Instantaneous Mortality Research Articles

Population Dynamics of Nile Tilapia (Oreochromis niloticus, L. 1758) in Lake Nubia, Sudan

This study aims to investigate the population dynamics of Nile tilapia (Oreochromis niloticus, Linnaeus, 1758) in Lake Nubia, Sudan. Monthly samples were collected from fishermen from January to December 2021, and recorded total lengths (TL) of 996 specimens nearest to 1.0 mm using a standardized measuring board; the lengths (TL) exhibited a range from 5.2 to 41.3 cm. Population parameters were assessed using the ELEFAN I routine within FiSAT II software, which produced von Bertalanffy growth parameters as follows: an asymptotic length (L∞) of 43.05 cm, a growth curvature (K) of 0.230 yr⁻¹, and a theoretical length at age zero (t0) of -0.1816. The growth performance index (Φ') was calculated to be 2.639. The instantaneous mortality rates were evaluated, revealing total mortality (Z) at 0.65 yr⁻¹, natural mortality (M) at 0.63 yr⁻¹, and fishing mortality (F) at 0.02 year⁻¹; While the exploitation rate (E) was determined to be 0.04 yr⁻¹. The size at first capture (Lc) was obtained as 5.2 cm, while L50 was estimated at 10.07 cm, both being below the size at first maturity (Lₘ) of 13.5 cm, and the longevity (Tmax) was noted to be 12.86 years. The results indicated poor utilization of the Nile tilapia population in Lake Nubia, and its size at first capture and L50 was below the size at first maturity. This situation is an indication of the need for a continuous process of monitoring and managing to reduce the harvesting of smaller individuals and to improve productivity toward achieving levels that optimize sustainable yield.

Assessing Blue Catfish population dynamics across varying introduction timelines in Georgia

AbstractObjectiveUnderstanding the dynamic rate functions of introduced fish populations is essential in guiding management strategies. Blue Catfish Ictalurus furcatus population dynamics have been well studied; however, there is a gap in knowledge from populations that have been introduced into novel systems.MethodsBlue Catfish were collected from the Altamaha, Ocmulgee, Oconee, and Satilla rivers in Georgia. Age estimates were obtained through otolith analysis. Multimodel growth analysis was used to describe growth patterns, and early life growth was modeled with linear regression. Instantaneous mortality of each population was estimated and compared by using a generalized linear model approach.ResultThe four introduced Blue Catfish populations exhibited rapid growth and low mortality rates during establishment; however, we found that populations with earlier introduction histories generally had slower growth rates and lower mortality. The Satilla River population is comparatively the most recently introduced population (first discovered in 2011) that exhibited the fastest growth and highest mortality.ConclusionOur results suggest that Blue Catfish in our study systems are in an intermediate stage of invasion and have not yet reached an equilibrium state. As density continues to increase in these river systems, we expect a decline in growth rates, delayed sexual maturation, and a greater observed maximum age. However, additional monitoring is needed to identify how population dynamics and reproductive characteristics vary over time.

Population Dynamics of Nile Tilapia (Oreochromis niloticus, Linnaeus.1758) from Khashm El-Girba Reservoir, Atbara River, Eastern Sudan

This study was conducted to assess the population parameters of Nile tilapia, Oreochromis niloticus, in the Khashm El-Girba Dam Reservoir in Eastern Sudan. Fish samples were collected from December 2019 to November 2020. Length-frequency data were collected from 1,671 specimens ranging from 5.1 to 34.2 cm in total length (TL). Analysis of the population parameters was determined using the ELEFAN I routine and the FiSAT II software computer program revealed that the estimated the Von Bertalanffy growth parameters were as follows: asymptotic length (L∞ = 36.75 cm), growth rate (K = 0.650 year -1) and age at length zero (t0 = -0.629) and the growth performance index (Φ') was calculated at 2.943. The instantaneous total mortality (Z), natural mortality (M), and fishing mortality (F) rates were determined using the length-converted catch curve and empirical models. The values obtained were Z = 2.38 year -1, M = 1.22 year -1, and F = 1.16 year -1, respectively. The exploitation rate (E) of the Nile tilapia was calculated at 0.49 year -1. The size at first capture (Lc) was estimated at 15.64 cm, which is slightly greater than the size at first maturity (Lm = 14.5 cm) and longevity (Tmax) was found to be 4.62 years. These findings indicate that the stock of the Nile tilapia population in Khashm El-Girba reservoir is overexploited, and that monitoring and management practices need to be employed to maintain the stocks at the optimum exploitation level.

