Increased parental care cost for nest-guarding fish in a lake with hyperabundant nest predators

Although parental care increases offspring survival, providing care is costly, reducing parental growth and survival and, thereby, compromising future reproductive success. To determine if an exotic benthic predator might be affecting parental care by nest-guarding smallmouth bass (Micropterus dolomieu), we compared nest-guarding behavior and energy expenditures in two systems, one with a hyperabundant recently introduced predator, the round goby (Neogobious melanostomus). In Lake Erie, USA, smallmouth bass vigorously defended their nests from benthic round gobies. In Lake Opeongo, Canada, smallmouth bass were exposed to fewer and predominantly open-water predators and were less active in their nest defense. From scuba and video observations, we documented that nest-guarding smallmouth bass chased predators (99% of which were round gobies) nine times more frequently in Lake Erie than in Lake Opeongo. This heightened activity resulted in a significant decline in weight and energetic content of guarding males in Lake Erie but no change in Lake Opeongo males. Bioenergetic simulations revealed that parental care increased smallmouth bass standard metabolic rate by 210% in Lake Erie but only by 28% in Lake Opeongo. As energy reserves declined and offspring became increasingly independent, males in both lakes consumed more prey and spent more time foraging away from their nests; however, nest-guarding smallmouth bass consumed few prey and, in Lake Erie, rarely consumed round gobies. Therefore, increased parental care costs owing to the presence of round gobies could affect future growth, reproduction, and survival if smallmouth bass approach critically low energy reserves. Copyright 2005.