Factors that influence cape fur seal predation on Cape gannets at Lambert’s bay, South Africa

Seabird populations experience predation that can impact their breeding density and breeding success. The Cape gannet Morus capensis is endemic to the Benguela upwelling ecosystem and is classified as Endangered by the IUCN. They are affected by several threats, including predation by the Cape fur seal Arctocephalus pusillus pusillus. Many fledglings succumb to predation during their maiden flight across waters around the island. To curb predation, the selective culling of individual predatory seals was implemented in 2014, 2015, and 2018. Our first study objective was to determine if selective culling of Cape fur seals significantly reduced predation probability on Cape gannets. We tested whether predation probability in 2014, 2015, and 2018 was affected by fish biomass, gannet fledgling numbers, and/or the presence/absence of selective culling

The influence of nest location and the effect of predator removal on Cape Gannet Morus capensis egg predation by Kelp Gulls Larus dominicanus vetula

The breeding range of the Cape Gannet Morus capensis currently extends to six of the ten islands formerly utilised by this species. The Cape Gannet is classified as an endangered species with a rapidly declining population. Since the mid-1950s, the global population has declined by 51% due to multiple causes, including egg predation by the Kelp Gull Larus dominicanus vetula. To assess the effect of this predation, we monitored 100 nests over an 11-week period in 2018 at the Lambert’s Bay colony in South Africa. To assess the effect of selective predator removal on the likelihood of predation, data were collected from 2006 and 2018. Our objective was to assess whether nest location and predator removal affected the likelihood of egg predation. The peripheral nests saw a higher level of egg loss (average 1.5 eggs per week) compared with the central nests (average 1 egg per week). Predator control of Kelp Gulls was implemented in 2015, 2017 and 2018. Between years, selective culling decreased the number of Cape Gannet eggs predated. However, within years, except for 2015, the predation rate on Cape Gannet eggs increased post-culling during the same year of implementation. In all three of the implementation years, predation started again (within 48 hours) after the culling commenced. Predation by this indigenous gull species is natural; however, certain human activities might have supported larger populations of Kelp Gulls leading to elevated predation intensity. The most notable being the ever-increasing existence of dumpsites and other sources of food. Predation is affecting the Cape Gannet breeding population; therefore, we suggest that an alternative, long-term, and sustainable solution be planned and implemented to reduce the effects thereof

Age and sex-specific foraging movements and energetics in an endangered monomorphic seabird

Abstract Senescence is the irreversible decline in physiological functioning and survival with age. While this phenomenon has been studied in a range of different taxa, including seabirds, it has seldom been assessed for both sexes of monomorphic species, and in conservation contexts. Here, we studied the effect of age and sex on the foraging trip characteristics and energetics of the monomorphic Cape gannet ( Morus capensis ). Between 2017 and 2020, we used GPS recorders and miniaturised three-dimensional accelerometers to obtain data on the foraging trip characteristics and energy expenditure of 39 Cape gannets rearing chicks on Malgas Island, South Africa. This sample included 11 females and 28 males between the ages of 4 and 23 years. No difference in foraging trip characteristics was apparent between sexes or individuals of different ages. The energy expenditure of aging females (> 17 years) was higher than that of aging males. Aging females spent both more energy flying and less energy resting than males, despite similar foraging trip durations and distances. Males spent more energy diving and taking off from the water than females. The age-related sexual differences in energy expenditure presented in our study might reflect niche and/or risk partitioning strategies to ensure adequate provisioning to the chick, or a possible earlier onset of senescence in females relative to males. The higher energy expenditure of aging females, which presumably requires a concomitantly higher energy intake, likely reduces their resilience to environmental change