Von Bertalanffy Growth Function Research Articles

Age, Growth, and Otolith Morphometrics of Trachinus draco (L., 1758) and Trachinus radiatus (Cuvier, 1829) in the Eastern Mediterranean

Trachinus draco and Trachinus radiatus are two bycatch species of low commercial value and no sufficient knowledge on their biological features. In the present study, the weight–length relationship, age, growth, and ten otolith morphometric variables of these species were investigated in the southwestern Aegean Sea for the first time. Positive allometric and isometric growth in the weight were defined in T. draco and T. radiatus. The weight–length relationship was described by the parameters α = 0.002415 and b = 3.35745 in T. draco and α = 0.007582 and b = 3.09452 in T. radiatus. The von Bertalanffy growth function parameters were L∞ = 44.51 cm, k = 0.15 year−1, and t0 = −1.31 years for T. draco and L∞ = 58.47 cm, k = 0.16 year−1, and t0 = −0.78 years for T. radiatus. Ten otolith variables (radius, length, width, area, perimeter, roundness, circularity, form factor, rectangularity, and ellipticity) showed a significant relationship with size for both species, except the ellipticity in T. radiatus. The mean values of all the otolith variables were higher in T. radiatus than in T. draco. The otolith of T. radiatus was found to become more rectangular with size as compared to the otolith of T. radiatus. The results of this work can support further research on the behavioral and ecological features of the two species.

Age and growth of the crocodile shark, Pseudocarcharias kamoharai, in the Eastern Tropical Pacific Ocean

ABSTRACT The age, growth, and longevity parameters of crocodile shark, Pseudocarcharias kamoharai, from Santa Rosa, Ecuador were estimated. A number of 328 organisms were analyzed, 158 females (69 to 117 cm total length, TL) and 170 males (72.5 to 110 cm TL). The relationship between the vertebra's radius and TL was moderate (r2 = 0.63), indicating a relation between structure growth and the organism's size. Females were four to 14 years old and males were four to 12 years. The multimodal approach determined that the suitable equations were: The Von Bertalanffy growth function model with a fixed L0 (45.5 cm TL), VBGM2P (L∞ = 118.4 cm cm TL, k = 0.15) for combined sexes with a weight of evidence (Wi) to its favour of 43.9%; logistic growth model (L∞ = 109.5 cm TL, k = 0.41, L0 = 33.1 cm TL) for females with Wi = 28.4% and VBGM2P (L∞ = 110.4 cm TL, k = 0.16) for males with a Wi = 39.4%. No model obtained a sufficient evidence to be declared the best adjusted. The calculated longevities were 18 years for combined sexes, 16 for females, and 14 for males.

Population dynamics of Variola albimarginata Baissac, 1953 and Variola louti Fabricius, 1775 (Perciformes: Serranidae) in Sulawesi Sea, Indonesia

Abstract. Achmad DS, Nurdin MS, Tilome AA, Moore AM. 2024. Population dynamics of Variola albimarginata Baissac, 1953 and Variola louti Fabricius, 1775 (Perciformes: Serranidae) in Sulawesi Sea, Indonesia. Biodiversitas 25: 978-989. The lyretail groupers Variola louti Fabricius, 1775 and Variola albimarginata Baissac, 1953 (Epinephelinae) are valuable foodfishes. IUCN Red List assessments classified both species as Least Concern, while noting that some stocks are overfished. The purpose of this study on the population dynamics of Variola groupers in Kwandang Bay was to evaluate the exploitation level for both species in this important grouper fishing area of the Sulawesi Sea, Indonesia. Population dynamics parameters were calculated based on length-frequency data collected from October 2022 to September 2023 using the ELEFAN I response surface analysis option in FISAT II. The asymptotic length at infinity TL? was 54.90 cm for V. louti and 54.40 cm for V. albimarginata with von Bertalanffy growth function K values 0.54 and 0.55, respectively. Recruitment occurred throughout the year, with monthly percentages of 1.08-13.52 % and 1.61-14.99%, respectively. Natural and fishing mortality were M = 1.04/year-1 and F = 1.17/year-1 for V. louti and M = 1.05/year-1 and F= 2.56/year-1 for V. albimarginata giving F/M ratios of 1.13:1 and 2.44:1. Beverton and Holt yield per recruit analysis gave exploitation rates (E = 0.53/year-1 and E = 0.71/year-1) exceeding the maximum sustainable value Emax = 0.37/year-1, indicating overexploitation of both species. To achieve the optimum exploitation rate of E50 = 0.24, fishing effort needs to be reduced by 29% for V. louti and 47% for V. albimarginata. Management options include setting a minimum legal size with recommended values of 32-33 cm and temporary closures during the peak reproductive season in May-June.