A method for estimating biomass of age-0 fish in case of protracted spawning leading to multiple larval cohorts in the population

We propose a new method for estimating the density and biomass of fish larvae and early juveniles when spawning is extended over time and the egg production in spawning groups varies widely with time. As a proof of concept, the method is applied to catch data for age–0 polar cod (Boreogadus saida), collected by the ichthyoplankton survey in the Kara Sea in 2019. The biomass among different size classes of age–0 fish was calculated based on the selectivity of a Bongo net with 500-μm mesh size. The age of larvae and juveniles in each group and average length at hatch (5.5 mm) were determined used for assessing average growth rate (0.18 mm/day) and hatching date for each age–0 fish assemblage. By fitting the population curve to the samples of age–0 polar cod collected in a small area sequentially over ten days, the instantaneous rate of natural mortality was estimated as ∼ 0.05 day-1. Changes in abundance and biomass over time were modeled by the Baranov's equation and power growth function. The average biomass for the time step of interest was calculated by projecting each cohort abundance to a selected point in time and taking a weighted average of all cohort biomasses.

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.

Phenotypic plasticity, and temporal and spatial variation in the relative abundance of lentic brook trout, Salvelinus fontinalis, across Ontario.

Brook trout (Salvelinus fontinalis) are a highly prized species found in lakes and streams throughout Ontario. A broadscale monitoring program (BsM) has been conducted in lakes throughout the province, in 5-year cycles, which targets Salvelinus fontinalis populations. The objective of this study was to use the data gained from the BsM and establish a contemporary baseline on the variation of relative abundance and demographics of natural lake populations of S. fontinalis in Ontario. Additionally, given the variability in environmental conditions across the landscape, an objective was to assess the factors, abiotic and biotic, that influence relative abundance among waterbodies. Over the three BsM cycles (2008-2022), 273 S. fontinalis waterbodies were assessed, some multiple times, and 124 were unique populations. S. fontinalis were sampled in 112 of these unique lakes. In total, 7487 S. fontinalis were caught and 5372 were fully sampled (length, weight, and age assessed). The mean catch-per-unit-effort (CPUE) in all waterbodies was 1.4 (0.12 standard error) S. fontinalis per net gang. There was not a significant trend in CPUE over the three BsM cycles nor did CPUE vary significantly among BsM cycles at the provincial scale, but CPUE varied significantly among fisheries management zones (FMZs). Multiple variables were examined to explain the variation in CPUE across the province; a negative association with species diversity was the only variable considered significant. Furthermore, S. fontinalis were more associated with the relative abundance of small cyprinids (i.e., chubs and shiners) and negatively associated with centrarchids, smelt, and other game species. Mean growth potential was greater for males than females but not significantly, whereas longevity favored females. Growth potential and parameters were similar between sexes within FMZs but varied among FMZs. Mean survival among these populations was 25.7%, ranging from 15.2% to 45.6%, with a mean instantaneous mortality of 1.41. This study provided a contemporary assessment of the current range and variability in relative abundance population dynamics of S. fontinalis in lakes within Ontario. This provides a benchmark to assess changes with the pending stressors of climate change and human expansion across the landscape.

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

The significance of shooting angle in seal shooting.

The present study aimed to investigate the relationship between shooting angle to the head and animal welfare outcomes in the hunt of young harp seals (Pagophilus groenlandicus). The study population consisted of young harp seals belonging to the Greenland Sea harp seal population. A sample of 171, 2-7 weeks old, weaned harp seals of both sexes were included. The study was conducted as an open, randomised parallel group designed trial during the regular hunt. The animals were allocated into four groups, A-D, according to the observed shooting angle to the head, defined as the angle between the direction of the shot and the longitudinal axis of the animal's head: (A) directly from the front; (B) obliquely from the front; (C) directly from the side; and (D) obliquely or directly from behind. Instantaneous death rate (IDR) and time to death (TTD) were the main variables. The mean IDR differed significantly between groups and was highest in group B (96.8%) and lowest in group C (66.7%). For all groups combined it was 84.2%. The mean TTD for seals not rendered instantaneously unconscious or dead (n = 27) differed significantly between groups and was shortest in group A (16 s) and longest in group C (85 s). However, the number of animals included in the TTD analysis was limited. In conclusion, based on the significantly higher IDR, the shooting angle obliquely from the front is recommended to help achieve the best animal welfare outcomes during the hunt of young harp seals.

