When humans become vending machines: cravings for fish hand-outs by pregnant dolphins
Written by Valeria Senigaglia
The following paper has just been published: Senigaglia, V. and Bejder, L. 2020. Pregnancy cravings: visitation at a food-provisioning site is driven by the reproductive status of bottlenose dolphins. Tourism in Marine Environments. Downloadable HERE.
Background and context
One of my dearest friends survived ten months on nothing but cakes while breastfeeding and didn’t gain a pound. This is partly because lactation is very energetically demanding, which means the body needs more calories to function (and produce energetically-rich milk) and thus more food. Dolphin mothers need 70% more energy while they lactate and some calves can feed on milk for up to eight years (although, on average, they start to become independent around the age of three years). While female dolphins might not crave fudgy brownies, they surely appreciate an easy treat.
Some female dolphins in Bunbury, Western Australia (WA), receive a small takeaway meal from humans as a part of a state-licensed food-provisioning program run for tourism purpose. In short, dolphins are fed one or two fish to attract them to the beach so that tourists can get a closer look. Unfortunately, my previous research (“Food-provisioning negatively affects calf survival and female reproductive success in bottlenose dolphins” published in Scientific Reports) shows that, while enjoyable for the tourists, food-provisioning is linked to low calf survival with fewer offspring of provisioned females not reaching adulthood.
The WA state permit limits the maximum amount of fish that can be given to each dolphin (max 500g of fish/day) but it is up to each female to decide whether to approach the beach to be fed or not. In our latest paper, Dr. Bejder and I used almost 20 years of citizen science data to explore what could drive female dolphins to visit the beach. Based on energetic requirements, we looked at whether female reproductive status might increase visitation rates and, since climate change can affect prey availability, we also considered the effect of climatic fluctuations. Our research shows that reproductive status (being pregnant or lactating) is the biggest predictor in influencing visitation rate to the provisioning site.
It may sound mere common sense that hungry lactating females would look for more food and thus, if already used to, approach humans more often, yet it carries some important and less obvious consequences. In fact, by accepting food from humans on a regular basis while still lactating, these females expose their calves to human contact from an early age, essentially teaching them to associate humans with food. As a consequence, those calves whose mothers often rely on fish hand-outs from humans, are now the most assiduous beggars, a maladaptive behaviour that increases the risk of entanglement in fishing gear, boat strikes and propeller injuries.
It is worthy to ask ourselves again if we are not loving dolphins too much for our own sake as sometimes even the best intentions can lead to unwanted negative consequences.
If you are interested in receiving more information, please contact Valeria Senigaglia.