Identifying critical foraging habitats of the green turtle (Chelonia mydas) along the Pacific coast of the Baja California peninsula, Mexico

Abstract

ABSTRACT1. The conservation of highly mobile and migratory species remains one of the most serious challenges to resource managers.2. Intense mortality of immature green turtles has been identified at principal developmentalfeeding habitats in Baja California, and is considered a great threat to the stability of the eastern Pacific population. Thus, coastal lagoons of the Baja California peninsula, such as Bah! ı ıa Magdalena, have been identified as high priority areas for their protection.3. Conservation efforts to date have focused on creating a sea turtle refuge in the northwestern part of the bay, but this area may not be sufficient for protecting all of the critical feeding areas used by green turtles.4. The diet of green turtles was investigated through analysis of digestive tract contents from 24 green turtles that were drowned incidentally in fishing nets at feeding grounds in Bah! ı ıa Magdalena and adjacent areas along the Pacific coast of the Baja California peninsula, Mexico.5. Mean straight carapace length (SCL) differed significantly between localities: mean: 55:5 cm (range: 47.7-76:9 cm, n ¼ 11) in Bah! ı ıa Magdalena; mean: 67:7 cm (range: 49-87 cm, n ¼ 11) in adjacent coastal waters.6. Green turtle diet consisted largely of marine algae and seagrasses, but food items varied spatially. The red algae Gracilaria pacifica, Gracilariopsis lemaneiformis and Hypea johnstonii were the most abundant diet items inside Bah! ı ıa Magdalena, and the seagrass Phyllospadix torreyi was the most commonly ingested food in coastal areas outside of the bay.7. Results indicate that green turtles utilize spatially distinct foraging habitats within this region. Therefore, it is recommended that any design of protected areas for sea turtles in Bah! ı ıa Magdalena

The Foragining Ecology of the Green Turtle in the Baja California Peninsula: Health Issues

“…However, data generated by our work suggest that sea turtles residing in Estero Banderitas are feeding in areas outside of the bay, most likely in coastal regions with high upwelling. These findings support those of López-Mendilaharsu et al (2005) and indicate that green turtles utilize spatially distinct feeding habitats within coastal areas. Therefore, we recommend that sea turtle protected areas be designed with an appreciation of regional rather than local scales in order to protect broader foraging areas.…”

“…Red algae, such as Gracilaria sp tend to reflect the environmental availability of metals but have higher bioaccumulation of Cadmium, Copper and Zinc than other macroalgal groups (Sánchez-Rodríguez et al, 2001;Roncarati, 2003). These same species are a major component of the green turtle diet along the Baja California Peninsula (Seminoff et al, 2002;López-Mendilaharsu et al, 2005), and we proposed previously (Gardner et al, 2006) that their foraging habits could account for the high metal concentrations found in this population. However, comparisons across plant species in the present study suggest that species differences in metal concentrations are minimal.…”

“…The only significant difference detected between plant species was that Cadmium was higher in Ruppia maritima than all other species, and higher in Gracilaria textorii than Codium amplivesiculatum. R. maritima was encountered in only one of the sea turtle stomachs analyzed, contributing a relatively small percentage of the overall diet (8.7%) in this study, and was absent from the diet of 24 green turtles analyzed in previous work (López-Mendilaharsu et al, 2005). Gracilaria textorii made up a larger proportion of the turtles' stomach contents (16.5%), but was similar in Cadmium concentration to most other plant species ingested by the green turtles.…”

“…These same species were also collected from the mangrove channel of Estero Banderitas with the exception of Neoagarddhiella baileyi, Pterocladiella capillacea and Ulva lactuca. Hypnea johnstonii, which has been previously reported as a major food item in green turtle diet (López-Mendilaharsu et al, 2005), was available in the bay but not found in the stomachs of the turtles. Gracilaria vermiculophylla was present in 60%of the turtle stomachs analyzed and made up the greatest total percent volume (36%).…”

“…The Foragining Ecology of the Green Turtle in the Baja California Peninsula: Health Issues 479 Peninsula (Seminoff et al, 2002), juvenile and adult green turtles preferentially consume soft red algae, especially species of Gracilaria (López-Mendilaharsu et al, 2005). Studies in Baja California have demonstrated that these same species of red algae tend to have higher enrichment factors of metals than other groups of seaweeds (Sánchez-Rodríguez et al, 2001), which could account for the high accumulation of metals in foraging green turtles in this region.…”