Instantaneous Natural Mortality Research Articles

Estimates on age, growth, and mortality of Leuciscus chuanchicus (Kessler 1876) in the Ningxia section of the upper reaches of the Yellow River, China

To investigate the age structure, growth pattern, mortality and exploitation rates of Leuciscus chuanchicus in the upstream Ningxia section of the Yellow River, four sampling surveys were conducted between 2022 and 2023. A total of 472 individuals were measured for their total length (TL) and body weight (W). Age determination was performed using otoliths. The collected samples had a range of total lengths from 4.52 to 37.45 cm, body weights ranging from 0.68 to 552.43 g, and ages ranging from 1 to 7 years old. The relationship between total length and body weight was expressed as W = 0.0052 L3.19 for all samples, which indicates that the growth of L. chuanchicus adheres to allometry. The Von Bertalanffy growth equation revealed that the fish had an asymptotic total length (L∞) of approximately 37.9 cm with a growth coefficient (K) value of approximately 0.461 yr−1. Using the age-based catch curve method, the calculated total instantaneous mortality rate (Z) for all samples was determined as being equal to approximately 1.1302 yr−1. Additionally, three methods were used to estimate the average instantaneous rate of natural mortality (M), resulting in an approximate value of 0.7167 yr−1 for all samples. Furthermore, the instantaneous rate of fishing mortality (F) for all samples was calculated as 0.4134 yr−1, leading us to determine that the exploitation rate (E) is 0.3658. It was concluded that the growth rate of L. chuanchicus in the upstream of the Yellow River is relatively fast, and L. chuanchicus has not been subjected to excessive exploitation, yet its relatively high natural mortality rate underscores the need for targeted management measures aimed at preserving its habitat.

Population dynamics and stock assessment of Queenfish (Scomberoides commersonnianus) from the marine waters of Bangladesh

AbstractThe Queenfish, Scomberoides commersonnianus, is a large commercial fish in Bangladesh. This is the first study on the Queenfish that aims to elucidate life history parameters and stock status to suggest authority for sustainable management and to support future research on this economically significant species in the region. We used three length‐based approaches to establish a standard for sustainable management of the fishery: (1) TropFishR to give the growth parameters and current exploitation status, (2) the length‐based Bayesian biomass estimation (LBB) to quantify stock biomass, (3) and Froese's sustainability indicators (LBI). The length–weight relationship of Queenfish was a negative allometric pattern (b = 2.84; R2 = 0.98). Growth parameters for Queenfish were L∞ = 124.22 cm, K = 0.31 year−1. Instantaneous total mortality Z = 0.71 year−1, instantaneous natural mortality M = 0.36 year−1, and instantaneous fishing mortality F = 0.35 year−1. Based on the LBB approach, the current estimated stock biomass was overexploited (B/BMSY = 0.65). We recommend strictly maintaining mesh size of nets to reduce harvest of immature fish shorter than 62 cm, while focusing harvest on fish 62–74 cm, to minimise recruitment and growth overfishing.

Fishery, population dynamics and stock assessment of flat needlefish Ablennes hians (Valenciennes, 1846) from the south-eastern Arabian Sea off Kerala coast, India

