Otolith Age Research Articles

Precision of Hard Structures Used to Estimate Age of Riverine Catostomids and Cyprinids in the Upper Colorado River Basin

AbstractUnderstanding the population dynamics of native and nonnative fishes is critical for guiding and evaluating management activities, but obtaining information on population dynamics is often dependent on identifying structures that provide precise estimates of age. We examined age estimation using various hard structures for native bluehead suckers Catostomus discobolus, flannelmouth suckers C. latipinnis, and roundtail chub Gila robusta, and nonnative white suckers C. commersonii, creek chub Semotilus atromaculatus, white sucker × bluehead sucker hybrids, and white sucker × flannelmouth sucker hybrids in a small headwater stream of the upper Colorado River basin (UCRB) in Wyoming. We evaluated between‐reader precision (i.e., between two readers) and agreement of otolith age estimates with estimates from scales, fin rays, cleithra, and opercular bones. Exact agreement between readers was highest for otoliths (66–96% among species) and fin rays (61–92%) and lowest for opercles (25–69%), cleithra (21–41%), and scales (15–48%). Age estimates from fin rays were almost exactly the same as those from otoliths for all species except creek chub, for which fin ray estimates were consistently lower than otolith estimates. Age estimates from scales were generally 1–4 years lower than those from otoliths for most species, and most discrepancies occurred when otolith ages were greater than 5 years. We recommend that fin rays be used to estimate age of native catostomids and roundtail chub in the UCRB because fin rays provide accurate estimates of otolith age and can be obtained without sacrificing fish. We further recommend that otoliths be used to estimate age of creek chub in the UCRB because accuracy of fin rays was poor and because sacrificing this nonnative species may benefit native fishes of the UCRB.

Asynchronous Bluegill Recruitment in Four South Dakota Impoundments

ABSTRACT We quantified recruitment patterns and modeled the relation of climatic variation to bluegill (Lepomis macrochirus) year-class strength in four South Dakota impoundments. Because year-class strength of many species in the northern Great Plains can be erratic due to abiotic factors, we hypothesized that recruitment among populations would be synchronous and that broad-scale climatic patterns would likely affect bluegill survival and subsequent recruitment. We used the residual method based on otolith age structure to assess relative year-class strength and examined six candidate models using the Akaike's information-theoretic approach to determine the influence of temperature, precipitation, and winter severity (and combinations of these variables) on bluegill recruitment. We found that bluegill recruitment was asynchronous, and all three single variable models performed similarly (Δi <1) and were more supported than combinations of variables. However, the single variable relationships were weak indicating that biotic influences likely had more influence than climate on bluegill recruitment in these systems.

Precision of Five Structures for Estimating Age of Common Carp

AbstractOtoliths (asteriscus) have been validated as an accurate structure for estimating age of common carp Cyprinus carpio. However, extraction and processing of common carp otoliths are time consuming and require sacrifice of fish. Therefore, we analyzed age estimation precision of four alternative structures relative to otolith age for 139 common carp collected from five eastern South Dakota lakes. All common carp were collected using daytime electrofishing. Each fish was assigned an identification number and measured to the nearest millimeter total length, after which aging structures were removed. Age was estimated from scales, vertebrae, opercles, pectoral fin rays, and asteriscus otoliths by methods similar to those recommended by previous researchers. Relative to otolith age, average percent error was 6.8% for scales, 15.4% for vertebrae, 9.9% for opercles, and 1.2% for pectoral fin rays. Compared with all other structures, ages from pectoral fin ray sections were nearly as precise as otoliths through age 13 (lowest average percent error); however, fin rays consistently underestimated the ages of fish older than 13 years. In most cases, pectoral fin ray ages matched otolith ages, thereby providing similar age estimates. We conclude that pectoral fin rays provide a precise, economical, and nonlethal alternative for estimating common carp age structure. Accuracy of common carp ages estimated from pectoral fin rays still requires evaluation.