Grinding as a slaughter method for farmed black soldier fly (Hermetia illucens) larvae: Empirical recommendations to achieve instantaneous killing.

At least 200 billion black soldier fly (Hermetia illucens) larvae (BSFL) are reared each year as food and feed, and the insect farming industry is projected to grow rapidly. Despite interest by consumers, producers, and legislators, no empirical evidence exists to guide producers in practicing humane - or instantaneous - slaughter for these novel mini-livestock. BSFL may be slaughtered via freezing, boiling, grinding, or other methods; however standard operating procedures (SOPs) and equipment design may affect the likelihood of instantaneous death using these methods. We tested how larval body size and particle size plate hole diameter affect the likelihood of instantaneous death for black soldier fly larvae that are slaughtered using a standard meat grinder. Larval body size did not affect the likelihood of instantaneous death for larvae that are 106-175 mg in mass. However, particle size plate hole diameter had a significant effect on the likelihood of instantaneous death, with only 54% of larvae experiencing an instant death when using the largest particle size plate (12-mm hole diameter) compared to 84% using the smallest particle size plate (2.55 mm). However, a higher percentage of instantaneous death (up to 99%) could be achieved by reducing the proportion of larvae that become stuck in the machine. We conclude by outlining specific recommendations to support producers in achieving a 99% instantaneous death rate through specific SOPs to be used with similarly designed machines. We also develop a protocol for producers that wish to test their own grinding SOPs.

The management of common carp fisheries using spawning potential ratio in the southeast of the Caspian Sea

AbstractSpawning potential ratio (SPR) is an important index used by fisheries biologists and managers to determine how a fishery should be harvested to prevent recruitment overfishing. In the southeastern Caspian Sea, Iran, 3430 common carp Cyprinus carpio were caught by beach seine in 2‐week intervals of two fishing seasons in 2019 and 2020. Fork length (FL) was measured to the nearest 1 cm. The age and maturity stage of 434 specimens, including 236 females and 198 males, were estimated by scale and gonad microscopic examinations. Estimated L∞ was 71.9 and K (growth constant) was 0.09. Instantaneous total mortality (Z) was 1.08, natural mortality (M) was 0.18, and fishing mortality (F) was 0.9. Estimated SPR at current fishing mortality (0.18) was lower than the reference point (0.4). Our findings indicated that fishing mortality should be reduced to F = 0.38 for C. carpio to meet the SPR reference point of 0.4. Further, higher minimum length limits should be set to reduce fishing mortality, and catch quotas for fishing cooperative corporations should be considered to meet the 40% SPR threshold.

Is the clinical phenotype impact the prognosis in dementia with Lewy bodies?

IntroductionThe first predominant clinical symptoms of dementia with Lewy bodies (DLB) are highly variable; however, the prognosis based on initial predominant symptoms remains poorly understood.MethodsMulticenter retrospective study in 4 French expert neurological centers. Patients were categorized in 3 groups according to their first more predominant symptoms: cognitive, psychiatric, or motor.ResultsAnalysis of 310 DLB patients. The mean age was 73.5 years old (SD 7.5) including 32.3% of women. The mean follow-up was 7.25 years (SD 3.6). We observed that the full clinical picture was more frequent in the motor group than in the cognitive group (p = 0.01); male gender and age at onset were associated with a significant excess risk of instantaneous mortality (p = 0.01).ConclusionInitial symptoms may affect the clinical course of patients, but no significant difference in mortality was observed.

Estimates of the Age, Growth, and Mortality of Triplophysa scleroptera (Herzenstein, 1888) in the Upper Reaches of the Yellow River, China

To investigate the age composition, growth pattern, mortality, and exploitation rate of Triplophysa scleroptera in the upper reaches of the Yellow River, we measured the total length (L) and body weight (W) of 347 individuals based on three sampling surveys from 2022 to 2023. The otoliths were used in this investigation to determine age. The total length of the collected samples ranged from 5.69 cm to 18.40 cm, body weight ranged from 1.65 g to 50.22 g, and the age ranged from 1 to 7 years old. The relationship of total length and body weight was W=0.009L2.942 for the total samples, and the growth pattern observed in the study belongs to the isometric type. The von Bertalanffy growth equation revealed that the fish had an asymptotic total length L∞ of 37.536 cm, and the growth coefficient K was 0.064 yr−1. Total instantaneous mortality rate (Z) of total samples calculated by the age-based catch curve method was 1.092 yr−1. The average instantaneous rate of the natural mortality (M), estimated by three different methods, for the total samples was 0.237 yr−1. The instantaneous rate of fishing mortality (F) for the total samples was calculated as 0.855 yr−1, and the exploitation rate (E) was determined as 0.783. As a whole, compared with other Triplophysa fishes, the growth rate of T. scleroptera in the upper reaches of the Yellow River is relatively slow, and the population of T. scleroptera has been overexploited. It is crucial to establish some effective management strategies to protect this species.

