Electronic Length Frequency Analysis Research Articles

Population dynamics of the data-poor tiger shark (Galeocerdo cuvier) in the Northwest Pacific Ocean: Measurement of growth parameters and mortality rates

Although tiger sharks (Galeocerdo cuvier) are found globally in major oceans, comprehensive biological and fishery data pertaining to the Northwest Pacific Ocean are scarce. Accordingly, this study was conducted to understand the challenges in measuring tiger sharks’key life history parameters, including von Bertalanffy growth and mortality rates, which are essential for the construction of robust stock assessment models. To evaluate these parameters, we used the TropFishR software package to analyse observer-recorded length-frequency data acquired from the Nanfangao fish market between January 2015 and December 2022. An electronic length-frequency analysis indicated that the asymptotic length and growth coefficient derived for the combined sexes of the tiger shark population were 366.087 FL cm and 0.245 year−1, respectively. Mortality rates were calculated using a length-converted catch curve and empirical models; the results revealed that the annual rates of total (Z), natural (M), and fishing (F) mortalities were 0.346, 0.168, and 0.178 year−1, respectively. Notably, the observed exploitation rate (E) was slightly high at 0.514 year−1. Our findings may facilitate the development of effective strategies for preserving the tiger shark population in the study region by leveraging this initial information for further stock assessment analyses, thereby enabling a more comprehensive evaluation in the future.

Stock Assessment of the Commercial Small Pelagic Fishes in the Beibu Gulf, the South China Sea, 2006-2020.

Long-term variations in population structure, growth, mortality, exploitation rate, and recruitment pattern of two major commercial small pelagic fishes (CSPFs) (Decapterus maruadsi and Trachurus japonicus) are reported based on bottom trawl survey data collected during 2006-2020 in the Beibu Gulf, South China Sea. All individuals collected during each sampling quarter over a period of 15 years were subjected to laboratory-based analysis. In this study, the stock of D. maruadsi and T. japonicus inhabiting the Beibu Gulf was assessed using length-based methods (bootstrapped electronic length frequency analysis (ELEFAN)) to complete stock assessment in different fishery management periods (the division of fisheries management periods was based on China's input and output in the South China Sea offshore fisheries over 15 years, specifically divided into period I (2006-2010), period II (2011-2015), and period III (2016-2020)). The results showed that the mean body length, dominant body size, and estimated asymptotic length of two CSPFs decreased, whereas their growth coefficient decreased, indicating miniaturization and slower growth, respectively. Estimated exploitation rates and catching body length for two CSPFs indicated that both stocks in the Beibu Gulf were overexploited in period I and moderately exploited after 2011. These stocks were taking a good turn in status in period III, with the exploitation rate much lower than the initial period and reversing the downward trend in catching body length. Furthermore, the variations in the spawning season of the two CSPF stocks and their barely satisfactory expected yield indicated the complexity of the current fishery management in the Beibu Gulf. These results suggest that management measures to reduce fishing pressure may have a positive influence on the biological characteristics of those CSPFs in the Beibu Gulf; however, the stock structure already affected by overfishing will be a huge challenge for the conservation and restoration of fisheries resources in the future. Given that the current stocks of D. maruadsi and T. japonicus in the Beibu Gulf still have low first-capture body length (Lc) and high fishing mortality (F) (compared to F0.1), we identify a need to refine population structure by controlling fishing efforts and increasing catchable size, and more consideration should be given to the local fishery resource status in fisheries management.

