Big Bend Abundance 2020
In the Big Bend BMU, a tuft of bear hair is collected by an FWC biologist at a barbed wire hair corral. The bear hair follicle contains DNA which can be used to identify an individual bear.
The Chassahowitzka black bear subpopulation, within the Big Bend Bear Management Unit (BMU), is the most genetically isolated and has the smallest estimated abundance of the seven bear subpopulations in Florida. Although bear numbers in Florida are generally increasing, the estimate of abundance for the Chassahowitzka subpopulation based on 2010 data remained low. Genetic diversity was also low in 2010, indicating persistent genetic isolation. Reported bear sightings in the Big Bend BMU suggested that bear abundance remained below the objective of the 2019 Florida Black Bear Management Plan of at least 200 adults per BMU.
In summer 2020, FWC biologists surveyed the Chassahowitzka black bear subpopulation and other portions of the Big Bend BMU that were likely to have resident bears. Biologists deployed a grid of hair corrals in the BMU to collect bear hair samples. Hair samples were collected then analyzed to genetically identify individual bears, which allowed biologists to estimate abundance in each study area and to measure genetic diversity. Read more about how biologists use hair corrals to estimate bear abundance. This noninvasive survey allowed the FWC to estimate abundance, density, and genetic diversity within the BMU and compare those values to estimates from 2010 and elsewhere in Florida.
Barbed wire hair corrals (dots) were deployed in 2020 to collect bear hair samples in three study areas in the Big Bend BMU: Lower Suwannee, Goethe, and Chassahowitzka. Corral dots are color-coded to show the number of unique bears that were identified at each corral. The area of abundance estimation is shown in yellow. The estimated bear range is represented by shades of tan to brown. View larger image.
This study provided a timely update on the status of the Chassahowitzka bear subpopulation and provided the first statistical estimate of abundance in the Goethe and Lower Suwannee areas. FWC biologists found that both abundance and genetic diversity remain very low in the Chassahowitzka subpopulation. They also found that bears in the rest of the Big Bend BMU continue to persist at low numbers, but occurrences have increased over the last decade, which has shifted the area of highest concentration north of the Cross-Florida Barge Canal.
FWC biologists estimated that there were approximately two resident bears living in Chassahowitzka, nine bears in Goethe, and 18 bears in Lower Suwannee areas. The combined abundance of all three study areas was 29 resident bears. These numbers do not include bears that may only occasionally visit or travel through the study areas. The true number of bears may be slightly higher or lower than these estimates. Compared to 2010, there were fewer bears in Chassahowitzka but more bears in Goethe and Lower Suwannee.
FWC biologists measured genetic diversity in each study area in ‘mean alleles per locus,’ where a higher number indicates higher genetic diversity. They found 2.25 mean alleles per locus in Chassahowitzka, 3.50 mean alleles per locus in Goethe bears, and 4.25 mean alleles per locus in Lower Suwannee bears. Compared to other areas of Florida, Chassahowitzka and Goethe had low genetic diversity and Lower Suwannee had average genetic diversity. As predicted, the Big Bend BMU remains below the minimum Florida Black Bear Management Plan objectives for abundance and for genetic diversity. The FWC hopes to see increased genetic diversity across all Florida subpopulations as bear occurrences expand and fragmented bear subpopulations reconnect through a network of bear habitat corridors. Results from this study have not yet been published, but you can view the final FWC report for more details.