By: Aaron Adams, Ph.D.
Magazine Articles
On the Line with Aaron Adams, Ph.D.
Walk into any fishing shop and you’ll likely overhear anglers recounting big-fish tales. Whether they’re talking about a 150 pound tarpon, 20 pound snook or 15 pound redfish, the story is just as exciting whether the fish was landed or not.
As an angler, I’ve both listened and told these stories myself.
But as a fish ecologist, my research focuses on understanding how such fish use coastal habitats to grow to the sizes that warrant such excited tales, and how such habitats support populations large enough to sustain the fisheries.
Anglers pursuing a trophy may not think about how much the fish depend on healthy habitats for survival, but as primary users of the marine environment – whose sport depends on healthy fish populations – they need to understand the importance of healthy habitats to the fisheries and help conserve the places where fish grow and live.
A local favorite – snook – is a good example of just how important healthy habitats are to an economically and ecologically valuable species.
Snook gather in aggregations to spawn during summers around the time of the full moon, on outgoing tides late in the day, usually in coastal inlets. Like most marine gamefish, snook gather in mixed-sex groups and males and females eject sperm and eggs into the open water. Egg fertilization is external in this process of “broadcast spawning.” One female may have hundreds of thousands of eggs.
The larvae that hatch aren’t recognizable as snook – they are clear and shaped differently. They live as plankton in open coastal waters and estuaries for a couple of weeks before moving into backwater mangrove creeks, wetlands and ponds. It’s been estimated that only one-tenth of one percent of the larvae survive, but that’s still a lot of snook being produced from the millions of eggs fertilized each spawning season.
Once in backwater habitats, the larvae metamorphose into miniature snook. These juvenile snook are able to survive in water with very little oxygen, which we think helps them avoid many fish predators that need water with a greater amount of oxygen. As they grow, the juveniles migrate down the creeks, eventually joining the adults in estuaries and along the coasts.
And as any angler who fishes for snook knows, adult snook are able to use most coastal habitats, including mangrove shorelines, mangrove creeks, rivers, seagrass beds and beaches.
So what does this say about the habitat snook need to reach that trophy size – the catch of a lifetime for many anglers?
The trophy fish’s parents had to have a good location with clean water and good tidal flow to spawn; The larva had to have clean water to survive and good current flows to provide access to backwaters; The juvenile needed a place with clean water, safe from predators, and with plenty to eat; The growing snook needed mangrove-lined creeks so it could move slowly toward more open habitats; The adult snook needed healthy habitats with plenty of prey. It’s been a successful – if complex strategy for snook.
And take a lesson: Knowing how snook use habitats at different times of the year, and at different points in their life cycle, anglers can focus efforts on the habitats most likely to harbor snook. After all, knowing more about where snook live and why can’t do anything but improve your odds at catching that once-in-a-lifetime fish.
Dr. Aaron Adams is manager of Mote’s Fisheries Habitat Program in the Center for Fisheries Enhancement and an avid fly fisherman whose been known to tell a few “fish-that-got-away” tales himself.
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