Recently, two geographically isolated common dolphin populations in North-East Atlantic (NEA) and New Zealand (NZ) were found to have lower reproduction rates than other common dolphins. European researchers are investigating the impact of potential stressors behind this observation.
Various stress conditions including nutrition, disease or pollutants could suppress reproductive function, inhibit growth and alter the behaviour in mammals. The timing of these effects may also be important, and females may be more vulnerable during ovulation or before implantation.
The EU-funded CETACEAN-STRESSORS
project will study the effect of stressors on a female’s reproductive potential, a vital question for the survival of a species
. Cetaceans are marine mammals and good indicators of environmental conditions with their long lifespan and fat stores serving as depots for anthropogenic pollutants that can cause toxic effects
as endocrine disrupting chemicals and interfere with normal reproductive function Nutritional stress in these animals is caused by reduced food availability and is a crucial determinant for ovulation
, length of lactation
, neonate size
..To study the reason behind the low reproductive rates seen in the dolphin populations of NEA and NZ, researchers are sampling stranded animals and performing post-mortem examinations (necropsies
). Among others, they are assessing the animals’ health, nutritional status, age, sex hormone levels and evidence of pollutants- and stress-related pathologies including reproductive abnormalities.So far an increased incidence of female reproductive tract pathologies such as tumours
, endocrine disorders
has been noted in NEA common dolphins and harbour porpoises. In male harbour porpoises of poor nutritional condition and health status, scientists have observed lower testicular weights
and in certain cases sterility
. Ongoing biochemical evaluation of the potential contaminants will reveal the aetiology behind these defects. Researchers are also exploring the possibility that environmental stressors may lower the animal’s immune responses
thereby inducing or at least exacerbating some of these pathologies.Study results will shed light into the impact of stressors on reproductive physiology and pathology which is essential for species conservation. A greater scientific understanding of the processes limiting reproductive success could help improve the overall conservation management
of European cetacean species.