Life history of the red-banded seabream Pagrus auriga (Sparidae) from the coasts of the Canarian archipelago

Summary Red-banded seabream Pagrus auriga (N = 615) were caught off the Canary Islands from January 2003 to December 2004. Total length ranged from 120 to 780 mm. The species was characterized by protogynous hermaphroditism. The male :female ratio was in favour of females (1 : 8.2). The reproductive season extended from September to February, with a peak in spawning activity in October–November. Fifty percentage maturity was reached at 387 mm total length by females and 533 mm by males. The length–weight relationship for all individuals was described by the parameters: a = 0.0086 and b = 3.014, when length is given in mm and weight in grams. Otolith age readings indicated that the population consists of 19 age groups, including a very high proportion of individuals between 0 and 7 years old. Growth analysis reveals that the species is slow-growing and relatively long lived (18 years). The von Bertalanffy growth parameters for the entire population were: L∞ = 803 mm, k = 0.081 year−1 and t0 = −2.17 year. Growth differed between males and females. The instantaneous rate of natural mortality for all fish was: M = 0.164 year−1.

Age and growth of larval Sardinella aurita (Pisces: Clupeidae) from northeastern Venezuela, determined by otolith microstructure analysis

Age and growth of Sardinella aurita larvae were analyzed based on daily growth increments in sagitta otoliths. Larvae were obtained from ichthyoplankton samples collected from the outer shelf off Margarita Island and from Mochima Bay (northeastern Venezuela), between March 1999 and January 2001. Total length, standard length (SL) and height of larvae were measured and the otoliths were examined under a light microscope. Larval size ranged from 1.35 to 15.90 mm SL, the Margarita Island larvae being signicantly larger than those from Mochima (t = 18.69; P &lt; 0.001). The three morphological parameters were significantly and positively correlated among themselves and with otolith diameter and age, and fitted to a linear regression model; hence, size growth as a function of age was not different between the localities studied (SL = 2.65 + 1.10 × age; r2 = 0.78, P &lt; 0.001). Growth rates per locality were also determined by backcalculating sizes, with no significant differences (F = 2.60, P &gt; 0.05) between them. The mean backcalculated growth rate was 0.99 mm day–1 and it was not significantly different from the mean growth rate obtained from fitted length-age data (F = 3.32, P &gt; 0.05). Morphological changes in otoliths were evident from the mean daily increment widths, with wider increments in larval otoliths from Margarita Island (H = 42.54, P &lt; 0.001).

An Evaluation of the Accuracy of Age Estimation Methods for Southern Lake Michigan Alewives

AbstractAn evaluation of otoliths, scales, vertebrae, and opercles taken from southern Lake Michigan alewives Alosa pseudoharengus was conducted to identify the best structure for estimating age. Based on percent agreement and coefficient of variation analyses, ages estimated from otoliths were significantly more precise than ages estimated from other structures. Mean frequency counts of annuli on scales, vertebrae, and opercles tended to overestimate the relative abundance of young fish and underestimate the relative abundance of older fish more than those of otoliths. Length frequency histogram analysis of alewives collected in 2003 corroborated the accuracy of otolith age estimates. The mean time necessary to estimate alewife ages did not differ significantly between structure types. Based on their precision, accuracy, and time efficiency, otoliths are recommended for estimating ages of southern Lake Michigan alewives.

First Evidence of a Nursery Habitat for Juvenile Gag in the Southern Gulf of Mexico

AbstractInformation on a nursery area for juvenile gag Mycteroperca microlepis in the southern Gulf of Mexico is offered for the first time in this study. A total of 817 gags that ranged in size from 1.5 to 34.5 cm standard length (SL) were captured with a small trawl net from January to December 2001 in a shallow sea grass bed (mainly turtle grass Thalassia testudinum, manatee grass Syringodium filiforme, and shoal grass Halodule wrightii). The gag biomass in the swept area was 217 ± 74 kg/km2 (mean ± SD) with a density of 48,393 ± 125 fish/km2. Peak ingress of gag was observed from March to May, when newly settled organisms (range, 1.5–2.8 cm SL; n = 28) and the smallest young of the year (age 0; 3.2–4.9 cm SL; n = 72) were caught. After settlement, juveniles reached maximum abundance by July (n = 186) with a size range of 8.0–18.2 cm SL and then began to leave the nursery area in September. The monthly occurrence of newly settled gag, length‐frequency analysis, and otolith aging indicate that age‐0 gag (range, 1.5–19.5 cm SL; n = 756) were present in this nursery area from March to December 2001 as a single discrete cohort. These results suggest that settlement is discontinuous for gag in this region. Back‐calculated hatching dates, estimated from otoliths of early juveniles captured in April (3.5–5.2 cm SL; n = 13), ranged between January 28 and February 10, 2001.

