A Landscape of Fear: Great-white Shark VS. Killer Whale

The landscape of fear is a unified ecological concept that has developed over the last two decades. It is widely documented in terrestrial (Laundre et al., 2010) and in some marine systems (Wirsing et al., 2008), focusing on prey and predator interactions. A species’ environment is composed of high to low risk areas of predation, resulting in alterations of its behaviour to avoid any high risks, with potential cascading ecosystem impacts

Marine top predators, such as large marine mammals and elasmobranch, are high-trophic consumers, maintaining ocean diversity through top-down control. They have few predators, and regulate prey populations through lethal kills and by intimidation. This results in prey altering their behaviour, including habitat and foraging strategies in order to avoid risk. However, knowledge on lethal and sub-lethal interactions between marine top predators and its ecological significance is lacking.

A new paper published in Nature’s Scientific reports, led by Dr. Jorgensen of Monterey Bay Aquarium, compiled observational data over 26 years (1987-2013) around the Southeast Farallon Island on the foraging behaviour of Great white sharks and the abundance of the Elephant seal and Killer whale populations. This, paired with electronically tracked data of 165 Great white sharks (2006-2013) around Central California, enabled the foraging behaviour of the Great white shark population in the presence of the Killer whale to be modelled around the South Farallon Island.

Based on their analysis, the Great white shark population consistently fled when Killer whales were present within 3km of the shore. They would flee to the extent that they would abandon the site entirely only returning the following season.

These interactions were restricted to the autumnal months, where over 219 Great white sharks are known to prey annually on the juvenile Elephant seal population before migrating offshore. The annual predation rate by Great white sharks on these populations in the presence of Killer whales saw a marked dropped by 62%.

Killer whales are sub-classified into groups of genetically distinct “ecotypes”, with varying diets, communication methods, social structure, and foraging strategies. The most commonly sighted eco-type was the mammal-eating Transient , with only one occurrence of the Offshore eco-type in 2009. A total of 18 sightings of Killer whale pods, ranging from 1-17 individuals were present during the autumnal months of years 1992, 1995-1998, 2000,2001,2009 and 2013.

The eco-type of the killer whale dictates whether the interactions between the two apex predators are competitive or predatory. The Transient killer whale eco-type is a direct competitor to the Great white shark and the only known Killer whale type to have led to a fatal attack and partial consumption of a Great white shark, recorded in 1997. Meanwhile, the elusive Offshore killer whale eco-type is potentially both a competitor and predator to the Great white shark, indicated by worn-down teeth and its documented attacks on other shark species.

This paper, through long-term data collection, led to an important discovery on the ecological interactions between two large marine apex predators. In particular, it confirmed that the Killer whale is a threat both as competitor and predator to the Great white shark. Non-lethal and behavioural mediated mechanisms shape the spatial and temporal use of the habitat and foraging activities of the Great white shark. These behavioural changes bring an inherent risk of reduced foraging ability and fitness before migrating offshore to an already vulnerable species. These interactions have a trickled down effect on lower trophic levels that can be both positive or detrimental to the ecosystem, here, benefiting its prey, the Elephant seal population.

If you'd like to learn more, below is a video of a dramatic reconstruction of 1997 predation event by Transient killer whales of Great white shark at the Farallon Islands and information on the Killer whale and Great white shark population in the documentary “The whale that ate Jaws” by National Geographic WILD.

References:

Eagle, T., Cadrin, S., Caldwell, M., Methot, R. and Nammack, M. 2008. Conservation Units of Managed Fish, Threatened or Endangered Species, and Marine Mammals Report of a Workshop: February 14-16, 2006 Silver Spring, Maryland.

Ford, J., Ellis, G., Matkin, C., Wetklo, M., Barrett-Lennard, L. and Withler, R. 2011. Shark predation and tooth wear in a population of northeastern Pacific killer whales. Aquatic Biology , 11 (3), 213-224.

Jorgensen, S., Anderson, S., Ferretti, F., Tietz, J., Chapple, T., Kanive, P., Bradley, R., Moxley, J. and Block, B. 2019. Killer whales redistribute white shark foraging pressure on seals. Scientific Reports , 9 (1).

Laundré, J. W., Hernández, L. and Ripple, W. J. 2010. The landscape of fear: ecological implications of being afraid. Open Ecology Journal , 3 , 1-7.

Wirsing, A. J., Heithaus, M. R., Frid, A. and Dill, L. M. 2008. Seascapes of fear: evaluating sublethal predator effects experienced and generated by marine mammals. Marine Mammal Science , 24 (1), 1-15.