Identifying barriers to save endemic trout in the Neretva River

A project aimed at identifying and prioritising in-stream barriers for removal to safeguard the endangered endemic trout in the Neretva River, providing a crucial lifeline for their survival.

Introduction

This project will concentrate on the Middle and Lower Neretva Valley, spanning from the Jablanica reservoir downstream. This initiative aims to compile an inventory of outdated concrete obstacles and barriers in the Middle and Lower Neretva Valley. The inventory will include location, height, width, photos, GIS mapping, and potential environmental and social risk identification. The project will then generate a list of barriers slated for removal, prioritising those with the most significant environmental impact while ensuring benefits to local communities.

The project targets the following rivers within its scope:

  • Doljanka: 18 kilometres long, with a watershed area of 69 km². Tributaries include Bijeli potok, Trn, Loznik, and Cvitan. The Doljanka spring is at 1,324 meters above sea level, with an estuary at 300 m.a.s.l.
  • Neretvica: 27 kilometres long, with tributaries including Otunski potok, Prolaz, Obaščica, Mala Neretvica, Zagrejčica, Gornji Čažanj, Donji Čažanj, Zagrejčica, and Gorovnik. The Neretvica spring is at 1,510 m.a.s.l.
  • Drežanka: 21 kilometres long, with a watershed area of 146 km². Tributaries include Meomača, Ledenica, Tisno, and Ždilac. The Drežanka spring is at 485 meters above sea level, with an estuary at 112 m.a.s.l.
  • Buna: 9 kilometres long, with two tributaries: Posrt and Bunica. The average capacity of the Buna spring is one of the greatest in Europe (43 m3/s).
  • Bunica: 6 kilometres long, featuring a 70-meter-deep spring—one of the deepest springs in Europe.
  • Bregava: 31 kilometres long, with a watershed area of 722.4 km². Radimlja is a tributary of Bregava.
  • Krupa: 9 kilometres long, with its own watershed of 74 km².
  • Trebižat: Neretva’s last and largest tributary spans 51.3 kilometres with a watershed of 646 km². Trebižat is a classical karst river, exhibiting a sink-and-surface flow phenomenon that gives it nine different names.

At a glance

Project typeBarrier identification and prioritisation
Project statusLive
CountryBosnia and Herzegovina
RiverNeretva and tributaries
Focal speciesSoft-mouth trout, marble trout and dentex trout
Project websitehttps://bit.ly/3QjeGut

Project context and opportunity

Until recently, the Neretva River boasted a diverse population of endemic trout species, including the endangered soft-mouth, marble, and dentex trout. However, the construction of dams in the main Neretva course has led to the fragmentation of these trout populations into several sub-populations, pushing them to the brink of extinction. It is estimated that only 12% of the historical trout population remains within the Neretva River Basin.

The dams’ construction forced the endemic trout to relocate to the tributaries and smaller streams within the catchment. Unfortunately, numerous obsolete obstacles in these smaller waterways further divide the populations. To stabilise and revive the endemic trout population in Neretva, the project’s primary conservation goal is to create space and ensure connectivity for the fish in the smaller streams and tributaries.

In addition to habitat fragmentation, the construction and operation of hydropower infrastructures in the Middle Neretva have impeded sediment transport to the Neretva Delta, resulting in an alluvial deficit and a sinking riverbed. Three decades after the last dam’s construction, the riverbed in the Neretva delta has deepened by 1.5 meters, significantly altering freshwater habitats. This has further fragmented the populations of endemic trout into several sub-populations facing extinction threats, as the dams have altered major flows and tributaries into various ecosystems.

The largest water areas and volumes are now confined to artificial reservoirs dominated by introduced species. Remnants of endemic trout can still be found in most reservoirs, but successful reproduction and juvenile recruitment are lacking. The remnants persist in deeper and colder areas, but migration in the lower and upper parts of the major watercourse to potential historical spawning grounds is hindered. While tributaries of Neretva reservoirs have the potential to serve as novel spawning grounds, various obstacles prevent successful spawning.

The local stock, once a commercial resource with an annual catch of 250 tons, has been impacted by dam construction in the middle course of the Neretva River, obstructing the upstream and downstream migration of the European eel. The Trebišnjica Hydropower Plants’ impact has reduced the European Eel population in Hutovo Blato wetland to a mere 1% of the historical biomass. The project aims to enhance the upstream migration of glass eel and the downstream migration of adult specimens, contributing to the conservation of this vital species.

Project aims

Local NGOs and volunteers will play a crucial role in the initial field research, providing valuable information about the location of barriers and obstacles along the 200-kilometre river network. The project’s expert team will conduct thorough field research following this preliminary research. In addition to barrier inventory, the team will perform ichthyology analysis to assess the impact of barrier removal on endemic fish spawning grounds. Hydrological data and the effects of barrier removal on sediment transport will also be analysed.

Communication activities are designed to mobilize local NGOs and exert additional pressure on local authorities. Media communication and PR materials will be consistently published, accompanied by other proven effective tools such as billboards, posters, and leaflets.

Direct engagement with local communities, cantonal and federal governments, and the water management agency overseeing the Neretva basin is a key aspect of the project. One round table and five meetings with relevant stakeholders will be organized to include all parties from the project’s inception. The project will develop a social impact study, analyzing and monitoring the social effects of planned barrier removal, ownership structure, and barrier usage by local communities.

This project represents the last opportunity to save the endemic trout species of Neretva. Introducing an innovative and unique solution never applied in the Balkans before, the project addresses a long-standing issue dating back to the construction of the first hydropower plant on Neretva, Jablanica, in 1947. Despite millions of euros in annual investments in the introduction of endemic trout, the situation has worsened. Today, these species are on the brink of extinction. Fish passages on high dams would not improve the situation, as each dam is associated with a large eutrophic reservoir unsuitable for trout thriving.

Partners