The Impacts of Harvesting Activities on Prey-Predator Fishery Model in the Presence of Toxin

The present paper discusses a prey-predator fishery model where both species are subjected to harvesting effort. Both species release some toxic substances to each other. The prey species obeys the law of logistic growth. The model is a modified version from the classic Lotka-Volterra predator-prey model. The equilibria of the model are obtained and the dynamical behaviors of the proposed system are examined. Simulations of the model are performed and bifurcation diagrams are studied. The effects of harvesting and toxin on the stability of steady states are examined. In the present research, we found that the impact of harvesting activities is more influential on the dynamical behaviors in the fishery model than that of the toxin

A Resource Based Stage-Structured Fishery Model With Selective Harvesting of Mature Species

In this paper we have considered a model in which revenue is generated from fishing and the growth of the fish depends upon the plankton which in turn follows a logistic law of growth. Here the fish population has two stages, a juvenile stage and a mature stage and we consider the harvesting of the mature fish species. Stability and permanence of the system are discussed. Maximum sustainable yield, maximum economic yield and optimal sustainable yield are obtained and different tax policies are discussed to achieve the reference points

Model Matematika Pemanenan Ikan dengan Kebijakan Panen Selektif

Pengelolaan sumber daya perikanan termasuk sebagai aspek penting yang dipertimbangkan oleh negara maritim. Kelimpahan sumber daya ikan dapat dipertahankan dengan strategi penangkapan ikan yang tepat, salah satunya adalah kebijakan panen selektif. Dalam studi ini, dinamika kepadatan populasi ikan dipelajari menggunakan model predator-prey yang dimodifikasi. Proses panen selektif yang memperhitungkan usia atau ukuran ikan siap panen dinyatakan sebagai penundaan waktu dalam proses panen. Analisis model dilakukan dengan menentukan titik kesetimbangan model dan stabilitas titik keseimbangan model. Ada empat titik keseimbangan model, yang mewakili kondisi trivial, kepunahan prey, kepunahan predator, dan eksistensi predator-prey. Perilaku dinamis model diilustrasikan melalui simulasi numerik dengan beberapa skenario. Hasil simulasi numerik menunjukkan bahwa waktu tunda mempengaruhi stabilitas beberapa titik setimbang, sehingga menghasilkan dinamika populasi yang lebih beragam

Spatiotemporal dynamics in a toxin-producing predator–prey model with threshold harvesting

In this paper, we propose a toxin-producing predator–prey model with threshold harvesting and study spatiotemporal dynamics of the model under the homogeneous Neumann boundary conditions. At first, the persistence property of solutions to the system is investigated. Then the explicit requirements for the existence of nonconstant steady state solutions are derived by studying the relevant characteristic equation. These steady states occur from related constant steady states via steady state bifurcation. Throughout the analysis of the amplitude equations of Turing pattern by the multiple scale method, pattern formation can be found. Finally, we display  umerical simulations to verify the theoretical outcomes

Long-term study on survival and development of successive generations of Mytilus galloprovincialis cryopreserved larvae

Shellfish aquaculture needs the development of new tools for the improvement of good practices avoiding the reliance on natural spat collection to increase production efficiently. The aim of this work was to improve the cryopreservation protocol for Mytilus galloprovincialis larvae described in Paredes et al. (in: Wolkers, Oldenhof (eds) Cryopreservation and freeze-drying protocol, methods in molecular biology, Humana Press, 2021, pp 2180, https://doi.org/10.1007/978-1-0716-0783-1_18 ). Moreover, the capability of producing adult mussels from cryopreserved 72 h-old D-larvae and potential long-term effects of cryopreservation through progenies were evaluated. The selection of 72-h old D-larvae for cryopreservation yielded 75% of recovery, higher than 50% from trochophores. The best combination was 10% Ethylene–Glycol + 0.4 M Trehalose in Filtered Sea Water (FSW) with cooling at − 1 °C/min and a water bath at 35 °C for thawing. Sucrose (SUC) solutions did not improve larval recovery (p > 0.05). At settlement, 5.26% of cryopreserved F1 larvae survived and over 70% settled. F2 cryopreservation produced 0.15% survival of spat and settlement varied from 35 to 50%. The delay of shell size showed on cryopreserved larvae declined throughout larval rearing without significant differences with controls from settlement point (p > 0.05). Long-term experiments showed that it is possible to obtain adult mussels from cryopreserved larvae and this tool does not compromise the quality of following progenies, neither for cryopreservation nor post-thawing development of them.Xunta de Galici