Population survey of Holothuria (Halodeima) grisea (Aspidochirotida: Holothuriidae) at its limit of geographic distribution in the Western South Atlantic

Introduction: The sea cucumber Holothuria (Halodeima) grisea Selenka, 1867 is a common echinoderm in intertidal regions along the Brazilian coast, which recently became the focus of unreported and unregulated fisheries. This study was carried out in sandy-rocky substrates at Armação do Itapocoroy, Penha, Santa Catarina (26o47’ S; 48o36’ W), near its southern limit of geographic distribution.
 Objective: To determine the densities (individuals*m-2) of Holothuria (H.) grisea within a spatial-temporal perspective as well as to determine biometric and growth characteristics of the population.
 Methods: Two-meter wide transects perpendicular to the coastline were carried out in winter and spring 2019 and in summer and spring 2020, in periods of spring low-tides. In each sampling occasion the total number of specimens of H. grisea were determined, and a group of 90 organisms was submitted to in situ biometrics (weight, length and width), and immediately returned alive to their habitat.
 Results: The densities of H. (H.) grisea were significantly higher in the subtidal sector and lower in the upper intertidal sector with no indication of significant differences among sampling campaigns. Depth was the primary factor explaining the observed density patterns and rugosity of the substrate was secondary but also important. The body length ranged from 5.2 to 22.5 cm, whereas the weight varied from 6.0 to 230 g. The mean and modal lengths were 12.54 and 13 cm, respectively. Approximately 75 % of the population sampled was between 10 and 14 cm and the average weight was 60 g. Estimates from von Bertalanffy growth function indicate that the youngest sea cucumber was one year-old, and the oldest had approximately two and a half years.
 Conclusions: This is the first study to determine biometric parameters for H. (H.) grisea in southern Brazil and the first one to estimate growth and age estimates for a wild population of this species. The densities recorded in the present study were lower than those previously reported for this region, suggesting anthropic influence.

Growth of two invasive cichlids (Perciformes: Cichlidae) in a natural thermal water habitat of temperate Central Europe (Lake Hévíz, Hungary).

The outflow of the natural thermal Lake of Hévíz is habitat of several fish species, with conservation relevance. In the past few years, numerous thermophile (tropically originated) fishes were reported in this waterbody, from which two species Parachromis managuensis (Günther, 1867), Vieja melanurus (Günther, 1862) characterized with strong, self-sustaining population. The aim of our research was to provide basic population data and to study their individual growth. The standard length of jaguar cichlid ranged from 37 to 283mm (mean SL = 110.21 ± 65.4mm), the redhead cichlid standard length varied between 30 and 203mm (mean SL = 93.91 ± 40.0mm). Slightly positive allometry (b > 3) was found in the case of both species. The von Bertalanffy Growth Function can be described as the following Lt = 343.6[1 - e-0.196(t+0.973)] in jaguar cichlid and Lt = 298.9[1 - e-0.113(t+0.997)] in the case of redhead cichlid. The Bertalanffy growth equations show slow growth for both species. Fulton's condition factor (K) values varied between 1.376 and 2.11 (mean K = 1.701 ± 0.17) in the case of jaguar cichlid, and between 1.391 and 3.033 (mean K = 2.237 ± 0.24) for redhead cichlid. These baseline population biology data from the first known self-sustaining, temperate-zone populations of two tropical cichlids provide information e.g., for future ecological risk assessments or comparative growth analyzes.

