Global and European regional assessment: Endangered (EN)
EU 27 regional assessment: Endangered (EN)

The Dalmatian Nase is endemic to the Neretva River system in Bosnia and Herzegovina and Croatia, and has a restricted range (extent of occurrence (EOO) c. 2,346 km², EU 27 Member States 203 km²), which meets the threshold for Endangered under Criterion B1 (EOO < 5,000 km²). It is present at two locations where the extent and quality of habitat are estimated to be declining due to a range of threats, including the construction of hydroelectric dams. Therefore, this species is assessed as Endangered under Criterion B (B1ab(iii)), both globally and for the EU 27 Member States.

This species is endemic to the Neretva River system in the Dinaric Karst region of southern Croatia and Bosnia and Herzegovina. It is present in the Neretva main stem and tributaries from the river's delta upstream to the Buna River, including the Baćina and Desansko lake basins, Vrgorsko polje (Vrgorska Matica River), the Crna Rijeka, Norin, Trebižat, Bregava and Krupa rivers, and the Hutovo Blato wetland. It has not been recorded from Imotsko polje in the upper Trebižat River.

It may have formerly occurred further upstream in the Neretva, prior to damming of the river's middle reaches (see 'Threats').

This species' current population size and trend have not been quantified, and the number of subpopulations is unknown. Field observations suggest that abundance has declined sharply since the turn of the century, but confirmation is required.

This species inhabits perennial karstic rivers and associated lakes, sinkholes and springs. Some of these habitats are located in poljes, which comprise depressed, flat, flood-prone plains enclosed by limestone ridges.

Little is known of its ecology, but it is likely to feed on periphyton and benthic invertebrates.

It undertakes annual spawning migrations into affluent rivers and streams between December and March. A series of karstic springs draining to Hutovo Blato are understood to comprise the most important spawning site, and juveniles utilise the wetland itself plus some associated canals as nursery zones.

This species is plausibly threatened by river regulation and other forms of anthropogenic habitat degradation. In particular, construction of four large hydroelectric dams along the middle section of the Neretva River main stem since the 1950s has altered natural flow and sedimentation regimes, and potentially blocked migration routes and markedly reduced the extent and quality of habitat for all life stages. The scale of annual flooding in the Hutovo Blato wetland has declined significantly due to reduced discharge of the Neretva and some affluent springs such as Čapljina, which is also exploited for hydropower generation. The southern part of the wetland was partially impounded in 1979, and a proposed plan to divert water from Hutovo Blato for domestic use may further reduce habitat quality. The Dalmatian Nase now regularly fails to spawn in the majority of springs around Hutovo Blato, but is observed to return in years when spring flooding conditions resemble the former natural situation.

Hydroelectric dams also create unnatural fluctuations in discharge and water temperature (hydropeaking) which bring about artificial dewatering of downstream river stretches and loss of stable nursery habitat for juveniles. Furthermore, the combined effect of hydropeaking, dam flushing operations and changes in land use is likely to have increased accumulation of fine sediments and negatively impacted foraging and reproductive success at some locations. The proposed construction of around 70 additional hydroelectric projects in the upper reaches of the river, plus an ongoing expansion scheme in the adjacent Trebišnjica River catchment (see below) together represent a plausible future threat to the entire Neretva ecosystem.

The extent and quality of habitat in the Neretva catchment has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or exploit water resources for irrigated agriculture. In the river's delta, only three of its original twelve branches remain and most former marshes and lakes have been reclaimed for agriculture since the 1960s.

Diffuse and point source agricultural, domestic and industrial pollution has resulted in eutrophication or discharge of toxic substances at some locations. For example, a number of springs in the Hutovo Blato basin are typically clogged with macrophytes due to increased nutrient loads caused by runoff from surrounding agricultural land. This has not only reduced the flow required for successful spawning but decreased dissolved oxygen as plant material decomposes.

The industrial extraction of riverine gravel and other sediments for urban development has taken place in the Neretva main stem since the 1970s, causing the river bed to become deeper in places and hampering the transport of heavy sediments.

Overharvesting during the annual reproductive period may also represent a threat, but few precise details regarding offtake are available.

A number of non-native fish species that are documented to exert negative effects on native ichthyofauna through predation, resource competition or habitat degradation are established within this species' range, including Eurasian Pikeperch (Sander lucioperca), Pumpkinseed (Lepomis gibbosus), Largemouth Bass (Micropterus salmoides), Eurasian Ruffe (Gymnocephalus cernua), Prussian Carp (Carassius gibelio), Common Carp (Cyprinus domestic strain), Topmouth Gudgeon (Pseudorasbora parva), Brown Bullhead (Ameiurus nebulosus) and Rainbow Trout (Oncorhynchus mykiss).

Future threats involve the channelling and pumping of water from isolated poljes (karstic plateaus) draining to the Buna and Bregava rivers in the lower Neretva catchment to an accumulation reservoir in the Trebišnjica River, within the framework of the ongoing (2023) "Upper Horizons" hydropower strategy. Once complete, the scheme is projected to significantly reduce discharge in the lower Neretva, with a range of negative impacts on Hutovo Blato and the river's delta region.

This species is harvested at the local scale, especially during the annual reproductive period when the ovaries of ripe females are particularly valued. The level of offtake is currently unclear.

This species is included in Annex III of the Bern Convention (misspelled as Chondrostoma kneri) and Annex II of the European Union Habitats Directive.

It is protected at the regional scale in the Federation of Bosnia and Herzegovina, and is currently assessed as Endangered for the National Red List of Croatia.

No specific conservation management plan exists, but parts of this species' range are located within protected areas. Among these, Hutovo Blato and the Neretva Delta are included in the Ramsar Convention on Wetlands, and a few sites are listed in the European Union's Natura 2000 network. A new, ostensibly more sustainable, management policy was implemented in the Hutovo Blato basin following a European Union co-funded LIFE project which ran from 2000-2002.

The proposed hydropower developments in the Neretva and Trebišnjica rivers have been opposed by local communities and several NGOs, leading to the publication of various news articles, reports, research projects and dissemination events, e.g., Neretva Science Week (July 2022).

A deeper understanding of this species' population trend, abundance, distribution and life history would likely prove useful in the establishment of future management efforts and priority conservation areas. The latter should ideally include the most important spawning sites in the Hutovo Blato wetland, which are strongly recommended for official protection and restoration activities.