The initial assessment of an important pelagic fish, Mackerel Scad, in the South China Sea using data‐poor length‐based methods

AbstractObjectiveScadsDecapterusspp. occur widely throughout tropical, subtropical, and temperate oceans and are both economically and ecologically important species. They are among the main commercial fish species caught by the light falling‐net fishery in the South China Sea, which is dominated by Mackerel ScadDecapterus macarellusand Shortfin ScadD. macrosoma. Stock assessment is an approach used to guide effective management and maintain fishery sustainability.MethodsTwo data‐poor methods, namely length‐based Bayesian biomass estimation and length‐based spawning potential ratio, were applied to assess the status of Mackerel Scad, the most dominantDecapterusspecies in the South China Sea. Electronic length–frequency analysis was used to estimate von Bertalanffy growth parameters (asymptotic lengthLinfand growth coefficientK) to serve as priors.ResultThe results show the estimatedLinfandKof Mackerel Scad in the South China Sea as 36.0 cm and 0.37/year, respectively. Estimated natural mortality was 0.74/year, and mean fork length at 50% sexual maturity was 24.29 cm. Length‐based Bayesian biomass estimation analysis showed that the estimated relative stock size had decreased from 1.3 in 2012–2014 to 0.7 in 2019–2021, indicating an overfished status. Length‐based spawning potential ratio analysis showed that the estimated spawning potential ratio for this fishery decreased from 13% to 12%, which is significantly below the limit reference point of 20%.ConclusionOur results obtained through length‐based methods indicate the lower SPR of Mackerel Scad stock was due to catching an excess of juveniles. Therefore, we highlight the need to increase the minimum mesh size in the fishing nets and strengthen international cooperation for conserving this shared stock in the South China Sea.

This is what we know: Assessing the stock status of the data-poor skipjack tuna (Katsuwonus pelamis) fishery in the South China Sea

Skipjack tuna (Katsuwonus pelamis) is a highly migratory species of significant value in global marine fisheries. The South China Sea (SCS) is the largest marginal sea in the northwestern Pacific Ocean, and many tuna and tuna-like species occur within it. Although a recent Western and Central Pacific Fisheries Commission report identified skipjack tuna in the western and central Pacific to be sustainably fished, the exploitation status of skipjack tuna in the SCS is still unclear, due to limited data. We apply two data-poor methods, length-based Bayesian biomass estimation (LBB) and length-based spawning potential ratio (LBSPR), to assess the status of skipjack tuna stock in the SCS. We use electronic length frequency analysis to estimate von Bertalanffy growth parameters (asymptotic lengthLinfand growth coefficientK) to serve as priors for LBB and LBSPR estimation. Estimates are calculated for SCS skipjack tunaLinf(68.3 cm),K(0.325 year−1), natural mortality (0.49 year−1) and mean fork length at 50% sexual maturity (36.7 cm). LBB analysis reveals the estimated relative stock size (0.29) indicates that the SCS skipjack tuna stock maybe heavily overfished. LBSPR analysis reveals the estimated spawning potential ratio for this fishery to be 3%, which is significantly below the limit reference point of 20%. Accordingly, for the SCS skipjack tuna stock we identify a need to reduce fishing mortality by controlling fishing effort and increasing catchable size.

Estimating growth from length frequency distribution: comparison of ELEFAN and Bayesian approaches for red endeavour prawns (Metapenaeus ensis)

Abstract Using length frequency distribution data (LFD) is cost-effective for estimating somatic growth in fish or invertebrates as length data are relatively easy to obtain. The recently developed R packages TropFishR and fishboot extend classic ELEFAN (Electronic LEngth Frequency ANalysis) programs and include more powerful optimization procedures and a bootstrap method for estimating uncertainties. Yet, the fundamental functions require users to provide search conditions (e.g. upper and lower limits for each parameter, length-class size, number of length-classes for the calculation of moving average), which can significantly affect the results. In this paper, we compare the ELEFAN approach with a Bayesian approach in analysing LFD, employing both standard and seasonal von Bertalanffy growth functions. We apply both approaches to a commercially valuable but poorly studied red endeavour prawn (Metapenaeus ensis) harvested in Australia's Northern Prawn Fishery. Sensitivity tests on ELEFAN confirm that any change in search settings would affect the results. Simulation studies on Bayesian growth models show that Linf and K can be accurately obtained even with modal progression of only one year-class and using non-informative priors. However, age information, including the theoretical age at length zero (t0), is difficult to estimate and requires LFD from multiple age classes and informative priors. The Bayesian models yield mean parameters of: Linf = 36.56 mm (carapace length), K = 2.74 yr–1, and t0 = -0.02 yr for the males, and Linf = 51.81 mm, K = 1.94 yr–1, and t0 = -0.02 yr for the females. Seasonal oscillation models fit the LFD better, but the improvement is small and the estimated season-related parameters have large variances.

