Abstract
Plastics are ubiquitous throughout global marine ecosystems. Due to their unique durable nature, and subsequent abundance and distribution throughout global oceans, marine plastics have gone from being an aesthetic issue to an economic and ecological threat. Marine microplastics can threaten the health of marine ecosystems and individual biota upon ingestion. To date, there has been limited research on the prevalence of microplastic ingestion by commercially important marine fish in the southern hemisphere, particularly in the South Pacific. To contribute to the current lack of knowledge, the primary aim of this thesis was to quantify ingested microplastics in commercial wild and farmed fish from southern New Zealand using visual techniques and Raman spectroscopy. This study examined eleven commercial fish species, ten of which were wild, and either pelagic or benthic, and one farm reared species of salmon. The number of ingested microplastics and the corresponding microplastic characteristics were compared across vertical habitat (i.e., benthic and pelagic) and rearing environment (i.e., wild and farm reared). Similar to previous research, vertical habitats were identified as being similar in regard to the number of ingested microplastics and their corresponding characteristics suggesting that microplastics are ubiquitous throughout the water column in southern New Zealand waters. Rearing environment (i.e., wild and farm reared) showed a greater influence on the quantity and nature of microplastics ingested. Farm reared fish had a higher ingestion rate of microplastics than the wild fish, and certain microplastic types, colours, and size ranges were observed more frequently in farm reared fish. High microplastic extraction from farm reared fish has been attributed to facility equipment and structures being made from plastic. In all examined species, regardless of location, polyethylene was the most common chemically characterised plastic polymer, followed by polypropylene, polyethylene and their associated additives and pigments, and semi-synthetic viscose. Spectroscopic techniques to chemically characterise microplastics are becoming an essential step in identification research. A detailed understanding of the polymer type enables inference of the effects on marine biota health associated with the particular polymer. Plastic has the potential to act as a vector for synthetic plastic additives, adsorbed chemical pollutants and microbes from the water column to fish via ingestion of plastic. Trophic transfer and bioaccumulation of these chemical additives, pollutants, and microbes through primary and secondary microplastic ingestion increases the associated risks to marine organisms and ultimately human consumers. This thesis is the first to examine microplastic ingestion in farm reared fish from New Zealand and commercial wild fish from southern New Zealand. The abundance of microplastics extracted from commercial fish stomach contents signifies the risk to human health through consumption of likely plastic contaminated fish.