Fishing Mortality Coefficient Research Articles

Growth parameters and stock assessment of Carangoides bajad Forsskal, 1775 (Carangiformes: Carangidae) in Jeddah fisheries

ABSTRACT The stock status of Carangoides bajad in Jeddah fisheries was assessed by estimating the growth parameters, mortality rates and size at first capture (Lc), then applying the results to estimate the yield and biomass per recruit. The length-weight relationship could be described by the power equation: W = 0.011 L3.019 (R2 = 0.99) for combined sexes. Von Bertalanffy Growth Parameters L∞, K and t0 were estimated to be 71.53 cm, 0.224 year −1, and −0.52 year, respectively. The total, natural, fishing mortality coefficients and exploitation were calculated to be 0.72 year −1, 0.337 year −1, 0.383 year −1, and 0.53 year −1, respectively. Beverton and Holt (1957) model was used to estimate the yield and biomass per recruit at Fcur and Lc and found to be Y/R = 291 g and B/R = 759 g. Compared with the two biological reference points Fmax = 0.56 year −1 and F0.1 = 0.346 year −1, the Fcur value was very close to the F0.1 value required to get the optimum Y/R. We recommend avoiding any increase in Fcur, and increasing Lc to be 38 centimetres to increase the B/R from 759 g to 793 g, which would increase the probability of sustaining sufficient recruitment to the fishery of C. bajad in Jeddah fisheries.

Growth, mortality, and resource utilization of Gymnocypris chui in Langcuo Lake of Tibetan Plateau, China.

To investigate the growth, mortality, and resource utilization of Gymnocypris chui in Langcuo Lake of Tibetan Plateau, we measured body length and body weight of 389 fish based on four sampling surveys from October 2018 to November 2019. We identified the ages through lapillus. Based on frequency distribution of body length, we estimated the growth and mortality coefficients of G. chui in Langcuo Lake and the utilization status of existing population resources according to the Beverton-Holt dynamic comprehensive model. The results showed that G. chui were mainly composed of individuals aged 2 to 19 years in Langcuo Lake, with a length-body weight relationship equation of W=0.0105L3.042. The von Bertalanffy growth equation revealed that the fish had an asymptotic body length of L∞=37.28 cm, growth coefficient of k=0.160, and theoretical growth starting age of t0=-0.887 a. The total mortality coefficient Z was estimated as 0.48, based on the length-converted catch curve method. According to Pauly's empirical formula, the natural mortality coefficient M was 0.34, fishing mortality coefficient F was 0.14, and exploitation rate E was 0.29, indicating that G. chui resources in Langcuo Lake were not over-exploited. Considering the growth and mortality of G. chui in Langcuo Lake, fishing is appropriate, with a recommended fishing length of Lc=22.37 cm.

Data-limited stock assessment of red mullet (Mullus barbatus) from the Iskenderun Bay, the north-eastern Mediterranean Sea

Stock size and status of red mullet Mullus barbatus were assessed via virtual population analysis and yield prediction analysis using on-board observed length-frequency catch data from the north-eastern Mediterranean Sea. The von Bertalanffy growth parameters obtained were L∞ = 35.4 cm, k = 0.42, t0 = 0.64, tanc = 0.59 and Φ′ = 2.72. Trawl-type selectivity ogive was calculated as 1.57 years corresponding to 17.1 cm TL. The virtual population analysis of M. barbatus indicated that the minimum and maximum fishing mortalities were 0.01 yr–1 and 11.1 yr–1 for the mid-length groups for 8.5 cm and 21.5 cm respectively. The estimated lowest mean biomass and yield were 3.541 t and 31 t at length 8.5, and the highest mean biomass and yield were 13.880 t at length 22.5 cm and 46.086 t at length 21.5 cm respectively. Biological reference points were FMSY = 5.85, F0.5 = 2.3, EMSY = 0.89, E0.5 = 0.77. The values for the current fishing mortality coefficient (Fcur) and the current exploitation rate (Ecur) calculated were 5.3 and 0.89 respectively. The present biological reference points indicate that the stock of M. barbatus in the investigated area is overexploited status and needs urgent management considerations.

