The blue whale is the largest animal on earth and an Endangered Species. The blue whale population has not only been affected by whaling activities but also by anthropogenic activities such as fishing entanglement, boat strikes, climate change and chemical emissions. Many of the resulting contaminants of the latter are found to reside in blubber and other lipid rich layers. Blue whales, and other large baleen whales, accumulate layers of earwax, known as cerumen, throughout their lifetimes. This wax builds up over time and produces dark and light colored layers, or laminae, which represent periods of feeding or migration. While early earplug analysis was used to age whales, it was recently discovered that it is possible to reconstruct lifetime profiles of hormones, mercury, and other pollutants. in whales. Similar to blubber, these contaminants build up in the whale’s earplug in large enough concentrations to quantify. Tumble et al. (2013) looked at the earplug of a male blue whale to examine lifetime contaminant and hormonal profiles. They found 24 different laminae and estimated the whale’s age to be 12 years ± 6 months. Looking at the hormone levels, they were able to age the whale’s sexual maturity. When the contaminants were examined, it was found that much of the contaminants came from mother during the first 12 months. The mercury profiles showed peaks as a result of environmental and anthropogenic mercury increase. —Chloe Mayne
Trumble, S., Robinson, E., Berman-Kowalewski, M., Potter, C., Usenko, S., 2013. Blue whale earplug reveals lifetime contaminant exposure and hormone profiles. PNAS published ahead of print September 16, 2013,doi:10.1073/pnas.1311418110.
Trumble et al. obtained an earplug from a 21.2 m male blue whale that was killed by a ship strike in 2007. The earplug was cut longitudinally with a saw to make the internal laminae more accessible. The earplug was found to have 24 distinct laminae. Each layer was examined under a microscope, removed from the section and stored in nitrogen at –30 °C . Next, the compounds were analyzed. Hormone analysis was completed using the Enzo Life enzyme kit for each respective hormone. Mercury was determined using the mercury analysis system approved by the EPA. The organic contaminants (POPs) were determined using a pressurized liquid extraction method.
The findings of this experiment looked at the lifetime profiles of cortisol (stress related hormone), testosterone (development hormone), POPs (persistant organic pollutants), and mercury. During the lifespan of the blue whale, cortisol concentrations doubled. Cortisol concentrations are a biomarker of stress in mammals and are in response to environmental, physical, and chemical factors. The large peak in cortisol concentration may have been related to breeding competition or social bonds, while the general increase during the animal’s life was due to migration, food, environmental conditions or contaminant exposure.
The results for testosterone showed a large peak at around 10 years, indicating sexual maturity. The testosterone levels ranged from a low of 230 to a high 93,000 pg/g. Of the 42 POPs analyzed, only 16 were measured in the cerumen. The POP concentrations peaked at 0–6 months and then decreased. This result showed that there was a large amount of maternal transfer during gestation & lactation. Around 20% of the whales lifetime burden can be attributed to maternal transfer. The lifetime burden is considered the uptake, metabolism & excretion of POPs. During feeding and fasting, these POPs are recirculated throughout the body but their effects are unknown.
The mercury profile showed two distinct peaks found at 60–72 months and 120–126 months. These peaks may be due to increases of environmental or anthropogenic mercury during the blue whale migration along the coast of California. Mercury in the environment can be harmful as it bioaccumulates and causes impaired neurological development.
This experiment was successfully able to create a lifetime profile of an individual blue whale by measuring the trace amounts of contaminants and hormones from the layers that build up in the cerumen of baleen whales. Using the earplug is much easier than analyzing blood, feces and blubber. In addition, earplugs provide a more comprehensive examination of the contaminants, hormones and persistent compounds. Earplugs are extremely advantageous because it is also now possible to analyze samples that were taken as early as the 1950s. Finally, examination of whale earplugs provides the opportunity to understand the anthropogenic effects on not only an individual whale, but the whole marine community.