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Atlantic Loggerhead Recovery Team Meeting

Meeting Minutes

22-26 September 2003

National Conservation Training Center, Shepherdstown, WV

Team Members in Attendance (in alphabetical order):

• Dr. Alan Bolten - Archie Carr Center for Sea Turtle Research, University of Florida
• Dr. Larry Crowder - Duke University Marine Laboratory (via conference call on 24 Sept)
• Mr. Mark Dodd - Georgia Department of Natural Resources
• Ms. Sandy MacPherson - U.S. Fish and Wildlife Service
• Ms. Barbara Schroeder - U.S. National Marine Fisheries Service
• Dr. Blair Witherington - Florida Fish and Wildlife Conservation Commission

Rapporteur:

• Ms. Kristy Long - U.S. National Marine Fisheries Service

Federal finding on loggerhead petition: The Services published a 12-month finding that the petition to list the northern and panhandle subpopulations of loggerhead turtles as distinct population segments with endangered status was not warranted at this time.  The Team will proceed as planned with recovery units in the revised recovery plan.  All recovery units must have demographic and recovery criteria satisfied before the loggerhead can be delisted.

Recovery units: The Team discussed the geographic boundary between the northern recovery unit and the south Florida recovery unit.  Pearce (2001) reported a tentative conclusion that there is an additional, separate nesting assemblage associated with beaches in Volusia County, Florida – which was within the area described by the Turtle Expert Working Group as comprising the northern subpopulation.  The subsequent analysis of samples from a larger number of areas and the resulting indication that the vicinity of Volusia County may have a separate nesting assemblage (Pearce 2001) suggests that the subpopulation may be further differentiated or that Volusia County may represent an area of overlap, including nesting females from both the northern and south Florida subpopulations.

Pearce, A.F.  2001.  Contrasting population structure of the loggerhead turtle (Caretta caretta) using mitochondrial and nuclear DNA markers.  MS Thesis. University of Florida, Gainesville

Due to these unresolved issues, the Team discussed going back to the findings of Encalada et al. (1998) and using Amelia Island as the boundary.  Encalada et al. (1998) found that loggerheads from various beaches within the range of the northern subpopulation from Amelia Island, in northeastern Florida, to North Carolina are indistinguishable based on mtDNA.

Encalada, S.E., K.A. Bjorndal, A.B. Bolten, J.C. Zurita, B. Schroeder, E. Possardt, C.J. Sears, and B.W. Bowen.  1998.  Population structure of loggerhead turtle (Caretta caretta) nesting colonies in the Atlantic and Mediterranean as inferred from mitochondrial DNA control region sequences.  Marine Biology 130:567-575.

The Team noted that there is a classic clinal change in haplotypes along the east coast.  Therefore, no one beach will be significantly different from an adjacent beach, although the two endpoints will be significantly different.  Ultimately, the Team agreed to use Amelia Island as the southern boundary for the northern recovery unit.

The Team discussed Alabama, Mississippi, Louisiana, and Texas relative to the Florida panhandle recovery unit.  Alabama records about 60 to 90 nests per year, while there are approximately 5 nests recorded each year in both Mississippi and Texas.  The Team decided to include Alabama, Mississippi, Louisiana, and Texas in the Florida panhandle recovery unit.  The Team discussed the geographic boundaries for the Florida panhandle recovery unit and noted that they will need to clearly explain how those boundaries were derived in the text of the plan.  In the case of an unclear boundary, the Team decided to identify research needs.

The Team discussed whether Boca Grande and the Marquesas should be included in the Dry Tortugas recovery unit.  The Team decided to primarily use haplotypes in determining recovery units, but where that information does not exist, they will use geographic boundaries.  One suggestion was to include anything west of Key West as part of the Dry Tortugas recovery unit.  Team members suggested using latitude or a county border to define boundaries.  The Team agreed that all nesting populations outside the United States that produce turtles, which migrate into U.S. waters at some time during their life history, will be included in the “Other” recovery unit.

Recovery criteria and the 5 listing factors: Ms. MacPherson gave an overview of the recovery criteria and listing factors.  The Team discussed and reviewed these objectives.  Team members noted that reaching a particular number of nesting females does not necessarily signal recovery or delisting because the other age classes could be severely depleted.  The recovery criteria should ensure that these recovery units will not require re-listing soon after delisting.  The Team reviewed the recovery criteria developed for the 1991 recovery plan.

