Chien-Chung Hsu

Reproductive biology of female Pacific bluefin tuna Thunnus orientalis from south-western North Pacific Ocean

Pacific bluefin is a highly valuable pelagic species that inhabits a broad range in the North Pacific Ocean. The reproductive biology, especially for the spawning aggregation in the south-western North Pacific Ocean, is not well understood. Thus, a total of 119 paired ovary specimens were collected from the Taiwanese longline fleet during the 1999 fishing season (late April through June) to gain a better understanding of important reproductivity-related stock parameters associated with this species. The following conclusions were made: (i) condition factor decreased from late May to early June; (ii) the sex ratio might be 1∶1 for spawners; (iii) the gonadosomatic index stayed at a relatively high level and markedly increased from late May to early June; (iv) histological examination of oocytes indicated that all specimens were sexually mature; (v) spawning activity appeared to start in May and peak in late May to early June; (vi) batch fecundity incre ased with fork length; and (vii) preliminary estimates of spawning frequency between batches ranged 2–4.5 days based on analysis of postovulatory follicles.

POPULATION BIOLOGY OF THE SWIMMING CRAB PORTUNUS SANGUINOLENTUS IN THE WATERS OFF NORTHERN TAIWAN

Abstract The growth, mortality, and reproduction of Portunus sanguinolentus were studied using size-frequency data obtained from crabs collected in pots in the waters off northern Taiwan from October 2000 to March 2001, and October 2001 to January 2002. The Bhattacharyas method and seasonal von Bertalanffy growth curve were used to estimate growth parameters. The growth curve for males was Lt = 204.75×{1 −e–[0.87t + 0.4(0.87/2 )sin2 (t)]} and the curve for females was Lt = 194.25×{1 −e–[0.97t + 0.4(0.97/2 )sin2 (t)]}. A size-converted catch curve was used to estimate the instantaneous total mortality rate (Z), and Paulys empirical equation was used to estimate the instantaneous natural mortality rate (M). For males, Z = 3.16/year and M = 1.65/year. For females, Z = 3.37/year and M = 1.8/year. The instantaneous fishing mortality rate (F) was 1.51/year and 1.57/year, and the exploitation rate (E) was 0.48 and 0.47 for males and females, respectively. The exponential relationships were presented for relationships of fecundity in number and weight of egg mass in terms of carapace width and body weight. Those relationships were statistically significant (P < 0.01), indicating that the fecundity increased with the size from 4.05 × 105 to 2.44 × 106 eggs.

The length-weight relationship of Albacore, Thunnus alalunga, from the Indian Ocean

Abstract To comply with the compilation of catch databases of Taiwanese gillnet fishery and stock assessment, a new length–weight relationship of albacore, Thunnus alalunga , from the Indian Ocean was determined using data from gillnet catches. Four different fitting algorithms were used. The four resultant formulae were not significantly different. However, the formula W =0.056907 FL 2.7514 , where W is the body weight in g and FL is the fork length in cm, estimated by least square of residuals excluding suspected outliers which were diagnosed by least median square of residuals, is considered as an acceptable and useful one. Consequently, the equation can be used to compile catch databases mainly from the surface gears and for other assessment purposes.

Total and organic mercury concentrations in the muscles of Pacific albacore (Thunnus alalunga) and bigeye tuna (Thunnus obesus).

Muscles of 115 North Pacific albacore (ALB, Thunnus alalunga) and 75 Pacific bigeye tuna (BET, Thunnus obesus), collected from 2001 to 2006, were analyzed. No ALB, but 13 large BET had organic mercury (OH g) concentrations exceeding 1 μg g(-1) wet weight. For both ALB and BET, total mercury (THg) and OH g concentrations were significantly and positively correlated with fork length (FL) and body weight. The muscle Hg bioaccumulation rates of BET were higher than those of ALB, particularly in the adult fish. Moreover, the lines had crossover points among the two species that imply the young BET (FL<110 cm) contains lower muscle Hg concentrations than ALB of the same size. The suggested weekly dietary intake of ALB and small-BET meats is 340 g, and of BET meat it is 150 g for a 60-kg person based on the provisional tolerable weekly intake (PTWI) of methylmercury set by the WHO.

