Length Frequency Data Research Articles

Length based spawning potential ratio of indian scad (Decapterus russeli, Rupell, 1928) in the South China Sea

Spawning Potential Ratio (SPR) could be used to investigate stock indicators in terms of data-limited fisheries assessment. This study was aimed to assess the Length-based SPR of Indian scad (Decapterus russelli) in South China Sea. The length-frequency data were collected from 2015 to 2019, with approximately 250 fish sampled monthly. Fish samples were obtained from the catch of purse seiner which landed at Pemangkat fishing port. LB-SPR model required length-frequency and life history parameters i.e growth and maturity. The parameters L∞ K, M, L50, and L95 were 23.92 cm, 0.60 year-1, 1.00, 15.80, and 22.00 respectively. The estimated LB-SPR from static life-history parameters was 41%, while the stochastic SPR about 22% with a wide confidence interval, due to uncertainty of L∞ and K. According to the LB-SPR model considering the uncertainty, the estimated stochastic SPR is more acceptable in the condition of poor data. Besides, the high fishing pressure (F/M>1) indicated that SPR was lower than the target reference point (40%). However, in terms of the length at first capture (SL50) was greater than a length at first maturity (L50), it should be a consideration to estimate the SPR. Therefore, SPR was determined by 20%-40% or stock status on fully-exploited.

Stock Assessment of Lates niloticus in Upper Victoria Nile and its Impact on Uganda’s Economy

This study investigated the growth, mortality, recruitment, and catch estimates of Nile perch, Lates niloticus (Linnaeus, 1758), in Upper Victoria Nile, basing on total catches and length-frequency data collected between 2008 and 2018. The asymptotic length (L∞) had a value of 93.45 cm TL, growth curvature (K) was 0.446 year-1, total mortality (Z) was 1.85year-1, natural mortality (M) was 0.79 year-1, fishing mortality (F) was 1.09 year-1, exploitation rate (E) was 0.59 and growth performance index(ᴓ) of (L∞) was 3.604. There were two peaks recruitment period, a minor one in March and a major one in August. These respectively accounted for 12.8 and 26.3 percent of the total catch. The optimum sustainable yield (E0.5), maximum sustainable yield (Emax) and, economic yield (E0.1) was 0.278, 0.421 and 0.355 respectively. The findings suggest that there is a decline in the population of Lates niloticus in Upper Victoria Nile. Therefore, strict management of the fishery by adhering to the recommended slot size of 50-85 cm TL and curtailing use of illegal gears is needed. This will be possible through enforcement of regulations, monitoring, control and surveillance in order to ensure sustainability of the Nile perch fishery and ecosystem restoration in the Upper VictoriaNile.Keywords: Lates niloticus; Catch rates; Growth parameters, Upper Victoria Nile.

Data-limited stock assessment of two horse mackerel species (Trachurus mediterraneus and T. trachurus) from the Mediterranean coast of Turkey

A preliminary assessment of stock size and status of Trachurus mediterraneus and T. trachurus species were investigated via virtual population and yield prediction analyses using onboard collected length-frequency data from Northeastern Mediterranean. The length-frequency based VBGF parameters and growth performance index were L∞=28 cm, k=0.62, t0=0.58, tanc=0.52 and Φ′=2.69 for T. mediterraneus and L∞=27.46 cm, k=0.54, t0=0.49, tanc=0.41 and Φ′=2.61 for T. trachurus. Trawl-type selectivity and maturity ogives were 16.73 and 19.2 cm TL for T. mediterraneus, and 17.59 and 19.8 cm TL for T. trachurus, respectively. The virtual population analysis of T. mediterraneus resulted that the minimum and maximum fishing mortalities were 0.02 and 1.09 yr −1 for the mid-length groups for 10.5 and 24.5 cm, respectively. The minimum and maximum fishing mortality of T. trachurus were 0.0 and 0.89 yr −1 at the size of 25.5 and 27.5 cm, respectively. Biological reference points of T. mediterraneus point out that the current fishing mortality (FCurr=1.62) is lower than the fishing mortality of FMSY, and the current exploitation rate (ECurr=0.63) is lower than the reference point target benchmarks E0.5 and EMSY, showing underexploited status. The current fishing mortality (FCurr=0.76) in T. trachurus was observed to be lower than the fishing mortality for the MSY (FMSY), and the current exploitation rate (ECurr=0.46) was lower than E0.5 and EMSY, indicating currently underemployed status.

