Length-converted Catch Curve Research Articles

Length-weight relationship, growth and mortality ofAnadara granosain Penang Island, Malaysia: an approach using length-frequency data sets

Length-weight relationship, growth parameters and mortality rates ofAnadara granosain the intertidal zone of Balik Pulau, Penang Island, West Coast of Malaysia were investigated based on monthly length-frequency data (December 2011 to November 2012). A total of 548 individuals ranging from 11.25 to 33.13 mm size were subjected to analysis. Logarithmic relationship between the length and weight was LogW = 2.328LogL − 2.537 (R2 = 0.922) for combined sexes. From this equation it was clear that the exponent ‘b’ value forA. granosashowed a negative allometric growth (b < 3). A von Bertalanffy growth function with an asymptotic length (L∞) of 35.40 mm and a growth constant (K) of 1.1 year−1was established from length frequency distributions. Thet0(−0.140) was estimated by substituting theL∞andKin the Pauly's equation. The sizes attained byA. granosawere 10.13, 14.36, 17.89, 20.82, 23.56 and 25.29 mm at the end of 2, 4, 6, 8, 10 and 12 months, respectively. The estimated growth performance index (Ø) was 3.13 while the estimated lifespan of the cockles was about 2.72 years at the study area. The estimated value of total mortality based on length-converted catch curve wasZ = 3.02 year−1. The natural mortality (M) and fishing mortality (F) rates were 1.84 and 0.48 year−1, respectively. The exploitation level (E) ofA. granosawas 0.20, which indicated slight fishing pressure on the stock.

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.

Total and natural mortality of red king crab (Paralithodes camtschaticus) in Norwegian waters: catch–curve analysis and indirect estimation methods

Abstract The red king crab (Paralithodes camtschaticus) is native to the Bering Sea, but was deliberately introduced to the Barents Sea during the 1960s. Since then, the red king crab has spread to Norwegian waters, and crab densities have increased sufficiently to support a coastal fishery. Information about total and natural mortality, which is important to ensure adequate management, is lacking. Estimates of annual total mortality (Z) were calculated using length-converted catch curves in three periods of different levels of exploitation. Separate analyses were run on trap and trawl data as well as on original and catch per unit effort-corrected data. Natural mortality was estimated using a linear regression of total mortality and exploitation level and by using indirect methods based on life history parameters. There was a significant increase in Z throughout the consecutive periods in both sexes. In males, the increase coincided with the increase in exploitation level. The increase in female mortality, which was not explained by exploitation level, is probably an effect of the increase in male mortality. Natural mortality (M), estimated using indirect methods, averaged 0.23 for both sexes. The estimated M using linear regression was 0.37/0.44, which may be an overestimate.

Growth and mortality of two small fishes, Toxabramis swinhonis Günther, 1873 and Hyporhamphus intermedius (Cantor, 1842), in a Yangtze shallow lake (China) assessed by length frequency analysis

This study examined the growth and mortality of two widespread small fish species, Toxabramis swinhonis (Cyprinidae) and Hyporhamphus intermedius (Hemiramphidae), from a shallow lake (Niushan Lake, China) along the Yangtze River, by analyzing monthly length frequency data (July 2005 to June 2006) with the FAO-ICLARM stock assessment tool (FiSAT). Estimated von Bertalanffy growth equation parameters were: L (asymptotic length)=145mm TL, and K (growth coefficient)=0.66year(-1) for T.swinhonis; L=189mm TL, and K=0.68year(-1) for H.intermedius. The instantaneous rates of natural mortality (M) calculated for T.swinhonis and H.intermedius were 1.35 and 1.28year(-1), respectively. The length-converted catch curve method gave the total annual instantaneous mortality rate (Z) of 2.92year(-1) for T.swinhonis and 1.53year(-1) for H.intermedius. Recruitment patterns of both species were continuous, displaying a single major peak event per year. Despite not being of direct fishing interest, T.swinhonis, with high abundance and productivity as indicated by a high Z-value, can be an important species in fisheries management as an excellent food source for aquatic organisms, especially for larger fishes of economic value. These results represent the first information on population characteristics of T.swinhonis and H.intermedius, and constitute a comparison base for future growth studies in other lake environments.