The age, growth, mortality parameters and stock status of Ablennes hians(Valenciennes, 1846) were assessed by using length frequency, catch, and effort datacollected from the commercial catches along the coast of Kerala (south-eastern ArabianSea) during 2015-2017. The growth parameters, L∞, K and t0 were estimated at 133.9 cm TL,0.72 yr-1 and -0.0026 yr, respectively. The instantaneous natural mortality (M), total mortality(Z), fishing mortality (F) and current exploitation rate (Ecur) were estimated as 0.95 yr-1,2.78 yr-1, 1.83 yr-1 and 0.66, respectively. Length at capture (Lc50) was estimated at 77.58cm TL, which is greater than Lm50. Beverton and Holt yield per recruit analysis, indicated thatmaximum Y/R could be obtained at an exploitation rate (Emax) of 0.75, suggesting scope foran increase in exploitation. In this analysis, spawning stock biomass (SSB) was not takeninto consideration, which is essential for maintaining recruitment in the future. In the presentstudy, E0.1 (0.61) and Ecur (0.66) were nearly equal, indicating that the fishery is running atan economic reference point i.e., maximum economic yield (MEY). Thompson and Bellprediction model showed that at the current level of exploitation, the SSB was reduced by20.49% and hence, there is no scope for further increase in fishing efforts to maintain the SSBat a relatively safe and sustainable level. The analysis revealed the maximum sustainableyield (MSY) of this species as 90.26 t, which can be obtained by increasing the present levelof fishing effort by 1.3 times but would result in the depletion of the SSB to a critically lowlevel of 15.65%. Therefore, a precautionary safe level of exploitation (E0.1), estimated at 0.61for the species, is recommended. Keywords:Belonidae, Fishery management, Population dynamics,Spawning stock biomass, Stock status

Estimates of adult Lake Trout mortality fromcoded wiretags in a population with developing natural reproduction in southern Lake Michigan

AbstractObjectiveOverfishing and Sea LampreyPetromyzon marinuspredation led to extirpation of Lake TroutSalvelinus namaycushfrom Lake Michigan in the 1950s. Large populations of hatchery‐reared fish were developed by the 1970s, but natural reproduction was limited until the early 2000s when it began to increase in the southern main basin. Hypothesizing that the relatively low mortality of spawning‐aged fish contributed to this reproductive success, we estimated the total annual mortality rate for this population.MethodsWe used catch curves to estimate the total instantaneous mortality rateZusing coded wire tags, which provided definitive ages. We made separate estimates from fish collected in three on‐going surveys: a spring gill‐net survey, a fall gill‐net spawning survey, and a sport fishery survey.ResultOur estimates ofZ ± SE were 0.297 ± 0.019, 0.239 ± 0.009, and 0.205 ± 0.007 for the spring, spawning, and sport fishery surveys, respectively. We suggest that the meanZ ± SE of all survey estimates of 0.247 ± 0.027 would be a reasonable estimate for this population, which equates to a total annual mortality of 22 ± 3%. This estimate is in the low range of rates reported for the species and is in the same range as other populations in the Great Lakes with well‐established natural reproduction.ConclusionWe concluded that these low total mortality rates contributed to the reproductive success in southern Lake Michigan through increasing spawning stock density and age structure and that previous estimates of another important population parameter, the instantaneous natural mortality rateM, were too high. Estimates ofMranged from 0.210 to 0.240 and were based on the Pauly equation, a growth‐ and temperature‐based estimator. We suggest maximum‐age‐based estimators ofMare more appropriate for Lake Trout. Several alternative maximum‐age‐based estimators produced estimates forMof 0.132–0.058, all of which are more compatible with our estimate ofZ.

Length-based assessment of an exploited coastal pike (Esox lucius) stock (Rügen, southern Baltic Sea) underscores the crucial relevance of growth and natural mortality for assessment outcomes

Many capture fisheries are considered data-poor, including the northern pike (Esox lucius) fishery in brackish lagoons in the southern Baltic Sea of Germany. The objective of our work was to assess the exploitation status of this stock, which is perceived by stakeholders to be in decline. Size structure data collected via rod-and-reel-angling, fyke nets, and gill nets, and empirical estimates of growth, maturation, and fecundity from the lagoon stock were used to fit the Length-Based Spawning Potential Ratio (LB-SPR) model. Parameter uncertainty in von Bertalanffy growth estimates and natural mortality in the Baltic Sea pike stock was considered in sensitivity analyses. Assessment outcomes were sensitive to estimates of growth rate, particularly asymptotic length L∞, instantaneous natural mortality M, and gear selectivity. Under-aging of old fish in scale-based age estimates overestimated terminal length and generated negative bias in the estimated stock status. Despite the sensitivity of assessment outcomes to life-history parameter choice, the stock status for the Baltic Sea consistently indicated a fully exploited situation with SPRs robustly above 0.4 and current fishing mortality rates between 0.2 and 0.4 yr−1. This result agreed with previous assessments using catch-only models. Our work serves as a reminder, that when using length-based methods, unbiased growth, and natural mortality estimates are critical for robust assessment outcomes.

