Aspects of the reproductive biology of two pelagic sharks in the eastern Atlantic Ocean.

This study used data provided by the Chinese Longline Fishery Scientific Observer Programme from the tropical eastern Atlantic Ocean to estimate the reproductive parameters of the blue shark (Prionace glauca) and crocodile shark (Pseudocarcharias kamoharai). Sizes ranged from 80 to 298 cm fork length (FL) for blue sharks and from 48 to 99 cm FL for crocodile sharks. Sexual segregation was observed during different months for both sharks. The sex ratio for blue sharks was 1.38 F:1 M, and 1 F:2.79 M for crocodile sharks. The size of adult blue sharks ranged from 144 to 280 cm for males and from 174 to 298 cm for females; and that of crocodile sharks from 63 to 97 cm for males and 78-99 cm for females. The size at 50% of maturity for blue sharks was estimated at 191.7 cm FL for females and 197.5 cm FL for males, and that of crocodile sharks was assessed at 84.9 cm FL for females and 78.5 cm FL for males. Most sexually matured females were pregnant; their means were 207.2 ± 16.4 cm FL for blue sharks and 89.4 ± 4.3 cm FL for crocodile sharks. Mature sizes for both species were significantly different among months. Embryonic sizes also varied widely among months for crocodile sharks, but a slight change was recorded for those of blue sharks. The observed mean size at birth and litter size were 34.5 cm FL and 37 ± 12 for the blue sharks, and that of the crocodile sharks, 39.5 cm FL and a dominant four embryos in the uterus. Due to the observed increasing catch trend of blue sharks and the slow reproductive cycle of crocodile sharks, this study presents the need of implementing conservation measures to ensure the sustainability of both species in their habitat.

How Well Do 'Catch-Only' Assessment Models Capture Catch Time Series Start Years and Default Life History Prior Values? A Preliminary Stock Assessment of the South Atlantic Ocean Blue Shark Using a Catch-Based Model.

CMSY++, an improved version of the CMSY approach developed from Catch-MSY which uses a Bayesian implementation of a modified Schaefer model and can predict stock status and exploitation, was used in the present study. Evaluating relative performance is vital in situations when dealing with fisheries with different catch time series start years and biological prior information. To identify the influences of data inputs on CMSY++ outputs, this paper evaluated the use of a nominal reported catch and a reconstructed catch dataset of the South Atlantic blue shark alongside different priors of the blue shark's productivity/resilience (r) coupled with different indices of abundance. Results from the present study showed that different catch time series start years did not have a significant influence on the estimation of the biomass and fishing reference points reported by CMSY++. However, uninformative priors of r affected the output results of the model. The developed model runs with varying and joint abundance indices showed conflicting results, as classification rates in the final year changed with respect to the type of index used. However, the model runs indicated that South Atlantic blue shark stock could be overfished (B2020/Bmsy = 0.623 to 1.15) and that overfishing could be occurring (F2020/Fmsy = 0.818 to 1.78). This result is consistent with the results from a previous assessment using a state-space surplus production model applied for the same stock in 2015. Though some potential could be observed when using CMSY++, the results from this model ought to be taken with caution. Additionally, the continuous development of prior information useful for this model would help strengthen its performance.

Size distribution patterns of silky shark Carcharhinus falciformis shaped by environmental factors in the Pacific Ocean.

Commercial fisheries, especially pelagic longline fisheries targeting tuna and/or swordfish, often land silky sharks (Carcharhinus falciformis), which are currently listed as vulnerable by the International Union for Conservation of Nature (IUCN). Due to increasing fishing effort and the fact that they overlap in habitat with target species, the population trend of silky sharks is declining worldwide. Understanding their relationships with environmental variables that lead to their capture by fisheries is critical for their management and conservation. Nevertheless, little is known about their size distribution in relation to environmental variables in the Pacific Ocean. Using data from the Chinese Observer Tuna Longline fishery from 2010 to 2020, this study developed a species distribution model (SDM) to analyze the relationships between silky shark size distribution patterns and environmental variables and spatio-temporal variability at fishing locations. Observed sizes ranged from 36 to 269 cm fork length (FL). The final model suggests that sea surface temperature (SST), primary production (photosynthetically available radiation, PAR), and ocean surface winds were the key environmental variables shaping size distribution patterns of silky sharks in the Pacific. A high proportion of larger silky sharks has been predicted in areas associated with productive upwelling systems. In addition, the model predicted that larger specimens (>140 cm FL) occur near the equator, and smaller specimens farther from the equator but still in tropical regions. Two regions in the eastern Pacific (the coastal upwelling area off northern Peru and the waters around the Galapagos Islands) seem to be important locations for larger specimens. The size distribution patterns of silky sharks in relation to environmental variables presented in this study illustrate how this species segregates spatially and temporally and presents potential habitat preference areas. The information obtained in the present study is critical in the quest for management and conservation of menaced species such as the silky shark.