Patterns of Juvenile Habitat Use and Seasonality of Settlement by Permit, Trachinotus falcatus

Permit, Trachinotus falcatus are economically and ecologically important throughout their range of the Caribbean, subtropical and tropical western Atlantic, and Gulf of Mexico. Despite their economic importance, little is known about the biology and ecology of permit, and most existing information is from Florida. While sufficient information is available to paint a general picture of permit life history, details are lacking for most life stages. For the juvenile life stage, nursery habitats and size and age at settlement have not yet been defined. Although six distinct habitat types (medium energy and low energy windward beaches, leeward beaches, and windward, leeward, and lagoon interior mangrove shorelines) were sampled to determine spatial patterns of habitat use by early juvenile permit at Turneffe Atoll, Belize, Central America, and the Florida Keys, USA, 99% of juvenile permit were found along medium energy windward beaches, indicating their role as nursery habitat for this species. A sub-sample of juvenile permit from Florida was examined to estimate spawning date and age at settlement from otoliths. Size-frequency distributions and otolith age analysis indicate that larval duration is approximately 15 – 20 days, and settlement occurs year-round. Since permit in Florida spawn March through July, from March through September in Cuba, and from February through October in Belize, year-round settlement indicates population connectivity via larval transport. These results lay the foundation for future research on larval supply, population connectivity, and juvenile ecology, and will aid in the ongoing formulation of a conservation plan toward a sustainable fishery for permit.

Evaluation of ageing accuracy of bocaccio ( Sebastes paucispinis) rockfish using bomb radiocarbon

The accuracy of bocaccio rockfish age assignments was evaluated using radiocarbon levels measured in otoliths collected from fish taken off the coast of Washington state (USA). Otoliths from 24 randomly selected fish with estimated birth years from 1950 to 1977, based on paired otolith age estimates, were used in this study. The level of radiocarbon measured in the core of each otolith was compared to a reference radiocarbon chronology based on radiocarbon levels in otoliths from known-age Pacific halibut. The degree of graphical phase correspondence between the two series was sufficient to support the hypothesis that the annuli were formed yearly in bocaccio otoliths but were somewhat difficult to identify. Statistical analysis of the ageing errors could not document a bias in production ageing of bocaccio. Pre-bomb radiocarbon levels measured in otolith cores confirm that bocaccio can live at least 37 years.

Corroborating the ages of walleye pollock (Theragra chalcogramma)

Fish ageing researchers have long recognised the importance of validating age-reading methodologies. The strongest age validations require the acquisition of ageing structures from fish of known-ages, or specimens whose ages are appropriate for bomb carbon validation. Often such specimens are extremely difficult or impossible to acquire so researchers have sought alternatives to validation. The alternative to age validation is age corroboration. Corroboration of a fish ageing method occurs when fish ages are found to be consistent with some ancillary information when comparisons are made in an unbiased manner. The question pursued in this study is how desirable are such comparisons from a scientific viewpoint. Information is presented that corroborates otolith ages for walleye pollock (Theragra chalcogramma), one of the largest groundfish fisheries in the world. Walleye pollock ages were corroborated using marginal increment analysis, ages following the strong 1978 year class in the eastern Bering Sea, and a comparison of ages read from otoliths with ages read from vertebrae. A new statistical method is suggested for comparing otolith and vertebra age readings. The walleye pollock example demonstrated that corroborating evidence can improve confidence in fish ages and ageing techniques.

