Exploitation Rate Research Articles

Effects of Trap Funnel and Finger Design on Sea Lamprey Entrance and Retention

Traps are used to catch adult sea lampreys during their upstream migration to estimate their abundance in streams and, in turn, provide a measure of the Sea Lamprey Control Program’s effectiveness. During 2015 and 2016, we experimentally compared two components of sea lamprey trap design: trap entrance funnel type and the presence of retention devices, using side-by-side instream test chambers as well as laboratory flumes. We modeled how likelihoods of entrance and retention were influenced by funnel type, retention fingers, water temperature, and lamprey sex. Likelihood of entrance was highest with bottom-oriented funnels and no retention fingers. As water temperature increased, the likelihood of entrance generally increased, but funnel type and retention fingers determined the magnitude of the increase. Likelihood of retention was highest with bottom-oriented funnels and retention fingers and was also influenced by water temperature. Overall, the likelihood of capture (result of entrance + retention) was highest for bottom-oriented funnels and varied by water temperature and lamprey sex but not retention fingers. Further testing on other components of trap design is needed. This type of controlled experimental design can help guide future work to improve trap exploitation rates.

A feasibility restoration particle swarm optimizer with chaotic maps for two-stage fixed-charge transportation problems

This paper delves into solving the two-stage non-linear fixed-charge transportation problem (two-stage NFCTP), where each arc is associated with fixed and variable costs that increase proportionally to the square of the units transported. The presence of fixed charges and non-linear components categorizes this problem as NP−hard, leading to computational challenges, inefficiencies, and the risk of local optima. To address these challenges, a feasibility restoration particle swarm optimizer with chaotic maps (CEPSO) is presented. The proposed algorithm introduces (i) non-linear adaptive inertia weight and acceleration coefficients to maintain better exploration and exploitation rates during the search. (ii) Ten chaotic maps are integrated into the acceleration coefficients to enhance optimization capabilities further. (iii) Feasibility restoration mechanisms, including constraint compliance adjustment and ratio adjustment procedures, are incorporated to ensure the feasibility of solutions generated by CEPSO. The algorithm’s performance is evaluated across small and large-scale NFCTPs, ranging from 35 to 1044 dimensions, and compared to existing PSO variants using various evaluation metrics. Experimental analyses demonstrate CEPSO’s superior optimization performance for two-stage NFCTPs, positioning it as an advanced framework in this domain and contributing to the novelty of this study. The related codes can be found using this link: https://github.com/ChauhanDikshit.

Production Simulation of Stimulated Reservoir Volume in Gas Hydrate Formation with Three-Dimensional Embedded Discrete Fracture Model

Natural gas hydrates (NGHs) in the Shenhu area of the South China Sea are deposited in low-permeability clayey silt sediments. As a renewable energy source with such a low carbon emission, the exploitation and recovery rate of NGH make it difficult to meet industrial requirements using existing development strategies. Research into an economically rewarding method of gas hydrate development is important for sustainable energy development. Hydraulic fracturing is an effective stimulation technique to improve the fluid conductivity. In this paper, an efficient three-dimensional embedded discrete fracture model is developed to investigate the production simulation of hydraulically fractured gas hydrate reservoirs considering the stimulated reservoir volume (SRV). The proposed model is applied to a hydraulically fractured production evaluation of vertical wells, horizontal wells, and complex structural wells. To verify the feasibility of the method, three test cases are established for different well types as well as different fractures. The effects of fracture position, fracture conductivity, fracture half-length, and stimulated reservoir volume size on gas production are presented. The results show that the production enhancement in multi-stage fractured horizontal wells is obvious compared to that of vertical wells, while spiral multilateral wells are less sensitive to fractures due to the distribution of wellbore branches and perforation points. Appropriate stimulated reservoir volume size can obtain high gas production and production efficiency.

Enhancement of AVR system performance by using hybrid harmony search and dwarf mongoose optimization algorithms

