Menhaden, often called "mossbunker" or "bunker," are small, oily fish that play a vital role in marine ecosystems. Belonging to the genera Brevoortia and Ethmidium, these forage fish are sometimes referred to as "the most important fish in the sea." This article delves into the diet of menhaden, their feeding habits, and the ecological consequences of their feeding behavior.
Menhaden Overview
Menhaden are characterized by their flat bodies, soft flesh, and deeply forked tails. These fish rarely exceed 15 inches (38 cm) in length and possess a bright silver coloration, marked by a series of smaller spots behind the main humeral spot. Gulf menhaden and Atlantic menhaden tend to have larger scales compared to yellowfin and finescale menhaden.
Filter Feeding Mechanism
Menhaden are filter feeders, meaning they consume food by straining plankton and algae from the water. They travel in large, slow-moving schools with open mouths, taking in "materials in the same proportions as they occur in ambient waters." This feeding behavior is crucial to their ecological role.
Dietary Components
The diet of menhaden primarily consists of phytoplankton and zooplankton. However, their dietary preferences change as they grow. Smaller menhaden, typically under one year old, primarily consume phytoplankton. As they mature, their diet shifts to include zooplankton.
Ecological Role
Menhaden serve as a critical link between plankton and upper-level predators. They consume and redistribute a significant amount of energy within and between estuaries and the coastal ocean. Along with oysters, menhaden help to filter water, playing a key role in the food chain.
Read also: Incorporating Fish into a Carnivore Meal Plan
Keystone Species
Menhaden are considered a keystone species because of their crucial role in the food web. They are a primary prey species for many predatory fish, including striped bass, bluefish, mackerel, flounder, tuna, drums, and sharks. Their abundance directly impacts the populations of these predators.
Mitigation of Algal Blooms
Menhaden's filter-feeding habits help mitigate toxic algal blooms, which can create hypoxic conditions detrimental to fish, bird, and marine mammal species. By consuming phytoplankton, menhaden help to control the growth of these blooms.
Life Cycle and Migration
Menhaden are pelagic schooling fish that migrate inshore during the summer and offshore during the winter. Juvenile and larval menhaden migrate to shore and inland waterways through currents during summer months, feeding on phytoplankton and eventually zooplankton as they mature. They reproduce in open oceans, releasing eggs and sperm into the water column at the planktonic level.
Commercial Uses
Menhaden are not typically consumed directly by humans. Instead, they are processed into fish oil and fish meal, which are used as food ingredients, animal feed, and dietary supplements. The flesh of menhaden has a high omega-3 fat content, making it valuable for these applications.
Reduction and Bait Fisheries
There are two main commercial fisheries for menhaden: reduction and bait fisheries. The reduction fishery processes menhaden into fish oil and fish meal. The bait fishery harvests menhaden for use by commercial and recreational fishermen. Commercial crabbers in the Chesapeake Bay area use menhaden to bait their traps, while recreational fishermen use ground menhaden chum as a fish attractant and whole fish as bait.
Read also: Choosing Fish on Keto
Omega-3 Fatty Acids
Menhaden oil is rich in omega-3 fatty acids, which are essential for regular and healthy body functions and growth in both humans and animals. Omega-3s help reduce inflammation and lower the risk of chronic diseases such as heart disease. Menhaden provide a significant amount of EPA and DHA, two key types of omega-3 fatty acids, surpassing other fish species like salmon. Fish oil from menhaden is also a top source of DPA, an intermediary of EPA and DHA that contributes to cardiovascular, cognitive, and neurological health.
Animal Feed
Menhaden oil and fish meal are also used in animal feed, providing enhanced memory, cognitive functions, reproductive health, strong bones, healthy joints, skin and coat health, and even increased lifespan for pets. Fish meal in pet foods has a high protein digestibility, allowing pets to absorb more nutritional benefits.
Marine-Based Ingredients in Aquaculture
Carnivorous fish like salmon rely on external sources of omega-3 fatty acids, which they obtain by eating other fish. Menhaden are a key ingredient in aquaculture feeds, providing these essential nutrients to farmed fish.
