Natural Mortality Research Articles

Growth, mortality, exploitation, and recruitment patterns of Labeobarbus altianalis (Boulenger, 1900) in River Kuja-Migori, Kenya

The Ripon barbel, Labeobarbus altianalis, a riverine fish found in the Lake Victoria Basin is regarded as species of less concern, but it is vulnerable to overfishing and population decline. This study aimed at determining growth, mortality, exploitation rate, and recruitment patterns of L. altianalis (Boulenger, 1900) in River Kuja-Migori. A total of 1,217 specimens with overall total lengths ranging from 9.5-41.5 cm (mean 28.5 ± 2.7) were collected monthly from January to December 2021. The fish were caught using an electrofisher in wadable areas and monofilament nets in deeper areas. Electronic length frequency analysis (ELEFAN) software in Fish Stock Assessment Tools (FiSAT II) program was used to analyze data. Natural mortality (M) Fishing mortality (F) and total mortality (Z) coefficients were 0.15 year-1, 0.52 year-1 and 0.67 year-1 respectively. The asymptotic length (L∞) was 44.94 cm TL while the instantaneous growth rate (K) was 0.15 year-1. The exploitation rate was 0.44 year-1 and the length-based growth performance index (Ø’) was 3.03. Results indicated that the longevity of L. altianalis was 9 years. Recruitment occurs throughout the year with bimodal annual recruitment peaks coinciding with the two rainy seasons in the region. This study provides important information for developing management advice for the L. altianalis riverine fishery.

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.

Insights into trypanosomiasis transmission: Age, infection rates, and bloodmeal analysis of Glossina fuscipes fuscipes in N.W. Uganda.

Tsetse flies (Glossina) transmit species of Trypanosoma which cause human African trypanosomiasis (HAT) and animal African trypanosomiasis (AAT). Understanding the epidemiology of this disease and controlling the vector rationally requires analysis of the abundance, age structure, infection rates and feeding patterns of tsetse populations. We analysed a population of G. fuscipes fuscipes in the Koboko district of Uganda. Seasonal variation in the abundance of tsetse was assessed from the numbers of tsetse caught in pyramidal traps. The age structure of the population was assessed by dissecting female tsetse to estimate their ovarian categories. Classical and PCR-based methods were utilised to determine the presence of the three major pathogenic species of salivarian trypanosomes: T. vivax, T. congolense and T. brucei in a subset (n = 2369) of flies. Further, bloodmeal analysis was carried using PCR to amplify and sequence a portion of the vertebrate cytb gene. The abundance and age structure of tsetse populations were relatively stable and a slight seasonal four-fold variation in abundance appeared to be correlated with rainfall. Analyses of age structure suggests a low natural daily mortality of 1.75% (1.62-1.88). Infection rates estimated were significantly greater (1.9-9.3 times) using the PCR-based method compared to the classical dissection-based method. Positive rates for T. brucei sl, T. congolense and T. vivax were 1.6% (1.32-2.24), 2.4% (1.83-3.11and 2.0% (1.46-2.63), respectively by PCR. The majority of bloodmeals were identified as cattle (39%, 30.5-47.8) and human (37% of meals, 28.4-45.6). The seasonally stable abundance, low mortality rate and high proportion of bloodmeals from humans may explain, in part, why this district has historically been a focus of sleeping sickness. Additionally, the high rates of cattle feeding indicate insecticide treated cattle may prove to be a useful vector control strategy in the area.

Do women state legislators and administrators make any difference in preventing natural disaster mortality? Evidence from India

Abstract We investigate the effect of women's political representation in the state legislative assembly and public administration on natural disaster mortality in 20 Indian states from 1981 to 2019. The paper combines two critical dimensions: political and administrative representation of women and disaster risk reduction. Results suggest that women's political representation reduces total disaster mortality after controlling socioeconomic and political covariates; however, the effects are statistically insignificant for the current and lag periods. We find that a one standard deviation increase in women's representation in public administration lowers total disaster mortality by 20.6 percentage points, which is 9.8 per cent of the sample mean. We observe the impacts of female administrative representation on gender-specific human development outcomes through reduced male and female disaster mortality, and we explain some mechanisms. Thus, women's political and administrative representation is crucial for addressing disaster mortality as it has major public health consequences.

