Impacts of plastic debris on Australian marine wildlife
Plastic debris is a pervasive problem throughout the world’s oceans, and various governments worldwide have officially recognised the importance of managing this issue. In response, efforts to define, monitor and reduce the problem of plastic debris in the sea are increasing, especially as it poses significant risks to protected species.
This study is a first attempt at compiling available data on interactions between plastic debris and marine wildlife in Australian waters. The geographic extent of the study included all Australian waters, including offshore and sub-Antarctic islands and Australian Antarctic Territories. The types of impacts from plastic debris include primarily entanglement and ingestions. This report provides an indication of the frequency, geographic extent, general magnitude and other details of these interactions and presents a summary of the impacts of plastic debris (including lost or discarded fishing equipment) on Australian marine wildlife. The earliest available record of these impacts was from 1974, and the most recent records were from June of 2008.
This study was prepared with information obtained from available publications, raw data and database extracts, media reports and anecdotal evidence wherever available. However, there is a paucity of information in Australia and an absence of any national, standardised database, data recording or reporting system that allows a comprehensive assessment of the interactions between plastic debris and marine wildlife. As a consequence, the magnitude of impacts of plastic debris on marine wildlife is difficult to determine.
Available information indicates that at least 77 species of marine wildlife found in Australian waters have been impacted by entanglement in, or ingestion of, plastic debris during the last three and a half decades (1974-2008). The affected species include six species of marine turtles, 12 species of cetaceans, at least 34 species of seabirds, dugongs, six species of pinnipeds, at least 10 species of sharks and rays, and at least eight other species groups. Most records of impacts of plastic debris on wildlife relate to entanglement, rather than ingestion. However, the rate of ingestion of plastic debris by marine wildlife is difficult to assess as not all dead animals are necropsied or ingested plastic debris may not be recorded where it is not considered as the primary cause of death. Species dominating existing entanglement and ingestion records are turtles and humpback whales. Australian pelicans and a number of cormorant species are also frequently reported.
The distribution of records of wildlife impacted by plastic debris in Australian waters reflects survey efforts. For example, some of the highest numbers of records come from coastal areas of north eastern Arnhem Land and south eastern Queensland where long-term surveys and regular beach clean-up activities are in place. Cetacean records are the most uniformly distributed, while records of pinnipeds and dugongs reflect the distribution of these species and occur primarily along southern Australia, and eastern Queensland, respectively. Seabird records tend to be concentrated around large urban centres, especially where zoos or wildlife rescue organisations receive dead and injured birds and maintain records, and on offshore islands where plastic ingestion by particular seabird species has been studied. Geographic areas where there are few, if any, records of wildlife impacted by plastic debris include the north western coastline of Western Australia, the Great Australian Bight, eastern Cape York, and offshore waters. Many animals that feed in offshore waters may return to coastal waters, where they are subsequently recorded. The absence of records for these areas is more likely to reflect an absence of regular observations and monitoring, not an absence of interactions occurring there.
Derelict fishing nets dominate the types of plastic debris observed entangling wildlife. A variety of plastic items are recorded as impacting marine species through ingestion. The most common items in the ingestion records are synthetic fishing line and hooks (especially in seabirds). The patterns of reports of entanglement in and ingestion of plastic debris by wildlife in Australian waters are likely to be influenced by factors such as the size and distribution of populations, foraging areas, migration patterns, diets, proximity of species to urban centres, changes in fisheries equipment and practices, weather patterns, and ocean currents, as well as the frequency of monitoring and/or observation of wildlife. While this study focuses on apparent trends in available data, it is beyond the scope of this project to draw conclusions about the causes of or influences on these trends by any of the factors outlined above.
To improve information on the impacts of plastic debris on marine wildlife, a national database needs to be established and a nationally consistent, systematic approach to monitoring and the recording of information needs to be implemented. Key future research priorities include:
- Determining the necessary statistical analyses required to develop a more accurate estimate of the magnitude of the impact of plastic debris on marine wildlife.
- Facilitating the collection of more necropsy data specifically aimed at detecting ingested plastic debris. Devise species-specific methods aimed to increase the probability of detecting ingested plastic (e.g. Francis 2007).
- Developing a method to assess cryptic mortality (unrecorded or unknown deaths) caused by impacts of plastic debris.
- Analysing climatic and oceanographic information to assist in detecting seasonal patterns in the impacts of plastic debris on marine wildlife.
- Devising a monitoring program, for feeding information into the national database from geographic locations currently devoid of data. Recommendations are given for the implementation of such a monitoring program.