Fisheries-Related Mortality and Turtle Excluder Devices (TEDs)
345
Research Council (NRC) study team previously had identified the fishery as a source of
mortality. Although unpopular with local fishermen, TED regulations implemented in
this finfish fishery were not contested in the courts.
Other bottom trawl fisheries in the western North Atlantic have been linked to
the mortality of sea turtles. In South Carolina, whelk trawling is allowed only when
water temperatures are less than 18 ∞ C (64 ∞ F) and since December 2000 whelk trawls
used in Georgia waters are required to have TEDs (NMFS Southeast Fisheries
Science Center, 2001).
13.4.5 T URTLE E XCLUSION
TED designs must be certified by NMFS, based on a specific protocol (Department
of Commerce, 1987b, 1990, 1992b). Foremost among the criteria for certification
is the requirement that a prospective design releases 97% of the turtles tested or
alternatively that it performs as well as a previously certified control TED. Certified
designs, therefore, are assumed to reduce mortality of sea turtles 97%. A number
of studies, however, indicate that the actual reduction realized is substantially less.
Strandings on South Carolina and Georgia beaches were reduced 37–58% (Crowder
et al., 1995; Royle and Crowder, 1998* as cited in Turtle Expert Working Group
[TEWG], 2000; Royle, 2000**, as cited in TEWG, 2000) and estimates of a post1990 multiplier of instantaneous mortality for benthic Kemp’s ridley turtles range
from 0.45 to 0.56, indicating a decrease in mortality coincident with the implementation of TEDs (Heppell et al., in press, a).
A recent analysis of strandings data revealed that the minimum opening of TEDs,
measured as the height and width of a taut triangle, is too small to exclude the larger
individuals of several species (Epperly and Teas, 2002). A significant proportion of
loggerheads stranding along the east coast of the U.S. and in the Gulf of Mexico
(33–47% annually), and a small proportion of green turtles, Chelonia mydas (1–7%
annually), were too large to fit through the opening; their body depths exceeded the
height of the openings. Loggerhead turtles were too large to fit through the opening
at a size where most are still immature. Thus, not all sizes of loggerhead and green
turtles are benefiting from TEDs since they cannot escape from the nets. Early
population models evaluating the potential effect of TEDs on the loggerhead population trajectory assumed that TEDs benefited all benthic life stages (Crowder et al.,
1994). TED size opening is not an issue for Kemp’s ridleys because they do not
attain a large size and all can fit through the existing minimum openings.
Genetic studies have indicated multiple demographic units within sea turtle
species and these are regarded as management units (Bowen, 1995; Fitzsimons et
al., 1995). Some of the loggerhead management units of the western North Atlantic
do not appear to be increasing and, given current population trajectories, will not
reach recovery goals formulated under the U.S. Endangered Species Act. Popula* Royle, J.A. and L.B. Crowder. 1998. Estimation of a TED effect from loggerhead strandings in South
Carolina and Georgia strandings data from 1980-97. Unpublished report, U.S. Fish and Wildlife Service,
Laurel, MD, 12 p.
** Royle, J.A. 2000. Estimation of TED effect in Georgia shrimp strandings data. Unpublished report,
U.S. Fish and Wildlife Service, Laurel, MD, 11 p.
1123 book.book Page 345 Thursday, November 14, 2002 11:50 AM
345
Research Council (NRC) study team previously had identified the fishery as a source of
mortality. Although unpopular with local fishermen, TED regulations implemented in
this finfish fishery were not contested in the courts.
Other bottom trawl fisheries in the western North Atlantic have been linked to
the mortality of sea turtles. In South Carolina, whelk trawling is allowed only when
water temperatures are less than 18 ∞ C (64 ∞ F) and since December 2000 whelk trawls
used in Georgia waters are required to have TEDs (NMFS Southeast Fisheries
Science Center, 2001).
13.4.5 T URTLE E XCLUSION
TED designs must be certified by NMFS, based on a specific protocol (Department
of Commerce, 1987b, 1990, 1992b). Foremost among the criteria for certification
is the requirement that a prospective design releases 97% of the turtles tested or
alternatively that it performs as well as a previously certified control TED. Certified
designs, therefore, are assumed to reduce mortality of sea turtles 97%. A number
of studies, however, indicate that the actual reduction realized is substantially less.
Strandings on South Carolina and Georgia beaches were reduced 37–58% (Crowder
et al., 1995; Royle and Crowder, 1998* as cited in Turtle Expert Working Group
[TEWG], 2000; Royle, 2000**, as cited in TEWG, 2000) and estimates of a post1990 multiplier of instantaneous mortality for benthic Kemp’s ridley turtles range
from 0.45 to 0.56, indicating a decrease in mortality coincident with the implementation of TEDs (Heppell et al., in press, a).
A recent analysis of strandings data revealed that the minimum opening of TEDs,
measured as the height and width of a taut triangle, is too small to exclude the larger
individuals of several species (Epperly and Teas, 2002). A significant proportion of
loggerheads stranding along the east coast of the U.S. and in the Gulf of Mexico
(33–47% annually), and a small proportion of green turtles, Chelonia mydas (1–7%
annually), were too large to fit through the opening; their body depths exceeded the
height of the openings. Loggerhead turtles were too large to fit through the opening
at a size where most are still immature. Thus, not all sizes of loggerhead and green
turtles are benefiting from TEDs since they cannot escape from the nets. Early
population models evaluating the potential effect of TEDs on the loggerhead population trajectory assumed that TEDs benefited all benthic life stages (Crowder et al.,
1994). TED size opening is not an issue for Kemp’s ridleys because they do not
attain a large size and all can fit through the existing minimum openings.
Genetic studies have indicated multiple demographic units within sea turtle
species and these are regarded as management units (Bowen, 1995; Fitzsimons et
al., 1995). Some of the loggerhead management units of the western North Atlantic
do not appear to be increasing and, given current population trajectories, will not
reach recovery goals formulated under the U.S. Endangered Species Act. Popula* Royle, J.A. and L.B. Crowder. 1998. Estimation of a TED effect from loggerhead strandings in South
Carolina and Georgia strandings data from 1980-97. Unpublished report, U.S. Fish and Wildlife Service,
Laurel, MD, 12 p.
** Royle, J.A. 2000. Estimation of TED effect in Georgia shrimp strandings data. Unpublished report,
U.S. Fish and Wildlife Service, Laurel, MD, 11 p.
1123 book.book Page 345 Thursday, November 14, 2002 11:50 AM