Mackerel is often mistakenly classified as a bottom feeder, but this is incorrect. Mackerel is a fast-swimming, migratory fish that actively pursues prey in the open ocean water column. Understanding the terminology marine biologists use to categorize fish habitats clarifies why mackerel belongs to a different group than true bottom dwellers. This classification determines their lifestyle, physical adaptations, and nutritional value.
Understanding Fish Feeding Zones
Marine life is categorized into distinct zones based on depth and proximity to the seabed. The term “bottom feeder” refers to species that inhabit the seafloor, or the benthic zone. These fish, such as flounder or sole, are adapted to forage directly on or within the sediment, consuming small invertebrates and organic detritus.
A separate category is the demersal fish, which live near the ocean floor. This group includes species like cod or haddock, which may hunt on the bottom but also feed in the water column immediately above it.
In contrast are the pelagic fish, which inhabit the open water, far from the shore and the seabed. Mackerel falls into this category, spending its entire life swimming and feeding in the mid-to-upper layers of the water column.
Mackerel’s True Habitat and Diet
Mackerel are built for a life in the open ocean. Their streamlined, torpedo-shaped bodies and deeply forked caudal (tail) fin are suited for powerful, sustained swimming and fast pursuit of prey. These physical adaptations differ fundamentally from the flattened bodies or inferior mouths common in true bottom feeders.
They are voracious predators that gather in large, dense schools, often near the surface during warmer months. Their diet consists primarily of small, energy-rich organisms found in the water column. This includes large volumes of zooplankton, small crustaceans like copepods and krill, and smaller baitfish such as sand eels, herring, and sprats.
The Atlantic mackerel and the Spanish mackerel are two common examples that share this pelagic feeding strategy. While they may occasionally descend to deeper water during the winter months, they remain suspended in the water column, not resting on the seabed.
How Mackerel’s Feeding Habits Affect Consumers
The lifestyle of a pelagic fish like the mackerel has a direct impact on its nutritional profile. Because they are active, cold-water swimmers that consume a diet of oily plankton and other fish, mackerel develop a high concentration of body oil. This oil is rich in the beneficial long-chain Omega-3 fatty acids, specifically Eicosapentaenoic Acid (EPA) and Docosahexaenoic Acid (DHA).
This high-fat content is a consequence of their constant motion and energy-dense diet, making them a highly valued food source for humans. The oil content can fluctuate seasonally, reaching its peak in the late summer and autumn after a period of intense feeding.
Contaminant Accumulation
The mackerel’s position as a mid-to-high trophic level feeder also influences the accumulation of environmental contaminants. While smaller mackerel species like Atlantic mackerel are relatively low in mercury, larger, longer-lived species such as King Mackerel accumulate higher concentrations of mercury over time.
This bioaccumulation effect is a consequence of consuming smaller contaminated prey. Consumers are therefore advised to moderate their intake of the largest mackerel species while the smaller, oil-rich varieties remain an excellent source of Omega-3s with low contaminant risk.