Informing Management of Atlantic Bluefin Tuna Using Telemetry Data

Sustainable management of exploited marine fish and wildlife populations requires knowledge about their productivity. Survival from natural causes of mortality is a key component of population productivity, but is notoriously difficult to estimate. We evaluate the potential for acoustic telemetry as a long-term monitoring tool to estimate rates of natural mortality. We present a Bayesian multistate mark-recapture model for telemetry data collected over a decade from 188 Atlantic bluefin tuna (Thunnus thynnus) and apply it to estimate the rate of natural mortality using only acoustic tag detections for all animals, or using acoustic tag detections for 96 single-tagged tuna plus acoustic tag detections combined with estimated positions from pop-up satellite archival tags for 92 double-tagged animals. We support the model for bluefin tuna with a simulation study to quantify bias in estimates of population dynamics parameters and investigate the effect of auxiliary information from satellite tagging on mortality rate estimates for different acoustic tag detection probability scenarios.We obtained posterior estimates of the instantaneous annual natural mortality (survival) rate across a decade of tagging for Atlantic bluefin tuna of 0.17 yr-1 (0.84 yr-1) both using only acoustic tagging data, and using a combination of acoustic and satellite tagging data. Use of a prior implying a higher rate of fishing mortality yielded an instantaneous annual natural mortality (survival) estimate of 0.10 yr-1 (0.90 yr-1), with combined acoustic and satellite tag data. Results from the simulation study indicate that the use of satellite tags can improve the precision and accuracy of estimates of detection probabilities, area-specific movement probabilities and mortality rates, where the extent of the improvement depends on true underlying acoustic tag detection probabilities. Our work demonstrates that long-term acoustic tagging data sets have strong potential for monitoring of highly migratory marine fish and wildlife populations, providing information on a number of key parameters, including survival and movement rates. However, improved information on tag reporting rates or fishing mortality is needed to better separate natural and fisheries mortality for Atlantic bluefin tuna.

Life-history traits facilitate the population success of the sergeant major Abudefduf saxatilis (Linnaeus, 1758, Perciformes: Pomacentridae) in the Caribbean Sea

ABSTRACT Trade-offs among life-history traits (e.g. growth, reproduction, and survival) are fundamental to the population success of living beings in the wild. This study describes the life-history traits of the sergeant major, Abudefduf saxatilis, one of those fishes most abundant in the coral reefs of the Caribbean Sea. The reproductive biology, age, growth, and abundance of a particular population of A. saxatilis from Mexico was explored using 12 monthly samplings to collect 414 specimens, and abundance monitoring through visual censuses for age-based demographic analysis. Our results indicated that A. saxatilis would have an opportunistic strategy with a type II survivorship curve since the studied population was characterized by fast growth, maturation at intermediate sizes (≈11 cm L T or 2.5 yrs. old), with batch spawning and indeterminate fecundity, protracted spawning season (January to September), high abundance of recruits, low instantaneous natural mortality (M = 0.114 year −1), high life expectancy at birth (e 0 ≈ 4.7 yrs.) and maturity (e α ≈ 2.8 yrs.), and high annual survival of adults and high survival to maturity (). All these life-history traits facilitate the population success of A. saxatilis, showing a high reproductive effort and a rapid population turnover, making this species an efficient colonizer.