Population Characteristics of the Etheostoma pallididorsum Distler and Metcalf (Paleback Darter), a Narrowly Distributed Endemic in the Ouachita Highlands, Arkansas

Etheostoma pallididorsum (Paleback Darter) is endemic to the headwater reaches of 2 river systems in the Ouachita Highlands of Arkansas. Records of low abundance and habitat alterations have resulted in the species' imperiled conservation status and being petitioned for federal listing under the Endangered Species Act. The objective of this study was to conduct seasonal surveys across the Paleback Darter's distribution to better characterize growth, spawning patterns, and mortality using the seasonal von Bertalanffy statistic with an optimized electronic length frequency analysis (ELEFAN), as well as assess sex ratios throughout a calendar year to better inform future conservation management decisions for the species. We established seasonal survey collection sites at 4 localities and sampled with a backpack electrofishing unit and dip nets from January 2016 to October 2017. The study indicated relatively high abundance, based on catch per unit effort (CPUE), across all sampled localities throughout the duration of the study, with representation of the entire population from 3 age classes: 0, 1, and 2. Growth and coarse spawning patterns, based on the seasonal von Bertalanffy statistic, were comparable between the populations, suggesting similar and stable environmental factors throughout the distribution. Lastly, there was evidence of multiple spawn events occurring during winter and late spring or early summer that has not been documented for this species, warranting additional research. Collectively, this study, though narrow in scope and with limited data, suggest that the Paleback Darter populations assessed are not impaired. The endemic status and narrowly fragmented distribution of the Paleback Darter, however, still renders this species vulnerable to extirpation or extinction by stochastic events.

Population parameters of several groupers (Famili Serranidae) in Labuan Bajo waters, East Nusa Tenggara

Labuan Bajo has a fertile aquatic ecosystem, one of them is the coral reef ecosystem. This condition happened because of the supply of nutrients that are carried through Indonesia Through Flow and the local upwelling phenomena. Various species of reef fish of various sizes have been caught in Labuan Bajo waters. In general, the type of reef fish that dominates is grouper fish catch by using handline fishing gear. Furthermore, there is damage that occurs in the coastal ecosystem causes changes in ecological functions and disrupted ecosystem benefits. In addition, pressure from overuse did not provide opportunities for resources to carry out recovery makes the condition of resource stocks threatened. This study aims to determine the parameter aspects of the population of several types of grouper fish in Labuan Bajo waters. The types of grouper studied included Plectropomus leopardus, P. maculatus, P. oligacanthus, and Variola albimarginata. Data collection was carried out by enumerators from April to August 2019 which included the daily data on the length and weight distribution of groupers. Length-frequency distribution data is analyzed by estimating fish population parameters using the Electronic Length Frequency Analysis (ELEFAN I) program which is packaged in the FAO-ICLARM Stock Assessment Tool II (FiSAT II) software. The results of the analysis showed the equation of growth parameters for Von Bartalanffy for P. leopardus is Lt = 89.06(1-e−0.24(t+0.52)); P. maculatus is Lt = 76(1-e−0.54(t+0.23)); P. oligacanthus is Lt = 72.32(1-e−0.66(t+0.19)); and V. albimarginata is Lt = 45(1-e−0.51(t+0.29)). The length at first birth of each species is Lt=0 P. leopardus = 10.45 cm, Lt=0 P. maculatus = 8.88 cm, Lt=0 P. oligacanthus = 8.52 cm, and Lt=0 V. albimarginata = 6.19 cm. Meanwhile, the exploitation rate (E) of P. leopardus, P. maculatus, P. oligacanthus, and V. albimarginata were 0.81; 0.53; 0.45; and 0.70.