Growth, Mortality and Exploitation Rates of African Moonfish (Selene dorsalis, Gill 1863) Encountered in the Coast of Ghana (West Africa)

Growth, mortality and exploitation rate of Selene dorsalis (Gill, 1863) from the continental shelf of Ghana (West Africa) were examined between July 2018 and June 2019. The study provided results on fishery dynamics parameters needed to estimate the stock status and characteristics of S. dorsalis in the coast of Ghana. Monthly length-frequency data were collected from 629 samples and analysed using fisheries models fitted in TropFishR package in R software. The von Bertalanffy growth parameters were utilised to analyse the population dynamics of the species using ELEFAN Simulating Annealing. Based on the estimates, the asymptotic total length (L∞) was 22.2 cm, the coefficient of growth (K) was 0.76 year-1, and the calculated growth performance index (phi) was 2.58 with Rn value of 0.55. The total mortality rate (Z) was 3.32 year-1 with a natural mortality rate (M) of 1.21 year-1 and fishing mortality rate (F) of 2.11 year-1. The exploitation rate (E) estimated for the species was above the optimum level of 0.5, which indicates that S. dorsalis is overexploited in the coast of Ghana. It can be concluded that the exploitation rate of S. dorsalis has exceeded the optimum limit, hence the need for enforcement and improvement of fisheries management measures such as mesh size regulations, capping of canoes, closed fishing seasons and compliance with fisheries policies.

Estimation of Growth Parameter on Sailfin Catfish (Pterygoplichthys pardalis) in Bengawan Solo River, Central Java Province

Bengawan Solo river 548.53 km is the longest river in Java Island Indonesia, which crosses provinces of Central Java and East Java. Bengawan Solo river is heavily polluted by agricultural, industrial and domestic wastes, especially in Surakarta Residence, Central Java. The impacts of pollution in Bengawan Solo river are poor water quality, the population of native fish has declined sharply and some were almost extinct. The fish that develop was Sailfin catfish (Pterygoplichthys pardalis) because these fish were resistant to pollution. The study aimed to determine the growth parameters of Sailfin catfish (P. pardalis) in Bengawan Solo river. Estimation of growth parameter using length frequency data analysis was done using the FISAT program package. The results of growth parameters of Sailfin catfish (P. pardalis) showed that infinity length (L∞) = 41.75 cm; acceleration of growth (K) = 0.48 cm/year. Natural mortality (M) = 1,1; fishing mortality (F) = 2.47; and total mortality (Z) = 3.57. Exploitation rate (E) = 0.69. The conclusion is the fishing mortality of Sailfin catfish is quite high, while natural mortality is low because the fish are resistant to pollution.

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 the anchovy Stolephorus commersonnii (Lacepède,1803) (Clupeiformes) caught off the coast of Tanga, Tanzania

The population dynamics of Stolephorus commersonnii (Lacepède, 1803) from a ringnet fishery operating off the northern coast of Tanga Region were evaluated based on monthly length-frequency data collected from August 2016 to August 2017. The total length (TL) and total weight (TW) of 14,410 individuals ranged from 22 to 130 mm and from 0.39 to 14.64 g respectively. S. commersonnii exhibited a negative allometric growth pattern with the length-weight relationship model: W = 0.00001 x L2.886. The von Bertalanffy growth function was Lt = 86.03 x (1 – e–1.19(t – (–0.01))) using ELEFAN I from the FiSAT II software tool package. Growth performance index and longevity were estimated at (ɸ) = 3.9 and Tmax = 2.5 yrs, respectively. The total (Z), fishing (F) and natural (M) mortalities were determined at 1.39, 0.53 and 0.86 yr-1, respectively. The current exploitation rate (Ecur) was estimated at 0.38. S. commersonnii exhibited a year-round breeding pattern, with two recruitment peaks in March and June/July. Length-at-first-capture (Lc50) and length-at-first-sexual maturity (Lm50) were 40.51 and 57.35 mm TL, respectively, suggesting growth overfishing. The stock of anchovy indicates an overfishing scenario requiring management intervention such as reducing fishing effort levels, increasing mesh sizes and introducing seasonal closures during peak spawning periods.