Organic and total mercury levels in bigeye tuna, Thunnus obesus, harvested by Taiwanese fishing vessels in the Atlantic and Indian Oceans.

Muscle samples of 121 and 110 bigeye tuna (Thunnus obesus) caught by Taiwanese long-line fishing vessels in the Atlantic and Indian Oceans, respectively, were used to analyze total mercury (THg) and organic mercury (OHg) content. The overall THg and OHg concentrations were 0.786 ± 0.386 (0.214–3.133) and 0.595 ± 0.238 (0.143–2.222) mg kg−1 wet weight, respectively, similar to the results of previous studies. Our findings, however, reflected the highest THg and OHg concentrations for the species in each ocean among the published data. Mean THg and OHg concentrations in Atlantic tuna were significantly (p < 0.05) higher than those in Indian tuna. Two of 121 samples of tuna from the Atlantic Ocean, but no samples from the Indian Ocean, had levels of OHg above 2 mg kg−1 wet weight set by the Department of Health Taiwan, and 13 of 121 samples of tuna from the Atlantic Ocean and three of 110 samples from the Indian Ocean had levels of OHg above 1 mg kg−1 wet weight set by US FDA and WHO. Accordingly, for adult Taiwanese men and women with average body weight of 65 and 55 kg, respectively, the maximum allowable weekly intake of bigeye tuna is suggested to be 170 and 145 g, respectively.

Abundance index for longline fishery targeting spawning Pacific bluefin tuna Thunnus orientalis in south-western North Pacific Ocean

Pacific bluefin tuna Thunnus orientalis is a highly migratory species, distributing throughout the Pacific Ocean. This species is among the quality tunas of high economic value and has been historically exploited mainly by Japanese, US, Mexican and Taiwanese fleets. Approximately 10% of catches were made by the Taiwanese fleet after 1999; particularly, the individuals caught were all giant spawners. Taiwanese small-scale longliners (vessels < 100 t) target the stock in the southwestern North Pacific from late April through June. Because of the significant catch of spawners, any assessment of this stock should include data from the Taiwanese fleet. Many reports have been issued to describe the stock status of the Pacific bluefin tuna during the past two decades; however, other than biological studies, therehavebeen fewstockassessmentswith the abundance index derived from Japanese fleets and purse seiners in the eastern Pacific Ocean. Because this species is exposed tomultiplefisheries overmost fishing grounds, historical statistics from different fishing parties is essential. To assess and propose management measures for the Pacific bluefin tuna, collection of catch and effort data as well as development of a reliable abundance index to represent the spawning stock are urged for the Taiwanese fishery. Therefore, the objective of this study was to model a time-series catch per unit effort (CPUE) that can be used as an index of abundance for the Taiwanese fishery from 1999 to 2004. Daily catch data from auction records and time records of vessels in and out, which can trace the fishing effort of each vessel, were collected and compiled at Tungkang port, where most bluefin tuna are landed. Two criteria were used in screening the daily record. First, catch with matching effort information for a vessel was screened. Second, the time difference between date of auction and date of disembarking fromport was no more than three days to obtain quality fishmeat for vessels without freezers. According to interviews with captains of small-scale longline vessels, approximately 1200–1600 hooks per day can be deployed regardless of vessel size. Large vessels can store more fish than small vessels and may stay at sea longer. Fishing effort was then converted from fishing days to number of hooks operated with an assumed average of 1400 hooks lifted daily. The estimated fishing days were decreased by two days because the vessel took approximately one day to travel from Tungkang port to the fishing ground and vice versa. Catch and effort information were summarized as CPUE. Based on the assumption that catch is proportional to the product of fishing effort and density, the ability to use CPUE as an index of abundance depends on being able to remove the influences of factors that change fishing efficiency among vessels and cause differences between trips for the same vessel other than abundance. A generalized linear model (GLM) was applied to remove the influential factors and, in the present analysis, the available factors for each vessel trip compiled in the catch and effort data include year (1999–2004), month (May and June) and size of *Corresponding author: Tel: 886-2-2362-2987. Fax: 886-2-2366-1198. Email: d91241003@ntu.edu.tw Received 27 December 2006. Accepted 16 October 2007. FISHERIES SCIENCE 2008; 74: 1336–1338

Management implication on Indian Ocean albacore from simple yield analysis incorporating parameter uncertainty

