Pathologic Findings and Trends in Mortality in the Beluga (Delphinapterus leucas) Population of the St Lawrence Estuary, Quebec, Canada, From 1983 to 2012

Abstract

An isolated population of beluga (Delphinapterus leucas) inhabits the St Lawrence Estuary, Quebec, Canada. This population has failed to recover despite the prohibition of hunting >30 years ago, suggesting the presence of other limiting factors. The authors summarize the reported causes of death and propose risk factors to explain the lack of recovery of this population. From 1983 to 2012, a total of 472 beluga were found stranded. Complete necropsies were carried out on 222 beluga, including 178 adults, 25 juveniles, and 19 newborn calves. Infectious diseases, the most prevalent cause of mortality in this population, accounted for the death of one-third of all beluga (32%). Verminous pneumonia was the cause of mortality of 13 juvenile beluga (52% of juvenile beluga). A total of 39 malignant neoplasms, diagnosed in 35 beluga, caused the death of 31 beluga (20% of beluga >19 years old). Median age at diagnosis of cancer was 48 years (range, 30-61 years). Dystocia and postpartum complications were the cause of death in 18 beluga, accounting for 19% of the females >19 years old examined. The occurrence of parturition-associated complications, as well as mortality of calves <1 year old, have increased recently in this population and may be the probable cause of the recent decrease in the size of this population. One of the hypotheses proposed to explain the unusually high occurrence of some of the pathologic conditions observed in this population is chronic exposure to environmental contaminants.

Causes of mortality of harbor porpoises Phocoena phocoena along the Atlantic and Pacific coasts of Canada

“…Infectious diseases, particularly pneumonia (bacterial and parasitic), were also a leading cause of mortality in other populations of harbor porpoises previously studied (Baker & Martin 1992, Siebert et al 2001. Similarly, they are the most prevalent cause of mortality in the isolated population of beluga Delphinapterus leucas in the St Lawrence Estuary (SLE) (Lair et al 2016) and a substantial cause of mortality in bottlenose dolphins Tursiops truncatus in coastal waters of South Carolina, USA (McFee & Lipscomb 2009). However, it is possible that animals of coastal species such as harbour porpoises, belugas and bottlenose dolphins debilitated by an infectious disease seek shallower waters to reduce energetic demands of swimming and are thus more likely to be found after death than animals dying as a result of other causes.…”

“…However, the category of emaciation/starvation included 2 recently born calves with marked atrophy of their epaxial muscle mass, indicating that some newborn harbor porpoises deprived of food may survive for some time on endogenous sources of energy. In the study of the SLE beluga population by Lair et al (2016), the cause of death of the vast majority of dependent calves examined also could not be clearly determined.…”

“…However, there is published evidence of an association between exposure to heavy metals and organic pollutants and increased susceptibility to infectious disease in harbour porpoises and other marine mammals (Bennett et al 2001, Jepson et al 2005, Reif et al 2015, Lair et al 2016). …”

“…Dystocia has been documented as a cause of death in a variety of marine mammal species including harbor porpoises. Lair et al (2016) observed a recent increase in occurrence of perinatal complications in the SLE beluga population and discussed the possible role of perinatal environmental stresses, nutritional stress, and endocrine-disrupting environmental contaminants as risk factors. Saxitoxin is a neurotoxin produced by dinoflagellates that is responsible for paralytic shellfish poisoning in humans and is capable of killing marine mammals (Geraci et al 1989).…”

“…As it is often logistically challenging to study marine mammals in the wild, it is particularly important to maximize the information obtained during stranding events in order to establish normal life history parameters and monitor anthropogenic causes of morbidity or mortality, emerging infectious diseases, and population demographics (Geraci & Lounsbury 2005). Analyses of causes of mortality of cetaceans have been re ported from several regions of the world (Cornaglia et al 2000, Parsons & Jefferson 2000, Jauniaux et al 2002, Camphuysen et al 2008, McFee & Lipscomb 2009, Bogomolni et al 2010, Arbelo et al 2013, van der Hoop et al 2013, Lair et al 2016.…”