Population Dynamics of the Common Carp (Cyprinus carpio L. 1758) Stock in Lake Arekit, Ethiopia: Implications for Management and Conservation

Cyprinus carpio is a widely distributed and commercially important fish species in Ethiopia. Effective management is essential to sustain fisheries and provide benefits to local communities. This study aims to estimate the growth, mortality, and exploitation rate of C. carpio using length-frequency data. A total of 194 C. carpio specimens (117 females and 77 males) were collected between June 2022 and May 2023. The population parameters were determined using FISAT (ELEFAN I) software. The Von Bertalanffy growth function estimations were L∞ = 51.45 cm total length, K = 1.1 year−1; t0 = −0.124 year, and growth performance index (Φ′) = 3.464. The total mortality rate (Z), natural mortality rate (M), and fishing mortality rate (F) were 2.55 year−1, 1.58 year−1, and 0.97 year−1, respectively. The estimated potential longevity (tmax) and average age at which C. carpio attains length at the optimum cohort biomass or yield per recruit (Lopt = 34.79) in Lake Arekit were calculated as 2.60 years and 1.29 years, respectively. The Z/K ratio (2.32), exploitation rate (E = F/Z = 0.38), and highest permissible yield per recruit for C. carpio (Emax = 0.421) suggest enhancing fishery production by increasing the exploitation rate of the underexploited C. carpio in Lake Arekit. The results of this study provide information on the stock of C. carpio, which can be used to guide management efforts. The fish catch in Lake Arkeit is currently far lower than it could be. Therefore, the fish harvest should be boosted through the use of permitted nets, the establishment of groups of fishermen who can catch fish effectively, and the linking of the benefits of fish farming’s supply chain to the potential of fisheries.

Biology of kawakawa Euthynnus affinis in the East China Sea: Growth, reproduction, and stable isotope ratios

This study elucidated the age–growth relationship, maturation body size, and stable isotope ratios of kawakawa Euthynnus affinis in the East China Sea. A total of 396 individuals were collected, of which 266 were captured off the west coast of Kyushu and 130 around Okinawa. Ages were determined from otolith analysis, and the estimated von Bertalanffy growth functions were FLt = 1007{1 – exp[–0.107(t + 3.835)]} near Kyushu and FLt = 640{1 – exp[–0.381(t + 1.111)]} around Okinawa, where FLt is fork length (mm) at age t for ages 0.25 to 5. The estimated fork lengths of the fish near Kyushu were larger than those around Okinawa. The smallest fork length of a fish in the spawning stages was about 440 mm. Mature females and males were observed from May to October near Kyushu and from March to July around Okinawa. Females in the spawning stages were observed from July to September near Kyushu and from April to June around Okinawa. The δ15N of fish captured near Kyushu (12.39‰ ± 0.55‰, mean ± standard deviation) was higher than that of those captured around Okinawa (9.94‰ ± 1.39‰). This suggests that the kawakawa caught in each area occupy distinct habitats, although some mixing of individuals between the two habitats might occur.

On the biology of the alien Red Sea goatfish, Parupeneus forsskali (Fourmanoir & Guézé, 1976) in the Aegean Sea, eastern Mediterranean

ABSTRACT The alien Red Sea goatfish (Parupeneus forsskali) was recently reported in the Mediterranean Sea, as a species that migrated two decades ago through the Suez Canal. In this work, efforts are being made to fill knowledge gaps on its biology, through information based on 131 Red Sea goatfish specimens collected from commercial fishing vessels in the south-eastern coasts of the Aegean Sea, Greece (Eastern Mediterranean). The largest specimen examined measured 26 cm in total length (Lmax), while otolith annual ring determination showed that the maximum recorded age was 4 years. The Von Bertalanffy growth function parameters were estimated as follows: L∞ = 32.44 cm, Κ = 0.31 y−1 and t0  = −0.08 y. The diet of the specimens was dominated by Decapoda and Amphipoda (IRI = 66%) with an estimated trophic level of 3.58 (±0.53), characterizing the species as carnivorous with preference for Crustacea prey. Length (Lm) and age (tm) at maturity were estimated to be 19.6 cm and 2.8 years, respectively. The species exhibited larger reproductive load (Lm/Lmax) in the non-native regions compared with its native distribution in the non-native regions compared with its native distribution. In conclusion, further research is required in order to elucidate differences of the species’ life-history traits between its native and non-native distribution.

