Steve Burton

Background: Free-ranging common bottlenose dolphins (Tursiops truncatus) can become entangled in fishing line
and other marine debris. Infrequently, dolphins can be successfully disentangled, released back into the wild, and
later examined postmortem to better understand the pathology and long-term effects of these entanglements.
Case presentation: An entangled common bottlenose dolphin (Tursiops truncatus) calf was observed in the Indian
River Lagoon, Florida, USA, with monofilament fishing line wrapped tightly around its maxilla. A multi-agency team
successfully disentangled the dolphin for immediate release back into its natural habitat. A year after
disentanglement, photos and observations indicated that the now independent calf showed a decline in body
condition, characterized by grossly visible ribs and a prominent post-nuchal depression. More than 2 years postdisentanglement,
the freshly dead carcass of this juvenile dolphin was recovered with extensive predation wounds.
Despite the forestomach being ~ 50% full of ingesta (fish), the dolphin was emaciated. During postmortem
examination, we collected and evaluated photographs and measurements of the maxillary damage resulting from
the entanglement.
Conclusion: The monofilament entanglement caused permanent, bilateral deformation of the maxillary dental
arcade, including a 4.0–4.2 cm long, 0.5 cm deep linear groove where the entanglement eroded the lateral edges of
the maxilla. There was no evidence of maxillary fracture and the dolphin survived for more than 2 years after
disentanglement. External evidence of propeller scars and a fishing hook discovered embedded in the laryngeal
mucosa at necropsy indicated repeated human interactions.
Keywords: Odontocete, Maxilla, Monofilament, Fisheries interaction

Odontocetes obtain nutrients including essential elements through their diet and are exposed to
heavy metal contaminants via ingestion of contaminated prey. We evaluated the prevalence,
concentration, and tissue distribution of essential and non-essential trace elements, including
heavy metal toxicants, in tissue (blubber, kidney, liver, skeletal muscle, skin) and fecal samples
collected from 90 odontocetes, representing nine species, that stranded in Georgia and Florida,
USA during 2007–2021. Samples were analyzed for concentrations of seven essential (cobalt,
copper, iron, manganese, molybdenum, selenium, zinc) and five non-essential (arsenic, cadmium,
lead, mercury, thallium) elemental analytes using inductively-coupled plasma mass spectrometry.
Risso’s dolphins (Grampus griseus) and short-finned pilot whales (Globicephala macrorhynchus) had
the highest median concentrations of mercury, cadmium, and lead, while dwarf sperm whales
(Kogia sima) had the lowest. Adult pygmy and dwarf sperm whales that stranded in 2019–2021
had higher concentrations of arsenic, copper, iron, lead, manganese, selenium, thallium, and zinc
compared to those that stranded in 2010–2018, suggesting an increasing risk of exposure over
time. The highest concentrations of many elements (e.g., cadmium, cobalt, copper, manganese,
molybdenum, thallium, zinc) were in fecal samples, illustrating the usefulness of this noninvasively
collected sample. Aside from fecal samples, hepatic tissues had the highest concentrations
of iron, manganese, mercury, molybdenum, and selenium in most species; renal tissues
had the highest concentrations of cadmium; skin had the highest concentrations of zinc; and
copper, arsenic, and lead concentrations were primarily distributed among the liver and kidneys.
Phylogenetic differences in patterns of trace element concentrations likely reflect species-specific
differences in diet, trophic level, and feeding strategies, while heterogeneous distributions of
elemental analytes among different organ types reflect differences in elemental biotransformation,
elimination, and storage. This study illustrates the importance of monitoring toxic contaminants in stranded odontocetes, which serve as important sentinels of environmental
contamination, and whose health may be linked to human health.