# Presentation: 556202

## 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**

## Talk Outline:

**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**

## Harvesting Mussels: A Short History

**Harvesting Mussels: A Short History**

_**Main Reasons**_
**● ****Shell collecting for natural pearls **
**   ****(18****th**** & 19****th**** Centuries)**
**● ****Pearl button industry (1800s-1900s) **
**● ****Shell beads to for cultured **
**   ****pearl industry (Present)**

**Baroque Pearls**

**Cultured Pearls**

**Pearls  Buttons**

## Translocation of Mussels:

**Endangered Mussels**

**Collecting Mussels**

**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**

## Parameter Estimation

**Parameter Estimation**

**● ****Key population dynamic parameters: **
**	****- population size (*****N*****)**
**	****- population growth rate (*****r*****)**
**	****- environmental stochasticity (      )**
**	****- carrying capacity (*****K*****)**
**	****- ****strength of density dependence, ****theta (****θ****) **
**	**

## Estimates of Population Size (N)

**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)
* *

## Estimates of Population Size (N)

**Estimates of Population Size (*****N*****)**

| 
Site | Epioblasma capsaeformis | Epioblasma brevidens | Dromus dromas |
| --- | --- | --- | --- |
| Wallen Bend | 23,356 | 3,337 | 1,112 |
| Kyles Ford | 35,340 | 4,500 | 3,000 |
| Brooks Island | 22,248 | 4,760 | 0 |
| Little E Island | 61,091 | 1,018 | 3,564 |
| Frost Ford | 90,216 | 6,684 | 10,694 |
| Swan Island | 2,398 | 600 | 3,300 |
| TOTAL | 234,649 | 20,899 | 21,670 |

## Population Growth Rate

**Population Growth Rate**

**● ****First, we need to convert mussel densities to **
**   ****an annual growth rate (lambda = ****λ****)**
**● ****For example, lets take oyster mussel quadrat**
**   ****density data and convert to ****λ**** values:**** **

| Year | Swan Island | Brooks Island | Kyles Ford |
| --- | --- | --- | --- |
| 1979 | 0.01 | 0.01 | 0.39 |
| 1988 | 0.01 | 0.10 | 0.10 |
| 1994 | 0.10 | 0.62 | 0.68 |
| 1999 | 1.0 | 4.46 | 2.54 |
| 2004 | 0.90 | 2.6 | 2.10 |

## Lambda values (λ)

**Lambda values (****λ****)**

**λ**** ****values from the discrete exponential growth equation:  **

**λ**** ****values cannot be averaged (arithmetic mean).    **

## r values

**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.    **

## Approximations of     and 

**Approximations of     and **

**Approximations to     and      , the variance in     can be computed using the following method:**

**non-yearly time intervals    **

**● ****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       .**

**transformed growth rate**

## Adjusted Time (Xi) & Log Transformed Growth Rate (Yi) Data

**Adjusted Time (X****i****) & Log Transformed Growth Rate (Y****i****) Data**

| Time | Xi | Yi  (Swan) | Yi  (Brooks) | Yi  (Kyles) |
| --- | --- | --- | --- | --- |
| 1979 | 3.0 | 0.0000 | 0.0000 | -0.4537 |
| 1988 | 2.5 | 0.9400 | 1.6849 | 0.7826 |
| 1994 | 2.2 | 1.0297 | 0.8824 | 0.5893 |
| 1999 | 2.2 | -0.0471 | -0.2413 | -0.0851 |
| 2004 | NA | NA | NA | NA |

## Regression Analysis

**Regression Analysis**

## Confidence Intervals

**Confidence Intervals**

## Population Growth Models

**EXPONENTIAL POPULATION GROWTH**

**LOGISTIC POPULATION GROWTH**

**● ****Density–independent:**
**	****- linear**
**	****- exponential**
**	****- no limits to growth**
**	****- but, can set a **
**             ****population ceiling**
**● ****Density-dependent:**
**	****- carrying capacity (K)**
**	****- theta (****θ****) = strength of**
**	****  ****density dependence **
**	****- theta-Ricker model**

## Population Stochasticity

**Population Stochasticity**

**Due to:**
** ****Demographics**
** ****Environment**

## e

*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

- Density-dependent Growth: Theta-Ricker

- Stochasticity

- K

- N

- 1

- r

- t

- 1

- t

- θ

- t

- N

- N

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- 

- (Harvest)

## 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

## OYSTER MUSSEL HARVEST 2006-2008

**OYSTER MUSSEL HARVEST 2006-2008**

| 
Site | Current Population Size | Harvest per Year | 
% |
| --- | --- | --- | --- |
| Wallen Bend | 23,356 | 20 | < 0.1 |
| Kyles Ford | 35,340 | 40 | ~ 0.1 |
| Brooks Island | 22,248 | 0 | 0 |
| Little E Island | 61,091 | 40 | < 0.1 |
| Frost Ford | 90,216 | 100 | ~ 0.1 |
| Swan Island | 2,398 | 0 | 0 |
| TOTAL | 234,649 | 200 | < 0.1 |

**● ****Permitted to move 200/yr for 3 years**
**● ****No effect threshold harvest strategy**

## ● Lower Clinch, healthy mussel populations

- ● Lower Clinch, healthy mussel populations
- ● Upper Clinch, populations in need of restoration

## 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 (*N**e*)

**Female Oyster Mussel, Clinch River**

**Tagged mussels**

## QUANTITATIVE CRITERIA FOR RECOVERY

**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:
- 	- >5-10% per year
- ● Spatial structure:
- 	- 3-5 sites restored

## Mussel PVA Modeling

**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  **

## Questions

**Questions**

- I would like to thank to James Vance and Jay McGhee for their input on model construction!
- Upper Clinch River