Dan Kerem

Two coastal dolphin species, the common bottlenose dolphin ( Tursiops truncatus —Tt) and the short‐beaked common dolphin ( Delphinus delphis —Dd), co‐occur along the southern Israeli Mediterranean coast, where the critically endangered Dd population faces ecological pressures, potentially including competitive exclusion by that of the Tt population. In this context, reliable acoustic differentiation between the two species is needed to supplement visual differentiation. This study aimed to assess whether species‐specific whistle characteristics could be used to acoustically distinguish between the two taxa using a novel manual contour extraction tool, Sound Annotator, combined with machine learning classification. A total of 940 high‐quality whistles (705 Dd, 235 Tt) from field recordings collected between 2018 and 2024 were available for analysis. Sixteen frequency, temporal, and shape parameters were derived from the extracted contours and analyzed with multiple classification models. Principal component analysis revealed high acoustic overlap, yet the XGBoost classifier effectively classified individual whistles, with minimum, median, and beginning frequency emerging as the most informative features. This framework facilitates non‐invasive, species‐specific monitoring of dolphin populations in challenging visual conditions, particularly at night, providing a foundation for conservation‐focused acoustic monitoring in the eastern Mediterranean.

Jellyfish (cnidarians and ctenophores) affect the marine food web through high feeding rates and feeding efficiency, but in contrast to their great importance in the ecosystem, our knowledge of their dietary requirements is limited. Here we present the results of respiratory and feeding trials of the rhizostome Rhopilema nomadica, the dominant scyphozoan in the waters of the Eastern Mediterranean, which often establishes massive swarms, mainly in the summer months. Through multiple measurements of oxygen demand in R. nomadica at bell diameters of 3–49 mm, we were able to assess its minimum energetic requirements. These, and the results of the feeding trials on individuals of the same bell diameter range, show that R. nomadica is a very efficient predator. When presented with prey concentrations of 100 prey items per liter, a single hourly feeding session provided between 1.15 and 3 times the estimated daily basal carbon requirement. Our findings suggest that R. nomadica is well adapted to its environment, the hyperoligotrophic waters of the eastern Mediterranean, able to efficiently exploit patches of plankton, possibly at rates even higher than what we observed under laboratory conditions.

During the last decade, the common dolphin (Delphinus delphis) has become the second most sighted species in Israeli coastal waters, after the common bottlenose dolphin. Documentation mostly relies on opportunistic, photo and/or video‐backed second‐party reports, delimited within a 10 km near‐shore strip. Sightings occur year round, are confined to the southern part of the Israeli coast and typically comprise relatively large groups (mean ± SD: 21.5 ± 13.3), often with young calves. Strandings are relatively scarce, typically one per year, and have so far yielded five upper digestive tract contents for diet analysis. Cephalopods comprised 1.2% of the estimated number of prey items in the combined content. Surprisingly, by far the most abundant and prevalent prey item found (57% of pooled prey items; present and dominant in four out of five tracts) was the Balearic eel (Ariosoma balearicum), a sand burrower which is also a major dietary component of the common bottlenose dolphins. Bottlenose dolphins in Israel are known to forage in association with bottom trawlers, leading to the notion that common dolphins also make use of this foraging mode. Indeed, in addition to their association with purse seiners, they have been documented accompanying bottom trawlers, by both day and night. The slender Balearic eels are frequently found protruding from the net's eyes, presumably making easy prey for both dolphin species. Information gaps on common dolphins include range extension to the south/south-west, abundance estimation and genetic flow/isolation. Even so, its unusual diet and the fact that the closest known populations to the north/north-west are from the Aegean Sea, were major considerations in the recent designation of the ‘Coastal Shelf Waters of the South-east Levantine Sea’ as a Mediterranean Important Marine Mammal Area.

Heterogeneous data collection in the marine environment has led to large gaps in our knowledge of marine species distributions. To fill these gaps, models calibrated on existing data may be used to predict species distributions in unsampled areas, given that available data are sufficiently representative. Our objective was to evaluate the feasibility of mapping cetacean densities across the entire Mediterranean Sea using models calibrated on available survey data and various environmental covariates. We aggregated 302,481 km of line transect survey effort conducted in the Mediterranean Sea within the past 20 years by many organisations. Survey coverage was highly heterogeneous geographically and seasonally: large data gaps were present in the eastern and southern Mediterranean and in non-summer months. We mapped the extent of interpolationversusextrapolation and the proportion of data nearby in environmental space when models calibrated on existing survey data were used for prediction across the entire Mediterranean Sea. Using model predictions to map cetacean densities in the eastern and southern Mediterranean, characterised by warmer, less productive waters, and more intense eddy activity, would lead to potentially unreliable extrapolations. We stress the need for systematic surveys of cetaceans in these environmentally unique Mediterranean waters, particularly in non-summer months.