Age and growth rate of juvenile bluefin tuna &lt;i&gt;Thunnus thynnus&lt;/i&gt; from the Mediterranean sea (Sicily, Italy)

The microstructural analysis of the sagittal otoliths of juvenile Atlantic bluefin tuna, Thunnus thynnus , can be used to estimate the age and growth rate of young-of-the-year individuals born in the Mediterranean. Samples of juvenile bluefin tuna, obtained as by-catch of the local small-scale pelagic fishery for Atlantic bonito and dolphinfish, were collected off the northern coast of Sicily between late August and early November 2002. Otolith age readings were carried out on 56 specimens ranging between 195 and 400 mm fork length and between 112 and 1266 g total weight. Based on microincrement analysis along a counting path from the otolith core to the antirostrum, juvenile fishes were found to be between 77 days and 153 days old. The estimated growth rate was practically linear over the whole size range, accounting for about 2.0-2.37 mm/day. Derived from the length-weight relationship and the estimated length-at-age data, the mean weight-at-age was 168, 429 and 813 g for 2, 3 and 4 month-old juveniles respectively. Furthermore, the hatching date distribution of bluefin tuna, obtained by means of the back-calculation of ageing data, indicated a spawning period of at least two months, namely from mid-May to mid-July, with a peak in mid-June. Our data indicate that juvenile bluefin tuna have a very high growth rate in the first part of their life, reaching a weight of more than 1 kg in four months.

Accuracy and Precision of Age Estimation of Crappies

AbstractA collection of known‐age black crappies Pomoxis nigromaculatus and white crappies P. annularis (ages 1–5) was used to evaluate the accuracy and precision of ages estimated from otoliths and scales by readers of varying experience levels. Age estimation accuracy for black crappie otoliths averaged 99.6%, whereas accuracy for scales was 77.6%. Accuracy of age estimates from white crappie otoliths averaged 98.5%, whereas accuracy of estimates from scales averaged 80.4%. For both species, age estimation precision was higher for otoliths than for scales. Reader bias (e.g., difference between true age and estimated age) tended to be greater for scales than otoliths in both species. Bias in otolith age estimation was minimal and only apparent for age‐5 crappies, which were consistently underaged. Bias in scale age estimation was most apparent for age‐4 and age‐5 crappies, which were also typically underaged. Reader experience influenced the degree of precision and bias; experienced readers produced more precise and less biased age estimates. The use of otoliths to improve crappie age estimate precision and bias has been well documented. Through the use of known‐age fish, we provide evidence that age estimate accuracy can also be improved.

Bomb radiocarbon and lead - radium disequilibria in otoliths of bocaccio rockfish (Sebastes paucispinis): a determination of age and longevity for a difficult-to-age fish

Longevity estimates for the bocaccio rockfish (Sebastes paucispinis) using traditional techniques range from less than 20 years to approximately 50 years. Otoliths of bocaccio are difficult to age, and previous attempts to validate ages have been unsuccessful. Because otolith age suggests the bocaccio are reasonably long-lived, lead–radium dating was used in an attempt to independently age bocaccio otoliths. The measured 210Pb and 226Ra activities were among the lowest reported and resulted in poor radiometric age resolution; however, the break-and-burn technique clearly underestimated age in some cases with the longevity of the bocaccio being at least 31 years. To provide better age resolution, the bomb radiocarbon approach was applied to individual otoliths. Based on measured radiocarbon levels relative to a reference time-series, several specimens were aged at approximately 30–40 years. To evaluate these determinations, the remaining otolith of the pair was sectioned and aged blind. The result was an excellent fit to the reference time-series and a validation of the age estimates. The maximum age from growth zone counts was 37 ± 2 years, which is consistent with a reported maximum age of approximately 50 years.

