A mixed-design passive acoustic array to support Gulf-wide marine mammal science and restoration

Limited understanding of connectivity across the deep Gulf of Mexico has impeded efforts to effectively manage offshore marine mammal populations. In 2020, an international team established a distributed passive acoustic sensor array across the deep water Gulf, combining eight long-term moored stations with four annually relocated short-term stations selected using a space-filling design. This design provides a balance between continuous temporal monitoring at fixed sites and expanded spatial coverage through short-term deployments. Weekly density estimates for eight marine mammal species were analyzed to identify spatial and temporal patterns of occurrence and potential activity hotspots. To evaluate the utility of this mixed monitoring strategy, we applied an information-theoretic approach, quantifying the incremental variance in species density explained by each short-term deployment when integrated into a baseline model using only long-term stations. Preliminary results suggest incorporating short-term stations captures key phenomena—such as rare species occurrences, relationships with transient oceanographic features, and anthropogenic noise impacts—that may be missed by relying on a limited number of long-term stations, particularly in regions influenced by mesoscale processes. Long-term stations provide an essential temporal context for seasonal and interannual variability. This mixed monitoring strategy appears effective for pelagic species in large, dynamic ecosystems like the Gulf of Mexico.