Life-history Parameters of Shield-Head Catfish Synodontis Schall (Bloch and Schneider, 1801) in the Nile River, Egypt

Age and growth, mortality, and exploitation level of the shield-head catfish Synodontis schall inhabiting River Nile, Egypt are studied to evaluate its fishery status and proposed some reference points for its sustainability. A total number of 805 specimens comprising of 306 males and 499 females with the size range of 16.7 - 37.8 cm TL (mean = 26.71 ± 3.58) were investigated. The weight of specimens ranged from 60.0 to 650 g (mean = 194.88 ± 26.58). Statistically, there is no difference between males and females in the longevity and population parameters so all parameters were estimated for sexes combined. The maximum life span of this species was 4 years based on the pectoral fin spine sections. Asymptotic total length (L∞) was 42.25 cm, growth coefficient (K) was 0.42 yr-1, and theoretical age at zero-length (t0) was -0.36 yr, while the growth performance index (Ø’) was 2.87. The instantaneous total, natural, and fishing mortality coefficients were 1.23, 0.54, and 0.69 yr-1, respectively. The Exploitation rate (E) was 0.56. The body length at first sexual maturity (Lm) and mean selection length (Lc) were estimated at 24.1 and 23.6 cm, respectively. There is selective fishing mortality towards smaller fish sizes reflecting the adverse impact of fishing effort. Therefore, for management purposes, it is recommended to increase the length at first capture to maintain sufficient spawning biomass for recruitment and monitoring the exploitation level to control the fishing effort.

Investigations on age, growth and mortality parameters of Ailia coila (Hamilton 1822) (Siluriformes: Ailiidae) from Brahmaputra River system of Assam, India

The present study deals with the detailed investigation on population dynamics of the near-threatened catfish Ailia coila (Hamilton, 1822), which inhabits the Brahmaputra River of India and forms an important component of freshwater inland fishery, providing nutritional and financial security to the local community. A total of 1034 individuals were collected by weekly sampling from the Uzanbazar and Dhubri landing centres of this river system from September 2013 to April 2014. The estimated asymptotic length (L∞), growth coefficient (K) and age at zero length (t0) of A. coila were 268 mm, 0.87 yr-1 and t0 = 0.000028 years respectively. Estimated total mortality (Z), natural mortality (M) and fishing mortality coefficient (F) were 5.76, 1.63 and 4.13 yr-1 respectively. Using von Bertalanffy growth formula (VBGF) the length attained at the end of first, second and third years of life were estimated at 156, 221 and 248 mm, respectively. The von Bertalanffy growth equation of this fish can be written as Lt = 268 {1-e-0.87(t+0.000027866)}. The exploitation ratio (U) and exploitation rate (E) and M/K ratio were estimated at 0.71, 0.72 and 1.87, respectively. Keywords: Ailia coila, Asymptotic length, Fishing mortality, Growth co-efficient, M/K ratio

Growth, mortality and yield of Atherina boyeri Risso, 1810 from Lesina lagoon (Adriatic Sea, Italy)

Population structure, growth, age, mortality and exploitation status of Atherina boyeri, caught in the period from June 2013 to May 2014 in the Lesina lagoon (Apulia region, southern Adriatic) was studied. Samples were taken each month by using beach seines . The length–weight relationship of all sand smell specimens was described by the equation W=0.012*TL 3.10; (R2= 0.84). Population parameters including the asymptotic length (L∞) and growth coefficient (K) were assessed to evaluate the stock status. The recruitment pattern was modeled with a FiSAT routine. The asymptotic length (L∞) was 111.0 mm, while the growth coefficient (K) was 0.68 year−1. The growth performance index ((φ’) reached 3.92. The total mortality coefficient “Z”, the natural mortality coefficient “M” and the fishing mortality coefficient “F” were estimated as 2.24, 1.48 and 0.76 year-1, respectively. Exploitation rate for the population of A. boyeri in the Lesina lagoon estimated as 0.34 was resulted still lower than the predicted maximum value of Emax 0.59. The probability of capture indicated that L50 was of 55.57 mm, indicating that the stock of sand smelt in Lesina lagoon is not being over-fished.

