Variation in Sea Turtle Life History Patterns
253
resources in the Pacific by water temperature; loggerheads inhabit cooler waters than
do olive ridleys (Pitman, 1993; Polovina et al., in review). Thus, as more is learned
about this life stage, further divisions in the Type 2 pattern may be required.
9.6 ANTHROPOGENIC IMPACTS ON THE EARLY
JUVENILE STAGE
The future is bleak. Early juvenile-stage sea turtles face a myriad of obstacles
irrespective of whether they are in the neritic or oceanic zone. Directed take of very
small turtles for food is not common. However, directed take for the souvenir trade
in polished shells or whole stuffed turtles, such as the once-popular but now illegal
tourist trade in Madeira, Portugal (Brongersma, 1982), still exists in some regions.
Indirect take in fisheries, whether it is the high seas drift nets, longlines, or
coastal trawlers, is a very serious problem for juvenile turtles (National Research
Council, 1990; Wetherall et al., 1993; Balazs and Pooley, 1994; Witzell, 1999; Bolten
et al., 2000). Throughout the world’s oceans, the size distribution of loggerhead
turtles caught in longline fisheries is the largest size class for the oceanic development
stage (Bolten et al., 1994; Ferreira et al., 2001; Bolten, in press), which has significant demographic consequences (Crouse et al., 1987; Heppell et al., in press).
The lethal and sublethal effects of debris ingestion and entanglement are also
major concerns (Balazs, 1985; Carr, 1987b; McCauley and Bjorndal, 1999; Witherington, in review b). Habitat loss, particularly in coastal areas, has been documented; habitat degradation in the oceanic zone is more difficult to document but
nonetheless acute when the effects of pollution are considered (Lutcavage et al.,
1997). Both oceanic and neritic ecosystems are changing as a result of overfishing
and pollution. Changes to the suite of species interactions and food webs in these
ecosystems are undoubtedly having a major negative impact on sea turtles.
9.7 CONCLUSIONS: RESEARCH DIRECTIONS
Our ability to solve the “mystery of the lost year” for those species for which the
early juvenile stages remain unknown has been improved by the development of
new research tools. Biotechnology is providing molecular tags to identify populations and track movements; biotelemetry is allowing researchers to evaluate movement and distribution patterns. Stable isotopes may provide clues about where to
look for early juvenile stages and also provide information on trophic relationships.
For researchers to make rapid progress in the study of early juvenile stages, multidisciplinary teams should be developed with expertise in the fields of physical and
biological oceanography, population genetics, statistical modeling, demography,
nutrition, and ecosystem analyses.
ACKNOWLEDGMENTS
My research on the oceanic juvenile stage has focused on the loggerhead population
in the Atlantic and has been conducted in collaboration with Karen Bjorndal, whose
1123 book.book Page 253 Monday, November 11, 2002 11:11 AM
253
resources in the Pacific by water temperature; loggerheads inhabit cooler waters than
do olive ridleys (Pitman, 1993; Polovina et al., in review). Thus, as more is learned
about this life stage, further divisions in the Type 2 pattern may be required.
9.6 ANTHROPOGENIC IMPACTS ON THE EARLY
JUVENILE STAGE
The future is bleak. Early juvenile-stage sea turtles face a myriad of obstacles
irrespective of whether they are in the neritic or oceanic zone. Directed take of very
small turtles for food is not common. However, directed take for the souvenir trade
in polished shells or whole stuffed turtles, such as the once-popular but now illegal
tourist trade in Madeira, Portugal (Brongersma, 1982), still exists in some regions.
Indirect take in fisheries, whether it is the high seas drift nets, longlines, or
coastal trawlers, is a very serious problem for juvenile turtles (National Research
Council, 1990; Wetherall et al., 1993; Balazs and Pooley, 1994; Witzell, 1999; Bolten
et al., 2000). Throughout the world’s oceans, the size distribution of loggerhead
turtles caught in longline fisheries is the largest size class for the oceanic development
stage (Bolten et al., 1994; Ferreira et al., 2001; Bolten, in press), which has significant demographic consequences (Crouse et al., 1987; Heppell et al., in press).
The lethal and sublethal effects of debris ingestion and entanglement are also
major concerns (Balazs, 1985; Carr, 1987b; McCauley and Bjorndal, 1999; Witherington, in review b). Habitat loss, particularly in coastal areas, has been documented; habitat degradation in the oceanic zone is more difficult to document but
nonetheless acute when the effects of pollution are considered (Lutcavage et al.,
1997). Both oceanic and neritic ecosystems are changing as a result of overfishing
and pollution. Changes to the suite of species interactions and food webs in these
ecosystems are undoubtedly having a major negative impact on sea turtles.
9.7 CONCLUSIONS: RESEARCH DIRECTIONS
Our ability to solve the “mystery of the lost year” for those species for which the
early juvenile stages remain unknown has been improved by the development of
new research tools. Biotechnology is providing molecular tags to identify populations and track movements; biotelemetry is allowing researchers to evaluate movement and distribution patterns. Stable isotopes may provide clues about where to
look for early juvenile stages and also provide information on trophic relationships.
For researchers to make rapid progress in the study of early juvenile stages, multidisciplinary teams should be developed with expertise in the fields of physical and
biological oceanography, population genetics, statistical modeling, demography,
nutrition, and ecosystem analyses.
ACKNOWLEDGMENTS
My research on the oceanic juvenile stage has focused on the loggerhead population
in the Atlantic and has been conducted in collaboration with Karen Bjorndal, whose
1123 book.book Page 253 Monday, November 11, 2002 11:11 AM