The dynamics of growth and maturation age in the scallop Adamussium colbecki in Tera Nova Bay, Antarctica

The endemic Antarctic scallop Adamussium colbecki, one of the most common bivalve species, plays an important ecological role in Antarctic ecosystems. In this study, we investigated the size frequency structure, shell height, and gonadosomatic index (GSI) of A. colbecki in coastal areas near Jang Bogo Antarctic Research Station in Terra Nova Bay. A generalized von Bertalanffy growth function was fitted to shell height-at-age measurements of 389 individuals (H∞ = 115.4 mm and K = 0.064 year−1). Large-sized individuals (70–84 mm) of A. colbecki were ∼2X as prevalent, accounting for more than 50% of the overall density. Individuals younger than 6 years showed a lower growth rate compared to that reported in previous studies. GSI indicated that sexual maturity of both females and males was observed in individuals over 50 mm shell height at the age of approximately 9 years. The maturity was delayed by two to four years when compared with previous data in Terra Nova Bay due to the low growth rates of the young population. Therefore, the low growth rate of young individuals and the delayed maturity age may have deleterious effects on population growth. The information reported here provides baseline scientific data that can be used to develop better informed management decisions and aid in defining an effective management strategy for Antarctic scallops.

Co-management of a high-value species with territorial use rights for fisheries: a spatial bioeconomic approach with environmental variability

Abalone is a high-value resource that is an important export market fishery of Mexico that is managed through territorial use rights for fisheries allocated to a coastal community. A specific age-structured spatial bioeconomic model was applied to this fishery to undertake stock recovery to target levels. The model incorporates uncertainty in the parameter k of a von Bertalanffy growth function with environmental variability. The risk of falling below and exceeding the target and bioeconomic limit reference points of the population with alternative fisheries management strategies was studied using a Monte Carlo analysis. The management strategy evaluation showed that Emin (minimum effort) and EmaxNPV (resource rent maximization effort) generated higher biomass levels and higher present value of resource rent than Emsy (effort in maximum sustainable yield) at the end of the simulation period, regardless of the bioeconomic reference points and assuming a reduction in fishing effort. Emin and EmaxNPV increased and maximized the present value of resource rent generated by the species while avoiding its overexploitation. The social consequences of the management strategies were considered with the participation of fishers of this co-managed fishery.

Developing predictive growth models for Asian seabass using four generations of data

Growth is an important trait in aquaculture breeding programs and production. Cost-effective and precise measurement of growth traits provides valuable information for growth monitoring, feed management, stocking density, size grading, and health management. However, in aquaculture species, precise measurement of growth traits is challenging. Predictive growth models based on large data sets have the potential to tackle this challenge. Here, we developed predictive growth models for the analysis of growth parameters for the Asian seabass using the dataset from four separate generations (F1-F4), aged between 90- and 768-days post-hatch (dph) in a 20-year selective breeding program. To analyze the length-weight relationship of the fish, the equation W=aLb was used to estimate the parameters a and b. Our results showed that there were high positive correlations between body length and weight in each generation. In addition, to explore the relationships between body weight and ages, for each generation of fish, we fitted two different models: the von Bertalanffy Growth Function (VBGF) and the Gompertz model to analyze the Age-Weight Relationship (AWR). Out of the two, the VBGF, showed a higher goodness of fit. These developed predictive growth models, in combination with digital imaging, will reduce the cost and time for measuring growth traits for breeding programs of Asian seabass, and the effective management of commercial production.

Age, growth and length-to-weight relationship of largehead hairtail (Trichiurus lepturus) in south-eastern Australia suggest a distinct population

The age, growth rates and length to weight relationships for the south-eastern Australian population of largehead hairtail (Trichiurus lepturus) were investigated for the first time. Age was estimated by counting annuli in sectioned sagittal otoliths, with a maximum age of 8 years estimated for males and females. We found no significant differences in the growth rates of males and females over the size (12–78 cm pre-anal length (PL)) and age (0–8 years) ranges sampled. However, females in our collection were larger on average than males, and all fish sampled >60 cm PL were female, suggesting that females may grow to larger sizes than males and that sampling of greater numbers of larger and older fish may be required in future. T. lepturus growth was described by the von Bertalanffy growth function parameters L∝ = 74.89 cm PL, K = 0.13yr−1 and t0 = −0.80 yr, with the L∝ being amongst the largest reported for the species. Growth was variable, with the sizes at any given age spanning up to 50 cm PL. Female T. lepturus increased in body weight relative to length faster than males, as has been reported in other populations. The length/weight relationship for the south-eastern Australian population was significantly different, with almost no overlap, from that reported for T. lepturus in the Arabian Sea. The substantial differences in growth rates, maximum sizes and body morphometrics of T. lepturus from south-eastern Australia in comparison to other populations globally are consistent with the hypotheses that it represents a distinct population, although investigations using additional population markers are required to verify this.