Age, Growth, Mortality and Reproduction Biology of the Black Seabream, Spondyliosoma cantharus in North Aegean Sea, Turkey, Mediterranean Basin

In the present study, the population parameters (length-length and length-weight relationships, age, growth, mortality) and reproductive biology (sex ratio, GSI, condition, length at first maturity, spawning period, fecundity) of black seabream (Spondyliosoma cantharus Linnaeus, 1758) were investigated. The length-length relationship and length-weight relationship were calculated as FL=0.911TL-0.0433 and W=0.0123TL3.0614 (R2=0.97), respectively. Parameters of the von Bertalanffy growth equation were: L∞=33.21 cm, K=0.21 per year, t0= −1.84 year and age varied between 0 and 8 years. The instantaneous rates of total mortality (Z) and natural mortality (M) were 0.64 and 0.47 per year, respectively. Rates for fishing mortality (F) and exploitation (E) were 0.17 and 0.27 per year, respectively. The spawning season extended from February to May and peaked in March and April. The female/male ratio was found to be 3.49/1 and sex inversion from female to male occurred after the 24 cm TL length group. Total lengths at 50% maturity were 22.25 cm for males and 20.59 cm for females. The mean absolute fecundity (F) was 109,457±8,011 oocytes, ranging from 59,666 to 182,589.

Estimating the natural mortality rate of saucer scallops (Ylistrum balloti) on the Queensland east coast from tag-recaptures

Saucer scallops (Ylistrum balloti) were tagged and released on four occasions inside two areas closed to fishing (Hervey Bay A, HBA; and Yeppoon B, YB) on the Queensland (Australia) east coast and their subsequent recaptures over the following months were used to measure the instantaneous rate of natural mortality (M). A total of 13,295 scallops were tagged and 526 recaptured over the 15 month-long experiment (May 2018 to August 2019). Three statistical approaches were applied to the experimental design and analysis of the tagging data, based on 1) the Brownie model, 2) a modified version of the Brownie model, and 3) a binomial logistic regression model of recaptures. Estimates of M based on the Brownie model were much higher for tagged scallops that were at liberty over summer months compared to those at liberty over the winter months, possibly indicating seasonal variation. The logistic model parameter estimates indicated the proportion of recaptures differed significantly with the lunar phase at recapture, scallop size class, the number of days the scallops were at liberty and the interaction between days-at-liberty and closure. All three approaches indicated M was higher in HBA compared to YB. Mean estimates of M for the whole fishery, derived by averaging estimates from both closures, ranged from a minimum of 1.461 year–1 for the logistic model, to 1.501 year–1 for the Brownie model, to 1.548 year–1 (variable recapture rate) and 1.594 year–1 (fixed recapture rate) for the modified Brownie model. Estimates from all three approaches were higher than the previous estimate that was published over 40 years ago and possible reasons for the increase are discussed.

Age, Growth, and Mortality of Atlantic Tripletail in the North‐Central Gulf of Mexico

AbstractIn the southeastern USA and the Gulf of Mexico (GOM), Atlantic Tripletail Lobotes surinamensis are increasingly targeted by recreational anglers, indicating that stock status should be assessed. A critical need for such assessments is age‐specific data; however, previous studies have drawn conflicting conclusions regarding the most appropriate structure for aging. Moreover, growth parameters and mortality rates for GOM Atlantic Tripletail are unknown. Therefore, the goals of this study were to (1) evaluate sagittal otoliths and first dorsal spines as aging structures; (2) model combined and sex‐specific growth; and (3) estimate mortality rates for GOM Atlantic Tripletail. From 2012 to 2019, Atlantic Tripletail (N = 230, including a near‐record‐size specimen) were collected from the north‐central GOM via hook and line and were aged using otoliths and first dorsal spines. Total length ranged from 212 to 940 mm, and age ranged from 0.07 to 5.27 years. Otoliths produced higher percent agreement (95.0%) and lower average percent error (3.0%) between readers compared to spines (82.9% and 6.5%, respectively). The von Bertalanffy growth parameters differed slightly between the otolith‐based data (mean asymptotic length [L∞] = 762.42 mm, Brody growth rate coefficient [k] = 0.69 year−1, and hypothetical age at which length equals zero [t0] = −0.58 year) and spine‐based data (L∞ = 718.83 mm, k = 0.79 year−1, and t0 = −0.56 year). For both otolith‐ and spine‐based sex‐specific data, the best‐fitting version of the von Bertalanffy growth function permitted L∞ to vary by sex. Chapman–Robson estimates of instantaneous total mortality rate and total annual mortality rate were 1.15 and 68.66%, respectively. Based on empirical, life history‐based methods, the instantaneous natural mortality rate was estimated at 0.75–0.97 and the instantaneous fishing mortality rate was estimated at 0.18–0.45, suggesting low levels of exploitation. These growth parameters and mortality estimates will provide information for future stock assessments, thereby ensuring sustainability of the GOM stock of Atlantic Tripletail.

