During the last two decades, reports of CS in Chile have been steadily increasing over time, urging an immediate response to understand the causes of this phenomena. Our dataset was built from official and non-official sources that enabled us to carry out the first comprehensive study that synthesized long-term records of CS in Chile. Overall, there were three critical results from our analyses. First, a large number of spatiotemporal clusters were detected along the Chilean coast, highlighting the need for monitoring and surveillance activities along the entire coast, giving particular relevance to Patagonia. Second, with our data, the occurrence of most clusters was established to take place during the last decade, which may be a reflection of augmented public awareness and reporting, policy changes, or the effect of oceanographic and ecological changes. Third, we provide applications for future stranding investigations by determining the time lag to monitor the event (±2 mo.) and the number of stranded individuals for the CS to be classified as a massive event (greater than 3 stranded individuals). Although most CS events would be restricted to a limited spatial extent (<1 km radius), monitoring should also consider about (±) 70 km radius of coastal extension. We also discuss the within-year variation of reporting, the identification of hot spots in different areas of Chile and the species composition of the dataset. In the last year, there have been 61 CS events, 15 of them (24.6%) occurring between December 2019 and January 2020 (last summer season). All these CS events reported a total of 92 stranded individuals that were extensively distributed in the Chilean coast. However, a single event including 29 individuals of B. borealis was reported from Chilean Patagonia, one the significant clusters reported here. This demonstrates how the combination of GIS applications, time series, and spatiotemporal analyses can be used to gain a better understanding for the management of CS events in an extended region.
Cetacean stranding events can provide insight into the distribution and population aspects for some species26. Here, it was expected that the number of CS events and stranded individuals would mirror the species richness and relative abundance in Chile27. In fact, from nine existent families, 24 genera and 41 species that have been reported in Chilean waters26, CS events reported here identified 88.9% of cetacean families, 87.5% and 85.4% of genera and species, respectively. In this context, live-dead CS metrics from different countries indicated that strandings showed greater species richness than live surveys and that species richness also increased with coastline length27. This was observable for most species, but it was unusually high for P. spinipinnis, reported in 43 events. Phocoena spinipinnis are a group of porpoises that regularly strand in coastal areas worldwide3. It has been described that the leading causes of death are from bycatch and naval presence28. In our study, the strandings of P. spinipinnis took place for the most part in major ports and fisheries located in central Chile. A different situation occurred with B. borealis (n = 387), with 13 reported CS throughout the study period. However, a single event reported about 95% of total reported stranded individuals. This UME occurred in Golfo de Penas and Puerto Natales24. The most likely cause of this UME was a toxic algal bloom, but other causes could not be ruled out24. In both cases, CS events are useful to understand species distribution and to contrast them with reported richness. Nevertheless, interpretation of these events needs to be taken cautiously.
In this study, it was shown that the distribution of CS events and significant spatiotemporal clusters (Fig. 3) were widely spread along the Chilean coast, indicating that stranding phenomena are relevant throughout the country. However, when looking at the magnitude or number of individuals stranded at each event, more than half of the stranded cetaceans were reported at the southernmost regions of Chile. In other words, these findings suggest that, although the likelihood of a CS event is a random process along the Chilean coast (North and Central zones), a mass stranding or an UME should be expected to take place in the Patagonia zone in the southernmost part of the country (First four significative clusters p < 0.001, Table 2). Since CS events have become widespread, implementing a national monitoring strategy would be a logical step, but in terms of an effective rescue and rehabilitation plan for stranded individuals, efforts should be focused in Chilean Patagonia. A feasible example of a risk-based and integrated monitoring plan would be the partnership with the Chilean salmon industry. Marine sites for salmon farming activities are scattered at the southern regions, mostly located at isolated areas and manned by staff and personnel for 24 hours a day for at least 10 months throughout the year. Such productive units can become voluntary monitoring stations and act as an early warning system for either single or multiple strandings. Also, our work provides key indicators (CS frequency, size, duration, extension, etc.) that can be of use for a number of initiatives that might promote management or conservation plans for cetaceans and other marine animals.
