Essays on fishery management

The goal of Yuanming Ni´s thesis is to propose modelling approaches and management guidelines that potentially improve our understanding of modelling and management. Photo: Wikimedia
PhD Defense

12 November 2019 11:01

Essays on fishery management

On Tuesday November 26 Yuanming Ni will hold a trial lecture on a prescribed topic and defend her thesis for the PhD degree at NHH.

Yuanming Ni
Yuanming Ni, PhD Candidate at the Department of Business and Management Science, NHH.

Prescribed topic for the trial lecture:

Age-structured models vs. biomass models in the analysis of optimal harvesting

Trial lecture:

10:15 in Karl Borch Aud., NHH

Title of the thesis:

Essays on fishery management


The three chapters in this thesis fall inside the research field of fishery modelling and management. The goal is to propose modelling approaches, innovative recipes and management guidelines that potentially improve our understanding of the topic. Each chapter employs a bioeconomic model with a specific numerical example to provide relevant discussions. The thesis focuses on multi-dimensional fishery modelling, with multiple cohorts or species or time increment lengths.

The first chapter studies the effects of recruitment patterns and environmental impacts on the optimal exploitation of a fish population. Based on a discrete-time age-structured bioeconomic model of Northeast Atlantic mackerel, the author finds that age-structured models are sensitive to parameter settings. Any parameter combination that favors the older fish tends to lend itself to pulse fishing pattern.

The second chapter is an attempt to treat seasonality in a systematic way while most of the extant literature tends to neglect periodicity. The authors present a multi-season multi-state bioeconomic model and apply a periodic Bellman approach using dynamic programming to obtain the optimal feedback policy of each season. The numerical illustration demonstrates that a seasonal dynamic optimization model allows for naturally occurring seasonal moratorium. The authors argue that this finding indicates an optimal closure of the fishery that a yearly model would overlook. This chapter is co-authored with Leif Sandal and is published in European Journal of Operational Research.

The third chapter investigates a predator-prey system of cod and capelin that confronts possible prey extinction under the first-best policy in a stochastic world. The authors discover a novel ‘super-harvest’ phenomenon that the optimal harvest of the predator is even higher than the myopic policy on part of the state space. The authors generate several heuristic policies that harvest more of the predator to promote prey recovery. This chapter is co-authored with Leif K. Sandal, Sturla F. Kvamsdal and Diwakar Poudel.


12:15 in Karl Borch Aud., NHH

Members of the evaluation committee:

Professor Anders Skonhoft (leader of the committee), NTN

Senior researcher Ayoe Hoff, University of Copenhagen

Lecturer Lone Grønbæk, University of Southern Denmark


Professor Stein Ivar Steinshamn (main supervisor), Department of Business and Management Science, NHH

Professor Leif Kristoffer Sandal, Department of Business and Management Science, NHH

The trial lecture and thesis defence will be open to the public.