Abstract
Sea gulls are important species in marine ecosystems acting as scavengers and sometimes predators.1 The interaction between seagulls and marine mammals has been documented mostly as scavenging on rookeries or dead carcasses at sea;2 however, recent studies report the negative effect of sea gulls on Southern right whale calves where they can cause large skin wounds that contribute to neonatal mortality3,4. Since 2008, perineal ulcers have been recognized in the reproductive colony of South American fur seals (SAFS) at Guafo Island, Chilean Patagonia. However, the cause of these lesions has remained unknown. From 2012 to 2017 austral summers we documented the presence and extent of perineal ulcers in SAFS pups during routine health assessments, in order to record their prevalence, clinical presentation, and identify possible etiologies for the lesions observed. Culture swabs were collected in 10 animals and biopsy and histopathology were performed in 4 pups. In 2015 and 2017, daily observations (3 hours per day) of Guafo Island fur seal rookery allowed to record more closely the interaction of kelp gulls (Larus dominicanus) and dolphin gulls (Leucophaeus scoresbii) with previously marked SAFS pups. The prevalence of perineal ulcers in SAFS pups ranged from 5 to 10% among reproductive seasons; however, prevalence differences were not significant (Chi-square 2.285, df=5, p-value=0.80). The severity of the lesions was also homogeneous throughout the seasons with 70 to 80% of the cases consisting of 1 or 2 oval, well-demarcated ulcers of 1 to 2 cm in diameter (mild to moderate severity). In 20 to 30% of the cases the lesions consisted in 3 or more ulcers, or a single ulcer of more than 2 cm in diameter (severe lesions). In some of these pups (5/46) the perineal region was very inflamed and the pups showed signs of systemic disease (lethargy, marked leukocytosis). Bacteriology of perineal ulcers yielded mixed growth of Staphylococcus sp., b-hemolytic streptococci, Escherichia coli and Klebsiella sp. Histologically, there was moderate to marked ulcerative lymphoplasmacytic and histiocytic dermatitis with marked proliferation of fibroblasts and small blood vessels (granulation tissue). On the edge of ulcerated areas there were small colonies of gram-positive cocci and gram-negative bacilli. In 2015 and 2017 kelp and dolphin gulls were observed approaching fur seal pups and picking the perineal area. This behavior usually occurred right after pup defecation, when gulls involved in consumption of pup's feces and picked the perineal areas spotted with fecal material. In rare occasions, sea gulls approached sleeping pups and picked the perineal region in a similar manner how they approach dead pups to scavenge internal organs. The observation of seagull behavior and close monitoring of marked pups allowed us to confirm that seagulls are the primary cause of perineal wounds. Although the adverse consequences of seagulls on SAFS pups' health is not as dramatic as in Southern right whale calves,3,4 in some occasions perineal wounds can become infected and cause systemic disease in SAFS pups.
Acknowledgements
Work partially funded by Morris Animal Foundation (grant D16ZO-413), Society for marine mammalogy small grants-in-aid and Rufford small grant foundation. We appreciate the field collaboration of Dr Lorraine Barbosa, Dr Ignacio Silva, Eugene DeRango and Dr Hector Paves. We thank the logistical support of the Chilean Navy and Guafo Island lighthouse crews.
Literature Cited
1. Bahamonde and Castilla
2. Mallory et al. 2003
3. Maron et al. 2015
4. McAloose et al. 2016