Model Matematika Persaingan Dua Spesies dengan Toksisitas dan Pemanenan Selektif

Persaingan merupakan interaksi biologi antar makhluk hidup untuk bersaing mendapatkan sumber energi yang terbatas, misalnya makanan yang dibutuhkan untuk tumbuh dan bertahan hidup. Beberapa spesies mempunyai strategi tersendiri dalam bersaing, diantaranya adalah kemampuan mengeluarkan racun. Pada jurnal ini, dikaji dua model predator-prey yang dipengaruhi oleh adanya toksisitas dan pemanenan selektif. Model pertama mengkaji model persaingan dua spesies dengan adanya toksisitas dan pemanenan selektif, sedangkan model kedua mengkaji model persaingan dua spesies dengan adanya toksisitas dan pemanenan selektif dengan Holling tipe III. Dari model pertama diperoleh 4 titik setimbang yaitu dan  Dari model kedua juga diperoleh 4 titik setimbang, yaitu dan . Titik setimbang  dan  tidak stabil, sedangkan , dan  stabil dalam kondisi tertentu. Hasil simulasi numerik menunjukkan bahwa kedua spesies pada model kedua mengalami peningkatan dibandingkan dengan model pertama. Hal tersebut dikarenakan adanya kecenderungan untuk mencari musuh yang lain ketika jumlah musuh mulai berkuran

Stability and bifurcation of a delayed diffusive predator-prey model affected by toxins

In this work, a diffusive predator-prey model with the effects of toxins and delay is considered. Initially, we investigated the presence of solutions and the stability of the system. Then, we examined the local stability of the equilibria and Hopf bifurcation generated by delay, as well as the global stability of the equilibria using a Lyapunov function. In addition, we extract additional results regarding the presence and nonexistence of non-constant steady states in this model by taking into account the influence of diffusion. We show several numerical simulations to validate our theoretical findings

Optimal harvesting policy of a prey–predator model with Crowley–Martin-type functional response and stage structure in the predator

In this paper, a three-dimensional dynamical model consisting of a prey, a mature predator, and an immature predator is proposed and analysed. The interaction between prey and mature predator is assumed to be of the Crowley–Martin type, and both the prey and mature predator are harvested according to catch-per-unit-effort (CPUE) hypothesis. Steady state of the system is obtained, stability analysis (local and global both) are discussed to explore the long-time behaviour of the system. The optimal harvesting policy is also discussed with the help of Pontryagin's maximum principle. The harvesting effort is taken as an effective control instrument to preserve prey and predator and to maintain them at an optimal level

Invasive non-native species and the management and exploitation of freshwater ecosystems

