This study examined the intraspecific, interpopulation, and individual variation of Hippocampus guttulatus and Hippocampus hippocampus within the Tejo and Sado Estuaries and the Ria Formosa Lagoon. Morphometric analyses were conducted using photo identification methods to identify individuals and analyse their morphometrics. Significant differences in height were observed between the Trafaria and Sol Tróia populations of H. guttulatus, particularly in head length and tail length, with Trafaria females showing disproportionately larger measurements. Both H. guttulatus and H. hippocampus individuals from Trafaria exceeded the maximum reported height and standard length values found in the literature. Further analysis is required for H. hippocampus individuals from Sol Tróia to determine their intrapopulation variation, but it is likely to follow a similar pattern. The study found no dispersion between populations for both species, indicating site fidelity within the study areas, and holdfast preferences differ between locations and species. Despite limitations in image number and quality variability between locations, this research provides initial comprehensive analyses of H. guttulatus and H. hippocampus populations in the Tejo and Sado estuaries. It highlights the importance of monitoring population characteristics to determine conservation status and assess the impacts of threats on these species.
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