Open AccessCONSTANT EFFORT AND CONSTANT QUOTAFISHING POLICIES WITH CUT‐OFFS IN A RANDOM ENVIRONMENT
Author(s) -
BRAUMANN CARLOS A.
Publication year - 2001
Publication title -
natural resource modeling
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.28
H-Index - 32
eISSN - 1939-7445
pISSN - 0890-8575
DOI - 10.1111/j.1939-7445.2001.tb00057.x
Subject(s) - constant (computer programming) , logistic function , population , mathematics , extinction (optical mineralogy) , steady state (chemistry) , range (aeronautics) , function (biology) , population size , statistical physics , yield (engineering) , statistics , probability density function , econometrics , computer science , physics , thermodynamics , demography , chemistry , materials science , evolutionary biology , sociology , optics , composite material , biology , programming language
. Consider a population subjected to constant effort or constant quota fishing with a generaldensity‐dependence population growth function (because that function is poorly known). Consider environmental random fluctuations that either affect an intrinsic growth parameter or birth/death rates, thus resulting in two stochastic differential equations models. From previous results of ours, we obtain conditions for non‐extinction and for existence of a population size stationary density. Constant quota (which always leads to extinction in random environments) and constant effort policies are studied; they are hard to implement for extreme population sizes. Introducing cut‐offs circumvents these drawbacks. In a deterministic environment, for a wide range of values, cutting‐off does not affect the steady‐state yield. This is not so in a random environment and we will give expressions showing how steady‐state average yield and population size distribution vary as functions of cut‐off choices. We illustrate these general results with function plots for the particular case of logistic growth.