Effective conservation is based on a variety of data such as species richness, life-history parameters of populations and temporal and spatial records. The collection of such data through extensive surveys is difficult and requires a lot of financial and personnel resources. Analysing stranding records, if documented sufficiently, can provide valuable information in this task – on species presence and distribution, anthropogenic impact, health, diet and more.
A group of scientists from the RMIT University in Victoria, Australia, took this as their chance to generate more knowledge on their data deficient region. As climate change already starts to show its effects in non-cetaceans, it is urgent to understand the current situation so changes in the marine mammal populations can be recognized thereafter.
Using records from the 424 cetacean stranding events between 1920 and 2016 in the area, the stranding of 907 individuals was analysed. Among the 31 different species, five had not been reported previously and almost half classified as data deficient. The events mostly consisted of single strandings. While most of the species did not show any significant ratio, adults tended to be stranded more often than immature individuals.
As for the temporal patterns, “the average annual number of stranding events per decade more than tripled from the 1970s to the 1980s”. Afterwards, the average annual stranding rate was consistent with about 10 stranding events per year (see Figure 1). Significant seasonal changes were not found.
The study further provided information on spatial patterns for the different regions along the shoreline, testing for significant occurrences of species and stranding rates between pooled embayments and inshore regions. Three species were found to be recorded outside their previously documented range.
Overall, analysing stranding reports can provide basic information for species richness – especially for data deficient species -, population demographics and habitat, and can illustrate changes in cetacean community composition and health. Therefore, they can be used as baselines to classify species conservation status and facilitate conservation actions.
On the downside, however, they rely heavily on the sufficiency of the descriptive data. Detection likelihood depends on the habitat and human density, thereby generating questionable spatial information. This way only “limited generalisations about population dynamics, status, and life history of the species” can be made.
Standardised protocols are recommended to generate more reliable sources with physical sampling only conducted by those with appropriate experience. While all records should be stored in a single, accessible database, collaboration between researches and governing bodies should be encouraged to allow “advances in knowledge to be more easily disseminated”.
The detailed report can be found here: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0223712
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