Terrapin Current State of Knowledge Adding up the pieces:

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TerrapinCurrent State of Knowledge - Adding up
the pieces
Terrapin public meeting February 7,
2007 Annapolis, Maryland
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In the face of limited resources for fishery-
dependent and fishery-independent monitoring of
Maryland diamondback terrapin, there is a large
body of information available to guide prudent
management of this species
Terrapin Life History A history of harvest and
regulation in Maryland Regional terrapin
fisheries and market force
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LIFE HISTORY.
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Terrapin Life History

• Slow growth
• Late first reproduction females 8-13 years
  males 4-8 years
• Low reproduction 13-39 eggs/year
• Long life 50 Years
• High nest/hatchling mortality 93 mortality
• Specific and limited habitat for successful
  reproduction

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How does this life history inform management?
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There is a wealth of history and study on the
population dynamics and management of long-lived,
low productivity species.Sharks and
RaysSturgeonSea TurtlesLarge reef
fishesWhalesElephantsGrizzly Bears
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Elasmobranchii

• most shark and rays that have been studied have
  slow growth and late maturity, and very low egg
  production or fecundity compared to bony
  fishes....These attributes result in very low
  intrinsic rates of increase.and very low
  resilience to fishing mortality.
• Musick, et al., 2000
• Fisheries Volume 24 12

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Long-lived Species

• Overexploitation appears to be particularly
  risky for long-lived species as is so graphically
  illustrated by the collapse of whale fisheries
  early this century. Many long-lived fishes, such
  as Pacific ocean perch, pelagic sharks, and
  orange roughy became overexploited within decades
  of their discovery by commercial fisheries.Some
  long-lived species also suffer depletion from
  incidental harvest (or bycatch), as evidenced by
  declining sea turtle and albatross populations.
• Heppell et al., 1999
• American Fisheries Society Symposium 23137-148

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But what about Maryland Terrapin?

• Well documented life history attributes will
  allow us to explore the sensitivity of the
  terrapin population to fishing pressure, under
  various regulatory regimes.

Male and female growth rates Size at age Survival
at age
W. Roosenburg
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For every 1,000 eggs, we can use growth and
survival information to calculate the maximum
reproductive weight in the absence of any
anthropogenic mortality.
Note, this is an example with rounded numbers.
The real analysis includes every age from 0-50
(0.07 1,000)
(70 0.25 )
Chance of surviving at a age 5 is multiplied by
the number of individuals surviving at age 4, and
so on for all ages from 0-50
Summed over all ages
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Now we can apply various regulatory structures
(size limits) and levels of human-induced
mortality and observe the effects on maximum
reproductive potential.
Maximum for males 5 inches
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Decline of terrapin spawning potential under 2
regulatory structures. Literature and research
supports that terrapin require 70 or greater of
their spawning potential for sustainability.
Human-induced mortality at a level greater than
0.05 is risky for this population.
These are instantaneous rates, not percentages.
An equivalency chart is presented on the
following slide
Human Induced Mortality
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(No Transcript)
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Human-Induced Mortality

• Used in place of the classic fishing mortality
  (F) because it must be divided among
• Removals by commercial fishing (F)
• Loss due to bycatch, roadkill, boatstrikes etc.
• Loss of nesting habitat

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Human-induced mortality levels in the Maryland
Bay?Tag return studies in the Patuxent River
allow us to estimate that levels of human-induced
mortality were between 0.15 and 0.25between 2001
and 2004. No harvest has been reported from the
Patuxent since 2004.
These are rough estimates from a cohort analysis
on W. Roosenburgs tag return data in the
Patuxent river, Md. A cohort, catch curve
analysis was conducted separately on turtles aged
7-22 for years following the 2000 oil spill, then
averaged over years. A survivorship of 86 was
assumed for adult turtles.
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LIFE HISTORY SUMMARY Terrapin are sensitive to
human-related sources of mortality. With
additional mortality of 0.05, terrapin
reproductive potential declines to 70 of its
maximum potential.Human-related sources of
mortality include fishing mortality, habitat
degradation, bycatch in recreational and
commercial fishing gears, roadkill etc.
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The History of Harvest and Regulation in Maryland

• Provides insight to management needs when placed
  in context with terrapin life history.

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Terrapin Harvest History From Catch
Reports 1945-2005
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Terrapin Harvest History From Watermen Catch
Reports
5-month season April-Oct closed 5 minimum
9-month season Feb-April closed 6 minimum
12-month season 6 minimum
9-month season May-July closed 6minimum
1977-1981
1929-1976
1982-1991
1992-2005
2006 4-7 inch slot took effect in
August Jan-April Fishery still in effect on
6-inch minimum August-October fishery on
slot Total 7-month fishery
2006 number is preliminary and is from catch
reports, not from the newly-instituted terrapin
harvester permit cards.
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Summary Harvest and Regulatory History

• Restrictions in 2006 followed a period of
  relative liberalization.
• Slot limit in 2006 was intended to protect
  breeding females unintended consequence was
  increased exploitation of smaller males and
  sub-adult females which had been protected in all
  years prior.
• Extensive research on sea turtles shows that
  sub-adults are the critical stage to protect to
  ensure population stability.

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Regional Fisheries and Market Forces

• Maryland, New York, New Jersey, Alabama and
  Louisiana are the only states on the
  Atlantic/Gulf seabords allowing a terrapin
  fishery.
• Double edge sword
• Concentrates fishery in Maryland
• Stable population in Virginia could provide a
  potential temporary source population
• Unpredictable market forces for terrapin

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Conclusions
The weight of evidence clearly shows that all
extra sources of mortality for terrapin need to
be minimized. Further restrictions on fishery
alone will not ensure that terrapin populations
will be protected and ultimately rebound The
loss of nesting habitat in Chesapeake Bay and
throughout the range of terrapin remains a
dominant threat to terrapin sustainability.