Revised fish aging techniques improve fish contaminant trend analyses in the face of changing Great Lakes food webs

Murphy, Elizabeth W.; Smith, Marian L.; He, Ji X.; Wellenkamp, William; Barr, Edward B.; Downey, P.C.; Miller, Kenneth M.; Meyer, Kathryn A.

doi:10.1016/j.jglr.2018.05.006

Cited by 23 publications

(32 citation statements)

References 19 publications

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“…Alewife has remained the most important component of lake trout diet (>50%), but the contribution of round goby has increased through the late 2000s, although it remains relatively small (<30%) (37, 46, 49, 50). Because of reduced quality in prey, the growth rate of lake trout in Lake Michigan has slowed (51, 52). To confirm whether invasive species have resulted in dietary shifts in lake trout, we utilized lipid-normalized δ 13 C (δ 13 C lipid-free ) and δ 15 N values (28).…”

Section: Resultsmentioning

confidence: 99%

“…S2)—and growth rates declined (51, 52). Due to slower growth, as previously noted, lake trout Hg concentration after 2000 was elevated relative to the early 1990s (51, 52).…”

Section: Resultsmentioning

confidence: 99%

“…Measurements of δ 15 N and δ 13 C lipid free provided evidence that this δ 202 Hg shift was not due to an altered dietary pathway (e.g., benthic versus pelagic) but rather from a change in Hg source that acted independently upon δ 202 Hg, resulting in a positive MDF shift. The coherent response of all 6- to 8-y-old fish (52) suggested a large change in source, such as a cessation of a δ 202 Hg-deplete point source.…”

Section: Resultsmentioning

confidence: 99%

“…During Hg source reductions, lake trout energetic pathways shifted either directly or indirectly to the benthos, which has dampened the expected reduction in MeHg concentrations in fish (28). This is additionally due to lake trout growth rate decreases (52). Furthermore, we have shown that sediment cores, often applied to show success of Hg mitigation strategies, do not predict MeHg trends in fish because they are inadequate to trace complex food web perturbations and the effect of Hg mitigation on Hg bioaccumulated in fish.…”

Section: Resultsmentioning

confidence: 99%

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Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

Lepak

Hoffman

Janssen

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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To understand the impact reduced mercury (Hg) loading and invasive species have had on methylmercury bioaccumulation in predator fish of Lake Michigan, we reconstructed bioaccumulation trends from a fish archive (1978 to 2012). By measuring fish Hg stable isotope ratios, we related temporal changes in Hg concentrations to varying Hg sources. Additionally, dietary tracers were necessary to identify food web influences. Through combined Hg, C, and N stable isotopic analyses, we were able to differentiate between a shift in Hg sources to fish and periods when energetic transitions (from dreissenid mussels) led to the assimilation of contrasting Hg pools (2000 to present). In the late 1980s, lake trout δ202Hg increased (0.4‰) from regulatory reductions in regional Hg emissions. After 2000, C and N isotopes ratios revealed altered food web pathways, resulting in a benthic energetic shift and changes to Hg bioaccumulation. Continued increases in δ202Hg indicate fish are responding to several United States mercury emission mitigation strategies that were initiated circa 1990 and continued through the 2011 promulgation of the Mercury and Air Toxics Standards rule. Unlike archives of sediments, this fish archive tracks Hg sources susceptible to bioaccumulation in Great Lakes fisheries. Analysis reveals that trends in fish Hg concentrations can be substantially affected by shifts in trophic structure and dietary preferences initiated by invasive species in the Great Lakes. This does not diminish the benefits of declining emissions over this period, as fish Hg concentrations would have been higher without these actions.