Climate Change May Cause Shifts in Growth and Instantaneous Natural Mortality of American Shad Throughout Their Native Range

AbstractAmerican Shad Alosa sapidissima is an anadromous species with populations ranging along the U.S. Atlantic coast. Past American Shad stock assessments have been data limited and estimating system‐specific growth parameters or instantaneous natural mortality (M) was not possible. This precluded system‐specific stock assessment and management due to reliance on these parameters for estimating other population dynamics (such as yield per recruit). Furthermore, climate‐informed biological reference points remain a largely unaddressed need in American Shad stock assessment. Population abundance estimates of American Shad and other species often rely heavily on M derived from von Bertalanffy growth function (VBGF) parameters. Therefore, we developed Bayesian hierarchical models to estimate coastwide, regional, and system‐specific VBGF parameters and M using data collected from 1982 to 2017. We tested predictive performance of models that included effects of various climate variables on VBGF parameters within these models. System‐specific models were better supported than regional or coast‐wide models. Mean asymptotic length (L∞) decreased with increasing mean annual sea surface temperature (SST) and degree days (DD) experienced by fish during their lifetime. Although uncertain, K (Brody growth coefficient) decreased over the same range of lifetime SST and DD. Assuming no adaptation, we projected changes in VBGF parameters and M through 2099 using modeled SST from two climate projection scenarios (Representative Concentration Pathways 4.5 and 8.5). We predicted reduced growth under both scenarios, and M was projected to increase by about 0.10. It is unclear how reduced growth and increased mortality may influence population productivity or life history adaptation in the future, but our results may inform stock assessment models to assess those trade‐offs.

Life history parameters of Yellowfin hind, Cephalopholis hemistiktos (Rüppell, 1830) in the coast of United Arab Emirates

The life history parameters, including age, growth, mortality and recruitment of Yellowfin hind, Cephalopholis hemistiktos were studied in monthly collected samples from January to December 2018. Otolith was used for age determination. Mean size by the end of each year of life was estimated and showed that, the highest annual increment was identified at the end of the first year of life then gradually decreased with increase of fish age. The estimated von Bertalanffy growth parameters were L ∞ =43.51 cm, K =0.26 per year, t 0 =-0.74 year. Asymptotic weight W ∞ was estimated as 1375.23 g. The length-weight relationship was W =0.0126 L 3.0746 with R 2 =0.94 for both sexes. The instantaneous rates of total mortality and natural mortality were estimated as 0.77 and 0.49 per year, respectively. The gonado-somatic index showed increasing from April to August with a peak in June for both sexes. Size at first capture (L c ) was estimated as 24.30 cm, which was smaller than the mean size at first sexual maturity 25.31 cm. The value of fishing mortality (F=0.28y -1 ) was slightly higher than the optimum (F opt =0.25y -1 ) and smaller than the limit (F limit =0.33y -1 ) biological reference point, indicating that species was exploited within sustainable limit. Estimated parameters and the relative yield-per-recruit analysis showed that this species is not over-exploited.