Innovations in control algorithms, integration of smart grid technologies, and advancements in materials and manufacturing techniques all push the boundaries of AVR performance. As the demand for power systems progresses with the complexity and variety of loads, conventional AVR designs may struggle to handle these ever-changing circumstances efficiently. Therefore, the need for new optimization methods is crucial to bolstering the efficiency, reliability, and adaptability of AVRs. Thus, this work aims to improve the performance of the AVR system controller by using a novel hybrid technique between the Harmony Search (HS) and Dwarf Mongoose Optimization (DMO) algorithms to tune the proportional-integral-derivative (PID) and proportional-integral-derivative acceleration (PIDA) parameters. The suggested hybrid approach ensures an accurate solution with balanced exploration and exploitation rates. The reliability of the proposed HS-DMOA is verified through comparison with different optimization techniques carried out on time and frequency performance indicators, disturbances in the form of changes to time constants, and dynamic input signals. The proposed hybrid HS-DMOA PID-based has better overshoot than PID-based HS, LUS, TLBO, SMA, RSA, and L-RSAM by 20.37%, 18.5%, 18.5%, 2.77%, 5.55%, and 2.77%, respectively. Regarding the phase margin, the proposed hybrid HS-DMOA PID-based is better than PID-based HS, LUS, and TLBO by 39%, 37%, and 38%, respectively. While the proposed hybrid HS-DMOA PIDA-based has a better overshoot than PIDA-based HS, LUS, and PID HS-DMOA-based by 14%, 17%, and 20%, respectively. Moreover, the robustness under dynamic disturbance proved the reliability of the proposed HS-DMOA PID and PIDA based through enhancement of overshoot around 0.3%~20% for different cases. Finally, the main contribution of the paper is to propose a relatively new hybrid optimization method to enhance the AVR PID and PIDA-based performance with detailed analysis in time and frequency domains under normal and dynamic disturbances.

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.

Marx and the Big Mac: An Empirical Exploration of Marx’s Exploitation Theory for Introductory Economics Courses

Undergraduate economics courses have low relevance, belonging, and growth mindset levels. For instance, Bayer et al. found that less than 30 percent of the students in their sample strongly agreed with the statement “The class gave me a useful framework for thinking about important issues.” Integrating pluralist methodologies into introductory economics classes may be one solution for overcoming this issue. This article introduces an empirical activity designed to teach students about Marx’s theory of exploitation. The activity utilizes the 10-K annual report from a publicly traded company, in this case, McDonald’s, to analyze the rate of exploitation of workers. Through this exercise, students delve into the theory of exploitation, analyze data from the 10-K, calculate the rate of exploitation, and engage in discussions about its application to contemporary social and political issues. JEL Classification: A22, P16, B24

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.

Estimating the fishing rate for maximum nutritional yield (FMNY) optimizes fish production for human health

Abstract Fisheries management is largely based on the principle of achieving the maximum sustainable yield (MSY) with little regard for nutritional value. Management strategies maximizing nutrients rather than yield, however, may provide a smarter contribution to global food and nutrition security. Here, we present a novel fisheries management strategy: fishing at maximum nutritional yield (FMNY), the exploitation rate at which essential nutrients are maximized. Combining top-down population modelling approaches with bottom-up nutrient compositional analysis, we compared nutrient yields across seasons for Europe’s most valuable fishery (Atlantic mackerel, Scomber scombrus). FMNY estimates differed between nutrients, but were equal to, or lower than, FMSY. An autumn fishery provided higher amounts of lipids, omega-3 fatty acids, and protein, whereas vitamin D3, and calcium were maximized in winter. Aligning national fisheries policies and nutrition objectives is paramount to realising the potential of seafood in building healthier food systems. Developing novel fisheries management strategies, such as FMNY, where fisheries are optimised for human nutrition will, therefore, contribute to nutrient sustainability and help improve human health and diets.

Evaluation of Some Aspects of the Growth Parameters and Exploitation Rates of Deep-Water Rose Shrimp (Parapenaeus longirostris) from the Sea of Marmara

Evaluation of Some Aspects of the Growth Parameters and Exploitation Rates of Deep-Water Rose Shrimp (Parapenaeus longirostris) from the Sea of Marmara

Enhancing Sustainability and Conservation of White Shrimp Penaeus schmitti in Northeast Brazil: Insights Into Life History, Reference Points, and Management Strategies for Beach Seining

ABSTRACTArtisanal fishing significantly not only contributes to socioeconomic development of numerous countries but also exerts pressure on natural populations. The white shrimp (Penaeus schmitti) is a key species in Brazilian artisanal fisheries, yet it is currently classified as data‐deficient. Conducting comprehensive studies on its population dynamics is essential to establish reference points that guarantee sustainable fishing. Therefore, we estimated population parameters to assess status of the white shrimp stock captured by beach seining in Northeast Brazil. Monthly samples of white shrimp were collected using a beach trawl. Based on population parameters, the white shrimp population in the study area, the sex ratio was 1 male to 1.29 females, with females larger and heavier than males. Weight–length relationships revealed positive allometric growth for males, females, and grouped sexes, with no significant difference between sexes. Asymptotic length, t_achor, and growth performance index also did not differ between sexes; however, the growth coefficient was higher for females. Beach trawling in northeastern Brazil predominantly targeted adult white shrimp, with carapace length at first capture (Lc50) averaging 2.12 cm for females and 2.19 cm for males. Mortality and exploitation rates were below maximum sustainable levels, so the stock was classified as underexploited. Overall, beach‐seine fishing was less harmful to this stock (F = 1.42) than motorized fishing and can be considered a sustainable fishing activity for the white shrimp population.

