Analyzing the Harvesting Game or Why are There So Many Kinds of Fishing Vessels in the Fleet?

Abstract

Harvesting of commercial marine fish stocks can be thought of as a game, with free entry of all kinds of players (the fishing vessels), and freedom for these vessels to choose their target species, and to switch targets at will. The result is a complicated and confusing mix of vessel types and activities. One is led to seek general principles, with which to bring some order into this chaos.

The fishing vessels and the fish can be thought of as a kind of artificial ecological community, with the vessels as predators, competing for a common prey. One of the most commonly cited doctrines in ecology is the principle of competitive exclusion: There can be no more competing predator species than there are common prey species-unless predators find ways of expanding the dimension of their common “niche space”, for instance through asymmetric partitioning of space or time. I shall show that this ecological principle, made precise, has its direct analogue in resource economics. Thereby I hope to make sense of the “harvesting game.”

I shall develop this theme by presenting a series of mathematical models. These will illustrate how bioeconomic forces can bring about modes of fishing vessel coexistence, involving respectively: time partitioning, resource partitioning, spatial partitioning, and risk partitioning. Technically the models, which have been developed in a series of articles over a period of several years, are of optimal control or differential game type—and they are quite different from the original models used to study the exclusion principle in ecology.