Mote Marine Laboratory

Seductive Snook

By: Patrick Maggard

Gulls skimmed and dived at the water as researchers pulled a seine along the beach at Cayo Costa on a hot, humid, sunny south Florida day in August. The 500-foot seine quickly rounded up scads of scaled sardines, getting the gulls’ attention and making at least one member of the research team feel like Tippi Hedren in Hitchcock’s famous movie "The Birds."

The attention of the crew, however, remained focused on the real prize in the net: snook, and quickly and carefully catching, tagging and releasing them unharmed.

Catching snook is something that Dr. Aaron Adams, manager of Mote’s Fisheries Habitat Ecology Program, knows something about. After all, he wrote a book about fishing for snook and other species in “Fisherman’s Coast: An Angler’s Guide to Marine Warm-Water Gamefish and Their Habitats.”

The book was a natural result of Adams’ research, which focuses on learning about the lifestyles of the common snook, Centropomus undecimalis, and other gamefish, including knowing which habitats are essential to their survival so that information may be used by managers to help ensure healthy stocks. The work is important because snook attract anglers and anglers make up Florida’s $5.4 billion recreational fishing industry.

Adams has already documented important habitat for juvenile snook — small creeks where young fish can hide out until they’re large enough to survive in estuaries — and how development or other changes around such creeks affects snook survival. This summer, he started a new three-year study of snook spawning habits.

“The first goal is to figure out what snook movement patterns are during the summer along the beaches,” Adams said. “We know, based on research, that snook spawn along beaches somewhat but mostly in the passes between May and September. What we don’t know are the specifics about whether the same fish are spawning at the same site each time. It’s unclear how many snook are spawning at one time, and how much they move — whether they go from Sanibel to Captiva, for example.”

Such a study is more complex than hooking and boating adult snook. It involves getting to the study area — Blind Pass at Sanibel and Captiva to the north end of Cayo Costa — soon after dawn, then spotting snook swimming along the beaches. The goal is to set a seine after a school of the popular fish is spotted then gather them up to measure, tag and track. Setting the net is as physically strenuous as the research is mentally meticulous.

A second goal of the study is to determine how snook react to red tide. Over the past several years, red tide has sporadically plagued Southwest Florida — a red tide is a population explosion, or bloom, of the single-cell alga Karenia brevis, which gives off a powerful neurotoxin that can kill fish and other marine animals and cause respiratory problems in humans.

“It appears, based on observation and conversations with fishing guides, that some snook are killed
by red tide, but many, or most, move,” Adams said. “Red tide approaches, and the snook move into the estuary. We need to figure out if that’s true. If it is, the next step is to determine whether that affects spawning success.”
The reason a snook migration into the estuary to avoid red tide during spawning season might be an issue is that snook eggs and sperm need high salinity to be viable. Karenia brevis needs high salinity, too, so if snook flee into estuaries, where salinity is lower than the Gulf of Mexico, they might be able to get away from Karenia, but they might not spawn effectively.

“Worst case: Red tide pushes snook inside the estuary, and the salinity is too low for them to spawn,” Adams said. “That might affect the number of juvenile snook next year.”

Fisheries managers might someday use data from Adams’s work as a tool to better protect the snook fishery. If fisheries managers know that the juvenile population is low for a particular year, they’ll be able to predict snook populations several years down the road and, possibly, tailor regulations specifically for those years. “There’s a lot of concern about the effects of red tide on tourism,” Adams said. “But, despite the economic importance of recreational fishing in Florida, we don’t have a handle on how fish are impacted by red tide.”

Before any management decisions can be made, of course, data must be collected. That all starts with catching snook.
Most mornings this summer, Mote’s snook team of Adams, senior biologist Kirby Wolfe, technician Ross Boucek and interns Dana Overcash from Villanova University and Marielle Terbio from the University of Guam were on the beaches just after dawn to set the seine.

The net is not allowed to “soak”: As soon as they deploy it in a semicircle with the open end toward the beach, they haul it in and put the snook in a floating pen made from net mesh and pool noodles. The snook team uses two pens, one to hold the fish before and one to hold them after they are “worked up.”

When all the snook from each set are in one pen, the first step is to check each fish for a passive integrated transponder, or PIT, tag to see whether it has been caught and tagged before. A PIT tag is a microchip inserted under the skin that can be read with an electronic wand, like the microchips popular in dogs and cats, which are about the size of pencil erasers.

Fish that already have tags are measured, the location of the catch recorded, and then the fish are released. If a fish doesn’t have a PIT tag, it gets one. Untagged fish are first put into a cooler filled with seawater and a dose of Alka Seltzer, which sedates them. The fish also get external tags inserted next to the dorsal fin. Some get sonic tags, which can be detected by an array of 12 underwater receivers and are used to track the snook’s movements. The scientists also record water-quality parameters, such as dissolved oxygen, temperature and salinity.

With the first season barely behind him, Adams isn’t ready to draw conclusions about snook spawning behavior. Science, he said, takes time, despite the public’s desire for immediate answers. “The expectation is for answers right now. If it were that easy, there would be no need for science,” he said. “But it’s not that easy, and when you’re working with ecological systems, it’s even more difficult. There’s a quote I use: ‘Ecological science isn’t rocket science. It’s a lot harder.’ With engineering, you make measurements, and you have a limited range of results. But ecological systems are constantly changing. There are a lot of natural variables, which make it harder to figure out what’s going on.”

Ultimately, Mote’s spawning snook study, and much of the work done in ecological sciences, is, Adams said, preventive medicine: Figuring out what’s going on in a system before it’s broken. “Once something is broken, it’s hard to fix,” Adams said. “Emergency room medicine is not very effective and is very expensive. Everything we do is toward fisheries conservation and habitat conservation, trying to figure out the intricacies so the system can be managed to be sustainable, so our kids and their kids can have something left to enjoy.”

The snook spawning study is supported in-part by the Florida Fish and Wildlife Conservation Commission. Additional funding is needed to continue the project. Anglers who want to support snook should contact Mote’s Development Division at (941) 388-4441, ext. 309.

Learn more about: Marine Stock Enhancement

You can't tell a snook by its cover. The snook, just another fish in the sea to some, is actually more of the most popular game fish in Florida waters. Science takes time and money but with your support, we can make sure there'll always be plenty to catch.