Florida State University

Back from the brink: Atlantic Goliath Grouper recovery in the southeastern U.S.

Dr. Chris Koenig (R), Dr. Jim Locascio (L), Goliath Grouper (center)

The Atlantic Goliath Grouper (Epinephelus itijara), a once abundant species in the southeastern U.S. (especially in Florida), experienced first slow and then rapid declines that started over 100 years ago. Water management projects in South Florida dating back to the early 1900s initiated the decline by reducing the quality and coverage of mangrove habitat essential as nursery habitat for the juvenile stage of this fish. Intense fishing pressure that started in the 1980s enhanced the decline dramatically. By the late 1980s, the decline was so obvious that a petition to the Gulf of Mexico Fishery Management Council (FMC) for a fishing moratorium from a single grouper fisherman met with virtually no opposition. The South Atlantic FMC and the Caribbean FMC followed suit, closing the fishery throughout the region in 1990. Goliath Grouper continue to be listed as overfished in the United States, although the population has made a continuous recovery over the last 24 years.

High quality mangroves habitat off southwest Florida, particularly in the Ten Thousand Islands, is key to the ongoing recovery of Goliath Grouper populations. This extensive habitat, which borders on and derives relatively pristine water from the Big Cypress Swamp, provides significant habitat for juveniles during their 5-year estuarine sojourn. Most of the mangrove habitat of South Florida, however, has been destroyed by development or has such low and variable water quality that its value as nursery habitat is nil.

Low-relief natural reefs and high-relief artificial reefs that dot the east and west Florida shelves, provide the architectural complexity that Goliath Grouper and many other reef fish seek. Goliath Grouper enhance the structural complexity of these reefs by excavating sediment from around the reef base, and in so doing, increase the abundance and diversity of other resident species. Artificial habitat, which is continually expanding as the Florida Fish and Wildlife Commission deploy more structures designed to enhance local fishing opportunities, are preferred by adult Goliath Grouper, and used as spawning sites off southeast and southwest Florida. Despite the expanding availability of artificial reef habitat, it is the diminishing mangrove habitat that presents a severe bottleneck to the full recovery of Goliath Grouper.

Mercurial views on a viable fishery--Adult Goliath Grouper in the Gulf of Mexico have heavy mercury contamination in both muscle and liver tissues. FSUCML doctoral student, Chris Malinowski, recently found mercury contamination in Atlantic populations that are at least as high in the muscle tissue (up to 3.5 ppm) and much higher in the liver (35 ppm in Atlantic, ~25 ppm in the Gulf). These levels are similar to those found in top level predators, which have the highest levels of mercury ever reported (including several species of shark, Swordfish Xiphias gladius, and Tilefish Lopholatilus chamaeleonticeps). Nearly all adult Goliath Grouper exceed the US Food and Drug Administration's (FDA) action level of 1.0 ppm -- the level above which the sale of any fish species is prohibited-- and far exceed the level that the Natural Resources Defense Council (NRDC) considers "very high." Indeed, at 0.5 ppm, the NRDC recommends that pregnant women and young children avoid these fishes in their diet because of the well-known negative effects of mercury on the health and neurological development of humans. It is hard to imagine a viable fishery based on capture of these fishes.

Dead or Alive! Revenues to Florida's Economy-- If a Goliath Grouper is caught in a fishery, it can only generate the market value of that one fish one time (a value deflated by the high levels of mercury in the tissues). However, the economic return from that same fish persisting in the wild will continue to increase because divers can see and photograph it repeatedly throughout its adult lifetime. For instance the dive industry reports tripling revenues over the last 5 years which they attribute to the resurgence of Goliath Grouper on offshore reefs. Divers from all over the world come to see the spectacle of scores of adult Goliath Grouper aggregating on reefs, with each fish exceeding 300-500 pounds. It is clear that maximum benefit to the fish, to Florida's economy, and to other reef fish (because of habitat-enhancing behaviors of Goliath Grouper) are gained by allowing Goliath Grouper to recover to its natural equilibrium level.