Comparison of age estimates and population characteristics for green sunfish using two otolith methods

Abstract

Dependent on the specific fishery, green sunfish (Lepomis cyanellus) can be viewed as a benefit or a detriment. Regardless, effective management of this species relies on precise age estimation, which is critical to detail age structure, growth and recruitment rates of their populations. To determine the most precise method for age estimation, estimated ages of whole and cracked otoliths of 422 green sunfish were compared from three small impoundments (0.6–16.2 ha) in Oklahoma. Green sunfish ages ranged from 0 to 7 for cracked otoliths and 0 to 6 for whole-viewed otoliths, depending on the population. High precision between readers was observed for whole (per cent agreement = 85%–96%; mean CV = 3.4%–4.8%; and average per cent error = 2.4%–3.4%) and cracked otoliths (per cent agreement = 92%–96%; mean CV = 0.3%–6.3%; and average per cent error = 0.3%–4.4%). Limited bias was observed for young fish (≤age 3) for evaluating between-reader precision using whole otoliths. When bias was present, ages generally exceeded the 1:1 line of equivalency. Final consensus ages for older fish (≥age 5) were sometimes underestimated using whole otoliths, compared to cracked otoliths. Fair agreement for final consensus ages (73%–87%) between whole and cracked otoliths was observed, compared to other otolith ageing studies in the literature. However, the results of the present study indicated no significant differences in growth or age-frequency estimates using ages derived from whole and cracked otoliths, suggesting the moderate level of consensus agreement was not sufficiently low to significantly impact population characteristics and subsequent management decisions. Green sunfish growth rates in Oklahoma appear sufficiently high to allow the use of whole otoliths for age estimation to age seven, unless slow growth is expected. To ensure precise age estimation, however, it is suggested that otoliths from green sunfish ≥age 5 be cracked, regardless of growth rates.