A case study of monofilament line entanglement in a common bottlenose dolphin (Tursiops truncatus): entanglement, disentanglement, and subsequent death

Abstract

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.

Staying Alive: Long-Term Success of Bottlenose Dolphin Interventions in Southwest Florida

“…Importantly, not all interventions are ultimately successful, so development of proactive strategies to reduce and prevent injuries from occurring must also be front and center in any mitigation strategies. Even rescues that appear to be shortterm successes can result in unexpected failure years later if animals face lingering impacts from their injuries (e.g., Marks et al, 2020). While only two of our cases were apparent failures prior to this analysis, an additional five individuals failed to survive a full year post-intervention bringing the overall longterm survival success rate to 74%.…”

Retrieval Operations of Derelict Fishing Gears Give Insight on the Impact on Marine Life

“…Once the bait from longlines is gone the chance of ghost fishing substantially drops (Matsuoka et al, 2005). However, ALD longlines still pose a significant entanglement threat to marine organisms, such as cetaceans (Garrison, 2005;Caitlin, 2017;Marks et al, 2020), pinnipeds (Butterworth, 2016), sharks (Afonso et al, 2012) seabirds (Collins et al, 2021), and sea turtles (Gless et al, 2008). The available entanglement data in ALDFG is limited and likely underestimated (Stelfox et al, 2016).…”

Demographics and viability of an estuarine community of Indo‐Pacific bottlenose dolphins

“…No adverse impacts from commercial fishing have been recognized for this community; however, five individuals and an additional three coastal dolphins who regularly use the Dawesville Channel, have been observed entangled in recreational fishing gear between 2016 and 2021. Discarded fishing gear has also been identified as a major threat to marine megafauna globally (Moore et al, 2009;Stelfox et al, 2016) with recreational fishing gear, mainly fishing line, affecting estuarine and coastal bottlenose dolphins (Mann et al, 1995;Marks et al, 2020;McHugh et al, 2021;Miketa et al, 2017;Wells et al, 2008Wells et al, , 2013. Educating the public on impacts of discarded fishing gear on wildlife is imperative to deal with the source of the problem while building capacity in local dolphin incident response to ensure quick disentanglement of individuals (Wells et al, 2008(Wells et al, , 2013.…”