Search

The article presents a study which examined the sperm whale distribution and habitat use around the Balearic Islands with the use of a novel analytical framework which combines transect and follow data. The sperm whales were located by listening along a search track and then followed acoustically. The probability of whale presence across the study area as a function of environmental variables was modeled by using the Logistic Generalized Additive Models, while the Generalized Estimating Equations were used in accounting for autocorrelation. Based from the result of the study, it was found out that the region is not used by the sperm whales uniformly and that their distribution is shaped by various factors such as topography.

Interactions between marine mammals and fisheries are a growing problem, and effective management requires assessment of the factors driving the interaction and of the impacts on fisheries. We used data from interactions between artisanal fisheries and bottlenose dolphins around the Balearic Islands to assess these factors and impacts. Observers collected data during 1,040 fishing operations over 3 yr. Location and year were important factors affecting interaction probability, with some areas showing large increases over the study period. We estimated the combined cost of catch loss and net damage as 6.5% of the total catch value (95% CI −12.3%, −1.6%), and the annual loss to be 3.4% (95% CI −6.5%, −0.1%) of the total catch by weight. This weight equates to the dietary needs of ∼12 dolphins (95% CI 0.2, 22), suggesting the fishery is not a vital food source for the dolphin population. Two dolphins died through entanglement during the observed fishing operations. We observed 3% of the total fishing activity, by weight, in 2003; scaling up this mortality directly suggests that as many as sixty dolphins may be dying in nets each year. This interaction likely has serious conservation implications for the dolphin population. [ABSTRACT FROM AUTHOR]

The habitat use of marine megafauna emerges from the complex interplay between access to patchy and variable food resources and several intrinsic biological factors, such as the interaction with conspecifics and offspring care, resulting in dynamic distribution patterns. Quantifying species' relationships with the underlying environment is further complicated by the scale-dependent nature of these processes. Multi-scale analyses that incorporate aspects of a species' biology and build on large datasets are therefore required to understand long-term distribution and inform appropriate management measures. In this study, we use monitoring data collected over two study periods (2003–2008 and 2012–2018) to assess the habitat use, trend in local occurrence, and change in distribution of sperm whales, Physeter macrocephalus , around the Balearic Islands (Spain), one of the few recognised breeding and feeding grounds for the 'Endangered' population in the Mediterranean Sea. Moreover, we investigate the differences in the habitat use of single animals and groups, to explore intra-specific niche partitioning in this highly social but behaviourally dimorphic species. Results suggest that overall the occurrence of sperm whales in the area has been increasing over time. Animals were found to associate with distinct bathymetric features, but the mechanisms generating these relationships, and the underlying oceanographic processes within this habitat, remained uncertain. Sperm whale distribution also underwent a significant shift between the two study periods, with an increased occurrence in the Mallorca channel and north of Menorca, which further points towards a dynamic use of the broader bathymetric range preferred around the archipelago. Finally, our analyses highlighted that single animals and groups used areas with different characteristics, with groups preferring deeper, warmer waters characterised by lower sea level anomaly, which resulted in some fine-scale spatial segregation. The results of this study shed light on the mechanisms underpinning the biogeography and complex social system of the species, and support the design of targeted conservation measures in this important breeding and feeding ground. • Marine megafauna habitat use is dynamic and affected by intrinsic biological factors. • We assess the habitat use of an endangered population of sperm whales over 15 years. • Local occurrence increased over time and distribution underwent a geographic shift. • Single animals and social groups used habitat with different characteristics. • Results support the design of targeted conservation measures in this important area. [ABSTRACT FROM AUTHOR]