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.

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The artisanal gillnet fishery around the Balearic Islands is experiencing a growing problem with bottlenose dolphins Tursiops truncatus depredating the bottom-set nets. The resulting catch loss engenders hostility from fishers, and interactions between dolphins and nets can result in bycatch mortality. One potential mitigation measure is the placement of acoustic alarms, or pingers, on the nets. However, as pingers have produced mixed results in studies of their effectiveness in other fisheries, direct evidence is needed on whether they will be effective in this fishery. We report on a large-scale experimental trial in which 59 different vessels from the artisanal fleet were each equipped with identical nets, and each vessel was assigned to 1 of 3 conditions: no pinger, inactive pinger or active pinger. Three brands of pinger were tested. During the trial, data on fishing operations were recorded by onboard observers. A total of 1193 fishing operations were observed. We analysed 2 response variables, the presence or absence of evidence that dolphins had interacted with the net, and standardized yields, using generalized linear mixed models. Overall net interaction rates were reduced by 49% with active pingers, but not all pinger brands were equally effective. Yields, measured as profit per unit effort, were increased by 9% in the active-pinger condition, but this was not statistically significant (p = 0.592). Our results suggest that pingers in the artisanal fisheries of the Balearic Islands reduced the rate of net interaction, but further study is required given dolphins' potential for habituation.

1. Sperm whales in the Mediterranean are classified as 'Endangered' by the IUCN. They are apparently isolated from adjacent Atlantic populations, and subject to anthropogenic pressures including interactions with illegal driftnet fisheries, ship strikes, ingestion of debris and underwater noise.2. Photo-identification data opportunistically collected from the western Mediterranean basin show that individual sperm whales regularly move in excess of 500 km across the western basin, suggesting that this area is occupied by a single population.3. The best abundance estimate for this region is approximately 400 animals, with confidence intervals between 200 and 1000. 4. Given the mortality levels reported in the literature, this figure suggests that the conservation status of sperm whales in this region is very serious. Immediate priority should be placed both on conducting systematic surveys for abundance estimation and on measures to reduce the mortality associated with driftnet fishing.

Sperm whales (Physeter macrocephalus) are the largest toothed whales and only living member of family Physeteridae. Present survey represents first report on cultivable faecal microbes and gastrointestinal helminths and protozoans infecting free-ranging sperm whales inhabiting Mediterranean Sea waters surrounding Balearic Archipelago, Spain. Twenty-five individual sperm whale scat samples, including one calf, were collected without disturbance of animals during the summer of 2016. Parasitological diagnostic methods, such as sodium acetate acetic formalin (SAF) method, carbol fuchsin-stained faecal smears, Giardia/Cryptosporidium coproantigen ELISAs and an Anisakis-specific PCR were applied for further identification. Five bacterial genera, i.e. Acinetobacter, Clostridium, Enterococcus, Staphylococcus and Streptococcus, and one fungus namely Cladosporium were identified. Parasitological infections included seven different parasite species with some of them bearing anthropozoonotic potential. Thus, four of these parasites were zoonotic, i.e. Anisakis, Balantidium, Diphyllobothriidae gen. sp. and Giardia. Additionally, Zalophotrema curilensis eggs, spirurid-like eggs and Cystoisospora-like oocysts were identified. Molecular characterization identified Anisakis physeteris as the species infecting these whales. This survey provides first records on occurrence of two zoonotic enteropathogenic protozoan parasites (Giardia and Balantidium) and of facultative pathogenic bacteria (Clostridium and Enterococcus) in sperm whales. Presented data should be considered as a baseline study for future monitoring surveys on anthropozoonotic pathogens affecting free-living sperm whale populations and enhance investigations on possible impact on public health as well as on isolated Mediterranean sperm whale subpopulation.