Frontiers in Marine Science (Dec 2015)
Evaluating a vertical slot fishway in the recolonization of upstream stretch of River Mondego that was not available to sea lamprey
Abstract
In 2011, the construction of a vertical slot fishway at the Açude-Ponte dam in Coimbra, has allowed the migration of adult sea lampreys (Petromyzon marinus L.) to important upstream spawning areas that were unreachable for the last 30 years. In the present study, conventional radio and sensor (electromyogram) telemetry was used to evaluate the migratory behavior of 24 adult sea lampreys before, during and after fishway transposition. Data obtained from tracking campaigns was related with sea lamprey larvae (ammocoetes) relative abundance assessed annually with electrofishing at 34 sampling stations distributed along the River Mondego and main tributaries. Electrofishing surveys were performed during fishway pre (2011) and post-operational periods (2012-2014). In 2013, 30% of the radio-tagged sea lampreys surpassed the Açude-Ponte, taking a median time of 11 days since they first encounter the obstacle. Lampreys tagged with electromyogram transmitters took approximately 3 hours to complete the passage and during this period their critical swimming speed was exceeded for about 1% of the total transposition time, confirming the hydraulic suitability of the fishway for this particular species. The fishway efficiency resulted in a significant increases of ammocoetes on the upstream areas, with the species presence increasing in 15% of the sampling stations and abundances growing 8 times in the downstream stretch and 10 times in the upstream areas, between 2011 and 2014. By 2014, most of the ammocoetes captured upstream the Açude-Ponte dam belonged to the 0+, 1+ and 2+ age classes, and the high abundance of larvae observed in some sampling sites located in River Ceira confirms the importance of upstream tributaries for sea lamprey spawning and ammocoete beds. This information clearly shows that the fishway is contributing to an improvement of the longitudinal connectivity in River Mondego and to an increase in the available habitat for sea lamprey.
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