Population parameters, exploitation rate and diet of black-chinned Tilapia, Sarotherodon melanotheron Rüppell, 1852 (Pisces: Cichlidae), from Badagry Creek, Lagos, Nigeria

The black-chinned tilapia (Sarotherodon melanotheron) is a member of the cichlid family, which can be cultured to complement the output from a predominantly catfish aquaculture industry in Nigeria. In order to achieve this objective, it is important to study the bio-ecology of the fish to ascertain the exploitation status and the potential for culture. Fish were collected monthly from February to November 2018 from three sampling sites (Topo, Akarakumo and Ajido) in Badagry Creek, Lagos, Nigeria using gears like cast net, gill nets and traps. The samples were analysed for length-weight relationship, population parameters and feeding preference. The population dynamics of the stock was assessed by the Von Bertalanffy growth model (VBGM) using Electronic Length Frequency Analysis. The parameters of VBGM; asymptomatic length (L∞) and growth coefficient (K) were 20.46 cm and 0.62 year−1, respectively. The growth performance index (Ǿ) was 2.41 and the potential longevity (tmax) was 4.84 years. The total, natural and fishing mortalities were 1.06, 0.68 and 0.38 year−1, respectively. The exploitation rate was estimated as 0.36. The length at first maturity (L50) was 13.79 cm and the length at first capture (Lc) was 12.27 cm. E0.1, E0.5 and Emax are 0.60, 0.38 and 0.70, respectively. The dominant food items in the gut of the fish belong to the algae phylum, Chlorophyta. The study showed that S. melanotheron from Badagry Creek are planktivores and the exploitation rate of the fish is currently close to optimum and should be sustained at this level to prevent overexploitation.

Length-Based Assessment of Fish Stocks in a Data-Poor, Jointly Exploited (China and Vietnam) Fishing Ground, Northern South China Sea

The Beibu Gulf is one of the most important fishing grounds in the South China Sea (SCS), and the fisheries resources in this area are exploited by both China and Vietnam. In recent decades, some indications of overfishing have appeared, including declining catch rates, frequently changing catch composition, and shrinking body sizes in main commercial fish species. Due to limited data availability, only a small subset of exploited fish stocks in this area has been assessed. Here, we applied two length-based methods, electronic length frequency analysis (ELEFAN) and length-based Bayesian biomass estimation (LBB), to stock assessment of nine exploited fish species in the Beibu Gulf. There were total 53, 652 length records of 30 target stocks used in this study during the survey period from 1960 to 2015. The results showed that the two length-based methods presented different ability in estimating exploitation rate (E), and the estimated E ranged from 0.34 to 0.87 using ELEFAN method while ranged from 0.26 to 0.86 using LBB method. The prior information from ELEFAN method was effective for LBB method, as there were significant differences in 66.7% of the 30 target stocks in estimated Linf, and 93.3% in estimated B/BMSY, using LBB method with and without prior information. The estimated Lc/Lc_opt and B/BMSY of LBB method suggest a pressing situation for the fisheries in the Beibu Gulf, as 86.7% of the 30 target stocks had been suffering from growth overfishing (Lc/Lc_opt < 1), and 83.3% had been overexploited or fully exploited (B/BMSY ≤ 1.2). In addition, we suggest using both ELEFAN and LBB methods to fit length-frequency data of data-poor fish stocks because they are complementary in estimating management reference points. We also emphasize collaboration mechanism should be established by China and Vietnam for the sustainability and recovery of fishery resources in the Beibu Gulf.

