Dynamics of Two Anadromous Species in a Dam Intersected River: Analysis of Two 100-Year Datasets

Abstract

Long-term time-series datasets are key for assessing the population dynamics of fish species with economic interest. This study examines two 100-year datasets for sea lamprey Petromyzon marinus and allis shad Alosa alosa from the Minho River. This basin on the Iberian Peninsula is home to one of the largest populations at the southern distribution limit of these critically endangered anadromous fish species. Besides assessing the importance of the environmental drivers of fish capture data (temperature, salinity, upwelling, precipitation, and climatic oscillation), this study also assesses how dam construction affected these populations using intervention analysis—A statistical tool to detect significant breakpoints in time series data. Results showed contrasting trends between sea lamprey and allis shad, with the number of captured fish from the first progressively improving from 1914 to 2017, and the latter recording a significant decline over time. Although no significant correlations were detected between fishing data and environmental variables, some of the identified breakpoints in the time series data matched the dates when the major dams in Minho River were built. Other historical activities associated with mining might explain the notable changes detected in the trends, while issues associated with illegal, unreported, and unregulated capture data are also discussed.

An Environmental Education and Communication Project on Migratory Fishes and Fishing Communities

“…Diadromous migratory fish species that constitute important fishery resources for local fishing communities and local economies [1,2], face threats from the sea, estuaries, and riverine basins [3,4]. Sea lamprey Petromyzon marinus Linnaeus, 1758 and allis shad, Alosa alosa Linnaeus, 1758 are anadromous fish species that migrate from marine to freshwater habitats to spawn and complete their life cycle [4]. Obstructions to spawning migrations through dams are one of the main threats [3][4][5][6].…”

“…Sea lamprey Petromyzon marinus Linnaeus, 1758 and allis shad, Alosa alosa Linnaeus, 1758 are anadromous fish species that migrate from marine to freshwater habitats to spawn and complete their life cycle [4]. Obstructions to spawning migrations through dams are one of the main threats [3][4][5][6]. In the geographical area of this study-Minho River Estuary (northern coastal of Portugal and Galicia-Spain)-the construction of the major dams in Minho River coincided with a period of sudden decline for allis shad [4,5].…”

“…Obstructions to spawning migrations through dams are one of the main threats [3][4][5][6]. In the geographical area of this study-Minho River Estuary (northern coastal of Portugal and Galicia-Spain)-the construction of the major dams in Minho River coincided with a period of sudden decline for allis shad [4,5].…”