Analisis Dinamik Model Predator-Prey dengan Efek Pemanenan Pada Populasi Ikan Nike (Awaous Melanocephalus) di Provinsi Gorontalo

Gorontalo Province is one of the areas directly adjacent to Tomini Bay, which is known for its rich natural resources, especially in the fisheries sector such as Nike fish (Awaous melanocephalus). Nike fish is the main food commodity for people in the Gorontalo region. However, intensive fishing activities can pose an extinction threat to this species. This study aims to understand the dynamics of the Nike fish population using a predator-prey model that integrates the effects of harvesting on the prey population. The research process includes formulation of assumptions, model building, model validation, and data analysis through mathematical analysis and numerical simulation. The analysis showed that the model has four equilibrium points, each with different stability conditions. Numerical simulations showed that an increase in harvesting rate and natural mortality of prey, as well as a decrease in birth rate, could threaten the viability of the Nike fish population. Thus, appropriate management efforts are needed to maintain ecosystem balance and the sustainability of the Nike fish population. The calculation results show that the Nike fish production threshold in Gorontalo Province is 8.470.858 kg per year. However, the amount of Nike fish production in Gorontalo Province in 2023 only reached 56,75% of the threshold. This indicates that the production of Nike fish in Gorontalo can still be increased as long as the harvest limit is observed to prevent extinction.

Management considerations of moose life‐history characteristics in Colorado, USA

Wildlife management agencies are obliged to provide evidence‐based management recommendations to stakeholders. However, allocation of resources towards the management of species is rarely uniform. The consideration of life‐history characteristics of moose offers wildlife managers a more robust understanding of population ecology, while also providing insight into potential limiting factors for long‐term management. From 2014–2020 we simultaneously measured survival of adult female moose, as well as calf productivity, in relation to the nutritional condition of adult females, in Colorado. Mean annual adult survival was high (93% and 95% confidence interval: 91–95%). Human hunter harvest was the leading source of mortality and lowered annual adult survival to 88%. Malnutrition was the leading source of natural mortality. Mean annual pregnancy rates were relatively low (77%) and highly variable (95% confidence interval: 65–88%). However, low pregnancy rates were compensated for by high apparent calf survival. The best predictor of moose pregnancy was nutritional condition. Our data suggest that bottom‐up ecological processes were affecting moose population growth, but populations were likely increasing during our study, with a simulated population growth rate of 1.04 (95% confidence interval: 0.94–1.17).

The Impact of Different Thinning Regimes on the Growth Dynamics of Pure Norway Spruce Stands in Lithuania

Forest growth under changing environmental conditions has been a major concern worldwide. The estimations of forests’ growth trends may provide significant insight on changing the value of Norway spruce (Picea abies (L.) H. Karst.) forests. The purpose of this study was to estimate the growth dynamics of thinned and un-thinned spruce stands in Lithuania by assessing their standing volume, gross volume yield, and stand density. For this purpose, two pure Norway spruce sites, established in 1990 and 1992, were selected. The thinning treatment scheme for each trial, comprised of five distinct stand density variants and eight different yield parameters, were analysed for each plot. Control plots exhibited the smallest growth in diameter, whereas stands that had been thinned once at a young age displayed the largest diameter increment (peak—1.4 cm/year). An increasing trend in tree stem volume was registered in all thinning treatment plots. The greatest competition index was found in the control plots, indicating an exceptionally high competition (peak—4.6–5.1) between trees for growth space. The competition index was four times smaller (2.0) in the moderately thinned stand. Intensifying natural mortality rate and signs of growth stabilization in the control plots (un-thinned) cannot guarantee them the positions of the highest productivity and accumulated stand volume in the future compared with thinned spruce stands.

