Optimal Harvest Control in a Singular Prey-Predator Fishery Model with Maturation Delay and Gestation Delay

This paper presents a singular prey-predator fishery model, where maturation delay for prey and gestation delay for predator are considered. Fishing efforts are introduced to harvest prey and predator population, which are developed as control instruments to investigate optimal utilization of fishery resource. By analyzing associated characteristic equation, local stability analysis is studied due to combined variations of double time delays. Furthermore, Pontryagin's maximum principle is utilized to characterize optimal harvest control, and the optimality system is numerically solved based on an iterative method

Modelling optimal control of harvested prey predator system incorporating a prey refuge

A Dissertation Submitted in Partial Fulfilment of the Requirements for the Degree of Master’s in Mathematical and Computer Sciences and Engineering of the Nelson Mandela African Institution of Science and Technologyprey-predator interactions have been an important role in the dynamics of species populations. This work presents mathematical model for Modelling Optimal control of Harvested prey- predator system incorporating a prey refuge using deterministic differential equations. This study, develops two harvested prey-predator species, in which both species are affected by over-harvesting, furthermore the predator is affected by prey refuge. The intention is to in- vestigate the impacts of over-harvesting to prey-predator species and suggest control strategies to alleviate the problem of loss of prey-predator species. The analysis of stability of equilib- rium points were done by Jacobian matrix, Global stability analysis is done using Lyapunov function while the analysis of optimal control was done using Pontrygians maximum principle (PMP) and Hamiltonian principle. The control strategy suggested is the creation of reserve ar- eas with restrictions of harvesting. The results obtained from theoretical and numerical analysis of the prey-predator with harvesting without control strategies showed that, harvesting affect the prey-predator species negatively. However, the results obtained from numerical analysis of the prey-predator model with control strategies showed that, the use of control strategy encourage the survival of both specie

Analysis of an Impulsive One-Predator and Two-Prey System with Stage-Structure and Generalized Functional Response

An impulsive one-predator and two-prey system with stage-structure and generalized functional response is proposed and analyzed. By reasonable assumption and theoretical analysis, we obtain conditions for the existence and global attractivity of the predator-extinction periodic solution. Sufficient conditions for the permanence of this system are established via impulsive differential comparison theorem. Furthermore, abundant results of numerical simulations are given by choosing two different and concrete functional responses, which indicate that impulsive effects, stage-structure, and functional responses are vital to the dynamical properties of this system. Finally, the biological meanings of the main results and some control strategies are given

A comparative analysis of ecosystem models of Lake Victoria (East Africa)

