Assessing the risks of marine debris ingestion to Procellariiform seabirds

Procellariiform seabirds are among the worlds most threatened species; with over half of species in population decline, and 44% of all species are threatened with extinction. There are 139 extant Procellariiform seabird species distributed globally, with the highest species density occurring in the Australasia region surrounding the Tasman Sea and Southern Ocean. Understanding the threats to seabirds is key for managing and planning for the conservation of this assemblage of threatened species. Ingestion of anthropogenic marine debris, particularly plastics, is common among seabirds globally, and considered an emerging threat to seabird populations. Despite growing awareness of the threat of marine debris, both the incidence of debris ingestion in Australasian seabirds, and the effect of ingested plastics on seabird health and mortality is poorly understood. Though the ubiquity of marine debris ingestion in seabirds is internationally recognised, there is currently no extant baseline data on quantified health effects or mortality associated with marine debris ingestion in seabirds. The nonexistence of baseline mortality data of this potential threat poses a serious impediment to assessing risk of debris interactions, conservation planning and managing declining populations in this group of threatened seabirds. This thesis aims to examine the factors that drive harm associated with ingestion of marine debris in Procellariiform seabirds and predict the scale of mortality expected in the current environment with current levels of marine debris pollution. Specifically, this thesis aims to examine (1) the incidence of marine debris ingestion in Australasian seabirds, (2) the mortality caused by the physical impacts of marine debris ingestion, and (3) the potential chemical and toxicological effects of ingested plastics on the growth, reproduction, and endocrine function of birds and finally (4) estimate the global seabird mortality associated with marine debris ingestion. (1) Procellariiform seabirds were collected dead as beach-wrecked, veterinary casualties and fisheries by-catch across Australia and New Zealand between Jan 2013 and March 2017 to determine the incidence of marine debris ingestion in Australasian seabirds. Following collection, the birds were necropsied and their gastro-intestinal tracts inspected for ingested marine debris, which was removed and quantified. We collected and necropsied 1734 individual seabirds of 51 Procellariform species, covering four families of Procellariiform seabirds; Diomedeidae, Procellariidae, Hydrobatidae and Pelecanoididae. Ingestion of marine debris was found in 32% of individual birds and 31 of 51 species examined. Ingestion of marine debris was found in all Procellariiform seabird families, though we observed considerable variation in the incidence and magnitude of ingested debris among the birds examined. Some taxonomic groupings demonstrated consistent patterns in both incidence and magnitude of marine debris ingestion, while other taxonomic groupings demonstrated great variability. We demonstrated that exposure to marine debris in the environment, diet, foraging strategy and taxonomic group are all important ecological factors driving the incidence of debris ingestion in Procellariiform seabirds. (2) Mortality resulting from physical impacts of marine debris ingestion in Procellariiform seabirds, such as gastro-intestinal obstructions and perforations, was quantified and analysed with statistical methods to establish a dose-response relationship. We found that there is a 20% chance of death from ingesting a single debris item, rising to 100% after consuming 93 items. Obstruction of the gastro-intestinal tract is the leading cause of death. Overall, balloons are the highest-risk debris item; 32 times more likely to result in death than ingesting hard plastic. (3) The potential chemical and toxicological effects of ingested plastic on avian development, reproduction and endocrine disruption was investigated by conducting a laboratory experiment. The experiment is designed to examine the toxicological effect of ingested plastic on endocrine function in a bird species, the Japanese quail, Coturnix japonica. Following OCSPP 890.2100: Avian Two-generation Toxicity Test in the Japanese Quail, we designed a multi-generational plastic feeding experiment to quantify effects of plastic ingestion in a bird. Quail were experimentally fed plastic to monitor the effect on their growth, reproductive output, and endocrine function. We found that the primary adverse effect of plastic ingestion in birds is increased chance of cysts in the male reproductive tract, reduced growth in chicks fed plastic and delayed onset of sexual maturity in females, however these changes did not affect survival or reproductive output. Contrary to expectations, we did not find any other plastic ingestion effects. These results demonstrate that it's likely that the effect of ingested plastic on a birds' heath is primarily driven by the physical space that it occupies and resulting dietary dilution, and that the chemical and endocrine impacts that may affect reproduction and survival are minimal. (4) By combining the incidence of debris ingestion, mortality resulting from the physical effects of debris ingestion and experimentally determined sublethal effects from the three previous chapters and the literature, we estimated global seabird mortality from debris ingestion. We found that over 60% of examined Procellariiform species have a 5% or greater chance of dying of a debris-related cause, and 9 species having a 30% or greater chance of debris-related death. Shearwaters, fulmarine petrels and prions are the assessed groups most likely to die from debris ingestion and would benefit most from initiatives to reduce debris entering the marine environment. Our analysis confirms that plastic pollution is a serious conservation concern to threatened and declining Procellariiform seabirds. By quantifying and modelling the estimated mortality associated with ingestion of marine debris by threatened Procellariiform seabirds, this study has provided baseline data and a framework by which to compare threats to seabirds. With this baseline data and mortality estimate, Procellariiform seabirds can be managed and conservation efforts planned accordingly in response to the marine debris pollution hazard changing through space and across time. This will be the first time internationally that the scale of the threat of marine debris to seabird populations has been quantified and can be included in analyses and decision making when planning conservation initiatives.