Parental investment theory predicts that parents should adjust the level of care given to offspring relative to brood size and stage of brood development. This variation in parental care results from a trade-off between the reproductive value of the current brood and the reproductive return that the parent can expect to receive from future broods. Our study, carried out in Charleston Lake, Ontario, Canada, examined how handling stress and brood predation associated with catch-and-release angling influenced parental care behaviors and, ultimately, nest abandonment decisions of male smallmouth bass Micropterus dolomieu. Individuals were divided into six treatment groups: two different controls (n ϭ 10 and 11) and four test groups that were either angled and then released (n ϭ 11), had broods reduced manually to simulate predation (n ϭ 12), received a combination of angling and brood reduction (n ϭ 10), or had their brood size augmented through the manual addition of larvae (n ϭ 10). Exposing the fish to a model brood predator revealed that, after catch-and-release events, angled males were less willing or less able to defend their broods than were control fish. In addition, with or without angling, males subject to simulated brood predation were the least aggressive in defending their remaining broods. Moreover, the only treatment groups that showed substantially greater rates of nest abandonment were those that included simulated predation.

Annual reproductive surveys monitored nesting location, reproductive success and the age and size of individually tagged male smallmouth bass Micropterus dolomieu that reproduced in Millers Lake, a 45 ha widening of the Mississippi River, Ontario, and in a 1Á5 km pool and riffle section of the river directly upstream. The vast majority of males displayed fidelity to either the river or the lake as reproductive habitat throughout their lifetimes. Nearly, half of the males that reproduced in successive years exhibited strong nest-site fidelity by nesting within 20 m of their previous year's nest site. In most years, when compared to those in the lake, reproductive males in the river differed significantly in reproductive characteristics including age and size at maturation and nesting success rates. A 3 year telemetry project identified two distinct habitat use patterns: lake-resident fish remained in the lake throughout the year and potamodromous individuals migrated from the lake to upriver spawning habitat in the spring and then returned to the lake prior to the onset of winter. Integration of habitat use and reproductive data suggests that there are significant differences in the life-history strategies of fish that reproduce in the river v. the lake.

Annual recruitment in fish is undoubtedly impacted by a vast number of biotic and abiotic factors. That is especially the case for fish species such as the black bass (species in the genus Micropterus), where there is extended parental care. Although much focus has been given in the past on determining the roles that many of these factors (e.g., temperatures, wind, flow rates, habitat change) play in determining recruitment among the back basses, little attention has been given to assessing what role reproductive success plays in that determination. To address this question, we conducted a long-term study on two adjacent smallmouth bass Micropterus dolomieu Lacepède, 1802 populations in eastern Ontario to assess the relationship between annual fry cohort size (i.e., population-wide reproductive success) and annual recruitment. To measure population-wide annual fry cohort size, we used snorkel surveys to conduct a complete census of nesting smallmouth bass males during the spawn from 1990 to 2015. During those surveys, we quantified mating success, determined which nests were successful or not, and calculated the number of independent fry produced each year by summing those numbers across all successful nests. Summer snorkel surveys from 1991 to 2016 assessed annual recruitment through visual counts of age 1+ juveniles. Results demonstrated a highly significant, positive, linear relationship between annual fry cohort size and annual recruitment.