Results of post-release monitoring studies have varied between oil spills and species as no two spills are the same and responses to oiling and rehabilitation vary inter-specifically (Goldsworthy et al. 2000; Wolfaardt et al. 2009b). The most relevant comparisons to the
Rena are those conducted on little blue penguins rehabilitated after the Iron Baron oil spill in Australia. This vessel struck the Hebe Reef in northern Tasmania on 10 July 1995 (Giese et al. 2000; Goldsworthy et al. 2000a; Goldsworthy et al. 2000b), spilling 325 tonnes of bunker fuel oil spilled into the marine environment of which half washed ashore (Goldsworthy et al. 2000a). This was a similar amount and fuel type to that spilled during the Rena oil spill. While on a global scale the Iron Baron (and Rena) spill was considered a small spill, as the oil contaminated important seabird foraging and breeding grounds, the impact on wildlife was profound. Many seabirds of a variety of species were oiled, with little blue penguins the most visibly affected species (Goldsworthy et al. 2000b). Considerably more oiled penguins were rescued and rehabilitated after the Iron Baron spill (1894 birds) than the Rena (383 birds). Captive survival rates were similar between the two spills (approximately 95%: Giese et al. 2000; Goldsworthy et al. 2000a; Goldsworthy et al. 2000b), but post-release survival and reproductive success were lower for rehabilitated penguins after the Iron Baron spill than the Rena spill (Table 4.1). The post-release monitoring results of this spill provide a good comparison to those from the Rena spill as although some spill conditions differed, the study species is the same.
122 Table 4.1. Post-release survival and productivity variables studied during the Iron Baron and
Rena oil spills. Productivity information presented for the Iron Baron spill is only from the first year studied so comparisons can be made to the one-year Rena study. A cross indicates that a significant difference was found between control and rehabilitated penguins (in all cases this represents a reduction, delay or protraction in the variable for rehabilitated penguins relative to control penguins). A tick indicates that a variable was similar (p-value >0.05) for rehabilitated and control penguins. A cross and a tick together indicates that there were both differences and similarities between the two groups.
Variable Rena oil spill Iron Baron oil spill
Breeding study
Timing of egg laying 9 X
Duration of egg laying 9 X
Clutch size 9 n/a
Hatching success X 9
Fledging success 9 n/a
Egg success 9 X
Pre-fledging chick masses 9 X
Survival study
Post-release survival 9 X
Breeding season survival 9 X
Moult period survival 9 9
Post-release masses 9 X /9
These comparisons indicate that in general penguins rehabilitated after the Iron Baron oil spill had lower survival and reproductive success than control penguins, whereas after the
Rena oil spill most parameters assessed were similar between the two groups. This suggests that the rescue, treatment and rehabilitation process conducted during the Rena oil spill was possibly more successful than that during the Iron Baron oil spill; this may be attributed to a few factors that differed between the two spills. Firstly, the Rena spill occurred 16 years after the Iron Baron spill therefore increased survival and productivity of rehabilitated
123 penguins may be due to improvements in oiled wildlife rehabilitation; animal husbandry and care may have also improved (Ben-David et al. 2002; Kuyper and Williams 2004; Newman et al. 2004; Ziccardi 2008; Wolfaardt et al. 2009b).
The response and preparedness of the oiled wildlife rescue operation may have also improved over time. Goldsworthy et al. (2000b) state that during the Iron Baron oil spill, island sites were visited 4-26 days after the spill. As one of their main study sites was an island (Ninth Island) this delay in rescuing oiled penguins increased the duration between the oiling and treatment of individuals, resulting in penguins losing mass and condition. Negative effects of oil contamination may have also manifested. Consequently, penguins from Ninth Island may have been more adversely affected by oiling and possibly less receptive to rehabilitation, resulting in the survival and productivity of these penguins being compromised by persistent oiling effects. During the Rena oil spill, the rescue operation was prompt and daily targeted night searches for oiled penguins were conducted. This minimised durations of oil exposure and thus possibly enabled more effective treatment of toxic oiling effects. This may have contributed to the increase in post-release survival and breeding success of rehabilitated penguins.
Lastly, following the Rena oil spill, rehabilitated penguins were released at their site of capture, whereas following the Iron Baron spill 53% of the rehabilitated penguins were translocated prior to release (20% were released 210 km from Low Head (one of the main sites oiled penguins were rescued from) and 33% were released 410 km away from Low Head)); survival of these translocated individuals may have been reduced due to unfamiliarity with the foraging grounds and the extra energy expenditure required to return ‘home’ (Goldsworthy et al. 2000b). Higher post-release following the Rena oil spill may therefore be partially explained by rehabilitated penguins being released at their capture site.
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