The unknown Baranov. Forty years of polemics over the formal theory of the life of fishes

Abstract The year 2018 marked the 100th anniversary of the publication of paper “On the question of the biological basis of fisheries” by F.I. Baranov considered a cornerstone paper of modern fishery science. Baranov formalized population dynamics by describing changes in population abundance using differential equations, introducing the concept of instantaneous fishing and natural mortality rates, and developing his catch equation, which is the foundation of most modern age-structured stock assessment models. Baranov was the first to show the effect of fishing on population structure based on theoretical grounds. At the time of its publication, Baranov’s paper did not receive much attention in Russia and was completely unknown to scientists in the West. The second publication (On the question of the dynamics of the fishing industry, 1925) received substantial criticism from many and sparked a furious debate between Baranov and his opponents that lasted for several decades. The history and content of those debates, expressed in multiple papers by Baranov, is still largely unknown. I describe the essence of arguments by Baranov and his opponents. The story of these scientific debates reveals how different philosophical concepts and dominant points of view evolved through time.

STOCK STATUS OF BLUE SWIMMING CRAB (Portunus pelagicus) IN TANAH LAUT, SOUTH KALIMANTAN, AND ITS ADJACENT WATERS

A study on the stock status of blue swimming crab (Portunus pelagicus Linnaeus, 1758) was conducted in Tanah Laut, South Kalimantan waters, based on data collected in March to November 2017. The results showed that the growth pattern of blue swimming crab in Tanah Laut waters was negatively allometric and the sex ratio of males to females was 1.0 : 1.7. The chi-square test indicated that the total males and total females of the blue swimming crab was significantly different. It means that there was an imbalance in numbers between males and females. The estimated length at first capture (Lc) was 127.26 mm (carapace width; CW), smaller than the length at first maturity (Lm) at 133.24 mmCW. The growth parameter of blue swimming crab was 1.1year with a maximum carapace width (L) of 204.3 mmCW. The estimated instantaneous total mortality (Z) and natural mortality (M) were 3.04/year and 1.24/year, respectively. While fishing mortality (F) and exploitation rate (E) were 1.80/year and 0.59/year, respectively, the estimated spawning potential ratio (SPR) was 11.1 %. Therefore, the stock status was categorized as overfishing. In order to ensure the sustainability of the blue swimming crab, a precautionary approach,, such as reducing fishing effort by 18 % of the current situation, is strongly recommended to apply.

Reproduction, Growth, Mortality and Yield of the Goatfish Upeneus sulphureus in Northern Bay of Bengal, Bangladesh

Information on stock condition and reproductive biology are important for fisheries conservation and management planning. This study examined reproduction, growth, mortality and yield of sulphur goatfish (Upeneus sulphureus Cuvier 1829), which is a low-value food fish abundantly caught as bycatch in artisanal and industrial fishing from the southeast coast of Bangladesh at northern Bay of Bengal. Data were collected monthly obtaining samples from local fish landing center. The gonadosomatic index indicated that U. sulphureus spawns twice a year during January–May and August–October. Fecundity of the fish was positively correlated with the body and gonad weight, and varied from 15 128–97 274 eggs with fish weight 11.30–58.73 g. Monthly length–frequency distribution was analyzed through FISAT software, thus the estimated seasonalized von Bertalanffy growth parameters were L∞ = 21.80 cm, K = 0.54 per year, C = 0.5, WP = 0.1 and Rn = 0.300, respectively. Moreover, the value of seasonalized total mortality coefficient Z (2.24) was smaller than that of the non-seasonalized Z (4.16). The instantaneous natural mortality and fishing mortality, calculated for non-seasonalized total mortality, were 1.31 and 2.86, respectively. Furthermore, the high exploitation rate (E = 0.69) was close to maximum exploitation level (Emax = 0.75) in yield-per-recruit analysis, suggesting that U. sulphureus is being exploited at the MSY (maximum sustainable yield) level. Therefore, further increase in fishing effort may reduce U. sulphureus stocks in the coastal waters of Bangladesh.

