Nursehound Scyliorhinus stellaris (Linnaeus, 1758) Egg-Case Encounters and Observable Condition Along the Tuscan Coast, Central Tyrrhenian Sea

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Abstract
Nursehound (Scyliorhinus stellaris) egg cases may be encountered repeatedly at the same locations, complicating the distinction between new deposition and persistence. We documented egg-case encounters and observable condition along the Tuscan coast of the central Tyrrhenian Sea through 71 standardized 45 min SCUBA surveys conducted from 2019 to 2026 across nine coastal areas. In total, 218 egg-case encounters were recorded, all involving cases attached to branches of the red gorgonian (Paramuricea clavata). Of these, 112 were classified as Empty, 20 had a visible embryo, and 86 were classified as ND–biofouling because their internal condition could not be reliably assessed. Environmental count models were not fitted because comparable water temperature and depth measurements were unavailable for surveys in which no egg cases were detected. Exploratory models of egg-case condition in the three most intensively surveyed areas revealed associations that were sensitive to temporal model specification, providing no robust evidence of environmental or seasonal effects. Individual labelling introduced in 2025 enabled nine re-sightings among 137 labelled cases, but insufficient follow-up data prevented estimates of persistence or developmental trajectories. Repeated encounters with unlabelled cases before 2025 could not be excluded. These findings provide a descriptive baseline and highlight the need for standardized environmental measurements, individual identification, and longitudinal monitoring.

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