Supplemental stocking of largemouth bass Micropterus salmoides has often resulted in limited success in large systems. We evaluated the contribution and relative abundance of advanced‐size (65–90 mm total length [TL]) hatchery Florida largemouth bass M. salmoides floridanus that were stocked into Lake Talquin (3,561 ha) to supplement year‐classes. Stocking density varied from 15 to 60 fish/ha from 2000 to 2003. Coded wire tags and unique nuclei in the sagittal otoliths of hatchery fish were used to identify stocked fish to estimate percent contribution and relative abundance. Hatchery fish released by May 15 used threadfin shad Dorosoma petenense as a primary food source at significantly higher (P < 0.05) frequencies than did wild age‐0 Florida largemouth bass examined from June to October. Dominant modal size‐groups (20–27 cm TL) of age‐0 hatchery fish in October electrofishing were larger than those of age‐0 wild fish (10–14 cm TL). Hatchery fish made up an estimated 17–40% of the age‐0 fish collected during October electrofishing from 2000 to 2003. The highest stocking density (60 fish/ha) resulted in a 40% hatchery contribution to electrofishing samples at age 0 and a 37% contribution to electrofishing samples at age 3. For the group stocked at the highest density, electrofishing catch per unit effort (CPUE) at age 0 (26 fish/h) and age 3 (8 fish/h) was higher (P < 0.05) than that for groups stocked at lower densities (15–39 fish/ha; age‐0 CPUE = 7–17 fish/h; age‐3 CPUE = 2 fish/h). Hatchery fish contribution to largemouth bass angler tournament catch in April–May 2004–2006 was estimated to be at least 20% after 4 years of variable stocking. Several factors, such as appropriate time of stocking, size at stocking, food supply, and age‐0 wild and stocked fish densities, influenced hatchery fish contributions to each year‐class and the fishery.
In an effort to aid in the conservation of black basses, the relative abundance, growth, and mortality of Suwannee bass Micropterus notius and largemouth bass M. salmoides were estimated from four Florida rivers. Fish were collected by electrofishing in the four rivers during 2001 and 2002. Electrofishing catch per unit effort of Suwannee bass was highest in the Wacissa River (95.1 fish/h), intermediate in the Santa Fe River (22.6 fish/h), and lowest in the Withlacoochee (5 fish/h) and Ochlockonee rivers (1.9 fish/h). Catch per unit effort for largemouth bass was also highest in the Wacissa River (50 fish/h), intermediate in the Santa Fe (19.8 fish/h) and Ochlockonee rivers (17.1 fish/h), and lowest in the Withlacoochee River (9.9 fish/h). Mean total length (TL) at age across the four Suwannee bass populations was described by von Bertalanffy growth curves as TL = 386.1 · (1 − e−0.3733(age+0.7772)) for females and as TL = 324.1 · (1 − e−0.4735(age+0.6543)) for males. Mean TL at age across the three largemouth bass populations was also described by von Bertalanffy growth curves as TL = 644.2 · (1 − e−0.2064(age+0.9840)) for females and TL = 427.8 · (1 − e−0.3164(age+0.9991)) for males. Suwannee bass exhibited sex‐specific growth rates similar to those of largemouth bass, females experiencing more rapid growth and attaining larger sizes than males (F1, 564 = 20.39; P < 0.01). Suwannee bass total annual mortality (A) averaged 40%, ranging from 28% to 46%. Similarly, largemouth bass total A averaged 40%, ranging from 35% to 46%. The current Florida minimum length limit on Suwannee bass directs fishing mortality almost solely to females, but estimates of fishing mortality are needed to determine whether this is a concern for black bass with a small native range.
High human demand for limited water resources often results in water allocation trade-offs between human needs and natural flow regimes. Therefore, knowledge of ecosystem function in response to varying streamflow conditions is necessary for informing water allocation decisions. Our objective was to evaluate relationships between river flow and fish recruitment and growth patterns at the Apalachicola River, Florida, a regulated river, during 2003-2010. To test relationships of fish recruitment and growth as responses to river discharge, we used linear regression of (i) empirical catch in fall, (ii) back-calculated catch, via cohort-specific catch curves, and (iii) mean total length in fall of age 0 largemouth bass Micropterus salmoides, redear sunfish Lepomis microlophus and spotted sucker Minytrema melanops against spring-summer discharge measures in Apalachicola River. Empirical catch rates in fall for all three species showed positive and significant relationships to river discharge that sustained floodplain inundation during spring-summer. Back-calculated catch at age 0 for the same species showed positive relationships to discharge measures, but possibly because of low sample sizes (n = 4-6), these linear regressions were not statistically significant. Mean total length for age 0 largemouth bass in fall showed a positive and significant relationship to springsummer discharge; however, size in fall for age 0 redear sunfish and spotted sucker showed no relation to spring-summer discharge. Our results showed clear linkages among river discharge, floodplain inundation and fish recruitment, and they have implications for water management and allocation in the Apalachicola River basin. Managed flow regimes that reduce the frequency and duration of floodplain inundation during spring-summer will likely reduce stream fish recruitment.
Introduction of flathead catfish, Pylodictis olivaris (Rafinesque), in waters of the USA has been widespread and often with negative impacts. Flathead catfish have been collected in Florida waters since the 1980s, and this study documents their impact on native fishes shortly after establishment. Four sites in the Choctawhatchee River, Florida, were sampled from 1997 to 2011, a time period spanning several years before and after the presence of flathead catfish at all sites. Flathead catfish expanded more than 91 river km in 2 years. The population increased rapidly and became the numerically dominant ictalurid at each site within 3 years of first detection at the site. Concurrent with the increases in flathead catfish was the precipitous decline of the native spotted bullhead, Ameiurus serracanthus (Yerger & Relyea). Electric fishing catch rates of flathead catfish significantly increased (P < 0.03) over time at all sites, while spotted bullhead catch rates significantly declined (P < 0.03) at three of four sites. Catch rates of flathead catfish and spotted bullhead were negatively correlated at all but the last site to be colonised by flathead catfish. This study provides evidence that introduced flathead catfish can quickly and significantly impact native ictalurids.
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