1. Shell/habitat dynamics in oyster restoration and fishery management
Shell/habitat dynamics in oyster restoration and fishery management. Supported by the Chesapeake Bay Trust. Award period 1/23/2017-2/28/2018 Collaborating investigators: Roger Mann*, Melissa Southworth, Marcia Berman, John Thomas, Tamia Rudnicky (all VIMS), James Wesson (retired, former VMRC), Mitch Tarnowski (MD DNR)
* Roger Mann, Virginia Institute of Marine Science
(cell))
presentation to
Chesapeake Bay Fisheries Goal Implementation Team
March 27, 2017

2. Reference points for oyster resource management: how did we get here and why the obsession with shell budgets?
Set a goal of No Net Loss of living oysters or shell substrate: these apply to BOTH restoration efforts and fishery management.
Recruitment (R) and growth dictate addition to the living component.
Natural mortality (M) and fishing mortality (F) dictate loss of oysters.
M contributes to the shell substrate, F does not.
High mortality rates result in low shell accumulation because contributing oysters are small – low mortality with oysters surviving to larger size contribute much more shell.
Shell is lost to burial (B) and biological and chemical degradation (D).
Shell loss rates are salinity dependent and independent of supply from mortality.
Accreting reefs require equilibrium between shell addition and loss requires sustained recruitment, growth and survival of oysters to large size prior to death.
Offsetting inadequate shell supply from natural processes through repletion (r) is NOT a single addition process – it requires continuing addition forever.
Single replenishment action to suitable bottom IS NOT restoration.
Examine the following shell budget diagrams where addition process are in BLUE and loss processes are in RED.
Mann - GIT – 3/27/2017

3. Description of shell pools and processes.
Addition process , loss processes
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, including disease adds shell to exposed pool
Substrate enhances recruitment
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

4. Consider the following shell budget scenarios in management of both restoration and fisheries: which are stable and which are not, and more so which will accrete and rebuild habitat?
Scenario # 1 2 3 4 5 6
Disease - +
Overfishing
Fishing
Repletion
Stable? Y? N
Mann - GIT – 3/27/2017

5. #1. Natural reef with accretion, no F, no r, shell accretes
As M>(B+D), system stable over extended periods.
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, adds
shell to exposed pool
Substrate enhances recruitment
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

6. #2. Natural reef, no F, no r, but increased M due to disease.
Decreased oyster longevity, lower shell addition rate to
exposed layer, no accretion as M<(B+D), system fails.
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, including disease adds shell to exposed pool
Decreased substrate enhancement
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

7. This is the reality of sanctuaries!
#3. Natural reef, no F, increased M (disease). Decreased oyster
longevity, lower shell addition rate to exposed layer, offset by
CONTINUAL replenishment until M=(B+D), system stable.
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, including disease adds shell to exposed pool
Increased substrate enhancement
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
This is the reality
of sanctuaries!
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

8. #4. Overfishing, no disease, no r, but F removes shell such
That M<(B+D), system fails as substrate disappears.
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, adds shell to exposed pool
Decreased substrate enhancement
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

9. Decreased oyster longevity in those not fished, lower shell addition
#5. Natural reef, no r, but with fishing, F, and increased M (disease).
Decreased oyster longevity in those not fished, lower shell addition
rate to exposed layer, no accretion as M<(B+D), system fails.
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, including disease adds shell to exposed pool
Decreased substrate enhancement
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

10. This is the reality of fisheries!
#6. Natural reef, limited fishing, F, and increased M (disease).
Decreased oyster longevity, lower shell addition rate to exposed layer
balanced by CONTINUAL replenishment until M=(B+D), system stable.
Fishing mortality, F, with loss of shell
Recruitment, R,
and growth:
S/R relationship
Live oyster population characterized
by density and demographics
Natural mortality, M, including disease adds shell to exposed pool
Continual substrate enhancement
Exposed shell layer (brown shell)
– substrate for recruitment
Replenishment, r
Loss to burial, B
Loss to biological
degradation and
chemical dissolution, D,
salinity dependent
This is the reality
of fisheries!
Reef structure - buried shell
mixed with sediment
Mann - GIT – 3/27/2017

11. Shell budget scenarios: long term observations in VA.1 2 3 4 5 6
Disease - +
Overfishing
Fishing
Repletion
Stable? Y N
Scenario #6 applies everywhere in VA except a limited number of reefs in James River which
exhibit very high recruitment to offset impact of reduced longevity on shell supply. All other
systems have varying levels of shell replenishment to maintain substrate cover.
Mann - GIT – 3/27/2017

12. Objectives for the current study.
Develop salinity dependent shell budgets for tributary – scale restoration sites in Maryland and Virginia under the 2014 Chesapeake Bay Program Agreement and for actively fished and rotational harvest reefs in Maryland and Virginia.
Analysis of shell amounts required to maintain sufficient shell and reef habitat based shell budgets derived from deliverable #1.
Estimates of future shell resource needs for different areas and/or management types.
Develop a report that outlines how to apply this methodology to other areas in the Bay .
Mann - GIT – 3/27/2017

13. Progress since beginning of project (~7 weeks)
The MD DNR survey database for monitoring (live oysters plus shell) has been obtained and is being reformatted at VIMS to as near as possible to format of VMS/VMRC monitoring database to facilitate analysis (Thomas, VIMS).
VIMS database for survey map coordinates (shape files)are being reformatted to allow item #3 - below. (Southworth, VIMS)
Writing of scripts to analyze/condense survey data to provide location dependent time series of live oyster and shell data in common format (Thomas & Mann, VIMS)
Items 1 through 3 above are requirements to development of rate budgets for live and shell components of the “graphic budgets” displayed in prior slides – this activity is planned for April-May period.
We have engaged VIMS CCRM expertise in GIS graphic development to portray all of these results in a parallel presentation format to complex databases (Marcia Berman plus support from Tamia Rudnicky). This builds on long term collaboration between Mann lab ad CCRM – Google VOSARA for an example. We will build from this template in the project effort.
Questions?
Mann - GIT – 3/27/2017