Growth, Mortality and Exploitation Levels of Sphyraena sphyraena (Pisces: Sphyraenidae) and Apsilus fuscus (Pisces: Lutjanidae) in Ghanaian Waters

Sphyraena sphyraena (Linnaeus, 1758) and Apsilus fuscus (Valenciennes, 1830) are commercially important fish species in Ghana. The stocks are exploited mainly by the artisanal and semi-industrial fisheries. Growth and mortality rates, and exploitation levels of the two stocks in inshore waters of Ghana were assessed as a contribution to fill the knowledge gap on the species. Samples were obtained from three landing sites along the coast of Ghana from February to July, 2017. Length-frequency data were used to estimate growth, mortality and exploitation ratios. The modal class for S. sphyraena was 37.0–39.9 cm total length (TL) and 34.0–35.9 cm TL for A. fuscus. The length and weight relationships established that growth in S. sphyraena was negative allometric, whereas that of A. fuscus was isometric. The estimated growth parameters from the length frequency data fitted with the von Bertalanffy growth function were asymptotic length (L∞) of 69.9 cm TL for S. sphyraena and 53.5 cm TL for A. fuscus. The growth constant (K) was calculated as 1.64 yr-1 for S. sphyraena and 0.50 yr-1 for A. fuscus. The mean length-at-first capture (Lc) was found to be lower than the mean length at sexual maturity (Lm) for both species. The sex ratio showed a dominance of females over males in S. sphyraena, and 1:1 for A. fuscus. The total mortality rate (Z) for S. sphyraena was more than for A. fuscus. The estimated natural mortality (M) was 1.88 yr-1 for S. sphyraena and 0.74 yr-1 for A. fuscus whilst fishing mortality (F) rate was 3.04 yr-1 for S. sphyraena and 0.93 yr-1 for A. fuscus. The exploitation ratio showed that both fish stocks were exploited over the optimum levels. The estimated population parameters of the species obtained from the study, therefore, might be useful for the sustainable management of the stocks.

Stock Assessment for Seven Fish Species Using the LBB Method from the Northeastern Tip of the Bay of Bengal, Bangladesh

Assessment of fish stock status is generally required for fisheries management, which is difficult when the data are limited. The length-based Bayesian Biomass (LBB) approach is a powerful and new method, where only the length-frequency data are used for estimating the status of fisheries resources. Here, we applied the LBB method to assess the status of seven commercially valuable marine fishes from the northern tip of the Bay of Bengal (BoB), Bangladesh. These species were Lepturacanthus savala, Pampus argenteus, Nemipterus japonicas, Nemipterus randalli, Ilisha filigera, Saurida tumbil, and Upeneus sulphurous. The current relative biomass (B/B0) ratios were smaller than the BMSY/B0 in five stocks, except for N. japonicas and N. randalli, and this indicates that, of the seven populations assessed, two are grossly overfished, three are overfished, and two are healthy stocks. Moreover, the length at first capture (Lc) was lower than the optimal length at first capture (Lc_opt) in all seven populations, which indicates growth overfishing, suggesting that increasing the mesh sizes would be beneficial. The present findings confirm that Bangladesh’s coastal water fishery resources are declining. More specific targeted management measures should be taken to recover the country’s marine fishery resources.

