What are the advantages of fish feeding on high lipid forage fish such as herring, mackerel and menhaden compared with feeding on invertebraes and crustaceans?
Fish feeding on high-lipid forage fish (such as herring, mackerel, and menhaden) gain several key nutritional and energetic advantages compared to feeding primarily on invertebrates and crustaceans (e.g., krill, shrimp, copepods, or benthic decapods like lobsters and crabs).These stem from differences in prey composition—lipid-rich fish prey offer higher energy density, better essential fatty acid profiles, and more efficient nutrient delivery. (LINK) (LINK)
### 1. Higher Energy Density and Caloric Value
High-lipid forage fish contain substantially more lipids (often 20–55% of dry mass in species like Pacific herring, capelin, or similar menhaden/herring stocks) and lower water content (typically 62–74% wet mass). This results in markedly higher energy density—up to 5–8 kJ/g wet mass (roughly 1.2–2 kcal/g)—compared to low-lipid prey. Lipids provide ~9 kcal/g versus ~4 kcal/g for protein, and lipid content alone explains ~83% of variation in energy density among prey fish. (LINK)
In contrast, many invertebrates and crustaceans (e.g., krill or shrimp) have much lower lipid levels and higher water/chitin content, yielding lower overall energy per gram wet weight. One quantitative example: it takes approximately 80 krill to deliver the same energy as a single high-lipid forage fish like a sardine or herring. Predators therefore obtain far more calories per item captured or per unit mass ingested, supporting faster growth, larger lipid reserves for migration or reproduction, and higher overall condition. (LINK) (LINK)
### 2. More Efficient Foraging and Energy Transfer
Because high-lipid fish pack dense nutrition into larger, energy-rich packages, predators expend less time and effort per calorie gained. This is especially beneficial for smaller or mid-sized predators (e.g., juvenile striped bass or seabirds) whose body plans favor pursuit of schooling pelagic fish. Switching to lower-energy invertebrate prey increases foraging costs dramatically and can lead to reduced reproductive success, survival, or population declines in predators like seabirds, salmon, or marine mammals. (LINK)
While some larger predators may shift toward easier-to-capture benthic crustaceans later in life (lower pursuit costs), the per-gram energy yield from forage fish remains superior, and crustaceans often carry digestive costs from chitin. (LINK)
### 3. Superior Provision of Essential Omega-3 Fatty Acids (EPA and DHA)
Forage fish like herring, mackerel, and menhaden efficiently concentrate long-chain n-3 polyunsaturated fatty acids (PUFAs) such as EPA and DHA from plankton. These are critical for predator membrane fluidity, neural/eye development, anti-inflammatory responses, reproduction, and overall health. Predators accumulate higher body levels of these when feeding on lipid-rich fish prey, directly boosting physiological performance. (LINK)
Many invertebrates and crustaceans contain some omega-3s (e.g., certain krill), but at lower concentrations and with different profiles; they do not match the bioaccumulation efficiency or total delivery of high-lipid fish. Marine fish prey generally outperform crustaceans and shrimps in total n-3 PUFA content. (LINK)
### 4. Higher Protein Density and Overall Nutritional Quality
Vertebrate prey (fish) typically contain 40–80% protein on a dry basis, versus 19–40% in many invertebrates. High-lipid forage fish also show higher protein in their lean dry matter (often 87–89%) and lower ash, delivering more complete nutrition per bite. Combined with lipids, this supports rapid growth and tissue building far more effectively than the leaner, higher-water invertebrate alternatives. (LINK) (LINK)
In summary, high-lipid forage fish act as an energy- and nutrient-dense “superfood” in marine food webs, enabling predators to thrive with lower foraging effort and superior physiological outcomes. Depletion of these prey forces switches to invertebrates/crustaceans, which are nutritionally inferior and often more costly to exploit, underscoring why species like herring, mackerel, and menhaden are foundational in predator diets.