Analysis of trophic and population ecology of an introduced (1968- 1969) alewife forage base and resident sportfishes (age 0 and older) indicated several negative trophic interactions within the community complex of Claytor Lake, Virginia. Alewife piscivority represents a potentially significant adverse impact on sportfish recruitment. Alewife consumed the young of at least four sport species. Larval alewife did not inhabit shallow coves and consequently were not a prey item of age 0 sportfish resident in that habitat. Dietary overlaps (Levins' equation) between adult alewife and young-of-year sportfishes indicated that competitive interactions may occur on a time/site-specific basis.
Alewife were demonstrated to be highly size-selective planktivores, preferring zooplankters >1.0 mm length. Electivity determinations indicated the importance of considering size distribution of prey species in food-habit studies. Electivity values were often positive for zooplankters ≥1.0 mm and negative for those <1.0 mm length.
Comparisons of the zooplankton community following an alewife die-off (1978) and after alewife recovery (1979) indicated that changes in abundance of predominate species were size-related with smaller forms dominating after alewife recovery. The sizes of Daphnia at onset of maturity were considerably smaller following alewife population recovery. Alewife-induced shifts in zooplankton composition toward small forms represent a potentially significant adverse impact on young-of-year sportfishes which are often size-dependent as well as size-selective planktivores.
Electivity determinations of young-of-year sportfishes (<50 mm TL) indicated that only striped and white bass positively selected a zooplankton species (Leptodora kindtii) that was concurrently preferred by alewife. Partitioning of the food complex among cove-inhabiting young sportfishes was in evidence. Predation upon one another, as well as cannibalism appeared to be a more critical trophic interaction than competition with each other or alewife.
Indirect trophic interactions between alewife and planktivorous sportfish stages may have affected first year growth rates of smallmouth bass, spotted bass, and white crappie which declined compared to results of a previous growth study made prior to alewife introduction. Following the alewife die-off, age 1 white bass and walleye growth rates significantly increased, perhaps in response to reduced competition with alewife.
Utilization of alewife (age 0 and age 1 only) by pelagic sportfishes (walleye, striped bass, white bass) and predation of other prey by littoral black basses suggested partitioning of the forage base. In the spring following the alewife die-off, pelagic sportfishes switched to alternative prey and competition among limnetic and littoral-inhabiting piscivores presumably increased.
Although alewife were shown to possess several negative traits for a forage fish, no forage species has proven ideal for southeastern reservoirs. Alewife introduction should be limited to systems too cold for threadfin shad, and that are managed primarily for pelagic predators with non-pelagic young or those that are maintained on a put-grow-take basis. Results of this study underscore the importance of assessing community impacts of an exotic species before wide-spread introduction. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/70570 |
| Date | January 1980 |
| Creators | Kohler, Christopher C. |
| Contributors | Fisheries and Wildlife Sciences |
| Publisher | Virginia Polytechnic Institute and State University |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xiii, 192, [3] leaves, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 6166457 |
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