Q and A

Q.Years ago several of us outdoor writers were on Long Cay, Bahamas and I asked Al McClane why is that for years on a specific tide bonefish will flood onto a flat. Then the numbers begin to diminish until after a while you rarely see one there--and that situation might last for years before the return. Al said bonefish graze the flat (like cattle to a pasture) until it is no longer economically worth while for them. I think many flats fishermen would be interested in this observation.

A. Al may have been correct. It is certainly possible that the bonefish could eat so much of the preferred prey on that flat that prey abundance declines to such an extent that it’s not worth the effort for bonefish to feed there, so they go somewhere else until the prey population recovers.

It’s also possible that the prey declines due to reasons unrelated to the bonefish. For example, when many marine organisms spawn, they eject eggs and sperm into the open water where fertilization occurs. The larvae that hatch from the eggs typically don’t look anything like the parents, and float in the open water as plankton for hours, days, weeks, or even months, depending on the species. If they survive their time as plankton, they metamorphose into miniature versions of the adults and take up residence in the same types of habitats as their parents. These larvae may find themselves in the same location as their parents or may find that the currents carried them to other locations. Sometimes the currents sweep larvae away from areas rather than toward them, and in these situations there may be a year or more when few larvae come in to replace the previous generations. This means that the prey population declines because there are too few younger individuals coming in to replace the older ones that are dying. Although bonefish didn’t directly cause the decline of the prey population, the result is the same – prey abundance on the flat becomes too low to make it worthwhile for the bonefish, so they go elsewhere.

Of course, it’s also possible that both the above are happening. A ttimes, bonefish may eat a lot of a particular prey, which keeps the prey abundance in check. This works fine as long as new prey successfully come in each year. But if there is a bad year or two, when few younger prey individuals come in, but the bonefish keep eating at their normal rate, the population may decline to levels too low to keep the bonefish coming back.

Another possibility is that the prey that bonefish prefer is for some reason replaced by an organism that the bonefish don’t like. The bonefish’s preferred prey and this other organism may compete with one another, and some years one species wins and other years the other species wins. In the years that the bonefish’s preferred prey wins you see bonefish, but in years that the other species wins the bonefish go elsewhere.

Bonefish may also change their behavior and locations due to spawning season (we think that is November – May in the Caribbean). An area that has plenty of food and protection from predators may be far from spawning locations, so during spawning season there may be fewer bonefish there and more bonefish on flats closer to spawning locations.

Overall, all of these possibilities highlight the great thing about fishing and studying fish. Just when you think you have it figured out they show you that you don’t. And it keeps it challenging.