The study was conducted on 3 captive Greater Caribbean manatees (Trichechus manatus manatus) housed at Dolphin Discovery (Puerto Aventuras, Mexico):
Cesar (22 years of age)
Quijote (16 years of age)
Fabian (13 years of age)
A two-bottle preference test of short duration was used (2 minutes).
The animals were simultaneously presented with two bottles:
- One containing seawater
- One containing a given concentration of a taste substance diluted in seawater
Seawater was used both as the solvent for the taste substances and as the alternative stimulus because freshwater is considered an important habitat feature for manatees, and their ability to detect freshwater and salt gradients is thought to rely on their sense of taste. Therefore using freshwater as a solvent for the taste substances and as an alternative stimulus could affect the taste preferences displayed by manatees in the two-bottle preference tests.
Five food-associated substances were used to represent the five taste qualities: sucrose for sweet, sodium chloride for salty, monosodium glutamate for umami, citric acid for sour, and quinine hydrochloride dihydrate for bitter.
In total I conducted 3 series of tests:
- The first concentrations chosen were selected because they are above the taste preference thresholds established for most mammal species tested so far (to ensure a high probability that these concentrations should be detectable for the manatees).
- Then the first concentrations were doubled (as the initial results indicated no clear preferences or avoidances for any of the taste substances).
- Finally, to determine how valuable freshwater is to the manatees, I did a test in which freshwater was presented against seawater, and the highest concentrations of each of the five taste substances, previously diluted in seawater, were diluted in freshwater and were presented against freshwater (to assess whether the results would be consistent with those obtained from the previous tests using seawater).
Do manatees have preferences or avoidances? Let’s have a look at the results!