Since January 2010, a female bull shark, identified based on a healed injury of its right lower jaw, has been regularly observed at the Shark Reef Marine Reserve. It was observed 67 times between January 1, 2010 and December 31, 2016, typically and most often in the first half of the calendar year (Table 1). Photographs that were taken in January 2010 (Figure 1A, B) and footage from April 2010 (Video 1) showed a small proliferation in the right corner of the shark’s mouth. This region looks like an erosion with a centrally located elongated dark fissure, compatible with a fishing hook or a lesion created by a detached hook. Only little growth, if any, was documented until May–June 2011 (Figure 1C). At the end of May 2011, a fishing lure can be seen attached to the right mandibular corner, with a discolored slightly sunken area of the gingival margin visible anteriorly to the lure (Video 2). The dark hook-compatible structure visible in April 2010 is visible and looks like a deep fissure central to an irregularly outlined wound in the corner of the mouth. By June 2011, the shark had lost the fishing lure and a mild light pink multi-lobulated tissue proliferation can be seen, forming a small, irregularly outlined mass where the fishing lure was attached. With the fishing lure gone, a downward deformation of the gingival area inferiorly to the lesion and lack of dentition in the affected region can be seen. Observations from March 2013 onwards reveal a large red-brown multi-lobulated mass, attached the gingival margin via a narrow, white stalk (Figure 1D–F, Video 3), similar in appearance to the proliferative lesion recently documented in a white shark Carcharodon carcharias. The stalk is long enough to allow the mass to move in and out from the oral cavity (Figure 1G). This female shark has been a regular feeder at the Shark Reef Marine Reserve. Direct observations show that the proliferation wobbles, and when the shark is taking a fish head from the feeder can dangle inside the mouth (Figure 1G). This likely leads to the shark chewing on the proliferation. Footage that was taken on January 5, 2017 shows the proliferation inside the mouth of the shark and seemingly being bitten (Video 4). This was, however, at a provisioning site and such biting on the proliferation might not occur or might occur less frequently during natural predation. The multi-lobulated surface is compatible with chronic proliferative processes including granulation tissue and fibrosis, but a neoplastic process cannot be excluded. The mandibular angle is deformed and ulcerated, the central fissure is still visible, and the skin adjacent to the lesion is irregularly pitted indicating of underlying remodeling processes within the jaw. By April 2014, the lesion is similar to March 2013, but a fishing hook can be seen embedded in the lower jaw anteriorly to the mass. In videos from January 2017, the pedunculated mass seems similar to 2014, but the lower jaw appears to have a more pronounced angular ventral deformity.
Origin of the proliferation
Based on macroscopic observation from photographs and videos, the most likely morphological diagnosis is chronic, proliferative gingivitis and cellulitis with necrosis and deformation of lower jaw cartilage due to multiple events of fishing gear embedded in the right mandibular angle. The persistent foreign objects (fishing hook or lure) resulted in a fibro-proliferative tissue response that created a pedunculated mass compatible with fibropapilloma. Histological evaluation of multiple biopsies or serial sectioning of the entire mass is required for a more precise diagnosis i.e. confirmation of a neoplastic transformation within the affected tissues. Based on observations of tissue responses in sharks with retained fishing gear or chronic lesions due to attached gut parasites, we speculate that a neoplastic transformation of the affected tissues is likely. Although gingival neoplasms have been reported in sharks previously, this is the first documentation that links them causally to retained fishing gear and expands the types of lesions caused by such gear in sharks.