Endogenous Fishing Mortalities: a State-Space Bioeconomic Model

A methodology that endogenously determines catchability functions that link fi shing mortality with contemporaneous stock abundance is presented. We consider a stochastic age-structured model for a fishery composed by a number of fi shing units (fleets, vessels or métiers) that optimally select the level of fishing effort to be applied considering total mortalities as given. The introduction of a balance constrain which guarantees that total mortality is equal to the sum of individual fi shing mortalities optimally selected, enables total fishing mortality to be determined as a combination of contemporaneous abundance and stochastic processes affecting the fishery. In this way, future abundance can be projected as a dynamic system that depends on contemporaneous abundance. The model is generic and can be applied to several issues of fisheries management. In particular, we illustrate how to apply the methodology to assess the floating band target management regime for controlling fishing mortalities which is inspired in the new multi-annual plans. Our results support this management regime for the Mediterranean demersal fishery in Northern Spain.This work was funded by the European Commission as part of the MINOUW project (H2020-SFS-2014-2, number 634495) and the Spanish Ministry of Economy, Industry and Competitiveness (ECO2016-78819-R, AEI/FEDER, UE

Comparative study on the catch efficiency and size selection of entangling nets in Lake Kainji, Nigeria

The relative catch performance and selectively of gillnets and trammel nets were investigated in 12 sampling stations in Lake Kainji, Nigeria. 3 types of nets with dimensions 50mx3m were constructed using 76mm and 178mm meshsizes for two gillnets, 76mm and 178mm meshsizes for the lint and ar mour nets of the trammelnets respectively. All the nets were randomly ganged together to form a fleet of nine nets each, and were set twice in each of the 12 stations which gave a total of 24 fishing operations. A total of 365 fish weighing 88.9kg and belonging to 16 different species were caught in all the nets. The trammelnet had the highest catch by number and weight constituting 60% and 69.22% of the total catch and weight respectively with a relative species Diversity Index of 0.82. This was followed by 76mm gillnet which constituted 38.63% by number, 28.09% by weight, 0.69 relative Species Diversity Index. The 178mm gillnet had the least catch of 1.37% and 2.9% by number and weight respectively with 0.25 relative Species Diversity Index. There was significant difference (P<0.05) in the number and weight of fish caught in the different nets. The minimum selection length for these species caught were the same for each net. The trammel net had a wider selection range that skewed to the right, a higher modal and median length indicating larger individual species being entangled in the ne

MAXIMIZING RESOURCE RENT FROM THE WESTERN AND CENTRAL PACIFIC TUNA FISHERIES

Rent generated by the tuna fisheries occurring in the waters of Pacific Islands Nations is estimated for various levels and combinations of purse-seine, pole-and-line, frozen tuna longline, and fresh tuna longline fishing effort, using a multi-species, multi-fleet bioeconomic model. The underlying population model integrates available information on the population dynamics of skipjack, yellowfin, bigeye, and Southern albacore tunas in the Pacific Ocean. The economic model utilizes the most recent data on fishing effort costs for the purse seine, pole-and-line, and longline fleets operating in the western and central Pacific Ocean, along with recent estimates of prices by species, method of capture and market, and estimates of demand elasticities. The results of the model indicate that fishery rent could be increased substantially above the current level by decreasing the size of all fleets, with the possible exception of the tuna longline fleet. The results also suggest that the countries of the region could benefit significantly by changing the level and structure of access fees levied as a percentage of total catch revenue.Resource /Energy Economics and Policy,

FISHRENT; Bio-economic simulation and optimisation model

Key findings: The FISHRENT model is a major step forward in bio-economic model-ling, combining features that have not been fully integrated in earlier models: 1- Incorporation of any number of species (or stock) and/or fleets 2- Integration of simulation and optimisation over a period of 25 years 3- Integration of effort and TAC-driven management policies 4- Three independent relations for stock growth, production and investments. The feedbacks within the model allow for a dynamic simulation. The main application of the model is scenario analysis of policy options. Complementary findings: The model formulates a complete set of mathematical relations, but it also con-tains a number of important assumptions, which remain to be tested empirically. Therefore the model presents a challenging agenda for empirical research, which should lead to further qualitative and quantitative improvements of the in-dividual mathematical equations and parameter values. Method: This model was developed during the EU-funded project 'Remuneration of spawning stock biomass'. Its aim was to generate consistent sets of scenarios for an assessment of potential resource rents in different EU fisheries. The model comprises six modules, each focussing on a different aspect of the functioning of the fisheries system: biology (stocks), economy (costs, earnings and profits), policy (TACs, effort and access fees), behaviour (investments), prices (fish and fuel) and an interface linking the modules together. Input, calculation and output are clearly separated. The model produces a standard set of graphics, which provide a quick insight into the results of any model run. All output of the model runs can be exported to database software for further analysis. The model has been built in Excel, which makes it accessible for most us-ers. It has been used in new applications and even translated to other software. The model is continually further developed

The New Member Problem in the Cooperative Management of the Northern Atlantic Bluefin Tuna

In this paper the new member problem faced by the regional fisheries management organisations is discussed for a typical highly migratory species: the northern Atlantic bluefin tuna. The analysis is based on simulation and optimisation results from a bio-economic model. The results, for both the East and the West Atlantic stocks, show that presently the threat of the new members is not relevant for the breakdown of the cooperative management. This is due to the very low level of the stock, which makes noncooperation a low payoff strategy. As the optimal cooperative strategy calls for an initial harvest moratorium the threat becomes progressively more relevant, showing that this is a dynamic problem which is aggravated in the long run. Two possible solutions for this problem are simulated: transferable membership and waiting period. The simulation results show that a transferable membership scheme, if properly implemented, is fully efficient in protecting the cooperative agreements of the regional fisheries organisations from the free rider actions of the prospective new members. The waiting period, although protecting the member countries generally does not preclude such behaviours.