Ecological and behavioural traits of the rusty blenny Parablennius sanguinolentus (Pallas, 1814) (Actinopterygii: Blenniidae) in the coastal zone of the Kerch Strait (Kerch Peninsula)

For the first time, a comprehensive study of the ecological traits of the rusty blenny Parablennius sanguinolentus (Pallas, 1814) has been conducted in the waters of the Kerch Strait. The study included an analysis of the size–age structure of the mature portion of the population, as well as feeding habits and behavioural characteristics.
Sampling was carried out in the western Kerch Strait (2021–2025, April–November) at four sites (Southwest of Cape Fonar, Kamysh-Burunskaya Bay, South of Geroevskoye, Cape Takil – Pechki tract). Fish were caught with hook‑and‑line gear on hard substrates. Standard biological analysis (Pravdin, 1966) of 120 specimens included length and weight measurements. The length–weight relationship was described by the equation (Ricker, 1979). Sex‑related differences in SL were tested with the Mann–Whitney U‑test (α = 0.05). Diet (n = 107 guts) was quantified by frequency of occurrence. Underwater visual censuses with photo‑video recording were used for behavioural observations. Abundance estimates followed Feitoza et al. (2003) with modifications.
Based on the examination of 120 specimens, it was established that individuals of 2–3 years of age predominated in the sample, with the modal group comprising fish of 9.5–10.0 cm standard length in males and 8.5–9.5 cm in females. The sizes of males and females in the sample differed only slightly: the Mann–Whitney U-test revealed no statistically significant differences (U = 1493, p = 0.128). On average, females measured 10.3 ± 0.32 cm (range 6.9–15.6 cm) and weighed 34.3 ± 3.90 g (range 7.6–108.9 g). Males ranged from 7.9 to 15.6 cm in length (mean 10.3 ± 0.22 cm) and from 11.2 to 100.4 g in weight (mean 30.9 ± 2.58 g).
Relatively high values of the regression coefficient in the length–weight relationship (exceeding 3.3) were obtained, which may indicate favourable growth conditions and high food availability in the Kerch Strait.
Dietary analysis revealed a predominance of plant components in the species' diet. Among green algae, representatives of the genera Cladophora, Ulva, and Bryopsis were recorded in the digestive tracts of the examined specimens; among red algae, Ceramium and Vertebrata; brown algae were represented by the genus Cystoseira. Zoobenthic organisms, represented by crustaceans and bivalve molluscs, were of secondary importance in the diet of P. sanguinolentus.
Behavioural observations indicated that the species is not strictly benthic; instead, it undertakes movements within the water–substrate contact zone, which allows it to exploit extensive areas of the coastal fringe.