Abstract
Cetaceans are considered environmental sentinels and their health often reflects either anthropogenic or natural spatio-temporal disturbances. This study investigated the pathological findings and mortality of small cetaceans with the aim of detecting hazards and monitoring health trends in a high-biodiversity area. Between 2007 and 2012, 218 stranded cetaceans were recorded on the Paraná coast, southern Brazil. Fifty-seven (26.1%) of these animals, including 50 Sotalia guianensis, 2 Pontoporia blainvillei, 2 Stenella frontalis, 1 Stenella longirostris, 1 Tursiops truncatus and 1 Globicephala melas were necropsied and samples were collected for histopathology. Causes of death were determined in 46 of the 57 (80.7%) animals and most (30 or 65.2%) were ascribed to anthropogenic activities, including fisheries bycatch (28/30) and trauma (2/30). The remaining 16 fatalities were considered natural, and attributed to pneumonia (10/16), emaciation (3/16), septicemia (1/16), neonatal pathology (1/16) and choking via food obstruction (1/16). Irrespective of the cause, bronchointerstitial pneumonia, associated with parasitism, lymphadenitis and membranous glomerulonephritis were common findings among all fatalities. These results suggest, that while anthropogenic activities are a leading cause of cetacean strandings in Paraná, underlying pre-existing diseases may contribute towards deaths. Although the studied area is considered a biosphere reserve by UNESCO, complex anthropogenic and natural interactions might be occurring, increasing cetacean susceptibility to hazards. This study may help facilitate developing an effective conservation plan for coastal cetaceans focusing on reducing fisheries interactions, habitat degradation and pollution as mechanisms for ultimately increasing species resilience.
Highlights
Numerous populations of marine mammals have declined in recent decades, largely due to anthropogenic activities [1]
Health assessments of coastal cetaceans can be used to indirectly monitor the quality of marine ecosystems, investigate the severity of anthropogenic impacts, and identify risks to humans utilizing the same habitats for exploiting natural resources or for recreation [2]
One of the key fishing gears used in southern Brazil is gillnets [36,37], which in many areas pose a conservation threat to several populations of marine mammals [38,39], especially S. guianensis and P. blainvillei; both of which historically are the most common, regionally caught cetaceans [40,41]
Summary
Numerous populations of marine mammals have declined in recent decades, largely due to anthropogenic activities [1]. Health assessments of coastal cetaceans can be used to indirectly monitor the quality of marine ecosystems, investigate the severity of anthropogenic impacts, and identify risks to humans utilizing the same habitats for exploiting natural resources or for recreation [2]. In the last 25 years, at least 10 morbillivirus epidemics, with high associated mortalities, have affected free-ranging pinniped and cetaceans worldwide [10,11]. Diagnosing such infectious diseases and characterizing etiological changes is challenging in free-ranging cetaceans [12]. Pathological examinations of stranded sick or dying marine mammals (often discarded from fishing activities) provide an opportunity to collect data for biological and health assessments [13,14]
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