Spawning Aggregations

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Spawning aggregations

Spawning aggregation is defined as a group of fish of the same species that are gathered together for the purpose of spawning—releasing sperm or eggs for the purpose of reproduction. The fish population that is together at this time is significantly greater than during periods the fish are not reproducing. For fish whose habitat is stable, drawing aggregations revolves around a relatively small area. In transient populations the individuals might travel for days or weeks in order to reach the aggregation site.

The U.S. Fish and Wildlife Service (FWS) oversees the recovery of species listed under the Endangered Species Act . For fish, that goal is tended through the National Fish Hatchery System—coordinating efforts between hatcheries and fisheries management. As a result, national fish restoration programs have returned abundance to the populations of various species, including the Great Lakes lake trout, the Atlantic coast striped bass, Atlantic salmon , and Pacific salmon. Much of the success has come through the agency's captive propagation programs. And, according to the FWS, "The success of captive propagation for recovery depends upon a number things, including careful genetics planning and management, concurrent habitat restoration, thorough evaluation studies—and funding. Propagation of imperiled fish species is often more than twice as costly as rearing non-native game fish due to genetic analyses, special diet requirements, and rearing conditions that enhance survival in the wild, along with rigorous monitoring and evaluation studies." A critical factor in the reproduction of endangered species is the understanding of spawning aggregations.

In various coastal systems in the United States and throughout the world, fisheries management relies on the knowledge of spawning aggregation locations. It is crucial to understanding how to protect the populations, as well as key to maintaining the ecological balance of marine life.

Reef fish are more vulnerable to disruption of spawning aggregations because many species only aggregate for brief time periods. If reef fish spawning aggregations are fished during the activity, then their populations are depleted due to unsuccessful reproduction. There are many reef fish species that reproduce in unprotected federal waters of the U.S. Caribbean, the Gulf of Mexico, and the South Atlantic. These species include the black grouper, cubera snapper, gag grouper, gray snapper, jewfish, Nassau grouper, red hind, scamp, and yellowfin grouper.

Two examples of decline in particular fish populations, according to Mark W. Sprague of the Department of Physics at East Carolina University in Greenville, North Carolina, in (2000) are the weakfish (Cynoscion regalis ), and the red drum (Sciaenops ocellatus ). It was his theory that using fish sounds could assist researchers in identifying their spawning activity. In the abstract presented for his presentation at the conference Sprague presented this preview of his presentation. "Weakfish and red drum, both members of family Sciaenidae, use their swim bladders to produce species-specific sounds associated with spawning activity. Large spawning aggregations of these fish can produce sound levels as high as 145 decibels (re: 1[mu]Pa), and these sounds will be presented for each species. Water depth, bottom type and contour, sound-speed gradient, and water current all affect the propagation of the fish sounds through the water. Measurements of these factors and the sound level of the fish calls are used to obtain an approximate range to the spawning aggregation." Sprague's work was supported by the North Carolina Division of Marine Fisheries and the U.S. Fish & Wildlife Service.

Some debate exists among those who fish commercially regarding whether the federal and state regulations for spawning aggregations are overly conservative. An example of one such debate appeared in Fishermen's Voice Monthly Newspaper a periodical of the fishing industry in Maine. The article recounted an aspect of the spawning issues in August 2000. The new plan unveiled there, "calls for a series of three rolling closures of one month duration. Flexible starting dates and options for extending the closures are designed to protect the fish only when they are spawning. Less astringent tolerance levels in the amended plan allow fishing within the closed areas provided the fish landed are less than 20 percent Stage V or Stage VI spawners." The purpose of regulation over spawning areas is intended to protect the spawning populations and therefore protect future populations so that overfishing does not become a problem.

The conservation of fish and the protection of marine wildlife species, such as sharks and whales , depends on the management of spawning aggregations. The debate over how that is best done will continue well into the twenty-first century.

[Jane E. Spear ]

RESOURCES

PERIODICALS

Zeller, Dirk. "Spawning Aggregations: Patterns of Movement of the Coral Trout Plectropomus leopardus (Serranidae) as Determined by Ultrasonic Telemetry." Marine Ecology (February 12, 1998).

OTHER

Darwin Initiative. Conversation of Whale Sharks & Fish Spawning Aggregations in Belize. [cited March 25, 2002]. <http://www.ayork.ac.uk>.

Fish Base. Global Information System on Fishes. [cited June 2002]. <http://www.fishbase.org>.

"Herring." Fishermen's Voice August 2000 [cited July 2002]. <http://www.fishermensvoice.com>.

Johannes. R. E. "MPA Perspective: Indo-Pacific Should Protect More Reef Fish Spawning Aggregation Sites." MPA News. March 2000 [cited July 2002]. <http://www.depts.washington.edu/mpanews>.

U.S. Fish and Wildlife Service. "National Fish Hatchery System." [June 2002]. <http://www.fisheries.fws.gov>.