Herring, horse mackerel and capelin frozen into large ice cakes have become part of the daily routine for the nine common bottlenose dolphins (Tursiops truncatus) living at Zoomarine as Italy faces its fourth heatwave of the summer.
The enrichment activity encourages the dolphins to explore, manipulate objects and interact with one another while helping them cope with the hottest days of the year. Beneath the surface, each individual displays its own strategy: some drag the ice cake along the bottom of the pool, others break it into smaller pieces, while some cooperate—or compete—to retrieve every last fish.
The ice cakes complement the dolphins’ controlled environment, where 7.5 million litres of seawater are maintained at temperatures below 28°C, within the optimal 22–29°C range recommended for the species.
Every dolphin has its own strategy
“The nine dolphins at Zoomarine live within a complex social group, where play and environmental enrichment also help shape relationships, roles and social hierarchies,” explained Andrea Velluti, marine mammal keeper at Zoomarine.
According to Velluti, Paco and Leah prefer to move away from the younger dolphins to enjoy their ice treats in peace. Luna and Maya quickly move from one ice cake to another in an attempt to collect as many as possible. Indy, the most adventurous individual, finishes his own first before helping himself to Zeus’s, while the more easy-going Zeus usually lets him. Thai, meanwhile, seems to favour the smallest ice cubes, collecting several in its mouth at the same time.
The frozen fish treats combine environmental enrichment with feeding, stimulating exploration, object manipulation and social behaviour.
During the warmer months, the dolphins receive highly palatable fish species such as herring, sprat, capelin, blue whiting and horse mackerel. In winter, mackerel is added to provide a higher-energy diet.
A challenge dolphins also face in the wild
Heatwaves are becoming an increasing challenge not only for animals under human care but also for wild dolphin populations as ocean temperatures continue to rise.
Although the common bottlenose dolphin is currently classified as Least Concern on the IUCN Red List, thanks in part to its remarkable adaptability and widespread distribution, populations in the Mediterranean still face multiple threats, including declining fish stocks, accidental capture in fishing gear, marine pollution and growing human pressure on coastal ecosystems.
