Florida Integrated Science Center
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Effects of Hurricanes Katrina and Rita (2005) on populations of non-indigenous Nile tilapia (Oreochromis niloticus) in southern Mississippi.
Authors Pamela J. Schofield, U.S. Geological Survey Mark S. Peterson, University of Southern Mississippi W. Todd Slack, Mississippi Museum of Natural Science
Participating agencies and universities
Acronyms used: USGS United States Geological Survey
Introduction Tilapia species are generally hardy fishes that are tolerant of a wide range of physiological conditions and, therefore, are used in aquaculture world-wide. Tilapias are highly invasive and exist under feral conditions in every nation in which they have been cultured or introduced (Canonico and others. 2005). Nonindigenous tilapias can compete with native fishes for food and/or space, spread disease, prey directly on native species, or alter the habitat and render it unsuitable for native species (Canonico and others 2005; McCrary and others 2007; Peterson and others 2006). Escape from farms is a common pathway for dispersal into native systems. The Nile tilapia (Oreochromis niloticus) is tolerant of a wide range of environmental factors, such as salinity and temperature. These factors have contributed to its widespread use in aquaculture as well as its invasiveness. In a review of the adverse consequences of introduced species worldwide by Casal (2006), Nile tilapia ranked third (after common carp [Cyprinus carpio carpio] and Mozambique tilapia [Oreochromis mossambicus]) due to the great number of reports of its adverse ecological impacts, number of countries into which it has been introduced, and number of countries reporting its establishment in the wild. The Nile tilapia has been raised in fish farms in southern Mississippi since the late 1980s (Peterson and others 2002). Similar to other regions where it has been introduced, the species escaped from aquaculture facilities into the wild and it has been observed in the rivers and marshes of coastal Mississippi since the mid-1990s (Peterson and others 2002). Prior to the 2005 storm events, Peterson and others (2005) mapped the detailed 2000-02 distribution of Nile tilapia in southern Mississippi.
Map of Mississippi coast showing areas sampled for Nile tilapia. A = aquaculture facility adjacent to Simmons Bayou; B = Graveline Bayou; C = Biloxi Back Bay. Grey coloration indicates areal coverage of flooding from Hurricane Katrina (from Federal Emergency Management Agency website:
In August 2005, Hurricane Katrina impacted coastal Mississippi with strong winds and an estimated 9-meter (30-foot) storm surge. Hurricane Rita followed less than a month later, and although its impact on coastal Mississippi was much less than that of Katrina, it reflooded much of the coastal ecosystem. Although these storms likely served to disperse Nile tilapia in southern Mississippi, the extent of the spread was unknown. Additionally, the storm devastated at least one aquaculture facility on the Mississippi coast (Simmons Bayou; Jackson County). The above-ground infrastructure at this site (buildings, tanks, etc.) was destroyed and partly carried off by the floodwaters and winds. However, Nile tilapia persisted within in-ground ponds after the storms and, therefore, could continue to function as a source population, dispersing farm fish out into the native habitat.
Nile tilapia collected from the aquaculture facility on Mississippi coast (Davis Bayou).
Objectives and Methods 1) Assess current distribution of Nile tilapia after the 2005 storms. We revisited sites previously sampled to determine whether Nile tilapia had spread beyond the boundaries established by Peterson and others (2005). We sampled with seines, dipnets and trammel nets where feasible during the fall of 2006. 2) Determine effectiveness of Nile tilapia control with rotenone. Working closely with the landowners and Mississippi state officials, we used rotenone to determine whether we could control Nile tilapia populations at the closed farm on the Mississippi coast. The site consisted of 14 ponds (ranging in size, up to about ¼ acre) and four vegetated ditches. All ponds and ditches with fish were treated with rotenone at a concentration of 5 ppm. After rotenone application, fish were collected each day for 3 days. Nile tilapia collected during the first 2 days post-rotenone application were measured (total length [TL] to nearest mm). Samples of fishes taken from the facility were deposited at the Mississippi Museum of Natural Science. Approximately 6 weeks after the rotenone application, the facility was re-sampled to estimate the efficacy of the control measures.
