Growth Function Parameters Research Articles

DINÁMICA POBLACIONAL DEL CORONCORO MICROPOGONIAS FURNIERI (PISCES: SCIAENIDAE) EN LA CIÉNAGA GRANDE DE SANTA MARTA, CARIBE COLOMBIANO

The “Coroncoro” fish Micropogonias furnieri has been one of the most important traditional fish resources in CGSM and CP. In order to determine exploitation status of its stock, aspects related to its biology and population parameters have been assessed. 38 Boletín de Investigaciones Marinas y Costeras - Vol. 35-2006 Mean maturity size was estimated in 20.7 cm at total length; whereas sex ratio was 2.39 females per male. Ripe individuals occurred throughout the whole year, with a maturation and spawning peak in the rainy season (november). Length-weight relationship showed no difference between sexes and a common equation with allometric growth W = 0.0064LT3.2 was estimated. The estimated parameters of von Bertalanffy growth function were L∞ = 34.0 cm, K = 0.44 yr-1, t0 = 0.301 yr and C = 0.5; with a growth index ranging between 2.67 and 2.73. Total (Z), natural (M) and fishing (F) mortality rates were estimated as 2.16, 0.84 and 1.32 yr-1, respectively. The estimated exploitation rate (E = 0.61) indicated that M. furnieri is being overexploited and thus it is recommended to adopt management actions to ensure resource sustainability.

The economic and environmental value of genetic improvements in fattening pigs: An integrated dynamic model approach1

The selection of animals for improved performance affects the profitability of pig fattening and has environmental consequences. The goal of this paper was to examine how changes in genetic and market parameters impact the biophysical (feeding patterns, timing of slaughter, nitrogen excretion) and economic (return per pig space unit) results describing pig fattening in a Finnish farm. The analysis can be viewed as focusing on terminal line breeding goals. An integrated model using recursive stochastic dynamic programming and a biological pig growth model was used to estimate biophysical results and economic values. Combining these models allowed us to provide more accurate estimates for the value of genetic improvement and, thus, provide better feedback to animal breeding programs than the traditional approach, which is based on fixed management patterns. Besides the benchmark scenario, the results were simulated for 5 other scenarios. In each scenario, genotype was improved regarding daily growth potential, carcass lean meat content, or the parameters of the Gompertz growth curve (maturing rate [], adult weight of protein [α], and adult weight of lipid mass []). The change in each parameter was equal to approximately 1 SD genetic improvement (ceteris paribus). Increasing , , daily growth potential, or carcass lean meat content increased the return on pig space unit by €12.60, €7.60, €4.10, or €2.90 per year, respectively, whereas an increase in decreased the return by €3.10. The genetic improvement in and resulted in the highest decrease in nitrogen excretion calculated in total or per kilogram of carcass gain but only under the optimal feeding pattern. Simulated changes in the Gompertz growth function parameters imply greater changes in ADG and lean meat content than changes in scenarios focusing on improving ADG and lean meat content directly. The economic value of genetic improvements as well as the quantity of nitrogen excreted during the fattening period largely depends on feeding. Improved genotypes can require changes in pig management pattern. Estimating the influence of the genotype on the nitrogen excretion without considering changes in the management pattern can result in flawed conclusions. To improve overall economic performance and to decrease the environmental footprint of fattening pig production, the pig producer can adjust the herd management pattern according to the pigs' genetics.

Growth and mortality of red lionfish, Pterois volitans (Actinopterygii: Scorpaeniformes: Scorpaenidae), in the Parque Nacional Arrecife Alacranes, southern Gulf of Mexico, as determined by size-frequency analysis

