We would like to congratulate Felix Thirion who just received his Master’s based on his project titled “Assessing patterns of trace metal bioaccumulation in caudal scutes of Crocodylus moreletii and Crocodylus acutus in Belize.”
Felix completed his Master’s under the supervision of the CRC, analyzing scutes CRC collected over the last three years throughout the country, and during his stay with the CRC last year. His project came at a significant time as the CRC began collecting data on the Morelet’s crocodiles of New River, utilizing crocodiles as a sentinel species to identify possible key pollutants that were causing the pollution crisis of the river, which included the high mortality and illness rate of the New River croc population. Below, you will find his abstract and a few highlights focused on New River and the Placencia Lagoon from this thesis. Felix and Dr. Tellez are currently working on publishing his work in a scientific journal.
Abstract: Crocodylus moreletii (Morelet’s crocodile) and Crocodylus acutus (American crocodile) are generalist, apex predators of subtropical aquatic habitats in Central America. As such, the status of their population can be considered indicative of that of the entire ecosystem – i.e., crocodiles constitute genuine indicator species. As top predators, crocodiles are exposed to high levels of trace metals via bioaccumulation that enter the food web as a consequence of human activities. In this study, I report on the concentrations of trace metals found in the caudal scutes of 178 specimens of Morelet’s and American crocodiles from Belize. The objectives were three-fold: 1) Investigate metal concentration differences from the scutes of Morelet’s and American crocodile’s populations to identify locations at risk, 2) uncover variations in metal concentrations between sexes, species and age classes within sites and 3) further assess crocodile scutes as bio-indicators for trace metal bioaccumulation from surrounding land use and sediment metal concentrations. All nine metals tested (Hg, Pb, Cd, As, Cu, Zn, Co, Cr, Ni) could be detected in at least several scutes. Higher and significant Hg concentrations were observed in adults from Chiquibul Forest (4.21 μg/g) and Ambergris Caye (1.26 μg/g). Significant differences were also reported for males displaying higher arsenic and copper concentrations than females, and a negative correlation between snout-vent length, copper and zinc, was observed in juveniles. Lead concentrations in the scutes were significantly elevated near urbanized areas while cadmium and zinc concentrations in the scutes were correlated to the concentrations of these metals in the sediments. Differences of trace metal bioaccumulation between the two species could not be tested due to species repartition in the locations surveyed.
– Lead concentrations were high in New River (2.93 ± 10.83 μg/g)
– In crocodilians, reproductive failure among Alligator mississippiensis captive groups was 18 attributed to chronic ingestion of lead (Lance et al., 2006). Since lead is considered analogous to calcium, it is furthermore hypothesized that a lack of calcium uptake might induce an altered development for bones where lead would become sequestered instead. Throughout 2019, high crocodile casualties were reported in the New River watershed with necropsies done by the Crocodile Research Coalition highlighting symptoms including whitening of the skin, soft bones, and glassy teeth (a sign of lack of calcium uptake). High lead concentrations in individuals could potentially concur with such symptoms. Trace metal accumulation is also worsened in stagnating watersheds with low elevation differences, as in the current case of New River.
– High lead levels are likely contributing to the skin necrosis observed amongst crocodiles of the New River watershed. Since 2016, the community of Orange Walk has observed and recorded lethargic and “white” crocodiles in addition to a rise of crocodile mortality. The results of this study combined with the information collected during necropsies that illustrated an advanced state of skin necrosis and organ failure of crocodiles from this area assists in identifying the cocktail of metals that could be negatively impacting the ecosystem.
– High mercury concentrations found in Toledo and other Southern Belize district locations such as Flower Camp [Placencia Lagoon] (n = 3 C. acutus, n = 1 C. moreletii, n = 2 hybrids; 1.18± 0.12 μg/g) could be attributed to agrochemical and nutrient runoff originating from large-scale agricultural bananas and citrus enterprises, aquaculture farms and open dump sites.
– Lead concentrations were high (6.4 ± 13.28 μg/g)
– Cadium: Flower camp (0.524± 0.378 μg/g) and Southern Toledo (0.669± 0.99 μg/g) displayed the highest concentrations, and a significant positive correlation was seen between cadmium concentrations found in the sediment samples and mean cadmium concentrations in scutes collected from crocodiles near the area of sediment sampling. Cadmium is similar to zinc in regard to their chemical properties and constitutes a by-product of the latter during production of various industrial products such as alkaline batteries, paints or plastics. It is considered of a high chronic toxicity because of its long retention time in organs such as renal tubules, leading to anaemia, hypertension and liver damage
– This study highlights that crocodiles and communities in less-urbanized areas or near protected areas (i.e., Chiquibul Forest, Southern Toledo watershed, Sittee River) are also exposed to higher levels of non-essential trace metals. Assessing sources of contamination and hydrological models near reserved areas is critical as agricultural run-off might have a greater impact in high trace metal concentrations.
Felix and Dr. Tellez plan to publish this study by the end of the year in a peer-reviewed scientific paper. Additionally, CRC has teamed up with a lab from North Carolina State University to further sample collection and analysis, examining the metals presented in Felix’s thesis, but also analyzing agrochemicals from croc scutes, fish tissue samples, and water.
The thesis has already been provided to the Belize Forest Department as well as to Dr. Percival Cho, the CEO in Ministry of Agriculture, Fisheries, Forestry, the Environment, Sustainable Development, and Climate Change.