Kelp and dolphin gulls cause perineal wounds in South American fur seal pups (Arctocephalus australis) at Guafo Island, Chilean Patagonia.

Mauricio Seguel,Diego Perez-Venegas,Héctor Pavés,Nicole Gottdenker,Felipe Montalva,Francisco Muñoz

doi:10.1098/rsos.170638

Abstract

During five reproductive seasons, we documented the presence, extent and origin of perineal wounds in South American fur seal pups (Arctocephalus australis) on Guafo Island, Northern Chilean Patagonia. The seasonal prevalence of perineal wounds ranged from 5 to 9%, and new cases were more common at the end of the breeding season (February), when pups were on average two months old and were actively expelling hookworms (Uncinaria sp). Histologically, wounds corresponded to marked ulcerative lymphoplasmacytic and histiocytic dermatitis with granulation tissue and mixed bacterial colonies. In 2015 and 2017, kelp gulls (Larus dominicanus) and dolphin gulls (Leucophaeus scoresbii) were observed picking and wounding the perineal area of marked pups. This behaviour occurred more frequently after the pups' defecation, when sea gulls engaged in consumption of pups' faeces. The affected pups usually had moderate to marked hookworm infections along with bloody diarrhoea and anaemia. Pups with severe wounds (23% of affected animals) had swollen perineal areas and signs of secondary systemic bacterial infection. We propose that seagulls on Guafo Island have learned to consume remains of blood and parasites in the faeces of pups affected by hookworm infection, causing perineal wounds during this process. We conclude that this perineal wounding is an unintentional, occasional negative effect of an otherwise commensal gull–fur seal relationship.

Highlights

Seagulls are important species in marine ecosystems, acting mostly as scavengers and/or predators [1,2]
The observation of seagull behaviour and close monitoring of marked pups allowed us to confirm that kelp and dolphin gulls are the primary cause of perineal wounds in South American fur seal pups
The prevalence of perineal wounds is not very high, and not comparable to the rates of wounding caused by kelp gulls in Southern right whales [11], the actual effect of sea gulls on pups’ health could be underestimated, because we only documented cases with a specific physical sequela due to pup–seagull interaction

Summary

Introduction

Seagulls are important species in marine ecosystems, acting mostly as scavengers and/or predators [1,2]. In most pinniped reproductive colonies, seagulls are a common inhabitant along with other scavengers [7,8] Their presence is mostly due to the large amount of food resources available, which includes placentas, carcasses of large territorial males that die during fights, and numerous dead pups due to the high neonatal mortality in many pinniped species [8,9]. One of the most bizarre and well-recorded interactions between gulls and marine mammals is the parasitism of kelp gulls on adult and neonate Southern right whales (Eubalaena australis) at Peninsula Valdes, Argentina [11,12] In this location, kelp gulls have learned over the course of 30 years, to open wounds in the skin and blubber of the whale’s back to feed on those tissues when the whales reach the sea surface to breathe [11]. The effect of this wounding can be quite dramatic, and is thought to be one of the factors related to the high mortality of Southern right whale calves at Peninsula Valdes [11,12]

Methods

Results

Conclusion