Lesions associated with drowning in bycaught penguins

Abstract

Fisheries bycatch, the incidental mortality that occurs as a result of entanglement in fishing gear, is an important conservation threat to penguins and other seabirds. Identification of entanglement and drowning in beach-cast carcasses of seabirds remains a challenge, as it is still unclear what lesions are to be expected in a bycaught seabird. We necropsied 2 Magellanic penguins Spheniscus magellanicus that were entangled and drowned in gillnets. Marked distension of the lungs with foamy red fluid and marked oedema of the dorsal visceral pleura were prominent lesions consistent with those described in cases of 'wet drowning' in humans. On the other hand, the air sacs contained very small quantities of liquid, suggesting that absence of water in the air sacs might not be a reliable sign to exclude drowning. Other relevant findings included cutaneous lacerations and bruising in one bird and cervical and pectoral rhabdomyolysis in both birds. While cutaneous or subcutaneous hematomas may be an indication of bycatch, especially if linear or cross-linear patterns consistent with fishing nets are present, these lesions might not always be discernible and their absence does not suffice to exclude the possibility of entanglement in fishing nets. Additionally, our findings suggest that the histological examination of skeletal muscles, particularly of the neck, may provide additional clues to corroborate the diagnosis of drowning in penguins.

Postmortem findings in Magellanic penguins (Spheniscus magellanicus) caught in a drift gillnet

“…The congestion of multiple organs (upon microscopy, more often seen in the brain, lungs and kidneys) and the pulmonary edema observed in both macroscopic and microscopic examinations of our cases ratify the findings of Vanstreels et al [22] and Simpson and Fisher [43] in seabirds, and were strongly suggestive of drowning. Generalized congestion was likely caused by increased pulmonary vascular resistance, cardiac dysfunction secondary to the extent and duration of hypoxia, and changes in acid-base balance (acidosis), that lead to decreased cardiac output [22,28,42], whereas pulmonary edema was caused by aspiration of saltwater and/or increased pulmonary venous pressure [28,29]. To the authors' knowledge, this is the largest study based on gross and microscopic pathology in penguins.…”

“…Even though the pneumonia findings were characterized as acute, the drowning event was fatal and could not have lasted long enough to promote such condition, in spite of the lung inflammation seen in near-drowned cases with seawater inhalation [44]. Granulocytic pneumonia was previously described in two drowned penguins [22]. We consider that the etiology of the pneumonia seen in our study was not related to the drowning event and that its causes remain unknown.…”

“…To the authors' knowledge, this is the largest study based on gross and microscopic pathology in penguins. Only recently, Vanstreels et al [22] reported the gross and microscopic findings of two Magellanic penguins that drowned and died after getting entangled in gillnet in southeastern Brazil: one in a floating (3 m) and the other in a bottom gillnet (12 m). Some of the previous studies with seabirds have relied solely on gross findings [43] or on histopathological examination of samples partially compromised by freezing [20,32] to diagnose drowning, when microscopic examination is essential for a more accurate diagnosis.…”

“…bycatch by trawl fisheries has been reported in Argentina [16][17][18][19]. In addition, Magellanic penguins presenting postmortem signs of fishing interaction or entanglement in fishing gear have been reported in Chile [20] and Brazil [21,22].…”

Consistent Site-Specific Foraging Behaviours of Yellow-eyed Penguins/Hoiho Breeding on Stewart Island, New Zealand

“…Although higher coverage of independent observers on gillnetter and inshore trawler boats is required to quantify bycatch landings, additional measures, such as surveys of beaches for dead penguins, can give an indication to the number of birds killed as bycatch that are not retained in nets that are hauled onto boats and those that may be removed from nets by fishers. Distinct characteristics in penguins associated with bycatch mortality can confirm these birds were indeed discarded individuals killed in gillnets [ 36 , 84 , 85 ]. Unlike South Island, no gillnet restrictions exist around Stewart Island.…”