Assessing the multifaceted repercussions of chemical insecticides on vegetable yield and human population: A modeling study

Vegetables stand out as invaluable reservoirs of essential vitamins, minerals, antioxidants, and vital dietary elements, yet their production faces a considerable threat due to insects. To tackle this challenge, farmers spray chemical insecticides to enhance vegetable yields by controlling the insect population. Nevertheless, the presence of insecticide residues in vegetables stands as a primary contributor to acute illnesses and chronic health conditions in humans. In the present research work, we formulate a novel nonlinear mathematical model meticulously designed to scrutinize the multifaceted repercussions of chemical insecticides on vegetable yield and the human population. In our model formulation, we adopt a dynamic approach where insecticide application on vegetables in agricultural fields correlates with the insect population. However, we acknowledge the consequential impact of insecticide usage on human health, which in turn reduces the growth rate of the human population. This study determines the critical value of the spraying rate of insecticide at which the human population reaches its maximum, ensuring that human needs for vegetables are met while minimizing the adverse effects of insecticide. Since various species of insects attack vegetables in the field and different insect species have different natural mortality rates, therefore we also identify the range of natural mortality rates of insects for which vegetable yield is minimal and fluctuates with time. Further, our research reveals that if the natural mortality rate of insects in a certain crop field lies within this identified range, then farmers should increase the insecticide spraying rate to avoid this upheaval situation and stabilize vegetable yield at a higher level.

Geese as keystone species in the Low Arctic of central Canada: the Karrak Lake Research Station

True abundance of lesser snow ( Anser caerulescens caerulescens, Linnaeus 1758) and Ross's geese ( Anser rossii, Cassin 1861, collectively referred to as “light geese”, in North America had been unknown in the 1980s. However, different indices of abundance suggested steady increases at the time. The Karrak Lake Research Station (KLRS) was established partly because it was not known if the breeding biology from more southern latitudes (the only information available at the time) was representative of more northern colonies where 90% of the midcontinent population of lesser snow geese nested. Visits in 1990 confirmed the continued importance of Karrak Lake and surrounding areas in Canada’s central Arctic to a large nesting concentration of both snow and Ross's geese documented previously. Key activities at KLRS were (1) colony-wide annual monitoring of nesting goose abundance and nesting performance and (2) large-scale marking efforts to monitor survival, range-wide abundance, distribution, and exploitation rate from hunter harvest and natural mortality rate. The scope of research expanded to include their interaction with local vegetation and other sympatric wildlife, including Arctic foxes ( Vulpes lagopus, Linnaeus 1758), king eiders ( Somateria spectabilis, Linnaeus 1758), long-tailed ducks ( Clangula hyemalis, Linnaeus 1758), and cackling geese ( Branta hutchinsii). Following exponential growth in the 1990s and 2000s, nesting populations of light geese at Karrak lake collapsed since 2012, presenting a unique opportunity to examine how local ecosystems recover and revert from heavy grazing by hyperabundant geese.

Absence of predator control increases cod extirpation risk in a Northwest Atlantic ecosystem: inference from multispecies modelling

Atlantic cod Gadus morhua in the southern Gulf of St. Lawrence (sGSL) declined to low abundance in the early 1990s and have since failed to recover due to high natural mortality, which has been linked to predation by grey seals Halichoerus grypus. Increased grey seal harvests have been suggested to improve cod survival; however, predicting the response of cod to changes in seal abundance in the sGSL is complicated by a hypothesized triangular food web involving seals, cod, and small pelagic fishes, wherein the pelagic fishes are prey for cod and grey seals, but may also prey on young cod. Grey seals may therefore have an indirect positive effect on pre-recruit cod survival via predation on pelagic fish. Using a multispecies model of intermediate complexity fitted to various scientific and fisheries data, we found that seal predation accounted for the majority of recent cod mortality and that cod will likely be extirpated without a strong and rapid reduction in grey seal abundance. We did not find evidence that reducing grey seal abundance will impair cod recovery by causing large increases in pelagic biomass so long as pelagic fishing mortality continues at historical levels.

