Why is the flathead catfish invasive

The Philadelphia Inquirer. August 26, Bottroff, L. Amant, and W. Addition of Pylodictus olivaris to the California fauna. California Fish and Game 55 1 Brown, J. Implications of Pylodictis olivaris flathead catfish introduction into the Delaware and Susquehanna drainages.

Northeastern Naturalist. Dahlberg, M. The freshwater fishes of Georgia. Bulletin of the Georgia Academy of Science Introductions of freshwater fishes in Georgia. Ellis, M. Fishes of Colorado. Etnier, D. The fishes of Tennessee. Fletcher, D. Response to NBS-G nonindigenous questionaire and other reports.

Fuller, P. The flathead catfish invasion of the Great Lakes. Journal of Great Lakes Research 44 5 Guire, C. Nichols, and R. Biological investigations of flathead catfish in the Cape Fear River. Hocutt, C. Jenkins, and J. Stauffer, Jr. Hocutt and E. Wiley, eds. Hubbs, C. Fishes of the Great Lakes region. Revised Edition. Hubert, W. Exotic fishes. Pages in Parish, T.

Anderson, eds. Exotic species manual. Wyoming Game and Fish Department. Laramie, WY. Hughes, R. Patterns in catch per unit effort of native prey fish and alien piscivorous fish in 7 Pacific Northwest USA rivers. Fisheries 37 5 Idaho Fish and Game. Fisheries Management Plan Appendix I - A list of Idaho fishes and their distribution by drainage. Jenkins, R. Freshwater Fishes of Virginia. Marsh, P. Predation by Ictalurid catfishes as a deterrent to re-establishment of hatchery-reared razorback suckers.

Southwestern Naturalist 34 2 Page, L. Volume Houghton-Mifflin Harcourt. New York, NY. Quinn, S. Stomach contents of flathead catfish in the Flint River, Georgia. Starnes, W. Odenkirk, and M. Proceedings of the Biological Society of Washington 4 Stefferud, S. Sublette, J. Hatch, and M. The fishes of New Mexico. Tomelleri, J. Fishes of the Central United States. Underhill, J. The fish fauna of the Laurentian Great Lakes, the St.

Lawrence lowlands, Newfoundland, and Labrador. Pages in Hocutt, C. The zoogeography of North American freshwater fishes. John Wiley and Sons. Yellow Bullhead can be found in many of the tributaries of the Chesapeake Bay. Margined madtom is a small, light colored, secretive fish less than 6 inches in length.

The long adipose fin is separated from the rounded tail caudal fin by a small notch. The vertical fins are darkly edged in clear water but may appear only dusky in turbid water. The upper jaw extends beyond the lower jaw. Typical size for a Margined Madtom is 3 — 5 inches. Margined madtoms can be found in gravelly riffles in streams. Tadpole madtom is generally smaller than the margined madtom. The adipose is also nearly continuous with the caudal fin with only a small notch separating the two.

The upper jaw is equal with the lower jaw. Tadpole madtoms are often darker gray or brown on the back, blending to a lighter color underneath. A dark line often runs along the side of the fish. Typical size for a tadpole madtom is inches. They are usually found in small, low gradient streams.

Stonecats are similar to the madtoms in physiological appearance. They have a pale or cream-colored area located on the back and on the margin of the caudal fin. They have a depressed or flattened skull and their upper jaw is much longer that the lower. Typical size for a Stonecat is inches. They are found in gravel or boulder streams in portions of Garrett County.

Skip to Main Content. Menu Menu. You must have Javascript enabled to see this menu. We also estimated instantaneous natural mortality M based on empirical estimators developed by Pauly ; Table 2 , Hoenig , Djabali et al. We based our selection of M estimators on those examined by Maceina and Sammons , given the similarities in data available. We omitted three estimators examined by Maceina and Sammons , including the Quinn and Deriso estimator, because of seemingly arbitrary selection of the parameter describing the proportion of fish reaching maximum age; the Chen and Watanabe estimator because of poor performance in the evaluation by Kenchington ; and the Kenchington estimator because it was derived as an estimator of Z and we were unclear how to calculate its inputs appropriately.

We estimated inputs for life-history traits for M estimators from age and growth studies discussed above, and calculated mean annual temperature for the Pauly estimator from the nearest continuously every 15 min recording U.