Age, Growth, and Reproductive Biology of Euchiloglanis davidi in the Middle and Lower Yalong River, China

In the present study, we investigated the age, growth, and reproductive characteristics of Euchiloglanis davidi, a species of Sisoridae fishes, from the Yalong River, China. Fish samples were collected from the tributaries of the middle and lower Yalong River in May 2013 and December 2015. Their standard length ranged from 67 to 190 mm, and the total weight ranged from 3.42 to 75.06 g. The age and growth pattern of E. davidi were determined using the vertebra. Furthermore, the sampled fish were categorized into 10 age groups (1–10 years old): the maximum age was 10 years and 9 years for male and female fish, respectively. The relationship between the standard length and weight was expressed as W = 6.744 × 10−5 L2.653, and the t-test showed allometric growth. The growth of E. davidi was defined by the von Bertalanffy growth function, described as Lt = 260.8(1−e−0.104(t+1.942)), Wt = 173.5(1−e−0.104(t+1.942))2.653, respectively. The growth inflection point was observed at 7.44 years, with corresponding length and weight values of 162.50 mm and 49.46 g. The fecundity ranged from 105 to 352 eggs, with an average of 205 eggs. The relative fecundity of weight (FW) ranged from 2.90 to 8.98 eggs/g, and the relative fecundity of length (FL) ranged from 0.71 to 2.11 eggs/mm. Altogether, these characteristics of slow growth and low fecundity demonstrated the vulnerability of E. davidi to exploitation in the middle and lower reaches of the Yalong River.

Assessment of Three Major Shrimp Stocks in Bangladesh Marine Waters Using Both Length-Based and Catch-Based Approaches

Penaeus monodon (tiger shrimp), Metapenaeus monoceros (brown shrimp), and Fenneropenaeus indicus (white shrimp) are the most economically important shrimp species in the waters of the Bay of Bengal, Bangladesh. This is the first analytical study to assess three major shrimp stocks using both length-based and catch-based methods, such as length-based Bayesian biomass estimation (LBB), length-based indicator (LBI), and a catch-based method entitled JABBA (Just Another Bayesian Biomass Assessment), to explore and process the data; estimate the growth parameters, with length at first capture; present relative biomasses; and approximate the reference points. The parameters of the von Bertalanffy Growth Function (VBGF) analysis for the tiger, brown, and white shrimps were L∞ = 113.0 mm, 85.4 mm, and 76.4 mm, respectively, for carapace length. Our results showed that the relative biomass level (B/BMSY) of the tiger shrimp was 0.43, suggesting an overfished status, and brown and white shrimps were 0.84 and 0.96, indicating that they were fully exploited but not overfished. This study, therefore, advised an optimum carapace length limit to catch from 57.0–70.0 mm for tiger shrimp, 44.0–53.0 mm for brown shrimp, and 40.0–48.0 mm for white shrimp. The estimated maximum sustainable yield (MSY) reference points were as follows: optimal biomass BMSY = 3116 mt, 15,885 mt, and 2649 mt for tiger, brown, and white shrimp, respectively, and optimal harvest rate uMSY = 12%, 33%, and 8% for tiger, brown, and white shrimp, respectively. The average annual catch values for the last ten years were 265 mt, 2396 mt, and 115 mt below the estimated MSY values of 389 mt, 4899 mt, and 209 mt for tiger, brown, and white shrimp, respectively. But, brown shrimp had the estimated highest carrying capacity (31,770 mt) and intrinsic growth rate (0.66) than the tiger and white shrimp, which was replicated distinctly in the graphical representation of the Kobe plot and the surplus production plot. Hence, the brown shrimp stock is estimated to be in a better state than the tiger and white shrimp stocks.