Background. Biological invasions represent a threat to the ecological stability of the ecosystem. Two lionfish species, the red lionfish and the devil firefish—both tropical marine predators native to the Indo–Pacific—were introduced to the Atlantic Ocean. However, only one—the red lionfish, Pterois volitans (Linnaeus, 1758)—has reached the level of an invasive species so far. It is crucial to learn its biology and ecology to understand trends of its invasion and impacts on native fauna, and to determine ecological changes as the invasion progresses. This study reports the growth and mortality of P. volitans in coral reefs of the Parque Nacional Arrecife Alacranes, off the northern Yucatan Peninsula, Mexico, in Southern Gulf of Mexico. Materials and methods. Lobster diver fishers participated in voluntary captures of lionfish during the lobster fishing seasons of 2010–2012. In the laboratory, lionfish were taxonomically identified, measured, and weighed. Their length–weight relation was determined according to the commonly used equation: W = aTLb. Fish total lengths were used to calculate the parameters of the von Bertalanffy growth function (VBGF) of lionfish based on the size-frequency analysis routine ELEFAN in the FiSAT II software. Results. A total of 776 lionfish (9.0 to 38.9 cm in total length, 7 to 874 g in total wet weight) were collected. The VBGF parameters estimated were L∞ = 42 cm, K = 0.88–1, t0 = –0.107 years. The total mortality instantaneous rate (Z) calculated by the total length converted catch curve was 2.06 year–1. Conclusion. This study provides first calculation of growth parameters and mortality of P. volitans in Southern Gulf of Mexico as determined by size-frequency analysis. Results contribute to the knowledge on the biology of P. volitans and to a better understanding of aspects of its biological invasion in the region.

Evaluation of using random-at-length observations and an equilibrium approximation of the population age structure in fitting the von Bertalanffy growth function

When paired age–length samples are collected from fishery data, estimation of the growth function parameters has typically assumed that each length observation is a random sample of fish for a given age (traditional method). An alternative methodology (length-conditional) assumes each age sample taken is random with respect to that length. The length-conditional method uses the underlying population age structure to derive predictions and therefore has been limited to implementation inside the stock assessment model. This paper used simulation methods to evaluate the estimates of the von Bertalanffy growth parameters outside the assessment model using the traditional method and a length-conditional method based on an equilibrium approximation to the population age structure derived from an estimate of the total mortality rate. Both random and length-stratified sampling designs were evaluated along with a range of sample sizes. With a random sampling design, both the traditional and approximate length-conditional methods produced unbiased estimates of Linf and K. However, only the approximate length-conditional approach produced unbiased estimates when samples were length-stratified. Variability in the length-at-age relationship was better estimated by the approximate length-conditional approach for both sampling designs. The approximate length-conditional method was robust to small errors in total mortality rate, but biased with increasing levels of mortality misspecification. With a reasonable estimate of total mortality, the approximate length-conditional approach may be a viable alternative to the traditional method when estimating growth parameters, especially the variability in growth.

POPULATION DYNAMICS OF Chrysichthys nigrodigitatus (Lac�pede, 1803) IN LOWER CROSS RIVER, NIGERIA

Silver catfish Chrysichthys nigrodigitatus (Lacepede, 1803) constitutes the main fishery offering diversified livelihood to the artisanal communities in southeast Nigeria and has been heavily fished over time without attempts at conservation. This study was conducted to estimate the current population parameters needed for its rational exploitation. Estimates of growth and mortality of catfish in the Lower Cross River, Nigeria, were obtained from length-frequency data of 6637 individuals collected on monthly basis from November 2011 to October 2012. The estimated von Bertalanffy growth function (VBGF) parameters were: asymptotic length L∞ = 120.23 cm total length, growth coefficient K = 1.50 year-1 and age at zero length, t0 = 0.0 years. The amplitude of growth oscillations C = 0.75, winter point WP = 0.50 or 1 July and growth performance index, φ = 4.336. The rates for natural, fishing and total mortalities were: M =1.58, F = 2.55 and Z = 4.31 per year, respectively. This study reveals growth overfishing and threat of extinction of C. nigrodigitatus in the Lower Cross River system characterized by heavy fishing pressure on the length group 34.5 - 94.5 cm TL, reduced life span from 5 to 2 years, change from a slow growth pattern typical of siluroids to a fast one with current exploitation rate, Ecur (F /Z) = 0.62, about 15.8% higher than the allowable maximum exploitation rate, Emax = 0.522. In order to restore ecosystem health, a community-based multisectoral stakeholder consortium invested with limited equity and access for exploiting the fishery in tandem with its bio-ecological dynamics should be encouraged. Other policy instruments such as periodic prohibition of fishing, controlled pricing and public education are recommended for the sustainability and conservation of the fisheries.

