The temporal dimension in fish recruitment: Birth date, body size, and size-dependent survival in a sunfish (bluegill: Lepomis macrochirus)

Many fish species are protracted spawners, producing fry over a several-week breeding season. We demonstrate that this time dimension has important implications for recruitment by relating the body size and survival of yearlings to the day that they were born. The production of bluegill sunfish fry was estimated throughout the 1993 spawning season in Lake Opinicon, Ontario. In 1994, yearlings were collected and otolith daily growth rings used to determine their 1993 date of birth. We found that yearling body size decreased with date of birth in 1993. There was a progressive decline in body size across the eight spawning bouts, resulting in a 50% difference in the size at age 1 of early- and late-born fry. This difference is apparently due to the longer growing season available to early-born fry. Fry born earlier in the season also had strikingly higher survivorship to age 1 than fry from the middle- or late-season bouts. Fry produced during the first trimester increased 231% in representation among yearlings. This increased survivorship is probably due to increased over-winter survivorship and possibly also size-selective predation. These results highlight the importance of the temporal dimension in understanding the nature of fish recruitment.