Th e Relationship Between Fish Length and Otolith Size and Weight of the Australian Ancnovy, En-graulis australis (Clupeiformes, Engraulidae), Retrieved from the Food of the Australasian Gannet, Morus serrator (Suliformes, Sulidae), Hauraki Gulf, New Zealand

Relationships between fish length and otolith length, width and mass were examined in the Australian anchovy Engraulis australis (White, 1790) recovered from the food of Gannet examined from colonies at islands of Horuhoru Rock and Mahuki Islands in the Hauraki Gulf, New Zealand. The relationships between otolith length- fish total length (TL), otolith-weight-TL, and otolith-width-TL were investigated by means of non-linear regression models (TL = 0.54 OL 16.86, TL = 4.39 OW 7.61 and TL = 26.19 OWe 2.2). This study characterizes the first reference available on the relationship of fish size and otolith size and weight for E. australis obtained from bird’s food in the Pacific Ocean region

Geographical, temporal and individual factors influencing foraging behaviour and consistency in Australasian gannets

Foraging is a behaviour that can be influenced by multiple factors and is highly plastic. Recent studies have shown consistency in individual foraging behaviour has serious ecological and evolutionary implications within species and populations. Such information is crucial to understand how species select habitats, and how such selection might allow them to adapt to the environmental changes they face. Five foraging metrics (maximum distance from the colony, bearing from the colony to the most distal point, tortuosity index, total number of dives and mean vectorial dynamic body acceleration were obtained using GPS tracking and accelerometry data in adult Australasian gannets ( Morus serrator ) from two colonies in southeastern Australia. Individuals were instrumented over two breeding seasons to obtain data to assess factors influencing foraging behaviour and behavioural consistency over multiple timescales (consecutive trips, breeding stages and years) and habitats (pelagic, mixed pelagic and inshore, and inshore). Colony, breeding stage and year were the factors which had the greatest influence on foraging behaviour, followed by sex. Behavioural consistency, measured as the contribution of the individual to the observed variance, was low to moderate for all foraging metrics (0.0–27.05%), with the higher values occurring over shorter timescales. In addition, behavioural consistency was driven by spatio-temporal factors rather than intrinsic characteristics. Behavioural consistency was higher in individuals foraging in inshore than pelagic habitats or mixed pelagic/inshore strategy, supporting suggestions that consistency is favoured in stable environments.

Inter- and intra-individual variation in the diet of Australasian gannets Morus serrator

Animal diets often vary according to age, sex, experience and/or individual preferences, which, when maintained over time, can lead to behavioural consistency and individual specialisations within populations. In addition, behavioural and dietary similarity within breeding pairs confers reproductive benefits in some species. We investigated inter- and intra-individual variation in diet in Australasian gannets Morus serrator through analysis of voluntary regurgitations, blood plasma stable isotopes and reconstructed diets. Samples were collected from nesting adults (mostly partners) over 4 breeding seasons (2012-2015) at 2 colonies (Point Danger, PD; and Pope’s Eye, PE), 215 km apart and with divergent oceanographic conditions. Inter-individual variation in δ13C and δ15N values and reconstructed diets was associated with colony, year, breeding stage and sex. The diet of PD individuals was dominated by pelagic schooling prey species, whereas PE birds consumed a substantial amount of benthic/inshore species. Correspondingly, the proportional similarity in diet of individuals was greater at PD, where individuals foraged within a relatively uniform environment, than at PE, where birds had access to a greater diversity of foraging habitats. Intra-individual variation in isotopic values indicated that trophic consistency was higher over medium timescales (between breeding stages within breeding seasons) than longer timescales (between breeding seasons), in accordance with recently documented temporal patterns of behavioural consistency. Lastly, nest partners consumed prey of similar trophic level (δ15N values), although a high degree of similarity did not confer a reproductive advantage to nest partners, and the mechanisms for such similarity are unknown.