Historical Diet Analysis of Loggerhead Sea Turtles (Caretta Caretta) in Virginia

Digestive tract contents were examined from 297 Loggerhead Sea Turtles (Caretta caretta) in Virginia during 1983–2002. Analyses revealed a shift from predominantly Atlantic Horseshoe Crab (Limulus polyphemus) during the early to mid-1980s to predominantly Common Blue Crab (Callinectes sapidus) during the late 1980s and early 1990s. Diet in the mid-1990s and in 2000–2002 was dominated by finfish, particularly Atlantic Menhaden (Brevoortia tyrannus) and Atlantic Croaker (Micropogonias undulatus). These diet shifts suggest that horseshoe crab and blue crab population declines have caused loggerheads to forage in nets or on discarded fishery bycatch.

Figure 1

(A) Frequency of occurrence (%F) of major prey groups in all digestive tract samples and necropsy data collected during 1983–2002; (B) biplot of time period and prey type principal components (PCs) from a correspondence analysis using %F values presented in (A). Row PCs: 83–87 (1983–1987), 88–92 (1988–1992), 93–97 (1993–1997), and 98–02 (1998–2002). Column PCs: H (horseshoe crabs), C (crustaceans), M (molluscs), and F (fish). PC1 accounts for 80.87% of the variation, and PC2 accounts for 17.98%.

Figure 2

Biplots of time period and prey type principal components (PCs) for PC1 and PC2 of a correspondence analysis using (A) %F, (B) %W, (C) %N, and (D) %IRI values of major prey items from all whole samples collected during 1983–2002. Row PCs: 83–87 (1983–1987), 88–92 (1988–1992), 93–97 (1993–1997), and 98–02 (1998–2002). Column PCs: B (Busycon whelks), BF (bony fish), Ca (blue crabs, Callinectes spp.), H (horseshoe crabs), He (hermit crabs), L (spider crabs, Libinia spp.), La (Lady Crab), P (Purse Crab), R (Rock Crab), and S (moon snails). PC1 accounts for 52.99%, 46.15%, 70.38%, and 54.62% of the variation in (A), (B), (C), and (D), respectively, and PC2 accounts for 33.78%, 42.06%, 22.76%, and 41.41%.

Figure 3

Percent index of relative importance (%IRI) of major prey items in whole samples collected during 1983–2002, as divided by (A) season and (B) size class (SCL).

Appendix 1.

Cumulative Prey Curves for Whole Digestive Tract Samples Collected from Loggerhead Sea Turtles in Virginia during 1983–2002 (N = 128), as Divided for (a) Interannual, (b) Interseasonal, (c) Size-specific, and (d) Sex-specific Analyses. Samples Were Randomized Ten Times And Numbers Of Prey Types Averaged. Error Bars Represent ±1 Sd

Contributor Notes

Section editor: S. F. Fox.

Received: 29 Jun 2005

Accepted: 05 Dec 2006