Remnants of the above-ground tanks at the aquaculture facility destroyed by the 2005 storms. Although not visible in this photo, debris remains high in the trees from the 30-foot storm surge that destroyed this facility.
Results A total of 25 species (2 decapods, 23 fishes) were catalogued from the facility.
The total number of Nile tilapia removed from the farm was 9,173. Subsequent resampling of the facility approximately 6 weeks after the rotenone application yielded only one Nile tilapia. Data from the re-survey after the storms and the eradication experiment are currently being prepared for a manuscript for submission to a peer-reviewed journal. Two Nile tilapia were collected in the Davis Bayou marsh. Subsequent seining in the marsh yielded no additional Nile tilapia. No Nile tilapia were collected from the two bayous adjacent to Davis Bayou (Graveline, to the east and Biloxi Back Bay, to the west).
Fish recovery from treated ponds.
Nile tilapia collected from the farm.
Discussion The conditions following the hurricanes of 2005 would have been advantageous for Nile tilapia to disperse and expand its range into low-salinity marsh areas beyond where they were recorded by Peterson and others (2005). However, we took only two Nile tilapia from Simmons Bayou (adjacent to the aquaculture facility) where they were previously known to occur and did not find any other Nile tilapia in adjacent bayous. Because the sampling done for this study was not comprehensive (that is, did not cover the entire Mississippi coastal area affected by the floods), it is possible that fish were displaced beyond their previous boundaries by the storms and not observed in our survey. However, at this time we have no evidence to suggest that the range of the species was expanded by the storms of 2005. Future plans include continued sampling for Nile tilapia along the Mississippi coast. Ongoing research into the salinity tolerance of the species will allow us to target specific sites for sampling that may yield additional tilapia. We will also continue to monitor the Nile tilapia population in Simmons Bayou.
Scientists working under the remnants of the Quonset hut.
Nile tilapia sampling in marshes and ditches surrounding Graveline Bayou.
For additional information Schofield, P.J., W.T. Slack, M.S. Peterson & D.R. Gregoire. 2007. Assessment and control of an invasive aquaculture species: An update on Nile tilapia (Oreochromis niloticus) in coastal Mississippi after Hurricane Katrina. Southeastern Fishes Council Proceedings 49: 9-15. Mississippi Museum of Natural Science information about Nile tilapia Nile tilapia factsheet from the USGS Nonindigenous Aquatic Species Program
References Cited Casal, C.M.V., 2006, Global documentation of fish introductions: The growing crisis and recommendations for action: Biological Invasions v. 8, p. 3-11. Canonico, G.C., Arthington, A., McCrary, J.K., and Thieme, M.L., 2005, The effects of introduced tilapias on native biodiversity: Aquatic Conservation: Marine and Freshwater Ecosystems v. 15, p. 463-483. McCrary, J.K., Murphy, B.R., Stauffer, J.R. Jr., and Hendrix, S.S., 2007, Tilapia (Teleostei: Cichlidae) status in Nicaraguan natural waters: Environmental Biology of Fishes v. 78: Peterson, M.S., Slack, W.T., and Woodley, C.M., 2002, The influence of invasive, non-native tilapiine fishes on freshwater recreational fishes in south Mississippi: spatial/temporal distribution, species associations, and trophic interactions: Report No. 206, Mississippi Department of Wildlife, Fisheries and Parks Annual Report (Grant No. F-129), 35 p. Peterson, M.S., Slack W.T., and Woodley, C.M., 2005, The occurrence of non-indigenous Nile tilapia (Oreochromis niloticus) in coastal Mississippi, U.S.A.: Ties to aquaculture and thermal effluent: Wetlands v. 25, p. 112-121. Peterson, M.S., Slack, W.T., Waggy, G.L., Finley, J., Woodley, C.M., and Partyka, M.L., 2006, Foraging in non-native environments: Comparison of Nile tilapia and three co-occurring native centrarchids in invaded coastal Mississippi watersheds: Environmental Biology of Fishes, v. 76, Ecophysiology of Non-native Fishes
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