The southern resident orcas are a group of orcas in the Salish Sea and Pacific Ocean near the Pacific Northwest. They are divided into three pods: The J Pod, the K Pod, and the L Pod. In each pod, all of the orcas in that pod have the same common ancestor. For example, every orca in the J Pod is related to each other because they are all descendants of the same mother. The J Pod has 25 orcas, the K Pod has 16, and the L Pod has 32, totaling to 73 orcas (as of December 2022). The population of the orca pods has been fluctuating since it started being measured. There has been a slow decline with the L Pod, a slight increase with the J Pod, and a mostly stable population in the K Pod. Although the decline of the total southern resident population is slow, it will eventually get too low unless action is taken to stop it.
Southern resident orcas have a different diet from most orcas around the world, because orcas can have very different diets depending on their location. Orcas can eat fish, birds, turtles, mammals, and cephalopods (cephalopods are mollusks like squid, octopus, nautilus, and cuttlefish). The southern resident orcas, however, only eat fish. About 97% of a southern resident's diet is salmon, specifically Chinook salmon (78%, highest in spring and fall), chum salmon (11%, highest in fall), coho salmon (5%), steelhead (2%), and sockeye (1%). The remaining 3% of fish they eat is Pacific herring and quillback rockfish. Healthy orcas require the consumption of 18 to 25 adult salmon per day to remain healthy and have enough energy. The total daily consumption of adult salmon for all southern residents must be 1,314 to 1,825 adult salmon for all pods to have enough energy and stay healthy.
Like all orcas, the southern residents communicate by making sounds underwater. There are three types of sounds produced by orcas: clicks, whistles, and calls. Some orca sounds cannot be heard by humans, because humans can only hear sounds below 20 kilohertz.
Clicks are used for echolocation, which is used to determine the surrounding terrain and prey. Clicks have also been used when interacting with other orcas, so it is possible that they are used for communication as well. Clicks have a very short duration, lasting a maximum of 25 milliseconds, but their duration can be as low as 100 nanoseconds. Clicks are usually produced sequentially, up to 300 times per second, but single clicks are also sometimes produced. The frequency of the clicking sounds can be from 4 kilohertz to 85 kilohertz.
Whistles are primarily used for long-range communication and interaction with other orcas. The peak frequency of whistles can be from 2 kilohertz to 18.5 kilohertz. Whistles consist of the high amplitude peak frequency combined with lower amplitude harmonic frequencies. Whistles can have up to 71 frequency modulations (warbles), but have an average of 5. Whistles usually last for about 2 seconds, but they can be as short as 60 milliseconds and as long as 18 seconds.
Calls are also used for communication, and they are the most common sound produced by orcas. Calls are repetitive sound pulses, and up to 4,000 pulses can be produced per second. The repetition rate and frequency of pulses repeatedly changes throughout a call. The frequency of pulses is usually 1 kilohertz to 6 kilohertz, but can be as high as 30 kilohertz. Calls usually last less than 2 seconds, but they are sometimes longer.
Recovery Plan for Southern Resident Killer Whales by the National Marine Fisheries Service, 2008
Center for Whale Research web site
All uncredited images and sounds are in the public domain.