The advent of ecosystem-based fisheries management (EBFM) in recent years has expanded the scope of fisheries management, where policies are aimed not only at maximizing production (or biological yield) but also maintaining an optimal balance between socio-economic and conservation objectives when utilizing aquatic living resources. Ecosystem models help to assimilate diverse information on the drivers of ecosystem change, thereby providing integrated assessment and advice that is needed for EBFM. Different ecosystem models, however, often provide different predictions, and this uncertainty is one of the major challenges impeding their use in EBFM. This thesis compares ecosystem models of Lake Victoria (East Africa), focusing on Ecopath with Ecosim (EwE) and Atlantis modelling frameworks, to get insights into sensitivity of fishing policy scenarios to model choice. The thesis is based on six papers. Paper I highlights the history of ecosystem modelling, both in African lakes and globally. Paper II describes temporal changes in food web of Lake Victoria using Ecopath models. Paper III compares a historic Ecopath model of Lake Victoria, fitted to time series data, to recent models that are not fitted to time series data to show how reliable none-fitted models are in terms of evaluating long-term ecosystem impacts of fishing. Paper IV compares EwE and Atlantis models of Lake Victoria to show how ecosystem impacts of fishing may be sensitive to model structure and complexity. Paper V explores socio-ecological trade-offs in Lake Victoria using both EwE and Atlantis models. Paper VI explores spatio-temporal variation in fishing patterns and fishing pressure in Lake Victoria in relation to the balanced harvesting approach (where fishing mortality is distributed across taxa or species in proportion to biological productivity). Overall, these studies contribute to understanding of how advice from ecosystem models can be affected by model structure, data assumptions and quality. The findings in this thesis suggest that simpler models may also support robust qualitative advice, which is vital for long-term strategic planning, but key ecological mechanisms explaining the differences in fishery responses between models (simple vs. complex, data-rich vs. data-poor) must be identified before hand. In view of this finding, the importance of multi-model simulations as an aid to guarding against the effects uncertainty on strategic management decisions can not be overstated. This further implies that the lack of model diversity observed on most African lakes requires urgent attention.Notkun vistkerfisnálgunar við stjórn fiskveiða á undanförnum árum hefur breikkað svið fiskveiðistjórnunar með því að ákvarðanir miðast ekki einvörðungu við hámörkun heildarafla eða afraksturs heldur er einnig tekið tillit til félagslegra og hagrænna þátta við nýtingu lifandi auðlinda sjávar. Vistkerfislíkön draga saman fjölbreytt upplýsingasöfn um hvað ræður vistkerfisbreytingum og gefa þannig samræmt heildarmat á ástandi og þá ráðgjöf sem þarf að nota fyrir vistkerfisnálgun við stjórn fiskveiða (ecosystem-based fisheries management, EBFM). Ólík vistkerfislíkön geta hins vegar gefið talsvert ólíkar spár um þróun. Slíka líkan-óvissa er talsverð hindrun við notkun þessara líkana við EBMF. Þær rannsóknir sem hér eru kynntar rýna í áhrif flækjustigs líkana og óvissu í gögnum á ákvarðanir um auðlindanýtingu í ljósi EBFM og eru niðurstöður kynntar í sex greinum. Í þessari ritgerð eru borin saman vistkerfislíkön fyrir Viktoríuvatn í Austur-Afríku, mest með Ecopath with Ecosim"(EwE) og Atlantis, til ˛ að sýna áhrif líkanavals á ályktanir um afleiðingar stjórnvaldsaðgerða. Ritgerðin byggir á 6 greinum. Í Grein I er gefið yfirlit um notkun vistkerfislínana á vötn í Afríku. Grein II lýsir líkani fyrir fæðuvef Viktoríuvatns stöðulíkani (Ecopath). Grein III ber saman sögulegt EwE líkan fellt að eldri tímaraðargögnum við jafnstöðu líkan lagt að nýrri gögnum. Tilgangurinn er að skilja áreiðanleika jafnstöðulíkana sem ekki nota formlega aðlögun að gögnum þegar þau eru notuð til að spá fyrir um afleiðingar stjórnvaldsákvarðana. Grein IV ber saman EwE og Atlantis líkön til að auka skilning á hvernig líkagerð, flækjustig og forsendur hafa áhrif á mat á stjórnvaldsaðgerðum. Grein V fjallar um mat á félagslegum og efnahagslegum áhrifum stjórnunaraðgerða með Atlantis og EwE. Grein VI metur breytileika í veiðimynstri og sókn í tíma og rúmi í samhengi við aðferðar jafnrar sóknar (balanced harvest strategy) þar sem sókn er sett sem hlutfall af framleiðslu tegundar. Sú heildarmynd fæst úr þessum tilraunum að ráðgjöf byggð á ólíkum líkönum getur orðið talsvert háð innri byggingu hvers líkans, gagnanýtingu og gæðum gagna. En niðurstöður benda líka til þess að einföld líkön geti veitt trausta almenna ráðgjöf, sem er mikilvæg fyrir langtíma áætlanagerð. Lykileiginleika vistkerfis, sem útskýra mun á spá einfaldra og flókinna líkana, þarf hins vegar að auðkenna fyrirfram. Í ljósi þessa er mikilvægi þess að prófa mörg líkön augljóst og nauðsynlegt að beina sjónum að fæð þeirri sem auðkennir breytileika í líkanagerð fyrir vötn í Afríku.United Nations University Fisheries Training Programme (UNU-FTP), Iceland

Effets des mesures de gestion halieutique sur la conservation d'une espèce vulnérable : le brochet (Esox lucius)