[Heterogeneity of growth and maturity of Larimichthys polyactis in the offshore waters of southern Zhejiang, China]. / 浙江南部近海小黄鱼生长和性成熟特征的异质性.

The variations of life history traits have been observed for many fish species, which gains much concerns in the study of aquatic biology and ecology. In this study, the biological characteristics were explored for yellow croaker (Larimichthys polyactis) in the offshore waters of southern Zhejiang, based on 4920 individuals collected from 13 fishery-independent seasonal surveys from autumn 2015 to autumn 2018. Linear mixed effects models were used to estimate the growth, maturity characteristics, and their heterogeneity. The body length of yellow croaker samples ranged from 13 to 215 mm with the dominant body of 110 to 154 mm. The body weight ranged from 0.5 to 182.2 g, with the dominant body weight from 20 to 55 g. The results showed that the linear mixed effects models with random effects from season, gender, and year performed best for length-weight relationship, with the lowest AIC and RMSE values. The effects of season were much larger than those of genders and years. When the length exceeded 160 mm, the weight gain rate of yellow croaker was faster in spring and summer, lower in autumn and winter, while the male individuals gained more weight than the females with the same body length. Among 4841 individuals of specimens with gonadal data, the individuals at maturity Ⅱ stage occupied 50.4%, and the individuals at maturity stage contributed to 19.6%. The results from the best linear mixed effects model showed that season had the most significant influence on the maturity of yellow croaker. The 50% maturity length (L50%) was much lower in winter (124.6 mm) with no much difference between other seasons, indicating that yellow croaker matures earlier in winter. Our results indicated that linear mixed effect model could reflect the biological heterogeneity of yellow croaker conveniently and that the growth and maturity of yellow croaker had significantly sexual and temporal variations, which should be considered in the stock assessment and fishery management for yellow croaker.

Modeling and comparison of count data containing zero values: a case study of Setipinna taty in the south inshore of Zhejiang, China.

To effectively use the fishery count data containing zero values, Setipinna taty in the coastal waters of south inshore of Zhejiang in China from 2017 to 2019 was used in this study. Environmental factors, such as water temperature, water depth, and salinity, were selected to establish models and compare based on the generalized additive model (GAM) of the Tweedie distribution (Tweedie-GAM) and two-stage GAM, Ad hoc method, and generalized additive mixed model (GAMM). The results showed that each station accounted for a higher proportion of zero values and the two-stage GAM model had a higher deviation interpretation rate, and GAM I and GAM II had 19.6% and 60.4% deviation interpretation rates. The cross-validation results showed that the performance evaluation of the two-stage GAM model was the best and showed the highest R2 value, the lowest average absolute error, and the relatively small root mean square error. This study found that the abundance of S. taty in the south inshore of Zhejiang was highest at around 21°C and 18°C in spring and autumn, and the abundance reached the highest at a water depth of about 20 m. In spatial distribution, the high value of the abundance of S. taty was mostly distributed in the coastal waters in the south of 28°N. In future research, models should be fitted and compared for different sampling zero-value ratios, and more environmental factors should be included to accurately find an optimal model and provide references for the conservation of fishery resources.

An evaluation of observer monitoring program designs for Chinese tuna longline fisheries in the Pacific Ocean using computer simulations.

This paper evaluates the performance of different observer coverage rates and 9 possible sampling designs to estimate via computer simulation the total catch of target and non-target species for Chinese tuna longline fisheries in the Pacific Ocean. The stratified random samplings include different stratification schemes (based on target species or fishing areas) with different strategies for allocating observers. The observer data from 103 vessels between 2010 and 2019 were assumed to be the "true" sampling population. We concluded that the accuracy of catch estimates had a significant positive relationship with species detectability and observer coverage rate. On average, the accuracy improved by 50% when the coverage rate increases from 5 to 20%. Current simple random sampling in Chinese tuna longline fisheries is less efficient for monitoring many species. Stratified sampling designs based on the target species tended to yield the most accurate estimates of the total catch. Allocating the observers based on the scale of the fleets in different stratum seemed to be less efficient. The proportion of observers between different fleets should be adjusted according to different monitoring objectives. In general, a large proportion of observers are recommended to be allocated onboard vessels targeting bigeye tuna (Thunnus obesus). This study has the potential to have a significant contribution to future designs of the observer monitoring programs in Chinese tuna longline fishery and many other fisheries.