Using LBB Tools to Assess Miter Squid Stock in the Northeastern South China Sea

Based on length frequency data of miter squid (Uroteuthis chinensis) collected in the northeastern South China Sea in 1975–1977, 1997–1999, and 2018–2019, asymptotic length, optimal length at first capture, relative mortality, and relative biomass of the stock were estimated using length-based Bayesian biomass estimation (LBB). The LBB-estimated asymptotic length for 2018–2019 was smaller. Optimal lengths at first capture for the later far exceeded average lengths in catches because of a major increase in fishing intensity. Between 1975 and 1977, relative total mortality (Z/K) was low, but it increased in the latter two periods, while relative natural mortality (M/K) showed a downward trend. Relative biomasses (B/B0 and B/Bmsy) indicated that the stock was close to unexploited between 1975 and 1977, but they declined to the levels of 6% and 4% in the later periods, which correspond to growth in fishing horsepower. Indeed, by 2018, fishing horsepower increased by nearly four times the optimal level. The analysis suggests that the stock of miter squid has been overfished since the mid-1980s and is now under heavy fishing pressure. To recover the stock, it is imperative to reduce fishing intensity and enforce size-at-first-capture regulations.

Pulse recruitment and recovery of Cayman Islands Nassau Grouper (Epinephelus striatus) spawning aggregations revealed by in situ length-frequency data

Abstract Fish spawning aggregations (FSAs) are vulnerable to overexploitation, yet quantitative assessments of FSA populations are rare. We document an approach for how to conduct such an assessment, evaluating the response of Critically Endangered Nassau Grouper (Epinephelus striatus) to protections in the Cayman Islands. We assessed pre-protection status on all islands using length data from fishery catch. We then used 17 years of noninvasive length-frequency data, collected via diver-operated laser calipers, to estimate recruitment and spawning biomass of Nassau Grouper on Little Cayman following protection. Bimodal length distributions in 2017–2019 indicated a large recruitment pulse (4–8× average) derived from spawning in 2011. Biomass recovered to 90–106% of the pre-exploitation level after 16 years, largely driven by the strong 2011 year class. Length distributions were also bimodal in 2017–2019 on nearby Cayman Brac, implying a synchronous recruitment pulse occurred on both islands. Our results demonstrate that: (i) in situ length data can be used to monitor protected FSAs; (ii) spatiotemporal FSA closures can be effective, but success takes time if population recovery depends upon sporadic recruitment; and (iii) FSA fishery management targets may need to be higher than commonly recommended (i.e. spawning potential ratio >0.6 instead of 0.4).

Comparison of Electronic Length Frequency Analysis (ELEFAN) for Estimation of Growth Parameters for Lollyfish, Holothuria (Holothuria) atra and Sand Sea Cucumber, Holothuria (Thymiosycia) arenicola (Holothuroidea: Echinodermata) in the North Arabian Sea, Pakistan

To estimate the growth parameters, the non-seasonal von Bertalanffy and Hoenig seasonal von Bertalanffy models were fitted to the length frequency data of Holothuria atra and H. arenicola obtained from coastal areas of Karachi in the northern Arabian Sea, Pakistan between January and December 2014. The Hoenig seasonal von Bertalanffy growth parameters were estimated as L∞=36.1 cm total length (TL), K=0.75 year-1 for H. atra and as L∞=34.9 cm TL, K=0.70 year-1 for H. arenicola. H. atra individuals reached 73.9% of their maximum total length at the one year old. For H. arenicola it was calculated as 72.7%. Monthly mean growth rate of H. atra at the same ages was calculated higher than H. arenicola. The seasonal oscillation in growth rate for H. atra (C=0.50) was larger than it was for H. arenicola (C=0.37). The time of the year when the growth is slowest corresponded to the middle of April (WP=0.30) in H. atra and at the beginning of August (WP=0.60) in H. arenicola may be the result of the extended both reproduction and poor nutrition periods due to monsoonal effects on the marine environment. The relatively high growth rates (K>0.7 year-1) of these two species may have important implications for high survival rate, particularly in environmental condition where cause biological stress and marine confusion but may also increase their potential as a candidate species for aquaculture.

