The Walleye Pollock, often simply called Alaska Pollock, is one of the world’s most commercially important fish, forming the basis for popular products like fish sticks, surimi, and fast-food fish sandwiches. This widespread use often leads consumers to question its origins and classification. A common point of confusion is whether pollock is a “bottom feeder,” a term that carries negative connotations regarding its quality and safety. To accurately understand this fish, it is necessary to examine its ecological behavior and define the specific zones of the ocean where fish live and seek their food.
Defining Fish Feeding Zones
Marine biologists categorize fish based on the vertical region of the water column they inhabit and feed in.
The Pelagic zone refers to the open water column, where fish like tuna and sardines swim freely, never venturing near the ocean floor. These fish typically feed on plankton or other free-swimming organisms in the upper layers.
In contrast, the Benthic zone describes the sea floor itself, including the sediment and substrate. Fish classified as strictly benthic feeders, such as flounder or halibut, spend most of their time resting directly on the bottom, where they primarily consume organisms living in or on the sediment.
A third category is the Demersal zone, which includes the area near the bottom, but not exclusively on it. Demersal fish, sometimes called groundfish, are often further divided into benthic fish that rest on the bottom and benthopelagic fish that swim just above the ocean floor. This distinction between living on the bottom and living near the bottom is crucial for understanding pollock’s true nature.
Pollock’s Primary Habitat and Diet
Alaska Pollock is scientifically classified as a semi-pelagic or benthopelagic schooling fish, meaning it occupies a wide range of the water column. While it is often found in the demersal zone, between 330 and 985 feet deep, it does not fit the definition of a classic benthic bottom feeder. Younger pollock tend to inhabit the mid-water region, while older pollock often dwell closer to the sea floor, sometimes as deep as 3,300 feet.
The diet of pollock further clarifies its semi-pelagic classification, as it primarily consists of small, free-swimming organisms. Its main food sources are zooplankton, specifically small crustaceans like copepods and euphausiids, which are found suspended in the water column. Larger pollock also incorporate small fish into their diet, demonstrating active predatory behavior rather than scavenging on the sea floor.
Pollock are highly migratory, moving between spawning and feeding grounds seasonally. They often exhibit diel vertical migration, rising toward the surface at night to feed on vertically migrating prey and descending during the day. This behavior confirms that pollock actively pursue their prey throughout the water column, distinguishing them from passive bottom dwellers.
Consumer Perception and Quality Assurance
The consumer concern behind the “bottom feeder” label often relates to the fear of contamination, particularly high levels of mercury. This concern arises because mercury bioaccumulates in the food chain, meaning species higher up and those that are longer-lived tend to have greater concentrations.
Pollock has a relatively short lifespan and occupies a low position on the food chain, feeding on plankton and small fish. This low trophic level ensures that pollock consistently tests low for mercury contamination, often lower than 0.031 parts per million, making it one of the safest commercial fish to consume.
Furthermore, the Alaska Pollock fishery is one of the largest and most responsibly managed in the world, with sustainability certifications from organizations like the Marine Stewardship Council. The perception of pollock as a low-quality fish is a misconception. It is a clean, versatile, and sustainable source of protein.