Seasonal changes in fish diversity, density, biomass, and assemblage alongside environmental variables in the Yangtze River Estuary.

The present study used multivariate techniques, to analyze the fish species diversity and distribution patterns in order to determine the possible role of environmental parameters as drivers of fish community structure and composition in the Yangtze River Estuary (YRE). This analysis was conducted using data obtained in the YRE from February 2012 to December 2014. Analysis of the catch data showed that species composition, total density, and total biomass varied significantly between stations and seasons. Thirty-eight species belonging to 18 families were collected. Sciaenidae was the most dominant family accounting for 40.8% of total captured specimens. In descending order, Collichthys lucidus, Cynoglossus gracilis, Chaeturichthys stigmatias, and Lophiogobius ocellicauda dominated catches in the YRE. These four species constituted 64.2% of the total catches and showed average dissimilarities of 74.19% between stations and 81.3% between months. The highest number of fish specimens captured was recorded in August 2012 while the highest species richness was observed in December 2013. The mean fish density and biomass for the YRE was 0.35 individuals/m2 and 2.5 g/m2, respectively. The mean density and biomass for the most important and dominant species changed significantly between stations and seasons. Canonical correspondence analysis indicated that salinity and chlorophyll-a were the key variables that structured the fish assemblage in the YRE. High total species density and biomass were recorded in high saline stations (North Branch) of the YRE. This study confirms that most species captured in the YRE needs estuarine conditions to complete their growth and development. Hence, the findings in this study are important to understanding and developing suitable conservation plans for the management of fish resources in the YRE.

[Niches and interspecific association of dominant shrimp species in the offshore waters of southern Zhejiang Province, China]. / 浙江南部近海主要虾类的时空生态位及种间联结性.

Based on data from November of 2015 (autumn), February (winter), May (spring), and August (summer) of 2016 in the offshore waters of southern Zhejiang Province, the relationships between major shrimps species were examined by niche breadth, niche overlap, variance ratio, chi-square test, association coefficient and species pair co-occurrence percentage. The results showed that temporal niche breadth of Atypopenaeus stenodactylu was the largest, spatial niche breadth of Solenocera crassicornis was the largest, and A. stenodactylu had the largest spatio-temporal niche breadth. The temporal niche overlap between Parapenaeus fissuroides and Parapenaeopsis tenella was the highest. The spatial niche overlap between Solenocera koelbeli and Penaeus chinensis, P. fissuroides and Heterocarpoides laevicarina were the highest. The spatio-temporal niche overlap between S. koelbeli and P. chinensis was the highest. The analysis of variance ratio showed that the main shrimp species were significantly positively correlated. Positive correlation existed in 13 pairs (χ2≥3.841). Results from the association coefficient (AC) and co-occurrence percentage (PC) indicated that the interspecific association tended to be positive. Our results provide supports for exploring niche breadth and niche overlap of major shrimp species and improving niche differentiation.

Evaluation of management procedures for a length-frequency data-limited fishery.

Management procedures (MPs) based on data-limited methods (DLMs) recently developed to give management advices for data-limited stocks worldwide are scarce or yet to be implemented on freshwater species. In this study, case studies (CSs) were developed using length-frequency data (LFD) of common carp species harvested from Dianshan Lake to estimate life-history parameters from existing methods. These CSs were later used to examine their influences when tested with various MPs under scenarios when operating models (OMs) were subjected to observation and estimation uncertainties. The results after management strategy evaluation (MSE) was run for various defined OMs showed that three MPs emerged best for providing managing advice. For high yield to be maintained during short-term periods, MinlenLopt1 suggested the smallest length at full retention (sLFR) to be 42.11 cm; while Slotlim and matlenlim2 suggested that to maintain biomass and stable spawning biomass (SBMSY) and also avoid overfishing from occurring in this fishery, sLFR should be 56.1 cm. Values given by these MPs allowed the removal of species that spawned at least once. Also, life-history parameters derived from CS4 presented the best results, being more reliable in presenting better inputs for effective management of the said fishery.