Fishing pressure and lifespan affect the estimation of growth parameters using ELEFAN

Length-based methods of stock assessment to support scientific fisheries management are desirable in data-limited fisheries where formal stock assessments are commonly constrained. Based on length-frequency (LFQ) data, Electronic length frequency analysis (ELEFAN) is widely used to fit growth curves, but the performance of this method is sensitive to various factors especially the quality of data. Fishing pressure is one of the main drivers that modify the length composition of fish stocks, but the consequent effects on ELEFAN are not well understood. This study aims to clarify the role of fishing pressure on the performance of ELEFAN given fish species with different life history traits. We designed a simulation-estimation framework to simulate the population dynamics of short-, medium-, and long-lived fish species, and to evaluate the performance of ELEFAN under varying fishing scenarios. The simulation results demonstrate that ELEFAN is robust to changes in size-structure due to fishing, while its accuracy and precision of outputs depends on the intensity of fishing pressure and the life-history characteristics. The estimates of the parameters of the von-Bertalanffy growth function (VBGF) are reliable in short- and medium-lived species, while for long-lived species, fishing may substantially bias the estimates depending on the intensity of fishing pressure. ELEFAN may yield >70% bias in the estimates of K along with large confidence intervals for long-lived species subject to heavy fishing intensity. ELEFAN will perform such better with prior knowledge about quantities such as lifespan. This study may contribute to the understanding of the reliability of ELEFAN for exploited fisheries and to increasing confidence for adopting ELEFAN in data-limited fisheries.

Age, growth, and mortality of starspotted smooth-hound, Mustelus manazo (Bleeker, 1854) in southern West Nusa Tenggara waters

Mustelus manazo (Starspotted smooth-hound shark) is one of the important catch for small scale fisheries in West Nusa Tenggara. This species belongs to the family Triakidae. According to the IUCN Red List, the conservation status of this species is data deficient, which means that there is insufficient information to conduct a proper assessment of conservation status. The objective of this study is to estimate the age, growth and mortality of M. manazo in southern West Nusa Tenggara waters. Length data were collected from January to December 2016 in Tanjung Luar Port, West Nusa Tenggara. Electronic length-frequency analysis (ELEFAN) in R Statistics with package “TropFishR” was used to estimate the population parameter. Length converted catch curve analysis was used to estimate the total mortality. The results showed that von Bertalanffy growth model for male was Lt=122 (1-e(-0.1(t+0.01))), for female was Lt=130 (1-e(-0.18(t+0.02))) and for combined sex was Lt=132 (1-e(-0.1(t+0.01))). Total mortality was estimated at 0.25 year −1. The results from this study represent basic information to support fisheries management of M. manazo in Indonesia.

Selecting optimal bin size to account for growth variability in Electronic LEngth Frequency ANalysis (ELEFAN)

Electronic LEngth Frequency ANalysis (ELEFAN) is a widely used method to fit von-Bertalanffy Growth Function (VBGF) using length frequency data for data-poor fisheries. However accuracy of this method depends on diverse assumptions, among which the variability of individual growth may be particularly influential. In addition, the selection of class interval of length frequency data, defined as bin size, is also considerable source of uncertainty. However, rare guidance exists on how to account for the growth variability and to select bin size. In this study, we considered the effects of growth variability and bin size together by testing whether appropriate bin size can reduce estimating bias due to growth variability. We used a Monte Carlo simulation framework to evaluate the performances of ELEFAN under scenarios of different bin size and levels of individual growth variability for 10 fish species. The results indicated that growth variability might result in large variations and biased estimation of growth parameters if the bin size was chosen arbitrarily. On the contrary, there was an optimal bin size for each species, which led to unbiased estimates even in a substantially high level of growth variability. Summarizing the optimal bin sizes of the 10 species, we proposed a rule of thumb to select optimal bin size (OBS) for the future applications of ELEFAN according to the maximum body length (OBS=0.23×Lmax0.6) and age (OBS=1.86×(Lmax/A)0.45) of fish species. The improvement of accuracy of VBGF parameter estimation will help to understand the growth characteristics and reduce the uncertainty for data-limited stock assessment methods.