Growth, mortality, and reproduction of Tagelus plebeius (Bivalvia: Solecurtidae) in Southeast Brazil

Tagelus plebeius (Lightfoot, 1786) is a stout razor clam that is economically exploited in several countries, including several local fisheries along the Brazilian coast. Despite its wide distribution and economic importance, there are few studies that have examined the population biology of this species. This study aimed to improve the current knowledge about the biology of T. plebeius by investigating its growth and mortality on a subtropical sandy beach in Southeast Brazil over a 1-year period. In addition, the reproduction of T. plebeius was analyzed through qualitative and quantitative histological analyses during the last 7 months of the study. The parameters of the von Bertalanffy growth function were estimated to be L ∞ = 74.14 mm, K = 0.52 year−1, C = 0.47, and WP = 0.94. The instantaneous mortality rate (Z) was 2.16 year−1, and the life span was 2.58 years. We confirmed variations (H = 651.35; P < 0.05) in the shell length over the months of the study, and the recruitment was higher—but still low—in summer. Four cohorts were observed in the distribution of shell length frequencies. The sex ratio of the population was 1:1 during the study period, and a synchronism in gonadal development and spawning was found between males and females. The high mortality (Z) and low recruitment rates can be interpreted as reflecting that the population of T. plebeius is under a low restoration process and could be an indication that this species has an endangered status in the study area.

Population dynamics of Japanese threadfin bream Nemipterus japonicus from Pakistani waters

Japanese threadfin bream Nemipterus japonicus (Bloch, 1791) is among the most abundant and commercially important species in Pakistan. From the coast of Pakistan, four demersal trawl surveys in October–November 2009 and May–June, August, October and November in 2010 were carried out. The purpose of this study is to estimate the population dynamics and status of the stock of the N. japonicus from Pakistani waters based on the research trawl surveys from the research area. The data consist of n=784 length-weight pairs and n=7 530 length frequency with the maximum length and weight of 29 cm and 358 g respectively. The length frequency data were analyzed using ELEFAN method in FiSAT computer package. The parameters of length and weight relationship were b=2.778, a=0.032 and R 2=0.973. The estimated von Bertalanffy growth function parameters were L ∞=30.45 cm, K=0.270 year−1. Based on length-converted catch curve analysis the total mortality (Z) during this study was estimated at 0.960 year−1. The natural mortality coefficient (M) was 0.74 year−1 using Pauly’s equation (the annual average sea surface temperature was 27°C), therefore, the fishing mortality coefficients (F) were 0.22 year−1. The yield per recruit analysis indicated that when t c was 2, F max was estimated at 1.2 and F 0.1 at 1.1. When t c was 1, F max was estimated at 0.95 and F 0.1 at 0.8. Because current age at first capture is about 1 year and F current was 0.22, F current is smaller than F 0.1 and F max, which indicated that the fishery is about in a safe condition. When using Gulland (1971) biological reference point, F opt was equals to M (0.74). The current fishing mortality rate of 0.22 was smaller than the target biological reference point.

Determining individual variation in growth and its implication for life-history and population processes using the empirical Bayes method.

The differences in demographic and life-history processes between organisms living in the same population have important consequences for ecological and evolutionary dynamics. Modern statistical and computational methods allow the investigation of individual and shared (among homogeneous groups) determinants of the observed variation in growth. We use an Empirical Bayes approach to estimate individual and shared variation in somatic growth using a von Bertalanffy growth model with random effects. To illustrate the power and generality of the method, we consider two populations of marble trout Salmo marmoratus living in Slovenian streams, where individually tagged fish have been sampled for more than 15 years. We use year-of-birth cohort, population density during the first year of life, and individual random effects as potential predictors of the von Bertalanffy growth function's parameters k (rate of growth) and (asymptotic size). Our results showed that size ranks were largely maintained throughout marble trout lifetime in both populations. According to the Akaike Information Criterion (AIC), the best models showed different growth patterns for year-of-birth cohorts as well as the existence of substantial individual variation in growth trajectories after accounting for the cohort effect. For both populations, models including density during the first year of life showed that growth tended to decrease with increasing population density early in life. Model validation showed that predictions of individual growth trajectories using the random-effects model were more accurate than predictions based on mean size-at-age of fish.

