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Tuesday, February 05, 2008

The Most Important Fish You've Never Heard of - H. Bruce Franklin

Overall, from the 1860s to the present, catching menhaden has been far and away the nation's largest fishery. In fact, during many of these decades and years, the annual haul of menhaden weighed more than the combined commercial catch of all other finned fish put together, including Atlantic and Pacific cod, tuna, salmon, halibut, pollock, herring, swordfish, had- dock, ocean perch, flounder, scup, striped bass, whiting, croaker, snapper, sardines, anchovies, dogfish, and mackerel.

All these roles menhaden have played in America's national history are just minor parts of a much larger story of menhaden in America's natural history. For menhaden play dual roles in marine ecology perhaps unmatched anywhere on the planet. And this is why the story of menhaden is the tale of the most important fish in North America. Although hardly any of those hundreds of billions of captured menhaden have ever been caught to eat, we do eat them. No, you won't see menhaden in the fish market or supermarket seafood section, but they are present in the flesh of many other fish lying there on the ice. Menhaden are crucial to the diet of Atlantic tuna, cod, haddock, halibut, mackerel, bluefish, weakfish, striped bass, swordfish, king mackerel, summer flounder, drum, and other predatory fish. The great nineteenth-century ichthyologist G. Brown Goode exaggerated only slightly when he declared that people who dine on Atlantic saltwater fish are eating "nothing but menhaden."

Each adult fish filters about four gallons of water a minute. Purging suspended particles that cause turbidity, this filter feeding clarifies the water, allowing sunlight to penetrate. This in turn encourages the growth of aquatic plants that release dissolved oxygen while also harboring a host of fish and shellfish. Even more important, the menhaden's filter feeding prevents or limits devastating algal blooms. Most of the phytoplankton consumed by menhaden consists of algae. Excess nitrogen can make algae grow out of control, and that's what happens when overwhelming quantities of nitrogen flood into our inshore waters from runoff fed by paved surfaces, roofs, detergent-laden wastewater, over-fertilized golf courses and suburban lawns, and industrial poultry and pig farms.

This can generate deadly blooms of algae, such as red tide and brown tide, which cause massive fish kills, then sink in thick carpets to the bottom, where they smother plants and shellfish, suck dissolved oxygen from the water, and leave dead zones that expand year by year. In the natural ecosystem, the bonanza of phytoplankton stimulated a tremendous profusion of another filter-feeding consumer of algae: oysters. These two wonderful filter feeders kept inshore waters clear, clean, balanced, and healthy: oysters clinging to the bottom and menhaden cruising through all the upper layers. But oysters have been driven to near extinction in many bays and estuaries by overfishing and pollution. Clams and mussels also filter-feed on the algae, but neither has the enormous mass of the bygone oyster reefs or the gargantuan menhaden schools.

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