Stocking Brook Trout in Virginia s reservoirs: dispersal, naturalization, and introgression p g with native trout populations R. Humston, K.A. Hemminger, N.D. Adkins (W&L 10), R.J. Else (W&L 11), J. Huss (W&L 10), B.A. Meekins (W&L 11), P.R. Cabe, and T.L. King Washington & Lee Universit, Department of Biolog U.S. Geological Surve, Leetown Science Center, Kearnesville WV
Stocking Hatcher Trout
Stocking Hatcher Trout Positives: Reduces fishing pressure on wild (native) populations. Restore populations where extirpated. More cost effective than translocation of fish f from intact populations. l Negatives: Non-native species / strain introductions Suppression of native stocks and genetic impacts
Genetic impacts of hatcher supplementation Poor fitness of hatcher lineages Homogenization of genetic structure among populations. Loss of functional diversit in native / wild stocks (e.g. local adaptation). Potentiall can hinder recover, persistence of wild stocks - e.g. Marie et al. 2010 Molecular Ecolog v.19
Direct / Indirect Genetic Impacts Direct Results of interbreeding Reduced genetic variabilit among populations (homogenization) Outbreeding depression and reduced fitness of subsequent generations Indirect: Reduced effective population size (Ne) Increased inbreeding, inbreeding genetic drift
Brook trout stocking in VA mountain reservoirs
Brook trout stocking in VA mountain reservoirs Put-and-grow stocking program Unique, troph fisheries in wilderness settings Open questions: Dispersal into feeder streams Reproduction / naturalization of stocked strains Hbridization with native populations
Stud Objectives: 1)) Determine if stocked brook trout disperse into and inhabit tributaries. 2) Determine if natural reproduction of hatcher-origin fish occurs in tributaries. 3) Assess degree A d off introgression i i (interbreeding) occurring between h h hatcher and d native i strains. i
Stud Sites - 2009
Moore Creek Reservoir Historic water suppl impoundment for Lexington. Stocked with brook trout since 1984. Moore Creek (feeder tributar) did not hold brook trout prior to stocking. Code name: STO
Historic water suppl & flood control impoundments. Stocked with brook trout since 1989. Wild (putative native) brook trout populations in feeder streams. Code named: MIX-1 & MIX-2 Coles Run Reservoir (MIX-2) Mills Creek Reservoir (MIX-1)
Kenned Creek Unstocked wild (native) trout t stream. Reference native population for subwatershed. Code name: NAT
Stocking Histor All fingerlings stocked in reservoirs from a single brood stock lineage (Paint Bank hatcher,va). Onl exception: Fingerlings stocked in 2008 derived from Rome Lab strain. This cohort would not have spawned in time to contribute offspring to population b summer 2009.
Stud Objectives: Determine if stocked fish disperse p into and inhabit tributaries. Sample Moore Creek (STO; no previous wild population) for trout. Use genetic data to distinguish hatcher hatcher-strain strain from native trout in Mills Creek (MIX-1) and Coles Run (MIX-2). ( )
Stud Objectives: Determine if natural reproduction p of hatcher-origin fish occurs in tributaries. Compare genotpes of 2008 ear class with known hatcher strains (Paint Bank, Rome Lab) to determine if Paint Bank strain naturall produced offspring in 2008.
Stud Objectives: Assess degree g of introgression g occurringg between hatcher and native strains. Use assignment assignment tests tests to identif potential hbrids, and examine individual genotpes to determine likelihood of hbrid status.
Field collections J June-Jul J 2009 Single-pass electrofishing Pelvic fin snips Measure in field (TL)
Hatcher samples Paint Bank brood stock and 2009 oung-of-ear Pelvic e v c fin snips s ps Rome Lab genotped in 2005 and 2009 (TL King (T.L. King, unpublished data)
DNA analsis Genotped p at ten (10) ( ) established, polmorphic microsatellite loci (T.L. King, g unpublished p data)) Non-coding regions of DNA p sequences q of 1-6 specific p base ppairs. Repeated Alleles var b length (number of repeats in a row). Highl versatile genetic markers
Data Analsis Genetic Data Program g Structure Groups individuals into clusters that best approximate distinct populations based on allele frequencies. Provides posterior probabilit of population membership for individuals (population assignment).
How to read Structure output The p probabilit of membershipp to each population is represented in a stacked bar chart with a bar for each fish.
