The heavy rains and tropical cyclones of La Niña and the warmer sea surface temperatures of El Niño can diminish the seagrass beds where dugongs forage, which may impact the birth and survival of calves in the Great Barrier Reef and off the east coast of Australia, according to new research.
Scientists from James Cook University used aerial surveys taken since the 1970s to estimate and model the proportion of calves in dugong populations off eastern Queensland, Australia, where the density of these sea cows is relatively high.
The researchers found that the proportion of calves dropped after heavy rains and cyclones in four areas: the Northern and Southern Great Barrier Reef, Hervey Bay and Moreton Bay, though these changes varied between sub-regions. The relative number of calves also dropped following elevation of sea surface temperatures in two areas: the Northern and Southern Great Barrier Reef.
Since dugongs forage on seagrasses that may be affected by climate, the researchers suggest in their recently published PLOS ONE study that calf declines may reflect a limited ability for female dugongs to acquire the fat reserves needed to bear and nurse their young. This is supported by the authors’ finding that declines in relative calf count lagged behind climatic factors by at least a year.
Mariana Fuentes, an adjunct senior research fellow at James Cook University and one of the study authors, said, “The relationships between dependent dugong calves and climatic drivers vary spatially and temporally, with climatic drivers influencing calf counts at sub-regional scales. Thus we recommend that the assessment of and management response to indirect climatic threats on dugongs should also occur at sub-regional scales.”
Although other environmental factors may affect both seagrass and dugong population sizes, the researchers recommend based on their findings that conservation management efforts assess and address threats to dugongs at sub-regional scales. Mitigating the indirect effects of climatic factors may require protecting habitats as well as managing the coast to help keep seagrass meadows healthy.
Research Article: Fuentes MMPB, Delean S, Grayson J, Lavender S, Logan M, Marsh H (2016) Spatial and Temporal Variation in the Effects of Climatic Variables on Dugong Calf Production. PLoS ONE 11(6): e0155675. doi:10.1371/journal.pone.0155675
Image Credit: Powerful Tropical Cyclone Ita Making Landfall in Queensland, Australia by NASA Goddard Space Flight via Flickr