Population Structure, Growth, Mortality and Fecundity of Palaemon adspersus (Rathke 1837; Decapoda: Palaemonidae) in the Parila Lagoon (Croatia, SE Adriatic Sea) with Notes on the Population Management

Baltic prawn, Palaemon adspersus population from the Parila lagoon (SE Adriatic Sea, Croatia) was studied between 2010-2011. Specimens were collected monthly in order to determine population structure, growth, mortality and reproduction of this important decapods species. The von Bertalanffy growth function parameters were found L∞=58.98 mm, K=0.975 year−1 and to=-0.0046 years for males and L∞=72.45 mm, K=1.058 year−1 and to=-0.0005 years for females. Growth performance (Φ') for females was higher (3.229) than that of males (3.121). Maximum calculated age was 3.07 and 2.83 years for males and females, respectively, while total mortality was estimated as 3.72 per year for males and 3.79 per year for females. The females carried on average 2157 eyed eggs per 1g of total body weight, but exhibited a high variability of fecundity. The results show overexploitation of the resource and therefore management rules based on the precautionary approach are proposed. These rules are based on the limitation of the fishing effort and the establishment of 'no-take' periods during the year as well as the proposal of two biological reference points based on a minimum landing size related to the size at- maturity and the fishing mortality at Maximum Sustainable Yield.

Use of the SLW index to calculate growth function in the sea cucumber Isostichopus badionotus.

Age and growth analysis is essential to fisheries management. Indirect methods to calculate growth are widely used; however, length frequency data analysis in sea cucumbers is complicated by high data variability caused by body wall elasticity. Here we calculated Isostichopus badionotus parameters of the von Bertalanffy growth function. In order to address bias produced by body wall elasticity, we compared the performance of four measurements and one compound index that combines different biometric parameters: the square root of the length-width product (SLW). Results showed that variability in length data due to body wall elasticity was controlled by using body length (Le) from the SLW compound index. Growth in I. badionotus follows a negative allometric tendency. Slow or zero growth periods were observed during October and November, when weather conditions were adverse.

Civil unrest and the poaching of rhinos in the Kaziranga National Park, India

Civil unrest and political instability have been associated with endangered species poaching. This paper accounts for a period of civil unrest in Assam, India, which saw a marked increase in rhino poaching. Census data on the greater one-horned rhinoceros (Rhinoceros unicornis) in the Kaziranga National Park in Assam are used to estimate a population growth function. In calibrating the growth function's parameters the census data are used in conjunction with rhino poaching data. The rhino population and poaching data are used to econometrically estimate a harvest function. The relationship between civil unrest and rhino poaching is identified as positive and significant. The analysis factors in the probable relationships between poaching and several additional variables — including black market rhino horn prices, potential size of black markets, and anti-poaching efforts. These variables are seen to have the predicted associations with poaching, and help isolate the latter's relationship with civil unrest in the regression models. The goodness of fit between the data on rhino population and poaching and the estimates from regression models are studied.

Age, growth, and reproductive biology of blacktail snapper, Lutjanus fulvus, around the Yaeyama Islands, Okinawa, Japan

Age, growth, and reproductive characteristics of blacktail snapper, Lutjanus fulvus, which is a commercial fish species, were investigated using 322 specimens (40–332 mm in fork length) caught around the Yaeyama Islands, Okinawa, Japan. Spawning season was estimated to be from April to October, and spawning was confirmed around the full moon and the last quarter moon. Age determination using sectioned otoliths revealed that ages ranged from 0 to 34 years and the majority was ≥ 3 years. Parameters of the von Bertalanffy growth function were estimated to be L∞ = 270 mm, k = 0.40, and t0 = −0.48 years for females, and 257 mm, 0.44, and −0.42 years for males. Initial growth was rapid during the first 3 years, attaining over 200 mm for both sexes, and then females grew larger than males. Sizes (ages) at the first sexual maturity were 225 mm (4 years) for females and 207 mm (3 years) for males. The wide range of age composition in catch with majority of ≥3 years old implied that the current fishing effort to harvest was not sufficiently large enough to collapse the stock immediately.