Life History Traits of the Stygophilous Amphipod Synurella ambulans in the Hyporheic Zone of the Lower Reaches of the Upper Sava River (Croatia)

Estimating the growth and population dynamics of crustaceans is important for understanding the role of species in ecosystems and for conservation and monitoring purposes. This study investigated temporal and spatial variation in population dynamics (growth rate, instantaneous mortality rates, and longevity) of the stygophilous freshwater amphipod Synurella ambulans (F. Müller, 1846), and influencing environmental factors. Seasonal sampling was conducted from December 2018 to October 2019 at two sampling sites (Jarun and Medsave) along the Sava River in northwestern Croatia. A Bhattacharya cohort analysis was applied to the length-frequency data using the FISAT software package. At least four cohorts were distinguished during the year. The possible influence of environmental factors on growth parameters was investigated using Canonical Correspondence Analysis (CCA), which revealed that the important environmental factors influencing S. ambulans abundance were water temperature and dissolved oxygen concentration. The average total body length (TBL) of females was 4.25 mm, while the TBL of males was 3.34 mm. The asymptotic length (L∞) and growth coefficient (K) were estimated to be 6.30 mm and 0.92 year−1 for females and 5.40 mm and 0.59 year−1 for males, respectively, at the Jarun site. L∞ and K were estimated to be 7.20 mm and 0.34 year−1, respectively, for females and 4.00 mm and 1.20 year−1, respectively, for males at the Medsave site. Estimated total mortality (Z) for each sex had higher values for males than females at both sampling sites. The lack of ecological knowledge on S. ambulans populations and relationships with invertebrate communities in the hyporheic zone of the large river ecosystems emphasises the importance of a detailed study for protecting this species and its vulnerable ecotonal groundwater-connected environment.

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.

Density, structure, growth, and mortality of the population of Ocypode gaudichaudii H. Milne Edwards & Lucas, 1843 (Brachyura, Ocypodidae) in Salaverry, Peru

Abstract The northern coast of Peru includes a series of dissipative desert beaches with varying levels of human impact. One endemic species to these beaches is Ocypode gaudichaudii, which has been shown to be an indicator of ecosystem disturbance. We measured population density, sex ratio, and cephalothorax length of O. gaudichaudii on three beaches near Salaverry between September 2021 and February 2022. The average population density was 0.15 burrows/m2. There was a higher proportion of males (56%); and average cephalothorax length was 28.8 ± 5.6 mm. Population, length, and sex variations during the study may be explained by behaviour of O. gaudichaudii and by temperature-dependent breeding. We also calculated the Von Bertalanffy growth parameters (, , ) and estimated the instantaneous mortality rate to be 0.84/year. These data indicate a high level of disturbance in the ecosystem, with few specimens approaching .

A generalized application of the catch-curve regression with comparisons of adult mortality and year-class strength between hatchery-stocked and wild-reared lake trout in US waters of Lake Huron

The recently developed approach to estimating the instantaneous total mortality of coded-wire-tagged lake trout ( Salvelinus namaycush) is generally applicable to catch-at-age data. We further formalized the technique to objectively incorporate the year-class and year effects into the model structure of catch-curve regression. We used this new method to compare adult mortality and year-class strength between the hatchery-stocked and wild-reared lake trout in US waters of Lake Huron, one of the Laurentian Great Lakes. Model comparisons showed no difference in adult mortality between the hatchery-stocked and wild-reared lake trout. Based on 95% confidence intervals, the estimate of adult mortality using the simple catch-curve regression with average number-at-age was not statistically different from the estimate using the linear mixed model with individual number-at-age of multiple year-classes and sampling years. The linear mixed model, however, also quantified lake trout year-class strength and indicated that since 2003, the increases in recruitment of wild-reared lake trout did not fully compensate for the rapid declines in recruitment of hatchery-stocked lake trout in Lake Huron.

