What if we could have a look at the future of Shannon dolphins?

Wouldn’t it be wonderful if we could look into the future of the Shannon dolphin population! Will the population still exist in the Shannon in, say, 100 years? Have the numbers increased or declined? Well, we can.

One of techniques available to population biologists is a Population Viability Analysis (PVA). A PVA is a pool of mathematic and informatics tools that allow a researcher to simulate how a population would change through time, given specific parameters, to explore a population’s future. This has important implications since PVA can be used to guide conservation and decision-making in relation to an endangered population or species, hopefully in sufficient time to tell a happy-ending story. However, care must be taken since, the use of deficient or insufficient data in a PVA can lead us to incorrect conclusions, misinforming our conservation actions, wasting time and money, and even worse, making the situation worse by providing wrong advice. After 27 years of the Shannon Dolphin Research Project, we have strong enough data to perform this kind of study.

Calf born to Dolphin ID006 taken on 29 June 2014 © Mags Daly/IWDG

So, how was it done? All available demographic knowledge on the Shannon dolphin population: birth and mortality rates, weaning periods, species lifespan, proportion of reproductive females, and of course, the number of dolphins in the population, were put into a PVA software called Vortex. Vortex works as a simulator and uses these parameters to construct a simulated population of dolphins, recreating how it changes over time. Applying current numbers and parameters, the PVA showed the population declining, very slowly, but declining. Don’t worry too soon, though; The Shannon population wouldn’t go extinct in the next 50 or even 100 years, so there is time to react!

But we wanted to look further. We wondered how changes in the baseline parameters would modify the fate of the simulated population. Thus, we asked ourselves: what if dolphins lived just for 30 years instead of 50?  What if two additional dolphins were killed each year due to say fisheries bycatch? What if we doubled calf mortality? What if a disastrous oil spill occurred in the estuary? What if we saved one female every year? No sooner said than done, these scenarios were run in Vortex and produced interesting outcomes. If two dolphins were killed annually due to bycatch, or a single catastrophic oil spill occurred or lifespan reduced to 30 years, these would all lead the population into a steep decline. Indeed, if a catastrophic oil spill happened once in 20 years the population would go extinct within 50 years! That’s serious stuff! On the other hand, just saving one adult female each year would lead the population to a smooth yet positive trend. However an increase in calf mortality, wouldn’t affect the population that much, which makes sense, as when a calf dies, its mother is available to mate again, and the dead calf is rapidly replaced.

Nala bowriding a tanker © Mags Daly/IWDG

All these fictitious scenarios serve to get some idea of how both small and large changes may have impacts on the viability of the Shannon dolphin population and that more effort should be made to measure the extent of these threats such as pollution or bycatch may have on this population.

Miguel was an international master student at the Galway-Mayo Institute of Technology, who carried out his thesis on the Shannon Dolphin population with the IWDG.


This article was prepared for the IWDG Magazine Flukes Summer 2020 issue, which is sent to all IWDG members and  is currently at the printers.

This research is just published in Aquatic Mammals


Shannon Dolphin Publications by the IWDG are available to IWDG Members on https://iwdg.ie/members/members-resources-1/