Biological and population parameters of Tiger Shark Galeocerdo cuvier, landed in Tanjung Luar, West Nusa Tenggara

Tiger shark is one of the important catch for small scale fisheries in West Nusa Tenggara. It is considered nearly threatened according the IUCN, thus information regarding to its estimated population is needed for conservative efforts. This study aimed to estimate the biological and population parameters of the tiger shark in Indonesia. Length data were collected from March to December 2018 in Tanjung Luar Port, West Nusa Tenggara. The length-weight relationship was calculated using equation W=aLb. Electronic length-frequency analysis (ELEFAN) in R Statistics with package “TropFishR” was used to estimate the population parameter. Length converted catch curve (LCCC) analysis was used to estimate the total mortality of the species. The results showed the length-weight relationship for combined sex, male and female was similar to the equation W=0.000001L3.15. The growth pattern for this species was positive allometric which means that the growth of weight is faster than its length. Total mortality was estimated at 0.33/yr, with natural and fishing mortality of 0.16/yr and 0.17/yr, respectively. The results from this study should be able to provide the basic information to support fisheries management of tiger sharks in Indonesia.

Stock Estimates of White Pomfret (Pampus argenteus) Based on Length and Weight Data in Pangandaran Waters

White pomfret (Pampus argenteus) is one of the economically important fish and includes the leading commodity in Pangandaran Waters. Information on fishing biology of those species were still limited. The purpose of this study is to determine stock estimates including length-weight relationship, age group, growth, mortality and exploitation rate of white pomfret. Monthly length-frequency data have been collected from November 2018 to August 2019 at Cikidang fish auction. Fish length-frequency distribution was separated into a normal distribution using the Bhattacharya method with software of FiSAT (FAO-ICLARM Stock Assessment Tools). Estimation of population parameters used analytical model application with ELEFAN-1 (Electronic Length Frequency Analysis) program. The results showed that lengths distribution of white pomfret ranged between 19.3 cm - 36.8 cmTL. Length-weight relations was negatively allometric (W = 0,1184L2,3719). Growth equation of white pomfret is Lt = 53.04 (1-e-0.26(t)). Natural mortality (M) was 0.60/year, fishing mortality (F) was 3.04/year and total mortality (Z) was 3.64/ year. The exploitation rate (E) was 0.84. It is mean that higher than optimal exploitation so that the white pomfret fish population in a state of overfished. It is necessary to better policy in the management of white pomfret through precaution approach and describing of biological and fishing aspect in Pangandaran Waters.

Studies on the growth and mortality of invasive Oreochromis niloticus (Linnaeus, 1758) in sub-tropical river Yamuna, part of Gangetic River system, India

Growth parameters, mortality, growth performance index and exploitation ratio of Oreochromis niloticus were assessed based on the length-frequency data collected fortnightly from the Allahabad stretch of the Yamuna, India, during September 2011 to August 2013. The size of the catch ranged between 70 and 495 mm total length. The data was analyzed using the Electronic Length Frequency Analysis module in FiSAT software. Asymptotic length and growth coefficient were estimated as 562 mm total length and 0.58 year−1, respectively. Total mortality, natural mortality and fishing mortality coefficients were 3.74, 1.015 and 2.725 yr−1, respectively. The growth coefficient index was calculated as 3.26. The exploitation ratio worked out as 0.667, indicated that the stock was slightly overexploited. Estimated growth at the end of I, II and III years was 247, 386 and 463 mm total length, respectively. The observed multi-year survivorship based on the length frequency data from the river Yamuna in O. niloticus suggested that it has successfully established in the non-native environment and is rapidly spreading in other tributaries of the river Ganga. The recruitment pattern was observed to be continuous throughout the year, with several micro-cohorts and two overlapping peaks of unequal pulse strengths. Estimated maximum sustainable yield for this species in the Allahabad stretch of the river Yamuna was 27.13 t. This study can form an important base for future research work in the management of this invasive species in the Gangetic river system in India.

Reproductive pattern and population dynamics of commercial red swamp crayfish (Procambarus clarkii) from China: implications for sustainable aquaculture management.

