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Marine Turtle Newsletter 46:4-5, © 1989

Guest Editorial: "Large Juveniles" also Crucial to Future Breeding Success of Sea Turtle Populations

Debby Crouse
526 Euclid Street, Raleigh, North Carolina 27604 USA

I read the lead article (Anonymous, 1989) and editorial (Canin, 1989) in MTN #44 with mixed feelings. On one hand, I am delighted to see international conservation concerns turn their focus toward the larger sizes of sea turtles. This is a direction I have favored for several years. On the other hand, I am apprehensive of a simplistic swing of the pendulum that may, in turn, focus entirely on mature breeders. There is great danger in setting our sights too high; that is, setting maximum size limits so large that we may not protect those size/age classes with the most to contribute to future population size.

First let me state that I agree entirely with Nat Frazer's assertion at WATS II (referred to in Canin, 1989) that reproductive value is highest in mature breeding turtles. However, it is important to note that the effective contribution of any age class of turtles to future population growth rate is a function not only of reproductive value, but also of the differential survival rate of each class and growth rates (i.e., age at first reproduction). Thus, in a recent exercise modeling the southeastern USA loggerhead sea turtles Caretta caretta), my coauthors and I concluded that the juvenile classes, in particular the 'large juvenile' stage class (straight carapace length [SCL]= 58.1-80.0 cm), may contribute the most to future population growth (Crouse et al., 1987). Indeed, at this time I would advocate full protection, from incidental as well as direct-harvest mortality factors, for all southeastern (USA) loggerhead turtles >58 cm (SCL). This action would protect not only the mature breeders (>87 cm SCL), but also the large juveniles and subadults, all of which represent decades of selective survival and are critically important to the future breeding success of their populations.

The modeling work I did was based on Frazer's preliminary life table (Frazer, 1983) for the Little Cumberland Island, Georgia, population of loggerhead sea turtles. This life table rests on one of the longest and most carefully collected data bases for a marine turtle population anywhere in the world. And yet, Frazer noted there were still uncertainties in some portions of the life table he developed. We know far less about most other populations and species. It is clear that we should focus protection on life stages not adequately protected, while focusing data collection in areas which will best refine our understanding of marine turtle demographics. Consequently, I recommend further studies to strengthen our estimates of first-year and small juvenile mortality rates, growth rates and age at first reproduction coupled with stronger protection for juveniles as well as adult turtles.

Finally, I am concerned that modeling efforts such as those done by Frazer and myself be used in a positive manner; that is, to support protection for marine turtles, rather than imply that harvest of some stages can now be considered justified. I realize that this was not the intent of the IUCN Resolution, nor the GREENPEACE editorial, and I also understand that some countries are simply not ready to accept a 'no harvest' policy. Thus I do not envy those who must carry these concepts abroad, but I urge them to be cautious and conservative in their interpretations and applications. I am not convinced we know enough yet about marine turtle demographics to appear to condone harvest of any life stage(s).

Anonymous. 1989. IUCN resolution urges maximum size limits, protection of habitat, TEDs. Marine Turtle Newsletter 44:1-2.

Canin, J. 1989. GREENPEACE Guest Editorial: IUCN resolution. Marine Turtle Newsletter 44:3-4.

Crouse, D.T., L.B. Crowder and H. Caswell. 1987. A stage-based population model for loggerhead sea turtles and implications for conservation. Ecology 68(5):1412-1423.

Frazer, N.B. 1983. Demography and life history evolution of the Atlantic loggerhead sea turtle, Caretta caretta. Ph.D. Dissertation, University of Georgia, Athens, Georgia USA.