Sockeye salmon
Sockeye salmon are one of the many species of fish that are anadromous. Individuals migrate to the same rivers in which they were born to reproduce. These migrations happen around the same time every year, but Quinn et al. 2007 shows that sockeye salmon found in the waters of the Bristol Bay in Alaska have recently undergone directional selection on the timing of migration. In this study two populations of sockeye salmon were observed (Egegik and Ugashik). Data from 1969-2003 provided by the Alaska Department of Fish and Game were divided into five sets of seven years and plotted for average arrival to the fishery. After analyzing the data it was determined that in both populations average migration date was earlier and was undergoing directional selection. The Egegik population experienced stronger selection and shifted 4 days. Water temperature is thought to cause earlier migration date, but in this study there was no statistically significant correlation. The paper suggests that fisheries can be a factor driving this selection because fishing occurs more in the later periods of migration (especially in the Egegik district), preventing those fish from reproducing.