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Pedro Ramiro Castillo Valderrama^1*Luis La Cruz²Carlos Valdez¹Gustavo Cuadros¹Daniel Grados¹Ketty Ferrel¹Marissela Pozada-Herrera¹Rodolfo Cornejo¹Aníbal Aliaga¹

• ¹Institute of the Sea of ​​Peru (IMARPE), Callao, Peru
• ²Instituto de Fomento Pesquero (IFOP), Valparaíso, Chile

The squat lobster, or munida (Pleuroncodes monodon), is the second most abundant species in the coastal zone of the Peruvian Current. Due to its high incidence of occurrence and biomass, it has been monitored by IMARPE through the "Hydroacoustic Assessment Surveys for Anchoveta and Other Pelagic Resources" since 1998. This study analyzes 59 surveys conducted between 1998 and 2024 to assess its spatial distribution, abundance, and ecological relationship with anchoveta (Engraulis ringens). The results showed that between 1998 and 2000, munida expanded its distribution range northward along the Peruvian coast. From 2001 onward, its distribution remained relatively stable. A clear seasonal pattern was observed: during winter and spring, both its spatial distribution area and inertia increased, and the species tended to occur farther from the coast. In contrast, during summer and autumn, the distribution contracted, except during anomalous oceanographic events (e.g., warm or cold conditions), which induced latitudinal and longitudinal displacements. Vertically, munida typically inhabits the surface layer down to approximately 168 meters. However, during the 2015–2016 El Niño event, it was recorded at depths reaching 203 meters. The average biomass throughout the study period was approximately 2.04 million tons, with a peak of 5.38 million tons observed during survey 1703-04. Munida is also the species most closely associated with anchoveta. When both species co-occur, their interaction varies depending on the time of day, likely reflecting diel vertical migration and differential aggregation behaviors.