[Comparison of generalized additive model and boosted regression tree in predicting fish community diversity in the Yangtze River Estuary, China]. / GAM模型和BRTæ¨¡åž‹åœ¨é•¿æ±Ÿå£é±¼ç±»ç¾¤è½å¤šæ ·æ€§é¢„æµ‹ä¸­çš„æ¯”è¾ƒ.

Yangtze River Estuary is the biggest estuarine ecosystem in the western Pacific Ocean. Evaluating fish community in this ecosystem can provide scientific basis for its restoration and mana-gement. Generalized additive model (GAM) and boosted regression tree (BRT) were built to examine the relationship between fish community diversity and environmental and spatio-temporal variables based on data collected during 2012-2014. Combined with linear regression analysis, a cross validation was used to evaluate the fitness and predictive performance of both models. We plotted the spatial distribution of fish community diversity and richness in each station of the Yangtze River Estuary in 2014. The results showed that salinity, pH and chlorophyll-a had the most contribution on diversity, while pH, dissolved oxygen and chlorophyll-a were the most contributive variables on richness. BRT models showed better fitness and lower prediction error than GAM models. In contrast to GAM models, BRT models could distinguish the fish community index in each station area with respect to the spatial prediction. The diversity index in external water was obviously greater than that in internal water. Meanwhile, the station at higher latitude had a higher diversity index in both external and internal water.

Complete mitochondrial genome of Toxabramis swinhonis (Cypriniformes, Cyprinidae).

Toxabramis swinhonis is a one of the main bycatch species in China's freshwater fishery and an important food resource for the larger fishes in the main rivers and lakes in China. For better understanding the biology of this species, the complete mitochondrial genome of Toxabramis swinhonis was determined and analyzed in this study. The complete mitogenome of T. swinhonis is 16 622 bp in length, which contains 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes and 2 non-coding regions: origin of light-strand replication (OL) and control region (D-loop). The determination of T. swinhonis mitogenome would play an important role in genetic diversity and evolution for Cyprinidae.

Genetic differentiation in blue shark, Prionace glauca, from the central Pacific Ocean, as inferred by mitochondrial cytochrome b region.

Six hundred and ninety-seven base pairs of cytochrome b gene of mtDNA was sequenced and analyzed for 78 blue shark Prionace glauca individuals from three sampled locations in the central Pacific Ocean (CPO). In total, three polymorphic sites were detected which defined four haplotypes. The haplotype diversity (h) ranged from 0.517 to 0.768, and nucleotide diversity (π) was between 0.0007 and 0.0011. Analysis of molecular variance indicated a non-significant differentiation among subpopulations. Furthermore, pairwise FST score analysis revealed a non-significant differentiation among three sampled regions. Generally, low genetic differences were found between different geographic locations in the CPO. This study suggests a single panmictic population of P. glauca in the CPO.

Complete mitochondrial genome of Hemiculter bleekeri bleekeri.

Hemiculter bleekeri bleekeri is a typical freshwater species that are mainly distributed in the river basins in China. The biological information of this species is very limited. In this study, we determined the complete mitogenome sequence of H. bleekeri bleekeri. The complete mitogenome of H. bleekeri bleekeri is 16 6173 bp in length, which contains 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes and 2 non-coding region, a rep region (33 bp) and a control region (D-loop). This work provides new information which is helpful for comprehending the molecular systematic, taxonomic status and evolutionary biology of this species.

Phylogeny analysis of complete mitochondrial DNA sequences for pelagic fishes from tuna fishery.

Pelagic fishes captured in the international tuna fisheries have attracted increasing attention in recent years because of declines in their populations. In this study, 58 complete mitochondrial genomes of pelagic species from the classes Teleostean and Chondrichthyans were analyzed. The length of the 58 mtDNA sequences ranged from 15,598 to 18,880 bp, and all of which contained 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 1 control region. Our results suggested that mitochondrial genomes could be a powerful marker for resolving the phylogeny of pelagic fishes. Phylogenetic relationships based on the complete mitochondrial among 58 species indicated that Teleostean and Chondrichthyans are well separated. However, the control region length of Mobula japonicais was much larger than the other species in this study. Additionally, the Prionace glauca was divided into the clade in the genus Carcharhinus which provided a prospective taxonomic status of P.glauca.

