Anthropogenic impacts on green turtles Chelonia mydas in New Zealand

Conservation strategies to sustain endangered green turtle Chelonia mydas populations must categorise and mitigate a range of anthropogenic threats. This study provides first insights into some of the adverse effects of anthropogenic activities on green turtles at a foraging area in New Zealand. Gross necropsies were conducted on 35 immature and sub-adult green turtles that were stranded in northern New Zealand between 2007 and 2013. Results revealed 54% (n = 19) of individuals exhibited human-related trauma, and 63% of these (n = 12) had ingested synthetic marine debris. The predominant plastic items ingested were soft plastics (e.g. single-use food packaging, plastic bags), and white, clear or translucent items. No correlation was observed between curved carapace length and the volume or number of synthetic debris items ingested. Propeller strike injuries were identified in 26% (n = 5) of turtles exhibiting human-related effects, while 10% (n = 2) had evidence of incidental capture in recreational fishing activities. Importantly, within New Zealand waters, anthropogenic effects predominantly associated with plastic ingestion are impacting the green turtle aggregation, and may be an important contributory factor to the stranding of immature and sub-adult green turtles in this region. Consequently, the threats identified in this study should be considered when developing population-specific conservation strategies.