Age, growth and reproductive biology of the saddled seabream (Oblada melanura) in the North Aegean Sea, Eastern Mediterranean

AbstractThis study determines the length distribution, length– weight relationship, age, growth parameters, mortality rate, sex ratios, length at first maturity and reproduction of saddled seabream (Oblada melanura) collected monthly by fishermen around the Northern Aegean Sea between November 2017 and October 2018. The length–weight relationship was calculated asW=0.0091×L3.11(R2=0.95) and positive allometric growth was found. The condition factor and GSI varied between 0.81–1.58 and 0.01–9.61, respectively. The spawning season extended from May to July and peaked in June. Total lengths at 50% maturity were 18.97 cm for males and 18.83 cm for females. Parameters of the von Bertalanffy growth equation were:L∞ =29.91 cm,K=0.27 per year,t0=−0.82 year and age varied between 1 and 8. The instantaneous rates of total mortality (Z) and natural mortality (M) were 1.36 and 0.58 per year, respectively. Rates for fishing mortalityFand exploitationEwere 0.78 and 0.57 per year, respectively. The mean absolute fecundity (F) was 117 075±23 243 oocytes, ranging from 19130 to 470 132.

Estimates of Red Drum Mortality via Acoustic Telemetry

AbstractSubadult (age < 3) Red Drum Sciaenops ocellatus support a valuable recreational fishery, and mortality estimates for young Red Drum are needed for proper management. To obtain these estimates, age‐1 and age‐2 Red Drum were implanted with acoustic transmitters and external Floy tags in two coastal Alabama rivers (Fowl and Dog rivers). Fates of tagged fish were inferred from stationary receiver detections and active relocations over 1 year. These fates were used in a Bayesian multistate model to estimate instantaneous monthly and annual mortality and emigration rates for each river and overall from both rivers. Instantaneous monthly fishing mortality (F) ranged from 0.001 to 0.112 (annual F = 0.414) in Dog River, from 0.001 to 0.126 in Fowl River (annual F = 0.309), and was 0.001–0.054 (annual F = 0.337) overall. Instantaneous monthly natural mortality (M) ranged from 0.001 to 0.002 (annual M = 0.069) in Dog River, from 0.001 to 0.036 (annual M = 0.178) in Fowl River, and from 0.001 to 0.017 (annual M = 0.090) overall. The overall annual estimate of instantaneous total mortality (Z) was 0.435. The median escapement percentage was estimated at 36.3% (95% posterior credible interval = 19.5–56.0%) using M and Z from the overall model. Unfortunately, the error on this estimate was large and inconclusive as to whether the 30% escapement goal for juvenile Red Drum to the adult population from Dog and Fowl rivers is being met. Monthly residency estimates were typically greater than 0.90, and overall annual residency was estimated at 0.716. Fishing mortality estimates from the current study are higher than recent catch curve estimates that did not include young Red Drum. These results demonstrate that young Red Drum need to be accounted for when generating mortality estimates and provide needed data for the Red Drum recreational fishery.

Length-weight relationship and population dynamics study of the giant catfish (Arius thalassinus) in the Bay of Bengal coast of Bangladesh

The present study investigated the length-weight relationship, population parameters and the instantaneous natural mortality rate of Arius thalassinus from two major landing center of Bangladesh using the FAO-ICLARM Stock Assessment Tools (FiSAT II). A total of 1789 specimens were collected between January 2016 and December 2017. The estimated values of the exponent “b” was ranged from 3.019 (pre-monsoon) to 3.293 (monsoon), indicating an isometric growth pattern of the species with high correlation coefficients (0.904 to 0.927). The equation of length–weight relationship was: W=0.005L3.181. Model parameters of the von Bertalanffy growth equation were: L∞ = 97.60 cm and K = 0.33-1 year. The estimated growth performance index (Ø) was 3.497. The instantaneous natural mortality rate (M) was 0.62-1 year and a high exploitation rate (E) 0.62 (>0.50) showed that this fish is over-exploited in the Bay of Bengal coast of Bangladesh.
 Res. Agric., Livest. Fish.6(3): 439-444, December 2019