Reproduction and growth of the spiny lebbeid shrimp, Lebbeus groenlandicus (Fabricius, 1775) (Caridea, Hippolytidae) in the East Sea of Korea

Reproduction and growth of the spiny lebbeid shrimp, Lebbeus groenlandicus (Fabricius, 1775), were investigated based on samples in the East Sea of Korea [= Sea of Japan], from January 2012 to April 2013. We collected 2964 shrimp samples during the study period, which included significantly more females than males (male : female ratio, 1.0 : 1.17). The females were generally larger than the males, and significant differences in the linear-regression slopes of carapace length (CL) versus body weight between the sexes indicate sex-specific differences in allometric growth. The gonadosomatic index (GSI) varied monthly, reaching a maximum in November 2012 (10.28) and a minimum in March 2013 (2.15). The proportion of ovigerous females varied from month to month. The highest values of the GSI coincided with the breeding period, and there was a significant difference between the mean GSI of females with non-eyed and those with eyed eggs, indicating that L. groenlandicus is a consecutive breeder. There was a significant correlation between CL and the number of eggs (EN) in the early egg stages. There was also a significant difference in the slopes of the regressions of CL versus EN between females carrying non-eyed and eyed egg stages. Based on the dry weights in the early egg stages, reproductive output was determined to be 0.18 ± 0.006. The Von Bertalanffy growth function parameters were CL∞ = 38.80 mm, year−1, , and WP = 0.4 for males, and CL∞ = 43.64 mm, year−1, , and WP = 0.6 for females. The growth performance index () was 2.86 for males and 2.89 for females.

Growth and reproduction of the deep-water rose shrimp, Parapenaeus longirostris (Lucas, 1846) (Decapoda, Penaeidae), in the Southern Tyrrhenian Sea

From June 2006 to May 2007, monthly samples ofParapenaeus longirostris(Lucas, 1846) were collected on land from the landings of two different, although contiguous, fishing grounds exploited by the bottom trawl fisheries of the two fishing harbours of Terrasini and Porticello, located on the north-western coast of Sicily. Carapace length (CL) of the female and male deep-water rose shrimp in Terrasini ranged from 9 to 32 mm and 13 to 26 mm, respectively, whereas in Porticello the length ranged from 8 to 31 mm and 13 to 26 mm, respectively. The Von Bertalanffy Growth Function parameters for Terrasini females and males were CL∞ = 38.5 mm, year−1and CL∞ = 32.5 mm, year−1, respectively. For Porticello females and males, the parameters were CL∞ = 40 mm, year−1and CL∞ = 30 mm, year−1, respectively. Analysis of maturity stages indicates that the deep-water rose shrimp is an asynchronous batch of almost continuous spawners, although one to two peaks of activity can be detected. In both fishing areas, the reproductive phase peaked twice, once in January and again from August to September. The sizes at first maturity (CL50%) were 27.8 and 26.6 mm CL for Terrasini and Porticello, respectively.

Temporal variation, growth and natural mortality of two species of mojarras (Perciformes: Gerreidae) from a tropical coastal lagoon: La Carbonera, Yucatan, Mexico