Health impact assessment of exposure to road traffic noise and air pollution according to pre- and post-densification scenarios in Helsingborg, Sweden

A prevalent solution to accommodate population growth due to urbanization is densification. However, this often pushes new residential housing closer to roads, increasing exposure to both noise and air pollution. The present study’s aim was to estimate the health impacts of road traffic-related noise and air pollution for a low-income area (Drottninghög) in Helsingborg, Sweden, according to pre-densification (2012) and post-densification (2030) scenarios.Road traffic noise was simulated at the façade of residential buildings using the Nordic prediction method, and exposure was assessed using SoundPLAN. Exposure-response functions (ERF) from the WHO were utilized for the following health outcomes associated with noise: annoyance, adverse sleep disturbance, ischemic heart disease (IHD) incidence and IHD mortality. Air pollution (nitrogen dioxide, NO2) was assessed using a Gaussian dispersion model (AERMODE). Health outcomes associated with NO2 included natural cause mortality, pediatric asthma, respiratory hospitalizations and low birth weight (LBW). ERFs were derived from meta-analyses. Health impact assessments were then performed for both scenarios.Densifying Drottninghög according to the municipality’s planned strategy would lead to a 15 % unit increase in the proportion of residents exposed to road traffic noise above the WHO’s health-based guideline value (53 dB(A) Lden). This was estimated to markedly increase the proportion of residents highly annoyed by traffic noise (7.4–13.9 %) as well as those highly sleep disturbed (3.0–4.9 %). IHD incidence and IHD mortality attributed to noise would increase by an estimated 49 % and 44 %, respectively, post-densification. NO2 exposure was estimated to increase slightly (0.7 µg/m3) post-densification, which would contribute to an estimated 4–6 % increase in natural cause mortality, pediatric asthma, respiratory hospitalization and LBW.Urban planning initiatives need to consider these prevalent urban environmental exposures and integrate a public health perspective into densification strategies. Doing so can create synergies in the built environment that promote healthy, sustainable cities.

Modeling movements improves capture–recapture estimates for mobile species with sparse data: Polar bears (Ursus maritimus) in Viscount Melville sound

AbstractWildlife management requires estimates of demographic parameters that are difficult to obtain for mobile species at low densities. Biased parameter estimates often result from capture–recapture (CR) studies due to small sample sizes and unequal recapture probabilities, the latter of which can be caused by animal movements with respect to the sampling area. We developed a multistate CR model designed to minimize biases by including multiple data types (capture, harvest, natural mortality, and telemetry) and accounting for temporary emigration. We applied the model to data collected intensively from 2012 to 2014, and intermittently since the 1970s, for the Viscount Melville (VM) subpopulation of polar bears (Ursus maritimus) in the Canadian Arctic. The number of bears within the VM subpopulation boundary likely increased from an average of 145 (Bayesian 95% credible interval [CRI] [109, 221]) in 1989–1992 to 235 (95% CRI [148, 569]) in 2012–2014. Survival probability increased for all sex and age classes except adult females, for which estimates declined due to unknown reasons. Polar bear movements exhibited Markovian dependence with approximately 28% of the subpopulation located outside of the sampling area each spring. This contributed to inaccurate parameter estimates when using a simpler, single‐state CR model that only included capture data. Although the interpretation of demographic status was complicated by statistical uncertainty and changes in study design, our findings suggest that—as of 2014—the VM polar bear subpopulation had likely recovered from an earlier period of overharvest, was stable, and had not exhibited detectable negative effects of climate warming.

Estimates of life-history and growth parameters of exploited fish species in lakes Edward and George: Implications on exploitation status, population dynamics, management, and conservation of native species.

Adequate knowledge is essential for responsible inland fisheries. However, many inland fisheries lack monitoring, and therefore, decision-making for fisheries management is not reliable. In this paper, we used data from surveys and literature to estimate the life-history and growth parameters of 16 exploited fish stocks in the Ugandan part of Lake Edward and Lake George (East Africa). The estimated parameters are pivotal indicators of fish stock status, particularly in data-poor fisheries. The estimated parameters included maximum length (Lmax) and mean length (Lmean) as indicators of size structure in experimental and commercial catches, coefficients of length-weight relationships, length at 50% maturity (Lm50), fecundity, von Bertalanffy parameters, total mortality (Z), and natural mortality (M). These parameters were estimated using empirical formulae, statistical methods, and analyses of length frequencies. Only two stocks of semutundu Bagrus docmak exhibited significant and increasing trends in Lmax (Lake Edward) and Lmean (Lake George). The estimates for the remaining parameters were consistent with those in FishBase and other literature resources, either for the same species or related species. This consistency indicates their reliability for application in decision-making and further assessments. Some parameters showed evidence of unsustainable fishing. For example, estimates of Lm50 for four of the assessed stocks belonging to two species (Nile tilapia Oreochromis niloticus and marbled lungfish Protopterus aethiopicus) were lower than baseline estimates in the studied waterbodies. Furthermore, the Lmean in catches for all the stocks were less than the optimum lengths (Lopt), which maximize catches with a minimal impact on biomass and size structure. No significant changes in Lmean, length-frequency distributions, and size at maturity could be attributed to the management changes implemented in 2018, probably because it is too early to observe changes in these parameters. However, there are positive signs attributable to the changes in management as shown by a high proportion of mature individuals in commercial catches for most of the stocks for which the proportion was calculated, and an increase in Lmean and Lmax for some stocks, such as B. docmak, in commercial or experimental catches. New estimates from this study will enhance decision-making and further assessments of fisheries. Routine monitoring is recommended to update and improve the estimates.

