Dolphin Prey Availability and Calorific Value in an Estuarine and Coastal Environment

Abstract

Prey density has long been associated with prey profitability for a predator, but prey quality has seldom been quantified. We assessed the potential prey availability and calorific value for Indo-Pacific bottlenose dolphins (Tursiops aduncus) in an estuarine and coastal environment of temperate south-western Australia. Fish were sampled using three methods (21.5 m beach seine, multi-mesh gillnet, and fish traps), across three regions (Estuary, Bay, and Ocean) in the study area. The total biomass and numbers of all species and those of potential dolphin prey were determined in austral summers and winters between 2007 and 2010. The calorific value of 19 species was determined by bomb calorimetry. The aim of the research was to evaluate the significance of prey availability in explaining the higher abundance of dolphins in the region in summer vs. winter across years. A higher abundance of prey was captured in the summer (mean of two summer seasons 12,080 ± 160) than in the winter (mean of two winter seasons = 7358 ± 343) using the same number of gear sets in each season and year. In contrast, higher biomass and higher energy rich prey were captured during winters than during summers, when fewer dolphins are present in the area. Variability was significant between season and region for the gillnet (p < 0.01), and seine (p < 0.01). The interaction of season and region was also significant for the calorific content captured by the traps (p < 0.03), and between the seasons for biomass of the trap catch (p < 0.02). The dolphin mother and calf pairs that remain in the Estuary and Bay year round may be sustained by the higher quality, and generally larger, if lesser abundant, prey in the winter months. Furthermore, factors such as predator avoidance and mating opportunities are likely to influence patterns of local dolphin abundance. This study provides insights into the complex dynamics of predator-prey interactions, and highlights the importance for a better understanding of prey abundance, distribution and calorific content in explaining the spatial ecology of large apex predators.

Applying the multistate capture–recapture robust design to characterize metapopulation structure

“…This agrees with other studies indicating that bottlenose dolphins are often more abundant in open coast environments where individuals tend to have larger home range size, which may reflect both food availability and foraging tactics (Sprogis et al . ; McCluskey, Bejder & Loneragan ).…”

Optimization of foraging and diet by the piscivorous Othos dentex (Serranidae)

“…dentex selects its prey based on size, rather than the morphological characteristic of a particular family or taxon and thus many species that come within its range constitute potential prey. Indeed, the energy derived from the prey obtained by each foraging episode could be sufficient to tide an individual over for a substantial time, especially since fishes have a substantial calorific value (McCluskey et al ., ). Since O .…”

Identifying the Relevant Local Population for Environmental Impact Assessments of Mobile Marine Fauna

“…These environments contain shallow and protected habitats that allow bottlenose dolphins to reside year-round (Wells, 1986;Brusa et al, 2016). Prey availability in these environments is also more continuous and dependable (Elliott and Whitfield, 2011;McCluskey et al, 2016) than in open and coastal regions, where prey is distributed patchily and prey availability is dictated largely by oceanic physical processes (Silva et al, 2008). The key ecological and demographic characteristics of dolphin communities in estuaries and embayments differ from those in coastal areas-e.g., inshore communities tend to be small and to exhibit weak to moderate levels of dispersal and immigration (Titcomb et al, 2015).…”