The 1982–1983 El Niño event recorded in dentinal growth layers in teeth of Peruvian dusky dolphins (Lagenorhynchus obscurus)

Abstract

Dusky dolphins (Lagenorhynchus obscurus) recorded the effects of the 1982–1983 El Niño event in the form of anomalous dentine deposited during 1983. This anomaly, which I call the El Niño mark (ENM), consists of a pair of hypocalcified incremental layers about 75 μm in width, located within the 1983 growth layer group. The anomaly was present in 15 of 18 mature females, 1 of 9 immature females, and only 1 of 14 mature and immature males. Teeth from other species inhabiting the upwelling system were examined and revealed no ENM. Dusky dolphins feed primarily on anchoveta (Engraulis ringens), the stocks of which collapsed during the 1983 El Niño; this collapse severely affected other anchoveta predators. It is possible that the ENM reflects the presumably low foraging success experienced by dusky dolphins in 1983. However, it is unclear why the ENM is present in most mature females and absent from most male specimens. The discovery of the El Niño mark in dusky dolphins provides the first convincing evidence in odontocete cetaceans of a direct environmental influence on the mineral quality of dentine deposited during a period of markedly abnormal climatic conditions.