Sea Turtle Distributions and Fisheries Interactions in the Atlantic
Reports (PDF): FY
2007, FY 2006,
Project researchers propose to run quantitative and qualitative analyses
of existing data on the ecology, distribution and fishery interactions
of leatherback and loggerhead sea turtles in both the North Pacific
and North Atlantic oceans. The primary goal is to use a comparative
approach to determine why populations of sea turtles in the Atlantic,
where fisheries interactions are common, appear to be stable or increasing,
while populations of the same species in the Pacific are declining.
Because of great concerns for their survival, and their protected status
under the Endangered Species Act, sea turtle take in pelagic fisheries
has resulted in complete closures (e.g., Hawaii, Grand Banks) or major
restrictions on effort and area for the US fleet (e.g., NE Distant Sector,
Atlantic). Scientific understanding of the extent and nature of worldwide
take patterns in pelagic fisheries, and impacts on stock rebuilding,
is incomplete, at best.
will conduct comparative and statistically rigorous analyses to eliminate
alternative hypotheses for the causes of sea turtle population declines
in the Pacific. Researchers will follow the assessment approach (not
previously applied for sea turtles) adopted by a recent National Research
Council Panel to evaluate Steller sea lion and fisheries interactions
in Alaska (NRC 2003). The proposed research fits within PFRP Program
target objectives of developing integrated statistical models of protected
species population dynamics and collaborative assembly of stock-wide
data bases for other marine turtle populations. This focus on the Pacific
ocean will be viewed against data analyses from the Atlantic, for a
more complete understanding of information available for both sea turtle
beach surveys indicate dramatic population declines for both leatherback
and loggerhead sea turtles in the North and Central Pacific. It is clear
that these populations are in trouble, but the causes of, and means
of slowing or preventing these declines are not obvious. Egg harvest
is believed to be a major cause of sharp reductions in numbers of leatherback
nests in Central America and Malaysia (Chan and Liew. 1996, Spotila
et al. 1996), but has not been a problem on Japan nesting beaches for
some time (Kamezaki et al. 2003). On the other hand, direct and delayed
incidental mortality through fisheries interactions has been identified
as a major contributing factor for sea turtle population declines worldwide,
and bycatch in pelagic fisheries has been implicated in observed Pacific
trends (Lutcavage et al., 1996; Eckert and Sarti, 1997; Eckert, 1997;
Spotila et al. 2000, Crowder 2000, Chaloupka 2003). In contrast, leatherback
and loggerhead sea turtles on the Atlantic and Gulf coasts of the U.S.
are stable or increasing, and some Caribbean nesting beaches also show
this trend (Eckert 1995; Dutton et al., Boulon et al. 1996, Pritchard
1996, TEWG 2000, NOAA 2002). How can there be such large differences
in recruitment success between the Atlantic and Pacific? Can fishing
effort and associated incidental take account for the disparity? Pelagic
fisheries operate in all major oceans, and alternative hypotheses that
could account for differences in recruitment success between the Pacific
and Atlantic stocks have not been examined. Like other pelagic species,
sea turtle populations are affected by anthropogenic factors (e.g.,
interactions with fishing gear, nesting habitat alteration, egg harvesting)
and environmental factors (e.g., ocean productivity, current regime
shifts, climate change). Researchers have addressed some of these components,
but these elements have not been linked, nor compared for different
sea turtles are rarely encountered at sea and are difficult to age,
there are insufficient data to run formal statistical stock assessments
for either leatherbacks or loggerheads. Nevertheless, a substantial
amount of data on migration, fishery interactions, life history, and
population trends have been gathered for both species in the Atlantic
and Pacific. Through combined expertise and collaboration with sea turtle
researchers in both ocean basins, project researchers hope to accumulate
and integrate these data. A collaborative approach is strongly advocated,
to put all the available data "on the table" to determine the role of
pelagic fisheries in sea turtle declines. The data do not exist to run
this assessment for any one population - there are too many unknowns,
which allows biased interpretations of trends to compete without validation.
Project researchers believe that a comparative analysis of data for
two species in two ocean basins, both incidentally taken by longline
fisheries but at different life history stages and levels of interactions,
holds the key to this management puzzle.
1. Compile published and unpublished data on the life history, at-sea
distribution, pelagic and coastal fisheries interactions, and history
of direct exploitation for loggerhead and leatherback sea turtle populations
in the North Pacific and North Atlantic oceans.
Identify and evaluate alternative hypotheses for population change for
each species in each ocean basin, by postulating the changes in abundance,
distribution, genetic composition or size distributions that would be
anticipated from these hypotheses.
Compare expected distributions of loggerhead and leatherback turtles
in each ocean basin based on habitat preferences and oceanographic regimes.
