The Influence of Hatching Date on Recruitment Dynamics of Bluegill

Bluegill Lepomis macrochirus are typically considered protracted spawners. Understanding survival, growth, and subsequent recruitment of larval bluegill cohorts to the juvenile stage is essential to better predict year-class strength, thus allowing for improved management practices. We examined cohort contribution of larval bluegill to the juvenile life stage (i.e., captured as fall age-0 fish and also compared growth and mortality rates for early- and late-hatched cohorts at both the larval and juvenile life stages. Larval and juvenile bluegill were collected from Pelican Lake, Nebraska on the Valentine National Wildlife Refuge. Larval fish were collected approximately every 10 d during the 2008, 2009 and 2010 spawning seasons. Juvenile fish were subsequently collected in the fall of each year with cloverleaf traps. Otoliths were extracted from both larval and juvenile fish and daily growth rings were counted to determine hatching date. Cohort contribution was evenly distributed between early and late-hatched larvae in 2008 but late-hatched larvae contributed most to fall age-0 recruitment in 2009 and 2010. Late-hatched larvae exhibited faster growth in 2010 but not in 2008 or 2009. Early-hatched juveniles exhibited faster growth in 2008 but not in 2009 or 2010. Early-hatched larvae experienced greater mortality compared to late-hatched larvae in 2008 and 2009 but not in 2010, while juvenile mortality rates were similar between early- and late-hatched fish. These results suggest that bluegill recruitment can be established as early as the larval stage but that recruitment dynamics (i.e., growth, survival) exhibited substantial variation in our study.