Problems of detection and interpretation of vertical migration

Abstract

Simple counts of organisms as functions of time and depth, or sonic scattering records, can yield only minimal estimates of range or velocity of vertical migrants. It is incorrect though common to equate mean population movements so determined to rates of motion of the individual animals. If migratory movements are not synchronized, conventional studies will generally show the population to have a bimodal depth distribution, but may not indicate any migration. A simple model based on hunger as a mediator and light as a synchronizer can explain many instances of apparently anomalous did migrations, and relate did to longer term migratory behavior. There are a number of alternative or supplementary investigative techniques which can and should be used to increase understanding of vertical migration. The uses and limitations of some of these aie discussed.