Leveraging Data From Defunct Gillnet Fisheries to Understand the Distributional Dynamics of a Rare Pelagic Fish, the Louvar (Luvarus imperialis)

The louvar (Luvarus imperialis) is an exceedingly rare circumtropical fish species with a poorly understood ecology. Catch data from defunct drift gillnet fisheries provide an unparalleled way to quantify the distributional dynamics of this species that, as a gelativore, is almost never taken as bycatch on fish- or squid-baited longlines that dominate modern open ocean fisheries. Here, we present the largest observational dataset assembled for louvar, combining > 30 years of observer presence–absence records from two such fisheries spanning a vast expanse of the pelagic North Pacific. We leverage these data to construct a species distribution model that quantifies the species' environmental preferences, enabling us to confront the knowledge gaps on its core distribution and investigate variability among seasons, years, and alternate phases of climate oscillations. We show that this enigmatic species favors waters with positive sea surface height and shallow mixed layer depth, consistent with high, but seasonally variable, model-predicted suitable habitat in the North Pacific Transition Zone and California Current. In addition, our results suggest that louvar have experienced slight loss of habitat from 1990 to 2023 in response to large-scale climate oscillations. This study highlights the value of using a species distribution model framework to synthesize diverse datasets, characterize species–environment relationships, and infer basic spatiotemporal dynamics for rare species that cannot be reliably sampled.