Early life history characteristics and genetic homogeneity of Conger myriaster leptocephali along the east coast of central Japan

To study the population structure of the Japanese conger eel, Conger myriaster, we investigated the age, total length, developmental stage and mitochondrial (mt) DNA genetic variation among the leptocephali collected from three different locations along the east coast of central Japan. A total of 79 individuals was collected at the same period of time in March 1998 from Iwaki (northern site), Odawa Bay (middle site) and Ise Bay (southern site). Results from morphological measurements and otolith age determination indicated that the mean total length of leptocephali from Iwaki was about 10 mm shorter than those from Odawa Bay and Ise Bay, the average age of the samples from Ise Bay was about 50 days older than those of the sample from Iwaki and Odawa Bay, and the leptocephali in metamorphic stage appeared only in Ise Bay samples. The otolith data also suggested the existence of at least two spawning seasons in 1997. These regional differences suggested that the early life history characteristics of the Japanese conger eel might differ between geographically different areas along the east coast of central Japan. Phylogenetic analysis based on mtDNA sequence data indicated no significant genetic differentiation between samples collected from different locations, implying intensive gene flow between geographically distant areas.

Assessing the use of sectioned otoliths and other methods to determine the age of the centropomid fish, barramundi ( Lates calcarifer) (Bloch), using known-age fish

The use of stocked fish of a known age provide an opportunity to determine the practicality of use of otolith morphometrics and fish length to estimate the age of barramundi ( Lates calcarifer) and determine accuracy of sectioned otolith age estimates. Otoliths were collected from 119 stocked barramundi and were compared against the known age of the fish (range: 0.75–8.64 years). The otoliths of barramundi appear to grow in three distinct phases when compared to the total length of the fish (TL), with a final change in otolith growth coinciding at the approximate size of sex change for this species (900 mm TL). Otolith growth is correlated linearly in all directions throughout to total growth of the otolith. Linear relationship of the sectioned otolith age estimates and known ages was highly significant ( r 2=0.89), with nearly 88% of the fish assigned to the correct age class with an index of average percent error (IAPE) of 3.2%. The otolith weight–age relationship for the known-age fish described by the equation, age=17.43 ( otolith weight )+0.981 , accounted for more than 71% of the variability. The use of any of the three otolith dimensions (length, breadth, width), otolith weight or fish total length (TL) provided a similar population age structure to that of sectioned otoliths ages ( P>0.05). Because of significant time savings and costs associated with the techniques, use of otolith weight or even fish TL relationships with fish age offer a real alternative to reading sectioned otoliths, as long as enough samples are used to account for any bias from sampling error. Use of otolith weight alone could reduce laboratory costs by 96% when compared to sectioned otoliths, and has real utility for use in long-term monitoring.

INDIVIDUAL VARIATION IN THE TIMING OF ONTOGENETIC NICHE SHIFTS IN LARGEMOUTH BASS

The transition to piscivory is a crucial ontogenetic niche shift for many primarily piscivorous fishes. An early transition to piscivory may increase growth, decrease mortality, and therefore enhance lifetime fitness. Although much is known about the extent and causes of variation in the timing of the shift to piscivory among species and among cohorts within a species, little is known about the extent and causes of variation in the timing of the switch to piscivory among individuals within a single cohort. Here, I link otolith age and growth analysis to direct diet and stable isotope analyses to examine variation in the timing of the transition to piscivory and its causes among individual members of the 1994 largemouth bass cohort in Paul Lake, Michigan. Stable isotope and direct diet analyses indicate that only a few members of the 1994 cohort were able to shift to and sustain piscivory in their first summer of life (early piscivores), while most cohort members would have to wait until their second summer of life to become piscivorous (late piscivores). Significant differences in growth rate between early and late piscivores emerged shortly after 18 June, the first date of possible piscivory by early piscivores, after which early piscivores began to grow at rates nearly twice that of late piscivores. Otolith and stable isotope analyses combined indicate that an early hatching date was necessary, but not sufficient, to explain variation in the timing of the transition to piscivory. All early piscivores were hatched early in the summer, but many early-hatched members of the 1994 cohort did not shift to piscivory in their first summer of life. A combination of at least 10 days of variation in hatching dates and higher-than-average growth rates was required for early piscivores to switch to and sustain piscivory in their first summer of life. Individuals that were able to make the early transition to piscivory most likely benefited from both increased survival and fecundity over much of their life, the combination of which would confer a substantial fitness advantage upon individuals able to make the early transition to piscivory.