The analysis of the within-year variation indicates that although CS events were reported at all times of the year, the months from February to April (summer and early autumn) and July (winter) account for 41% of all CS events. The patterns of late spring and summer strandings have been previously reported for patterns in different species29,30,31, likely due to the seasonality of the animals’ movements and foraging habitat29,31. Summertime also favours more visibility because of longer and increased daylight, reduced rainfall, and being coincidental with the “summer holidays”, thus making it more likely for people to detect and report CS events. This potential “observer bias” in reporting is also apparent in July, where, despite low light and poor weather, the “winter holidays” increase the number of observers and reports of CS events. There are additional factors that can also explain the seasonality of CS events reported here, including the intensification of fishing efforts32, cetacean breeding activities33 or species-specific patterns34. Unfortunately, we were not able to accurately classify the source or entity of the reporting for each event (primary reporting entity), i.e., naval personnel, fishery inspectors, researchers or visitors. We were also unaware of whether or not this information was collected in the field. The reporting entity is important as it can provide insights about the value of citizen science as a way to contribute to the wealth of information about population structures, distribution, and behaviour, as well as providing assistance with cetacean conservation35. We acknowledge the potential for volunteers (‘citizen science’) in environmental monitoring to bring value, both economic and educational, into wildlife research36. Our study highlights the importance of the implementation of a systematic collection of CS events, particularly how the entity that reported each event should be specified in order to quantify the value of potential stranding network partners.
From the output of the spatiotemporal analysis (Table 2), it is possible to suggest key indicators that may enhance future monitoring and surveillance activities in Chile. For example, for all significant spatiotemporal clusters (p < 0.001), the median extension size (radius) was 27 km and the median time frame (months) was 2 months. These indicators may suggest that whenever a CS occurs, response activities are expected to be in place for about 2 months and to extend over 50 km of coastline. Moreover, it is possible to obtain the median value of the expected number of stranded cetaceans, which may reflect the expected number of stranded cetaceans in a given event. In this study, this indicator ranged from 3 to 10 stranded animals, suggesting that a massive CS should be declared if 3 or more animals are found. Outputs from our spatiotemporal approach provide key indicators for guidance on preparedness and response in an ongoing stranding and also for the evaluation of monitoring activities. Implementing such a technique can be applied in other regions where records of CS are available, including location (geographic coordinates), and number of individuals and species (all data related to CS).
There are few studies in other regions of the world that investigate stranded cetaceans involving periods longer than 25 years. These studies include CS at the Irish coast from 1901 to 1995 (529 events in 94 years)37; on Sable Island in Nova Scotia, Canada, (102 events in 28 years) from 1970 to 199838; in Costa Rica (35 events in 33 years) from 1966 to 199939; in the Galapagos Islands (87 events in 80 years) in Ecuador from 1923 to 200340; in the main Hawaiian Islands from 1937 to 2002 (202 events in 65 years)41, in Tunisia (132 events in 72 years) from 1937 to 200942; and in South Australia (1,078 events in 127 years) from 1881 to 200843, which is the most extensive, in terms of time, of all assessed studies. Roughly speaking, the proportion of events per year considered in these studies was estimated at 3.95 (i.e., average number of events divided by years in the study). In our study, this proportion was estimated at 7.1 events per year, which is 80% higher than the global estimate. The only region to report an even greater proportion was South Australia43. We hypothesized that main drivers for this higher reporting of events in Chile would be associated to the country cetacean richness (40% of all cetaceans reported worldwide are present in Chilean waters37), the extensive distribution of coastal human populations and activities related to fisheries and aquaculture, and some side effects due to climate change, such as increasing toxic algal bloom in Patagonia24, which is linked to changes in water nutrient availability in some areas44.
The need to increase the reporting of strandings is evident. As a consequence, it is recommended that the marine mammal network of sightings in Chile should be strengthened by NGOs, Sernapesca and Directemar, and that a national stranding network should be established, integrating the participation of a wide range of actors from civil society and collecting information in a centralized database with the latitude and longitude of the events for further spatial analysis (including GIS tools). The implication of such CS studies may promote the allocation of resources towards more effective monitoring and surveillance of these events in that region. In addition, it is critical to be able to respond quickly and efficiently to these events by bringing together a multidisciplinary team for the investigation and sampling of these events. Future research correlating standings with oceanographic/climatic conditions may help to explain documented patterns, but the effects of increased monitoring efforts need to be accounted for as well.
In conclusion, this study provides insights into the historical patterns of cetacean strandings along the Chilean coast. Reports of CS events have increased alarmingly during the last two decades, particularly in Patagonia. However, it is not clear whether changes in human population, facilities used for reporting, general awareness or climate change would account for variability in reported strandings and explain potential biases. In any case, the use of spatiotemporal analyses provides results that may enhance current monitoring efforts by defining the expected numbers of stranded cetaceans, and the spatial and temporal extension needed after the report of a CS event. The composition of the species in the strandings database reflects the high diversity of cetaceans in Chile, with only ten species known to occur in Chilean waters not recorded in strandings. This is probably associated with more cryptic species with few records in Chile and lack of recognition of some stranded specimens. Our work here provides key indicators (frequency, size, duration, and extension of CS, among others) that can be of use for a number of initiatives that would promote conservation plans for cetacean and other marine animals.
Source: Ecology - nature.com
