Pacific.

The sharptail mola, Masturus lanceolatus , is one of the largest teleost fishes in the world, and can be found in warm temperate and tropical regions worldwide. The increase of sharptail mola catch in the eastern Taiwan in recent years stimulated a concern that increasing exploitation of this species might lead to a decline of the stock. However, biological information of this species is very limited. Hence, this study provides the first information on age and growth of this species in the waters off eastern Taiwan based on 265 specimens (105 females and 160 males) collected from January 2003 to November 2006 at the Nanfanao and Hualien fish markets, eastern Taiwan. The relationships between whole weight ( W ) and standard length were expressed as: W = 9.98 × 10 −4 SL 2.45 ( n = 105, p W = 3.33 × 10 −4 SL 2.68 ( n = 160, p L ∞ ) = 262.5 cm SL, growth coefficient ( k ) = 0.046 yr −1 , age at zero length ( t 0 ) = −3.350 yr ( n = 80, p L ∞ = 231.0 cm SL, k = 0.059 yr −1 , t 0 = −1.852 yr ( n = 135, p

To examine the age, growth and reproduction of silky sharks, Carcharhinus falciformis , in the waters off northeastern Taiwan, 469 specimens (213 females and 256 males) were collected from August 2000 to January 2002 at the Nanfanao fish market, northeastern Taiwan. The relationship between body weight ( W ) and total length (TL) for both sexes combined was expressed as: W = 2.92 × 10 −6 TL 3.15 ( n = 469, p R ) for both sexes combined data was estimated as: TL = 25.979 + 18.197 R ( n = 250, p L ∞ ) = 332.0 cm TL, growth coefficient ( k ) = 0.0838 year −1 , age at zero length ( t 0 ) = −2.761 year ( n = 250, p

This study establishes the bioenergetics budget of juvenile whitespotted bamboo shark Chiloscyllium plagiosum by estimating the standard metabolic rate (RS), measuring the effect of body size and temperature on the RS, and identifying the specific dynamic action (RSDA) magnitude and duration of that action in juvenile whitespotted bamboo sharks. The mean ±s.d. (RS) of six fish (500–620 g) measured in a circular closed respirometry system was 30·21 ± 5·68 mg O2 kg−1 h−1 at 18° C and 70·38 ± 14·81 mg O2 kg−1 h−1 at 28° C, respectively. There were no significant differences in RS between day and night at either 18 or 28° C (t-test, P > 0·05). The mean ±s.d. Q10 for 18–28° C was 2·32 ± 0·06 (n = 6). The amount of oxygen consumed per hour changed predictably with body mass (M; 295–750 g) following the relationship: (n = 40, r2= 0·92, P < 0·05). The mean magnitude of RSDA was 95·28 ± 17·55 mg O2 kg−1 h−1. The amount of gross ingested energy (EI) expended as RSDA ranged from 6·32 to 12·78% with a mean ±s.d. of 8·01 ± 0·03%. The duration of the RSDA effect was 122 h. The energy content of juvenile whitespotted bamboo shark, squid and faeces determined by bomb calorimeter were 19·51, 20·3 and 18·62 kJ g dry mass−1. A mean bioenergetic budget for juvenile whitespotted bamboo sharks fed with squid at 18° C was 100C = 29·5G + 31·9RS+ 28·2RSDA+ 6·7F + 2·1E + 1·6U, where C = consumption, G = growth, F = egestion, E = excretion and U = unaccounted energy.

Four juvenile whale sharks, Rhincodon typus were tagged using smart position and temperature transmitting (SPOT2) satellite tags (Wildlife Computers Ltd.) during 2002 and 2004. Transmissions from three males (4.0–4.5 m total length) were successfully received via the Argos satellite system. Two sharks tagged in April had similar routes after being released. They spent the most time in open sea suggesting that it is an important period in the life history of juvenile whale shark in the Northwestern Pacific. In addition, they generally occupied areas where the water temperatures were between 23 and 32 °C. Another shark tagged in November moved above the sea ridges in the first month after being released then migrated along the eastern and northern coastal waters of Taiwan during winter. This shark stayed in the Kuroshio Current region where the water temperature was between 25 and 29 °C, then moved to the edge of the China Coastal Current region where the temperature was low (14–21 °C) and remained there. In the last 15 days of the tracking, the shark shifted to the coastal waters of Taiwan where the temperature was between 17 and 24 °C. Three individuals dive deep into waters where the temperature was 6 °C. The average swimming speed was between 28.3 and 34.6 km/day. They could accelerate to 11–13 km/h for a very short time period. Their movement patterns appeared to be related to boundary currents, which may bring abundant prey, and sharks stayed in waters with higher plankton densities for a longer time. These results provide important information on migratory routes of whale sharks in the Northwestern Pacific, and can be used as a reference for the conservation and management on the world's largest fish.

