Otoliths versus scales: evaluating the most suitable structure for ageing largemouth bass, Micropterus salmoides, in South Africa

Abstract

The suitability of scales for ageing Micropterus salmoides was determined by comparing the precision of growth zone counts on scales with those obtained from sectioned sagittal otoliths from a sample of 496 fish collected from Wriggleswade and Mankazana Impoundments in the Eastern Cape, South Africa. Otoliths (1.4% rejected) were more readable than scales (41.7% and 7.5% rejected) for Wriggleswade and Mankazana Impoundments respectively. Otolith readings were more precise (average percentage error (APE) = 13.6%; coefficient of variation (CV) = 15.8%) than scales (APE = 18.0%; CV = 21.9%) for the total sample. Growth zone counts between structures were not symmetrically distributed around the agreed ages (otolith age = scale age) of the fish from Wriggleswade Impoundment (Bowker's test H 2 : Å 2 = 136, d.f. = 27, P < 0.05) and graphical comparison showed that scales tended to underestimate age, particularly for fish older than five years. Scales are therefore not suitable structures for ageing South African M. salmoides which may attain ages of up to 13 years.

Evaluation of Anal Spines, Dorsal Spines, and Scales as Potential Nonlethal Surrogates to Otoliths for Estimating Ages of Largemouth Bass and Smallmouth Bass

“…). Additionally, Taylor and Weyl () recommended otoliths for estimating Largemouth Bass ages in South Africa unless strong evidence exists that the population is composed of young fish (≤ age 5).…”

“…If age information is needed from Largemouth Bass or Smallmouth Bass and there is no concern with sacrificing fish, we recommend that otoliths be used. However, if sacrificing fish is not an option, we are also in agreement with the body of literature that has suggested scales may be used to estimate ages of young fish (e.g., Maceina and Sammons ; Taylor and Weyl ; Morehouse et al. ).…”

“…). Furthermore, scales were found to underestimate the ages of Largemouth Bass compared with the use of otoliths in two South Africa impoundments (Taylor and Weyl ), and scales were found to be ineffective for estimating ages of Largemouth Bass in North Carolina because of their low precision (Besler ). Scale resorption, presence of false annuli, and annuli crowding on the scale edges are often cited as reasons for difficulty in estimating fish ages with scales.…”

“…Additionally, age estimates from scales were found to have the highest CV for both Largemouth Bass (14.6%) and Smallmouth Bass (12.1%) in a study that compared age estimates of dorsal spines, opercles, otoliths, and scales of fish collected from Lake Champlain, New York (Sotola et al 2014). Furthermore, scales were found to underestimate the ages of Largemouth Bass compared with the use of otoliths in two South Africa impoundments (Taylor and Weyl 2012), and scales were found to be ineffective for estimating ages of Largemouth Bass in North Carolina because of their low precision (Besler 1999). Scale resorption, presence of false annuli, and annuli crowding on the scale edges are often cited as reasons for difficulty in estimating fish ages with scales.…”

Evaluation of ageing accuracy with complementary non‐lethal methods for slow‐growing, northern populations of shoal bass

“…Although otoliths were not used, ageing precision results from scales used in this study were similar to other studies of black bass that used otoliths (from 0.04% to 15.8%; Besler, ; Long & Fisher, ; Maceina & Sammons, ; Taylor & Weyl, ; Rude et al., ; Sotola et al., ). By contrast, accuracy of scales from shoal bass in the upper Chattahoochee River basin was poor (57%) compared to what has been reported for otoliths from other black bass species [from 92% to 100% (Buckmeier & Howells, ; Heidinger & Clodfelter, ; Klein et al., ); but see Howells, Betsill and Prentice () who reported accuracy from 39% to 47% for known‐age 6–8‐year‐old largemouth bass].…”