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

Climate variability has the potential to affect ecosystems in very dramatic ways. This research tracks the predation interactions between great white sharks (Carcharodon carcharias) and Cape fur seals (Arctocepahus pusillus) on the coast of South Africa and pairs the analysis with temperature and weather datasets over the course of 15 years (1999–2013). This dataset spans 941 shark attacks on seals.

The dataset covers two types of predator-prey interactions: $K$, kills, and $AP$, attempted predations. The researchers tracked kill rate ($\frac{K}{hr}$) and total predation rate (${K+AP}{hr}).

The results? Water temperature had an impact on predation rates: Colder water meant fewer predation events, but the researchers mention that this could either be due to a lower shark metabolism (and thus a lower calorie requirement) or due to factors associated with prey availability. However, other factors, such as water visibility, wind, and weather events like El Niño or La Niña, played a greater role in predation rates: This is probably because sharks are partially endothermic, and so their metabolic modulation response to changes in weather is less pronounced than fully ectothermic animals.

So the take-home message here is that I don’t think we don’t quite understand the ways in which climate change directly affect predation rates; especially because this signal appears to have some pattern to it that cannot be explained just by weather differences. I wonder if it’s possible that the predation events are different — perhaps less visible to researchers — in certain conditions, which obfuscates the actual signal in the dataset.