Length-converted Catch Curve Research Articles

Growth and mortality, recruitment and yield of the fresh-water shrimp, Macrobrachium völlenhovenii, Herklots 1851 (Crustacea, Palaemonidae) in the Fahe reservoir, Côte d'Ivoire, West Africa

We studied the growth, mortality rates and recruitment pattern of an exploited fresh-water shrimp ( Macrobrachium völlenhovenii) population in the Fahe reservoir of the San-Pedro River, Côte d'Ivoire using 12 consecutive months (January to December 1995) length–frequency samples and FISAT software (which incorporates both the ELEFAN and LSFA programs). A fit of the seasonalized von Bertalanffy growth equation to the length–frequency data gave the following results: L ∞=18.0 cm total length, K=0.91 year −1, C=0.92, WP=0.44 of year (i.e. July), and an R n value of 0.45. We also estimated the instantaneous total mortality coefficient Z=3.69 year −1 through the seasonalized length-converted catch curve procedure. The instantaneous natural mortality coefficient M was 1.97 year −1 while the instantaneous fishing mortality coefficient was 1.72 year −1. An exploitation rate E of 0.47 implies that the stock is almost optimally exploited. The results of our yield-per-recruit analysis lend further credence to this assertion. The distribution of juveniles and ovigerous females in the samples show that there is one reproduction peak in August and one recruitment peak from September to November. We back-projected our length–frequency data set on to an arbitrary one-year scale. The results also show that there is one recruitment in a year.

Life history of the red porgy Pagrus pagrus (Teleostei: Sparidae) off the Canary Islands, central east Atlantic

Red porgy Pagrus pagrus ( N = 1858) caught off the Canary Islands between May 1985 and April 1986 and between January 1991 and September 1993 were studied. Total length was in the range 4.7–57.2 cm. Females predominated at the smaller sizes and males at the larger sizes. Protogynous hermaphroditism was found. The overall ratio of males to females was 1:3.29. The reproductive period extended from December to May, with most gonadal activity between February and March. Fifty per cent maturity was reached at 22.6 cm total length by females and 26.7 cm by males. The length-weight relationship for all fish was described by the following parameters: a = 0.017947, b = 2.9583. Fish aged 0–14 years old were present in the samples. The von Bertalanffy growth parameters for all fish were L ∞ = 63.96 cm, and k = 0.144 year −1. Mortality rates for all fish, estimated from a length-converted catch curve, were Z = 0.56 year −1, F = 0.24 year −1 with M = 0.32 year −1 derived from Pauly's empirical formula. The exploitation rate was E = 0.43. Total length at first capture was 15.2 cm.

Zebra Mussel,Dreissena polymorpha: Population Dynamics and Notes on Control Strategies in a Reservoir in Western Greece

ABSTRACT Growth, mortality and yield were investigated in the zebra mussel, Dreissena polymorpha (PALLAS) from the Kastraki artificial reservoir, Central Greece. Allometric relationships were defined using shell length and total wet weight of the sampled individuals. The parameters of die Gompertz, von Bertalanffy and logistic growth curves (both length and weight) were estimated and gave L∞ = 4.05 cm, K = 0.808 per year, length-at-birth = 39 μg and weight-at-birth = 19 μm. The length-frequency distribution showed 5 distinct modes from which the last 2 (IV and V) are considered the same due to high similarity and therefore, die longevity of the species (tλ) is about 4 years. The natural mortality (M) is considered equal to die total mortality (Z) because die population is commercially unexploited and thus, fishing mortality is 0. The Z was estimated to be about 2.15 according to both die Wetherall method and the length converted catch curve analysis. Control strategies of this population include either th...

Comparison of age-structured and length-converted catch curves of brown trout Salmo trutta in two French rivers

Age-structured catch curves (ACC) and two different types of length-converted catch curves (LCC), covering the same size/age range of trout Salmo trutta (Pisces: Salmonidae) in two French rivers, were used to estimate total mortality ( Z). It is shown that standard LCC overestimate Z when ACC are used as controls, while LCC explicitly considering seasonal growth oscillations produce unbiased estimates. The implications of this finding for length-based fish stock assessment are discussed.

Population biology and stock assessment of Pristipomoides filamentosus on the Mahe Plateau, Seychelles

The population of P. filamentosus around the periphery of the Mahe Plateau was studied using data derived from commercial handline fishing operations between November 1989 and December 1990. Sex ratio was close to one. Fork length was in the range 25.6–79.8 cm: at first sexual maturity, 36–38 cm for females and 40–42 cm for males. Spawning occurred from October to April peaking between February and April and in November. The length (f.l., cm)–weight (kg) relationship was W=0.00005353 ×f.l.2.7004. The von Bertalanffy growth parameters, estimated from length frequency data, were K=0.2875 and Linf=81.7 cm. Mortality rates, estimated from length converted catch curve analysis, were Z=0.811, F=0.277 with M=0.534 derived from Pauly's empirical formula. Jones' length cohort analysis gave an estimate of F= 0.294 for the fully exploited part of the stock, and a density of 2.59 t km−2 for the periphery of the plateau from 75 to 150 m depth. The Lesley constant catchability model, applied to the results of intensive fishing around isolated banks, derived a mean density estimate of 2.99t km−2. The sustainable yield was estimated to be 233–268 tonnes per annum and the catch in 1990 was 200 tonnes.

