GOLIATH HABITAT

BIG THINGS START FROM SMALL BEGINNINGS

During spawning, eggs are released into the open water column. Those that are fertilized will drift for a short period of time before they hatch, emerging first as free swimming pelagic larvae supported by a yolk-sac until they grow large enough to feed themselves. By this time the tiny fry are still smaller than a grain of rice, but now large enough to be seen by other – although small predators. From here, their existence is at its most perilous until they are delivered by the currents back to a coastline offering river mouth and lagoon type estuaries where they can find shelter among the mangrove’s tangled roots.

Estuarine habitats play a pivotal role in the juvenile development of these fish, provided there are juveniles to populate it. It was not until four years after the closure that a discernible number of juveniles started to reappear in regions like the Ten Thousand Islands in southwestern Florida.

From the data collected by Dr. Koenig and his colleagues during the first phase of the distribution, a regional density and habitat study revealed the vast majority of juvenile fish sampled between 1994 and 1997 just started to exceed 400 mm (15-16 inches) in length. While most were in the one to three-year age group, only a few fell in the four to six-year bracket.

Coastal mangrove and sea grass habitats are constantly subjected to environmental shifts in water salinity and temperature. During heavier than normal rainy seasons and when severe cold snaps in winter are fast and sudden, juvenile mortality can become excessively high. In addition to natural shifts in nature, the constant growth rate of human habitation in Florida has also had a harmful effect on coastal estuaries through construction of sea walls, docks and piers. If that isn’t enough, there is also the issue of runoff carrying pollutants like pesticides and herbicides from urban areas every time it rains.

One of the worst natural environmental shifts on record to affect juvenile goaliths since the study began in 1990 took place the first week of January, 2010 when a massive cold front pushed inshore water temperatures (recorded by the Everglades National Park) to as low as 5° Celsius / 41° Fahrenheit. The sudden plunge in water temp had such a detrimental affect on marine life in the shallow mangrove and sea grass beds, that it triggered a wide-scale fish kill up and down the Florida coast, essentially wiping out six full years of juvenile goliath development in one night.

Each smaller than a grain of rice; seen here is a photo of a goliath egg alongside an illustration of a goliath fry.

It takes six years on average for a goliath to transition from a tiny egg that would fit on the end of pen, to a juvenile like the one above, to a 3-foot long, 50-lb. brute ready to move offshore and begin life as a reef inhabitant. Photo: Jennifer Schull

HOMEBODIES

Once a goliath has made it to sub adult age (5 to 6-years) they are then ready to move out of the estuary nursery grounds to begin their new life in deeper water. Surprisingly, for a big fish, goliaths favor shallow water. While we think of them on structures like wrecks, caves and large undercut ledges on a reef, they also have a propensity for taking up residents beneath large piers and bridges along the southern Gulf and Florida’s east coast.

The most consistent places both divers and fishermen will find goliath groupers are on wrecks and large artificial reefs. One of these steel structures can harbor anywhere from one to more than a dozen of these giant groupers. To understand why they prefer these man-made structures over most natural reef habitats, ask yourself which would you prefer to live in: a mansion or a tent? Either way, wreck, reef, pier or bridge, once they have established a home base on a suitable site, they rarely stray far from it.

Studies show that eight out of ten mature fish rarely roam more than a kilometer from their home base. Those who do move about, usually pay a short visit to a neighboring location where food is likely more abundant. In human terms, they are big, lazy couch potatoes that will occasionally make a trip to the convenience store should there be no snacks closer at hand or in the fridge. The one exception to this stay-at-home behavior is romance. When mating season rolls around, goliaths will back up and swim considerable distances to join a spawning aggregation.

As goliaths repopulate south Florida reefs, evidence shows that they do not devour what’s already there, and in fact many reef structures show a net increase in marine life when the goliaths return. This can be attributed to the big fish’s tendency to excavate silted ledges or create depressions in the sea floor, creating a net increase in shelter, which other animals share. This large overhang on a small reef in Hobe Sound, just north of Jupiter did not exist until the first goliath moved in 6-7 years ago.

Over time, as more adult fish moved in, I watched the reef transform, exposing several large undercuts high enough for a diver to pass under. Today, with its 15-16 resident goliaths, the same reef features ledges and overhangs wide enough to drive a car under.

Changing the reef’s profile from what it was (originally 4 feet at its highest) to opened up as it is now created a major attraction point for additional species of fish, including gag grouper, snook, snapper, and jacks on a regular basis.

While these big fish find artificial structures more suitable, reefs with high profiles affording deep undercut ledges are also worthy of homesteading. If neither is readily available, in some cases, goliaths will excavate the sand from around the base of a limestone formation. By doing so, they expose and enlarge the space beneath a ledge that was buried in the sand.

Since it’s beginning, in the early 1990s, part of the Goliath Grouper Recovery Study involved placing tags in both juvenile and adult fish. To more effectively track their movements, a large number of adult fish were also fitted with small transmitters surgically implanted in the body cavity. Each time one of these fish would come within 100 meters of a specific listening receiver mounted on the sea floor, that fish’s transmitter ID would be logged in.

Dr. Koenig (left) prepares a fish for surgical placement of a transmitter that will allow his team to track the goliath’s movements over time. Photo © Kara Wall.