Fishing is removing fish from the ocean waters. Fish stocks are continuously being depleted by fishing, while at the same time they are regrowing due to fish reproduction.
Even though Philippino regulations reserve the coastal waters solely for municipal fishers, tuna is a migratory fish that moves between coastal and non-coastal waters. In the model, we make the assumption that municipal fishers1 as well as commercial fishers2 both remove fish from the same fish stock. Overfishing by either group of fishers yields to fish scarcity for both.
The products of fishing differ. Municipal fishers, who catch primarily adult fish, produce sashimi-grade tuna to be sold fresh to consumers. Commercial fishers catch mainly juveniles for the canning and packing industries.
Key Parameters and Observables
- Population Each fisher group is represented by a population. For municipal fishers, this is represented as a number of fishing families. For commercial fishers, this is represented as a number of boats in the commercial fishing fleet.
- Effort The number of hours that fishers, municipal as well as commercial, dedicate to fishing, adding together all populations active in the fishery.
- Catch per unit of effort (CPUE) The product of fishing, in tonnes of fish extracted, for each hour of effort.
- Catchability coefficient The CPUE is dependent of two factors: the fish stock (so that the more abundant fish are, the easier it is to catch them) and a catchability coefficient, which models the relative efficiency of the fishing gear in removing fish from the water.
- Catch The total tonnage of fish that is taken out of the water and into the fishing boats.
Effort and population may both change over time, as governed by the logic of municipal and commercial fishers. Stocks go up or down over time under the combined effect of catch and reproduction. The catchability coefficient remains constant over the years, unless the efficiency of the boats changes. (e.g., With interventions that improve the quality of their fishing gear.)