The precision of otolith radiometric ageing of fish and the effect of within-sample heterogeneity

Ageing of fish using radiometric methods applied to otoliths is a widely accepted and valuable technique for validating annulus counts. Initially, whole otoliths were analysed, but it is now more frequent, and requires less stringent assumptions, to analyse otolith cores. Data from published studies were used to calculate typical ageing errors, assuming linear growth in otolith mass. These errors increase with increasing age, are much smaller if an improved method for measuring 226Ra is used, and, for older ages, are greater when cores are used (nevertheless, the use of cores, rather than whole otoliths, is recommended because the stronger assumptions required for the latter are hard to justify or verify). It is common to use more than one otolith per sample (sometimes more than 100) so as to provide sufficient sample mass, and to assume no within-sample heterogeneity in otolith age and mass-growth rate. A simulation experiment was carried out to determine whether any violation of this assumption was likely to have a significant effect on the accuracy of estimated ages. Plausible levels of heterogeneity were found to produce only a negligible decrease in precision and small bias (&lt;10%).

Validation of otolith age determination in Australian longfinned river eels, Anguilla reinhardtii

The primary objective of the present study was to validate the annual nature of growth rings in otoliths of 'yellow eel stage' (fully pigmented, premigratory) Australian longfinned eels (Anguilla reinhardtii) in New South Wales, Australia, using a combination of laboratory and field experiments. Eels were injected with oxytetracycline (OTC) and tagged with external 'T-bar' tags. Microscopic examination of thin transverse sections of the sagittal otoliths from recaptured eels showed that one opaque annulus was typically formed in the otolith during each year subsequent to OTC marking. The seasonal timing of opaque annulus formation was highly variable, but generally occurred between May and November. Supernumerary (false or incomplete) rings were observed in many of the otoliths. Examination of otolith sections from a sample of very small, untagged yellow eels verifed the age at first annual increment formation. Marked and tagged longfinned eels did not have a significantly higher mortality rate than controls in the laboratory experiment, but tag loss rates may be high. The field study also indicates that Australian longfinned eels generally have a very restricted home range of 300 m or less. This study is believed to provide the first otolith age validation of a tropical anguillid.

Comparison of Aging Methods and Validation of Otolith Ages for the Rainbow Darter, Etheostoma caeruleum

Abstract Etheostoma caeruleum were sampled from the James River, southwest Missouri, during eight months, July 1996 through May 1997. Ages were estimated from whole and sectioned otoliths (sagittae) and from scales by counting annuli. Edge analysis indicated that otolith annuli (opaque zones), visible in whole and cross-sectioned otoliths, formed yearly, primarily during July through September. In contrast, scale edge analysis indicated no clear pattern of annulus formation. Independent readers agreed on 63–73% of ages using otoliths but only 38% of ages using scales. Sectioned and whole otolith age estimates made by one experienced reader agreed for 68% of individuals. Scales underestimated age compared to otoliths, and maximum otolith age was five years.

Validity of Otoliths and Pectoral Spines for Estimating Ages of Channel Catfish

Abstract Basal recess and articulating process sections of pectoral spines are often used to estimate the age of channel catfish Ictalurus punctatus. However, identification of annuli in pectoral spine sections can be difficult. We developed and validated a method for estimating the age of channel catfish by using sagittal otoliths. We also validated a new method using pectoral spines in which a single cut is made through the dorsal and anterior processes (hereafter termed cut spines) and annuli are enhanced with side illumination. Age estimates from otoliths and cut spines were compared with age estimates from traditional articulating process sections of pectoral spines for channel catfish of known ages (1–4). Age estimates by the three methods were correct for more than 90% of fish after two experienced readers independently estimated ages and resolved disagreements by mutual examination. Otoliths were more accurate and less variable in estimating age. Otolith age estimates were always within 1 year and...