In FunkyFish we will investigate suitable habitats for fish populations that spawn in hydropower reservoirs and suggest a sampling protocol for how to map such recruitment habitats in a cost-efficient manner. Traditionally, when fish populations in reservoirs are negatively affected by hydropower production, stocking with juvenile fish from hatchery facilities has been used to compensate for reduced fish biomass. However, according to modern guidelines in Norway, stocking is only to be used when natural fish recruitment is permanently lost. If not lost, environmental legislation requires that habitat measures that support natural reproduction should be implemented. It is, however, often difficult to evaluate whether lack of suitable recruitment habitat is the limiting factor for the fish recruitment, or if other issues like lack of food or increased competition is the reason for reduced fish biomass. The main reason for this is that identifying spawning sites may be logistically challenging, particularly in deeper lake areas. Given the high number and often large sizes of Norwegian hydropower reservoirs, it is not realistically possible for hydropower companies to perform detailed habitat mapping in all reservoirs. Therefore, FunkyFish aims to develop a better system for identifying recruitment habitats in reservoirs. In the project, we will focus on brown trout and Arctic char, the two most commonly occurring fish species in Norwegian reservoirs. We will study several case reservoirs in detail and use different field methods to map habitat qualities and fish habitat use, to identify which field methods are most efficient. Based on this, we will create a sampling protocol that can aid power producers and environmental managers in mapping recruitment habitats in hydropower reservoirs. Moreover, we will suggest potential habitat measures that can improve fish recruitment.
FunkyFish will provide new knowledge that facilitates balancing biodiversity protection in hydropower reservoirs with flexible energy production. Self-reproducing fish populations are a basic requirement for a functioning freshwater ecosystem. However, the knowledge of habitat requirements of fishes spawning in reservoirs is limited. Fish stocking has been used as a mitigation measure in Norwegian reservoirs for decades, aiming to compensate for lack of natural fish recruitment caused by hydropower impacts. Today stocking is only used when natural fish recruitment has been permanently lost, as the primary aim is to implement habitat improvement measures to support natural reproduction. However, evaluating whether lack of suitable recruitment habitat is a bottleneck for the fish population is often difficult, because identifying spawning sites may be logistically challenging, particularly in deeper areas. Given the high number and often large size of Norwegian hydropower reservoirs, it is not realistic that hydropower companies are able to perform detailed habitat mapping in all reservoirs. Therefore, FunkyFish aims to develop a cost-effective sampling protocol to identify recruitment habitats in reservoirs. Past studies of reservoir spawning have largely been limited to mapping of already known or assumed spawning areas. However, through detailed field work in several case reservoirs where we will use several complementary methods to collect both physico-chemical and biological parameters, we aim to create a sampling protocol that can be used to also identify unknown spawning habitats in a cost-efficient way. This is strongly needed by the scientific community, environmental managers, and hydropower companies, as little is known about the early life stages of reservoir fishes.