Ecosystem Services 3.7
What is causing the decline of little penguins (Eudyptula minor) on Granite Island, South Australia?
| ID Number | Project Number | Manager | Start Date | End Date | Total Project Funds ($) |
| SVE-5453F | RD06/0401 | Goldsworthy, Simon | 01-Feb-2006 | 30-Nov-2006 | 4,700 |
Executive Summary
The number of little penguins at Granite Island has been declining since the early 1990s. Large numbers of tourists visit Granite Island to view the penguins and the island is inhabited by non-native black rats (Rattus rattus) and water rats (Hydromys chrysogastes) whereas nearby West Island does not have any tourists nor land-based predators. Data on the little penguin population size, breeding success, diet composition, foraging behaviour and predation by both rats and New Zealand fur seals (Arctocephalus forsteri) were collected at Granite and West Islands to determine the likely onshore or offshore factors that may be causing the decline in the Granite Island population. In 2006, the percentage of chicks that fledged was significantly less at Granite Island (37%) compared to West Island (54%). Although there was little overlap (9%) in the foraging areas used by penguins at each site, there were no significant differences in prey species consumed or the mass of stomach contents at Granite (45.0 ± 33.1 g) (mean ± SD) and West Islands (46.0 ± 35.0 g). Both sites showed a similar delayed onset of breeding in 2006 and population surveys in 2006 indicated that both sites might be in decline, suggesting that tourism and predation by rats are not solely responsible for the decline in the Granite Island population. New Zealand fur seals consumed adult penguins at both sites, indicating that they may be causing part of the decline at Granite and West Islands and accordingly, ongoing monitoring of fur seal diet is required.