Spotting the Seatrout: Researchers from NOAA Reveal the Reasons for the Angler’s Curtailed Catch

 

Adjacent to Everglades National Park, Florida Bay encompasses the shallow waters, mangrove islands, and grassy banks between mainland Florida and the Keys, an area about 1,000 square miles in size. With an average depth of only 3 feet, the bay is home to a number of marine populations, as well as a vital nursery ground for commercial and recreational reef fish species and pink shrimp that support one of the highest valued fisheries in Florida.

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Upside down Jellyfish, Cassiopeia spp., hang suspended in the shallow waters of Florida Bay. Large cassiopeia blooms explode with mesmerizing blue and brown bells in areas where seagrass die-off has occurred. This can be a concerning sign for researchers studying the health of Florida Bay.

 

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Because of its importance as a nursery, the bay also plays host to a group of researchers from NOAA’s Atlantic Oceanographic and Meteorological Laboratory (AOML) and the Southeast Fisheries Science Center (SEFSC) who are investigating how habitat changes in Florida Bay are impacting juvenile sportfish populations, with a focus on the Spotted Seatrout. Sportfish are fish that are targeted for recreational fishing purposes, and can include barracuda, redfish, kingfish, and seatrout. The study aims to examine the relationship between juvenile Spotted Seatrout abundance, salinity, temperature, and seagrass, and use the data to quantify and predict the impacts of Everglades Restoration.

 

Researchers can use indicator species – whose abundance changes based on environmental conditions – to assess changes in the ecological state of Florida Bay. Seatrout are used as an indicator species because they spend their whole life in the bay and are sensitive to salinity fluctuations. Seatrout make up 30% of the catch of recreational fishing in the bay. Other tracked species include Gray Snapper, Lane Snapper, Spiny Lobster, and Barracuda[1].

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On sampling trips, researchers make observational assessments of bottom conditions in the bay, estimating the percent Cassiopeia jellyfish, sand, and seagrass cover. They have found a high correlation between the percent of seagrass cover and the seatrout abundance of an area. The different species of seagrass in the area include Thalassia testudinum (Turtle grass), Halodule wrightii (Shoal grass), and Syringodium filiforme (Manatee grass).20160627-IMG_20932

The research team collects samples using an otter trawl towed behind the boat at each sampling station spread out across the bay. The contents of the tow are then emptied into a container on the back of the boat for sorting. At 12 of the 81 stations, the team keeps all species brought up in a tow, called a total collection. For the remaining stations, they record the type, size, and amount of sportfish species, and then release the catch.

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The team also collects juvenile pink shrimp that show up in their trawl. Larval pink shrimp spawned offshore near the Dry Tortugas- an island group about 130 miles West- find their way into Florida Bay to grow up. After a few months as juveniles, they head back to the Tortugas as near adults to restart the life cycle with spawning. NOAA Fisheries is interested in acquiring a reliable estimate of shrimp abundance, and monitoring migration.

 

Pictured above, a Striped Burrfish and an Inshore Lizardfish are two examples of non-target species sometimes caught in the trawl, and then released.

 

 

 

The Juvenile Sportfish Research Study began in 2004. During the first three years, populations of Spotted Seatrout remained high in the bay, due to elevated levels of precipitation that included the three hurricanes of 2005. Since 2007, there have not been two consecutive abnormally wet seasons, and the team has noticed much lower abundances. In 2014, calls began coming in from fishermen stating they had significantly lower catches of adult Seatrout in the bay.

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Researchers sample 81 stations each month, from May to October. If temperatures are abnormally high, they also conduct sampling in November due to a higher likelihood of observing juvenile seatrout, who would normally not be found once temperatures drop to 20 degrees Celsius. Sampling stations are chosen through a Stratified Random Sampling Design, which divides the bay into regions and then randomly picks which stations are sampled each month.

map1.pngThis map shows data from an extreme hypersaline event in the bay in July 2015. The x-axis and y-axis at left show latitude and longitude, respectively. The y-axis at right shows salinity in ppt (parts per thousand). Average seawater salinity is 35.5 ppt. The ideal salinity range for Spotted Seatrout 25-36 ppt. Further research into the impacts of changes in salinity on seatrout in required to accurately assess how environmental shifts impact species population.

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This map shows the corresponding seagrass die-off after the July extreme hypersaline event. The y-axis at right shows the percent of seagrass cover in the bay.

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