Stock exploitation status of silver croaker (Pennahia argentata) from the East China Sea

Silver croaker (Pennahia argentata) is an important economic species in the East China Sea (ECS); however, its population has been declining, and studies on its status are scarce. This study collected biological data, including length, weight, and gonadal maturity of silver croaker from the southern coastal waters of Zhejiang Province between 2015 and 2021, to evaluate its life history and assess stock status. Methods from the TropFishR package were employed to estimate population growth and natural mortality parameters. Two widely used length-based data-limited models, length-based bayesian biomass estimation method (LBB) and length-based spawning potential ratio method (LBSPR), were applied to assess the stock status of silver croaker in the ECS. The results indicated that with a maximum age (Amax) of 4 years, the asymptotic length (Linf) was 23.80 cm, growth rate (K) was 0.74/year, and natural mortality coefficient (M) ranged from 1.068 to 1.376. Under the assumption of Amax = 5 years, Linf was 26.77 cm, K was 0.63/year, and M ranged from 0.818 to 1.193. The LBB and LBSPR models showed that, except for scenarios with L∞ = 23.8 cm, M/K = 1.46, and L∞ = 26.77 cm, M/K = 1.30, 1.38, or 1.48, the selectivity at length parameters L50SandL95S for silver croaker exhibited an increasing trend over the years. In the LBB model, L50S for different years consistently fell below the optimum length (Lc_opt), indicating that most individuals did not reach the size at first sexual maturity or optimal catch length. Moreover, under high fishing pressure, the Spawning Potential Ratio (SPR) and the unfished biomass ratio (B/B0) for silver croaker showed a decreasing trend, despite some stability or recovery in recent years. However, in all scenarios, SPR values were below 0.2, and B/B0 values were below 0.5, suggesting a significant risk of population collapse for silver croaker in the ECS due to intense fishing pressure. Therefore, it is recommended to reduce the current fishing pressure and increase the minimum catch size of this species for effective conservation and management in this region.

Stock assessment of the mud crab (Scylla olivacea) collected from the terrestrial edge of the Sundarbans mangrove forest, Bangladesh

We estimated mud crab (Scylla olivacea) population parameters to determine recruitment patterns, asymptotic carapace width (CW∞), growth coefficient (k), mortality rate (Z, M, and F), exploitation rate (E) and relationship between body weight and carapace width (BW - CW) in the terrestrial edge of the Sundarbans mangrove forest, Bangladesh. Baited long lines and traps were used to collect crab samples from the terrestrial edge of the mangroves (up to 10 km inside of the Sundarbans mangroves) monthly for a year (Jan 2021–Dec 2021). These CW frequency data were utilized to determine population characteristics. Based on the BW × CW relationship, male S. olivacea crabs increased their BW faster (b = 2.89, R2 = 0.86) than females (b = 2.29, R2 = 0.82). Crabs displayed negative growth allometry, b significantly differed from the isometric growth (b = 3). Both male and female CW∞ was estimated to be 126.00 mm and 113.40 mm, with k values of 0.50 yr−1 and 0.48 yr−1, respectively. The total mortality (Z), natural mortality (M), and fishing mortality (F) of male and female crabs were 1.89 yr−1 and 1.84 yr−1, 0.79 yr−1 and 0.80 yr−1 and 1.10 yr−1 and 1.04 yr−1 respectively. Both sexes were recruited using a bimodal recruitment strategy, with a significant peak from March to June. However, young crabs were present year-round. The virtual population analysis (VPA) shows that males and females are caught at smaller sizes (60–90 mm). The estimated exploitation rate (E) exceeds (0.58 for males and 0.57 for females) the optimum exploitation level (E = 0.50) and E values were close to the projected maximum yield per exploitation rate (Emax = 0.655 for males and 0.647 for females) which indicated over-exploitation of the mud crabs from the territorial edge of the Sundarbans mangrove forest of Bangladesh and hence suggested for proper management.