Optimal shape of the harvest control rule for different fishery management objectives

Abstract To determine the optimal shape of the harvest control rule (HCR) achieving common fisheries management objectives (maximizing the average catch, reducing the deviation of yields, and avoiding stock collapse) and ensure robustness to observation errors, we estimate the optimal values of biological reference points (BRPs) composing the HCR. While traditional HCRs usually consist of three BRPs based on the fishing mortality coefficient (F3-HCR), we introduce an alternative HCR defined by 21 BRPs based on the catch levels (C21-HCR) to cover various possible shapes of HCR including smooth ones. We compare the shape and the performance between the optimal C21-HCR and the optimal F3-HCR and conclude that the optimal HCR can be composed of the gradual combination of the basic strategies: the constant escapement strategy, the constant harvest rate (CHR) strategy, and the constant catch strategy. However, the current F3-HCR does not necessarily allow this combination and generally returns lower performance levels than the optimal C21-HCR (since the basic strategy is confined to CHR) excluding the range of low biomass. This result will provide a clear perspective to improve HCR according to the magnitude of assessment errors and to compromise multiple fisheries management objectives when various stakeholders are involved.

Assessment of the fishery, growth and mortality characteristics of the cassava croaker, Pseudotolithus senegalensis (Sciaenidae) from coastal waters of Ghana

This paper reports on the fishery and some population parameters of the cassava croaker (Pseudotolithus senegalensis) at Anlo Beach near Shama (5°01’ N, 1∘37’ W) in the Western Region of Ghana. The study was conducted from July 2012 to June 2013 to contribute to information on the dynamics of demersal stocks in the country. Beach seining was the prime fishing method in the area with the fishing season spanning July to March. Catch per unit effort (CPUE), determined as catch per net haul per day was 9.5 kg in July 2012, 110 kg in January–February 2013 and 47 kg in March 2013. The species was absent from the fishery from April 2013 to June 2013. Monthly catches varied from 2295 kg to 31,500 kg, and specimens of the fish measured 7.5 cm TL to 105.4 cm TL and weighed 2.9 g to 7634 g. The length–weight relationship of the population was described by the equation: BW = 0.005TL3.04 (r=0.99), and grouping the fish at 5 cm class intervals showed modal lengths at 15.0–19.9, 35.0–39.9 and 60.0–64.9 cm TL. Analysis of the length-frequency distribution using the ELEFAN programme indicated an asymptotic length (L∞) of 110.3 cm TL, a growth coefficient (K) of 0.2 yr−1, and total (Z), natural (M) and fishing (F) mortality coefficients of 0.68 yr−1, 0.42 yr−1, and 0.26 yr−1 respectively, for the population. Longevity of the fish was estimated to be 15 years. A low exploitation level of the stock is suggested by the calculated exploitation ratio, E=0.38. These population characteristics are compared with those of other West African P. senegalensis populations.

Sinusoidal growth, recruitment, mortality, yield-per-recruit analysis of Buried fan scallop Mimachlamys funebris (Reeve, 1853) and their implications for mariculture

This study described the growth, mortality, recruitment pattern and exploitation rate of the Buried fan scallop (Mimachlamys funebris) in Asid Gulf, Philippines. Monthly length-frequency data (N=3988) from April 2018 to March 2019 were used to examine population parameters using FISAT II. Two estimates of natural mortalities were used to compare variability of limit exploitation rates. Modelling through the oscillating von Bertalanffy growth function revealed that the species is fast growing (K=1.1 year–1) attaining SH∞ of 10.5 cm. Adequacy in the use of the sinusoidal version of the growth formula hinges on the mean annual temperature difference reported in the gulf to be 2°C. Recruitment pattern was continuous and bimodal throughout the year with two high pulses in April–May and September consistent with the reproductive seasonality reported for congeneric species. Fishing mortality coefficients (4.26 and 4.82 year–1) were higher than the natural mortality coefficients (0.543 and 1.1 year–1). Yield and biomass-per-recruit analysis showed that the current exploitation rates are 112% (Ecurr1 = 0.90) and 92% (Ecurr2 = 0.80) higher than the biological reference points adopted for the study particularly E50. These results demonstrate that M. funebris stock is overexploited, which necessitates effective management measures including mariculture.

Demographic structure and stock status of Lethrinus lentjan in Saudi coastal waters of the Red Sea.

