Premium
Size Sorting in Bonytail Skews the Sex Ratio of Stocked Fish
Author(s) -
Diver Tracy,
Harrison Alexis,
Knight William,
Ulibarri Manuel,
Wilson Wade
Publication year - 2019
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1002/nafm.10283
Subject(s) - stocking , biology , sex ratio , sexual dimorphism , effective population size , population , population size , ecology , zoology , fishery , demography , genetic diversity , sociology
For sexually dimorphic species, size‐based management can cause changes in the sex ratio of the target population. Bonytail Gila elegans populations in the Colorado River basin are augmented annually in an effort to re‐establish wild populations. To increase survival rates of stocked individuals, the Lower Colorado River Multi‐Species Conservation Program's Habitat Conservation Plan implemented a minimum stocking size. Anecdotal reports on hatchery populations suggest that females grow at a faster rate and reach larger sizes than males. If this observation is correct, a minimum stocking size may cause skewed sex ratios of stocked populations. To test this prediction, we compared average male and female lengths in 3‐year‐old fish from two cohorts before and after they were sorted by size. Our data support the observation that size in Bonytail is sexually dimorphic by age 3, with females being the larger sex. This is also the age at which fish begin to reach the minimum size to meet stocking requirements. As predicted, size‐grading produced a significantly skewed sex ratio in the animals slated for release. The consequences of augmenting wild populations with groups of animals having skewed sex ratios are largely unknown but could include increased mate competition, inadvertent artificial selection, or a reduction in genetic diversity.