Florida’s Snook Population Gets a Boost from Release of Hatchery Fish

On Friday, Aug. 15, scientists with Mote Marine Laboratory and Florida’s Fish and Wildlife Conservation Commission released hatchery-reared juvenile snook into the wild as part of an ongoing program designed to find the most effective methods to replenish and enhance wild snook populations.

Stocking Snook

The species is one of Florida’s most popular sport fish and plays an important role in drawing recreational anglers to the state. According to the American Sportfishing Association, Florida is the top-ranked state in economic output from recreational fishing, which draws $8.6 billion to the economy annually. Saltwater fishing alone generates 80 percent – $6.8 billion – of that income.

Snook, along with red drum, are the main test species for restocking efforts statewide. This project – which involves tagging and then releasing more than 2,200 snook into Sarasota Bay during over three days – is designed to determine whether snook that have been conditioned for release at Mote have better growth and survival rates in the wild.

This event is a key example of Mote’s efforts to develop and support public-private partnerships for the conservation and sustainable use of our marine resources. The snook release is possible now thanks to a private donation to Mote and from funding provided by FWC. For more than 25 years, Mote and FWC scientists have partnered on studies designed to increase the effectiveness of stock enhancement in Florida; their work on the topic is followed globally.

Snook In Hatchery

Past Mote and FWC research conducted through pilot snook releases that took place between 1997 and 2006 has shown that hatchery-reared fish released into the wild can indeed contribute to the local fishery with the fish growing to adulthood. And, in fact, tag data recovered following these small-scale pilot release experiments showed that using the knowledge we gained, we were able to improve the survival rate of stocked fish by more than 200 percent.

“We’ve found over time that we can improve the survival of hatchery snook released into the wild by 10 times just by choosing the right habitat,” said Dr. Kenneth Leber, Associate Vice President for Mote’s Directorate for Fisheries and Aquaculture. “We also know that there are limits on how many fish you can put in each habitat before you start to lose hatchery snook. These pilot studies we’re doing now are further defining the best methods for snook stock enhancement.”

Fingerling Snooki

Such findings are key to developing large-scale stocking techniques that are financially and environmentally feasible that can help rapidly boost populations of species affected by overfishing or natural phenomenon like the 2010 winter cold spell that resulted in the deaths of millions of snook and the closure of the fishery. Snook populations have only recently rebounded on the Gulf Coast from that event enough that FWC was able to reopen the fishery earlier this year.

This latest experiment will look at the survival in the wild of 2,000 juvenile snook that were born and raised at Mote Aquaculture Park in eastern Sarasota County. The Park is Mote’s aquaculture research and development test-bed where we are developing new methods for spawning, hatching and rearing marine species for restocking purposes and for human consumption. Many of these studies are conducted in partnership with FWC biologists.

“FWC and Mote Marine Lab have worked together since 1985 to advance marine stock enhancement in Florida,” said Chris Young, Director of FWC’s Stock Enhancement Program. “We’re excited to continue our partnership with Mote Marine Lab in support of these snook releases.”

Releasing Snook

For this release, FWC and Mote biologists inserted PIT tags – passive integrated transponder tags – in the juvenile snook before release. These small, 23 mm-long tags are about the size of a pencil eraser and each one transmits a unique identifying number. The transmissions will be picked up by underwater antennae placed by scientists near the release site in the wild. These antennae will listen for the released snook as they swim by and each time a tagged snook passes through the array, a receiver will record the movement.

Scientists will also use seine nets to periodically gather snook and evaluate growth rates, compare performance between wild and hatchery snook and determine whether the released fish are contributing to overall snook abundances.

One key to the study is the conditioning that some of the snook have undergone prior to release, Leber said. “We have a control group of fish that have been raised in traditional aquaculture manner – in bare tanks using artificial feed. We also have a group of conditioned fish that have been fed live prey for three days prior to their release. We’ve also placed structures into their tanks, which mimics the structure fish will have in the wild. We think these two factors will help hatchery-reared snook be more prepared for life in the wild – with a better ability to hide from predators and ready to hunt for prey of their own.”

Underwater Robots from Mote and USF Monitor Red Tide, Ocean Conditions in Gulf of Mexico

Robot Waldo

Robot Bass

The bloom – first reported offshore in a statewide update issued July 25 by the Florida Fish and Wildlife Conservation Commission (FWC) – is presently offshore of Hernando and Pasco Counties and appears to be 80 miles long, 50 miles wide and 40-90 miles offshore, according to satellite images. (See the latest update from FWC.)

While satellites capture the bloom’s surface appearance, only underwater robots and water sampling crews can verify the presence of the red tide algae, Karenia brevis, and detect the bloom beneath the surface. While scientists on boats can return water samples to the lab for more detailed analyses, robots can stay in the environment much longer, work in challenging weather and gather more data per mission.

