Influence of Environmental Parameters on the Abundance of Tub Gurnard, Chelidonichthys lucerna, in the Eastern Sea of Marmara

Tub gurnard, Chelidonichthys lucerna, is a common and widely distributed species throughout the Sea of Marmara (SoM). The knowledge on the spatial distribution of tub gurnards in the SoM in association with environmental factors is limited. The relationship between tub gurnard abundance and environmental variables (depth, temperature, dissolved oxygen, pH, and spatial variability) in the eastern Sea of Marmara (ESoM) was analyzed by means of the generalized additive model (GAM) in the present study. Additionally, the size distribution of tub gurnards was examined in relation to depth and season. Data were collected over an 11-year sampling period (2014–2024) within the scope of scientific demersal trawl surveys in the ESoM. The GAM results revealed that while all the analyzed variables influenced the spatial distribution patterns of tub gurnards, temperature and depth were the most significant contributors in the ESoM. The abundance of tub gurnard exhibited a strongly nonlinear relationship with the explanatory covariates. Regarding the depth distribution patterns of tub gurnards in association with fish size, statistical tests showed significant differences between the size frequency distributions in the two depth ranges, of which the mean total lengths were 24.1 ± 6.90 and 23.5 ± 4.27 cm for depths >80 and <80 m, respectively. A preferred depth was obviously expressed, with tub gurnards moving into deeper water as they grew larger. The mean sizes (range) were 23.56 ± 6.92 cm (13.1–69.6 cm), 24.8 ± 5.35 cm (17.1–58.5 cm), 24.9 ± 8.14 cm (13.1–56.5 cm), and 23.0 ± 5.22 cm (14.2–46 cm) for winter, spring, summer, and autumn, respectively. Therefore, the observed distribution patterns highlight the influence of environmental factors on the abundance of tub gurnard species.