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Section: Resultsmentioning

confidence: 99%

“…S2)—and growth rates declined (51, 52). Due to slower growth, as previously noted, lake trout Hg concentration after 2000 was elevated relative to the early 1990s (51, 52).…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

Lepak

Hoffman

Janssen

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…For lake trout, the precision and bias of age estimation structures and preparation methods have rarely been evaluated based on one or more reads of a single sample using multiple age-readers (see Sharp and Bernard 1988;Murphy et al 2018). However, an age comparison study using a wide range of multiple paired reads from individual fish that includes age estimates > 30 years using whole and thinsectioned otoliths, and pelvic fin-ray sections has not been conducted.…”

Section: Introductionmentioning

confidence: 99%

Age estimation comparison between whole and thin-sectioned otoliths and pelvic fin-ray sections of long-lived lake trout, Salvelinus namaycush, from Great Bear Lake, Northwest Territories, Canada

et al. 2021

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Studies to determine precision and bias of both methods and age-readers are important to evaluate reliability of age data used for developing fisheries management objectives. We assessed within-reader, between-reader, and between-method precision (coefficient of variation, CV%) and bias of age estimations for long-lived lake trout, Salvelinus namaycush, from Great Bear Lake using three readers with different levels of experience. The assessment used independent age estimates (n = 3 per reader) from whole and transverse-sectioned otoliths (range = 1–67 years), and pelvic fin-ray sections (range = 3–26 years). We also examined between-method differences in assigned confidence scores. Within readers, age estimates from sectioned otoliths were more precise (2.6–3.0%) than whole (3.6–4.5%) otoliths. Between whole and sectioned otoliths, precision of age estimates was 5.4% and bias was low up to age 20. Age was typically under-estimated from whole otoliths compared to sections for fish ≥ 34 years. Increased reader confidence was correlated with greater precision and younger age estimates, particularly for whole otoliths, but less so for fin rays. Age was estimated with higher confidence from otolith sections than other methods. The least experienced reader estimated age with the lowest precision, and between-reader bias was evident among older ages. Age was consistently under-estimated and less precise from pelvic fins compared to sectioned otoliths, and are therefore an unsuitable non-lethal alternative. Sectioned otoliths revealed longevity was greater (67 years) than historically documented using whole otoliths (53 years) for these fish. Our findings contribute to those relying on otoliths or pelvic fin rays to estimate ages of long-lived lake trout populations, which are a key component of freshwater fauna in polar North America.

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Accuracy and Precision of Otolith‐Derived Age Interpretations for Known‐Age Lake Trout

Osborne

Robinson

Lantry

et al. 2022

N American J Fish Manag

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Catch-at-age data are used to inform important management decisions for recovering populations of Lake Trout Salvelinus namaycush. Age data for Lake Trout are commonly derived from interpretation of annual growth marks (annuli) on the fish's otoliths. Due to the tendency for annuli to vary in appearance and the subjectivity that is inherent to any age interpretation method, it is important that the common sources of interpretation error be well understood for any aging method used to inform management plans. In this study, coded wire tags were used to establish true ages for 153 Lake Trout to measure the precision and accuracy of age interpretations made from transverse-sectioned otoliths and to identify sources of potential age interpretation error that researchers and managers may encounter when using this method. Precision of age interpretations, as measured by average coefficient of variation, ranged from 7.9% to 9.2%. Accuracy of age interpretations varied among readers, with exact matches ranging from 41.8% to 53.6% and accuracy within AE1 year ranging from 81.0% to 83.0%. Age interpretation errors were more likely to be overestimates of true age for Lake Trout under age 7 and underestimates for Lake Trout over age 13. However, only reader 1 exhibited significant systematic bias in their age interpretations. Poor clarity of the first annuli, growth checks resembling annuli, and faintness of narrow annuli near otolith margins in older fish were identified as likely sources of interpretation error in this study. A digital reference collection of known-age Lake Trout otoliths is provided as supplemental material in the online version of this article. This collection can be used for training new readers, measuring the accuracy of age interpretations, and monitoring for aging bias by anyone using otoliths to obtain age data for Lake Trout.

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Revised fish aging techniques improve fish contaminant trend analyses in the face of changing Great Lakes food webs

Cited by 23 publications

References 19 publications

Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

Mercury source changes and food web shifts alter contamination signatures of predatory fish from Lake Michigan

Age estimation comparison between whole and thin-sectioned otoliths and pelvic fin-ray sections of long-lived lake trout, Salvelinus namaycush, from Great Bear Lake, Northwest Territories, Canada

Accuracy and Precision of Otolith‐Derived Age Interpretations for Known‐Age Lake Trout

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