In the new issue of the journal Acta Adriatica, published by our Institute, special attention should be given to a review paper that makes a significant scientific contribution to understanding the difference between true rarity and elusiveness in marine fishes.
The author of this paper, Dr Marcelo Kovačić, senior curator at the Natural History Museum Rijeka, is one of the foremost Croatian ichthyologists and an internationally recognised scientist in the systematics and biogeography of marine fishes, with a particular focus on gobioid fishes. Through his involvement in the description and naming of several dozen new species, he has made a lasting contribution to global taxonomy.
In ichthyological terms, rarity refers to a genuinely low number of individuals or a narrow geographic distribution, whereas elusiveness denotes a low number of published records or detections with reliable identification, rather than true biological scarcity. To distinguish between these phenomena, Dr Kovačić conducted a systematic review of published records of Mediterranean gobies (Gobiidae and Oxudercidae) and applied quantitative criteria based on the number of publications, localities, and recorded individuals, using clearly defined spatial boundaries and explicit rules for data acceptance.
The application of these criteria showed that many gobioid species are not truly rare, but have historically been considered so because they are elusive and infrequently recorded. Of the 64 native Mediterranean species analysed, 25 meet at least one criterion of elusiveness, while a further 13 species previously regarded as rare are now being recorded more frequently. These species are concentrated in the northern and eastern Mediterranean, primarily in areas with the highest research effort. They are almost exclusively very small coastal fishes, with no clear association with a particular substrate type or depth.
The review emphasises that true rarity is a genuine biological property of a species, often linked to an increased risk of extinction, whereas elusiveness primarily reflects gaps in data and limited knowledge. Dr Kovačić therefore warns that confusing elusiveness with rarity can lead to unclear or incorrect assessments of conservation status and highlights the need for systematic, quantitative syntheses of occurrence data and research approaches that increase the number of reliable records, such as extensive field surveys and collaborative, synthetic studies.
Sometimes the sea does not lack life, but knowledge. Many fishes that are considered rare are not rare because their populations are small, but because they are small-bodied, cryptic, or outside the focus of conventional research methods. Distinguishing true rarity from elusiveness is therefore not a marginal issue, but a fundamental requirement for understanding how marine ecosystems function and how they can be protected responsibly.
