Golden Shiner Notemigonus crysoleucas is found in many lakes and ponds across the southeastern United States. Though it is a common species, otolith age validation methods have not been published. The objective of this study was to confirm annulus formation in lapillar otoliths of Golden Shiners collected monthly from September 2015 through August 2016 in Lake Jackson, Florida (Leon County). We collected at least 12 individuals each month of similar length (168–249 mm; presumably of the same cohort) to document annulus formation throughout the year. We sacrificed a total of 177 individuals from the 2013 year class, and we used their lapillar otoliths for marginal incremental analysis to calculate an index of completion and validate annulus formation. The monthly index of completion was highest from January through March and lowest in May and June, indicating that annuli were deposited once per year and confirming that lapillar otoliths are a valid age estimation structure for Golden Shiners.
Accurately estimating the age of fishes is important for properly assessing populations and managing fish species. Fish ages are used in determining various population parameters including growth, recruitment, and mortality. Estimating age of fish using otoliths is a common fisheries technique (Devries and Frie 1996). For otoliths and other structures to have value in estimating the age of fish, validation is necessary to reduce overestimated and underestimated ages and to prevent nonrandom errors (Beamish and McFarlane 1983). Fish have three sets of otoliths (sagittal, lapillar, and asteriscus), and accurate age estimation with otoliths has been validated for many species, (e.g., Largemouth Bass Micropterus salmoides, Hoyer et al. 1985; White Sucker Catostomus commersonii, Thompson and Beckman 1995; Common Carp Cyprinus carpio, Brown et al. 2004; Notchlip Redhorse Moxostoma collapsum and Brassy Jumprock Scartomyzon brassieus, Bettinger and Crane 2011; Yellow Perch Perca flavescens, Blackwell and Kaufman 2012; Spotted Sucker Minytrema melanops, Strickland and Middaugh 2015), but using otoliths to determine age has not been validated for Golden Shiner Notemigonus crysoleucas.
Golden Shiner is found in North America from the Rocky Mountains to the Atlantic Coast and in some areas of the western United States (Tomelleri and Eberle 1990). In Florida, its range extends throughout the state (Robins et al. 2018), and it is commonly found in systems with dense submerged aquatic vegetation. Golden Shiner exhibits fast growth, reaching sizes exceeding 100 mm within its first year of life, and short life cycles, leading to the formation of distinct cohorts (Lazur and Chapman 1996). Shiners serve as an important forage species for numerous gamefish species (Scott and Crossmm 1973; Keast 1980; Johannes et al. 1989). Golden Shiners also support valuable fisheries in the southeastern United States where they are collected and used as live bait in the quest for many sportfish species, most notably Largemouth Bass. In Florida, commercial and recreational anglers harvest and sell Golden Shiners to bait-and-tackle shops, but the harvest is not regulated. Although Golden Shiners are widely produced by commercial aquaculture facilities, anecdotal reports from Florida anglers who utilize Golden Shiners as bait indicate a preference for wild-caught fish over commercial fish. Little information exists on the population dynamics of the Golden Shiner, in part because there is no validated method for estimating the age of the species. Therefore, biologists are unable to assess the effects of harvest on the population. A validated age estimation method is needed to characterize life-history parameters and provide insight into management of the species. Thus, we sought to validate annulus formation in lapillar otoliths of Golden Shiners using marginal increment analysis (Campana 2001), in which annuli are measured on fish collected monthly to determine timing of annulus deposition (Strickland and Middaugh 2015).
We collected Golden Shiners monthly from Lake Jackson, Florida (Leon County) via boat electrofishing (Smith−Root 7.5 GPP) with direct current at 120 pulses per second and 1,000 V (Figure 1). We collected at least 12 Golden Shiners from the same cohort (i.e., year class) each month within 5 d of the middle of the month from September 2015 through August 2016 to complete an annual cycle. We selected a single cohort because of the rapid growth and short longevity of Golden Shiners. Fish from different cohorts exhibited discrepancies in total length (TL) at time of capture; these variations in TL allowed for classification of individual fish to cohorts and limited overlap in cohorts. The use of a single cohort also allowed for the exclusion of any variability between cohorts (Campana 2001). We excluded from analysis any fish collected not from the cohort of interest.
We placed fish on ice and took them to the laboratory for analysis. In the laboratory, we measured each fish (mm TL), and removed lapillar otoliths by cutting through the ventral side of the cranial region. As in Strickland and Middaugh (2015), we selected lapillar otoliths in place of the more commonly utilized sagittal otoliths because of their large size, which facilitated easier removal and ageing. Once removed, we cleaned, air dried, and stored otoliths in labeled glass vials until processing. Because Golden Shiner otoliths are small and difficult to read, we used whole otoliths for age estimation and marginal increment analysis.