Mote’s robot, an autonomous underwater vehicle (AUV) nicknamed “Waldo,” carries a Mote-designed red tide detector called an optical phytoplankton discriminator, nicknamed the “BreveBuster.” This instrument examines microscopic algae in the water and tells scientists how closely they resemble K. brevis. In addition, Waldo’s equipment measures salinity and temperature – two physical factors that can affect blooms and help scientists develop better short-term forecasts of bloom movement.

USF’s AUV, nicknamed “Bass,” collects physical and optical oceanography data, including chlorophyll from algae, oxygen levels and water clarity. Data from both AUVs will support mathematical modeling of the bloom for short-term forecasts developed by the USF-FWC Collaboration for the Prediction of Red Tides.

“The team effort between our AUVs is crucial,” said Dr. L. Kellie Dixon, manager of the Ocean Technology Program at Mote. “The bloom is large and one AUV would have difficulty surveying all of it within a reasonable amount of time. Each AUV also has its own strengths – Waldo is equipped to sense the presence of red tide, important for ground-truthing the satellite images, while Bass is designed to make deeper dives further offshore.”

Waldo is programmed to move south along the shallower eastern edge of the bloom while Bass is set to move south along the deeper, western edge. Both gliders will dive up and down, collecting data at various depths and then surfacing every few hours to send updates to scientists using satellite transmitters in their tails.

Results so far: Since deployment on Friday, Waldo has been patrolling to within about 40 miles from the Pasco/Hernando border and has found red tide at the surface and to depths of about 25 meters (82 feet) in areas where it was indicated by satellites. Bass has been transecting the outer portion of the bloom and has found elevated chlorophyll associated with the red tide into waters as deep as 40 meters (131 feet).

Both gliders indicate stratified (or layered) water, with warmer and fresher water on the surface, and an abrupt transition to colder, saltier water at mid-depth.

Where are Waldo and Bass?

The public can see Waldo’s position by visiting: http://coolcloud.mote.org and clicking “Glider Operations,” and Google Earth users can see Waldo and Bass’ positions at: http://ooma.marine.usf.edu/CROW/

Through underwater robot missions and other monitoring efforts, Mote and USF are partners in a major environmental monitoring collaboration called GCOOS – the Gulf of Mexico Coastal Ocean Observing System. GCOOS provides timely information about the environment of the U.S. portion of the Gulf of Mexico and its estuaries for use by decision-makers, including researchers, government managers, industry, the military, educators, emergency responders and the general public. Both gliders are reporting data to GCOOS’s Data Portal (http://gcoos.org/products/) in support of these efforts.

“In the future, we’d really like to compliment satellite imagery in the Gulf of Mexico with our underwater robots’ findings continuously, so that we can see what’s going on below the surface before a bloom initiates and starts killing fish and potentially impacting our coastlines,” said USF’s Chad Lembke, recently named leader of the Gulf Glider Task Team organized by GCOOS to assist in the coordination of glider efforts in the Gulf region. (“Glider” is another name for these AUVs or underwater robots.)

Red tide resources:

Statewide red tide updates and info from FWC: http://myfwc.com/redtide
Statewide updates in the HAB Bulletin from NOAA: http://tidesandcurrents.noaa.gov/hab/
Red tide information from Mote, including FAQs and the Beach Conditions Report: a monitoring system for red tide impacts on multiple Florida beaches: http://mote.org/news/environment-updates#RedTide
Learn about red tide on Facebook from this FWC-Mote page about Florida’s harmful algal blooms: www.facebook.com/flhabs
Latest model forecasts from USF-FWC Collaboration for Prediction of Red Tides at: http://cprweb.marine.usf.edu/

Founded in 1955, Mote Marine Laboratory & Aquarium is an independent, nonprofit 501(c)3 research organization based in Sarasota, Fla., with field stations in eastern Sarasota County, Charlotte Harbor and the Florida Keys. Mote has 24 research programs and a variety of initiatives dedicated to today’s research for tomorrow’s oceans with an emphasis on world-class research relevant to conservation and sustainable use of marine biodiversity, healthy habitats and natural resources. Mote’s vision includes positively impacting public policy through science-based outreach and education. Showcasing this research is The Aquarium at Mote, open from 10 a.m. to 5 p.m. 365 days a year. Learn more at www.mote.org.

NOAA Great White Shark Study Offers Optimistic Outlook

From the 90’s onward, NOAA scientists say, white shark numbers have slowly increased, mostly thanks to limited harvest.

Studies including hook-and-line captures indicate white sharks are recovering to safe numbers in Atlantic Waters off the U.S. coast.

Great White Shark

White sharks are among the largest, most widespread apex predators in the ocean, but are also among the most vulnerable. A new study, the most comprehensive ever on seasonal distribution patterns and historic trends in abundance of white sharks (Carcharodon carcharias) in the western North Atlantic Ocean, used records compiled over more than 200 years to update knowledge and fill in gaps in information about this species.

Scientists from NOAA Fisheries and colleagues added recent unpublished records to previously published data to present a broad picture of 649 confirmed white shark records obtained between 1800 and 2010, the largest white shark dataset ever compiled for the region. Their study was published June 11 in the journal PLOS ONE.

