Measuring the Growth Rate in Three Populations of Larval Lampreys with Mark–Recapture Techniques

<p>The growth rate of larval lampreys (ammocoetes) is of critical importance for scientists and managers seeking to better understand, control, and protect lamprey populations. To date, measurements of ammocoete growth have often relied upon indirect methods (e.g., length frequency), but direct measurements of growth rate in wild populations are rare. Lamprey ammocoetes in three streams were individually marked with visible implant elastomer and were subsequently recaptured. Ammocoete growth was variable among sites and among sample events (from –0.035 to 0.18 mm/d; from –0.0022 to 0.012 g/d), and maturation to the juvenile or adult stage was estimated to take 4–10 years, with some animals possibly requiring more time. American Brook Lampreys <i>Lethenteron appendix</i> grew 0.13 mm/d or 0.0055 g/d on average, whereas the growth of Sea Lampreys <i>Petromyzon marinus</i> was variable, with ammocoetes experiencing significantly higher mean growth at one site (0.12 mm/d; 0.0025 g/d) than at the other site (0.032 mm/d; 0.00039 g/d). These estimates provide support for the generally long growth periods of ammocoetes but also suggest that variability plays a wider role even within populations. The variability in growth rate may provide ammocoetes with a highly flexible life history, allowing them to exploit habitats under a variety of conditions potentially encountered during development.</p> <p>Received June 16, 2016; accepted October 12, 2016 Published online December 12, 2016 </p

The model, equation number used in the present study, number of samples (n), model AIC value, the difference in AIC units (ΔAIC) from the top model in the family, mean squared error (MSE), mean absolute error (MAE), a measure of model efficiency, and parameter estimates (mean ± SE).

The model, equation number used in the present study, number of samples (n), model AIC value, the difference in AIC units (ΔAIC) from the top model in the family, mean squared error (MSE), mean absolute error (MAE), a measure of model efficiency, and parameter estimates (mean ± SE).</p

The residuals regressed against the fitted values of the Δδ²H (a-d), Δδ¹³C (e-h), Δδ¹⁵N (i-l) models, with the equation listed in each panel.

The residuals regressed against the fitted values of the Δδ2H (a-d), Δδ13C (e-h), Δδ15N (i-l) models, with the equation listed in each panel.</p

Muscle sample a) δ²H, b) δ¹³C, and c) δ¹⁵N before and after lipid extraction.

Boxplot midlines are the median, the boxes enclose the 1st-3rd quartiles (i.e., 50% of the data points), and the whiskers are 1.5 times this interquartile range. Measured values that boxplots are drawn from are represented as points and are jittered to make them more easily distinguishable. The difference before and after extraction for each paired value is shown as a light grey line between groups.</p

Fig 3 -

a) The δ13Cbulk and b) the δ15Nbulk of lamprey muscle and their C:N ratio, colored by the month in which they were collected. The species collected is denoted by shape (ABL = American brook lamprey, LBL = least brook lamprey, SL = sea lamprey).</p

Fig 5 -

a) The ΔMLδ2H (δ2Hextracted−δ2Hlipid) and b) the ΔMLδ13C (δ13Cextracted−δ13Clipid) plotted by the month of collection and color for the river they were collected from.</p

S2 Fig -

The a) δ2H, and b) δ13C for lipid (grey) and lipid extracted muscle (white) samples for lamprey collected in Maryland. Boxplot midlines are the median, the boxes enclose the 1st-3rd quartiles (i.e., 50% of the data points), and the whiskers are 1.5 times this interquartile range. Measured values that boxplots are drawn from are represented as points and are jittered to make them more easily distinguishable. (TIFF)</p

S1 File -

Stable isotope ratios in organisms can be used to estimate dietary source contributions, but lipids must first be accounted for to interpret values meaningfully. Lipids are depleted in heavy isotopes because during lipid synthesis light isotopes of carbon (12C) and hydrogen (1H) are preferentially incorporated. Prior work in larval lampreys has noted unusual lipid effects, which suggest lipids are enriched in the heavy isotope of carbon (13C), but still depleted in the heavy isotope of hydrogen (deuterium; 2H); nitrogen, a relatively rare element in lipids, has not been identified as being as sensitive to lipid content. Our objective was to determine if stable isotope ratios of hydrogen, carbon, and nitrogen behaved as expected in larval lampreys, or if their lipids presented different isotopic behavior. The δ2H, δ13C, and δ15N were measured from the muscle of four lamprey species before and after lipid extraction. In addition, muscle of least brook lamprey (Lampetra aepyptera) was collected every three months for a year from two streams in Maryland. Isotopic ratios were measured in bulk and lipid-extracted muscles, as well as in extracted lipids. The difference between muscle samples before and after lipid extraction (Δδ2H, Δδ13C, Δδ15N) was positively related to lipid proxy (%H or C:N ratio) and were fit best by linear models for Δδ2H and Δδ15N, and by a non-linear model for Δδ13C. The difference between lipid-extracted muscle and lipid δ13C (ΔMLδ13C) was negative and varied between months (ANOVA, F3,53 = 5.05, p 13C, this is not a universal rule; however, the depletion of 2H in lipid synthesis appears broadly true.</div

Fig 4 -

a) The Δδ2H (δ2Hextracted−δ2Hbulk) of muscle samples regressed against the percent hydrogen in the unextracted muscle sample. b) The Δδ13C (δ13Cextracted−δ13Cbulk) and the c) Δδ15N (δ15Nextracted−δ15Nbulk) of muscle samples regressed against the C:N ratio in the bulk muscle sample. The lines of best fit are overlain; the solid line is y = ax +b, the dashed line is y = a∙ln(x) + b, the dotted line is y = (ax + b)/(x + c), and the dot-dash line is y = (ax + b)/x.</p

Fig 2 -

a) The δ2Hbulk of muscle and the C:N ratio measured during δ13C/δ15N analysis in a separate subsample. b) The percent hydrogen in a δ2Hbulk sample regressed against the C:N ratio measured during δ13C/δ15N analysis in another subsample. c) The muscle δ2Hbulk sample regressed against the percent hydrogen which is measured simultaneously to δ2H. Also shown on plots are the linear fits (solid black lines), the 95% confidence intervals of the fit (grey region), the linear model’s equation, and its R2 values. Although not used for linear fitting, the samples are colored by month of collection, and the species collected is denoted by shape (ABL = American brook lamprey, LBL = least brook lamprey, SL = sea lamprey).</p