Trends in summer presence of fin whales in the Western Mediterranean Sea Region: new insights from a long-term monitoring program

Phytoplankton spring bloom in the NW Mediterranean Sea under climate change

The spring phytoplankton bloom is the main event influencing ecosystem richness in the pelagic realm of the Northwestern Mediterranean Sea (NW Med Sea). The Marine Strategy Framework Directive requires the achievement of a good ecological status for the pelagic habitat, and phytoplankton bloom phenology has been used as an indicator of the status of offshore waters. In this work we investigate interannual changes in the timing and magnitude of the phytoplankton bloom in the NW Med Sea, using phenological metrics. Daily maps of Chl-a concentration from 1998 to 2022 obtained by CMEMS were used to analyse bloom phenological metrics in 5 representative sites in the area. Chlorophyll-a data from 1998 to 2007 were used for determining the climatological behaviour, while 2008-2022 was identified as the study period. For this latter period, yearly spring bloom were identified and interannual variability and overall trends were analysed for each of the phenological metrics considered. Winter oceanographic and meteorological data were analysed to investigate possible correlations with the subsequent spring bloom. The frequency of anomalous years is increasing, both for bloom intensity and sea temperature. Bloom analysis revealed a negative trend only in some areas, but a steep decrease in the last 7 years was noticeable for all sites considered. Correlations of the Chl-a concentration during bloom with oceanographic variables revealed the importance of temperature, both marine and atmospheric, while Mixed Layer Depth played a lesser role. This work contributes to a better understanding of the dynamics of an area already under severe threat from human activities.

Encounter rate and relative abundance of eight cetaceans off the central Catalan coast (Northwestern Mediterranean sea)

This study provides information on cetacean occurrence in the central Catalan coast (NE Iberian Peninsula), an area characterised by an underwater canyon system. Encounter rates (ER), relative abundances (RA) and seasonality were assessed for eight species. This information was combined with physiographic features of the seafloor to understand their influence on cetacean distribution. Data were collected along 189 surveys from January 2017 to December 2022. In total, 479 sightings of eight species of cetaceans were recorded. Striped, bottlenose and Risso's dolphins and fin whales were the most frequently sighted. ER and RA were similar or higher than in other areas of the Mediterranean Sea. Species were distributed differently according to physiographic features: bottlenose dolphins in coastal waters and Risso's dolphins and fin whales above the Garraf underwater canyon system. These results highlight the importance of the central Catalan coast, particularly the underwater canyon system, for at least four species of cetaceans.

MONICET: The Azores whale watching contribution to cetacean monitoring

Background

The Azores islands have been historically linked to cetaceans, becoming an example of a successful transition from whaling to whale watching. Twenty-eight cetacean species have been sighted in these waters, making the archipelago one of the most recognised whale and dolphin watching destinations worldwide. The business is well-established in the region, operates in four of the nine islands year-round or seasonally and provides an excellent opportunity to collect long term information on cetacean distribution and abundance in an affordable way. Continuous monitoring is indeed essential to establish baseline knowledge and to evaluate cetacean response to potential natural or anthropogenic impacts. Opportunistic data greatly complement traditional dedicated surveys, providing additional support for appropriate management plans.

New information

The MONICET platform has been running continuously since 2009 as a collaborative instrument to collect, store, organise and disseminate cetacean data voluntarily collected by whale watching companies in the Azores. In the period covered by this dataset (2009-2020), 11 whale watching companies have voluntarily provided data from the four islands of the archipelago where whale watching takes place. The dataset contains more than 37,000 sightings of 25 species (22 cetaceans and three turtles). This manuscript presents the first long-term whale watching cetacean occurrence dataset openly available for the Azores. We explain the methodology used for data collection and address the potential biases and limitations inherent to the opportunistic nature of the dataset to maximise its usability by external users.

Cetacean presence and distribution in the central Mediterranean Sea and potential risks deriving from plastic pollution

The Sardinian and Sicilian Channels are considered hotspots of biodiversity and key ecological passages between Mediterranean sub-basins, but with significant knowledge gaps about marine mammal presence and potential threats they face. Using data collected between 2013 and 2019 along fixed transects, inter and intra-annual cetacean index of abundance was assessed. Habitat suitability, seasonal hot spots, and risk exposure for plastic were performed using the Kernel analysis and the Biomod2 R-package. 661 sightings of 8 cetacean species were recorded, with bottlenose and striped dolphins as the most sighted species. The north-eastern pelagic sector, the coastal waters and areas near ridges resulted the most suitable habitats for these species. The risk analysis identified the Tunis, Palermo, and Castellammare gulfs and the Egadi Island as areas of particular risk of plastic exposure. The study represents a great improvement for cetacean knowledge in this region and contributes to the development of effective conservation strategies.

Fin Whale (Balaenoptera physalus) in the Ligurian Sea: Preliminary Study on Acoustics Demonstrates Their Regular Occurrence in Autumn

The patterns of movement of the fin whale (Balaenoptera physalus (Linnaeus, 1758)) in the Mediterranean Sea are still a matter of debate. Feeding aggregations are well known in the Corso-Liguro-Provençal Basin from July to September, but little is known for the autumn and winter seasons. Passive acoustic monitoring (PAM) was implemented in the Ligurian Sea to overcome this gap and to investigate the temporal and spatial variation of fin whale acoustic presence. From July to December 2011, five autonomous recorders were deployed at between 700 and 900 m depths. Fin whale calls were automatically detected almost every day, with higher vocalization rates in October, November, and December. Furthermore, daily vocalization rates were higher during light hours, and closer to the coast. These outcomes suggest that not all the individuals migrate, staying in the area also during autumn for feeding or breeding purposes. The dial cycle of vocalization might be related to feeding activities and zooplankton vertical migration, whereas the proximity to the coast can be explained by the morphology of the area that promotes the upwelling system. Although this work only represents a six-month period, certainly it suggests the need for a larger spatial and temporal PAM effort, crucial for species management and for mitigating possible impact of anthropogenic activities at the basin level.