Demographic criteria: The Team discussed whether to include a target number of nests or nesting trends under demographic criteria.  The 1991 recovery plan discusses both; some Team members felt both should also be included in the revision.  The 1991 plan requires that the identified nesting target must be met over a period of 25 years.  However, the Team feels that number likely needs to be revised because new information suggests 25 years is an underestimate of age to maturity.  Currently, sexual maturity for loggerheads is estimated at 32-35 years.  The longest tag return known from nesting female loggerheads is approximately 22 years.  The Team discussed using longevity of nesting females data from other populations of loggerheads, e.g., South Africa (Hughes) or Australia (Limpus).  The Team decided to use a generation time of 45 years as the time period for recovery.  A generation time of 45 years was developed using 32-35 years to maturity plus half the longest tag return (~22 years).  This rationale will be explained in the introductory text of the revised plan.  Another suggestion was to use one benchmark for demographic criteria similar to the manatee plan, e.g., average annual population growth rate is greater than zero.  Some Team members were uncomfortable with just requiring “increasing” number of nests.

One Team member thought it might be worthwhile to use more than one generation for recovery, e.g., 2 to 3 generations, because achieving a stable age distribution usually takes more than one generation.  Therefore, an unstable age distribution could still be occurring within one generation, while noting that turtles may never reach stable age distribution.  The Team decided that given other criteria, one generation is acceptable.

The Team discussed when the 45-year period should begin.  They agreed that the 45-year generation time should begin when consistent nesting surveys first began.  The 45-year period can start at any time after consistent surveys began, such that recovery criteria are met.  For the south Florida recovery unit, the Team decided to use 1989 since this is when standardized monitoring of core index nesting beaches began.  In the Dry Tortugas, the most recent nest monitoring program began in 1995.

The Team discussed using historical data, where available, to determine a target number of nests and to leave a blank where data are unavailable.  If data are available, the Team discussed using it to determine targets individually for each recovery unit.  There was some concern as to whether these data sets are accurate and representative of the whole recovery unit.  One Team member suggested using the current number of nests as an absolute minimum.  The Team was comfortable using this method for the south Florida recovery unit, but not for the northern recovery unit.  The Team expressed concern over extrapolating from one nesting beach to a whole recovery unit.  They decided to use the same starting year of nesting data for beaches within a recovery unit.

Mr. Dodd summarized some nesting data from the northern recovery unit for the Team.  Nesting data from Georgia (30-year time series) showed a significant decline of 1.2% annually. Loggerhead nest counts from aerial surveys conducted in South Carolina showed a significant decline of 3.1% annually.  No trend was detected from North Carolina nesting data.  The Team commented that intensive shrimping had been occurring for at least 15-20 years prior to documented stranding levels.  The Team discussed shifting baselines and how to address this issue in the plan.

The Team discussed various ways of analyzing nesting data and the pros and cons of each method.  One suggestion was to go back a generation from the best estimate of the population.  The Team agreed that using a number as a minimal baseline is better than leaving a good estimate out completely.  The Team discussed setting a baseline number of nests and then calculating the annual rate of increase required to reach that target.

The Team discussed two ways of determining target numbers of nests for the northern recovery unit: 1. Use available data to project forward 45 years based on regression analysis, or 2. Use a 3.1% increase over 45 years (to offset the 3.1 percent annual decline in nesting documented by the South Carolina Department of Natural Resources aerial surveys that have been conducted since 1980).  The Team noted that each of these methods would result in a demographic target representing a minimum number of nests.  Mr. Dodd went back to 1958 using regression analysis and estimated there were 7,980 nests in South Carolina, and 1,656 in Georgia.  The Team noted a few caveats, including that average clutch frequency must be known and variation between years must be known and increasing.  One Team member noted that 1958 is before shrimping began, however egg harvest and direct harvest of adults was occurring.  Additionally, the error bars for the estimate get larger the farther back the extrapolation is taken.  During the 1950s there are very few reliable fisheries landings data in North Carolina; turtles were only recorded some years and not by species.  Team members agreed to send all historical published and anecdotal information to Dr. Bolten to compile for the text.

The Team reviewed these estimates in relation to the existing recovery plan.  A Team member suggested adding a safety factor to the estimate since the current estimate does not incorporate direct harvest prior to 1958.  The safety factor would incorporate those sources of mortality that we cannot reliably estimate.  The Team also noted that adding a safety factor at the end of the process of estimating a target number of nests would be more reasonable than building the safety factor into every step of the analysis.

Also, the Team discussed estimating a target number of nests for the Florida Panhandle and South Florida recovery units.  The Team reviewed the Florida Manatee recovery plan and noted the term “statistical confidence,” which could also be used in terms of standardized surveys for the loggerhead plan.  The Team noted that including confidence limits may be useful to readers.  They also want to ensure that readers use the entire trend line and not just the highest point.

The Team discussed how many loggerheads can nest on one kilometer of beach and then multiplied that number by total available beach habitat as a means of exploring density effects.  They also discussed picking a few density targets based on historical information for each of the recovery units (e.g., Jekyll Island and Cape Island).  One issue is that not all beaches are created equal.  For example, a reef could be located just off the beach and nesting is reduced, such as some of the beaches offshore Indian River County, Florida.