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.

Estimating Fishing Exploitation Rates to Simulate Global Catches and Biomass Changes of Pelagic and Demersal Fish

AbstractRobust projections of future trends in global fish biomass, production and catches are needed for informed fisheries policy in a changing climate. Trust in future projections, however, relies on establishing that models can accurately simulate past relationships between exploitation rates and ecosystem states. In addition, historical simulations are important to describe how the oceans have changed due to fishing. Here we use fisheries catch, catch‐only assessment models and effort data to estimate regional fishing exploitation levels, defined as the fishing mortality relative to fishing mortality at maximum sustainable yield (F/FMSY). These estimates are given for large pelagic, forage and demersal fish types across all large marine ecosystems and the high seas between 1961 and 2004; and with a ‘ramp‐up’ between 1841 and 1960. We find that global exploitation rates for large pelagic and demersal fish consistently exceed those for forage fish and peak in the late 1980s. We use the rates to globally simulate historical fishing patterns in a mechanistic fish community model. The modeled catch aligns with the reconstructed catch, both for total catch and catch distribution by functional type. Simulations show a clear deviation from an unfished model state, with a 25% reduction in biomass in large pelagic and demersal fish in shelf regions in recent years and a 50% increase in forage fish, primarily due to reduced predation. The simulations can set a baseline for assessing the effect of climate change relative to fishing. The results highlight the influential role of fishing as a primary driver of global fish community dynamics.

Disruption of natural disturbance regime decouples habitat and life stage in a keystone species

AbstractAnthropogenic disturbance of stream ecosystems, often chronic in nature, has been studied extensively. However, when disturbance is driven by more than one resource policy over many decades, feedback between habitat evolution and biological adaptation can be disrupted and ecological function affected in unforeseen ways. We analyzed over 100 years of Chinook salmon (Oncorhynchus tshawytscha) length frequency trends associated with fisheries management and changes in available spawning substrate (habitat) linked to flow regulation in a highly altered California river. Over time, salmon lengths generally decreased, fluctuating with exploitation (ocean harvest) and hatchery production rates. Female size reduction, coupled with a degrading and coarsening channel, and perching peripheral habitat related to past mining activity, indicates available spawning substrate may be too large to support the current salmon population. Assuming a salmon can move material ~10% of her body length, length frequency data and current substrate size distribution suggest that increasing salmon sizes to historic distributions could increase available spawning habitat by as much as 13%. Alternatively, decreasing spawning substrate size could support a greater portion of the current population. To test the latter hypothesis and inform future management actions, we monitored two spawning riffles where large and small gravel was placed on top of a cobble. We observed an immediate spawning activity increase that was more pronounced where smaller gravel was deposited. Following a decade of habitat decline, the two sites were both replenished with medium gravel. Elevated spawning use occurred immediately at both sites, commensurate with this intermediate size, further supporting our hypotheses. Sediment coarsening and habitat disconnect below dams, combined with reduced salmon size, indicate the natural spawning process may be decoupled from available habitat below dams in the foreseeable future without continuous intervention. Actively managing salmon population demographics through modified hatchery and size‐selective harvest practices and developing a coarse sediment budget with size‐appropriate material for regulated anadromous rivers could produce immediate benefits for ecosystem services, including salmon populations. However, these management actions will require continued maintenance and informed socio‐ecological goals to remain successful.

Exploitation and catch and release of salmonids in Idaho high mountain lakes

AbstractObjectiveHistorically, most high mountain lakes in western North America were devoid of fish, but during the past century, many have been stocked with salmonids to diversify angling opportunities. Basic information on harvest and catch and release (C–R) for high mountain lake fisheries is lacking, as is information on factors influencing catch in such settings; our objectives were to fill these knowledge gaps.MethodsUsing angling gear, we captured and implanted T‐bar anchor tags into 1163 salmonids of various species (fish of wild origin or hatchery fish stocked as fry; they could not be distinguished) in 103 high mountain lakes scattered across Idaho. Angler‐reported tag returns were used to estimate annual rates of exploitation and C–R, and a model selection approach was used to investigate factors influencing the angler catch of tagged fish.ResultAnglers reported the catch of 125 tagged fish from 52 different lakes. The mean number of days at large for reported fish was 318 days, with a range of 1 to 1465 days. Annual exploitation was 5.8 ± 7.1% (mean ± 90% confidence interval), the annual C–R rate was 8.5 ± 8.5%, and total annual catch (i.e., exploitation plus C–R) was 14.2 ± 11.0%. Of the predictive factors that we investigated, the likelihood of a fish being caught by an angler was negatively associated with hiking distance and positively associated with shoreline development index and fish length.ConclusionOur results indicate that exploitation of salmonids in Idaho high mountain lakes is low even with liberal (six‐fish daily bag limit) harvest regulations. Consequently, angler harvest is unlikely to be substantively affecting the abundance or size structure of salmonid populations in these lakes. Continued tagging would improve the precision of exploitation and C–R estimates, especially for comparisons among species.