“White sharks in the Northwest Atlantic are like a big jigsaw puzzle, where each year we are given only a handful of pieces,” said Tobey Curtis, a shark researcher at NOAA’s Greater Atlantic Regional Fisheries Office in Gloucester, Mass. and lead author of the study. “After decades of effort by a lot of researchers, we finally have enough puzzle pieces for a picture to emerge on distribution and abundance patterns. We are pleased to see signs of population recovery.”

Among the findings: White sharks occur primarily between Massachusetts and New Jersey during the summer, off Florida during winter, and with a broad distribution along the U.S. East Coast during spring and fall. The sharks are much more common along the coast than in offshore waters. The annual north-south distribution shift of the population is driven by environmental preferences, such as water temperature, and the availability of prey. In recent years, white sharks have been increasingly associated with the return of gray seal colonies off the coast of Massachusetts.

Many whites travel north in summer to waters off New England, south to waters off Florida in winter.

Great White Shark Movemen

“White sharks possess life history traits that make them vulnerable to exploitation,” said Nancy Kohler, chief of the Apex Predators Program at NOAA’s Northeast Fisheries Science Center (NEFSC) and a study co-author. “These sharks can live 70 years or more, mature late, and do not produce many young. Their status and highly valued jaws and fins have made them the target of recreational and trophy fisheries in areas where their populations are not protected.”

Opportunistic capture and sighting records remain the primary source of information on this species. The updated information in this study is aimed at improving the conservation and management of white sharks both regionally and internationally, and providing a new baseline for future study.

This study updates understanding of white shark relative abundance trends, seasonal distribution, habitat use, and fisheries interactions, most of which occur with rod and reel, longline, and gillnet gear. White shark records were collected from landings data, commercial fishery observer programs, recreational tournament information, scientific research surveys, commercial and recreational fishermen, and other sources. The records were further classified, based on biological information such as length and life stage – neonate, young of the year, juvenile, or mature. Distribution patterns of each life stage were examined.

In the 1970s and 1980s, relative abundance data indicated that white shark populations declined, likely due to expanding commercial and recreational shark fisheries. However, from the early 1990s onward, abundance has increased.

“Both the declines and, more notably, the increases in abundance seen in our study were supported by multiple data sources” said Cami McCandless, a biologist in the NEFSC’s Apex Predators Program and a study co-author. “The increase in relative abundance is likely due, in part, to the implementation of management measures. The U.S. has managed its shark fisheries since 1993, and banned both commercial and recreational harvesting of white sharks in 1997.”

Sightings of white sharks have increased considerably in recent years along much of the East Coast.

Great White Shark Sightings

Newborn white sharks, as small as 4.0 feet long, regularly occur off Long Island, New York, suggesting this area may provide nursery habitat. The largest shark in the study considered accurately measured was a female landed on Prince Edward Island, Canada, in August 1983. The animal measured 17.26 feet from the tip of its snout to the fork in its tail.

White sharks of all ages and sizes are present in continental shelf waters year-round, but their distribution varies by season. During winter, most white sharks are found off the northeast coast of Florida, the Florida Keys, and in the Gulf of Mexico offshore of Tampa Bay, Florida, where they have generally been considered rare. In spring, the distribution expands northward, and by summer most sharks occur in the waters off New York and southern New England, and around Cape Cod. In August some large juvenile and mature individuals reach Newfoundland and the Gulf of St. Lawrence, the northernmost limit of their range. During fall, most sharks remain in northern latitudes, but begin to shift southward in November and December.

Most of the sharks were found in water depths shallower than 330 feet, although they seem to use deeper and colder waters as their size increases. The authors note that, in general, “white sharks remain an uncommon and sparsely distributed predator in the Northwest Atlantic Ocean.”

“We have improved our understanding of white sharks in the Northwest Atlantic in recent years through field research and technology,” said Kohler. “But we still have many questions about life history, population structure and size, behavior, habitat preferences, feeding habits, movements, and migration.”

White sharks live 70 years or more and mature late, so are highly vulnerable to over-harvest despite their formidable predatory capabilities.

Great White Shark Mouth

Questions include when and where the sharks mate and give birth, their use of offshore habitats beyond the continental shelf, and whether the timings of white shark migrations in the Northwest Atlantic are similar to those in the Pacific and Indian Oceans. More observations, fishery captures and analyses of occasional specimens, along with tagging and telemetry studies, are needed to help answer these questions and improve conservation strategies.

In addition to Curtis, Kohler, and McCandless, study authors include Lisa Natanson and John Hoey from the NEFSC’s Narragansett Laboratory in Rhode Island; John Carlson from NOAA’s Southeast Fisheries Science Center Laboratory in Panama City, Florida; Greg Skomal of the Massachusetts Division of Marine Fisheries; George Burgess from the Florida Museum of Natural History at the University of Florida in Gainesville; and Harold “Wes” Pratt, Jr. from Mote Marine Laboratory’s Tropical Research Laboratory in Summerland Key, Florida, a former member of the NEFSC’s Apex Predators Program.

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