The effects of climate warming, hydrological intensification, and eutrophication are driving unfavourable shifts in phytoplankton communities. In particular, harmful algal blooms (HABs), dominated by toxic cyanobacteria, are becoming increasingly common and often lead to ecosystem collapse and unsafe drinking water. Freshwater ecosystems are also vulnerable to the establishment of invasive non-native species (INNS), whose prevalence has rapidly accelerated through the expansion of global travel, trade, and transportation. INNS can drive significant changes in habitat suitability and native community composition. I investigated how INNS affect the tipping points of freshwater ecosystems, between clear water and phytoplankton-dominated states, and influence phytoplankton community structure and cyanobacteria abundance. Through a meta-analysis of the global impacts of INNS on freshwater lake ecosystems, I identified that molluscs were potential drivers of a clear water state in lake ecosystems, encouraging system recovery and delaying ecosystem collapse. Invasive fish and crustaceans, however, were identified as potentially pushing systems towards a turbid state and resisting recovery. I further assessed the effects of invasive molluscs by quantifying the impacts of quagga mussels (Dreissena rostriformis bugensis) in UK reservoirs. I identified that impacted sites demonstrated: an increase in overall reactive silica and soluble reactive phosphorus concentrations; reductions in overall diatom, cyanobacteria and Aphanizomenon sp. abundance; and an increase in chlorophyll a concentration. However, no significant changes were seen in overall green algae, Microcystis sp., Anabaena sp., or Euglena sp. abundance, ammonium concentration or turbidity. The selective grazing behaviour of quagga mussels has been shown to vary between studies, an effect hypothesised to be driven by phenotypic plasticity or genotype selection between mussel populations. I explored putative population level differences in the discriminatory grazing behaviour of quagga mussels by observing mussels from both lentic and lotic environments, as hydrology is a known driver of phenotypic plasticity in mussels. I show that different populations of quagga mussels have the potential to drive different outcomes in phytoplankton communities. While both populations expressed comparable clearance rates and cleared green algae (Chlorella vulgaris) at a higher rate than cyanobacteria (Synechococcus elongatus), mussels from lotic environments ejected significantly greater quantities of cyanobacteria in pseudofaeces. Rejection of cyanobacteria by invasive mussels may drive HABs. Beyond invasive mussels, I also assessed the allelopathic effect of invasive plants Hydrocotyle ranunculoides and Crassula helmsii on phytoplankton communities. The allelopathic effect of each plant was tested in both a whole, and crushed state, to test for natural excretion of allelochemicals. In its whole state, H. ranunculoides supressed the growth of green algae (C. vulgaris), whereas crushed C. helmsii supressed the growth rate of both green algae and cyanobacteria (Synechocystis sp.). The species-specific nature of these allelopathic interactions suggests that the use of allelopathy for controlling phytoplankton abundance may have to be assessed on a case-by-case basis. Although, a sophisticated understanding of this differential sensitivity may also allow for some targeted management of phytoplankton populations towards specific desirable end points. Finally, I explored the potential role of invasive zebra mussels (Dreissena polymorpha) in the novel concept of Synthetic Ecology. I investigated how zebra mussel grazing behaviour could be harnessed to maintain favourable conditions for the cultivation of commercially valuable algae species in outdoor raceways by supressing the growth of competing cyanobacteria. Their potential was confirmed through the consistent preference for cyanobacteria (Synechocystis sp.) over green algae (C. vulgaris) observed across all treatment conditions. The results of this thesis suggest, in certain contexts and where risks are appropriately managed, there may be opportunities to harness INNS in order to drive favourable changes in the alternative equilibria of freshwaters, reducing both overall phytoplankton and cyanobacteria abundance in biologically depleted ecosystems

Sea urchin chronicles. The effect of oxygen super-saturation and marine polluted sediments from Bagnoli-Coroglio Bay on different life stages of the sea urchin Paracentrotus lividus

none11In marinas and harbours, the accumulation of pollutants in sediments, combined with poor exchange of water with the open sea, poses a major environmental threat. The presence of photosynthetic organisms and the related oxygen production, however, may alleviate the negative effects of environmental contamination on heterotrophic organisms, enhancing their physiological defences. Furthermore, possible transgenerational buffer effects may increase the ability of natural populations to face environmental stress. Here we tested the occurrence of transgenerational effects on larvae of the sea urchin Paracentrotus lividus, whose parents were exposed, during the gametogenesis, to contaminated sediments subject to two temporal patterns of water re-suspension events and normal- (90%) vs. super-saturated (200%) levels of O2. The study site was Bagnoli-Coroglio (Gulf of Naples, southern Tyrrhenian Sea), a historically polluted brownfield and Site of National Interest for which environmental restoration options are currently under exploration. Larvae from different adult populations were significantly, although not linearly, affected by the interaction of all factors to which parents were exposed, at both 24h and 48h post fertilization. Specifically, the exposure of larvae to elutriates from contaminated sediments determined a developmental delay, a reduction in size and an increased percentage of abnormalities in all larval populations independently of their parental exposure. On the contrary, larvae from parents exposed to contaminated sediments, when reared in clean filtered sea water, succeeded in developing until the echinopluteus stage after 48h, with size and abundance comparable to those of larvae from control parents. Pre-exposure of parents to contaminated sediments did not successfully buffer the negative effects of elutriates on their offspring, and no positive effects of ‘super-saturated’ levels of O2 in response to contaminants were observed, suggesting that the Bagnoli-Coroglio area is currently not suitable for the re-stocking or re-introduction of this species.embargoed_20220328Chiarore A.; Musco L.; Bertocci I.; Gallo A.; Cannavacciuolo A.; Mutalipassi M.; Caramiello D.; Giomi F.; Fusi M.; Danovaro R.; Munari M.Chiarore, A.; Musco, L.; Bertocci, I.; Gallo, A.; Cannavacciuolo, A.; Mutalipassi, M.; Caramiello, D.; Giomi, F.; Fusi, M.; Danovaro, R.; Munari, M