Proposal Draft II
Dr. Van Tets: Adv Exp Design
Oct. 20, 2009
Title Ecological effects of the Alaska blackfish (Dallia pectoralis) invasion in
Cook Inlet Basin, Alaska
The Alaska blackfish, Dallia pectoralis, is a small nongame fish native to freshwaters of Beringia. Its natural range extends from 72º to 55º N latitude on the Chukchi Peninsula of eastern Siberia, across western Alaska from the Colville River to the Alaska Peninsula, and inland through the Yukon-Tanana drainage to Fairbanks (Mecklenburg and Mecklenburg 2002.) Fish were introduced on St. Paul Island as well as in Lake Hood in the Anchorage area during the 1950s, and recent reports list them in most southcentral area lakes (Morrow 1980, Stratton and Cyr 1995, Mecklenburg and Mecklenburg 2002).
Blackfish are legendary for their cold tolerance, although anecdotes of fish freezing and then being thawed out alive are unsupported by laboratory investigations (Scholander
et al. 1953; Scholander et al. 1957). A unique esophageal air-breathing organ shared only by one other known teleost, the Asian swamp eel (Monopterus alba), enables them to facultatively breathe atmospheric air (Crawford 1974), thus surviving anoxic conditions associated with shallow swamps in summer or iced-over lakes in wintertime.
Blackfish reach sexual maturity at age 2-3 for Lake Alegnagik (Bristol Bay) populations. River residents are potamodramous, migrating out of wintering grounds in springtime when temperatures increase by 10-15ºC. Adults paddle through dense wetland grasses to spawn upstream in small side channels or shallow lakes in summer (Blackett 1962). Males develop pink-to-red fin margins during spawning (Scott & Crossman 1973) and in samples from Siberia are larger and more numerous than females (Gudkov 1998).
Lake Alegnagik blackfish are isochronal spawners during a 2-week season in July (Aspenwall 1965), in contrast to observations of Fairbanks specimens which appear to spawning heterochronally, throughout the summer (Blackett 1962). Blackfish are gonochoristic and deposit adhesive eggs on benthic vegetation within slow-moving waters of ponds, lakes, and streams. Female ovaries contain two egg types: 2.0-mm yellow-colored eggs for the present spawning season and 1.0-mm colorless eggs for the following season’s spawning (Aspenwall 1965). Fecundities range from 100-300 ova, depending on fish size (McPhail and Lindsey 1970). Hatch occurs within 9 days at 12.2º C, and larval growth is rapid during the first summer, to 20mm by September (Scott and Crossman 1973). Blackfish are likely to be repeat spawners (Morrow 1980.)
Blackfish feed on small aquatic invertebrates including ostracods, cladocerans, Dipteran larvae, and surface insects (Ostdiek 1956, Morrow 1980.) Piscivory on juvenile northern pike and other blackfish is reported for Bristol Bay blackfish (Armstrong 2007), and fish may also consume plants when preferred prey is unavailable (Eidam, personal observation.)
Blackfish populations introduced to southcentral Alaska are poorly described, and their impacts on local ecosystems are not understood. Research on native blackfish in Russia and western Alaska yields limited information on life history and trophic ecology. The objectives of this study are to describe and compare two life history aspects of introduced blackfish in southcentral Alaskan waters. Specifically, diets of fish from three distinct aquatic habitats over a one-year period will be analyzed. In addition, female life-history traits including size and age at reproduction, clutch size, egg size, timing of egg development, and overall reproductive effort will be studied. Breeding populations will be studied to determine whether they are isochronal or heterochronal spawners. Comparisons to life histories of native blackfish from western and interior Alaska will be made. Negative impacts on native game fishes such as coho salmon and nongame species such as threespine stickleback will be discussed based on diet analyses and female life history traits.
Invasive species have ecological effects on ecosystems. How does an invader of Cook Inlet Basin, Dallia pectoralis, the Alaska blackfish, affect the trophic ecology of lakes, streams, and wetlands within this region? Two life history traits, diet and egg production, can serve as indicators of ecological impact of a fish species on an ecosystem. Fish diet is variable over space and time, and predation of blackfish on aquatic invertebrates and native fishes may affect the trophic ecology of a particular aquatic habitat. In addition, female life history traits vary depending on the species of fish, the specific population, and individuals within that population. Reproductive success is dependent on egg production, overall fecundity, and timing and duration of the spawning season.
