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Energy Density and Size of Pelagic Prey Fishes in Lake Ontario, 1978–1990: Implications for Salmonine Energetics
Author(s) -
Rand Peter S.,
Lantry Brian F.,
OˈGorman Robert,
Owens Randall W.,
Stewart Donald J.
Publication year - 1994
Publication title -
transactions of the american fisheries society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.696
H-Index - 86
eISSN - 1548-8659
pISSN - 0002-8487
DOI - 10.1577/1548-8659(1994)123<0519:edasop>2.3.co;2
Subject(s) - alewife , piscivore , pelagic zone , smelt , energetics , forage fish , fishery , predation , zooplankton , oncorhynchus , ecology , environmental science , biology , fish <actinopterygii> , predator
We describe dynamics of energy density and size of Lake Ontario alewife Alosa pseudoharengus and rainbow smelt Osmerus mordax , and we use a bioenergetics model of a common pelagic piscivore, chinook salmon Oncorhynchus tshawytscha , to demonstrate the effect of these factors on piscivore daily ration during 1978–1990. The energy density of alewives varied more than twofold between peaks in September (age 1) or October–November (age ≥2) and the lows in May (age 1) or July–September (age≥2). The previously described seasonal pattern of energy density of Lake Michigan alewives was similar except that energy density of older alewives (age≥3) was markedly higher in Lake Michigan. During 1978–1990, the spring energy density of Lake Ontario alewives peaked in 1979 (6,259 J/g wet weight), declined irregularly until 1985, and then remained stable through 1990 (at approximately 4,600 J/g). The initial decline may have been a density‐dependent response to a burgeoning alewife population, but the lack of an increase in alewife condition in the late 1980s, when alewife biomass fell, suggests a decline in lake productivity. Energy density of rainbow smelt increased with age in Lake Ontario and condition was invariant during 1978–1990 despite a threefold change in rainbow smelt biomass. Rainbow smelt energy density was lower and fluctuated less seasonally in Lake Ontario than in Lake Michigan. Mean weight of alewives aged 2 and older dropped from 41 g in 1978 to 19 g in 1989 in Lake Ontario. Rainbow smelt aged 2 and older showed a drop in mean weight from 13–17 g in 1978–1982 to 8 g in 1990. This downward trend in mean size of alewives was correlated with the sizes of alewives consumed by Lake Ontario chinook salmon during 1983–1987. For adult chinook salmon to maintain a constant growth rate during 1978–1990, mean individual daily ration during June–October had to increase from a low of 2.2% body weight/d (or 1.5 prey fish/d) in 1979 to 3.1% body weight/d (3.7 prey fish/d) in 1988. This increase in forage demand may have caused the observed declines in individual condition of salmonines over this period.