In red tide’s wake, snook science to the rescue
Common snook illustration by Hayley Rutger
During fall 2018, Florida red tide—a harmful bloom of Karenia brevis algae—intensified to a level that many marine animals could not survive. Of special concern was the impact on spawning female snook. If snook females full of eggs were dying, what would that mean for future generations? What did that mean for recreational fishing? What could be done to help?
Common snook, Centropomus undecimalis, is a highly sought after sportfish, known for its impressive size and exhilarating fight. State regulations do not allow commercial harvest or sale of snook, so to enjoy a tasty snook meal you have to catch it yourself. Snook occupy diverse near-shore habitats and don’t tolerate cold very well. All these factors combine to make snook fishing in southwest Florida an attraction for local and visiting anglers alike, contributing to Florida’s multi-billion-dollar, recreational fishing economy.
Snook are also important pieces of the puzzle in a properly balanced ecosystem, serving as both predators and prey. It’s no wonder that communities were seriously concerned by the sight of spawning female snook dying off during the bloom of Florida red tide—dying off with them were eggs that represented future generations.
In September 2018, three fish-friendly organizations joined forces to help snook rebound. Mote Marine Laboratory, Coastal Conservation Association of Florida (CCA), and the Florida Fish and Wildlife Conservation Commission (FWC) banded together to launch the Adopt-A-Snook program, a coordinated fundraising and stock enhancement effort to place more than 5,000 juvenile snook back into upstream habitats that would contribute to areas hit hard by red tide, notably Lemon Bay and Charlotte Harbor. This effort would cost nearly $200,000, with anglers and businesses supporting the effort by “adopting” their very own snook to be released. Releases took place at two sites in May, June and July 2019.
At Mote, the Adopt-A-Snook spawning and restoration program was coordinated by Staff Scientist Dr. Ryan Schloesser from the Fisheries Ecology & Enhancement Research Program. Snook were spawned and raised prior to release at Mote Aquaculture Research Park (MAP) in east Sarasota County in 100% recirculating systems (recycling all their salt water). Mote Senior Scientist Dr. Kevan Main has refined and championed the use of these systems. When recirculating aquaculture is optimized through research, it is an important, sustainable technology for both seafood production and fisheries enhancement.
Getting 5,000-plus snook ready for release in response to a mass mortality event doesn’t happen overnight. Check out the months of preparation and the years of Mote research behind this effort.
_____________________________________________________________________________________________________________________________________
|
Stage of current project |
Science behind this stage |
|
SPAWNING STAGE:
Broodstock snook—adult males and females—live at Mote Aquaculture Research Park (MAP) in controlled conditions that let staff simulate breeding conditions in the wild. In October 2018 and again in January 2019, staff “set the mood” with the right temperature and light conditions and induced the snook to spawn. Thousands of eggs were collected and moved into a hatchery system. |
SPAWNING STAGE SCIENCE:
Getting snook to spawn “on command” is the key first step in being able to respond to any mass mortality event, which can include cold stuns and red tide fish kills. Past stock enhancement efforts relied on collecting eggs from wild snook while they were spawning naturally. However, such a system would not have made the Adopt-A-Snook program possible, as by the time red tide had ended, wild snook had limited spawning potential. Instead, Adopt-A-Snook was possible thanks to years of research at MAP. That research identified the environ¬mental conditions needed to spawn snook any time of year, allowing Mote scientists to respond rapidly to mass mortalities in the wild. |
|
RAISING STAGE:
As little larval fish, the snook relied on a diet of rotifers and artemia—tiny zooplankton cultured onsite at MAP. As the fish developed into juvenile snook, they were moved to larger tanks for continued rearing. This phase allowed the fish to grow and allowed staff to control their environment to simulate mangrove habitat, into which the fish would eventually be released.
During the final growing phases, staff implanted a passive integrated transponder (PIT) tag into each and every fish (5,000 plus) that would be released. These microchips, similar to those used in pets, allow scientists to monitor how well fish do and where they spend time after release. |
RAISING STAGE SCIENCE:
Caring for thousands of juvenile fish that exhibit cannibalism is not easy either! Over time, Mote staff realized that adding structure to the tanks is one way to decrease the amount of cannibalism and result in more snook being produced. |
|
RELEASING STAGE:
Two sites in Charlotte County, Ainger Creek and Tippecanoe Environmental Park, were selected for the release of 5,000-plus snook, based on several factors, including the watershed that each creek system fed into. Adopt-A-Snook’s goal was to address mortality in certain locations, so fish were released into Ainger Creek to help the population in Lemon Bay, and at Tippecanoe to augment the hard-hit snook population in Charlotte Harbor. |
RELEASING STAGE SCIENCE:
Once Schloesser and partners knew what watersheds to target for snook stock enhancement, years of data from past efforts helped the Adopt-A-Snook team narrow down the best timeframe and location for the releases. Data has shown that survival rates of released juvenile snook are highest between May and September when releasing into high quality habitat. The highest survival rates from past releases also came from habitats with plenty of places for the fish to hide from predators, good water quality and abundant prey options, such as well-vegetated, natural shorelines. The upstream habitat of both Ainger Creek and Tippecanoe fit the bill, and the releases happened in spring-summer 2019. |
|
TRACKING STAGE:
To monitor for the released snook, Mote installed antenna arrays along the shore downstream of the fish release sites. Since release, the arrays have been scanning the unique PIT tag number of each snook in range and logging the date and time. This data is used to determine the survival and emigration rates for each snook release to assess the effectiveness of the Adopt-A-Snook program. |
TRACKING STAGE SCIENCE:
Without this intense monitoring effort after a release, scientists can’t know what does and doesn’t work. For every snook with an individual PIT tag number, Mote scientists know how that fish was raised, its size, when and where it was released, and if it made it downstream out of protected nursery habitats. Using that data, Mote scientists can continue to make adjustments to every step of the process to reduce post-release mortality, acclimate the snook properly to their new environment, refine release times and locations, and improve the cost-effectiveness of the whole process. |