Survival Traits of Naturalized, Hatchery, and Hybrid Strains of Anadromous Rainbow Trout during Egg and Fry Stages

Abstract

Two strains of anadromous rainbow trout Oncorhynchus mykiss, naturalized steelhead and “kamloops” (not the pure Kamloops strain from British Columbia, hence not capitalized) currently inhabit the Minnesota waters of Lake Superior and may have the potential to hybridize. This could compromise the genetic integrity of the naturalized steelhead population. Both strains are supplemented by annual stocking, despite the fact that the steelhead population reproduces naturally. Egg viability and fry behavior experiments were undertaken to evaluate the potential for hybridization and to provide information for future management of the two strains. The kamloops eggs were slightly smaller, but sizes overlapped substantially with steelhead egg sizes. Mortalilty of kamloops eggs from spawning to hatching was greater than steelhead eggs. Steelhead fry exhibited a greater fright response (wariness) than kamloops fry when startled by movement over their tanks. Hybrid egg survival and wariness traits were intermediate to those of the pure strains, but more closely resembled those of the maternal strain. These traits appeared to be heritable. Reevaluation of steelhead and kamloops management will be necessary in the future, taking into account the popularity of the kamloops fishery and the potential for degradation or elimination of the naturalized steelhead strain.

Steelhead return rates and relative costs: A synthesis of three long-term stocking programs in two Minnesota tributaries of Lake Superior

“…In addition, differential tolerances to stream temperature fluctuations are circumvented in the hatchery by maintaining optimal development temperatures (Negus, 1999), but most hatchery selection is avoided because few behavioral attributes are expressed prior to swim-up. Evaluations of fry stocking through smoltification to adulthood are rare, and many studies of "fry" stocking actually involve juveniles reared well beyond the swim-up stage through various periods of feeding (e.g.…”

“…These rivers have low alkalinities ranging from about 15 to 50 ppm, and low productivity (Waters, 1977), minimal groundwater input, are subject to high spring runoff and widely fluctuating flows, and in some years form anchor ice with surface flows in winter. Spring water temperatures often exceed optimum temperatures of 7 to10°C for rainbow trout egg development (Kwain, 1975;Negus, 1999) or up to12°C (McCullough, 1999). The temperature maximum (12 to13°C) for successful smoltification (Adams et al, 1975;Hoar, 1988;Zaugg and Wagner, 1973) is also exceeded in some spring seasons (Negus, 1999).…”

“…Spring water temperatures often exceed optimum temperatures of 7 to10°C for rainbow trout egg development (Kwain, 1975;Negus, 1999) or up to12°C (McCullough, 1999). The temperature maximum (12 to13°C) for successful smoltification (Adams et al, 1975;Hoar, 1988;Zaugg and Wagner, 1973) is also exceeded in some spring seasons (Negus, 1999). Summer water temperatures can exceed optimal growth temperatures of 11 to19°C for juvenile steelhead (Cech and Myrick, 1999;Hokanson et al, 1977), and daily mean temperatures occasionally exceed 24°C in the lower reaches in some years (French River unpublished data).…”

“…Wild STT naturally exhibit greater wariness than KAM, whose hatchery propagation over generations has selected for fish that lack wariness and respond aggressively to overhead feeding even at the fry stage (Negus, 1999). Thus, although the larger hatchery smolts had a size advantage for avoiding predation, the smaller streamreared smolts had the advantage of heightened wariness and experience in the wild, providing much higher return rates.…”

“…Although Minnesota stream temperatures can exceed the optimal range for egg and fry development (Negus, 1999), water temperatures in Lake Superior are routinely at the lower extreme for growth of steelhead (Negus et al, 2008), which prefer 13°t o 20°C (Niemuth, 1970;Talmage and Coutant, 1980;Wismer and Christie, 1987). Mean monthly temperatures occupied by STT and KAM in Minnesota waters fall within this optimal range only from July through September, and the lowest monthly means of 3°C or less occur in February and March (M. Negus, unpublished data).…”