Selective foraging within estuarine plume fronts by an inshore resident seabird

Abstract

The distribution of predators relative to specific abiotic and biotic factors within estuarine plume fronts is largely unexplored due to the lack of fine-scale temporal and spatial oceanographic data. Defining preferred foraging conditions of seabirds in these areas is critical to identifying important foraging habitats. Here, we use data obtained from Ships of Opportunity to improve the way we quantify oceanographic conditions at scales that match marine animal foraging activities within these areas. Using biologgers and data from a Ship of Opportunity, we assessed the fine-scale habitat utilization of the Little Penguin (Eudyptula minor) within an estuarine plume in Victoria, Australia. We assessed how environmental conditions within the home-range (transit and foraging) and core-range (subset area of intensive foraging within the home-range) of this inshore seabird differed to environmental conditions in the accessible, but non-utilized range (i.e., non-foraging range). Penguin foraging ranges occurred in waters with higher Chl-a, turbidity, temperature and lower salinity than non-foraging ranges. High Chl-a biomass was the most important explanatory variable of penguin distribution. Environmental conditions between the core-range and less used home-range also differed. Waters in the core-range were less productive, less turbid and less dynamic. We suggest penguins are foraging in these core-ranges due to the productive yet stable environmental conditions that likely offer a higher degree of prey predictability than the fluctuating conditions in the wider home-range. Furthermore, penguins may spend a greater proportion of their time in core-ranges as these waters have relatively low turbidity and may improve the ability of penguins to detect and capture their prey. Our results highlight the ability of a small-ranging, visual predator to selectively forage in waters with favorable conditions at fine-scales as a potential means to improve foraging efficiency.

Oceanographic drivers of marine mammal and seabird habitat-use across shelf-seas: A guide to key features and recommendations for future research and conservation management

“…Resultant productivity levels are high (Cloern, 1991), and attract large numbers of zooplankton and forage fish (Govoni et al, 1989;Kingsford and Suthers, 1994;Kaltenberg et al, 2010;Phillips et al, 2017), which may be concentrated at the surface signature of the front due to additional convergent flows (Govoni et al, 1989). A number of piscivores, such as black and red throated diver Gavia stellata/arctica, bottlenose dolphin, common guillemot, little penguin, northern fur seal and sooty shearwater Ardenna grisea, forage at estuarine plume and tidal intrusion fronts (Skov and Prins, 2001;Mendes et al, 2002;Pelland et al, 2014;Zamon et al, 2014;Kowalczyk et al, 2015a;Phillips et al, 2017). The location, occurrence and strength of these features may be tidally mediated and/or dependent upon local current patterns, rainfall and wind events (Sharples and Simpson, 1993;Kingsford and Suthers, 1994;Choi and Wilkin, 2007;Schlacher et al, 2008).…”

Seasonal variation and annual trends of metals and metalloids in the blood of the Little Penguin (Eudyptula minor)

“…It is possible that this could be a result of a partial overlap in the foraging range of the two sampled colonies during their non-breeding period. As central place foragers (Orians and Pearson, 1979), Little Penguins are restricted in their home range during the breeding season (Collins et al, 1999;Kowalczyk et al, 2015a). Due to the consistent and reliable presence of clupeoid fish in suitable size classes (6-10 cm) within Port Phillip Bay (Hirst et al, 2010;Hirst et al, 2011), adult St Kilda Little Penguins feed exclusively within Port Phillip Bay throughout the year (Preston et al, 2008;Kowalczyk et al, 2015a).…”

“…As central place foragers (Orians and Pearson, 1979), Little Penguins are restricted in their home range during the breeding season (Collins et al, 1999;Kowalczyk et al, 2015a). Due to the consistent and reliable presence of clupeoid fish in suitable size classes (6-10 cm) within Port Phillip Bay (Hirst et al, 2010;Hirst et al, 2011), adult St Kilda Little Penguins feed exclusively within Port Phillip Bay throughout the year (Preston et al, 2008;Kowalczyk et al, 2015a). Phillip Island penguins forage near their colony in the open waters of Bass Strait during the breeding season, but enter Port Phillip Bay during the winter months for the benefits of more reliable prey and calmer waters (McCutcheon et al, 2011;Chiaradia et al, 2012).…”

“…Metals and other pollutants stored in marine sediments can become bioavailable when these sediments are physically disturbed and toxicant particles are re-suspended in the water column (Hedge et al, 2009;Edge et al, 2015;Fetters et al, 2015). EPA Victoria, the environmental governing body of the state, have executed a monthly monitoring protocol of water quality measures since 2000 for several stations within the bay (EPA, 2015), including Hobsons Bay, which is within the known foraging range of St Kilda penguins (Preston et al, 2008;Kowalczyk et al, 2015a). These measurements recorded a number of spikes in total suspended solids (TSS), Cr, Cu, Pb and Zn for Hobsons Bay in 2008 and 2009 (Fig.…”

Predator–prey interactions influenced by a dynamic river plume

“…Increased abundances of predators near river plumes (Ashford et al 2013;Zamon et al 2014;Kowalczyk et al 2015) suggests that these physical features may be hotspots for predator-prey interactions.…”