Develop a modeling framework for assessment of population-level impacts
of pelagic fisheries on sea turtle populations that are subject to multiple
Collaborator workshop to identify the scope of the problem, existing
data and hypothesis formation
The approach is that inductive reasoning from the experience of researchers
and fishermen can be combined with deductive reasoning from ecological
principles to develop alternative hypotheses for sea turtle population
declines in the Pacific. By comparing two species in two locations,
researchers hope to eliminate some competing hypotheses. For example,
possible reasons for stark differences in apparent recruitment success
between Atlantic and Pacific oceans include:
1. recruitment failures due to recent or continued egg harvest.
2. recruitment failures due to interception of juveniles (and adults)
by inshore and artisanal fisheries.
3. time lags in the response of nesting female counts to management
measures, or other changes in productivity.
4. recruitment failures due to changes or differences in juvenile
dispersal patterns that result in higher mortality rates from predation
or inadequate forage.
5. population bottlenecks.
Synthesis and statistical comparisons of existing data
For each species in each ocean basin, project researchers will work
with collaborators to compile existing data on: population trends,
life history, size distributions, stock structure, spatial distribution/overlap
with pelagic and coastal fisheries, correlations with oceanographic
features, location and history of conservation/mitigation methods,
and large-scale environmental variability.
Data synthesis is a critical element as it will integrate data across
national boundaries and ocean basins into a comprehensive dataset.
Demographic and Assessment models
An important element to understanding the current population status
is to reconstruct the demographic history of these populations. A
comparative analysis of the divergent demographic and fisheries data
for the two species in both ocean basins will identify influential
parameters that account for the differences in observed trends between
species and basins. Furthermore, this approach synthesizes existing
data, linking fishery dependent and independent data in an integrated
Mapping distributions with oceanographic models
In consultation with Dr. David Kirby (SPC, New Caledonia), Dr. Lutcavage's
lab will collect and map oceanographic information from remote sensing
databases that will be used to examine sea turtle dispersal patterns
obtained in the preceding phases. The scope of these analyses will
depend on the quantity and extent of spatial and temporal data concerning
these species and their life history stage. Considering the rapid
decline of leatherback and loggerhead populations in the Pacific Ocean,
it is critical for management purposes that at least a basic understanding
of what designates essential pelagic habitat is reached as soon as
possible. Project researchers will tackle this aspect by exploring
the link between sea turtle distribution and oceanographic features
using information from satellite tracking projects in the Atlantic
The following steps will be taken to examine the dispersal and habitat
use patterns for each species and ocean basin:
1. Plot known nesting beaches and model dispersal of post-hatchlings
and juveniles through simulations of their trajectories against relevant
ocean current systems. Establish where post-hatchlings and juveniles
are likely to be. Verify model with known distributions of post-hatchling
and juvenile loggerheads in the Atlantic.
2. Examine resulting distributions in relation to oceanographic features
and primary productivity.
3. Examine known dispersal patterns and habitat preferences of adults.
4. Examine modeling results for distribution of juveniles and adults
in relation to primary productivity and forage base.
5. Examine resulting distributions in relation to fishing effort (coastal
and pelagic) and fishing mortality rates for size classes.
Review results, identify data needs and compare management scenarios
To highlight analyses to date and serve as a means of linking findings
across work phases. This review will also be used to identify the
gaps in the current data sets available, and point to additional analyses
for Year 2 of the project. Given the management imperative of reducing
sea turtle bycatch, the goal is to place the Year 1 ecological data
into a management context. Year 1 findings will also be used to evaluate
and compare bycatch reduction management scenarios, which will be
one topic for discussion in the workshop meeting in Year 2.
1. A summary of the meeting of turtle experts and collaborators
that includes a list of research recommendations to fill critical data
gaps that will allow the elimination of remaining alternative hypotheses.
2. A table of hypotheses for the effects of pelagic fisheries and other
human induced stressors on sea turtle populations, with expected impacts
on population growth rates, time lags in measurable impacts, and shifts
in size distributions for the 4 stocks. (YEAR 1)
3. A report on the qualitative evaluation of those alternative hypotheses
for Atlantic and Pacific stocks of leatherback and loggerhead sea turtles,
including details on model formulation and evaluation. (YEAR 1)
4. A report on the development of new assessment models and the quantitative
evaluation of population dynamics and oceanic dispersal/distribution
for Atlantic and Pacific stocks of leatherback and loggerhead sea turtles,
including details on sensitivity analysis to investigate the role of
uncertainty. (YEAR 2)
5. Manuscript on the demographic assessment, oceanographic distribution
analysis, and deductive assessment process for a peer-reviewed publication.
funding for this 2-year project to be awarded in fall 2004.
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