When Nature Cracks the Whip

When Nature Cracks the Whip

Last winter's cold kill will bring good changes, too.

By R. Grant Gilmore, Ph.D.

It might be a good time to reconsider that catastrophic cold kill we saw about a year ago now, during last January. Many people were concerned about what long-range effects it might have on our fisheries, but truth be told, Old Florida anglers were never too worried. They know that some fish die, some fish do not—but the ones that belong here come back. They also know that there are many Florida fish species that can take cold water and actually thrive in it. The largemouth bass, red and black drum, striped bass, American shad and Atlantic sturgeon paid no attention to the recent freeze.

Such extreme conditions do bring benefits as well as loss to the ecosystem. In last January's cold kill, considered the most severe since 1977, both native and exotic tropical fish popped to the surface that were rarely seen before, or at least, not known to have been as abundant as they were in the body count this past January. I examined a group of dead mullet on the shore of the Indian River Lagoon and discovered they were all Lisa, Mugil liza, a tropical mullet species that basically replaces the more temperate striped or black mullet, M. cephalus, throughout the Caribbean. Yet the striped mullet are likely to increase in numbers due to the cold weather as they did in 1977.

Young striped mullet and pinfish numbers increased by an order of magnitude in 1977 and 1978 during those freeze events. These fish are cold hardy and were busy spawning offshore during the fall and winter. But why, exactly, did the numbers of young increase during the freeze? One hypothesis is that striped mullet and pinfish were not preyed upon by king mackerel that year while they were spawning off east Florida. Most king mackerel, being sensitive to cold water, migrated to the Florida Keys that winter. This meant the most abundant winter predator off east Florida was no longer present and the cold hardy striped mullet and pinfish may have been able to spawn unmolested, thus produce more offspring. So the extreme weather changed predation patters and in this case gave the prey a break.

We call this predator release when a population of animals experiences reduced predation, and as a consequence, increases in abundance. The great freeze of 2010 may give us more striped mullet and pinfish. In turn, the remaining snook, spotted seatrout and red drum that were not killed by the cold will benefit from this increase in prey if and when it does occur. There was record snook recruitment to the Florida coastal waters in 1982-1983, five to six years after the great freeze of 1977. It is likely that it may take that long for the snook fishery to recover after the 2010 event.

After the freeze, I also examined a large, 52-pound red-bellied pacu, Piaractus brachypomus, killed by the cold in the St. Lucie River. The red-bellied pacu is a tropical Amazonian fruit eating fish that is common in the aquarium trade as a small juvenile. Like the Burmese python, the pacu was likely one of the many illegal pet releases that negatively impact the native Florida fauna. The pacu's death, along with thousands of exotic tilapia and armored catfish throughout the state, benefits our native species. These intruders were not part of the original Florida fish fauna and have actually displaced many of our natives. Exotics have a negative impact on entire native ecosystems. However, do not expect them to be completely extirpated. They have likely found thermal refuge in warm springs or other locations where they will breed the next generation of exotics.

These are examples of how mother nature takes care of herself and of us, if we give her a chance, and in some cases like this winter's cold kill, whether we like it or not.