Plastic ingestion by green turtles (Chelonia mydas) over 33 years along the coast of Texas, USA.

Despite exponential growth of anthropogenic marine debris in recent decades, plastic ingestion by marine turtles in the Gulf of Mexico is not well understood. Gastrointestinal tracts were examined from 464 green turtles that stranded in Texas between 1987 and 2019, and 226 turtles ingested plastic (48.7%). This number doubled from 32.5% in 1987-1999 to 65.5% in 2019, but mass of ingested items was lowest in 2019. No turtles showed evidence of death directly related to plastic ingestion. Compared to other regions, plastic ingestion was low. Small turtles (<25 cm straight carapace length) ingested plastic more frequently and in greater amounts than larger turtles. Small turtles also ingested more hard plastic while larger turtles ingested more sheet-like and thread-like plastics, which may correspond to size-based habitat shifts. This is among the largest marine turtle ingestion studies to date and demonstrates an increasing prevalence of plastic ingestion.

Conservation hotspots for marine turtle nesting in the United States based on coastal development.

Coastal areas provide nesting habitat for marine turtles that is critical for the persistence of their populations. However, many coastal areas are highly affected by coastal development, which affects the reproductive success of marine turtles. Knowing the extent to which nesting areas are exposed to these threats is essential to guide management initiatives. This information is particularly important for coastal areas with both high nesting density and dense human development, a combination that is common in the United States. We assessed the extent to which nesting areas of the loggerhead (Caretta caretta), the green (Chelonia mydas), the Kemp's ridley (Lepidochelys kempii), and leatherback turtles (Dermochelys coriacea) in the continental United States are exposed to coastal development and identified conservation hotspots that currently have high reproductive importance and either face high exposure to coastal development (needing intervention), or have low exposure to coastal development, and are good candidates for continued and future protection. Night-time light, housing, and population density were used as proxies for coastal development and human disturbance. About 81.6% of nesting areas were exposed to housing and human population, and 97.8% were exposed to light pollution. Further, most (>65%) of the very high- and high-density nesting areas for each species/subpopulation, except for the Kemp's ridley, were exposed to coastal development. Forty-nine nesting sites were selected as conservation hotspots; of those high-density nesting sites, 49% were sites with no/low exposure to coastal development and the other 51% were exposed to high-density coastal development. Conservation strategies need to account for ~66.8% of all marine turtle nesting areas being on private land and for nesting sites being exposed to large numbers of seasonal residents.

Satellite tracking of sympatric marine megafauna can inform the biological basis for species co-management.

CONTEXT: Systematic conservation planning is increasingly used to identify priority areas for protection in marine systems. However, ecosystem-based approaches typically use density estimates as surrogates for animal presence and spatial modeling to identify areas for protection and may not take into account daily or seasonal movements of animals. Additionally, sympatric and inter-related species are often managed separately, which may not be cost-effective. This study aims to demonstrate an evidence-based method to inform the biological basis for co-management of two sympatric species, dugongs and green sea turtles. This approach can then be used in conservation planning to delineate areas to maximize species protection. METHODOLOGY/RESULTS: Fast-acquisition satellite telemetry was used to track eleven dugongs and ten green turtles at two geographically distinct foraging locations in Queensland, Australia to evaluate the inter- and intra-species spatial relationships and assess the efficacy of existing protection zones. Home-range analysis and bathymetric modeling were used to determine spatial use and compared with existing protection areas using GIS. Dugong and green turtle home-ranges significantly overlapped in both locations. However, both species used different core areas and differences existed between regions in depth zone use and home-range size, especially for dugongs. Both species used existing protection areas in Shoalwater Bay, but only a single tracked dugong used the existing protection area in Torres Strait. CONCLUSIONS/SIGNIFICANCE: Fast-acquisition satellite telemetry can provide evidence-based information on individual animal movements to delineate relationships between dugongs and green turtles in regions where they co-occur. This information can be used to increase the efficacy of conservation planning and complement more broadly based survey information. These species also use similar habitats, making complimentary co-management possible, but important differences exist between locations making it essential to customize management. This methodology could be applied on a broader scale to include other sympatric and inter-related species.