This study reports seasonal variation, growth parameters and natural mortality for Eucinostomus gula and Eucinostomus argenteus inhabiting La Carbonera, a tropical coastal lagoon on the northwestern coast of theYucatan Peninsula, Mexico. Specimens were collected between April 2009 and March 2010. A total of 2700organisms of E. gula (&gt; 80% in rainy season ) and 1577 organisms of E. argenteus (&gt;50% in dry season)were collected during the study period. Length-weight relationship (LWR) obtained was W = 8.323E-03Lt2.92 in E. argenteus and W = 7.314E-03 Lt2.92 in E. gula. Growth parameters of von Bertalanffy growthfunction (VBGF) by length frequency analysis were in E. argenteus: L∞ = 13.65 cm, k = 0.54 year-1 and t0= - 0.37 years; and in E. gula: L∞ = 12.60 cm, k = 0.68 year-1 and t0 = - 0.28 years. Additionally, estimatednatural mortality in E. gula was 1.50 year-1 and in E. argenteus was 1.9 year-1. This study presents the firstestimation for both species of model parameters, growth performance index and mortality for the Yucatan Peninsula, which is relevant for the proper implementation of conservation measures for E. gula and E. argenteus in an important coastal zone of the Yucatan Peninsula.Se reportan la variación temporal, los parámetros de crecimiento y la mortalidad natural para Eucinostomus gula y Eucinostomus argenteus que habitan en la laguna costera tropical La Carbonera, al noroeste de la península de Yucatán, México. Los especímenes fueron recolectados entre abril de 2009 a marzo de 2010. Un total de 2 700 organismos de E. gula (&gt; 80% en la estación lluviosa) y 1 577 organismos de E. argenteus (&gt; 50% en la estación seca) fueron recolectados durante el período de estudio. Se determinó la relación peso-longitud (RPL) como: P = 8.323E-03 Lt 2.92 en E. argenteus y P = 7.314E-03 Lt2.92 en E. gula. Para E. argenteus, los parámetros de crecimiento de la ecuación de crecimiento de von Bertalanffy (ECVB) fueron: L∞ = 13.65 cm, k = 0.54 año-1 y t0 = - 0.37 años; mientras que para E. gula fueron: L∞ = 12.60 cm, k = 0.68 año-1 y t0 = - 0.28 años. La mortalidad natural en E. gula fue 1.50 año-1 y en E. argenteus fue 1.9 año-1. Este estudio presenta la primera estimación para ambas especies de los modelos de crecimiento, el índice del desempeño de crecimiento y la mortalidad natural para la península de Yucatán, lo que es relevante para la adecuada implementación de medidas de conservación de E. gula y E. argenteus en una valiosa zona costera de la península de Yucatán.

Population biology of the gastropod Olivella minuta (Gastropoda, Olividae) on two sheltered beaches in southeastern Brazil

The structure, dynamics and production of two populations of the olivid gastropod Olivella minuta were analyzed through monthly sampling from November 2009 through October 2011 on two sandy beaches, Pernambuco (very sheltered) and Barequeçaba (sheltered) in São Paulo state (23°48'S), southeastern Brazil. On both beaches, samples were taken along five transects established perpendicular to the waterline. Parameters of the von Bertalanffy growth function were estimated for both populations from monthly length-frequency distributions. The production and turnover ratios were determined using the mass-specific growth rate method. The population on the less-sheltered Barequeçaba Beach was less abundant (120.02 ± 22.60 ind m−1) than on Pernambuco Beach (3295.30 ± 504.86 ind m−1 (±SE)), which we attribute to the greater environmental stability of the latter. Conversely, the mean length, size of the largest individual, and body mass were higher at Barequeçaba than at Pernambuco. The significant differences in the growth of individuals and the mortality rate (Z) between the beaches suggest that density-dependent processes were operating at Pernambuco Beach. The production and P/B ratio at Pernambuco (12.12 g AFDM m−1 year−1 and 1.91 year−1) were higher than at Barequeçaba (0.82 g AFDM m−1 year−1 and 1.06 year−1). The difference in production can be attributed to the higher abundance on Pernambuco, while the higher P/B ratio resulted from the scarcity of smaller individuals in the intertidal zone of Barequeçaba. The P/B ratio estimated for the Pernambuco population is the highest found so far for sandy-beach gastropods. This study reinforces the theory that biological interactions are important regulators of sheltered sandy-beach populations. Future studies with multi-beach sampling are needed to better understand the life-history variations of O. minuta along gradients of degree of exposure of sandy beaches.

Evaluation of von bertalanffy growth curves for the introduced red king crab (Paralithodes camtschaticus) in Norwegian waters

The introduced red king crab (Paralithodes camtschaticus) is abundant in the coastal waters off northern Norway. We developed Bayesian hierarchical models to estimate growth parameters of a von Bertalanffy growth function using tag–recapture data. Individual variability in L∞ (asymptotic length) was incorporated in the analysis. The models successfully estimate female red king crab lengths at intervals where data were sufficient. The length of small males was overestimated. The results indicate a difference in growth rate of male and female juvenile red king crab. The importance of including individual variability was confirmed: Variability in L∞ for individuals was high compared to population variability in L∞. The model that incorporated individual variation resulted in more plausible values for the growth parameters and increased the precision of length estimates compared to the model that estimate a common L∞.

