Hydrological connectivity drives longitudinal movement of endangered endemicChileandarterPercilia 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 alterations to river connectivity due to human activity. Still, the movement of these small benthic fish remains poorly understood, partly because of their small size and their cryptic nature. This applies toPercilia 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, the authors investigated movement patterns ofP. irwinifrom populations inhabiting different parts of the Biobio catchment, with different levels of connectivity due to natural and/or human-induced features. The authors combined chronological clustering with random forest classification to reconstruct lifelong movements from multi-elemental otolith microchemistry transects. The majority of the movements detected occurred in an undisturbed part of the catchment. These were directional upstream movements occurring between capture sites from the lower and the middle reaches of the river, representing a distance of nearly 30 km, a distance much larger than previously thought. Nonetheless, in the part of the catchment where connectivity was affected by human activity, no such movements were identified. This study shows that connectivity alteration could impede naturally occurring movement and further threaten the resilience of populations ofP. irwini. Furthermore, the results presented are used to discuss advantages and disadvantages of microchemistry analysis for studying movement of small benthic fish.

Automated summary

The movement of small benthic fish, specifically the endangered small darter Percilia irwini in south-central Chile, is crucial for its management and conservation. Research shows that most movements occur in undisturbed parts of the catchment, with longer distances than previously thought, but no movements were identified in areas with altered connectivity due to human activity. This suggests that connectivity alteration may obstruct natural movement and further threaten populations' resilience. The study also discusses the use of microchemistry analysis for studying small benthic fish movement.