Abstract
Understanding the foraging ecology of a species provides essential knowledge to inform evidence-based conservation management. This study used GPS and dive data loggers, and eDNA metabarcoding to determine the foraging behaviour and diet of breeding tawaki/Fiordland crested penguins (Eudyptes pachyrhynchus) in Tamatea/Dusky Sound, New Zealand, during the guard stage of the 2023 and 2024 breeding seasons. Colonies selected for GPS deployment were located near the mouth of the fjord and were latitudinally separated, with Anchor Island acting as a north-south barrier between them.
Diverse foraging behaviours were observed, with offshore foraging over continental slope waters, inshore foraging in open-fjord waters as well as inshore foraging in the reef and coastal environments. The foraging ranges of colonies did not overlap inside the fjord, with minor overlap observed offshore in 2024. Individuals tended to be exclusively inshore or offshore foragers, with only two of the 13 tracked tawaki conducting both inshore and offshore trips. Inshore foraging was primarily within the surface 30 m where individuals conducted over 50 dives per hour with dive durations of between 50 and 60 seconds. These parameters remained relatively constant throughout daylight hours. Offshore foragers undertook 25-35 dives per hour to depths below 70 m with dive durations that frequently exceeded 100 seconds. Offshore foragers exhibited plasticity in diving behaviour. The increased their foraging effort at midday, indicating the depth of their dives was limited by light availability.
During both years, we opportunistically collected scat samples for eDNA metabarcoding from colonies throughout the fjord. Phylogenetic diversity did not differ significantly between colonies, yet species richness did. The core diet of tawaki was composed of the small forage fish pennant pearlside (Maurolicus australis) and hoki (Macruronus novaezelandiae). These two species were detected at every colony and 69% and 45% of samples respectively. Eleven other species of fish, eight species of crustaceans and six species of cephalopods were also detected. Over 60% of detected prey items at all colonies were from the epipelagic and mesopelagic marine environments. Six of the detected species are commercially fished in New Zealand. Although tawaki would have targeted the larval and juvenile form of these species, our findings indicate greater resource competition with fisheries than previously thought. Tracked tawaki were not seen to forage in the marine protected areas of the fjord, suggesting the current spatial management of Tamatea/Dusky iv Sound does not protect tawaki from incidental bycatch. Furthermore, eDNA metabarcoding revealed the crepuscular foraging activity seen in dive data was targeted to a vertically migrating prey species such as the lanternfish (Myctophids) or cephalopods, highlighting the compatibility of these two methods in tawaki research. As climate change alters the distribution of marine organisms, tawaki will likely be faced with shifting prey communities. Whether future prey communities will meet breeding tawaki’s nutritional requirements is uncertain and should be a future research priority. Our results provide key baseline knowledge to which future studies of tawaki diet and foraging strategies in southern Fiordland can be compared. Overall, plastic foraging strategies and a diverse diet show tawaki can adapt their foraging strategies to best exploit their local environment. This adaptability bodes well for tawaki in a rapidly changing climate.