Malheur Carp Age & Growth Report_original

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This unpublished report is for the internal use of the U.S. Fish and Wildlife Service only; it is not to be publically distributed, cited, or published by others.

Completion Report to:

US Fish and Wildlife Service Malheur National Wildlife Refuge

For

Age Structure and Growth of Invasive Common Carp Populations in the Malheur National Wildlife Refuge1

Submitted by

Michael E. Colvin2, Clay L. Pierce3, and Linda Beck4

2Department of Natural Resource Ecology and Management, Iowa State University 3U.S. Geological Survey – Iowa Cooperative Fish and Wildlife Research Unit

4U.S. Fish and Wildlife Service, Malheur National Wildlife Refuge

March 2012

1Disclaimer: Per U.S. Geological Survey Policy (500.14), this unpublished report is provided to the U.S. Fish and Wildlife Service for their internal use only. This evaluation was funded by the U.S. Fish and Wildlife Service through the Iowa Cooperative Fish and Wildlife Research Unit Cooperative Agreement (G11AC20176). This unpublished material is not to be publicly distributed, cited, or published by others. This unpublished report is not an official dissemination of the U.S. Geological Survey and must not be released to the public in any form until the report has been released by the U.S. Geological Survey or until the U.S. Geological Survey Director has authorized release by the agency.

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EXECUTIVE SUMMARY

Fish age and growth information provided by analysis of hard structures can improve fish

population management. Common carp (Cyrpinus carpio) is one of the most widely distributed

nuisance fish species in the United States. Accurate age and growth estimates are especially

important for managing this nuisance fish. Common carp were collected opportunistically using

multiple gears at varying times (June 2010, January-July 2011) from four locations within

Malheur National Wildlife Refuge. Dorsal spines and otoliths were used to compare age

estimates, evaluate proportionality of structures to fish length, determine the most appropriate

structure for aging and back calculating length at age, fit the age-length data to a von Bertalanffy

growth function, and calculate site specific mean back-calculated length at age. Dorsal spine age

estimates were similar to otoliths for fish less than 5 years old but underestimated otolith age

estimates for fish exceeding 5 years of age. If lethal sampling is permissible, otoliths should be

used to estimate age. Dorsal spines and otoliths were both found to be proportional to fish length

and therefore appropriate to use for back-calculating length at age. Parameter estimates for k and

Linf of a von Bertalanffy growth function varied among sites, representing two types of

populations. Fish captured at the fish barrier were younger and faster growing (i.e., high k, low

Linf), while fish captured at the remaining sites were slower growing, older fish (i.e., low k, high

Linf). Collection of fish in the fall will facilitate age estimation by allowing the previous annulus

to fully form and eliminate the need to count the structure edge as an annulus. If the objective is

to create an age length key, fish should be collected in length bins (i.e., 10-15 per 2.5 cm length

interval). This will facilitate assigning ages to fish based on length. Age and growth among-site

variability indicates that analysis of strategies to suppress carp may need to be on a site-by-site

basis rather than a refuge-wide policy.

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INTRODUCTION

Age and growth information provided by analysis of hard structures can improve fish

population management. Age estimates are used to quantify population age structure, growth

rates, and dynamics. Individual age estimates and fish length can be fit to growth functions (e.g.,

von Bertlanffy), from which coefficients can be used to estimate population growth rates and

mortality (Hoenig 1983; Hewitt and Hoenig 2005; Miranda and Bettoli 2007). Biased age

estimates can lead to erroneous mortality and growth estimates, which in turn can lead to

misguided fish population management. Back-calculated lengths at age can reflect many years

of growth history in long lived fish which can be used to evaluate environmental correlates and

standards of growth (Isely and Grabowski 2007; Jackson et al. 2008). Identifying environmental

conditions associated with high growth rates can also provide managers with additional

population management information. However, proportionality of hard structures with fish

length is a critical assumption required to back calculate length at age (Isely and Grabowski

2007).

