Unveiling The Invisible Fishery: Advancing Bycatch Management and Sustainability in Papua New Guinea’s Tuna Fisheries

Papua New Guinea's (PNG) purse seine tuna fishery is a major part of the Western and Central Pacific Ocean (WCPO) tuna industry, supporting regional food security, employment, and economic development. Yet bycatch—the incidental capture of non-target organisms—receives considerably less attention than target tuna landings. This study examined bycatch dynamics in PNG's purse seine fishery using observer data from 2014 to 2024. The research quantified dominant bycatch species, tracked temporal trends, compared species composition between Drifting Fish Aggregating Device (Drifting FAD) and Free-School sets, and assessed retention and discard patterns to identify opportunities for sustainable utilization.

Bycatch composition in the fishery is highly uneven. Silky shark (Carcharhinus falciformis) contributed the highest biomass, followed by whale shark (Rhincodon typus), rainbow runner (Elagatis bipinnulata), Bryde's whale (Balaenoptera edeni), false killer whale (Pseudorca crassidens), sei whale (Balaenoptera borealis), and mackerel scad (Decapterus macarellus). Biomass for these species varied considerably across the study period. Several species exhibited peaks in recorded biomass during the late 2010s, followed by lower or relatively stable recorded totals in subsequent years. Annual fluctuations may reflect changes in fishing effort, observer coverage, reporting practices, the spatial distribution of fishing operations, or environmental conditions; these influences were not separately tested.

Recorded bycatch composition differed between the two fishing modes analyzed. Within the two-mode analysis subset, free-school sets accounted for most of the silky shark, whale shark, Bryde's whale, and blue marlin biomass. Rainbow runner and mackerel scad, by contrast, were closely associated with Drifting FAD operations. Retention patterns followed a similar split: Recorded whale shark and cetacean biomass was entirely discarded, whereas nearly all silky shark biomass was discarded (99.76%).

Separate Kruskal–Wallis tests detected differences in the distributions of recorded biomass among years, fishing set categories and species identities. Species identity produced the largest Kruskal–Wallis statistic among three separate group comparisons; this result does not identify a causal driver. This study points to an "invisible fishery" within PNG's offshore sector. Teleost bycatch species like rainbow runner and mackerel scad hold under-recognized potential for food security, local consumption, processing, and aquaculture feed. Most of the recorded biomass for rainbow runner and mackerel scad was discarded in the dataset; the feasibility and safeguards of potential utilization require further assessment.

The findings point to the need for stronger observer monitoring, targeted mitigation strategies, and species-specific data in fisheries policy. The teleost bycatch that makes up this "invisible fishery" deserves more scientific and policy attention. Properly managed, it could support fisheries diversification and long-term resilience in PNG's offshore sector.