Observational evidence of the association between aerosol properties and lightning characteristics in the Indian subcontinent

Abstract Lightning is a leading cause of natural disaster-related mortality in the Indian Subcontinent. Currently, there is a lack of observational evidence supporting the role of aerosol composition in modulating lightning intensity and trends in this region. In this study, we analyzed satellite and reanalysis datasets to examine the association between aerosol properties and lightning intensity over three contrasting geographic regions of Indian subcontinent during the premonsoon season (1998-2022). By comparing lightning and non-lightning days, we found a 0.1 unit increase in total aerosol optical depth specifically on lightning days in all three study areas. Additionally, we observed that the aerosol composition of a region influences convective activity. The presence of dust alongside fine aerosols acts as efficient ice nuclei, thereby stimulating lightning activity in all three regions. Therefore, considering aerosol composition together with local meteorology is essential for accurately predicting lightning flash rates in a region.

Fishery and stock dynamics of ribbonfish Trichiurus lepturus (Linnaeus, 1758) in the Indian Exclusive Economic Zone

The fishery and stock dynamics of Trichiurus lepturus (Linnaeus, 1758) were studied in the Indian Exclusive Economic Zone (EEZ) for the period 2014-2019. The average annual landing was 2,09,285 t and varied from 1,77,259 to 2,39,355 t. Trawl nets were the majorgear, contributing more than 85% with an average annual catch rate of 4.56 kg h-1. The annual catch rate decreased over the years from 5.40 to 3.85 kg h-1. Landings (23,155-40,354 t) and catch rates (4.24-8.67 kg h-1) were highest during the post-monsoon months (September-December). Around 63% of the landings (1,32,072 t) were from the north-west coast, with Gujarat alone contributing three-fourth (98,296 t) of it, followed by the south-west coast (17%, 36,017 t), the south-east coast (12%, 25,322 t) and the north-east coast (8%, 15,875 t). The von Bertalanffy’s growth equation was Lt = 143.8 [1-e–0.48 (t + 0.03285)]. Natural mortality, Exploitation ratio and Maximum Sustainable Yield (MSY) were 0.76; 0.65 and 1,59,504 t respectively. Recruitment was substantial throughout the year with a single modal peak during June-October. With lower lengths at first capture and recruitment and with exploitation above the maximum permissible level and landings higher than MSY; the species appears to be overexploited along the Indian coasts. The present study is the first holistic report on the population parameters and stock status of T. lepturus from the Indian EEZ. Keywords: Cutlass fishes, Management, Recruitment, Stock dynamics

Length-weight relationship and exploitation of Macrobrachium species in the Burhi Gandak River, North Bihar, India