Common carp (Cyrpinus carpio) is one of the most widely distributed nuisance fish

species in the United States (Nico et al. 2012). Accurate age and growth estimates are especially

important for managing this nuisance fish. Dynamic rates and indexes estimated from age data

can be used to parameterize age structured population models and evaluate potential population

suppression strategies (e.g., Brown and Walker 2004; Weber et al. 2011). Otoliths are preferred

aging structures, however otolith retrieval is lethal and non-lethal surrogates are required when

lethal sampling is unacceptable, such as mark-recapture population estimates. Pectoral fin rays

have been evaluated for precision and accuracy for common carp and found to give reliable age

estimates up to 13 years of age (Phelps et al. 2007). Relative to pectoral fin rays, dorsal spines

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are preferred due to greater between-reader precision and ease of preparation (Jackson et al.

2007). While common carp dorsal spines offer good precision and a non-lethal method to

estimate age, they have not been formally compared to otoliths to evaluate how well dorsal spine

annuli correspond to otolith annuli. Back-calculated lengths are frequently used to quantify size

structure of common carp populations (e.g., Jackson et al. 2008); however to our knowledge the

proportionality assumption has never been assessed for dorsal spines.

The objectives of this study were to:

1. compare age estimates of common carp derived from dorsal spines and otolith

2. evaluate proportionality of these structures

3. determine the most appropriate structure for aging and back calculating length at

age in common carp

4. fit the age-length data to a von Bertalanffy growth function for each sampling site

5. calculate site-specific mean back-calculated length at age

METHODS

Study area.—Common carp were introduced in the Malheur National Wildlife Refuge

(MNWR; 43°18'58.7",-118°47'29.6") in the 1920s (Ivey et al. 1998). MNWR is a complex

aquatic system representing varying aquatic habitat types (e.g., lake, river, springs, flooded

fields, ponds). The refuge consists of Malheur Lake (20,114 ha), the Donner Und Blitzen River

which flows into the lake from the south, the Silvies River which flows into the lake from the

north, and an area of springs on the western edge of the refuge. The springs on the western

refuge edge are separated from Malheur Lake and tributaries by Mud Lake, an alkali lake.

Common carp occupy the numerous ponds, small lakes, spring, rivers, and flooded fields within

MNWR.

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Fish and age structure collection.—Common carp were collected opportunistically at

varying times (June 2010, January-July 2011) from four refuge locations. Multiple gears were

used to capture a total of 100 fish of varying size at each sampling location. A combination of

electrofishing, dip netting, minnow trapping, angling, trammel netting, and cast netting was used

to capture fish of varying sizes. Collection methods and effort were not standardized among

sites.

Total length was recorded for captured fish and aging structures removed. Otoliths were

removed using the “up through the gill” method (Secor et al. 1991). Dorsal spines were removed

as closely to the body as possible with a pair of side-cut pliers. Dorsal spine and otolith pairs

were assigned a unique identification number for comparative analysis. All field work was

completed by MNWR staff and structures shipped to Iowa State University for processing and

analysis.

Structure preparation, aging, and measuring.—Dorsal spines and otoliths were

embedded in epoxy and thin sectioned to 0.8-1.0 mm for spines and 0.4 mm for otoliths using a

diamond wafering blade on a low speed saw (Brown et al. 2004; Koch and Quist 2007; Phelps et

al. 2007). Otoliths were sequentially sectioned to ensure the nucleus was reached and mounted

on glass slides to facilitate age estimation. Otoliths and spines were viewed using a dissecting

microscope (0.8x–11.5x magnification), oblique light, and a drop of immersion oil. A digital

image (Appendix 1) was taken of each structure and viewed with an image analysis system.

Structure radius was measured (mm) for each image using image analysis software (ImagePro

6.0, www.mediacybernetics.com). Age was estimated for paired otoliths and dorsal spines by

two readers without prior structure knowledge (i.e., size, location sampled). Otolith and dorsal

spine annuli were determined as translucent rings following opaque rings (Appendix 1) (Brown

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et al. 2004)). Age estimate discrepancies between readers were resolved by re-examination of

the structure to determine consensus age. Structures where an age estimate could not be agreed

on were excluded from analysis.

Data analysis

Age comparison.—Bias in dorsal spine age estimates were evaluated using linear

regression. The linear model: A�� = β�• A�� was fit to the data where, A�� is the

dorsal spine age estimate, A�� is the otolith age estimate, β� is the slope of the linear

relationship. Otolith annuli have been validated to represent annual growth increments and

therefore otolith age estimates were assumed to be true (Brown et al. 2004). If age estimates are

unbiased equation 1 should fit the data with β� being approximately equal to 1 (i.e., 95%

confidence interval contains 1). The linear model was fit by ordinary least squares using the R

program (R Development Core Team 2010).