For age determination, we placed an otolith in a petri dish, covered it with water, and examined it under a dissecting microscope under external fiber-optic illumination over a dark background. We counted annuli (opaque zones) from the nucleus to the distal (outer) edge of the otolith. We aged otoliths in a simple random order. Two readers read each otolith independently; a third reader resolved any disagreement. Readers were blind to the sample date to reduce potential bias. All readers had experience in using otoliths to age a variety of other fish species. We assigned January 1 as a date of birth; thus, an otolith with two rings in December was assigned an age of two, whereas an otolith with two rings in January was assigned an age of three. Assigning ages to individual fish facilitated the use of only fish from the 2013 cohort in marginal increment analysis.
We used marginal increment analysis by calculating an index of completion (C) for each otolith (C = Wn/Wn−1, as in Tanaka et al. 1981; Murie and Parkyn 2005; Strickland and Middaugh 2015). The measurement from the beginning of the outermost (distal) annulus to the edge of the otolith is Wn. The measurement for the most recent complete increment (beginning of the previous [proximal] annulus to the beginning of the outermost [distal] annulus) is noted as Wn−1 (Figure 2). We calculated mean and standard error values for C for each sampling month using raw C values for individual fish. A single reader took otolith measurements by using a microscope eyepiece micrometer on a direct horizontal plane (Figure 2). If opaque rings (annuli) are formed annually and at the same time for all fish within the population, the monthly mean C will have one maximum and one minimum value per year, coincident with formation of a single new distal opaque ring (annulus).
We collected a total of 177 individuals (representing the 2013 year class) from September 2015 through August 2016 and used them for marginal increment analysis (Data S1, Supplementary Material). Age assignment identified an average of 21 (range: 14–28) individuals per month from nontarget cohorts that we excluded from the analysis. Age-2 Golden Shiners collected in September 2015 averaged 188.8 mm TL (range: 168–228 mm TL; standard deviation: 14.4 mm; Table 1), whereas in August 2016, the same cohort averaged 235.6 mm TL, at age 3 (range: 227–249 mm TL; standard deviation: 8.1 mm; Table 1). The plot of monthly mean C across the year of the study showed a sinusoidal pattern with one maximum and one minimum, indicating that the distal annuli were formed only once during the study (Figure 3). The monthly mean C was highest from January through March and lowest in May and June, indicating that annuli were deposited once per year, during April and May (Figure 3).
We conclude that lapillar otoliths are a valid age estimation structure for Golden Shiners. We found that annulus formation occurred only once per year, as in many other freshwater fishes (e.g., Largemouth Bass, Hoyer et al. 1985; White Sucker, Thompson and Beckman 1995; Spotted Sucker, Strickland and Middaugh 2015; and Common Carp, Brown et al. 2004). We recommend the use of lapillar otoliths for age estimation of Golden Shiners to determine population characteristics including annual mortality, growth, and recruitment. However, extraction of otoliths from individuals < 150 mm TL can be challenging because of the small size of the otolith structures.
Our findings allow fisheries managers to better understand and evaluate population dynamics of Golden Shiners. Fast-growing, short-lived fish such as Golden Shiners possess increased vulnerability to overfishing. Unregulated harvest of Golden Shiners in some systems may have detrimental impacts on both the wild-caught commercial shiner industry and natural food webs. Future research needs include estimating mortality and commercial harvest of exploited Golden Shiner populations and consider potential harvest regulations where appropriate.
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Data S1. Golden Shiner Notemigonus crysoleucas collected from Lake Jackson, Florida including: identifying number, month and year collected, annulus count, age, Wn, Wn−1, and index of completion (Wn/Wn−1).
Found at DOI: https://doi.org/10.3996/082019-JFWM-069.S1 (47 KB XLSX).
We thank Ted Alfermann and Wendy Peffercorn for valuable assistance in the field and with study design. We thank Dan Nelson, Eric Nagid, Drew Dutterer, Journal of Fish and Wildlife Management reviewers, and the Associate Editor for helpful reviews.
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Citation: Strickland PA, Bisping SM, Hatcher HR. 2020. Validation of annulus formation in Golden Shiner otoliths. Journal of Fish and Wildlife Management 11(1):258–262; e1944-687X. https://doi.org/10.3996/082019-JFWM-069
The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.