Orcas have a diverse diet, and they feed on several types of fish, squid, marine mammal species, seabirds, penguins, sea turtles and even other types of whales. It is believed that orca populations in various parts of the world, specialize in only one or few kinds of prey.
In the Norwegian Sea, orcas move between coastal and offshore waters following the seasonal movements of the Norwegian spring-spawning herring and orcas have always been found within the fjords in the winter months. In the late 1960s, however, this herring stock collapsed as a result of overfishing. During the recovery, the herring changed its migratory pattern and started spending winters closer to the Norwegian coast instead of offshore waters between Iceland and Norway.
In the past few years, the presence of the orcas has developed the opportunity for tourists to enter the water and observe the natural behavior of the orcas as they feed. Despite being a fast-growing tourist attraction, little is known about these orca populations. To add complexity to the situation, in recent years, humpback whales have started entering the fjords, following the same prey that the orcas are following: herring.
Schooling in vast numbers, herring form the base of the food chain and are an important resource for both marine mammals and people. Interactions between humans and marine mammals in the Norwegian Arctic have been steadily increasing. The oil, gas, and fishing industries—the most important industries in the country—present risks for marine communities, and cetaceans in particular, if not properly managed. Exploring the seabed to look for oil produces loud sounds that can affect the whales’ prey, their feeding success, and their ability to communicate. The high number of fishing boats in the winter, traveling in the dark, increases the possibility of collisions with whales. And as more tourists participate in whale watching, more boats encroach on whale habitat.
The area is spectacularly beautiful, featuring steep mountains that plunge into the sea, numerous fjords and lakes, the famous midnight sun, and some of the most spectacular northern lights (depending upon the time of year and the weather). Thanks to the warm current of the Gulf Stream, Vesterålen has relatively mild winters and moderately warm summers and this creates perfect conditions for the spawning of herring. The main wintering area of the North Atlantic herring is in the three fjords Tysfjord, Ofotfjord and Vestfjord in Northern Norway. The estimated amounts of herring overwintering in the fjords were 6 million tonnes in 2003, and 7 million tonnes in 2004. The stock stays in these fjords from mid-October to January. The herring is every year accompanied by around 1500 killer whales, specialized on the herring as their main prey species. The killer whales have evolved a fascinating feeding technique, called “carousel feeding.” During this procedure they circle around a school of herring to get it tight and bring it to the surface; the surface then acts as a barrier which prevents the herring from escaping. When the school is tight enough the whales slap their tail flukes through it, to stun or kill the fish. After that they eat the motionless fish one by one.