Eastern Mediterranean sea turtles in their epipelagic phase: First records of monthly growth rates and effects of a plastic pollutant

Abstract

Most sea turtle conservation efforts worldwide are focused on nesting beaches. After hatchlings reach the sea, however, monitoring, research, and conservation are not prioritized, and little is known about the next life stages, when turtles are passively drifting in pelagic habitats. We study the biology of and threats to hatchling to juvenile loggerhead (Caretta caretta) and green (Chelonia mydas) sea turtle subpopulations in the Mediterranean Sea, using a dataset composed of cases of injured sea turtles that were brought for treatment to Israel's Sea Turtle Rescue Center from 1999–2020. Using length distribution of minimum curved carapace lengths, we calculated for the first time the month-specific growth rates of both turtle species. Loggerhead turtles grew at a rate of 0.76 cm month^–1 in the first 19 months of life and green sea turtles grew 0.92 cm month^–1 in the first 11 months of life. We also found that a major cause of injury for epipelagic phase turtles, ≤ 40 cm curved carapace length, was entanglement in polypropylene sacks. The proportion of epipelagic phase turtles treated in Israel's Sea Turtle Rescue Center due to these entanglements increased from 20 % of the epipelagic phase cases in 2008–75 % by the last year of this study (2020). We suspect that livestock carriers are the origin of these sacks, and preventing this type of marine pollution is crucial for populations prosperity and requires international collaboration.