Protracted reproduction in sunfish: the temporal dimension in fish recruitment revisited

Understanding how life histories influence reproductive success under uncertain conditions is necessary to predict population dynamics. For many organisms, protracted reproduction may increase expected offspring recruitment in variable environments, requiring that temporal patterns of reproduction be considered when developing management or conservation strategies. We explored the interrelationships among birth date, production of embryos on nests, survival of larvae to the open‐water stage, and survival of juveniles through the first fall and winter of life for bluegill and pumpkinseed sunfish (Lepomis macrochirus and L. gibbosus) in Lake Opinicon, Ontario, during May 1998 through May 1999. Age‐0 sunfish were sampled with nesting surveys for embryos, surface tows for free‐swimming larvae, and seining/trawling for juveniles. Age of juveniles (days post swim‐up) was quantified using otoliths. The abundance of embryos on nests and the density of open‐water larvae were unrelated across all dates and sites. Although 40% of larvae had appeared in the open water by 12 June, most juveniles sampled in the fall were produced after that time, suggesting that high mortality of early produced larvae occurred. Larval survival to the juvenile stage was generally unrelated to the abundance of edible zooplankton taxa during swim‐up from nests. Larval survival was often highest at temperatures >23.5°C. Fall length of age‐0 sunfish increased with increasing age. Both age‐specific length and mean lengths shifted positively between October 1998 and May 1999, suggesting that growth of all individuals and perhaps selective mortality of small juveniles occurred.

Although early reproduction may increase sizes reached by fall and thereby improve overwinter survival, early hatched larvae are subject to variable environmental factors that may reduce survival. Late‐hatched larvae may reach relatively smaller sizes by fall, but have higher survival probabilities during this life stage. Protracted reproduction appears to be a response to variable environmental factors influencing growth and survival across multiple life stages. As such, all reproducing adults, rather than those perceived to produce offspring during typically favorable times, must be protected from exploitation or other human‐induced perturbations.