Ingestion of plastic marine debris by longnose lancetfish (Alepisaurus ferox) in the Hawaiʻi-based shallow-set longline fishery

Marine debris has become a persistent and a widespread threat to the oceanic environment, impacting species on most trophic levels, including pelagic fish. The most problematic type of marine debris are those comprised of plastic due to its slow degradation, chemical composition and ability to attract hydrophobic persistent organic pollutants that may absorb into the tissues of fish when ingested. While plastic debris ingestion by planktivorous fish in the North Pacific Ocean has been studied, few studies have focused on piscivorous fish. Longnose lancetfish have a voracious diet and are often caught throughout the water column by the Hawaii-based pelagic longline fishery where they are considered a discard. The objectives of this study were to: 1) determine the presence, diversity (i.e., different types of plastic), and abundance of ingested plastic marine debris; 2) investigate if a relationship exists between longnose lancetfish morphometrics and the surface area of plastic marine debris; and 3) examine the geographical location and date of capture of longnose lancetfish with ingested plastic in relation to body mass, the amount of plastic, and chloropigment concentrations during the shallow-set longline fishing season. Results indicate that 24% of longnose lancetfish (n=192) ingested various types of plastic marine debris. There is a 95% chance that 19 to 31% of longnose lancetfish in the shallow-set fishery will have ingested plastic marine debris. Plastic fragments were the most frequent type of plastic debris ingested (51.9%). Ropes (21.3%), nets (20.4%), straps (3.7%) and a piece of plastic bag (1.9%) were also present in stomach contents. No relationship existed between the surface area or the amount of plastic debris and the length and weight of longnose lancetfish. Although the longnose lancetfish is not directly consumed by humans, it is common prey for fish species such as bigeye tuna (Thunnus obesus) and swordfish (Xiphias gladius) that are commercially harvested for human consumption. Further research is needed to assess the effects of chemicals associated with plastic marine debris, biomagnification and the potential contamination of the food web.