Density-Dependent, Trophic Level Responses to an Introduced Run of Sockeye Salmon (Oncorhynchus nerka) at Frazer Lake, Kodiak Island, Alaska

Abstract

Sockeye salmon (Oncorhynchus nerka) have developed into a major run at Frazer Lake, Kodiak Island, Alaska, reaching over 600 000 adults 34 yr after the first egg-plant in 1951. In the last nine years (1978–86), escapements have averaged over 250 000 with a record high of 486 000 adults in 1985. The increase in escapements were inversely related to seasonal macrozooplankton densities (p < 0.05; r2 = 0.42) but directly correlated with increases in the cladoceran to copepod ratio (p < 0.001). In addition, the average body length of the smallest macrozooplanker (Bosmina) has shifted below the observed threshold length of 0.40 mm for juvenile sockeye prey. We also found an inverse relationship between greater parental escapements and age 1. smolt length (p < 0.01; r2 = 0.75). Small-sized smolts produced from a density-dependent rearing environment indicate that spawning capacity equals or exceeds rearing capacity. Juvenile recruits from larger escapements (~400 000) exerted a controlling, density-dependent influence on the secondary trophic level which drastically reduced subsequent adult returns. Moreover, adverse trophic level changes, particularly after the largest escapements, also appeared to reduce the rearing efficiency for lower densities of juveniles, as subsequent smolt sizes from smaller escapements were less than expected. Thus, these findings not only provide a rationale for suggesting that fewer spawners would provide recruits more closely matching the rearing capacity of this lake, but also provide empirical evidence for the potential adverse density-dependent effects of large escapements.

Smolt-to-AduIt Survival Patterns of Sockeye Salmon (Oncorhynchus nerka): Effects of Smolt Length and Geographic Latitude when Entering the Sea

“…Simply increasing escapements and thus reducing age 1. smolt sizes (Kyle et al 1988) may lower adult returns as SAS decrease below a smolt length of 98-100 mm at about 0.3-0.5 (96) SAS -mm -" (Fig. 4, 6 , and 8).…”

Variability of kokanee and rainbow trout food habits, distribution, and population dynamics, in an ultraoligotrophic lake with no manipulative management

“…Density dependent growth of sockeye (Burgner, 1964;Johnson, 1965;Goodlad et al, 1974) and kokanee populations (Rieman & Myers, 1992;Martinez & Witzius, 1995) has been well documented in many lakes in the United States and Canada, and is commonly thought to result from intense size-selective predation and corresponding reductions in number and size of zooplankton prey (Johnson, 1965;Goodlad et al, 1974;Kyle et al, 1988;Rieman & Myers, 1992). The decline in kokanee growth with increasing density in Crater Lake is similar to the continuous exponential decline shown for a series of oligotrophic lakes in Idaho (Fig.…”

“…At high density, relative to lake productivity, sockeye (Ricker, 1937;Goodlad et al, 1974;Kyle et al, 1988), kokanee (Martinez & Witzius, 1995;, and other salmonids in mountain lakes McNaught et al, 1999;Donald et al, 2001) may greatly reduce zooplankton abundance and shift dominant taxa from large-bodied crustaceans to small-bodied crustaceans or rotifers. It is unclear to what extent kokanee regulate zooplankton abundance and community structure in Crater Lake.…”

Effects of a Whole-lake, Experimental Fertilization on Lake Trout in a Small Oligotrophic Arctic Lake

“…Although increased primary production can result in increased secondary production (Brett & Goldman, 1997;Budy et al, 1998) the strength of the response to nutrient addition decreases with each subsequent trophic level (McQueen, 1990;Brett & Goldman, 1996;Micheli, 1999). In addition to causing increased productivity at higher trophic levels, eutrophication can affect community structure Kyle et al, 1988;Smith et al, 1999). As oligotrophic lakes undergo eutrophication, oligotrophy-tolerant fish species such as salmonids and coregonids are replaced by more eutrophy-tolerant species such as perch and cyprinids (Hasler, 1947).…”