Conservation Highlights

Florida Pioneers Improved Bass Ageing Techniques

by Summer Lindelien

Black bass are the most sought-after freshwater fish in America according to a 2016 U.S. Fish and Wildlife Service survey. In Florida, these include Florida bass, largemouth bass, spotted bass, Choctaw bass, shoal bass, and Suwannee bass. Focusing on Florida bass, the FWC statewide regulation allows 5 Florida bass to be harvested per angler per day, with no minimum length limit, but only one of the 5 may be 16 inches or longer. This regulation guides harvest towards young and small Florida bass and protects larger and older fish. Most Florida bass anglers release their catch, so many Florida bass fisheries have low harvest rates, particularly for trophy bass (8 pounds and heavier). Catch-and-release trophy bass fisheries have grown in popularity; therefore, so have programs like TrophyCatch (Freshwater Regulations page 4).

(1) Historically, fishery biologists have estimated the ages of Florida bass by counting the number of rings (annuli) that are deposited in the ear bones (otoliths) of bass, similar to counting rings on a tree. Otoliths form behind the brain of the fish and help with sound and hearing. However, to remove the otoliths from the inner ear of the fish, the fish must be sacrificed. The high social and recreational value placed on Florida bass and their live release, as well as the reluctance of some fisheries personnel to sacrifice large bass to collect age data, encouraged biologists to explore a way to age bass in a nonlethal manner.

(2) Biologists examined all Florida bass fin rays and spines to estimate their age and determined that dorsal (back) spines were the best option because they could be taken from the fish in a nonlethal and unharmful way.  Biologists also collected dorsal spine samples from multiple waterbodies statewide to compare the age estimates to otoliths. However, differences in age were observed between both approaches.

(3) With knowledge that dorsal-spine ages tend to be underestimated for older, larger Florida bass, fishery scientists tested another novel nonlethal ageing method that was suggested to be as accurate as otoliths. Called epigenetic age estimation, this new nonlethal technique involves collecting pelvic fin clips and extracting and sequencing their DNA. This genetic information contains time-sensitive indicators that can be used to estimate age. In Florida bass, the method had very high agreement between otolith-derived age and predicted age for the epigenetic clock and was more accurate than the previous fin ray and fin spine age estimates. Fishery scientists also documented that the technique is more accurate for older fish. This new tool should be highly reliable and suitable for determining the age of the largest fish for trophy bass research and management applications. It could be particularly useful to biologists tasked with managing threatened or small populations of black basses in Florida like shoal bass. To FWC staff’s knowledge, this is the first epigenetic clock developed for a wild freshwater fish, and it will contribute to a bright future for Florida bass conservation and management.