From the 1st April 2012 to 31st March 2015, 1449 marine animals were reported to the Scottish Marine Animal Stranding Scheme (SMASS) ; 798 seals, 638 cetaceans, five basking sharks and eight marine turtles. Of these, 251 cases (17.3%), comprising 161 cetaceans, 88 seals, and two marine turtles underwent a detailed necropsy to establish a cause of death. An additional 72 (4.9%) animals were tissue sampled, comprising 59 cetaceans, 10 seals, and three basking sharks. The harbour porpoise, (Phocoena phocoena), was by far the most commonly reported species, representing 43.8% (n=280) of all cetacean strandings. In subsequent, decreasing order of incidence are the long-finned pilot whale (Globicephala melas) 10.8% (n=69), short10 beaked common dolphin (Delphinus delphis) 9.7% (n=62) and white-beaked dolphin (Lagenorhynchus albirostris) 5.9% (n=38). This is a change to the previous three year period where after harbour porpoise, minke whale (Balaenoptera acutorostrata), white-beaked dolphin and Atlantic white-sided dolphin (Lagenorhynchus acutus) were the most commonly recorded animal. In contrast to other UK averages, Scotland sees a significantly higher number of pelagic dolphin and whale species than any other UK region with the possible exception of a cluster of common dolphin strandings in south-west of England. This period saw an increase in seal carcases, attributed to increased reporting effort rather than mortality. Grey seals (Halichoerus grypus) made up the majority of reports representing 51% of all seal strandings. Physical trauma followed byinfectious disease, primarily pneumonia were the most commonly observed causes of death.. For cetaceans the picture is more complex as it is species dependent, although live strandings, pneumonia and generalised bacterial infections are commonly diagnosed. Scanning surveillance for threats to marine mammals has shown a new type of traumatic lesion in seals and porpoises, characterised by a single, continuous spiral cut running caudally from the head of the animal with associated flensing of the skin and blubber from the underlying musculature. Termed ‘corkscrew’ lesions, the number of animals exhibiting these lesions has been increasing and represents a potential cause of concern. Recent observations over the last two years however demonstrated adult male grey seals predating both grey seal juvenilesand adult harbour seals . It is therefore likely that many of these type of trauma lesions are the result of seal attacks. More detail about this is provided in section 11 of this report. Ivestigations into this emerging type of mortality involved collaborations with the Sea Mammal Research Unit (SMRU) and the Royal Society for the Prevention of Cruelty to Animals (RSPCA) and demonstrated the importance of an integrated and multidisciplinary approach to marine mammal research. Since early 2013, significant effort has been put into increasing the reporting of strandings to the scheme and availability of strandings data to both the scientific community and members of the public. In early 2014 a succession of volunteer training courses were undertaken with the aim of providing the scheme with a network of trained volunteers able to visit strandings and accurately collect photographs, data and samples from animals not deemed suitable or inaccessible for collection and necropsy. This ‘citizen science’ programme has proved very useful and its development is ongoing.