L'objectif de cette thèse a été de déterminer la pertinence des lâchers comme mode de gestion des pêcheries récréatives de brochet (Esox lucius). Une synthèse bibliographique a d'abord permis d'identifier les potentialités et les risques liés aux lâchers de brochets. La construction d'une vaste base de données sur les lâchers et sa mise en relation avec des données de pêche électrique a permis de démontrer que les lâchers ont un effet positive sur l'occurrence du brochet mais pas d'effet sur son abondance malgré que l'efficacité des lâchers augmente avec la taille des poissons lâchés. Deux études génétiques ont permis de mettre en évidence un fort taux d'hybrides permis les juvéniles et un taux relativement modéré parmi les adultes. D'une manière générale, les lâchers un bon potentiel d'amélioration des pêcheries mais présentent des risques pour la conservation de l'espèce. Ce travail se termine par des recommandations sur l'usage des lâchers et une réflexion sur les stratégies alternatives de gestion.The objective of this PhD was to determine the relevance of stocking for pike (Esox lucius) recreational fisheries management. First, we identified benefits (for recreation) and risks (for conservation) of stocking of pike through a bibliographic review. Second, we used a large dataset (96 sites, 6 years) to evaluate the actual and potential effects of stocking on pike populations. We found that pike stocking programs actually positively affect pike occurrences but not pike abundance despite we found that the effect of stocking on pike abundance increases with the size of the stocked pike. Third, we measured the genetic impact of stocking. We found a high rate of hybridization among juveniles but a moderate rate of hybridization among adult pike. Overall, stocking has good potential to enhance fisheries yet it carries conservation risks. We conclude with recommendations for the use of stocking and discussion about alternative management strategies

Book of Abstracts

ICES Annual Science Conference, 19 – 23 September 2011, Gdańsk Music and Congress Center, Gdańsk, Poland. IMR contributors: Benjamin Planque, Torild Johansen, Tuula Skarstein, Jon‐Ivar Westgaard, Halvor Knutsen, Kristin Helle, Michael Pennington, Marek Ostrowski, Nils Olav Handegard, Mette Skern‐Mauritzen, Edda Johannesen, Ulf Lindstrøm, Harald Gjøsæter, Ken Drinkwater, Trond Kristiansen, Geir Ottersen, Esben Moland Olse

2004/2005 Annual report (Hatfield Marine Science Center)

Report year ends June 30

Do bacteria thrive when the ocean acidifies? Results from an off-­shore mesocosm study

Marine bacteria are the main consumers of the freshly produced organic matter. In order to meet their carbon demand, bacteria release hydrolytic extracellular enzymes that break down large polymers into small usable subunits. Accordingly, rates of enzymatic hydrolysis have a high potential to affect bacterial organic matter recycling and carbon turnover in the ocean. Many of these enzymatic processes were shown to be pH sensitive in previous studies. Due to the continuous rise in atmospheric CO2 concentration, seawater pH is presently decreasing at a rate unprecedented during the last 300 million years with so-far unknown consequences for microbial physiology, organic matter cycling and marine biogeochemistry. We studied the effects of elevated seawater pCO2 on a natural plankton community during a large-scale mesocosm study in a Norwegian fjord. Nine 25m-long Kiel Off-Shore Mesocosms for Future Ocean Simulations (KOSMOS) were adjusted to different pCO2 levels ranging from ca. 280 to 3000 µatm by stepwise addition of CO2 saturated seawater. After CO2 addition, samples were taken every second day for 34 days. The first phytoplankton bloom developed around day 5. On day 14, inorganic nutrients were added to the enclosed, nutrient-poor waters to stimulate a second phytoplankton bloom, which occurred around day 20. Our results indicate that marine bacteria benefit directly and indirectly from decreasing seawater pH. During both phytoplankton blooms, more transparent exopolymer particles were formed in the high pCO2 mesocosms. The total and cell-specific activities of the protein-degrading enzyme leucine aminopeptidase were elevated under low pH conditions. The combination of enhanced enzymatic hydrolysis of organic matter and increased availability of gel particles as substrate supported higher bacterial abundance in the high pCO2 treatments. We conclude that ocean acidification has the potential to stimulate the bacterial community and facilitate the microbial recycling of freshly produced organic matter, thus strengthening the role of the microbial loop in the surface ocean

The European Landing Obligation. Reducing Discards in Complex, Multi-Species and Multi-Jurisdictional Fisheries

This open access book provides a comprehensive examination of the European Landing Obligation policy from many relevant perspectives. It includes evaluations of its impacts at economical, socio-cultural, ecological and institutional levels. It also discusses the feasibility and benefits of several potential mitigation strategies. The book was timely published, exactly at the time where the Landing Obligation was planned to be fully implemented. This book is of significant interest to all stakeholders involved, but also to the general public of Europe and to other jurisdictions throughout the world that are also searching for ways to deal with by-catch and discard issues