Three freshwater habitats-- wetland, stream, and lake—will be selected within southcentral Alaska based on year-round presence of blackfish. A wetland site has been identified within the Matanuska-Susitna Valley lowlands between the Matanuska and Knik rivers, and consists of a marsh containing a shallow manmade rectangular pool with a thriving Dallia population (the only fish species present) including young of the year (YOY), juveniles, and adults. A nearby stream, Rabbit Slough, provides passage for adult fish migrating from lower reaches to inland spawning grounds during early summer, and is also a thriving nursery ground for juvenile coho salmon. Delong Lake in Anchorage is stocked with hatchery-reared rainbow trout and Chinook salmon and also contains a population of introduced blackfish. Once a month during a 12-month period, blackfish will be harvested from each of these three locations. 20-50 1/4” and 1/8” mesh unbaited minnow traps will be placed at each site and checked for fish every 2-3 hours from time of placement. Any fish captured will be immediately killed with an overdose of MS-222 and fixed in 10% buffered formalin. All specimens will be weighed (wet weight) to the nearest 0.1g, and standard length (SL) and eye diameter measured to the nearest 0.1mm using digital calipers. The length and number of gill rakers on the first right arch will also be recorded. Stomach contents will be dissected, identified based on genus-species (fishes and plants) or family (invertebrates), and enumerated. Preserved ovaries will be excised and weighed, and ova will be categorized according to developmental stage, following protocol described by Heins and Baker (1993) and Karve (2004.) Fecundity will be computed in nearly ripened females.
Alaska blackfish have successfully expanded their native range from western and northern Alaska inland to Cook Inlet Basin waters including lakes, streams, and wetlands. Invasive blackfish within the Cook Inlet Basin are predicted to exhibit life histories similar to native blackfish in western and northern Alaska. An ability to adapt temporally to variable prey availability is predicted to be a survival strategy of blackfish. Seasonal diet changes are expected to occur across all three aquatic habitats. Lake fish are predicted to show seasonal diet shifts as follows. During winter, diet may consist of zooplankton due to low prey availability and slowed metabolism in near-freezing waters, while springtime diet is predicted to shift to ominivory as fish feed on macrophyte seeds and more abundant zooplankton. Finally, carnivory on small crustaceans as well as fish during summer is expected. Wetlands blackfish are predicted to feed year-round on vegetation, small crustaceans, and aquatic insects. Stream populations are expected to show a temporal shift in predation from omnivory during springtime to piscivory on juvenile salmonids in summer and early autumn months. Wintertime feeding will be greatly reduced in stream fish due to slowed metabolic rates of fish in near-freezing water.
Reproductive strategies of invasive blackfish in Cook Inlet Basin waters are expected to vary with habitat. Within lakes, blackfish may be isochronal spawners which produce mature eggs within a 2-4 week period, similar to Lake Alegnagik blackfish (Aspenwall 1965.) In contrast, stream fish are predicted to be heterochronal batch spawners which release a few mature eggs at regular intervals from May through August (Blackett 1962, Morrow 1980.) Finally, wetlands blackfish are expected to be batch spawners during May through August.
Alaska blackfish are successful invaders of lakes, ponds, and streams in the Cook Inlet Basin. Survival strategies reflect native blackfish life histories as well as plasticity of adaptation to new inland aquatic environments. Both feeding and reproduction are key life history traits for fish survival. Analyses of temporal changes in feeding will provide useful information for comparing survival strategies of lake, wetland, and stream populations. Diet composition during a one-year period will demonstrate the degree of blackfish predation on native salmonids within Cook Inlet Basin waters. Analyses of female life-history traits including clutch size and timing of egg development for fish within all three habitats will highlight successful reproductive strategies of invasive blackfish. Both feeding and reproduction are predicted to show high levels of plasticity in Alaska blackfish life history, therefore highlighting their successful invasion of Southcentral Alaskan waters.
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