Dinámica poblacional de <i>Donax denticulatus</i> (Bivalvia: Donacidae) en playa Carenero, costa sur oriental de Cuba

Bivalve molluscs of Donax genus are a very important component of macro-invertebrate assemblages of sandy beaches, and some species are of commercial value in different countries. Although in Cuba Donax denticulatus is not a currently exploited species, the information concerning a stock assessment is a basic step for future use of this resource. With the aim to generate new data on this species structure, growth and secondary production, monthly samples of D. denticulatus were taken from a beach of the Southeastern coast of Cuba, from February to December 2008. Samples were taken from four stations located along the beach; three strata were marked (P1, P2 and P3) per station across the intertidal zone. Three replicated samples of sediments were taken from each stratum with a 0.025 m2 PVC core and were posteriorly sieved with a 1 mm mesh. Histograms of shell length were constructed based on 1 mm intervals and growth parameters were estimated using ELEFAN I routine of FISAT. Mean density ranged from 146.67-855.55 ind./m2 and no differences were found among months (ANOVA, p > 0.05) but among strata (Scheffé, p < 0.05). An association of recruits, young and adults abundances with the strata (chi2, p < 0.01) was found. Most of the recruits were found in the upper strata while young and adult individuals were abundant in the mid-lower strata. Size frequency histograms of this population showed recruitment between March-June. Growth parameters estimated by Von Bertalanffy were Linfinity = 27.5 mm and K = 1.5/year; and the life spam was estimated in 1.5 years. Using the length-converted catch curve, the mortality rate (Z) was estimated in 4.97/year. Based in terms of Ash free dry mass (AFDM), mean biomass was estimated in 0.47 g/m2.year and the somatic production in 12.4 g/m2.year. The renewal rate (P/B) estimated for this population was 26.38, the highest among other Donax populations. High densities, fast growth and high somatic production indicate that this population can be exploited for fishing purposes for which some management measures are proposed.

Length Frequency Distribution, Mortality Rate and Reproductive Biology of Kawakawa (Euthynnus affinis-Cantor, 1849) in the Coastal Waters of Tanzania

This study explored important aspect of the basis for the highly complex population of kawakawa (Euthynnus affinis) within the coastal waters of Tanzania; by investigating length frequency distribution, mortality rate and reproductive characteristics. This information is essential for the sustainable management of the regionally-important recreational and economic E. affinis fishery. Fish were sampled on a monthly basis for two monsoon seasons using a ring net and artisanal fishermen boat. Maximum and minimum total length was 85 and 31 cm, respectively. Nonlinear least square fitting provided a complete set of von Bertalanffy growth estimates: L8 = 89.25 cm total length and K = 0.78. The estimated value of total mortality based on length converted catch curve using these growth parameters is Z = 1.78 year(-1). Natural mortality based on growth parameters and mean environmental temperature (T = 26.9 degrees C) is M = 1.09 year(-1). The estimated annual instantaneous fishing mortality (F = 0.69 year(-1)) was considerably grater than the target (Fopt = 0.43 year(-1)) and limit (Flimit = 0.58 year(-1)) biological reference point indicating that E. affinis is heavily overexploited. Reproductive aspects were assessed whereby female E. affinis was reported to reach maturity earlier than males which is an indication of phenotypic response toward a decline in population. Two peaks was revealed by the use of Gonad-Somatic Index (GSI), however an extended spawning period was noticed in a period between November to February following an increased water temperature. Although, these findings presents a snapshot concerning population structure and reproduction of E. affinis, further studies covering the entire coastal waters of Tanzania are recommended to aid the management and conservation strategies.

