Francesca Ellero

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.

Whale shark aggregations in tropical coastal systems are linked to environmental variability and prey dynamics, yet the drivers of surface sightings remain poorly understood. In Nosy Be, Madagascar, a seasonal aggregation of immature whale sharks occurs within a productive coastal ecosystem. This study investigated the relationship between daily environmental conditions and whale shark surface sighting probability while accounting for heterogeneous sampling effort. Boat-based survey data collected from 2019 to 2025 were aggregated by sampling day, and daily whale shark surface sighting probability was analysed using a bias-reduced grouped binomial Generalized Linear Model. Environmental covariates included sea surface temperature, sea surface chlorophyll-a concentration, cloud cover, wind speed, and precipitation, while El Niño–Southern Oscillation variability was assessed as an interannual climatic descriptor. Using data from 103 recorded whale shark surface sightings, chlorophyll-a emerged as the strongest predictor, showing a positive association with daily sighting probability, whereas other environmental variables exhibited weaker and inconsistent effects. These findings suggest that whale shark surface sightings in Nosy Be are primarily associated with prey aggregation processes driven by local productivity rather than with direct responses to local physical environmental conditions. By integrating environmental variability and sampling effort into ecological models, this study provides insights into whale shark habitat use and supports ecosystem-based management of sustainable whale shark tourism in tropical coastal ecosystems.

Monitoring large elasmobranchs can employ standardized photo-identification protocols to manage diverse and progressively expanding photographic datasets. This study examines the interpretation of performance metrics generated by a dorsal fin–based photo-identification protocol implemented using the semi-automated IDENTIFIN software. The protocol was applied to dorsal fin photographs of bronze whaler shark collected along the South African coast between 2024 and 2025, facilitating the creation of a structured, individual-specific database. Archival photographic data of white shark (2012–2019) served as a methodological reference, providing context for software outputs under different dataset conditions. Analyses focused on the behavior of similarity scores associated with validated matches and on their relationship with image ranking position, a common metric for assessing software performance. Results indicate that similarity scores exhibit comparable distributions across species-specific datasets, supporting their potential use as an operationally complementary metric for interpreting IDENTIFIN outputs. While operator-based visual validation remains essential, this study provides preliminary methodological insights into the interpretation of similarity scores as supportive information within the individual identification process.

The spinner shark is a widely distributed coastal species that faces significant anthropogenic pressures, yet information on its ecology in the western Indian Ocean remains poorly documented. This study provides preliminary baseline observations on temporal occurrence, sex ratio, and size distribution of a bait-attracted spinner shark aggregation in Hulhumale (North Malé Atoll, Maldives) and presents the first individual-level photo-identification (photo-ID) catalogue for the species based on underwater observations. Surveys were conducted in November 2024 and November 2025 using underwater photography, video recordings, and laser photogrammetry. In total, 69 individual spinner sharks were identified using the standard photo-ID protocol which proved to be valid. On the contrary, the preliminary application of the semi-automatic Identifin software indicated possible effectiveness for individual recognition; however, its performance cannot be reliably validated in this area because of poor image quality and environmental turbidity. Six individuals were re-sighted across years, demonstrating the feasibility of non-invasive repeated, long-term monitoring through photo-ID. Although interannual variation in sex ratio of sharks observed was detected (χ² = 10.56, p = 0.0012), this pattern should be interpreted cautiously due to provisioning-related sampling bias and unequal sampling effort across years. Total length measurements (n = 28) indicated predominantly adult and subadult individuals, with no apparent interannual differences in size distributions. Overall, this study establishes a methodological baseline for spinner shark photo-ID in the Maldives and highlights the importance of multi-year and multi-season monitoring to robustly evaluate aggregation dynamics, site fidelity, and population-level patterns in this region.

Nosy Be in the northwestern Madagascar hosts one of the largest known seasonal feeding aggregations of whale sharks. However, the environmental drivers influencing whale shark surface feeding behaviour in this area remain poorly understood. This study investigates the relationship between environmental variability and surface feeding strategies of immature whale sharks at Nosy Be. Boat-based surveys were conducted in November 2018, 2019, 2022, and 2023, resulting in the photo-identification of 88 individuals and the recording of 85 surface feeding events. The influence of environmental factors on feeding behaviour was assessed using multicollinearity among the environmental covariates and three-level step approach: permanova, multinomial logistic regression, marginal effects, and Cochran’s Q, to evaluate whether environmental conditions discriminate feeding-behaviour categories and to quantify how individual covariates relate to behavioural composition under a multi-step framework. Results showed that there is not a strong enough predictive signal for behaviour based on environmental variables; however, thanks to the marginal effects, it is possible to better assess the probability of a certain type of eating behaviour in the presence of an increase in one of the environmental variables, for example, chlorophyll-a appears to be the most interesting, because its increase is associated with a greater probability of some behaviours instead the others. These preliminary observations provide the first insights to evaluate environmental influences on immature whale shark surface feeding behaviour in Nosy Be, highlighting that it is therefore necessary to deepen and increase data collection to have long and significant series of data, integrated also with data on the preys subject to feeding behaviour and to evaluate which other unobserved aspects, perhaps linked precisely to the consistency and quality of the prey, could allow us to predict feeding behaviour. Improving the understanding of these relationships is essential for predicting whale shark habitat use and for supporting conservation and management strategies in a region increasingly affected by climate variability and anthropogenic pressures.