Hydrological connectivity drives longitudinal movement of endangered endemic Chilean darter Percilia irwini (Eigenmann, 1927)

Movement is a fundamental aspect of fish ecology and it therefore represents an important trait to monitor for the management and conservation of fish populations. This is especially true for small benthic fish, as they often inhabit part of the catchment where their movement may be restricted by river connectivity alteration due to human activity. Still, movement of these small benthic fish remain poorly understood, partly because of their small size and their cryptic nature. This applies to Percilia irwini, an endangered small darter native to the south-central region of Chile. Its habitat has been affected by the presence of large hydroelectric dams, and is currently threatened by the construction of several others. In this study, we investigated movement patterns of P. irwini from populations inhabiting different parts of the Biobio catchment, with different level of connectivity due to natural and/or human-induced features. We combined chronological clustering along with random forest classification in order to reconstruct life-long movements from multi-elemental otolith microchemistry transects. The majority of the movement detected were in an undisturbed part of the catchment. These were directional upstream movements occurring between capture sites from the lower and the middle reach of the river, representing a distance of nearly 30 km, a distance much larger than previously thought. However, in part of the catchment were connectivity has been affected by human activity, no such movements were identified. This study shows that connectivity alteration could impede naturally occurring movement and further threat the resilience of populations of P. irwini. Furthermore, the results presented are used to discuss advantages and limitations of microchemistry analysis for studying movement of small benthic fish. This article is protected by copyright. All rights reserved.