The pelagic thresher shark, Alopias pelagicus , is a cosmopolitan species and abundant in Taiwan waters. Some of its biological information has been documented yet its population dynamics are poorly known. The purpose of this study is to assess the pelagic thresher shark stock status in the eastern Taiwan waters. The whole weights ( W ) of 51,748 individuals of the pelagic thresher shark landed at Nanfanao and Chengkung fish markets, eastern Taiwan from 1990 to 2004 were converted to precaudal length (PCL) based on the W –PCL relationship ( W = 2.25 × 10 −4 × PCL 2.533 , n = 2165). The sexes combined VBGE L t = 189.5 × (1 − e −0.10( t +6.47) ) was used to estimate the age for each length group. Total mortality rates ( Z ) obtained with length-converted catch curves ranged from 0.208 to 0.277 year −1 . Natural mortality rate ( M ) estimated from Hoenig method was 0.132 year −1 , and exploitation rate ( E ) ranged from 0.069 to 0.127 for 1990–2004. Annual abundance was estimated to range from 97,551 in 2000 to 153,331 in 2003 from virtual population analysis, and the highest fishing mortality occurred in ages 8–18 years. There were four different scenarios being simulated in this study. Scenario 1 indicated that spawning per recruit (SPR) ranged from 23.07% in 2001 to 47.71% in 1990 with a mean of 36.41% for the period of 1990–2004. The mean SPR of pelagic thresher for 1990–2004 was below the BRP of SPR = 35% in scenarios 2–4 suggesting that this stock was slightly overexploited. Therefore, to ensure sustainable utilization of this stock, reduction of fishing effort and close monitoring on A. pelagicus are needed.

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 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

The reproductive value and population status of the big eye in the north-eastern Taiwan waters was estimated by demographic analysis using available life-history parameters. Life-history tables were constructed using estimates of natural mortality (M) of 10.4920/year for age 0 and 0.3256/year for ages 1–9, with a maximum age of 9. Age-specific batch fecundity (Fe) was from Fe = 1391.34e0.1782FL. The age-specific proportion of maturity was estimated from the relationship between the proportion of female maturity (Pr) and fork length (FL): Pr = 1/(1 + e15.081−0.796FL). Females mature at age 3 and mature females reproduce every year. The population increase rate (λ) was estimated to be 20.5% per year and the generation time (G) was 6.25 years without exploitation. The net reproductive value (R0), generation time and intrinsic rate of natural increase (r) decreased with increased fishing mortality. For fixed fishing mortality, when F = 1.2/year and fishing started at age 3, R0 was estimated to be 1.0 and the population was considered to be in equilibrium. For age-specific fishing mortality, when fishing started at age 3, R0 was estimated to be 0.96/year, G being 6.18 years, and the population decreased 0.7% per year. The big eye population had a strong resilience as long as F = 1.2/year) started at age 2 or younger. Sensitivity analysis indicated that the mortality of age 0 is the most sensitive parameter in demographic analysis.

Yellowfin tuna (Thunnus albacares ) is an economically important species for longline and trolling fisheries in the waters off the southwestern coast of Taiwan, yet this species' movement patterns remain poorly understood. This study provides the first information on the movement and behaviour of adult yellowfin tuna using pop-up satellite archival tags in the waters off the southwestern coast of Taiwan. In total, 11 tuna (ranging from 116 to 135 cm in fork length) were tagged and released from 2011 to 2013. Seven fish were successfully tracked to provide information on depth and temperature preferences as well as horizontal movements. The majority of the vertical movements (30.3%) of yellowfin tuna occurred in the 50-m depth range in mixed layers. The mean swimming depth was 74.4 m (±50.7 m) during the daytime and 94 m (±72.5 m) at nighttime, which was a contrast to the findings in other waters. The maximum diving depth was 1000 m, where the water temperature was approximately 4 °C. This value was similar to the measurements made by a CTD near a depth of 1000 m, where the water temperature was approximately 4.2 °C and the O2 level was 3.0 mg l−1 . One of the tuna travelled 190 NM (straight distance) in 37 days, with most of its horizontal movements (70.6%) occurring at temperatures that ranged from 26 to 28 °C, suggesting that yellowfin tuna have a preference for this temperature range throughout the period of PAST observation.

Reproductive biology of the big eye, Priacanthus macracanthus, is described based on 601 specimens caught by otter trawl in north-eastern Taiwan waters and landed at Tahsi fishing port from December 1997 to November 1998. Four methods, macroscopic appearance of ovary, gonadosomatic index, oocyte diameter frequency distribution, and histological examination suggested that the spawning season of the big eye in north-eastern Taiwan waters is from April to July and peaks in May and June. Five stages of oocyte development were determined based on histological examination and ovarian development can be divided as undeveloped, developing, matured, and spent stages. Mean fecundity (± SD) was estimated to be 131 112 ± 33 379. Size at first maturity estimated from the Logistic model was 18.9 cm FL corresponding to a 3-year-old specimen.

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 Pauly's 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.

Reproductive aspects ofAlopias superciliosus in the northwestern Pacific were described in detail, on the basis of 629 specimens (429 females and 200 males) collected from January 1984 to October 1984 and from October 1992 to March 1994.Alopias superciliosus embryos are oophagous. Six developmental stages (3 encapsulative and 3 posthatching) based on embryonic morphology and source of nutrition were recognized. The species bears 2 embryos per litter, their size at birth being between 135 and 140 cm TL. The sex ratio of embryos was 1∶1. Total length of females at maturity was 332–341. 1. cm; of males 270.1–287.6 cm. The gestation period could not be determined because most adult females were pregnant throughout the year. The typical reproductive strategy ofA. superciliosus is the production of a few large embryos per litter, with no fixed mating or birthing season.

Catch-per-unit-effort (CPUE) data for lake whitefish Coregonus clupeaformis in Michigan waters of Lake Huron were examined with time analysis to test if they can describe the abundance of lake whitefish. Relations between lake whitefish CPUE and environmental and biological data were investigated with cross-correlation analysis. A 4-year time lag, corresponding to the age at maturity, was found for lake whitefish CPUE. Cross-correlation analysis indicated that lake whitefish CPUE was negatively correlated with monthly air temperatures and abundance of sea lamprey Petromyzon marinus in previous years, and CPUE was positively correlated with fishing effort 1 year later. The results indicated that fishermen track lake whitefish abundance and that CPUE can describe fluctuations of the lake whitefish population.