Animals breeding only once late in life should spend most of the time during their one reproductive season attempting to reproduce. Contrary to this prediction, we found that the individuals of three species of sticklebacks (Pisces: Gasterosteidae) spent very short periods of time on their breeding ground. Tidal flooding of the site controlled patterns offish immigration and emigration. Inundations early in the breeding season brought in new immigrants which replaced most resident fish. However, towards the end of the breeding season there was less immigration and a higher percentage of the residents remained in their pools. We expected to see movements among pools by surplus males searching for sites to establish a territory; instead, few fish moved among pools, and most ofthose that did were females. A high energetic cost of breeding in this unstable habitat may best explain these residency patterns
