Fishes: The Animal Answer Guide

5. Fish Ecology

61 Do fishes migrate? Many fishes are very mobile, undertaking daily, seasonal, reproductive, and life cycle migrations. Daily migrations can be measured in meters or feet, whereas annual and life cycle migrations can crisscross entire oceans. Fishes in both fresh and sea water move back and forth between habitats on a daily basis. In most locales, fishes feed during either the day or night. When not feeding, fishes rest, usually in a place safe from predators. This change in activity often requires a change in habitat because the best places to feed, such as up in the water or over a sandy area, are not good places to hide. Fishes usually migrate between feeding and resting locales at dawn and dusk. Migrations may involve movement of a hundred meters (325 feet) or less between a reef and nearby grassbed or just a few meters for fishes that hide in the reef but feed in the water directly above it. These movements, at very predictable times and places, provide feeding opportunities for another ecological group, the predatory fishes. Predators do not migrate but instead position themselves along the migrators’ corridors, picking off individuals that move too early or too late or depart from the safety of the migrating school. On coral reefs, damselfishes, surgeonfishes, parrotfishes, herrings, drums, squirrelfishes, and grunts make daily feeding migrations. In kelpbeds , silversides, seabasses, surfperches, damselfishes, wrasses, and croakers move between daytime and nighttime habitats. In temperate freshwater habitats, freshwater eels, catfishes, minnows, and yellow perch move between habitats at dusk and dawn. At a larger scale, scalloped hammerhead Chapter 5 Fish Ecology 62 Fishes: The Animal Answer Guide sharks (Sphyrna, Sphyrnidae) make daily movements between daytime locales above seamounts and nighttime foraging areas in open water, several kilometers (miles) away. One other type of daily migration that occurs at small and large scales is the vertical migration of fishes that live in the water column. In the ocean, dozens of species move at dusk from deep, cooler waters to feed in shallow, warmer waters at night. Some of these fishes, such as lanternfishes, lampfishes , bristlemouths, lightfishes, and cookie cutter sharks, travel as much as 500 meters (1600 feet) upward in the evening. On coral reefs, damselfishes , butterflyfishes, small anthiine seabasses, and triggerfishes feed up in the water by day and are replaced at night by cardinalfishes, squirrelfishes, and copper sweepers. The nighttime feeders hide by day inside coral heads, where they are replaced in the evening by the daytime feeders. In temperate lakes, alewife (Alosa pseudoharengus, Clupeidae) migrate upward in the evening to feed on small mysid shrimp that also move up and down. Coelacanths (Latimeria, Latimeriidae) are among the few fishes that move down to feed at night. Seasonal, annual, and reproductive migrations occur in the ocean and in large rivers. These migrations often involve movement among the different habitats that fishes occupy at different times in their lives. Many reef fishes migrate several kilometers (miles) to spawn at traditional locales, including seabasses, snappers, wrasses, parrotfishes, and surgeonfishes. More than a hundred thousand Nassau Grouper (Epinephelus striatus, Serranidae) moved from as far away as 110 kilometers (68 miles) to spawn at one site in the Bahama Islands, until their predictability allowed them to be fished out. Large catfishes in the Amazon (South America) and Mekong (Southeast Asia) rivers move hundreds of kilometers (miles) upstream during annual spawning migrations. Their young move downstream with currents to nursery habitats. For many of these and other tropical river species (osteoglossid Arapaima, mormyrid elephantfishes, large characins, minnows, and gymnotid knifefishes), adults migrate up tributaries and onto floodplains to spawn. Colorado Pikeminnow (Ptychocheilus lucius, Cyprinidae) make similar long-distance migrations in the Grand Canyon, as do sturgeons and paddlefishes in the Yangtze River of China (or at least they did before pollution, overfishing, and dams exterminatedthem).AtlanticHerring(Clupeaharengus, Clupeidae) spawn off southern Norway and then move to feeding grounds aroundIceland,adistanceofabout1,700kilometers(1,000miles).Theyoung develop in northern Norway before moving to the feeding grounds. Many open ocean fishes are called “highly migratory species” because their movements carry them around and through entire ocean basins. Included are tunas, billfishes, and some sharks. The Blue Shark makes return trips between North America and Europe, a distance that exceeds 16,000 63 Fish Ecology kilometers (9,900 miles), and White Sharks are now known to migrate between central California and Hawaii, a minimum one-way distance of 3,800 kilometers...