Crecimiento y mortalidad de la madreperla &lt;i&gt;Pinctada mazatlanica&lt;/i&gt; en poblaciones naturales del litoral oriental de Baja California Sur, México

The Mexican Pacific mother-of-pearl Pinctada mazatlanica was placed in forbidden fisheries status for the Mexican Federal Government and considered in extinction danger since 1939. This decree was modified in 1994 to allow the capture of spat for research or marine culture. We estimated the growth and mortality of mother-of-pearl from the eastern littoral of South Baja California wild stock in the periods 1992-93 and 1997-99. We used 38 sample stations at 2 bays and 6 insular complexes. The maximum length was 187.22 mm (179.83-195.81 mm, P > 0.95). Seasonal von Bertalanffy growth (ELEFAN I routine) values are: L(infinity) = 193.31 mm, k = 0.54 year(-1), t(0) = -0.1805 year, C = 0.49 and WP = 0.75. The growth performance index was Phi' = 4.305. The total mortality was calculated from a length-converted catch curve Z = 2.03 año(-1). Length-weight relationship W(i) = 0.0005418 * L(i)(2.7301). The growth parameters were similar to those for Pinctada margaritifera var. cumingi (open ocean wild stocks). The wild stock oysters differ from culture individuals at experimental repopulation conditions in Paz Bay. The total mortality is similar to that for Pinctada radiata in the Red Sea.

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.

How does seasonal variability in growth, recruitment, and mortality affect the performance of length-based mortality and asymptotic length estimates in aquatic resources?

Abstract Hufnagl, M., Huebert, K. B., and Temming, A. 2013. How does seasonal variability in growth, recruitment, and mortality affect the performance of length-based mortality and asymptotic length estimates in aquatic resources? – ICES Journal of Marine Science, 70: 329–341. We tested the sensitivity of eight methods for estimating total mortality from size frequencies (modified Wetherall; Powell; Beverton and Holt; Jones and van Zalinge; Hoenig; Ssentongo and Larkin; seasonal and non-seasonal Length Converted Catch Curve) to violations of basic assumptions, such as seasonal growth, mortality, recruitment and variable asymptotic length L∞ or growth parameter K. For each method, bias was estimated by simulating length frequency distributions with different combinations of known L∞, Z and K values, calculating θ (Z/K) and L∞ estimates, and comparing the true input with the estimated output values. Input mortality was generally underestimated by all methods and in 27% of all simulations no method provided estimates within θ ± 1. Spring recruitment especially negatively influenced the mortality estimate. A decision tree was developed that provides general guidance in selecting appropriate methods despite violated assumptions, but species-specific case studies are recommended. An example of a species-specific study is provided for the brown shrimp, Crangon crangon. Despite inherent limitations for all methods, the results illustrate that estimates of θ and Z for brown shrimp can be improved substantially by selecting suitable methods and correcting for observed bias.

Population dynamics of Niger River prawn (Macrobrachium felicinum) in Lower Taylor Creek, Niger Delta, Nigeria

The population dynamics of Macrobrachium felicinum (Holthuis, 1949) in Lower Taylor Creek, Niger Delta, Nigeria, was analysed using monthly length-frequency data (June 2008 – May 2010). This study was aimed at determining the status of fishery and establishing the levels of exploitation that will give sustainable yields. The FAO-ICLARM stock assessment tool (FISAT II) software was used to estimate population parameters. The growth parameters obtained from the seasonalised Von Bertalanffy growth function were L∞ = 10.24 cm total length, K/year = 1.40, C = 0.85; and WP = 0.79 (September). Using a length-converted catch curve, total mortality (Z) was estimated at 9.50/year, natural mortality (M) at 3.04/year, while fishing mortality (F) was estimated at 6.46/year. From the probability of capture estimation, the length-at-first capture (Lc ) for M. felicinum was 4.55 cm. One major recruitment peak per year was established for M. felicinum, while the relative yield-per-recruit analysis predicted the maximum ex...

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.

Population biology and stock status of planktonic shrimp Acetes indicus (Decapoda: Sergestidae) in the coastal waters of Malacca, Peninsular Malaysia

Reproductive cycle, growth, mortality and exploitation rate of Acetes indicus were examined in the coastal waters of Malacca, Malaysia between February 2005 and March 2007. Monthly length frequency data were analyzed using FiSAT software for estimating population parameters of A. indicus, including asymptotic length (L∝), growth co-efficient (K) and exploitation rate (E) to assess the status of the stock. The annual mean L∝ and K for males were estimated at 29.93 mm and 1.60 yr−1, and for the females were 40.95 mm and 1.20 yr−1. Mean growth performance index (φ′) was calculated as 3.15 and 3.31 for males and females, respectively. Maximum life span (tmax) of males and females was 1.88 and 2.50 years. Total mortality (Z) by length converted catch curve was estimated at 4.30 yr−1 for males and 3.62 yr−1 for females. The rate of natural mortality (M) for males and females was calculated as 2.54 yr−1 and 1.93 yr−1, and the fishing mortality (F) was 1.77 yr−1 for males and 1.70 yr−1 for females. Recruitment pattern of A. indicus was continuous throughout the year with two major peaks. The exploitation rate (E) of males was 0.41 and that of females was 0.47, though the exploitation rates were slightly less than the optimum level of exploitation (E = 0.50). Thus, the stock of A. indicus is under pressure in the coastal waters of Malacca, Malaysia.