Fishes of the family Lethrinidae form a considerable portion of the catch from both the Red Sea and the Arabian Gulf in Saudi Arabia, and the species Lethrinus lentjan (Lacepède, 1802) is one of the most important among these fishes. This study was conducted to evaluate the demographic structure coefficients, survival rate, and stock status of L. lentjan from the Red Sea coast of Saudi Arabia. A total of 593 samples were collected on a monthly basis for a period of one year from the landing site for fishing boats operating in Red Sea waters off Jeddah. The results indicated that 88.87% of the specimens were female; the maximum total length recorded was 43.5 cm with the most frequent length (14.67%) being 23–23.9 cm. The maximum age recorded for both males and females was 6 year-plus, and the 1 year-plus age category represented the majority of the samples (57.67%). The total mortality coefficient, natural mortality coefficient, and fishing mortality coefficient were 1.538, 0.315, and 1.223, respectively; all mortality coefficients in the female fishes were higher than those in the male fishes. The survival rate of males was higher (0.617) than that of females (0.214). The results of the present study indicate that L. lentjan is subjected to overfishing and a new management strategy is necessary to improve the stock status of this fish species.

Population biology of common carp, Cyprinus carpio (Linnaeus, 1758), in Lake Naivasha, Kenya

AbstractThe common carp (Cyprinus carpio) is an exotic fish, being one of the commercially important species in Lake Naivasha. The present study investigated its growth, mortality, maturity, condition and exploitation. Sampling was done monthly from January to December 2017 with gillnets of 2–5 inches mesh size. Each individual fish was measured (cm) and weighed (g) in the field. The specimens were preserved in ice and transported to the laboratory for analysis of maturity. The fish lengths ranged from 12.0 to 69.0 cm TL, and weighed between 32 and 6,840 g. The overall population sex ratio was 1:1.66 (female:male). The length at first maturity (Lm50) was calculated to be 54.0 and 49.0 cm for females and males, respectively. The length at first capture (23.9 cm) was lower than its length at first maturity, suggesting the capture of immature fish. The mean condition factor for all fish was 1.05. The peak condition values were observed during April (1.35), September (1.59) and October (1.80). The highest (1.377) mean condition was observed for size class 56–60 and the lowest (0.933) in class 26–30. The asymptotic length (L∞) was 73.5 cm, and the growth curvature (K) was 1.05 year‐1, with a growth performance index (Ф) of 3.72. The total (Z), natural (M) and fishing (F) mortality coefficients were 2.85, 1.34 and 1.78 year‐1, respectively. The exploitation rate (E) of 0.57 year‐1 was higher than the optimum sustainable yield (E0.5) of 0.32, but was not different from the maximum sustainable yields (Emax) 0.54 and economic yield (E0.1) 0.46. The results of the present study provide parameters of fish biology and population that should prove useful in managing the fishery of Lake Naivasha.

Population Biology of Nile tilapia (Oreochromis niloticus) in Lake Naivasha, Kenya

AbstractThe Nile tilapia (Oreochromis niloticus) was introduced into Lake Naivasha to provide exploitable fisheries, being one of the commercially important fish providing livelihoods to communities around the lake. Its stocks in the lake have been declining, however, because of intense fishing, ecological changes and effects of other exotic species. The present study was undertaken to investigate the population and biological parameters of Oreochromis niloticus. Fish samples (1,021) were caught monthly from January to December 2017, collecting a total of 1,021 O. niloticus, with an overall sex ratio of 2.21:1.0 (male: female). The length of the fish ranged from 9.0 to 40.0 cmTL and weighed between 20 and 1,220 g. The mean length and weight for all fish was 22.6 cm and 272.6 g. The slope b of length–weight relationship was 2.86 for all fish, indicating negative allometry. The mean condition factors were 0.99, 1.04 and 1.01 for male, female and all fish, respectively. The length at first maturity (Lm50) was estimated to be 28.0 cmTL for all sexes, indicating the fish matures at smaller sizes. The length at first capture (Lc50) was calculated to be 19.38 cm, a value much lower than its Lm50, reflecting the capture of juvenile fish. The asymptotic length (L∞) was 42 cm, the growth coefficient (K) was 0.21/year, and the growth performance index (Ф) was 2.57. The natural (M), fishing (F) and total mortality (Z) coefficients were estimated to be 0.55, 0.26 and 0.80/year, respectively. The optimum sustainable yield (E0.5), maximum sustainable yield (Emax) and maximum economic yield (E0.1) indices of 0.23, 0.35 and 0.26, respectively, imply an optimal exploitation of O. niloticus. The results of the present study provided some important insights into the biology and management needs of the O. niloticus fishery in Lake Naivasha, as well as revealing a gap for further research on its reproductive biology.

