Long-Term Dynamics of the Northern Humboldt Current System Pelagic Fish Community: A Look Into Community Shifts

Abstract

The northern Humboldt Current System (nHCS) has high environmental variability that impacts key demographic and community-scale processes. Understanding the role and ecological implications of these interannual or long-term events is crucial in describing the dynamics of the nHCS community. Using catch data from pelagic assessment surveys from 1983 to 2019 and the community trajectory analysis framework, we tested and characterised the patterns and compositional dynamics of the nHCS pelagic fish community over space and time. Spatially, changes were evaluated for ecological regions with similar community composition. We found that the community has experienced constant interannual variability consistent with the long-term warm and cold periods previously identified in the system. Two shifts in 1990 and 2001 were identified and associated with a change in the average oceanographic conditions in the system. Coastal fish species dominated the community after 2001, while oceanic and tropical species were more abundant before 1990. We found lower and higher interannual variability for the coastal and oceanic areas, respectively. Moreover, the coastal area reported a higher change in the community structure from 1983 to 2019. Temperature and oxygen were two oceanographic variables significantly associated with the main changes in the community, finding that warmer and less oxygenated years lead to higher diversity. This study helps to understand the magnitude, direction, and mechanisms involved in the long-term changes of the nHCS pelagic fish community.