Water temperature data were available beginning in October at the Cartersville gage; therefore, we calculated the mean from 1 January to 31 December We conducted all analyses in R version 3. Empirical natural mortality M estimators and estimates from life-history information pooled from the period to for tidal James River, Virginia, Flathead Catfish Pylodictis olivaris. When estimating growth by collection year, there were no obvious trends over time in growth parameters Table 3 or trajectories Figure 1.

Diagnostic plots generally supported the use of an additive error structure although some heteroscedasticity was evident for and Data S1, Supplemental Material. Sample sizes n , maximum observed age, and parameter estimates for von Bertalanffy growth models fit to length-at-age observations for Flathead Catfish Pylodictis olivaris from the tidal James River, Virginia, by year. Standard errors for parameter estimates provided in parentheses.

Total length-at-age observations for Flathead Catfish Pylodictis olivaris in the tidal James River, Virginia black circles with fitted von Bertalanffy growth models red lines by year from to The youngest fish among all sample years were age-2, whereas all samples had fish as old as 7 y.

Consequently, the age range 2—7 y was used for growth comparisons. Of the 15 pairwise comparisons we examined for growth models, 10 were significantly different and 5 were not Table 4.

Statistically similar growth years were not always nearest to each other temporally. Often, there were significantly different years of growth between years with similar growth. The years with the two largest sample sizes and were significantly different from all other years we compared.

Matrix of likelihood ratio test results from pairwise comparisons of von Bertalanffy growth models fit to length-at-age data collected from to for tidal James River Flathead Catfish Pylodictis olivaris in Virginia.

Of the mean RGI values by year, none were below Table 5. However, RGI of a single age-1 fish collected in was estimated as Many mean RGI values were above the 95th percentile. All age classes were above the 50th percentile when multiple fish were collected. Examination of fitted growth curves also supported fast growth in the James River Figure 2. Mean relative growth index RGI values by age and sampling year standard deviation in parentheses for tidal James River Flathead Catfish Pylodictis olivaris collected by Virginia Department of Game and Inland Fisheries from to Percentile range for RGI values shown as shades of red.

Empty boxes indicate no fish were collected. Fitted von Bertalanffy growth curves for 7 native and 11 nonnative Flathead Catfish Pylodictis olivaris river populations. The fitted curve for the tidal James River, Virginia, was estimated from the current study with length-at-age observations pooled over six sampling years from to We modeled gravimetric growth for Flathead Catfish collected from to ranging in age from 1 to 15 y.

Weight-at-age observations for Flathead Catfish Pylodictis olivaris in the tidal James River, Virginia black circles with a fitted weight parameterized von Bertalanffy growth model red line with observations pooled from to Examination of the age structure of the entire sample revealed age-3 fish were most abundant and served as the starting point for catch curve regression.

After excluding age classes with fewer than five fish, age fish were the oldest included in mortality estimation. Natural mortality estimates varied from 0. Although Blue Catfish receive a great deal of attention in the Chesapeake Bay region as a result of their abundance and spatial range, Flathead Catfish likely have also generated concern for at-risk fishes. James River Flathead Catfish are known to consume at-risk Alosa spp.

Consequently, managing Flathead Catfish is imperative to limit a source of additional mortality to these at-risk fishes. Prior to this study, synthesized information on James River Flathead Catfish was limited to diet information collected opportunistically during a study focused on Blue Catfish Schmitt et al. The current study provides critical information on population characteristics for use in population assessments to understand fishing levels necessary to reduce Flathead Catfish abundance and potentially reduce predation mortality on at-risk species.

Further, growth and mortality parameters are components of consumption estimators e. Flathead Catfish in the James River appear to grow faster in terms of length than most populations evaluated in published indices, but may exhibit nearer to average growth when compared with other nonnative populations. Several studies have examined the growth of nonnative and native Flathead Catfish, with findings indicating that nonnative populations generally grow faster Kwak et al.

However, Massie et al. We found that James River Flathead Catfish grew faster than range-wide standards, but studies used in the development of the RGI for Flathead Catfish featured mostly native populations Jackson et al. Interpreting the results from growth standards should be done with caution if there is reason to believe native and nonnative populations for a given species exhibit differences in growth and were not expressly considered in development of the index.

Despite annual differences in length-based growth rates, we did not find any discernable temporal trends in growth for James River Flathead Catfish. Invasion ecology would lead us to predict that growth would decline over time as nonnative populations become established, densities increase, and resources become less abundant.