Current status of Liza ramada (Risso, 1810) (Mugilidae) caught by trammel net (Ballah) at El-Gamil region, Manzala Lake, Egypt

Liza ramada, the target species caught by trammel net (Ballah) at El-Gamil region, north of Lake Manzala, is studied to estimate the life history parameters by using length–frequency data of 842 specimens. The life span was estimated as 4 years. It exhibited a negative allometric growth (b=2.94). The von Bertalanffy growth parameters were L∞= 30.45cm, K= 0.48 yr−1 and t0 =-0.339 yr−1 with a derived growth performance index of O′ =2.6 .The mean annual instantaneous total, natural and fishing mortality coefficients were 1.47, 0.71and 0.76/year, respectively. The exploitation rate was estimated as 0.52. The probability of capture ensured that 50 percent (Lc) of the fish caught was estimated at length 12.18 cm which is 31.2% lower than the length at first sexual maturity (17.7 cm) and lower by 40.1% than the estimated Lopt value (20.4 cm). This result reflects the smaller mesh sizes of the inner layer of nets used by fishermen. Therefore an urgent recommendation should be applied to prevent the illegal fishing gears, increase the mesh sizes especially for the inner layer of trammel net used as well as improving the quality of water discharged into the lake to increase the yield per recruit of Liza ramada, protect fish stocks and to secure a profitable fisheries and optimum catch efficiency for the future.

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

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

Population Dynamics and Management of Two-barred Seabream <i>Acanthopagrus bifasciatus</i> in the Red Sea, Egypt

The present study is the first study on the population dynamics and management of the <i>Acanthopagrus bifasciatus</i> in the Egyptian sector of Red Sea. A total of 729 specimens were monthly collected from the Egyptian Red Sea during January 2015 to December 2015. Results showed that, the longevity of <i>A. bifasciatus</i> is 9 years in the Egyptian Red Sea and age group three was the most frequent one for combined sexes forming up to 26.61% of the total catch. The age group one was absent in the collected samples and the highest growth in length was observed at the end of the second year of life (24.6 cm) after which the annual increment decreases gradually with increase in age. The growth in weight was isometric. The length at first capture was 25.31 cm with corresponding age 2.22 year. The total, natural and fishing mortality were estimated as 1.99, 0.46 and 1.53 yr^-1, respectively. The exploitation ratio E was estimated at 0.77 indicating a high level of exploitation. The yield per recruit analysis showed that the present level of fishing mortality is much higher than that gives the maximum yield per recruit by about 48% and the reduction of current level of fishing mortality coefficient from 1.53 to 0.8 / y will be associated with an increase in the yield per recruit from 242.71 to 250.56 g (≈3%).

A stock assessment for Illex argentinus in Southwest Atlantic using an environmentally dependent surplus production model

The southern Patagonian stock (SPS) of Argentinian shortfin squid, Illex argentinus, is an economically important squid fishery in the Southwest Atlantic. Environmental conditions in the region play an important role in regulating the population dynamics of the I. argentinus population. This study develops an environmentally dependent surplus production (EDSP) model to evaluate the stock abundance of I. argentines during the period of 2000 to 2010. The environmental factors (favorable spawning habitat areas with sea surface temperature of 16–18°C) were assumed to be closely associated with carrying capacity (K) in the EDSP model. Deviance Information Criterion (DIC) values suggest that the estimated EDSP model with environmental factors fits the data better than a Schaefer surplus model without environmental factors under uniform and normal scenarios. The EDSP model estimated a maximum sustainable yield (MSY) from 351 600 t to 685 100 t and a biomass from 1 322 400 t to 1 803 000 t. The fishing mortality coefficient of I. argentinus from 2000 to 2010 was smaller than the values of F0.1 and F MSY . Furthermore, the time series biomass plot of I. argentinus from 2000 to 2010 shows that the biomass of I. argentinus and this fishery were in a good state and not presently experiencing overfishing. This study suggests that the environmental conditions of the habitat should be considered within squid stock assessment and management.