Characterization of the complete mitochondrial genome of Sickle pomfret Taractichthys steindachneri (Perciformes: Bramidae).

The complete mitogenome sequence of Taractichthys steindachneri was sequenced and analyzed in this study. The complete mitogenome of T. steindachneri is 16 723 bp in length, which contains 22 transfer RNAs, 2 ribosomal RNAs, 13 protein-coding genes and 2 non-coding region, a rep region and a control region (D-loop). This study will be useful for studying on the molecular systematic, taxonomic status and conservation genetics.

Complete mitochondrial genome of the Taractes rubescens (Perciformes: Bramidae).

Taractes rubescens is a high vulnerable species which widely distributes in tropical and subtropical water in Pacific and Atlantic Ocean. The complete mitogenome sequence of T. rubescens was determined in this study. The complete mitogenome of T. rubescensis 16 720 bp in length, which contains 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs and a control region (D-loop). Furthermore, base composition of A, C, G and T is estimated to be 27.6%, 30.9%, 15.8% and 25.7%, respectively. The complete mtDNA sequence of T. rubescens provides a useful data for studying on the molecular systematic, stock assessment and conservation genetics.

[Demographic analysis of the blue shark, Prionace glauca, in the North Atlantic Ocean].

The blue shark, Prionace glauca, is the main by-catch species in tuna longline fishery. As one of top species in the oceanic food webs, the blue shark plays an important role in the marine ecosystem. Traditional stock assessment methods are difficult to accurately evaluate the population dynamic for this shark because of limited data. Based on life-history parameters of the blue shark in the North Atlantic, demographic analysis was employed to estimate the demographic parameters and evaluate the potential exploitation for the blue shark. Moreover, we discussed the relationship between age at first capture and critical value of fishing mortality corresponding to the value of intrinsic rate of natural increase 0. The results showed that the survival rate (S) of blue shark from 0.719 to 0.820, intrinsic rate of natural increase (r0) from 0.250 to 0.381, time of population doubling (tx2) from 1.819 to 2.773 years, reproduction rate per generation (R0) from 6.600 to 22.255, and generation time (G) from 8.498 to 10.162 years. The sensitivity analysis for the life history parameters revealed that the uncertainties of natural mortality existed in the first age class, age at maturity and maximum age had slight influence on the demographic parameters. Fishing mortality (Fc) increased with the age at first capture. When the age at first capture (tc) was more than five, there was no obvious relationship between Fc and tc.

Complete mitochondrial genome of the crocodile shark Pseudocarcharias kamoharai (Lamniformes: Pseudocarchariidae).

In this study, we determined the complete mitogenome sequence of Pseudocarcharias kamoharai. The complete mitogenome of P. kamoharai is 16,694 bp in length, which contains 13 protein-coding genes, 22 transfer RNAs, 2 ribosomal RNAs and 2 non-coding regions: control region (D-loop) and origin of light-strand replication (OL). Overall, base composition of mitogenome is estimated to be 32.06% for A, 23.63% for C, 13.21% for G and 31.10% for T. The complete mtDNA sequence of P. kamoharai provides a useful data for the studies on the molecular systematic phylogeography and population genetics.

[Estimation of biological parameters and yield per recruitment for Coilia nasustaihuensis in Dianshan Lake, Shanghai, China].

Coilia nasustaihuensis is the most abundant species in Dianshan Lake and plays an important role in the lake ecosystem. From July 2010 to August 2011, a total of 3107 samples of C. nasustaihuensis were collected from Dianshan Lake. Based on length data of these samples, ELEFAN I technique was employed to estimate growth and mortality parameters, and the Beverton-Holt dynamic model was used to evaluate the population dynamics trend for C. nasustaihuensis. Growth of this species was described using avon Bertalanffy model, and the estimated parameters were Linfinity = 35.70 cm, k = 0.54, and t0 = -0.48 a. The turning point for body mass growth curve of the stock was situated at t = 1.37 a. Natural mortality coefficient M was then estimated using Pauly's empirical equation and found to be 0. 872. Length-converted catch curves were used to estimate the total mortality coefficient Z, which was found to be 2.121. Accordingly, the fishing mortality coefficient (F) was equal to 1.249, and the current exploitation rate was 0. 589, suggesting the stock was over-exploited. According to the Beverton-Holt dynamic model, the minimum capture size for C. nasustaihuensis should be 21.42 cm (age 1.22 years).