However, growth rates during establishment may not always follow expected patterns Masson et al. Similarly, Massie et al. This may also influence the current study where Flathead Catfish were likely introduced 32 y before the first age and growth samples were collected in Regardless of a lack of simple trends in growth, the current study supports heterogeneity among years, which could be related to annual differences in climatic variables such as sunshine fraction, wind speed, evapotranspiration rates, and flooding Kwak et al.

Sample sizes may have been too small in some years to observe statistical differences in growth—we found the 2 y with the largest sample sizes were significantly different from all other years we compared. Further, small sample sizes may have caused imprecise estimation of growth parameters and maximum age Kritzer et al. Despite small sample sizes, significant differences in growth by year suggest that future population assessments should consider temporal growth heterogeneity when size-based Flathead Catfish ecology is of interest.

James River Flathead Catfish are subject to higher mortality rates than many other native and nonnative populations. Published studies on native populations reported Z -estimates ranging from 0. Our estimates of M appear to be higher than published values— M for a native population in Lake Wilson, Alabama, averaged 0.

Further, Marshall et al. James River Flathead Catfish may experience high mortality rates as a result of commercial and recreational harvest including testing of commercial electrofishing; Trice and Balazik or environmental factors characteristic of dynamic estuarine systems.

In addition, mortality rates in the current study may be overestimated as a result of a truncated age structure.

This could be due to continued maturation of the population as it approaches stabilization Sakaris et al. Further, the lack of older fish in the sample may be related to size-based selectivity of low-frequency electrofishing for Flathead Catfish based on anecdotal evidence summarized by Bodine et al.

Future studies may consider the addition of trotline sampling to target large individuals Bodine et al. In addition, Flathead Catfish exist above the fall line in the James River and currently we lack information on how fish above and below the fall line are related.

Flathead Catfish is a highly mobile species that makes long seasonal migrations Vokoun and Rabeni It is possible that fish could migrate into or out of tidal portions of the river, violating assumptions of negligible losses and additions due to movement. If managed for fisheries, overestimates of mortality may mean that Flathead Catfish are less productive and less resilient to fishing than analyses imply Harry However, if managed as an invasive species, overestimates of mortality rates could lead to ineffective strategies to reduce population sizes if actual mortality rates are lower than believed or desired.

Consequently, assessments evaluating management strategies should include sensitivity analyses to evaluate the influence of potential biases in mortality estimation. Flathead Catfish present a threat to native species in the James River, but information is limited. Published studies cover topics of diet and distribution using data that were opportunistically collected. Future work directed toward Flathead Catfish behavior and ecology would help managers understand the species within the James River and beyond.

Further, Flathead Catfish are exploited as part of the James River commercial catfish fishery, but available harvest data lacked details on species identity until recently, when Blue Catfish were segregated Virginia Marine Resources Commission, unpublished data.

Many scientists and the public have called for increased harvest to reduce invasive catfish abundances. Flathead Catfish removal efforts in the Satilla River, Georgia, have resulted in lower biomass per effort in electrofishing runs, as well as truncated size structures Bonvechio et al.

Therefore, it may be prudent to require species-level reporting for catfish harvest moving forward. Information on Flathead Catfish harvest would help fishery analysts estimate population sizes and evaluate responses to harvest. Invasive catfish management in the Chesapeake Bay features numerous conflicts among user groups, between user groups and management agencies, and between management agencies.

Using growth and mortality estimates presented in the current study as inputs in population assessments, consumption estimators, and simulation studies may help management agencies see what the possibilities and uncertainties are for management of Flathead Catfish in the Chesapeake Bay region. This may facilitate more discussions with stakeholders and begin the process of defining objectives for management to promote cooperation and satisfaction among diverse stakeholder groups and development of management plans.

Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding author for the article. Data S1. Data presented and analyzed in the current study organized in three sheets Fish, Growth Parameters, and Diagnostic Plots.

Biological data presented are from Flathead Catfish—specific low-frequency electrofishing surveys, targeting areas known to support the species. Location refers to the river system from which otoliths were sampled from Flathead Catfish. Estimates of t 0 from Bonvechio et al. Bonvechio, Georgia Department of Natural Resources, personal communication and have been corrected in the Growth Parameters sheet.

Diagnostic Plots : Diagnostic plots to assess assumptions of homoscedasticity and normality from von Bertalanffy growth model fitting with additive and multiplicative errors by year fish were collected. Orth was supported in part by the U. Fish and Wildlife Service. We thank K. Keretz, three anonymous reviewers, and the Associate Editor for comments that improved a previous version of this manuscript.

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