Population dynamics of vermiculated sailfin catfish, <em>Pterygoplichthys disjunctivus</em>, Weber 1991 (Family Loricariidae) in Victoria (Central province) and Kalawewa (North-Central province) reservoirs, Sri Lanka

Introduction of alien invasive species has created adverse impacts on biodiversity in many places in the world. Scientific studies on such populations are important to formulate control measures of invasive species. In this study, population dynamics of invasive P. disjunctivus were studied in Victoria reservoir and Kalawewa reservoir in Sri Lanka. Present study was based on the fish landing sites harvested with 80 mm meshed gill nets in two reservoirs. Fish samples: 2454 from Victoria and 1515 from Kalawewa were studied once a month in two years of duration from January 2015 to December 2017 and standard length (SL) frequency data (LFD) were recorded. LFD were analyzed for fitting von Bertalanffy growth model for growth. An initial estimate of asymptotic standard lengths (L∞) was obtained using Powell- Wetherall method as implemented in the FiSAT II (version 1.2.2) software package. Asymptotic standard length and growth constant (K, yearly basis) were then determined by ELEFAN routine which were consistent with L∞ estimated using Powell-Wetherall method. Total mortality (Z) was calculated using original LFD by the length-converted catch curve method. Natural mortality (M) was estimated. Initial estimate of asymptotic standard lengths (L∞) were Victoria: 33.15 cm and Kalawewa: 35.28 cm. Asymptotic standard length and growth constant (K, yearly basis) estimated by ELEFAN were: 34.13 cm and 34.87 cm in Victoria and Kalawewa reservoirs, respectively. Total mortality (Z) values were reported as 1.22/y in Victoria and 1.32/y in Kalawewa. Estimated natural mortality (M) values were 0.87/y in Vicoria and 0.80/y in Kalawewa. Relative yield-per-recruit analysis and probability of capture with FISAT II software indicated that relative yield-per-recruit was 0.075 and 0.065 in the current exploitation rate in Victoria and Kalawewa reservoirs, respectively. Probabilities of capture of fish for Victoria and Kalawewa were 50% at 16 cm and 50% of 20 cm, respectively. It also revealed that there will be a great potential to optimize the fishery by increasing exploitation ratio from the present levels by increasing length at first capture from the present levels of 16.2 cm to 20.0 cm and 20.1 cm to 21.0 cm for Victoria and Kalawewa reservoirs, respectively. Gill nets can be used to increase harvest potential by increasing fishing effort to control and to produce value added products this species.

Pertumbuhan dan Mortalitas Ikan Endemik Opudi (Telmatherina prognatha Kottelat, 1991) di Danau Matano, Sulawesi Selatan

Lake Matano is an ancient lake that has a high endemicity. Opudi fish (Telmatherina prognatha) is an endemic fish that is vulnerable to extinction and needs to be preserved. The threat of invasive species and habitat degradation can cause a decrease in opudi fish populations. This study aimed to examine the growth parameters associated with growth coefficients and mortality in Lake Matano so that population can be sustainable. The study was conducted at Lake Matano from March 2018 to February 2019. Samples of fish were caught using a net bag measuring 30 m long, 2 m wide with a mesh size of 0.5 inches. Analysis of fish growth was based on total length-frequency data. These data were analyzed using the FISAT II software. The sizes of male and female opudi fish obtained ranged from 30-70 mm. Growth patterns of von Bertalanffy butina in male fish are male Lt = 76.50 [1-e-0.46 (t + 0.47)] and female fish Lt = 74.05 [1-e-0.51 (t + 0.52)]. The total mortality value of male fish was higher (Z = 1.65) compared to female fish (Z = 1.50), the natural mortality value of male opudi fish was lower (M = 0.84) compared to that of female fish (M = 0.91).
 
 Keywords: endemic fish, growth, mortality, Telmatherina prognatha

Can a length-based pseudo-cohort analysis (LBPA) using multiple catch length-frequencies provide insight into population status in data-poor situations?