Three species of the Palaemonidae family, namely Macrobrachium dayanum (Henderson, 1893), Macrobrachium lamarrei (Milne Edw., 1837) and Macrobrachium malcolmsonii (H. Milne Edw., 1844) were investigated for their length-weight relationship and exploitation status in the Burhi Gandak River between July 2020 and June 2021. A total of 907 specimensof M. lamarrei, 942 M. dayanum and 962 M. malcolmsonii were collected using trap net (locally named Ghana Jal), Saalbhar Jal, Pelni, Dhonijal and Khorjal and traditional boats such as Nauka and Donga. M. lamarrei was found to be the dominant species among them in the catch composition. Peak landing was observed from June to August. The maximum length was recorded for M. malcolmsonii (16.8 cm) followed by M. dayanum (8.0 cm) and M. lamarrei (6.1 cm). The length-weight relationship of M. lamarrei, M. dayanum and M. malcolmsonii indicated negative allometric growth with slope (b) values of 2.7692, 2.6027 and 2.7513, respectively. The von Bertalanffy growth parameters viz., asymptotic length (L∞), growth coefficient (K) and age at zero length (to) were 5.67 cm, 2.3 y-1 and -0.5913 y-1 for M. lamarrei ; 10.08 cm, 0.990 y-1 and 0.6684 y-1 for M. dayanum and 16.59 cm, 0.730 y-1and -0.7289 y-1 for M. malcolmsonii , respectively. Fishing mortality was lower than natural mortality which was estimated as 1.71 for M. lamarrei, 0.15 for M. dayanum and 0.18 for M. malcolmsonii. The present study revealed that the smaller length groups had higher natural mortality, whereas larger length groups had higher fishing mortality. The current exploitation rate was 0.26 for M. lamarrei, 0.06 for M. dayanum and 0.09 for M. malcolmsonii. The research fills a critical gap providing essential insights into the population dynamics and exploitation of the three prawn species in the Burhi Gandak River, revealing their underexploited status, highlighting opportunities for sustainable harvesting and informed fishery management to support biodiversity conservation and local livelihoods. Keywords: Bihar, Burhi Gandak River, Length-weight relationship, Macrobrachium, Stock assessment

Bayesian estimation of spatially varying mortality risk using tagged animal data

Abstract The survival of animals is impacted by landscapes of spatially varying mortality factors including habitat type, predation risk or harvest risk, among others. Characterization of these spatial mortality processes is important for managing animal populations and their habitats, yet this information has proved challenging to capture. Advances in telemetry now make it possible to monitor tagged individuals' locations through time for a wide range of taxa, providing opportunity to assess movement and mortality simultaneously through spatial time‐to‐event data. Existing time‐to‐event modelling frameworks have largely ignored spatially varying mortality processes or have treated an animal's location as fixed at a regional level. Here we present a general spatial survival model for analysing time‐to‐event data arising from animal telemetry. Our model has a flexible Cox regression form and can estimate the effects of conventional non‐spatial risk factors (size, seasonality, etc.), spatial covariates (e.g. habitat type) and spatial variation in risk not explained by covariates on mortality. We show how to fit our model using Bayesian methods and demonstrate applications of our model with several simulated examples and two animal telemetry case studies. Our model produced consistent and unbiased parameter estimates throughout simulations with a variety of spatial and non‐spatial hazards. In the first case study, data from 147 tagged caribou in British Columbia, Canada, revealed a spatially heterogeneous mortality landscape with caribou survival varying by elevation, likely in response to space use by predators. Our second case study involved a dataset of 390 acoustically tagged Atlantic cod in a southern Norwegian fjord where a marine protected area (MPA) was established during the study. We found that the MPA led to a shift from mostly fishing mortality to mostly natural mortality within the fjord and that these risks had markedly different spatial hazard patterns. Our spatial time‐to‐event model can make use of data from a variety of widely used telemetry technologies to characterize landscapes of mortality risks for different taxa. Our work provides new opportunities to inform the spatial ecology and management of fish and wildlife populations.

Bifurcation analysis and exploration of noise-induced transitions of a food chain model with Allee effect

Seeking shelter from threats is a widespread instinct across species, specially employed by prey to avoid direct confrontations with predators. The present investigation centers on a three-species food chain model wherein the basal prey, characterized by logistic growth, seeks refuge to evade the intermediate predator, while the intermediate predator, in turn, seeks refuge to avoid encounters with the top predator. Additionally, our model assumes that the presence of the top predator induces a mate-finding Allee effect among the intermediate predator. We investigate how varying levels of refuge, along with other critical parameters such as the reproduction rate of the basal prey and the natural mortality rate of the top predator, influence system’s dynamics within the biparametric planes. Our model displays multistability and undergoes transcritical, saddle–node, Bogdanov–Takens and cusp bifurcations across different parameters. Moreover, the external environmental noise can induce interesting dynamics in the predator–prey system, resulting in noise-induced frequent transitions between distinct interior attractors or from interior to axial attractors. This phenomenon is particularly notable in scenarios where the deterministic model exhibits tristability. In summary, our findings offer potential new avenues for developing control strategies within the realm of community ecology in constant as well as fluctuating environments.