Threats to Menhaden Populations
Overfishing has been a significant threat to menhaden populations. In 2012, the Atlantic States Marine Fisheries Commission declared that the Atlantic menhaden was depleted due to overfishing. Decreases in menhaden populations can disrupt the food chain and leave predators like striped bass vulnerable to disease.
Management and Conservation Efforts
In response to declining populations, the Atlantic States Marine Fisheries Commission (ASMFC) has implemented measures to manage the menhaden harvest. In October 2020, the ASMFC put a cap on the Atlantic menhaden harvest, marking the first coast-wide harvest cut for menhaden. This decision considered ecological reference points, accounting for menhaden's role in the food chain when setting catch limits.
Read also: Healthy Fish Recipes
Chesapeake Bay Foundation's Role
The Chesapeake Bay Foundation (CBF) has been actively involved in advocating for a healthy menhaden population in the Chesapeake Bay. They support sustainable menhaden management to ensure that this fish can continue to fulfill its key role in the food chain.
Menhaden and the Chesapeake Bay
Menhaden are particularly important in the Chesapeake Bay, where they serve as a food source for commercially important species like striped bass. They also help manage algal bloom occurrences by consuming phytoplankton. The Bay is one of the most important nurseries for menhaden, sustaining the population along the Atlantic coast.
Concerns and Challenges
Over the past two decades, concerns have been raised about the concentration of fishing effort in and around Chesapeake Bay waters, which could disrupt the Bay's food chain. In 2019, Omega Protein purposefully exceeded the Chesapeake Bay harvest cap, leading to a finding of noncompliance with interstate fishery rules.
Multispecies Benchmarks
In August 2020, the ASMFC adopted new multispecies benchmarks, known as ecological reference points (ERPs), to account for menhaden's role in the food chain and set catch limits accordingly. These benchmarks estimate and account for the needs of predators and are specifically formulated to meet the needs of the coastwide rockfish population.
Ongoing Research and Advocacy
In 2023, Virginia passed SB1388, directing the Virginia Institute of Marine Science to study the ecology, fishery impacts, and economic importance of menhaden populations in the Chesapeake Bay. Despite unanimous support, the science plan remains unfunded. The CBF continues to fight for improved menhaden science to promote sustainable menhaden management and a healthier Chesapeake Bay ecosystem.
The Menhaden Fishery and Its History
The menhaden fishery has a long history in the United States. Native Americans used menhaden to enrich the land, and entrepreneurs in the eighteenth century began building facilities to reduce menhaden into oil and meal. By the mid-twentieth century, numerous facilities dotted the east coast and the Gulf of Mexico.
Technological Advancements
The introduction of hydraulic vacuum pumps in the 1950s revolutionized the menhaden fishery, making it possible to catch millions of menhaden from larger nets. This led to the consolidation of the industry, with only one company, Omega Protein, remaining by 2006.
Uses in Agriculture and Supplements
Menhaden micronutrients are used to make fertilizers, and a small portion of the fats are used to make human nutritional supplements, such as fish oil pills containing omega-3 fatty acids. The market for omega-3 supplements has grown significantly, driven by claims linking omega-3 consumption to a reduced risk of heart disease.
Animal Feed Industry
The real money in the menhaden industry lies in menhaden proteins and fats, which have become ingredients in animal feed for industrial-scale aquaculture, swine, and cattle growing operations. Omega Protein's customer base includes major companies in the animal feed and human supplement industries.
Ecological Consequences of Menhaden Fishing
The large-scale fishing of menhaden has significant ecological consequences. In 2009, fisheries scientists reported that the Atlantic menhaden population had shrunk to less than 10 percent of its original size. This decline has impacted predator species like striped bass and osprey.
Impact on Predator Species
Striped bass, a major predator of menhaden, have been affected by the decline in menhaden populations. Osprey, another menhaden predator, have also seen a decline in their diet composition, with menhaden making up a smaller percentage of their food intake.
Regulatory Measures
In December 2012, the Atlantic States Marine Fisheries Commission implemented the first coast-wide regulation of the menhaden fishery, cutting the harvest by 20 percent to safeguard the population from further decline.