Structure proportionality.—Linear regression was used to assess the assumption of hard

structure proportionality to fish length. The structure-body length relationship was assessed

using the model: R = β�+ β

�• L��, where R is the aging structure radius, β

� is the

intercept of the linear relationship, and β� is the slope of the linear relationship and Lcapture is the

length of fish at capture. If dorsal spines and otoliths are proportional to fish length the linear

model should fit the data and no curvature should be detected in residual plots. The linear model

was fit by ordinary least squares using the R program (R Development Core Team 2010).

von Bertalanffy growth function.—A von Bertalanffy growth function (VBGF) was fit to

otolith estimated age-length data for each site. The VBGF: �� = ��,� • �1 − !"#•�$!%&�,

where L(A) is length at age, Linf,i is asymptotic average length for site i, A is fish age, ki is the

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growth coefficient for site i, and t0 is the theoretical length of a fish at age 0, was fit to the age-

length data. The VBGF was fit via maximum likelihood assuming normally distributed errors

(Hilborn and Mangel 1997). In the model fitting the parameters k and Linf were allowed to vary

among sites and t0 was assumed to be the same for each site.

Back calculated length.—Length at age for individual common carp was estimated by

back-calculation of length at previous ages using the Dahl-Lee (direct proportion) method (Isely

and Grabowski 2007). The Dahl-Lee formula is LA=(SA/Sc)•Lc, where La is back-calculated fish

body length at age A, Lc is total fish length at capture, Sa is mean aging structure length at

annulus a, and Sc is aging structure total length. Back calculated lengths from otoliths were used

to calculate site specific mean length at age.

RESULTS

Age estimates.—The distributions of common carp ages estimated from otoliths varied

among sites (Figure 1), but because fish sampling methods and effort were not standardized

between sites, apparent among-site differences should be interpreted with extreme caution.

Bias and proportionality.—Age estimates varied from 0 to 12 for dorsal spines and 0 to

18 for otoliths. Dorsal spine age estimates were similar to otoliths for fish less than 5 years old

and underestimated otolith age estimates for fish exceeding 5 years of age (Figure 2). There was

significant bias in older fish with β�

=0.45 (95% C.I. = [0.44, 0.50]). Dorsal spines and otoliths

were found to be proportional to fish length, since there was no curvature detected in residual

plots and the proportion of variance explained was high (R2=0.89; Figure 3).

VBGF and back-calculated growth.—VBGF parameter estimates, k and Linf, varied among

sites (Table 1). Length at age of fish estimated from the fitted VBGF varied among sites

(Figure 4). Back-calculated mean length at age varied among sites (Table 2) (Figure 5).

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CONCLUSIONS AND RECOMMENDATIONS

If lethal sampling is permissible, otoliths should be used to estimate age. Collection of

fish in the fall will facilitate age estimation by allowing the previous annulus to fully form and

eliminate the need to count the structure edge as an annulus. If the objective is to create an age

length key, fish should be collected in length bins (i.e., 10-15 per 2.5 cm length interval). This

will facilitate assigning ages to fish based on length, although it may be difficult to fill each

length bin and therefore bin interval should be set at the discretion of the refuge fish biologist

and with knowledge of the populations. Apparent among-site variability among age and growth

parameters indicates that strategies to suppress carp may need to be on a site-by-site basis rather

than a refuge-wide policy. For example, strategies to suppress smaller, faster growing young

fish may be different from slower growing, older populations (Brown and Walker 2004).

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LITERATURE CITED

Brown, P., C. Green, K. P. Sivakumarin, D. Stossel, and A. Giles. 2004. Validating otolith annuli for annual age determination of common carp. Transactions of the American Fisheries Society 133:190-196.

Brown, P., and T. I. Walker. 2004. CARPSIM: stochastic simulation modelling of wild carp (Cyprinus carpio L.) population dynamics, with applications to pest control. Ecological Modelling 176:83-97.

Hewitt, D. A., and J. M. Hoenig. 2005. Comparison of two approaches for estimating natural mortality based on longevity. Fishery Bulletin 103:433-437.

