The incidental capture of seahorses by fishing trawlers along three different coastlines in the Gulf of Thailand was investigated from July to November, 2014. Two seahorse species, Hippocampus spinosissimus and H. trimaculatus, were commonly found during the surveys. Higher proportions of H. spinosissimus than H. trimaculatus were found in both the eastern and southern coasts, whereas H. trimaculatus were found in a higher proportion in the central coast. Biological parameters for both species, including their size, dry weight, and reproductive state were significantly different spatially, but the sex ratio was not different as a whole. The most prevalent size classes H. spinosissimus in the southern coast were larger than those in the eastern and central coasts. For H. trimaculatus, the most prevalent size classes in the central coast were the largest. The findings of this study provide the basic information for future fishery management in the Gulf of Thailand.