River- and Sex-Specific Annual Survival Rates of Mature Anadromous Alewife (Alosa pseudoharengus)

During multiple annual spawning runs from 2013 to 2021, over 9,000 mature anadromous alewife (Alosa pseudoharengus A. Wilson, 1811) were monitored with passive integrated transponders (PITs) in four rivers of the Chignecto Isthmus, Bay of Fundy, Canada. A subsample of 384 individuals tagged during 2016–2019 were aged from 3 to 6 years (mean ± SD; 4.2 ± 0.7 years, n = 232, males; 4.5 ± 0.7 years, n = 152, females). Biotelemetry revealed that one unsexed individual survived seven years post tagging, possibly making it 10–13 years old. Return rates varied among the rivers, with the lowest rates in the most anthropogenically impacted river. Biotelemetry and ageing data were used to estimate apparent annual survival rates ranging from 0.25 to 0.50 depending on the river and the year. Based on capture-mark-recapture (CMR) analysis of biotelemetry data from the three less impacted rivers, the estimated overall annual survival was 0.396, total instantaneous mortality (Z) was 0.93, and future life expectancy from time of release was 1.08 years. Frequency distribution of ages 4–6 for alewife pooled from all four study rivers estimated a lower annual survival rate of 0.301, Z = 1.20, and a future life expectancy of 0.83 years. The biotelemetry detection rates were 0.89–0.98 but varied depending on the river and the year, with the lowest rates in one river during 2017-2018 possibly related to a malfunctioning tide gate preventing upstream fish passage and subsequent detection. Based on CMR, males had a higher survival rate compared to females, which translated into an overall mean survival increase of 0.05. Alewife survivorship in our study highlighted that a limited ecosystem-based management period is required to mitigate river connectivity and mortality issues to avoid loss of population cohorts and decrease the risk of extirpation.

Net-chasing training improves the size homogeneous of freshwater prawn Macrobrachium rosenbergii reared at high stocking density through behavioral regulation

Heterogeneous growth is a major concern for the intensive culture of prawns. Social interaction is believed to be one of the major contributions to the dispersed prawn size. We used net-chasing training to improve the size homogeneous of freshwater prawn Macrobrachium rosenbergii reared at high stocking density through the behavior regulation. Two stocking densities (low and high densities corresponding to 40 and 80 prawns m−2) and two training modes (no-chasing and 25%-exhausted net-chasing training) were applied. The prawns were cultured under four treatments (2 stocking densities × 2 training modes) using three replicates for 45 days. The fighting behavior, mortality and organ loss, and size heterogeneity were determined in a 9-day interval (on days 9, 18, 27, 36, and 45). The results showed that high stocking density induced an increase of fighting frequency and mortality with organ loss. The instantaneous mortality with organ loss was positively correlated with fighting frequency. The increased frequency of fighting and cannibalism induced by high density can be reduced by 25%-exhausted net-chasing training; however, the positive effects of net-chasing training on these behaviors were seen after 18 days of chasing. The size heterogeneity was increased at high stocking density, but can be further improved by at least 18 days of net-chasing training. The net-chased prawns reared at high density still showed obvious growth dispersion on days 9. These findings indicate that net-chasing training suppressed the behavior of fighting and cannibalism, producing a homogeneous prawn size at high density. The net-chased effects on the behavior and size heterogenous depended on the time of training, and long training periods (i.e., at least 18 days) should be employed when using net-chasing training to improve the heterogenous growth of prawns.

Applying a novel state-space stock assessment framework using a fisheries-dependent index of fishing mortality

State-space models have a hierarchical framework that assumes the observed data are derived from a time series of unobserved latent states. State-space stock assessment models have emerged as an alternative framework to conduct stock assessment in Canada, the east coast of the United States of America, and in Europe though little research has investigated where and how they are optimally used and if they would be appropriate in other geographical contexts. We built a novel state-space stock assessment model with process variation in recruitment and time- and age- specific catchability. We fit the model to commercial trap net and gill net catch and effort data of Lake Michigan lake whitefish using a marginal likelihood that integrated over latent states. Compared to the previously employed statistical catch at age model, the state-space model estimated dome-shaped, rather than asymptotic selectivity for both fisheries, 15% lower average total instantaneous mortality, and 20% higher average recruitment. To our knowledge this is the first application of a state-space stock assessment model fit by maximum likelihood in the Laurentian Great Lakes and the first such model to not include a fisheries-independent survey. These results demonstrate the feasibility of employing a maximum likelihood state-space framework in fisheries that lack such fishery independent indices of abundance and instead use catch per unit effort as an index of abundance. This work presents a novel approach to applying state-space stock assessment modeling and offers insights and suggestions for future use in the Great Lakes and in similar circumstances of data availability.