The Team discussed a variety of approaches using slope and target annual nest numbers to establish demographic recovery criteria.  The Team discussed getting input from Dr. Crowder to determine the rate of increase for smaller recovery units, e.g., Dry Tortugas and Florida panhandle.  Since Dr. Crowder was unable to attend the meeting, the attending Team members called him on 24 September to discuss demographic criteria.

Dr. Crowder explained that some new population viability analysis (PVA) techniques are available that examine long term trend data, assuming there are not enough population data to run a full scale population model.  Traditional PVA is based on trends like the ones available from index nesting beach data or long-term monitored sites.  Models assume that the fit is not just based on the average rate of increase or decrease, but how variance, in terms of stochasticity, broadens possible outcomes as you project into the future or past.  There are several new methods for PVA on small populations, which Dr. Crowder and Dr. Heppell have been using for turtle populations in the Pacific.  It is possible to examine trend data that are deemed most reliable and enter it in the model.  Need to keep in mind the point at which genetic diversity will be lost in small populations, e.g. <50 adults, 25:25 sex ratio.  The Team noted that they would do a literature search for papers on minimum viable population size and the minimum number of breeders necessary for maintaining genetic diversity.  Research on terrestrial mammals illustrates that a population is in demographic trouble before genetic trouble from small numbers.  A skewed sex ratio is acceptable for some species.

The Team will decide on specific data to examine and Dr. Crowder will work with Dr. Heppell to run the model and determine when a recovery unit will go extinct or drop below 50 nesting females.

Dr. Crowder also mentioned another available model from Eli Holmes to determine population viability analysis when there are not enough data for a stochastic model. For declining populations, e.g., northern recovery unit, it is possible to estimate what proportion of runs would drop to below 50 females in 2-3 generations.  Data sets with consistent effort and long time series, around 10-15 years, are ideal.  There are also ways to account for missing years. One Team member noted that this model is not useful for the Dry Tortugas or Florida panhandle recovery units, which are on the cusp of losing genetic diversity. For these recovery units, the Team will address minimum viable populations. There are approximately 1,100 total nests per year in the Florida panhandle recovery unit (including Alabama, Mississippi, Louisiana, and Texas nests), so the Team was less concerned about genetic effects. However, the Team noted that there probably are genetic effects in the Dry Tortugas recovery unit.  Some Team members suggested asking NMFS scientists such as Dr. Peter Dutton. Dr. Crowder will also check with some terrestrial population ecologists.

The Team also discussed using data from other oceans and felt it would be helpful to get a sense of the populations.  Minimum viable population size should be based on strong demography, not genetic diversity.  A few bad years of nesting with 50-100 females will drive the population down very quickly.  The Team noted that it might not be possible to quantitatively demonstrate vulnerability of the Dry Tortugas and Florida panhandle, so they will document their rationale in the text.  Dr. Crowder will draft some text on general concepts of minimum viable population sizes and explain both genetic and demographic perspectives.

The Team discussed demographic criteria that are related to clutch frequency and remigration interval, which are reflective of foraging and trophic changes due to fishing.  However, Team members questioned whether growth rate of immature animals affects adult reproductive physiology.  Growth rate is an indirect measure.  Clutch frequency and remigration interval are indirect measures of the number of nests and nesting females.  Some studies are beginning to provide empirically derived data but very few data exist for the northern recovery unit and other recovery units that encompass turtles that do not forage in U.S. waters.  The Team noted concern over using remigration intervals because of their variability.  Some researchers are counting numbers of nesting females and assuming a certain remigration interval to estimate population size.  Therefore, there might actually be fewer nesting females than previously thought due to an increase in remigration intervals.

The Team discussed using in-water abundance as a demographic criterion to forecast what will happen on nesting beaches.  However, many foraging habitats contribute to a single nesting beach.  Additionally, there is no way to separate out recovery units on the foraging grounds since multiple stocks mix at those sites.  The Team noted that continued genetic sampling is imperative for future assessments.  The Team decided to include a demographic criterion stating that composite estimates of in-water abundance must be increasing at or above the rate of annual nest count increase specified for the various recovery units over a generation.

The Team discussed and decided to omit sex ratio as a demographic criterion because few data exist on the subject.  At this point, it is unknown whether a female biased sex ratio is good or whether a 50:50 sex ratio is ideal.  The Team noted that one recovery action could focus on identifying sex ratios.  Physiological status depends on many variables and it is unknown whether a lot of slow growing turtles or a few fast growing turtles is better for the population.  The Team also discussed blood chemistry and health, both of which will be included under the disease and predation listing factor.

