Harvest and Translocation of Freshwater Mussels for Population Restoration

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Harvest and Translocation of Freshwater Mussels
for Population Restoration
Jess Jones U.S. Fish and Wildlife
Service Department of Fisheries and Wildlife
Sciences Virginia Polytechnic Institute and
State University
Photo credit Illinois Natural History Survey
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Talk Outline
? A short history of mussel harvesting ?
Estimation of population parameters ? The
stochastic harvest model ? Restoration of
oyster mussels to upper Clinch River ?
Model simulations
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Harvesting Mussels A Short History
Main Reasons ? Shell collecting for natural
pearls (18th 19th Centuries) ? Pearl
button industry (1800s-1900s) ? Shell beads to
for cultured pearl industry (Present)
Baroque Pearls
Cultured Pearls
Pearls Buttons
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Translocation of Mussels ? Translocation ?
harvest, but in practice is very similar ?
Recommended in recovery plans as a recovery
tool ? Suitable for species with large
population sizes ? Translocation unlikely to
cause extinction ? e.g., birdwing
pearlymussel
Endangered Mussels
Collecting Mussels
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Parameter Estimation
? Key population dynamic parameters -
population size (N) - population growth rate
(r) - environmental stochasticity ( ) -
carrying capacity (K) - strength of density
dependence, theta (?)
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Estimates of Population Size (N)
? Quadrat sampling to obtain number of mussels
per m2 or species density ? Species density X
shoal area (m2) ? Estimate N from CRM 172-192 ?
70 of sites completed (2004-2005)
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Estimates of Population Size (N)
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Population Growth Rate
? First, we need to convert mussel densities to
an annual growth rate (lambda ?) ? For
example, lets take oyster mussel quadrat
density data and convert to ? values
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Lambda values (?)
? values from the discrete exponential growth
equation
? values cannot be averaged (arithmetic mean).
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r values
Convert values to r values using the
formula
? r values can be averaged
? Convert to using the formula
? Oyster mussel population grew 18.7 per year.

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Approximations of and
Approximations to and , the variance in
can be computed using the following method
non-yearly time intervals
transformed growth rate
? Perform linear regression of (x,y) with
y-intercept set to zero. ? The slope of the
regression line is an estimate of and
mean squared error is an estimate of .
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Adjusted Time (Xi) Log Transformed Growth Rate
(Yi) Data
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Regression Analysis
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Confidence Intervals
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Population Growth Models
EXPONENTIAL POPULATION GROWTH
? Densityindependent - linear -
exponential - no limits to growth - but, can
set a population ceiling ?
Density-dependent - carrying capacity (K) -
theta (?) strength of density dependence -
theta-Ricker model
LOGISTIC POPULATION GROWTH
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Population Stochasticity

• Due to
• Demographics
• Environment

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A Stochastic Harvest Model for Mussels
Density-dependent Growth Theta-Ricker
ù
é
?
ö
æ
N
t

ú
ê
-

ç
Stochasticity
1
r
N
(Harvest)
K
ú
ê
ø
è
e


û
ë
1
t
N
t

• where
• Nt is the population size at time t
• r is the population growth multiplier (0.12
  max.)
• K is the carrying capacity
• ? determines the strength of density dependence

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Harvest Management

• Harvests can be modeled in several ways
• Fixed harvest a fixed number every year
• Proportional harvest a fixed proportion every
  year
• Threshold harvest a proportion above a set
  limit
• ? No Effect Threshold Harvest harvest with no
  significant
• effect on simulated population trajectories

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OYSTER MUSSEL HARVEST 2006-2008
? Permitted to move 200/yr for 3 years ? No
effect threshold harvest strategy
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? Lower Clinch, healthy mussel populations ?
Upper Clinch, populations in need of restoration
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Restoration of Endangered Oyster Mussel To Upper
Clinch River

• Cleveland Island, VA
• ? managed by TNC VDGIF
• ? excellent mussel habitat
• Translocation of adults
• ? stock from lower Clinch, TN
• ? 200/year for 3 years
• ? 600 total
• Release of cultured juveniles
• ? 3000-5000/year
• Population monitoring
• ? mark recapture methods
• ? survival of adults juveniles
• ? of displaying females
• ? effective population size (Ne)

Female Oyster Mussel, Clinch River
Tagged mussels
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QUANTITATIVE CRITERIA FOR RECOVERY
? Oyster mussel carrying capacity (K) - lower
Clinch, TN ? K is 2-5/m2 - upper Clinch, VA ?
set K at 1/m2 ? Population size (N) -
Cleveland, VA ? set N at 5000 ? Cohort
structure - model healthy cohort structure
from population in lower river ?
Recruitment - gt5-10 per year ? Spatial
structure - 3-5 sites restored
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Mussel PVA Modeling
? Population Viability Analysis (PVA) is a
modeling technique used to estimate future
population sizes ? Results are expressed in
terms of the probability that a population
will persist to a pre-defined time
horizon ? Conduct example model simulations
using MUSSEL PVA MODEL - model harvest
in lower Clinch - model restoration in upper
Clinch
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Questions
I would like to thank to James Vance and Jay
McGhee for their input on model
construction! Upper Clinch River