158
Selina S. Heppell, Deborah T. Crouse, and Larry B. Crowder
the net (Henwood and Stuntz 1987; National Research Council 1990). But TED
development and requirements were highly controversial; members of the shrimping industry complained of potential shrimp losses, gear entanglement, and crew
injuries from the new devices (Sea Turtle Conservation and the Shrimp Fishery
1990). They also noted that nest protection projects were yielding significant
increases in hatch success and releasing large numbers of hatchlings at relatively
low costs and with little socioeconomic impact. A classic management dichotomy
was thus established: should managers require the disliked technology (TEDs) in
an industry already in financial trouble or opt for more low-cost and widely
popular nest protection projects?
To investigate the relative trade-offs between these disparate management alternatives, Crouse and co-workers (1987) developed a stage-based matrix model for
southeastern Loggerheads, using a preliminary life table developed by Frazer
(1983a). The model was based on stages identified by size classes because little
was known about age in sea turtles, and most data were collected for turtles of
different size classes. The model assumed a postbreeding census and included
seven life stages: eggs/hatchlings, three successively larger juvenile stages, and
three adult stages reflecting different fecundities as nesting females matured.
Both sensitivity and elasticity analyses of the matrix pointed to annual survival
of the three juvenile size stages, particularly large juveniles (50–80 cm carapace
length), as most important in determining future population growth rates (e.g., see
Crouse et al. 1987 for assumptions). Most important, the model predicted that
100% survival of the egg/hatchling stage was unlikely to reverse current population declines. The model also indicated that future research should focus on
refining our estimates of small juvenile survival and growth rates of all three
juvenile stages. Refinement of fecundity and hatchling survival estimates would
not change the qualitative predictions of the model. Due to the uncertainties in
some of the model parameters and the obvious need for populations to reproduce,
Crouse and associates (1987) did not advocate terminating nest protection
projects but rather noted that nest protection projects without concurrent reductions in juvenile mortality (through the use of TEDs or some other mechanism)
would likely be futile. Based in large part on this model, a National Academy of
Sciences review panel recommended requiring TEDs “in most trawls at most
times of the year” (National Research Council 1990). In December 1992, NMFS
expanded seasonal TED regulations to require TEDs in all southeastern shrimp
trawls by December 1994 (57 Fed. Reg. 57348-57359, Dec. 4, 1992).
Crowder and colleagues (1994) recently revised the original Loggerhead model
(see Fig. 10.1b), reducing it to five stages by combining first-time breeders,
remigrants, and the remaining adults into one adult stage. The authors used the
population growth rates to compare the time it might take to see the results of TED
regulations on nesting turtle numbers. Depending on how large a change in
nesting numbers is required to produce an effect in the field (nesting turtle numbers fluctuate considerably from year to year anyway) and how much TEDs
reduce annual mortality rates, it may be decades before we can be sure of the
effect of TED requirements by counting adult females on the beach. However, the
Selina S. Heppell, Deborah T. Crouse, and Larry B. Crowder
the net (Henwood and Stuntz 1987; National Research Council 1990). But TED
development and requirements were highly controversial; members of the shrimping industry complained of potential shrimp losses, gear entanglement, and crew
injuries from the new devices (Sea Turtle Conservation and the Shrimp Fishery
1990). They also noted that nest protection projects were yielding significant
increases in hatch success and releasing large numbers of hatchlings at relatively
low costs and with little socioeconomic impact. A classic management dichotomy
was thus established: should managers require the disliked technology (TEDs) in
an industry already in financial trouble or opt for more low-cost and widely
popular nest protection projects?
To investigate the relative trade-offs between these disparate management alternatives, Crouse and co-workers (1987) developed a stage-based matrix model for
southeastern Loggerheads, using a preliminary life table developed by Frazer
(1983a). The model was based on stages identified by size classes because little
was known about age in sea turtles, and most data were collected for turtles of
different size classes. The model assumed a postbreeding census and included
seven life stages: eggs/hatchlings, three successively larger juvenile stages, and
three adult stages reflecting different fecundities as nesting females matured.
Both sensitivity and elasticity analyses of the matrix pointed to annual survival
of the three juvenile size stages, particularly large juveniles (50–80 cm carapace
length), as most important in determining future population growth rates (e.g., see
Crouse et al. 1987 for assumptions). Most important, the model predicted that
100% survival of the egg/hatchling stage was unlikely to reverse current population declines. The model also indicated that future research should focus on
refining our estimates of small juvenile survival and growth rates of all three
juvenile stages. Refinement of fecundity and hatchling survival estimates would
not change the qualitative predictions of the model. Due to the uncertainties in
some of the model parameters and the obvious need for populations to reproduce,
Crouse and associates (1987) did not advocate terminating nest protection
projects but rather noted that nest protection projects without concurrent reductions in juvenile mortality (through the use of TEDs or some other mechanism)
would likely be futile. Based in large part on this model, a National Academy of
Sciences review panel recommended requiring TEDs “in most trawls at most
times of the year” (National Research Council 1990). In December 1992, NMFS
expanded seasonal TED regulations to require TEDs in all southeastern shrimp
trawls by December 1994 (57 Fed. Reg. 57348-57359, Dec. 4, 1992).
Crowder and colleagues (1994) recently revised the original Loggerhead model
(see Fig. 10.1b), reducing it to five stages by combining first-time breeders,
remigrants, and the remaining adults into one adult stage. The authors used the
population growth rates to compare the time it might take to see the results of TED
regulations on nesting turtle numbers. Depending on how large a change in
nesting numbers is required to produce an effect in the field (nesting turtle numbers fluctuate considerably from year to year anyway) and how much TEDs
reduce annual mortality rates, it may be decades before we can be sure of the
effect of TED requirements by counting adult females on the beach. However, the