Population dynamics of thresher shark (Alopias pelagicus) landed at the Kutaraja fishing port, Banda Aceh

At the Kutaraja Fishing Port, the shark species Alopias pelagicus accounts for the vast majority of shark catches. The purpose of this research was to ascertain the length distribution of A. pelagicus, the length at which it was first captured, the sex ratio, the von Bertalanffy growth parameters and functions, the mortality rate, and the exploitation rate. This study was carried out in the Kutaraja Fishing Port from December 2021 to February 2022. The incidental sampling method was used to collect 406 samples in total. The FAO-ICLARM Stock Assessment Tools were utilized to analyze population dynamics parameters. The male, female, and combined length distributions of A. pelagicus ranged from 186-295cmTL, 205-304cmTL, and 186-305cmTL, respectively. The length of the first capture was 249.40 cmTL, 252.29 cmTL and 250.78 cmTL, sex ratio of males and females is 1:2.24, the asymptotic length (L∞) was 344.25 cmTL, fish age at length 0 (t0) was 0.066/year, with a growth rate (k) of 0.50/year, 0.36/year dan 0.19/year, 374.83 cmTL and 378.92 cmTL, 0.058/year dan 0.048/year. Natural mortality (M) was assessed to be 0.59/year, 0.47/year, and 0.31/year, fishing mortality (F) was 2.08/year, 2.47/year, and 2.20/year, and total mortality (Z) was 2.67/year, 2.94/year, and 2.51/year. The A. pelagicus exploitation rate (E) was 0.78/year, 0.84/year, and 0.88/year, demonstrating complete exploitation of the male, female, and combined populations.

Assessing fishery status and sustainable exploitation of spotted seabass (Dicentrarchus punctatus) in Bardawil Lagoon, Eastern Mediterranean, Egypt

The growth and population parameters of spotted seabass (Dicentrarchus punctatus) in Bardawil Lagoon were investigated to assess their fishery status and propose concrete recommendations for sustainable exploitation. The samples (n = 271) were collected from commercial catches during 2021. As revealed by examining the otoliths, D. punctatus has a short life span of a maximum of four years based on the mean lengths of 20.2, 25.3, 29.7, and 33.5 cm for age groups from I to IV, respectively. The total length-weight relationship equations were W = 0.0120TL2.9672 for males, W = 0.0127TL2.9486 for females and W = 0.0124TL2.9563 for the combined sexes. The von Bertalanffy growth function was Lt = 40.50(1-e-0.38(t+0.66)). The study determined the total and natural mortality rates as 1.58 and 0.79 year−1, respectively, with an exploitation rate (E) of 0.49, which was found close to the optimum value (0.5). However, based on management policies, E was greater than the value corresponding to 50% relative biomass per recruit (E0.5), which indicates that the current fishing effort is unsustainable. Therefore, to maintain the biomass of spawning stocks, the study recommends a 22.4% reduction in the current exploitation rate through the application of fishing regulations that decrease fishing efforts. Such recommendations can help ensure the sustainable exploitation of spotted seabass in Bardawil Lagoon.

Population dynamics and stock assessment of two major eels (Muraenesox bagio and Congresox talabonoides) from the marine waters of Bangladesh

Muraenesox bagio (black eel) and Congresox talabonoides (brown eel) are two major eels (Muraenesocidae) species which are commercially significant in the marine catch of Bangladesh, but population dynamics and stock assessment of marine eel fishery in Bangladesh are yet to be studied. This study is the first endeavour to analyze the population dynamics and stock assessment of this marine eels collected from July 2021 to May 2022 using three length-based methods namely TropFishR, the Length Based-Spawning Potential Ratio (LB-SPR) & the length-Based Indicators (LBI) and two catch-based methods including Depletion-Based Stock Reduction Analysis (DB-SRA) and the Catch-Maximum Sustainable Yield (CMSY). A slightly positive allometric growth pattern (b=3.10) for the black eel and a negative allometric growth pattern (b=2.33) for the brown eel were observed in the length-weight relationship. The parameters of von Bertalanffy Growth Function (VBGF) and the linearized length-converted catch curve (LCCC) analysis for black eel and brown eel were L∞=190.67cm and 166.63cm, k=0.18 year-1 and 0.16 year-1, and the total mortality, Z=0.70 year-1 and 0.45 year-1. The eel fishery is calculated to be overfished due to overexploitation and the stock’s spawning biomass (SPR=19% for black eel and 21% for brown eel) is close to the limit reference point but well outside the targeted range because the majority of the catches were found to have below-maturity levels. This study advised an optimum length limit to catch from 93 to 114 cm for black eel and 83 to 101 cm for brown eel. Though the estimated reference points of the CMSY were more optimistic than those from the DB-SRA, the tendency of the status of eel stock has been displayed moving towards overexploitation from a safe stock scenario. This study, therefore, recommended an annual landing limit of 250 mt as OFL (Over fishing limit) for the next ten years in association with existing management measures to maintain the present stock biomass of eel fishery over the BMSY level.

