Fecundity and spawning potential ratio of shoal bass Micropterus cataractae in the lower Flint River, Georgia, USA

Abstract

Shoal bass Micropterus cataractae are endemic to the Apalachicola River system in Alabama, Georgia, and Florida, USA. Despite maintaining popular fisheries, little is known about their biology and ecology. Fecundity of this species was estimated from the lower Flint River, Georgia, to better understand egg production of this species and relation with length and weight. Further, these data were used to estimate the spawning potential ratio (SPR) of this population under the current 305-mm minimum-length limit (MLL) and a more restrictive 381-mm MLL. An age-structured model was used to examine changes in yield and SPR across a range of exploitation at three levels of natural mortality. Fecundity of shoal bass ranged from 909−35,502 oocytes with a mean estimate of 10,424 ± 1089 (SD), and increased with length (r2 = 0.46; P < 0.0001), weight (r2 = 0.51; P < 0.0001), and age (r2 = 0.59; P < 0.0001). Thus, nonlethal measures of length or weight of field-collected fish may be used to predict the potential of each fish to contribute a large number of eggs to a hatchery operation. Regression equations derived in this study suggested that hatchery operations may be streamlined by utilizing fish at least 457 mm in length or 1482 g in weight to maximize number of oocytes collected per fish, as these fish should have fecundities higher than the median. Population dynamics modeling predicted that at the lowest estimate of natural mortality, growth overfishing would occur once exploitation exceeded 30 % under the 305-mm MLL, but not under the 381-mm MLL. There was little difference between MLLs at higher levels of natural mortality. At all three levels of natural mortality, the 381-mm MLL did a better job at protecting SPR than the 305-mm MLL, which only approached the 0.20 level at exploitations higher than 60 %. When adjusted for recruitment variability at expected levels of exploitation, SPR at the lowest level of natural mortality approached the 0.20 level during periods of poor recruitment under the 305-mm MLL. Given that the critical level of SPR is unknown for shoal bass, managers should protect this important fishery by adopting a more stringent regulation.