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

Evaluation of mechanical behaviour of vegetal FRCM composites through the DIC technique: Effects of textile pre-impregnation and short flax fibres

FRCM composites are intended for the reinforcement of structural elements such as concrete and masonry. In the current environmental context, vegetal FRCM made from plant textiles such as flax, hemp or jute represent a promising alternative to synthetic FRCM typically made from carbon or glass textiles. However, the mechanical behaviour and damage mechanism of these vegetal composites are intricate and require further investigation to improve their appeal for real-world applications. This paper investigates the global and local tensile behaviour of vegetal FRCM composites using Digital Image Correlation (DIC). Three different types of textiles have been selected for Flax-FRCM (flax textile), Jute-FRCM (jute textile) and Carbon-FRCM (carbon textile) composites, which serve as references. The objective is to evaluate the influence of the physical and mechanical properties of the textiles, the addition of short flax fibres to the mineral matrix, the pre-impregnation of the plant textiles in the mineral matrix and the reinforcement ratio on the mechanical performance of the composites. The results showed that these parameters significantly affect the FRCM mechanical response in terms of the stress-strain curves, tensile properties, crack spacing, crack widths and their evolution during loading, failure mode and the exploitation rate of the textile in the composite (efficiency factor, crucial for structural applications). Furthermore, combining textile pre-impregnation with the addition of short flax fibres showed the best tensile performance for vegetal FRCM composites, notably through a significant reduction in crack widths and textile failures in the centre of the specimen.

An adaptive gravitational search algorithm for optimizing mechanical engineering design and machining problems

The gravitational search algorithm (GSA) is widely used for solving optimization problems because it performs in a superior manner as compared to various competing evolutionary and swarm-based metaheuristics. However, GSA frequently gets trapped in local optima due to a lack of solution diversity. Although chaotic gravitational search algorithm (CGSA) can resolve this issue to some extent but its degraded exploitation rate and convergence speed may not result in desired outcome. To this end, diversity-based chaotic GSA (DCGSA) has exhibited its capability to resolve the issues encountered with GSA and CGSA to a certain extent for unconstrained problems. DCGSA achieves this characteristic through the use of an adaptive gravitational constant, which varies according to the diversity values of the population. Since most real-world problems are subjected to some constraints, it is prudent to improve the performance of GSA in solving constrained optimization problems. The present study integrates the enhanced search capability of DCGSA with a generalized constraint handling mechanism to improve the performance of GSA in solving constrained problems. It is observed that DCGSA significantly outperforms GSA on both CEC (Congress on evolutionary computation) 2006, 2010 and 2017 functions and competes strongly with CGSA. Diversity analysis shows that the capability to balance exploration and exploitation rates is enhanced using CGSA and DCGSA. Furthermore, DCGSA algorithms outperform GSA and CGSA on real-world machining and CEC 2020 mechanical design problems. Comparison with state-of-the-art algorithms is made to analyze the performance of the algorithms from a larger perspective.

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.

Exploring the ecosystem structure of Zanzibar archipelago, trophic flows and fisheries interaction by using a mass balance modelling approach

The marine ecosystem in the Zanzibar archipelago has great economic and ecological importance due to high fisheries productivity. Yet, limited information is available on its status and possible impacts of fishing on it. Ecological models have been recognized as powerful tools for assessing the structure and function of ecosystems and forecasting the impacts of human activities on marine ecosystems. However, the use of ecological models in understanding ecosystems in the Western Indian Ocean region is inadequate. This study constructed a model to examine the ecosystem functioning, trophic flows, and fisheries interactions of the marine region affected by fishing gears in the Zanzibar archipelago using Ecopath with Ecosim software. The model includes 34 functional groups and 10 most common fishing gears, the input parameters were gathered from published reports. The ecosystem indicators showed that the Zanzibar ecosystem is in the early developmental stage contributed by strong fishing pressure that reduces the stability and maturity of the ecosystem. The total catch estimated at 5.538 t km−2year−1 showed a sign of the high exploitation rate of fisheries resources. The catch is dominated by higher trophic level fish as reflected in the mean trophic level of the fishery (3.2). The keystoneness analysis identified pelagic cephalopods, sharks and rays, turtles, tuna and tuna like species and toothed whales for their importance in the Zanzibar marine ecosystem. Fishing pressure on the ecosystem of Zanzibar is high, hence for better management, the focus should be for coral reef and pelagic species that are highly targeted by number of gears while protecting keystone species as important groups of the ecosystem. Fisheries harvest data collection system should be improved to collect information at species level and focus on all target species, including invertebrates.