Assessing the Size-Structured Stock of the Swimming Crab Callinectes amnicola (Crustacea: Portunidae) in the Cross River, Nigeria

Abstract An important aspect of the size-structured stock is the assumption that individuals progress from one size class to another after a certain time. In this study, a total of 2581 monthly samples of the swimming crab Callinectes amnicola were collected from the landings of the artisanal crab fishery in the Cross River, Nigeria over a period of 13 months, from January 2021 to January 2022. Crabs ranged in length from 6.5 cm to 15.5 cm, with most crabs caught during the dry season. The fewest crabs (n=23) were caught in August 2021, and the most (n=662) were caught in January 2021. Because moulting and other physiological obstacles make it difficult to determine crab age, length frequency data were used instead. Swimming crab assessment was based on some basic growth parameters of the von Bertalanffy growth function and the Beverton and Holt growth model. The results showed that the asymptotic length and growth rate were 16.28 cm and 0.940 per year, respectively. The best growth index was estimated to be 2.40, while longevity and mortality were 3.19 years and 3.46 per year, respectively. The calculated exploitation rate of 0.41 was below the guideline of 0.5 and the maximum yield per recruit of 0.421, confirming an underfished stock. Sustainable exploitation of the Cross River swimming crab was recommended by reducing efforts on already exploited fishery resources.

A biological and ecological study of the invasive pufferfish Torquigener hypselogeneion (Bleeker 1852) [conspecific Torquigener flavimaculosus Hardy & Randall, 1983] in the Eastern Mediterranean

The highly toxic orange-spotted toadfishTorquigener hypselogeneion(Bleeker 1852) [conspecificTorquigener flavimaculosusHardy & Randall, 1983] is now a very common invasive fish in the Eastern Mediterranean. Its small size, well under 20 cm, may have concealed the danger it represents, and little is known about its biology or ecology. Here, the spawning seasons, gonado- and hepato-somatic index and condition factors ofT. hypselogeneionfrom 3 locations of the Eastern Mediterranean are presented, based on a total of 1360 individuals sampled, i.e., 216 from Finike, 817 from Fethiye (both Turkey), and 327 from Cyprus. Our results show thatT. hypselogeneionis a carnivorous species that forages on sandy bottoms, with a preference for small invertebrates, especially the small invasive gastropodCerithium scabridum, crustaceans (hermit crabs, other crabs and barnacles), and sea urchins; however, at least in some localities, they appear to forgo eating during their peak reproductive period. The parameters of the von Bertalanffy Growth Function forT. hypselogeneionin the Eastern Mediterranean were: asymptotic length = 17.4 cm (total length; TL) and K = 0.96 year-1, implying a longevity of about 4 years, while the mean length at first maturity was about 10 cm (TL) for both sexes. An average-sized adult female (13 cm TL, 45.7 g live weight) was found to contain 1,250 eggs per gram body weight. Based on its high invasiveness and negative impacts to ecology of the Eastern Mediterranean and the human health, we suggest thatT. hypselogeneionshould be listed as a priority invasive species and that its population closely monitored within the Mediterranean Sea.

Life-history traits in two invasive species of tilapias in Morocco

Life-history traits (LHT) of Oreochromis niloticus in the Sidi Mohamed Ben Abdellah reservoir (BA reservoir) and Oreochromis aureus in the Nador Channel were studied and compared with those of other populations in the world. Specimens were collected between June 2018 and June 2020. Females of both species were smaller at first sexual maturity than males (O. niloticus: 204 vs. 255 mm, O. aureus: 147 vs. 158 mm). The age of maturity for each species was estimated from seasonal otolith growth marks, based on the von Bertalanffy growth function. The asymptotic length was higher in O. niloticus (males 296 mm and females 339 mm) than in O. aureus (males 171 mm and females 169 mm). Based on a literature survey and the results of this study, the type of ecosystem (reservoir vs. river) influenced growth performance indices (φ and φ′) in both species, with reservoirs leading to a higher asymptotic length in both O. niloticus and O. aureus than rivers. Moroccan populations presented the lowest growth index in the populations assessed. These observations suggest that while both invasive species were able to colonise and adapt to their new environments, this was at the expense of limiting their growth and reducing their size at first sexual maturity.