Assessment of Sea-Turtle Status and Trends Integrating Demography and Abundance (2010) / Chapter Skim
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6 Integrating Demographic Information with Abundance Estimates
6 Integrating Demographic Information with Abundance Estimates
Pages 91-108
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From page 91... ...
. In this chapter, the committee reviews some of the quantitative tools used in assessment of populations, reviews which tools have been applied to seaturtle assessments and discusses the procedures that are routinely used in fishery assessments to ensure scientific rigor and could be adopted for future assessments of sea turtles.
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From page 92... ...
In contrast, detailed simulation models may require a large amount of bio logical information to produce precise or reliable estimates of population size or to predict response to perturbations. Regardless, models that are to be used for assessment, prediction, and management decisions require solid demographic data, preferably as time series of information that can be analyzed for changes in response to stressors, population density, or environmental variability (Hilborn and Mangel, 1997)
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From page 93... ...
. Linear regression is often used to identify an exponential growth rate for each nesting beach and used with data that is pooled by region (e.g., National Marine Fisheries Service Southeast Fisheries Science Center, 2001)
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From page 94... ...
Increased accuracy is tied to model complexity and the need for detailed biological information. Stochastic Projections and Diffusion Approximation of Extinction Risk The simplest form of populationviability analysis projects a time series of abundance or an index of abundance and evaluates the prob ability of extinction (or recovery)
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From page 95... ...
. Because time series of seaturtle abundance are based on counts of nests or nesting females, the trend and variance through time must be adjusted to account for the relationship between nest number and adultfemale number (clutch frequency, that is the num ber of clutches deposited by an individual turtle in a nesting season)
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From page 96... ...
The models do not include age struc ture but can be modified to include time lags. To determine parameter estimates through data fitting, the models require a time series of abun dance data that can accurately demonstrate densitydependent popula tion processes.
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From page 97... ...
Matrix models that describe lifecycles can be simple or include complex population struc ture, such as the life stages shown in the conceptual model in Chapter 3; values are assigned to parameters on the basis of empirical estimates of survival, growth, or fecundity and estimates of dispersal if life stages are spatially explicit. Matrix models for simulation purposes can include assigning values to parameters through model fitting when time series of abundance, recruitment, or age structure are available (e.g., the model for Kemp's ridley [Lepidochelys kempii]
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From page 98... ...
. Integrated Population Dynamics Models Stochastic simulation models outlined above are the most compre hensive models developed so far to explore the population dynamics of sea turtles and to evaluate the potential effects of exposure to anthro pogenic hazards on those populations.
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From page 99... ...
The Bayesian belief net work model constructed for the workshop showed (given limited data and uncertainty about turtlefisheries interactions) that trawl fisheries, gillnet fisheries, and coastal development were hazards most likely to have major effects on the viability of the Southeast Asian seaturtle populations.
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From page 100... ...
. All of the published sea turtle assessment reports (e.g., the Turtle Expert Working Group reports and National Marine Fisheries Service [NMFS]
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From page 101... ...
Fishery Assessment The review procedures for stock assessments vary regionally in the United States depending on the fishery management council that is responsible for managing the stock, but they follow a general pattern wherein panels of experts review input data series, models, and refer ence points. The review workshops are the Stock Assessment Workshops and the Stock Assessment Review Committees in the northeastern United States; the Southeast Data, Assessment, and Review in the southeast and Gulf of Mexico regions; and the Stock Assessment Review and the West ern Pacific Stock Assessment Review in the Pacific region.
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From page 102... ...
Although some data that are typically used in fishery assessments are not available or directly appli cable to sea turtles, the approach of comprehensive data review holds value as a potential component of seaturtle management. It might have value in evaluating surveys, such as nestingbeach counts, strandings and inwater mark–recapture efforts, and length distributions.
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From page 103... ...
Marine-Mammal Assessment Like sea turtles, marine mammals are protected species in the United States that face threats of mortality often caused by direct and indirect interactions with fisheries. Section 117 of the Marine Mammal Protection Act specifies requirements for stock assessments of marine mammals.
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From page 104... ...
. Recovery teams update the recovery plans for each species, which are split by ocean basin; recovery plans use existing models or published model results to set recovery criteria (e.g., National Marine Fisheries Service and U.S.
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From page 105... ...
. A more complex evaluation of expected changes in population growth that might result from reductions in anthropogenic mortality used agestructured models with Monte Carlo sampling of vitalrate distributions to try to cope with uncertainty; the result was a nearly incomprehensible amalgamation of possible population responses (National Marine Fisheries Service Southeast Fisheries Science Center, 2009)
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From page 106... ...
A lack of sufficient infor mation on survival rates resulted in a range of a factor of five to ten in estimates of population sizes among bestfit models for Kemp's ridley sea turtles even though cohort strength (annual hatchling production) was well known on the basis of extensive monitoring of nests for the entire species (Turtle Expert Working Group, 2000; Heppell et al., 2005)
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From page 107... ...
Vitalrate estimation is essential for these slowgrowing species, as trends in nestingbeach abundance provide information about only a tiny fraction of a seaturtle population. Some data that can be used to deter mine changes in vital rates already exist, including time series of juvenile abundance (or indexes of abundance)
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From page 108... ...
0 ASSESSMENT OF SEA-TURTLE STATUS AND TRENDS develop a toolbox for seaturtle assessment that can provide standardized methods for evaluation and review of datapoor and datarich species. They would include methods that use available data on trends and size distributions of turtles to reduce the possible ranges of unknown values of parameters and estimates of abundance through model fitting.
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