BackgroundThe red swamp crayfish, Procambarus clarkii (Girard, 1852), is one of the most promising freshwater species for aquaculture in China. Understanding its reproductive pattern and population dynamics is crucial for sustainable management, but there is currently a lack of fundamental knowledge of commercial P. clarkii populations. Therefore, the purpose of this study was to investigate the reproductive pattern and population dynamics of commercial P. clarkii throughout the yearly cycle.MethodsA total of 2,051 crayfish (1,012 females and 1,039 males) were collected from March 2016 to February 2017 in the area of Selection and Reproduction Center of Crayfish. The reproductive pattern was evaluated by the gonadosomatic index (GSI), hepatosomatic index (HSI), ovarian development and fecundity. Growth, mortality rates and exploitation rate were estimated by electronic length frequency analysis by R package “TropFishR” based on data of cephalothorax length (CTL).ResultsOur results demonstrated that spawning activities of P. clarkii took place from September to November, with a mean fecundity of 429 ± 9 eggs per female. There were two recruitments yearly, a major one from October to November and a minor one from March to May. With respect to population growth, five growth cohorts were identified for both females and males. Crayfish grew faster but attained smaller asymptotic maximum CTL as indicated by higher growth coefficient (K), growth parameter index (Ø′) and lower asymptotic CTL (Linf). The estimates of total mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were 1.93, 1.02, 0.91 year−1 for females and 2.32, 0.93, 1.39 year−1 for males, which showed that the mortality of male crayfish was mainly caused by fishing. The estimates of exploitation rate (E) indicated that male crayfish were overexploited, with the values of 0.47 and 0.60 year−1 for females and males, respectively.DiscussionP. clarkii spawned from September to November while two recruitments were observed yearly. We inferred that some eggs, prevented from hatching by low water temperature in winter, were more likely to hatch in the next spring. Moreover, the fishing mortality rate was relatively high for males, which might be related to the males-directed selection during the reproductive period. The higher values of exploitation rate in our study confirmed that males P. clarkii were overexploited and were under high fishing pressure. We thus suggest reducing fishing intensity on immature crayfish and avoid sex selection during the reproductive period to improve the overall sustainability of commercial P. clarkii populations.

Assessing sources of uncertainty in length-based estimates of body growth in populations of fishes and macroinvertebrates with bootstrapped ELEFAN

The determination of rates of body growth is the first step in many aquatic population studies and fisheries stock assessments. ELEFAN (Electronic LEngth Frequency ANalysis) is a widely used method to fit a growth curve to length-frequency distribution (LFD) data. However, up to now, it was not possible to assess its accuracy or the uncertainty inherent of this method, or to obtain confidence intervals for growth parameters within an unconstrained search space. In this study, experiments were conducted to assess the precision and accuracy of bootstrapped and single-fit ELEFAN-based curve fitting methods, using synthetic LFDs with known input parameters and a real data set of Abra alba shell lengths. The comparison of several types of bootstrap experiments and their outputs (95% confidence intervals and confidence contour plots) provided a first glimpse into the accuracy of modern ELEFAN-based fit methods. The main components of uncertainty (precision and reproducibility of fit algorithms, seed effects, sample size and matrix information content) could be assessed from partial bootstraps. Uncertainty was mainly determined by LFD matrix size (months x size bins), total number of non-zero bins and the sampling of large-sized individuals. A new pseudo-R² index for the goodness-of-fit of von Bertalanffy growth models to LFD data is proposed. For a large, perfect synthetic data set, pseudo-R²Phi’ was very high (88 to 100%), indicating an excellent fit of the growth model. The small Abra alba data set showed a low pseudo-R²Phi’, from to 54% to 68%, indicating the need for more samples (length measurements) and a larger LFD data matrix. New, robust, bootstrap-based methods for curve fitting are presented and discussed. This study demonstrates a promising new path for length-based analyses of growth and mortality in natural populations, which are the basis for a suite of methods that are included in the new fishboot package.

Studies on the growth and mortality of Indian River shad, Gudusia chapra (Hamilton, 1822) from Panchet reservoir, India.