Population Dynamics of Horse Mackerel (Trachurus Mediterraneus Ponticus) in the Bulgarian Black Sea Coast

The horse mackerel Trachurus mediterraneus is a commercially important pelagic fish species in the Black Sea fishery. The present investigation was carried out between May and December 2010 along the Bulgarian coast of the Black Sea. Population parameters of horse mackerel from the trawl and fishing nets catches were estimated from length frequency data, by using ELEFAN-I computer program. The ELEFAN-I analysis gave the following Von Bertalanffy Growth Function (VBGF) parameters: the asymptotic length cm, growth coefficient value was , and the hypothetical age at which length is zero was . Based on these growth parameters, the total mortality coefficient () during the study period was estimated to be 2.99. The estimated value for natural mortality () was 1.08; hence, the fishing mortality coefficient () was 1.91. The estimated value for the exploitation rate () using the length converted catch curve was 0.64. The estimated sizes of T. mediterraneus at 25, 50, and 75 percent probabilities of capture were 16.80 cm, 18.72 cm, and 20.64 cm, respectively.

Growth and mortality of small yellow croaker (Larimichthys polyactis) inhabiting Haizhou bay of China

Length frequency data of small yellow croaker (Larimichthys polyactis) were acquired from the survey vessel in May, July, September and December, 2011 in Haizhou Bay of China. In this study, 921 fish individuals were analyzed for the estimation of growth and mortality parameters. Between length and weight, the power coefficient b was 2.7321, 2.9703, 3.0418 and 2.7252 for the 4 surveying months, respectively. The estimated von Bertalanffy growth function parameters were 230mm (L ∞) and 0.26yr−1 (K) as were calculated with ELEFAN method equipped in FiSAT computer package. With length-converted catch curve analysis, the total mortality rate (Z) and its 95% confidence interval were 2.16 (1.69–2.64) yr−1, 0.59 (0.15–1.04) yr−1, 1.16 (0.80–1.52) yr−1 and 0.96 (0.70–1.23) yr−1 for the 4 surveying months, respectively, with the pooled data the value was 1.15 (0.81–1.48) yr−1. The natural mortality rate (M) was 0.516 yr−1 as was calculated with Pauly’s equation (the annual average sea water temperature was 11°C). Therefore, fish mortality rate was 0.634 yr−1. The yield-per-recruit analysis indicated that when t c was 1, F max was 0.7 and F 0.1 was 0.55. Currently, the age at first capture is about 1 year and F current was 0.634. Therefore, F current was larger than F 0.1 and less than F max. This indicates that current fish mortality is at a dangerously high level. With Gulland method, the biological reference point for fishery (F opt) was estimated as 0.516 yr−1, lower than current fish mortality. Accordingly, reducing catch in the region was strongly recommended.

Spatial variation in life history reveals insight into connectivity and geographic population structure of a tropical estuarine teleost: king threadfin, Polydactylus macrochir

Understanding the life history of exploited fish species is not only critical in developing stock assessments and productivity models, but has a dual function in the delineation of connectivity and geographical population structure. In this study, patterns in growth and length and age at sex change of Polydactylus macrochir, an ecologically and economically important protandrous estuarine teleost, were examined to provide preliminary information on the species’ connectivity and geographic structure across northern Australia. Considerable variation in life history parameters was observed among the 18 locations sampled. Both unconstrained and constrained (t0=0) estimates of von Bertalanffy growth function parameters differed significantly among all neighbouring locations with the exception of two locations in Queensland's east coast and two in Queensland's Gulf of Carpentaria waters, respectively. Comparisons of back-calculated length-at-age 2 provided additional evidence for growth differences among some locations, but were not significantly different among locations in the south-eastern Gulf of Carpentaria or on Queensland's east coast. The length and age at sex change differed markedly among locations, with fish from the east coast of Australia changing sex from males to females at significantly greater lengths and ages than elsewhere. Sex change occurred earliest at locations within Queensland's Gulf of Carpentaria, where a large proportion of small, young females were recorded. The observed differences suggest that P. macrochir likely form a number of geographically and/or reproductively distinct groups in Australian waters and suggest that future studies examining connectivity and geographic population structure of estuarine fishes will likely benefit from the inclusion of comparisons of life history parameters.