This study evaluated the biodegradability of PBS fishing gear in marine sedimentary environments, which is a major cause of unintended catches caused by discarded fishing gear, known as “ghost fishing”. Based on the biodegradation analysis according to ISO 19679, the PBS fishing gear was converted into carbon dioxide by 27.3% for 180 days. After biodegradation, the remaining PBS exhibited a characteristic molecular weight decrease, indicating bulk erosion, but there was no change in crystallinity and thermal properties. Ultimately, degradation of the PBS proceeded primarily through surface abrasion with metabolic utilization of hydrolysis products by microorganisms. Biological studies showed that the Rhodococcus genus was the dominant microbe for PBS biodegradation. In an accelerated evaluation experiment using a lipase enzyme known to be produced by dominant bacteria, the PBS showed a high biodegradability of 48% in 10 days. From the perspective of biodegradation, biodegradable fishing gear can not only replace existing nondegradable fishing gear but also prevent ghost fishing through biodegradation in the marine sedimentary environment after use.