Chipola River Habitat Critical to Shoal Bass Spawning

Biologists report the results of a study investigating shoal bass spawning behavior and habitat in the Chipola River.
Juvenile-Shoal-Bass.jpg
Shown here is a juvenile shoal bass. The shoal bass is one of four black bass species native to Florida.
 

Fish and Wildlife Research Institute (FWRI) researchers have gathered important information about shoal bass (Micropterus cataractae) spawning behavior and habitat. These observations will be useful in determining management strategies that benefit this vulnerable species, its habitat and the anglers who fish for it.

The shoal bass is one of four black bass species native to Florida, and Florida’s Wildlife Legacy Initiative lists it as a species of greatest conservation need. The Endangered Species Committee of the American Fisheries Society lists the shoal bass as a vulnerable species because of its limited range – a few rivers systems in Alabama, Florida and Georgia. The only known reproducing population in Florida is located in the Chipola River in the northwest region of the state.

To learn how to better protect the shoal bass population in Florida, scientists conducted a study in the Chipola River to evaluate spawning behaviors and environmental factors that affect spawning success. They documented and captured on film for the first time the following:

Video footage of a shoal bass spawning event. Researchers observed this behavior only a few times during the two-year study period.
  • spawning behavior
  • parental guarding of eggs
  • eggs hatching
  • maturation of hatched fry
  • predation by other fish species

Biologists collected data in 2011 and 2012, from mid-April to mid-May, by surveying 6.5-mile stretch of the river for male shoal bass guarding beds (nests). FWRI researchers recorded 97 bed locations over the course of the two-year study. Each time a bed was located, they recorded water temperature and velocity, water depth and habitat type.

Biologists compared environmental data to number of eggs and newly hatched fry to determine how conditions affected spawning success, which was defined in two ways: the number of eggs that survived to hatching and the number of hatched fry in a bed.

Shoal-Bass-Eggs.jpg

Researchers found shoal bass typically lay eggs on bedrock in 1.5-6 feet of water.

Researchers found shoal bass typically lay between 300 and 2,000 eggs per bed, which is the lowest number for any black bass species. Eggs hatched into fry 5-6 days after being laid. The study showed the number of hatched fry – ranging from 15 to 1,293 – varied greatly among beds.

Beds were located on limestone bedrock in water 1.5-6 feet deep, with temperatures ranging from 66 to 78 degrees Fahrenheit. These differences in depth and temperature were not found to have an effect on spawning success. Researchers also noticed eel grass (Vallisneria americana) and boulders were often located adjacent to shoal bass beds.

Researchers expected water velocity to be a major factor influencing spawning success, and preliminary results suggest beds located in areas with lower flow velocity contained more eggs and more hatched fry on average. Scientists think one possible reason for this is beds located in areas with faster currents may be subjected to higher densities of an unexpected predator species, blackbanded darters (Percina nigrofasciata).

 
Researchers recorded this video of blackbanded darters eating shoal bass eggs.

A group of these predators can significantly deplete the number of eggs, especially when the male shoal bass leaves the nest for even a short period of time.

The results of this study highlight the importance of shoal and shallow bedrock habitats in the Chipola River. Researchers will use the information to identify additional areas of high-quality shoal bass spawning habitat along the entire Chipola River.



FWC Facts:
Seagrasses occupy only 0.1 percent of the sea floor, yet are responsible for 12 percent of the organic carbon buried in the ocean, which helps reduce atmospheric carbon dioxide.

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