Winter Survival of Age-0 Largemouth Bass Relative to Size, Predators, and Shelter

Winter mortality of age-0 largemouth bass Micropterus salmoides is sometimes size dependent, with smaller fish experiencing higher mortality. We conducted this study to determine if the presence of predators influenced winter mortality of young largemouth bass, if predators influenced all sizes of young equally, and if increased shelter availability moderated a possible relation between predator-induced mortality and fish size, We stocked 0.06-ha experimental ponds with largemouth bass (30 fish/pond) of five length groups (55–100, 101–125, 126–150, 151–175, and 176–200 mm total length), with and without predators (three largemouth bass 250–350 mm long), and four levels of shelter (0, 10, 16, and 26% brush coverage of surface area of ponds). In ponds without shelter, survival ranged from 10 to 97% in the presence of predators and from 77 to 93% in the absence of predators. Fish less than 126 mm long had gradually lower survival in the presence of predators, but near 80% survival in the absence of predators; fish 126 mm long or longer had more than 80% survival in the presence or absence of predators. In ponds with predators and shelter, survival increased with fish length and amount of shelter, but the lifesaving value of increased length and shelter relative to winter survival faded in fish 126 mm or more in length. We suggest that in lower latitudes predators may be a major source of mortality of small age-0 largemouth bass in winter, and that the effects of predators can be tempered by shelter.