Population dynamics of the mullet fish, Rhinomugil corsula (Hamilton, 1822), in the Sitakunda coast of the Bay of Bengal

Population dynamics of the mullet species, Rhinomugil corsula, was studied, using FiSAT-II program, with the length-frequency data of 2480 fish specimens. The asymptotic length (L∞) and growth coefficient (K) of this fish were estimated to be 31.4 cm and 1.0/year, respectively. The instantaneous rate of natural mortality (M), fishing mortality (F) and total mortality (Z) were estimated to be 1.73, 1.20 and 2.93, respectively. The recruitment pattern of the species was prolonged with two peaks, major peak during June to December and a minor peak during January to April. The L25, L50 and L75 were found to be 8.61, 10.42 and 12.23 cm, respectively. The relative yield per recruit (Yʹ/R) and biomass per recruit (Bʹ/R) were 0.751 and 1.731, respectively. The value of exploitation (E) was found to be 0.41 which indicated that R. corsula was not over fished (E > 0.50) in the study area. The maximum exploitation (Emax) value was 0.55. The growth performance index (ϕ´ = 2.99) of R. corsula in the Sitakunda coast of the Bay of Bengal was found to be moderate.
 Bangladesh J. Zool. 47(2): 305-314, 2019

Karadeniz'de 2013-2014 Av Sezonunda Avlanan Hamsinin (Engraulis encrasicolus) Büyümesinin ve Ölüm Oranlarının Farklı Modellerle Belirlenmesi

Bu çalışma, Eylül 2013 ve Nisan 2014 tarihleri arasında Doğu Karadeniz sahillerinde avcılık yapan ticari gırgır teknelerinden örneklenen hamsi balığının yaşa dayalı altı farklı büyüme modeline göre (von Bertalanffy, Gompertz, Lojistik ya da Richards, Üssel, Morgan Mercer Flodin ve Weibull) büyümesi ve dört ölüm oranı modelline göre (Pauly, 1980; Djabali vd., 1993; Alagaraja, 1984 ve Srinath, 1998) ölüm oranının belirlenmesi amacıyla yürütülmüştür. Toplamda 5486 balık örneklenmiş ve 1265 balığın yaş tayini yapılmıştır. Dişilerin ortalama boyu erkeklerden daha büyük hesaplanmıştır (P < 0,05). Erkekler için Weibull (AIC = 2593,5; L∞ = 19,6 cm ve K = 0,031 yıl-1) ve Morgan Mercer Flodin (AIC = 2593,8; L∞ = 17,0 cm ve K = 0,108 yıl-1), dişi için ise von Bertalanffy (AIC = 5725,42; L∞ = 11,1 cm ve K = 2,064 yıl-1) ve Üssel (AIC = 5725,4; L∞ = 11,1 cm ve K = 2,065 yıl-1) büyüme modellerinin en uygun modeller olduğu belirlenmiştir. Av eğrisi yöntemine göre hesaplanan dişilerin toplam ölüm katsayısı (Z = 3,5 yıl-1) erkeklerden (Z = 3,3 yıl-1) daha büyük hesaplanmıştır. Dişi ve erkek bireyler için hesaplanan doğal ölüm oranı (M) en düşük Djabali vd. (1993) modelinde, en yüksek ise Srinat (1998) modelinde hesaplanmıştır. Farklı büyüme modeli parametreleri kullanılarak hesaplanan doğal ölüm oranları ve M verileri kullanılarak hesaplanan işletme oranı (E) değerleri 2014-2015 av sezonunda hamsi stokunun optimum değerden (E = 0,5) daha yüksek bir derecede işletildiğini yani av baskısı altında olduğunu göstermiştir.