Population biology and stock assessment of Pristipomoides filamentosus on the Mahe Plateau, Seychelles

The population of P. filamentosus around the periphery of the Mahe Plateau was studied using data derived from commercial handline fishing operations between November 1989 and December 1990. Sex ratio was close to one. Fork length was in the range 25.6–79.8 cm: at first sexual maturity, 36–38 cm for females and 40–42 cm for males. Spawning occurred from October to April peaking between February and April and in November.The length (f.l., cm)–weight (kg) relationship was W=0.00005353 ×f.l.2.7004. The von Bertalanffy growth parameters, estimated from length frequency data, were K=0.2875 and Linf=81.7 cm. Mortality rates, estimated from length converted catch curve analysis, were Z=0.811, F=0.277 with M=0.534 derived from Pauly's empirical formula. Jones' length cohort analysis gave an estimate of F= 0.294 for the fully exploited part of the stock, and a density of 2.59 t km−2 for the periphery of the plateau from 75 to 150 m depth. The Lesley constant catchability model, applied to the results of intensive fishing around isolated banks, derived a mean density estimate of 2.99t km−2. The sustainable yield was estimated to be 233–268 tonnes per annum and the catch in 1990 was 200 tonnes.

Some aspects of the biology of the red bass, Lutjanus bohar (Forsskal), from the Tigak Islands, Papua New Guinea

The growth rate, food, reproduction and mortality rates of the red bass, Lutjanus bohar, are described for fish associated with coral reefs in the Tigak Islands of Papua New Guinea. Spawning intensity by month was investigated by examination of gonad maturation stages. The length–at–maturity of female L. bohar was estimated from the relationship between changes in gonad index with increasing size. Female fish matured at about 45–0 cm fork length. The Petersen method was used to obtain age–at–length data from length frequency data of L. bohar captured by hook–and–line fishing. The growth of L. bohar was described by a von Bertalanffy growth curve with the parameters AT=0.27 and L∞= 81.7 cm. There was a positive correlation between water depth (D) and the length of L. bohar (L) that was described by L= 318–8+ 3.050 D. The mortality rates (Z) of L. bohar from shallow (≤30m) and deep (≤80m) water were estimated from length converted catch curves and were 1–181 and 0–64 respectively. The high Z value for the shallow water population of L. bohar was ascribed to the migration of larger specimens into deeper water. The deep water population of L. bohar remains unfished and the estimate of Z was believed to be equivalent to the natural mortality rate (M). An empirical method of calculating M gave an estimate of 0.59. Lutjanus bohar is a carnivorous piscivore that feeds throughout the water column.

Growth, reproduction and mortality of the sea hare Dolabella auricularia (Gastropoda: Aplysiidae) in the Central Visayas, Philippines

The growth parameters W∞ and K of the von Bertalanffy growth equation were estimated from size-frequency data of the sea hare Dolabella auricularia using an objective, computer-based method. The results obtained from two locations in the central Philippines were comparable, although based on only a few individuals; the means for both sites were W∞=493 g and K=0.9 (yearly basis). A value of Z=3.66, corresponding to an annual survival rate of 2.6%, was estimated for the juveniles and adults from a length-converted catch curve. Spawning and recruitment were found to occur throughout the year with peaks in May to July and September to October.

Growth and mortality of sleeper fish, Bostrychus africanus from upper new Calabar river, Rivers state, Nigeria

Bostrychus africanus samples were collected over a period of twenty months (January 2015 to August 2016) from the Upper New Calabar River. This was aimed at ascertaining the present state of the stock following increased exploitation Analyses were run using the FISAT package. Growth estimates by the Von Bertalanffy equation showed that mean length infinity was 19.69.±1.5795cm,, growth coefficient (parameter of curvature (K) was 1.37±0.9595cm/year,, tmax value obtained was 2.3±0.94295 years,. Recruitment analysis showed that the mean relative yield per recruit was 0.063±0.007 and biomass per recruit as 0.45±0.134. Exploitation rate was 0.395±0.088, while mortality estimates calculated by length converted catch curves and Pauly’s equation showed that total mortality was 4.01±2.84, natural mortality 2.25±1.21 and mean fishing mortality was 1.75±1.64. Exploitation was found to be inadequate, judging from the values of the natural and fishing mortalities. This was corroborated by the figures obtained for the prevailing exploitation rate.Key Words: Growth, mortality, population, recruitment, exploitation, sleeper fish