Have you ever eaten a fish? Have you ever questioned where they came from and who caught them? In order to provide the fish you see in grocery stores, people travel far out into the ocean (even as far as the arctic!) to catch fish in large quantities, there are a lot of humans to provide for after all! However, we mustn’t forget that we live amongst other animals that rely on the same food. Imagine suddenly one day that your favorite food you eat randomly disappears, naturally you’re curious, who’s stealing my food? Unfortunately this is the reality for many sea critters including killer whales (Orcinus Orca) that rely on a specific fish called the Patagonian toothfish (Dissostichus eleginoides) as part of their diet. Sometimes humans can be greedy and not share with our sea friends which leads sea creatures to more creative avenues. Fisheries are regions in the ocean where fishermen throw out large nets or a multitude of hooks to catch a surplus of fish. When killer whales discovered this, some of them decided to use these fisheries to their advantage (by eating the caught fish), engaging in a behavior known as depredation. While this put them in conflict with humans and at times injuring themselves (human-wildlife conflict) on fishing equipment, this allowed foraging time to be significantly lowered. How did this behavior come to be? A group of scientists asked the same question and decided to begin their research.
Everyone has a unique fingerprint, similarly killer whales have natural markings that make them distinct from each other. Using a technique called mark-recapture, scientists were able to identify killer whales through a large variety of photographs spanning over many years to determine depredation behavior. For this study two types of killer whales were classified, Regular and Type-D. The main difference between them is their diet with one feeding inshore and offshore and the other feeding only in offshore waters.
Scientists found in both types, depredation behavior increased over the span of multiple years. Since the growing population for both species remain relatively unchanged (lacking of new offspring), scientists predicted the observed behavior was likely due to existing members in the population(s) developing depredation as a new behavior. Now onto the real question: why was this behavior observed? Scientists propose four possible answers to this: (1) Killer whales differ in their levels of specialization for their diet (think of a picky eater versus someone who eats anything) (2) New behaviors are learnt socially and can spread from one group to another (3) Individuals may resort to depredation due to scarcity of natural prey (4) The development of depredation as a behavior took a few years to increase due to the risks associated with it. Ultimately this study shows how human activities (like fishing) can alter the available food sources and how a species might respond to these changes. For killer whales, a known top-predator of the sea, adapting quickly to new feeding opportunities is key to their survival and how they interact with other sea animals in the environment.
References
Amelot M, Plard F, Guinet C, Arnould JPY, Gasco N, Tixier P. 2022. Increasing numbers of killer whale individuals use fisheries as feeding opportunities within subantarctic populations. Biology Letters 18: 2021/03/28. https://doi.org/10.1098/rsbl.2021.0328