Hilborn, R., and M. Mangel. 1997. The ecological detective: confronting models with data. Princeton University Press, Princeton, New Jersey.

Hoenig, J. M. 1983. Empirical use of longevity data to estimate mortality-rates. Fishery Bulletin 81:898-903.

Isely, J. J., and T. B. Grabowski. 2007. Age and Growth. Pages 187-228 in C. S. Guy, and M. L. Brown, editors. Analysis and interpretation of freshwater fisheries data. American Fisheries Society, Bethesda, MD.

Ivey, G. L., J. E. Cornely, and B. D. Ehlers. 1998. Carp impacts on waterfowl at Malheur National Wildlife Refuge, Oregon. Transactions of the 63rd North Amercian Wildlife and Natural Resources Conference:66-74.

Jackson, Z. J., M. C. Quist, and J. G. Larscheid. 2008. Growth standards for nine North American fish species. Fisheries Management and Ecology 15:107-118.

Jackson, Z. J., M. C. Quist, J. G. Larscheid, E. C. Thelen, and M. J. Hawkins. 2007. Precision of scales and dorsal spines for estimating age of common carp. Journal of Freshwater Ecology 22:231-239.

Koch, J. D., and M. C. Quist. 2007. A technique for preparing fin rays and spines for age and growth analysis. North American Journal of Fisheries Management 27:782-784.

Miranda, L. E., and P. W. Bettoli. 2007. Mortality. Pages 229-278 in C. S. Guy, and M. L. Brown, editors. Analysis and interpretation of freshwater fisheries data. American Fisheries Society, Bethesda, MD.

Nico, L., and coauthors. 2012. Cyprinus carpio. USGS Nonindigenous Aquatic Species Database, Gainesville, FL. http://nas.er.usgs.gov/queries/factsheet.aspx?speciesID=4 (Accessed: 3 March 2012).

Phelps, Q. E., K. R. Edwards, and D. W. Willis. 2007. Precision of five structures for estimating age of common carp. North American Journal of Fisheries Management 27:103-105.

R Development Core Team. 2010. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.

Secor, D. H., J. M. Dean, and E. H. Laban. 1991. Manual for otolith removal and preparation for microchemical examination. Electric Power Research Institute, and the Belle W. Baruch Institute for Marine Biology and Coastal Research, Palo Alto, California.

Weber, M. J., M. J. Hennen, and M. L. Brown. 2011. Simulated population responses of common carp to commercial exploitation. North American Journal of Fisheries Management 31:269-279.

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Table 1. Site-specific sample summary statistics and population characteristics. Brackets contain 95% confidence intervals for point estimates.

Length (mm)

Site N k Linf Mean Minimum Maximum Maximum age

Otter Pond 100 0.08[0.05,0.11] 877.8[719.2,1036.4] 438.2 320 871 18

Double O 88 0.15[0.01,0.20] 581.0[521.3,640.7] 432.8 246 646 17

Silvies River 100 0.06[0.02,0.09] 1151.1[756.1,1546.1] 283.5 19 740 17

Fish Barrier 100 0.09[-0.02,0.20] 648.1[90.5,1205.8] 219.3 96 462 8

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Table 2. Site-specific mean back calculated length at age. Brackets contain 95% confidence intervals. Confidence intervals were not calculated for age groups with insufficient numbers. Age Otter Pond Double O Silvies River Fish Barrier 1 109.5[107.2,111.8] 113.7[112.4,115.0] 105.8[104.3,107.3] 78.3(77.5-79.1)

2 239.8[237.6,242.0] 206.6[205.1,208.1] 207.2[205.8,208.6] 163.8[162.8,164.8]

3 301.7[299.6,303.8] 258.5[256.8,260.2] 312.8[305.4,320.2] 202.4[197.7,207.1]

4 340.5[338.1,342.9] 302.0[299.8,304.2] 406.6[398.2,415.0] 250.5[238.5,262.5]

5 374.0[371.3,376.7] 335.6[333.3,337.9] 447.5[438.4,456.6] 331.9[308.3,355.5]

