The size of the teeth of South American sea lions reflects historical changes in population abundance

A new study published in Peerj reveals that the teeth of South American sea lions (Otaria Byronia) have valuable clues on past population dynamics. Researchers from the Instituto de Biología de Organismos Marinos, the Centro para el Estudio de Sistemas Marinos, and the Universidad Nacional de la Patagonia San Juan Bosco analyzed changes in tooth size and growth layer groups (GLGs) over the past century. Their findings suggest that tooth size serves as a reliable indicator of the effects of density dependence on somatic growth.

In this study, male sea lion teeth were compared with male teeth from two different periods. It is a commercial harvest period, when the population reaches its peak, and a post-harvest period when the number is significantly reduced. By measuring tooth length, diameter, and GLG width, the researchers revealed clear differences between the two periods.

The key findings are as follows:

Teeth growth reflects the growth of the body. That is, a significant correlation was found between the body length and tooth length of the individual after harvest. Small teeth at peak population density – 10 minutes of harvest season teeth were significantly shorter and thinner than those in the post-harvest period. Thinner GLGS suggests competition for resources. Individuals during harvest season have narrowed growth levels, possibly due to increased intraspecies competition and reduced resource availability.

“Our results show that tooth size and internal growth layers can provide insight into how population density affects somatic growth,” says lead author Dr. Ilyn Sosa Drowville. “In the commercial seal era, food competition was fierce and somatic cell growth could have decreased. As the population declined, individual sea lions had better access to resources, larger teeth, and thicker dentin layers.”

Conservation and impact on ecology

This study highlights the possibility of stiff structures like teeth as historical records of ecological conditions. Understanding how population density affects growth can help scientists assess past environmental pressures and predict how marine mammals will respond to future changes in population dynamics.

“These findings reinforce the importance of long-term data in understanding how wildlife populations adapt to changes in environmental and anthropogenic pressures,” added co-author Dr. Mariano Coscarella. “This knowledge is particularly useful in managing sea lion population recovery and predicting the ecological outcomes of future abundance fluctuations.”