The Value of Strandings Scheme Data

One common theme through this work is that these method development and validation approaches would not have been possible without the samples and data provided by the Scottish Marine Animal Strandings Scheme. Trends in marine mammal stranding rates can provide useful information on life history parameters, seasonal and spatial species distribution, species abundance, human-induced mortality rates and disease (Gulland and Hall, 2007; Prado et al., 2016). Analysis of these spatial and temporal trends have been used with the aim of developing cost-effective ways of monitoring at-sea cetacean populations in order to provide indicators of conservation status, and thus focus conservation efforts to drive policy (McFee et al., 2006; Siebert et al., 2006).

As well as demographic data, necropsy data from stranded animals have been used to assess diet (Gannon et al., 1997; Santos et al., 2004), and contaminant concentrations in top marine predators

(Jepson et al., 2016; Law et al., 2012). The increased risk of mortality from infectious disease associated with high contaminant burdens has also been estimated from stranded animals (Hall et al., 2006). Strandings scheme data are vital for investigations of unusual mortality events and mass strandings. For example, examinations of carcasses and tissue analyses have linked unusual mortality events to harmful algal blooms (Fire et al., 2011; Lefebvre et al., 1999; Scholin et al., 2000), and the Deepwater Horizon oil spill (Venn-Watson et al., 2015; Williams et al., 2011). Studies of the gas bubble-associated lesions found in mass-stranded beaked whales following naval exercises have provided a possible explanation of the relationship between anthropogenic, acoustic (sonar) activities and the stranding of these deep diving animals (Fernández et al., 2005; Jepson et al., 2005). Finally, a collaborative effort and coordination of standings scheme resources across five countries allowed an international and comprehensive investigation into the largest sperm whale (Physeter microcephalus) mortality event ever recorded in the North Sea in 2016 (Ijsseldijk et al., 2018).

Strandings networks can therefore provide a unique opportunity for data collection on the biology of different species. Here, blubber tissue samples and accompanying metadata collected by the SMASS were invaluable for new biomarker method development and validation. The value of these data were three-fold. Firstly, using samples from stranded animals allowed the collection of tissue samples large enough for multiple and repeated processing and extraction methods. This overcomes the small sample mass constraints typical of biopsy samples from live animals. Importantly, different measures can then be compared for the same individuals. Secondly, samples from stranded animals allowed sampling of the full blubber depth in order to put the results of shallow depth, remotely obtained biopsy samples from live animals into context. Variation in biomarkers of interest through the full blubber depth also provides broader insights into blubber function and how this differs between species, as seen with variations in lipid content in Chapter 2. Thirdly, the metadata associated with each of the blubber samples are not available for free- ranging cetaceans. Information in terms of sex, age-class, pathological processes, cause of death and importantly, morphometric measurements allowed the variation in biomarker results to be put into life-history context.

These approaches highlight the importance of strandings scheme datasets and sample collection protocols in terms of the information that can be gathered from these efforts. Here, there were likely sources of variability in the way in which the morphometric measurements were taken. This could affect the accuracy of the long-term dataset. Personnel changes for example, or the difficulties of necropsies being performed under different conditions at the stranding site or in a laboratory, can introduce sources of measurement error. Sources of variation and measurement errors will also vary for animals of different sizes. Balaenopterids and beaked whales for example, are more logistically challenging to handle compared to the smaller porpoises and the delphinids. As a result, these errors were likely then propagated through downstream analyses. Even though the morphometric measurements and sampling protocols were standardised, it is not possible to retrospectively calculate the error associated with the morphometric measurements used here for

body condition indices calculations. These errors could have masked some relationships between the morphometric measures and other covariates of interest. Large sample sizes would help to ensure that while there will always be some measurement error, analyses are as robust as possible. There may be some biases associated with sampling in terms of how representative dead stranded animals are of the population as a whole, and therefore how these results can be accurately extrapolated. In addition, using carcasses for sampling means that there is no control over which individuals are available for incorporation into any given study. For example, the samples from stranded balaenopterids in Chapter 2 and 3 were largely from juveniles which meant that robust analyses of differences between age classes was not possible. Of course, the issues associated with the representativeness of stranded animals, and the choice of which individuals to target for any particular study can be overcome by lethal sampling. While lethal sampling can provide huge amounts of physiological and ecological information about different species and different populations (Enoksen et al., 2016; Haug et al., 2017; Solvang et al., 2017), there are obviously ethical considerations and implications of these approaches that are not in keeping with the research objectives and ethos of many institutes and research programmes. So, even with these caveats, standings schemes can provide suiTablesamples and accompanying data for the investigation and validation of novel health markers. These investigations illustrate the need for their continuation into the future.