The Team discussed using trends in strandings data as a possible demographic criterion.  The Team noted there is a new paper out regarding Texas stranding data.  However, it is difficult to unequivocally attribute strandings to particular sources of mortality.  The Team discussed linking stranding data to in-water abundance, e.g., linking a particular size class to nesting females.  Rationale for using strandings is that if strandings are increasing at the same rate of increase as in-water abundance then the population is likely not recovering.  One Team member noted that a population model could be used to compare the rate of increase of strandings with the projected rate of population increase.  However, strandings depend on many factors, including currents, wind speed, and direction, etc.  The Team felt the relationship between strandings and in-water abundance should be captured in the demographic criteria.  However, they were unsure how to incorporate increased population abundance and increased standings.  The Team discussed comparing the stranding dataset to in-water datasets.  Strandings should not be increasing at the same rate as in-water abundance especially when considering age distributions.

The Team discussed what the appropriate rate of expected increase should be at in-water sampling sites.  Because in-water abundance estimates are composites of recovery units, the Team discussed using the highest rate of population increase on the nesting beach as the target rate of increase at in-water sites.  Currently, we cannot identify and assign individual turtles to a recovery unit.  The criterion could incorporate the need to be on a trajectory in terms of the population rate of increase and, therefore, possibly use at least that rate of increase for in-water population criteria.  The Team decided that the overall trend has to be linear in terms of contribution from each recovery unit.

The Team discussed density dependent factors, such as whether to include a criterion that incorporates population growth rate instead of number of nests or nesting females.  Based on Dr. Bolten’s graph, “Population abundances at which sea turtles fulfill ecological roles,” the Team discussed which level populations should be restored to.  Since habitat has been lost, the ideal number will not likely be equal to historic populations.

Recovery criteria:  The Team decided to use the threats assessment to gauge whether recovery criteria were warranted for particular threats.  The Team discussed whether some recovery criteria can apply to all recovery units or if there should be separate criteria for each unit.

Team members discussed the possibility of drafting a recovery criterion that addresses in-water habitat, e.g., certain habitats cannot be reduced such that turtles can fulfill their ecological role.

The Team reviewed the Service’s draft recovery guidance and noted that for ESA listed marine mammals, there can be recovery goals for delisting plus separate goals for optimum sustainable populations under the Marine Mammal Protection Act.

The Team discussed adding a recovery criterion to address the threat from beach erosion and washouts.  However some Team members thought it might be an unattainable goal for delisting.  Currently, there is no way to predict which nests should be moved to reduce these threats because this changes every year.  The Team decided to explain their rationale in the text and possibly include a recovery action that describes when a nest should be relocated as well as recommends a robust study to examine the relationship between washovers and hatching success.

Recovery narrative outline:  On the last day of the meeting, the Team divided into two groups and revised the recovery narrative outline from the existing recovery plan.  The revised recovery narrative outline is broken into two parts: terrestrial and marine.

Next steps:  The Team decided to include the graph from “Population abundances at which sea turtles fulfill ecological roles,” the National Center for Ecological Analysis and Synthesis (NCEAS) articles, and anecdotal/historical information on population abundance in the introduction section and/or before the demographic criteria to illustrate the Team’s rationale for the demographic criteria.  The Team discussed divvying up recovery actions for the recovery narrative into 6-8 assignments to be discussed at the January 2004 meeting.  The Team decided to develop the implementation schedule via conference call.  A small subgroup will compile all parts of the plan and send out a draft before the April 2004 meeting.  Tentative completion date was set for Fall 2004.

Next meeting:  The Team decided to hold conference calls at 10am on October 17 and December 4 to finalize demographic goals.  The next Team meeting will be held 2-6 February 2004 in Jacksonville, Florida.

Threats table:  The Team decided to round numbers on the summary table and to stipple those cells for which the threat is not manageable (i.e., from natural sources).  The summary table will be recalculated after all the individual tables are cleaned up.

Assignments:

Ms. MacPherson will get information on the first terrestrial recovery criterion (“maintaining at least the current % of protected land that already exists”) for Florida and Mr. Dodd will do the same for the northern recovery unit.

Dr. Witherington will send an updated comment (including 2^nd year of data) for cell C3 of the species interactions threats table.

Dr. Bolten will draft language explaining how generation time was calculated.  Mr. Dodd and Dr. Witherington will send longevity information from tag returns to Dr. Bolten.

Dr. Crowder will run a diffusion model for the northern recovery unit.  Dr. Crowder will also draft a paragraph on small populations to be included under the narrative for the Dry Tortugas recovery unit.

Dr. Bolten will compile all historical anecdotal population information supplied by the Team.

Ms. Long will review cell C6 on the species interactions page and add parentheses (other sources of mortality are lumped with predation).  She will also add stippling to summary table cells H5, H6, and J3.

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