Abstract Many studies have been conducted to estimate the parameters of Indian Ocean albacore ( Thunnus alalunga ) fishery. Various estimates on the same parameter from these studies have resulted in uncertainty and confusion when management strategies are made. This study incorporates these estimates in the simple yield-per-recruit model through Monte Carlo simulations to derive management implication under parameter uncertainty. The results provided an optimal management suggestion under the following conditions. First, the probability of obtaining feasible simulation results was greater than 95%; second, the probability of increase to yield-per-recruit after regulatory change was also greater than 95%. Under these conditions, the results suggested if the goal of management was to increase the relative yield-per-recruit of the Indian Ocean albacore stock by 30% and more, the relative selection size should be changed by +0.15 to +0.25 and the exploitation rate by −0.5 to +0.15.

Sex-Variant Morphometrics of the Swimming Crab,Portunus Sanguinolentus(Herbst),from the Waters off Northern Taiwan

In April 1998 and May 1999,two survey cruises were carried out in seven coral reefwaters(Meiji,Dongmen,Chigua,Yongshu,Nanxun,Zhubi and Huayang Reef)by handline,Iongline and gillnet fishing.180 species of fishes were caught in these reef waters,93% ofwhich were reef fish species,10 of which were common species occurring in at least 5reef waters,and species similarity coefficients between various two reefs were less than30%.Thus,high diversity and low species similarity are two main characteristics of fishfauna of the seven reefs.Compared with Fanning Island(1972-1973)& Taiaro Atoll(1994)in the Pacific Ocean,and Reunion Island(1989-1990)in the Indian Ocean,species similarity coefficients are 11%,8.2% and 8.5%,respectively;Compared with south-western continental shelf waters of the Nansha Islands,northern continental shelf waters of South Chinasea and Beibu Bay,species similarity coefficients are 2.6%,3.8% and 3.5%,respectively.

Fishing‐induced changes in adult length are mediated by skipped‐spawning

Elucidating fishing effects on fish population dynamics is a critical step toward sustainable fisheries management. Despite previous studies that have suggested age or size truncation in exploited fish populations, other aspects of fishing effects on population demography, e.g., via altering life histories and density, have received less attention. Here, we investigated the fishing effects altering adult demography via shifting reproductive trade-offs in the iconic, overexploited, Pacific bluefin tuna Thunnus orientalis. We found that, contrary to our expectation, mean lengths of catch increased over time in longline fisheries. On the other hand, mean catch lengths for purse seine fisheries did not show such increasing trends. We hypothesized that the size-dependent energetic cost of the spawning migration and elevated fishing mortality on the spawning grounds potentially drive size-dependent skipped spawning for adult tuna, mediating the observed changes in the catch lengths. Using eco-genetic individual-based modeling, we demonstrated that fishing-induced evolution of skipped spawning and size truncation interacted to shape the observed temporal changes in mean catch lengths for tuna. Skipped spawning of the small adults led to increased mean catch lengths for the longline fisheries, while truncation of small adults by the purse seines could offset such a pattern. Our results highlight the eco-evolutionary dynamics of fishing effects on population demography and caution against using demographic traits as a basis for fisheries management of the Pacific bluefin tuna as well as other migratory species.

Arsenic and five metal concentrations in the muscle tissue of bigeye tuna (Thunnus obesus) in the Atlantic and Indian Oceans

White muscle concentrations of As, Cd, Cu, Fe, Se, and Zn were investigated in Atlantic- and Indian-bigeye tuna (BET) (Thunnus obesus) from 6 regions. As and Cd muscle concentrations were significantly higher in the Indian-BET than in the Atlantic-BET, whereas the Indian-BET caught in the waters off South Africa revealed the highest As, Se, and Zn muscle concentrations. Accordingly, multidimensional scaling separated them into two oceanic groups. Positive linear relationships between muscle Cd concentration and fork length (FL) were established in both oceans. For the other elements, only muscle-Fe and FL relationship was found in the Atlantic-BET. 10.3% of BET > 145 cm FL from both oceans possessed muscle Cd concentrations exceeding the food safety limit (0.1 μg g-1 wet weight) set by the European Commission. Increased Cd, Cu and Zn pollution was found in the Atlantic Ocean compared with previous data, with higher levels found in the Indian Ocean.