Growth and mortality of the exploited mangrove crab Ucides cordatus (Ucididae) in N-Brazil

Reliable estimates of growth and mortality parameters are crucial for understanding how populations of exploited species may respond to shifts in fishing pressure. Results of previous studies on growth of the ecologically and economically important mangrove crab Ucides cordatus in Brazil differ strongly and age estimates for minimum legal capture size (60 mm carapace width) range between less than 1 and 6–10 years. These discrepancies are probably due to inherent problems of the applied methods, namely laboratory based observations and cohort-analyses. The present paper takes a new approach by measuring individual growth increments of U. cordatus in situ. Crabs were measured, tagged, released into 100 m² field enclosures and periodically recaptured. There was no indication of an enclosure effect and 209 growth increments were obtained from specimens measuring 20.5 to 89.5 mm in carapace width (CW). For improving the size coverage of the von Bertalanffy growth curve, first instar juveniles were reared in the laboratory up to an age of six months. Their average percent size increase (PI) was 22.57 ± 6.75% during biweekly measurements, resulting in a CW of 7.8 to 11.5 mm after six months. Average PI of the enclosure crabs ranged between 10.87 ± 1.17% (indiv. < 40 mm CW) and 1.43 ± 0.87% (indiv. > 80 mm CW) per moult and two large females had moulted without growing. Growth analysis revealed a larger asymptotic size in males than in females (89 mm versus 72 mm) while the growth parameter K of the von Bertalanffy growth function (VBGF) was lower in males (0.17 versus 0.25), resulting in similar growth performance of the two sexes (males: 1.16; females: 1.10). Age at legal minimum capture size estimated by the inversed VBGF was 6.13 years in males and 7.38 years in females, corroborating the mid to upper range of earlier growth estimates. Mortality parameters (Z, M and F) were calculated using length converted catch curves. Z in males was higher than in females (0.69 versus 0.49), as expected from the male-biased fishery. M, F and the exploitation rate E were estimated for three different scenarios taking into account the uncertainty of the age/size of functional maturity. Our study provides key information for the sustainable management of the U. cordatus fishery and confirms that the species is relatively slow growing and long-lived (> 10 years), suggesting a high vulnerability to overfishing.

Population dynamics of &lt;i&gt;Gerres abbreviatus&lt;/i&gt; Bleeker, 1850 from the Parangipettai waters, Southeast coast of India

The population dynamics of Gerres abbreviatus from the Parangipettai waters, Southeast coast of India was investigated based on length frequency data, using FiSAT software. Growth parameters of G. abbreviatus were estimated using ELEFAN I method. The theoretical ages at length zero (t 0 ) were estimated by substituting the asymptotic length (L ∞ ) and growth coefficient (K) in Pauly's equation. The fitted von Bertalnaffy's growth equations for male and female G. abbreviatus were L t =27.8 [1 - exp {-1.30(t+0.1236)}] and L t =28.2 [1-exp {-1.36 (t+ 0.1175)}] where L ∞ values are in cm, K values are on annual basis and t 0 values are in years. The estimated growth performance index (O) for male and female G. abbreviatus were 3.002 and 3.034 respectively while the estimated life spans of male and female G. abbreviatus were 2.18 and 2.08 years. Instantaneous rates of total mortality (Z) estimated by length converted catch curve for male and female G. abbreviatus were 3.06 and 2.99 yr -1 respectively. Natural mortality (M) estimated by Pauly's empirical equation for male and female G. abbreviatus were 2.24 and 2.29 yr -1 and the estimated fishing mortality for male and female G. abbreviatus were 0.82 and 0.70 yr -1 respectively. Relative yield per recruit analysis incorporating probabilities of capture indicates that G. abbreviatus in the Parangipettai waters is exploited below the optimum level indicating scope for increase in fishing efforts without leading to overexploitation. DOI: 10.4038/sljas.v11i0.2219 Sri Lanka J. Aquat. Sci. 11 (2006): 1-19

