Lake Gatun and Panama Canal IMMA

Criterion A: Species or Population Vulnerability

This IMMA encompasses the habitat of the Caribbean manatee (Trichechus manatus manatus), recognized as the Antillean manatee by the Society for Marine Mammalogy’s Committee on Taxonomy. The West Indian manatee (Trichechus manatus) as a species is globally assessed Vulnerable on the IUCN Red List (Deutsch and Morales-Vela, 2024), but the Caribbean sub-species is considered Endangered (Morales-Vela et al. 2024). At local levels, the Caribbean manatee is also listed and protected as Endangered by the Ministry of Environment of Panama (Resolution N0. DM-0657, 2016). Self-Sullivan and Mignucci-Giannoni (2012) reported population estimates for Panama and Costa Rica at 100 individuals each, with minimum counts of 10 and 30, respectively, suggesting a critical status.

Criterion B: Distribution and Abundance

Sub-criterion B1: Small and Resident Populations

In 1964 ten individual manatees – one male Amazonian manatee (Trichechus inunguis) and nine Greater Caribbean manatees from the Changuinola region in the north of Panama – were translocated into Lake Gatun, an artificial lake created during the construction of the Panama Canal (Nillipour, 2022; Muschett and Vianna, 2015).   The original motivation for bringing in these manatees was to control growth of the water hyacinth (Pontederia crassipes), which was thought to create breeding habitat for mosquitoes (MacLaren, 1967, Nillipour, 2022; Muschett and Morales 2020).

A study conducted in 2007 using aerial, small boat and interview surveys estimated the population to contain a minimum of 16 individuals, including newborn calves and juveniles, and noted that vegetation in the lake included many species known to feature in manatee diets: Eichhornia crassipes, Pistia stratiotes, Pontederia rotundifolia and Hydrilla verticillata, (Muschett and Vianna, 2015).  This minimum estimate is thought to be a significant underestimate, given the frequency of reports from interviewed villagers, and the turbidity of the water that hindered boat- or aerial based observations (Muschett and Morales 2020).

A more recent population viability modelling exercise determined that the survival of the original population may only have been possible with the immigration by individuals that entered the Canal from the Caribbean through the Canal locks (Muschett and Morales 2020), and there is even speculation, based on an observation of an Antillean manatee on the Pacific side of the Panama canal, that at least one animal from the Lake Gatun population may have crossed over into the Pacific (Guzman and Real, 2022).  However, the authors indicate that such immigration and emigration is unlikely to occur regularly given the complexity of the lock systems and the high volumes of vessel traffic using the system, and that for most practical purposes the population should be considered discrete and isolated (Muschett and Morales, 2020; Guzman and Real, 2022).