Individual foraging habits of bottlenose dolphins

Everybody is unique. This is true not just for humans but many other animal species as well. When individuals within a population use different resources such as habitat type, we call that individual specialization. Additionally, special conservation strategies must be employed for populations comprised of individual specialists. Thus, understanding the role of individual specialization in bottlenose dolphin populations is critical. Yet, because dolphins capture and consume prey underwater, knowing if all dolphins find and consume fish in the same habitat type (such as seagrass or open water) is difficult. Fortunately, a laboratory technique known as “stable carbon isotope analysis” performed on small samples of body tissue can give us an indication of where a dolphin foraged over its lifetime. High carbon isotope values (δ13C) indicate foraging on fish associated with seagrasses while low isotope values suggest a dolphin foraged in open water habitat.

Carbon isotope values of bottlenose dolphin tooth material over a lifetime indicate individual habitat use. Age estimates are obtained from growth layer groupings of material used for stable isotope analysis. Each line represents a single individual
Carbon isotope values of bottlenose dolphin tooth material over a lifetime indicate individual habitat use. Age estimates are obtained from growth layer groupings of material used for stable isotope analysis. Each line represents a single individual

We performed stable isotope analysis on annually deposited layers of teeth from dead stranded dolphins. These layers are called growth layer groupings, and they provide a time series of what habitat types dolphins used over their lifetime. Carbon isotope values showed that bottlenose dolphins tended to consume fish in the same habitat type over their lifetime (see figure). This may be because dolphins learn how to capture and consume fish during the long time period a calf spends with its mother. A dolphin reared in seagrass habitat may tend to use seagrass habitat later in life while an individual reared in open water may tend to use open water.

The finding that bottlenose dolphins demonstrate individual specialization has significant implications for conservation. Many conservation strategies focus on protecting one habitat type or prey resource. However, in populations where individuals utilize different resources, promoting a single resource will only help a few individuals. Additionally, specialist individuals will be more severely impacted by disturbances to their preferred habitats. Because some specializations in habitat type will increase exposure to disease, assessing individual specialization will play a critical role in understanding both conservation and certain phenomena in disease ecology, including unusual mortality events.

This article was published on page 8 in the November 2014 issue of Nicks n Notches