Metals and metalloids in Little Penguin (Eudyptula minor) prey, blood and faeces

Piscivorous species like the Little Penguin (Eudyptula minor) are particularly at risk of being negatively impacted by pollution due to their heightened exposure through aquatic food chains. Therefore, determining the concentration of heavy metals in the fish prey of seabirds is an essential component of assessing such risk. In this study, we report on arsenic, cadmium, mercury, lead and selenium concentrations in three fish species, which are known to comprise a substantial part of the diet of Little Penguins at the urban colony of St Kilda, Melbourne, Australia. Metal concentrations in the fish sampled were generally within the expected limits, however, arsenic and mercury were higher than reported elsewhere. Anchovy (Engraulis australis) and sandy sprat (Hyperlophus vittatus) contained higher Hg concentrations than pilchard (Sardinops sagax), while sandy sprat and pilchard contained more selenium. We present these findings together with metal concentrations in Little Penguin blood and faeces, sampled within weeks of the fish collection. Mercury concentrations were highest in the blood, while faeces and fish prey species contained similar concentrations of arsenic and lead, suggesting faeces as a primary route of detoxification for these elements. We also investigated paired blood - faecal samples and found a correlation for selenium only. Preliminary data from stable isotope ratios in penguin blood indicate that changes in penguin blood mercury concentrations cannot be explained by trophic changes in their diet alone, suggesting a variation of bioavailable Hg within this semi-enclosed bay.

Fine-scale dietary changes between the breeding and non-breeding diet of a resident seabird

Unlike migratory seabirds with wide foraging ranges, resident seabirds forage in a relatively small range year-round and are thus particularly vulnerable to local shifts in prey availability. In order to manage their populations effectively, it is necessary to identify their key prey across and within years. Here, stomach content and stable isotope analyses were used to reconstruct the diet and isotopic niche of the little penguin (Eudyptula minor). Across years, the diet of penguins was dominated by anchovy (Engraulis australis). Within years, during winter, penguins were consistently enriched in δ (15)N and δ (13)C levels relative to pre-moult penguins. This was probably due to their increased reliance on juvenile anchovies, which dominate prey biomass in winter months. Following winter and during breeding, the δ (13)C values of penguins declined. We suggest this subtle shift was in response to the increased consumption of prey that enter the bay from offshore regions to spawn. Our findings highlight that penguins have access to both juvenile fish communities and spawning migrants across the year, enabling these seabirds to remain in close proximity to their colony. However, annual fluctuations in penguin isotopic niche suggest that the recruitment success and abundance of fish communities fluctuate dramatically between years. As such, the continued monitoring of penguin diet will be central to their ongoing management.