Population Dynamics of a Whip Fin Silverbiddy Gerres filamentosus Cuvier, 1829 from the Parangipettai Waters, Southeast Coast of India

The present study was undertaken to get information on the maximum size, age and growth parameters and mortality of Gerres filamentosus. The length frequency data were grouped sex wise into 1 cm class intervals, sequentially arranged for two years and used for estimation of growth and mortality. L∞ and K values were obtained by electronic length frequency analysis of computer based method. Value of ‘t0’ (age at ‘0’ length) was estimated by substituting the L∞ and K in the Pauly’s empirical equation. Natural mortality was estimated using Pauly’s method. Fishing mortality rate (F) was calculated from the F = Z – M relationship. The asymptotic length (L∞) and growth coefficient (K) were found to be 26.9 cm and 1.45•year -1 , respectively in males, and 27.11 cm and 1.50•year -1 in females. The ‘t0’ values estimated by substituting the L∞ and K in Pauly’s equation were 0.1109 in males and -0.1073 in females. Instantaneous rates of mortality (Z) estimated by length converted catch curve for male and female were 3.14 and 3.27. Natural mortality (M) estimated by Pauly’s empirical equation for male and female were 2.41 and 2.47 and the estimated fishing mortality for male and female were 0.73 and 0.80, respectively. The computed current exploitation ratios (E) were 0.23 and 0.24. It is concluded that because computed current exploitation rates (E) are lower than the predicted E, the stock is not overexploited and the fishing pressure on the stock is not excessive. As the G. filamento

Breeding seasonality and population dynamics of the catfish Schilbe mystus (Schilbeidae) in the Cross River, Nigeria

Twelve consecutive months length frequency data (N = 6999) and FiSAT software were used in the study of the dynamics of exploited population the catfish Schilbe mystus in the Cross River Nigeria. Variation in monthly mean gonadosmtic index showed two peaks, March and September and this indicates that the species spawned twice in a year. Fitting the seasonalized von Bertalantffy growth function to our length frequency data gave the following growth parameters: L&infin; = 38 cm, k = 0.33 y-1, C = 0.42 and WP = 0.96. The seasonalized length converted catch curve procedure gave the instantaneous total mortality coefficient Z = 2.97 y-1, the instantaneous natural mortality coefficient M = 0.81 Y-1, the instantaneous fishing mortality coefficient F = 2.16 y-1 and the current exploitation rate E = 0.73. This high value of E points to the high fishing pressure on the stock. The analysis of probability of capture of each length class showed that the length at first capture Lc 28.67cm. The predicted maximum exploitation rate of Emax = 0.59. This stock was deemed overexploited because E>Emax. Relative yield isopleths were used to demonstrate the response of relative yield per recruit of the fish to variation Lc and E. Suitable management procedure must be instituted to avoid the collapse of the fishery.Keywords: Breeding, population dynamics, Schilbe mystus Cross River estuary.

Estimating total mortality and asymptotic length of Crangon crangon between 1955 and 2006

Abstract Hufnagl, M., Temming, A., Siegel, V., Tulp, I., and Bolle, L. 2010. Estimating total mortality and asymptotic length of Crangon crangon between 1955 and 2006. – ICES Journal of Marine Science, 67: 875–884. Total mortality (Z, year−1) of southern North Sea brown shrimp (Crangon crangon) was determined as Z = θK, based on the von Bertalanffy length–growth constant (K, year−1) and θ derived from length-based methods. Mortality estimates were based on length frequency distributions obtained from four long-term dataseries (1955–2006): German Demersal Young Fish Survey, Dutch Demersal Fish Survey, and two German Bycatch series (Büsum and East Frisia). Four methods to estimate θ and L∞ were evaluated. Highest total mortality (Z = 8 year−1) was estimated for the early 1990s, and the lowest (Z = 4 year−1) for the 1960s. Accounting for these differences, a median Z rather than mean values was calculated for the whole series, and the value ranged from 5.74 (Ssentongo and Larkin method), through 5.65 (Beverton and Holt method) and 5.64 (Jones and Zalinge method), to 5.35 (length-converted catch curves). Over the whole period, an increase in θ and a decrease in the proportion of shrimps &gt;60 mm in the catch was observed, whereas asymptotic length L∞ remained constant (at 79.3 mm total length).