How to read Structure output Paint Bank Hatcher strain Rome Lab Hatcher strain Native strain 33.3% Paint Bank 33% Paint Bank 100% Native 33.3% Native 67% Native 33.3% Rome Lab MIX1-108 MIX1-109 MIX1-110
Assignment Rules Rules Paint Bank Hatcher strain Rome Lab Hatcher strain Native strain 8% PB 90% 18% PB 94% PB 92% Native 82% Native 6% Native MIX1-111 MIX1-112 MIX1-113
Results:: STRUCTURE Results Best solution = 3 p populations p in collection
Results:: STRUCTURE Results Hbrids
Results:: Dispersal into Tributaries Results Sample Location STO MIX-1 MIX-2 NAT Paint Bank Rome Lab Total Size Range Native (mm TL) 38 66 180 66-180 0 54 47-235 43 44 46-245 33 40 41 216 41-216 100% 30 74-321 45 NA 251 41-321 N No Native Pop n: STO Paint Bank 38 7 10 Hbrids 0 4 0 100% 100% Mixed Native / Stocked: MIX-1 MIX-2 Rome Lab Paint Bank Rome Lab 1 0 1 Rome Lab Native Paint Bank Rome Lab Admixed Native Native
Results:: Hatcher Strain Spawning Results All age-1 stocked fish should be Rome Lab strain. Age-0 40 Age-2 Age-1 Moore Crk -> Paint Bank Hatcher STO Æ Paint Bank Coles / Mills -> Paint Bank Hatcher Coles / Mills -> Native MIX Æ Paint Bank Frequenc 30 MIX Æ Native 20 10 0 0 50 100 150 Length (mm TL) 200 250
Conclusions Hatcher fish do disperse p into streams from reservoirs, even where native populations p p exist. Not a big surprise.
Conclusions Hatcher fish do reproduce p in streams even where native populations exist, and can establish naturalized populations. p p Promising for re-establishment of extirpated stocks. Suggests fitness of hatcher stocks ma not be an impediment to interbreeding.
Conclusions Introgression g has been limited over the 20+ ear stocking histor in these sstems. Assortative mating? Richards et al. 2008
Conclusions Good news scenario: Direct impacts to native genotpe has been minimal. Potential issues: Naturalized hatcher strains could lead to future introgression g in native populations. p p
New Questions: Stream residents or lacustrine migrants? g Timing of upstream dispersal? Ratio of dispersers : staers? Exclusionar processes? Indirect genetic effects? Environmental factors, e.g. stream ph?
Acknowledgements Larr Mohn, Paul Bugas, g Jason J Hallacher, Aaron Coffman (VA DGIF) Dawn aw Kirk (USFS) (US S) Barb Lubinski (USGS) Eric Hallerman, Hallerman Joanne Davis Davis, Jamie Roberts (VA Tech Fisheries & Wildlife) Funding F di ffrom Hess H Scholars S h l Program P (W&L), Mellon Foundation
Results: Hatcher / Native Results: Introgression Paint Bank 0 10 100 90 20 80 30 70 40 60 50 50 60 Native Paint Bank Rome Lab Hbrid 70 80 40 30 20 90 10 100 Rome Lab0 0 10 20 30 40 50 60 70 80 90 100 Native
Data Analsis Length Data MIXDIST p package g in R Age structure and age-specific size distributions. Estimates average size-at-age and standard deviation from collective length data. Assumed 4 age classes in collection (0 3)
Histogram of Lengths in Collections 10 F Frequenc 8 6 4 2 0 0 50 100 150 Total Length (mm) 200 250 300
Results from MIXDIST Histogram of Lengths in Collections 2008 Year Class
Power Analsis Use data from known (NAT, PB) strains to generate hpothetical populations: Parent generation F1, F2 generations back-crossings HYBRIDLAB Nielson HYBRIDLAB, Ni l et al.l 2001 Analze A l simulated i l d populations l i using i Structure, determine frequenc of missed assignments. assignments
Power Analsis Correct identification of parent p generations (NAT, PB strains): 100% Correct identification of F1, F2, 1st B-C generations as hbrids: ~100% 100% Withh our sample Wi l sizes, i we would ld d detect introgression as low as 3% of population with ith 95% percentt accurac.
Hatcher supplementation and native brook trout Previous studies mixed, but generall suggest levels of introgression between native and hatcher brook trout are low. Possible exception: hbridization between northern / southern strains, Great Smoke Mountains
How to explain low introgression despite widespread stocking? Low fitness of hatcher stocks Fraser 1989
How to explain low introgression despite widespread stocking? Genetic differences between native and hatcher lineages ma be small (difficult to distinguish strains) Technolog ma be inadequate to detect introgression (poor markers ) Context-dependence; p ; different strains,, different sstems