Stock status for many medium- and small-scale fisheries is unknown due, for example, to a lack of catch data and the absence of scientific observer programs. However, length-frequency data are often available for such fisheries because they are the cheapest and easiest data to obtain. Various stock assessment methods have been developed that use length-frequency data and make equilibrium assumptions regarding both recruitment and fishing mortality. These assumptions raise questions regarding the reliability of the results, particularly when the method is applied to a single sample of length-frequency. We developed a Length-Based Pseudo-cohort Analysis (LBPA) model whose parameters can be estimated using multiple length frequencies and penalized maximum likelihood, under the assumption that using more than one length-frequency sample reduces the effects of the equilibrium conditions assumed in the model. We explored the performance of LBPA using simulations that examined the implications for estimation of the spawning potential rate (SPR) and the relative fishing mortality (F/FMSY). These simulations considered scenarios related to exploitation rate, steepness, numbers of years and sample sizes for length-frequency, and data weights. The performance of LBPA was compared to that of length-based spawning potential ratio (LBSPR). LBPA performed better with additional length-frequencies than with increased sample size, irrespective of how the data were weighted, and generally outperformed LBSPR. Estimates were more accurate and less biased when exploitation rates were high. This work provides guidelines that should be considered when using length-based pseudo-cohort models for data-poor fisheries.

Stock Status Assessments of Five Small Pelagic Species in the Atlantic and Pacific Oceans Using the Length-Based Bayesian Estimation (LBB) Method

A rising trend in catches of non-targeted species have recently been observed in major fisheries including tuna longline fisheries, yet most of these species are unmanaged. Given their importance to local economies and sustainable livelihoods in many coastal countries, there is a need to provide plans for their management. However, most non-targeted species are data-limited which hampers the use of conventional assessment methods. This study applied a novel length-based Bayesian biomass estimator (LBB) method to five species from the Atlantic and Pacific Oceans. Estimates of growth, length at first capture and present relative biomass (B/B0, B/BMSY) of these species were gotten from length-frequency (LF) data. Of the ten populations (5 species from 2 regions) assessed, one has collapsed, one grossly overfished, and three overfished. Six populations had the ratio of mean lengths at first capture (Lc) on the mean length at first capture, which maximizes the catch and biomass (Lc_opt) greater than unity, indicating the presence of large-sized specimens in the populations. Two species faced intense fishing pressure in the Atlantic while one stock collapsed in the Pacific Ocean. Our results indicate that even non-targeted pelagic can be prone to over-exploitation. Therefore, there is an urgent need for stakeholders and fisheries managers to focus on improving fishery statistics and to conduct periodic monitoring of stock status indicators for non-target species.

Growth, mortality, sexual maturity and exploitation of the ribbonfish, Trichiurus lepturus (Linnaeus, 1758) (Pisces: Trichiuridae) in Ghanaian waters

The ribbonfish, Trichiurus lepturus is actively and locally exploited by commercial fishers along the coast of Ghana. As a contribution to fill the knowledge gap on this species, size composition, growth and mortality as well as sexual maturity and exploitation of the stocks were assessed. Samples were collected from major fish landing sites along the coast of Ghana from September, 2018 and August, 2019. Length-frequency data were used in the estimation of growth and mortality rates and exploitation ratio. Total lengths of T. lepturus sampled ranged between 24.8 and 103.9 cm with a unimodal distribution of 55 cm. The length and weight relationship established that growth was positively allometric. The asymptotic length (L∞), growth coefficient (K) and age at zero length (to) for T. lepturus were estimated as 133.66, 0.46 yr-1 and -0.88 respectively. Total (Z), fishing (F) and natural (M) mortality rates of were estimated at 2.69 yr-1, 2.03 yr-1 and 0.66 yr-1 respectively. The length at first capture (Lc) was lower than the length at first maturity (Lm). Spawning occurred all year round with a peak spawning period from March to June. Fecundity was estimated to be 17,440 ± 1,250 eggs (mean ± SE). There was no significant difference observed in the sex ratio between males and females. The species showed to be vulnerable to overfishing. There is therefore the need for a reduction in fishing pressure of the stocks to promote proper management of this fishery resource.