Artisanal Fishery of the Exploited Population of Macrobrachium vollenhovenii Herklot 1857 (Crustacea; Palaemonidae) in the Asu River, Southeast Nigeria

River prawn in Nigeria sustains viable commercial fisheries, which, however, are poorly studied. In this study we evaluated the migrant prawn fishery in the Asu River and the relevance of length-frequency data to the estimation of Macrobrachium vollenhovenii population dynamics using the data collected monthly from January 2007 to December 2008. The length-frequency data were analysed using the FAO-ICLARM stock assessment tool. Over 80% of captured prawns were M. vollenhovenii with peak catches attained in July. Growth parameters of L∞ = 23.65 cm, K = 1.14 year-1 and (t0) = -1.45, were estimated. The estimated longevity of 2.10 years and the growth performance index (Φ') of 2.80 compared favourably with the available information on the species, authenticating reliability of our results. The instantaneous rate of total mortality estimated from the length-converted catch curve was 6.47 years-1. Natural and fishing mortality were 2.14 years-1 and 4.33 years-1 respectively, which yielded the exploitation rate...

Population dynamics of the African river prawn, Macrobrachium vollenhovenii, in Dawhenya Impoundment

Studies were conducted on the growth and mortality parameters, recruitment pattern, probability of capture, yield-per recruit, and present rate of exploitation of the African river prawn, Macrobrachium vollenhovenii from Dawhenya impoundment, Ghana. Estimation of the von Bertalanffy growth parameters gave; L∞ = 14.2 cm, K = 1.0 yr -1 , and to = -0.195 yr -1 with the growth performance index, Ф' of 2.303. From the linearised length-converted catch curve, total mortality, Z was 5.36 yr -1 . Natural mortality, M calculated from Pauly’s empirical formula was 2.20 yr -1 and fishing mortality, F calculated from Z - M was 3.16 yr -1 . From the mortality estimations, the present rate of exploitation, E calculated from F/Z was 0.59 indicating that, the species is on the verge of being over-exploited in the impoundment. Using the estimated value of the growth coefficient, K, the longevity was found to be about 3 yrs. Estimations from the probability of capture routines gave the length-at-first capture, Lc as 3.07 cm while the size distribution of the catches suggest two recruitment pulses in a year. It is therefore recommended that, the property right-based system for fisheries management should be implemented so that fishermen can cooperate in the management of the Macrobrachium fishery.

Vital population statistics based on length frequency analysis of the exploited Japanese eel (Anguilla japonica) stock in the Kao-Ping River, southern Taiwan

Summary Vital statistics such as growth, mortality, and maturity parameters are crucial in understanding the population dynamics of a species. A total of 7 074 Japanese eels (Anguilla japonica) in the lower reach of the Kao-Ping River, southern Taiwan, were collected with eel tubes in 1998 ∼ 2004 and shrimp nets in 2004 ∼ 2007. Data from 2004 were excluded due to mixed gear information and escapement of cultured eels; in subsequent years escaped cultured eels were identified and excluded from analyses. The estimated asymptotic length in the von Bertalanffy growth function (84.5–110 cm) was smaller, while the Brody growth parameter (0.30–0.44 year−1) was higher using electronic length frequency analysis (ELEFAN) than when using Shepherd’s length composition analysis (SLCA). The total instantaneous mortality rate (Z) was around 1 for periods 1998–2003 and 2 year−1 for 2005–2007 using length-converted catch curves. The 95% confidence intervals of Z did not overlap for two of the periods, suggesting that the mortality rates were significantly higher during 2005–2007, possibly due to the introduction of shrimp nets. The maturity function differed significantly between sexes, indicating that females become silver eels at a larger size. The Japanese eels in the lower reach of the Kao-Ping River were likely heavily exploited, thus management and conservation actions are strongly recommended.