The Indian river shad, Gudusia chapra (Hamilton, 1822), is a commercially important freshwater clupeid that contribute to the livelihood of subsistence and marginal fisheries in inland open waters of India and its adjacent countries. The present study was carried out on the growth and mortality of Indian River shad, Gudusia chapra (Hamilton, 1822) based on the commercial length-frequency data collected monthly during October 2014 to September 2015 of a large reservoir located in the border of Jharkhand and West Bengal. The ELEFAN-I (Electronic Length Frequency Analysis) module in FiSAT (FAO-ICLARM Stock Assessment Tools) was used for estimation of growth parameters (L∞, K). The total mortality was estimated following Pauly (ICLARM Fishbyte 2(1):9-13, Pauly 1983) whereas exploitation ratio and maximum sustainable yield were calculated following Gulland (1979). The asymptotic length (L∞) and growth coefficient (K) were estimated as 194mm and 1.23year-1, respectively. The species grows to 141.56 and 182.91mm at the end of the 1st and 2nd years of life. The total natural and fishing mortalities were 6.63, 2.45 and 4.18year-1 respectively. The value of growth performance index was 2.69. The exploitation ratio (E) was estimated as 0.63. As the exploitation ratio (E) is slightly beyond the optimum, there is likelihood of some threat of overexploitation. Though recruitment was continuous, major pulse was observed during April-May. The present investigation is a first report from Indian reservoir. The maximum sustainable yield of this species was estimated as 485.6t against the present annual yield of 612.3t. Avoiding overfishing and wise use of available resources are of prime importance for sustainable fishery management of the reservoir.

Population parameters and reproduction of the piranhaSerrasalmus marginatusin the Negro river, Pantanal, Brazil

This paper aimed to define the reproductive period and population parameters of Serrasalmus marginatus relative to local environmental features, such as day length, rainfall and mean river level. The study site was a floodplain in the Negro river, Pantanal, Brazil, and samples were collected bimonthly using gill nets and cast nets with meshes from 1.5 to 8 cm between adjacent knots. The reproduction period, as determined by gonadosomatic index (GSI) and percentage of gonad stages, varied significantly along the year (F4,116 = 77.5; p < 0.01), but it was well defined from October to December. Reproduction period was positively correlated with rainfall (rs = 0.97; p < 0.01) and photoperiod (rs = 0.92; p = 0.02), but not with the rise of river level (rs = 0.10; p = 0.86). Rainfall and photoperiod may act as predictive factors, providing cues to fish to begin reproduction in order to find the best conditions for offspring in the following months, during the flooding season, when the river level reaches its peak and extends to the plain. We have herein reported the first population parameters described for this species in the Brazilian Pantanal, including growth rate (k = 0.53/year), asymptotic length (L∞ = 32.74), lifespan (A0.95 = 5.65) and mortality (M = 1.11), showing that this population has better growth performance when compared to data reported for this same species in the Paraná river since the population in the Negro river is characterized by lower growth and mortality rates, and S. marginatus achieved longer lengths and lifespan. This latter parameter was compatible with six cohorts estimated by Electronic Length Frequency Analysis (ELEFAN). The size at first maturity (L50 = 18.26 cm A50 = 1.56 years) was also larger and later than the population in the Paraná river, likely a consequence of the the lower mortality and the maintenance of larger specimens in the Negro river.

Extending electronic length frequency analysis in R

AbstractElectronic length frequency analysis (ELEFAN) is a system of stock assessment methods using length‐frequency (LFQ) data. One step is the estimation of growth from the progression of LFQ modes through time using the von Bertalanffy growth function (VBGF). The option to fit a seasonally oscillating VBGF (soVBGF) requires a more intensive search due to two additional parameters. This work describes the implementation of two optimisation approaches (“simulated annealing” and “genetic algorithm”) for growth function fitting using the open‐source software “R.” Using a generated LFQ data set with known values, the accuracy of the soVBGF parameter estimation was evaluated. The results indicate that both optimisation approaches are capable of finding high scoring solutions, yet settings regarding the initial restructuring process for LFQ bin scoring (i.e. “moving average,”) and the fixing of the asymptotic length parameter (L∞) are found to have significant effects on parameter estimation error. An outlook provides context as to the significance of the R‐based implementation for further testing and development, as well as the general relevance of the method for data‐limited stock assessment.