6 414.7[410.2,419.2] 365.7[362.9,368.5] 488.6[474.9,502.3] 255.2 7 468.7[462.5,474.9] 394.7[391.7,397.7] 519.6[501.2,538.0] 267.7 8 499.5[492.8,506.2] 414.3[410.5,418.1] 532.9[516.2,549.6] 302.3 9 520.1[513.2,527.0] 438.7[434.4,443.0] 554.9[540.7,569.1] 10 544.2[537.0,551.4] 457.9[452.5,463.3] 591.6[582.4,600.8] 11 561.5[554.1,568.9] 470.8[464.8,476.8] 610.4[601.4,619.4] 12 579.0[571.4,586.6] 473.5[466.0,481.0] 625.9[617.6,634.2] 13 604.5[596.7,612.3] 498.3[486.8,509.8] 637.5[629.0,646.0] 14 617.8[607.9,627.7] 511.2[496.5,525.9] 657.0[649.6,664.4] 15 636.7[615.3,658.1] 524.1[504.0,544.2] 679.4[671.0,687.8] 16 669.3[621.1,717.5] 561.0[528.4,593.6] 692.7[680.5,704.9] 17 691.1[607.8,774.4] 572.7[542.0,603.4] 695.3[668.4,722.2] 18 749.1[611.2,887.0]

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Figure 1. Age frequency distribution for common carp captured at each site. Age estimates were derived from analysis of otoliths. Fish sampling was not standardized between sites, so apparent among-site differences should be interpreted with extreme caution.

0

5

10

15

20 A: Otter Pond

0

2

4

6

8

10 B: Double O

0

10

20

30

40

50

60 B: Fish barrier

0

10

20

30

40

50

60

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

D: Silvies River

Estimated age

Fre

quen

cy

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Figure 2. Common carp dorsal spine (y-axis) age estimates plotted against otolith age estimates (x-axis) and. Data points are jittered (a small random offset) from integer values to minimize overplotting. The solid line represents a 1:1 line.

0 5 10 15

0

2

4

6

8

10

12

Otolith estimated age

Dor

sal s

pine

est

imat

ed a

ge

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Figure 3. Distance from structure center (y-axis) plotted against total length at capture (x,axis) for common carp otoliths (Panel A) and dorsal spines (Panel B). The lines denote linear (solid line) model fit to the data, Rotolith=202.7+1.68Length (R2=0.89) and Rspine=24.5+1.14Length (R2=0.89) for otoliths and dorsal spines respectively.

0 200 400 600 800

200

400

600

800

1000

1200

1400

1600 A: Otolith

0 200 400 600 800

200

400

600

800

B: Dorsal spine

Total length at capture (mm)

Dis

tanc

e fro

m s

truct

ure

cent

er (m

m)

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Figure 4. Estimated length at age given site-specific maximum likelihood parameter estimates of a von Bertalanffy growth function.

0 5 10 15

100

200

300

400

500

600

700

800

Estimated age

Est

imat

ed le

ngth

at a

ge

Otter PondDouble OSilvies RiverFish Barrier

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Figure 5. Site-specific back calculated length at age. The solid horizontal line in the boxes represents the medians. Boxes represent the bounds of the 25th and 75th quartiles of the data. Whiskers represent the lower and upper bounds of the data.

0

200

400

600

800

1000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

A. Otter Pond

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

B. Double O

0

200

400

600

800

1000 C. Silvies River

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 1 2 3 4 5 6 7 8

D. Fish Barrier

Bac

k ca

lcul

ated

leng

th (m

m)

Estimated age

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APPENDIX 1. SUPPLEMENTAL IMAGES ILLUSTRATING HARD STRUCTURE IMAGE ANALYSIS.

Figure 6. Images of dorsal spine (top panel) and otolith (bottom panel) thin-sections used to estimate age and back calculate growth for a common carp. The yellow line illustrates the measurement axis used to measure structure radius. Red ticks with an “A” prefix demark annuli and the tick with the “B” prefix marks the edge.

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Figure 7. Images of thin-sectioned dorsal spines (left panels) and otoliths (right panels) from two relatively old common carp. The numbers of annuli visible in dorsal spines sections were less than the number of annuli visible in otoliths.

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Figure 8. Images of thin-sectioned dorsal spines (left panels) and otoliths (right panels) from two relatively young common carp. The numbers of annuli visible in dorsal spine sections were equal to the number of annuli visible in otoliths.

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Malheur Carp Age & Growth Report_original