*2.2. Data Acquisition*

We obtained geographic range data for fish species designated as critically endangered (CR) based on the IUCN Red List integrated with the critically endangered fish species listed by the Hellenic Zoological Society (HZS) Red List (Table 1). The distributional range of CR species have been developed during the conservation status assessment of EU species of conservation concern [18]. Furthermore, we included three additional fish species not yet evaluated since they display extremely restricted distributional ranges in Greece.

**Table 1.** Freshwater fish species of Greece listed as Critically Endangered (CR) under IUCN and/or the HZS Red Lists. Categories: CR, Critically Endangered; EN, Endangered; VU, Vulnerable; LC, Least Concern; and DD, Data Deficient. Transl. in brackets denotes species that are introduced as translocated populations, not the original wild stock. Species with an asterisk are currently presumed extirpated or extinct in Greece.


In total, 25 freshwater fish species were included in our dataset: 19 by IUCN, three species under the HZS Red List (*Barbus pergamonensis, Knipowitschia goerneri, Oxynoemacheilus theophilii*), and three additional species which are not yet formally evaluated (*Caspiomyzon graecus, Eudontomyzon* sp. Almopaios, *Valencia robertae*), displaying however restricted distributional ranges (Table 1). The European eel, *Anguilla anguilla* (L.), a widespread euryhaline fish of marine origin, was excluded from our dataset due to its broad distributional range in the country, considering that this species could confound our analyses.

The geographical distribution of NIFS in Greece was compiled based on data from two different sources: a) a bibliographical survey for lentic ecosystems and b) survey data from standardized field surveys in lotic ecosystems (rivers, streams, canals, and springs) in the framework of various national and local projects. The derived matrix summarized records from 169 lakes, 154 with at least one NIFS and 15 with none, within the Greek territory (Figure 1). Data of fish species in lentic waters—lakes, reservoirs and ponds—were obtained from both field surveys and bibliographical data between the years 2001 and 2020 (107 artificial and 62 natural). Fish sampling data in lotic waters were acquired from research surveys conducted between the years 2001–2017 by the Hellenic Centre for Marine Research (HCMR); these cover the entire mainland as well as the major islands of Greece. Most of the sampled data have been recently published [14,19]. Field samplings were conducted primarily through a standardized electrofishing procedure following the FAME research project guidelines [20] with some modifications; for a detailed description of the sampling procedure see [21]; in some cases seine nets and other methods were also used to ascertain fish presence. In total, 265 lotic sites with at least one NIFS and 366 sites without NIFS in Greece were compiled (Figure 1). Barbieri et al. [17] was used for species taxonomy and nomenclature. Species that are introduced by humans beyond their native freshwater ecoregion, but are native to a part of the country, are designated as translocated species [22]. NIFS include both alien and translocated species in all analyses.

**Figure 1.** Map of Greece indicating the location of lentic (points) and lotic (triangles) ecosystems used in this study. Red symbols indicate locations occupied with NIFS and blue NIFS-free locations.
