Scientists have analyzed the proportion of stable isotopes of nitrogen and carbon in a collection of cetaceans stranded in the Canary Islands, Madeira and Azores since 1996.
A new study by the Spanish Institute of Oceanography (IEO-CSIC) in collaboration with the Institut de Ciències del Mar (ICM-CSIC) and other Spanish and Portuguese centers has analyzed the position in the food chain of several species of dolphins in recent years through the analysis of stable isotopes in samples from a collection of specimens stranded in the Canary Islands, Madeira and Azores since 1996.
The work, recently published in the journal Marine Ecology Progress Series, demonstrates how recent changes in ocean productivity and prey availability have modified the position of dolphins in the food chain. Thus, the study's findings suggest that the most oceanic species, such as the common dolphin, have progressively increased their position in the food chain, each time having to feed on species that are also high in the food chain.
"These changes are interpreted as a response to the decrease in primary productivity and in the populations of some fish, such as the sardine, indicated in previous studies," states Antonio Bode, researcher at the Spanish Institute of Oceanography and first author of the study.
However, in species with more coastal habits, such as the striped dolphin, their position in the food chain has decreased as they have had to move to more oceanic areas, where they feed on species belonging to lower levels of the chain.
"On the other hand, the study demonstrates that dolphins, due to their high mobility and relatively long life span, can be good indicators of large-scale changes in the ecosystem, acting as sentinel species of oceanic changes," explains Joan Giménez, from ICM-CSIC.
"These long-lived and highly mobile organisms are very efficient bioindicators, as they are able to integrate ecosystem conditions over large geographic and temporal scales," adds Bode in this regard.