Wetland ecologists often recommend including an island in the middle of wetlands to increase the retention time during minor flood events. One ecologist argues that the island does not increase retention time because the travel velocity is increased along with travel length. Dye studies are used to measure retention time in 5 wetlands with islands and 7 wetlands without islands, with the following time (hours):

With islands: 23, 19, 26, 16 20
Without islands: 18, 27, 21, 19, 28, 18, 24

Is there a significant difference in retention times?