Patterns of long-term climate variability and predation rates by a marine apex predator, the white shark Carcharodon carcharias

Abstract

Understanding potential responses of aquatic animals to climate variability is important, given the wide-ranging implications of current and future climatic change scenarios. Here, we used long-term data from natural predator−prey interactions between white sharks Carcharodon carcharias and Cape fur seals Arctocephalus pusillus pusillus in False Bay, South Africa, paired with environmental monitoring to examine potential relationships between temperature variability and shark predation rates on seals. Based on generalized linear modelling of a dataset of 941 shark attacks on seals collected over 15 years (1999−2013) during the austral winter (May−September) season, we found water temperature was included as a significant predictor of daily and monthly variability in predation rates. However, the signal of temporal variability over the season emerged as a more predominant predictor. Moreover, inter-annual variability in predation rate appeared linked to other environmental factors (wind, water visibility, and the occurrence of El Niño and La Niña events) rather than water temperature. These data suggest that water temperatures on an intra-annual scale might contribute to predation patterns in white sharks either directly or indirectly (e.g. due to associated changes in prey availability), but do not implicate water temperature as a primary driver in this scenario, or at an interannual scale. It is possible that (1) the metabolic demand of white sharks may be modulated against temperature variability by their partially endothermic nature, and (2) the predation patterns of white sharks on seals are the result of a complex interplay between ambient physical conditions and broader oceanographic, biological, and ecological factors.KEY WORDS: Predator ecology · Climate variation · El Niño · Shark · Seal · Temperature Resale or republication not permitted without written consent of the publisher Editorial responsibility: Alistair Hobday,

Disappearance of white sharks leads to the novel emergence of an allopatric apex predator, the sevengill shark

“…S3). Furthermore, previous work at Seal Island found no influence of temperature on inter-annual variations in white shark predation rates 24 . Taken together, while our results are correlative, we are not aware of any major environmental or biological perturbations across the study period that we can attribute to the appearance of sevengill sharks at Seal Island in 2017 and 2018, with the exception of the disappearance of white sharks from our surveys.…”

“…While the seal population size in False Bay remains relatively high and stable 10,23 , there could be undocumented declines or distributional shifts in alternative prey needed to sustain this apex predator. Changes in water temperatures associated with climate variability are unlikely to be a driver of the declines as a previous study at Seal Island found no impact of water temperature on inter-annual variations in white shark predation rates 24 . Determining the drivers and scale of the white shark declines documented in this study is a priority area for future research.…”

Quantifying habitat selection and variability in habitat suitability for juvenile white sharks

“…Thus, habitat modeling is an important tool managers can use to forecast how species distributions may shift in the coming years. Furthermore, El Niño Southern Oscillation events have been found to affect documented sub-adult and adult white shark predation rates in South Africa [63].…”

Variation in predator diet and prey size affects perceived impacts to salmon species of high conservation concern

“…However, including information about predatorprey relationships remains relatively uncommon in practice, likely due to data limitations (Marshall et al 2018). Even in "data rich" situations, predator-prey relationships in aquatic ecosystems are often complex because they can be mediated by abiotic and biotic factors that vary on seasonal and annual time-scales (Smout et al 2014;Lee et al 2016;Furey and Hinch 2017;Skubel et al 2018), and are also influenced by other factors like migration (Schindler et al 4 2013; Furey et al 2018). Consequently, in most systems predation rates vary spatially and temporally, and collecting enough data to adequately represent these dynamics in a mathematical model for management presents a formidable challenge.…”