Individual growth analysis of the Pacific yellowlegs shrimp Penaeus californiensis via multi-criteria approach

Length-frequency data of juveniles and sub-adults of Penaeus californiensis were analyzed, collected from January 2002 to January 2003 in the Agiabampo lagoon system and adjacent marine coastal zone. Six models were parameterized with four criteria, in addition to a mixed criterion (fat-tail and depensatory), to estimate the parameters that best fit the growth curve. The model that best fit was the Johnson model with the mixed criterion in females and males: k = 6.02 (5.93-6.12); L∞ = 188.8 (186.3-191.8); t0 = 0.0221 (0.0207-0.0234); and: k = 8.98 (8.85-9.12); L∞ =153.3 (151.7-155.0); t0 = 0.0386 (0.0378-0.0394), respectively. The conclusion is that: 1) the mixture approach found in this study as best leads to the application of a very high-performance objective function to analyze individual length-at-age variability, 2) shows that the best model to describe the growth trajectory of P. californiensis in marine and estuarine environments is a sigmoid curve with an inflection point near to cero age (Johnson model).

Ecology and population dynamics of silver catfish, <I>Chrysichthys nigrodigitatus</I> (Siluriformes: Claroteidae), of the Cross River, Nigeria

Chrysichthys nigrodigitatus forms the most commercially important freshwater single species fishery in the Cross River, Nigeria. Studies were conducted on the dynamics of the exploited population of the species and the influence of rainfall on its catch rate. The objectives were to assess the level of exploitation and impacts of rainfall on its catch rate. A time series of length frequency and meteorological parameters was conducted. Length frequency data were analyzed using FiSAT software to estimate population parameters. The asymptotic length, Lı was 105 cm, growth constant (K) was 0.68 year-1, total mortality (Z) was 2.48 year-1, Natural mortality (M) was 0.99 year-1 and fishing mortality (F) was 1.49 year-1. The exploitation rate was 0.60 year-1, indicating overfishing. Natural mortality accounted 40% of the total mortality, presenting a worrisome trend in the fishery. There was a correlation between rainfall and catch rate, which increased at the onset of rains but decreased at the peak of the rains due to increased depth of the river. For management purposes, it is recommended that the fishing effort should be reduced by the regulation of the number of boat-days; for conservation, domestication of the species should be adopted as an adaptation to climatic influence.
 Keywords: Freshwater Catfish, Fishing Mortality, Exploitation Rate, Overfishing, Rainfall Impact, Niger Delta.

Estimation of growth parameters integrating tag-recapture, length-frequency, and direct aging data using likelihood and Bayesian methods for the tropical deepwater snapper Pristipomoides filamentosus in Hawaii

Pristipomoides filamentosus is an economically and culturally important species of deepwater snapper found throughout the tropical Indo-Pacific. From 1989–1993, the State of Hawaii initiated a tagging program with fish opportunistically recaptured by scientists and fishers to quantify growth and other life history parameters. Over approximately 10 years, 10.5 % of 4179 tagged P. filamentosus were recaptured. We used these data to compare von Bertalanffy growth parameters estimated using Bayesian and likelihood approaches. Next, we defined an objective cost function to estimate growth parameters that integrated the tagging data with direct aging and length frequency data used in previous regional growth studies. Our results reconcile 30+ years of effort from various methods to estimate growth parameters for P. filametosus in Hawaii (L∞ = 68.14 cm FL [95 % Confidence Interval (CI): 65.42–69.54] and K = 0.22 yr−1 [CI: 0.20–0.25]), demonstrate the importance of individual variability in the species due primarily to the asymptotic length parameter L∞, and suggest the effects of sexual dimorphism on growth as a focus of future inquiry. These results have direct management implications as growth is a critical input for age-based stock assessment models and often used as a proxy for other life history traits.