Biological responses of small yellow croaker (Larimichthys polyactis) to multiple stressors: a case study in the Yellow Sea, China

Temporal changes in biological characteristics of small yellow croaker Larimichthys polyactis in the Yellow Sea were examined for the period of 1960–2008. The body size and age of small yellow croaker decreased substantially, in particular, average length of fish in 2008 was reduced by ~85% than those occurring in 1985, and at that time ~93% of the total catch was dominated by one-year-old individuals. Correspondingly, growth parameters also varied significantly over the years, i.e., k (growth coefficient) and t 0 (zero-length age) gradually increased from 0.26 and–0.58 year in 1960 to 0.56 and–0.25 year in 2008, respectively. Although, L∞ (body length) sharply decreased from 34.21 cm in 1960 to 24.06 cm in 2008, and t r (inflexion age) decreased from 3.78 year in 1960 to 1.61 year in 2008. There was a great increase both in natural mortality coefficient and fishing mortality coefficient. However, according to the gray correlation analysis, changes in the biological characteristics of small yellow croaker were induced by different stressors ranked as: fishing vessel power>feeding grade>sea surface temperature. This study suggests that the active fishery management measures for biological characters of fish populations should be considered.

Ridge virtual population analysis to reduce the instability of fishing mortalities in the terminal year

AbstractTuned virtual population analyses are widely used for fisheries stock assessments. However, accurately estimating abundances and fishing mortality coefficients in the terminal year using tuned virtual population analyses is generally difficult, particularly when there is a limited number of available abundance indices. We propose a new method of integrating the tuned virtual population analyses with a ridge regression approach. In our method, penalization in the ridge regression is applied to the age-specific fishing mortalities in the terminal year, and the penalty parameter is automatically selected by minimizing the retrospective bias. Therefore, our method is able to simultaneously obtain a stable estimation of fishing mortality coefficients in the terminal year and reduce retrospective bias. Simulation tests based on the northern Japan Sea stock of walleye pollock (Gadus chalcogrammus) in the Sea of Japan demonstrated that this method yielded less biased estimates of abundances and avoided overestimations of fishing mortality coefficients in the terminal year. In addition, despite limited abundance indices, our method can perform reliable abundance estimations even under hyperstability and hyperdepletion conditions.

Case Study: A Simulation Model of the Spawning Stock Biomass of Pacific Bluefin Tuna and Evaluation of Fisheries Regulations

This study proposes a simulation model that well reproduces the spawning stock biomass of Pacific bluefin tuna. Environmental factors were chosen to estimate the recruitment per spawning stock biomass, and a simulation model that well reproduced the spawning stock biomass was developed. Then, effects of various fisheries regulations were evaluated using the simulation study. The results were as follows: 1) arctic oscillations, Pacific decadal oscillations and the recruitment number of the Pacific stock of Japanese sardine were chosen as the environmental factors that determined the recruitment per spawning stock biomass; 2) spawning stock biomass could be well reproduced using a model that reproduced the recruitment per spawning stock biomass and the survival process of the population that included the effect of fishing; and 3) the effects of various fisheries regulation could be evaluated using the simulation model mentioned above. The effective regulation in the simulations conducted in this paper was a prohibition of fishing for 0- and 1-year-old fish in terms of recovering the spawning stock biomass. The reduction of fishing mortality coefficients for all age fish to 50% of actual values also showed a good performance. The recent reductions of the recruitment and spawning stock biomass were likely caused by heavy harvesting, especially of immature fish, since 2004.

Capture production and stock assessment of Solea aegyptiaca Chabanaud, 1927 (Soleidae: Pleuronectiformes) in Bardawil Lagoon, Egypt

Capture production from Bardawil Lagoon was described and analyzed. Fish samples of Solea aegyptiaca were collected for growth study. Otoliths were extracted from each specimen and used for age determination. Back-calculated lengths-at-ages were estimated and used to determine growth rates in length and weight. The von Bertalanffy growth parameters; L∞, K and t0, were determined. Growth in length could be described by the von Bertalanffy growth equation “VBGE”: Lt=37.52 [1−e−0.42(t+0.4)]. The total mortality coefficient ‘Z’, the natural mortality coefficient ‘M’ and the fishing mortality coefficient ‘F’ were estimated to be 2.35, 0.63 and 1.72year−1, respectively. The current exploitation rate ‘Ecur’ was 0.73year−1. Beverton and Holt’s relative yield per recruit Model (1966) was used to estimate the relative yield and biomass per recruit of S. aegyptiaca in Bardawil Lagoon. The yield-based biological reference points Emax and E0.1 were determined and found to be 0.717year−1 and 0.62year−1, respectively. Results indicated that the stock of S. aegyptiaca in Bardawil Lagoon is currently over-exploited. The current exploitation rate should be decreased to the widely adopted target reference point, E0.1=0.62year−1 for sustainable fishery production of S. aegyptiaca in Bardawil Lagoon.