Growth and Condition of Alewives in Lake Michigan, 1984–2001

Abstract

Diets of salmonines in Lake Michigan have been dominated by alewives Alosa pseudoharengus since the 1960s, and information on alewife population dynamics is critical to the management of salmonine fisheries. We monitored alewife size at age and condition (K) at several different locations in Lake Michigan during fall 1984–2001. Alewives were aged by enumerating annuli on otoliths. The results indicated that alewife length at age did not trend upward or downward between 1984 and the late 1990s but decreased from the late 1990s to 2001. Alewife weight at age was relatively constant between 1984 and the mid‐1990s but decreased from the mid‐1990s to 2001. Mean condition for a given alewife age was, on average, 13.7% higher during 1984–1994 than during 1995–2001. This decline in alewife condition was not a density‐dependent response by the alewife population because alewife abundance trended neither upward nor downward during 1984–2001. The decline in alewife condition was possibly due to the lakewide decrease in the abundance of Diporeia spp. during the 1990s. Apparently, the availability of the large‐bodied invertebrates Diporeia and Mysis spp. was an important regulator of adult alewife growth because alewives attained a substantially larger size in Lake Michigan, where these invertebrates were relatively important constituents of the adult alewife diet, than in Lake Ontario, where these invertebrates were not readily eaten by adult alewives. For age‐2 or older females, mean length was 2–9 mm greater than for males. Alewife size at age and condition were slightly higher on the eastern side of Lake Michigan than on the western side.

Measures of larval lake whitefish length and abundance as early predictors of year-class strength in Lake Michigan

“…This decline is relevant to the health of nearshore fishes because diporeia is an energy-rich food source and an important prey for several fishes, including alewife, yellow perch, and slimy sculpin (Wells 1980). Alewife condition declined by about 14% after 1995 (Madenjian et al 2003), suggesting a link between reduced alewife condition and diporeia abundance. More recently, Madenjian et al (2006) (also see the Status of Planktivore Populations chapter) reexamined the energy density of alewife using bomb calorimetry.…”

“…In many areas, lake whitefish have shifted from being a predominately benthic-feeding fish to feeding on pelagic organisms like Mysis and zooplankton Pothoven 2005). Growth and condition of lake whitefish began to decline after 1992 (Madenjian et al 2003;Schneeberger et al 2005aSchneeberger et al , 2005b, and that decline continued through roughly 2002-after which both growth and condition of lake whitefish appeared to stabilize and even increase slightly. Unfortunately, the presence of dreissenid mussels and an altered food web will likely continue to suppress growth and condition of lake whitefish.…”

“…Average condition during 1995-2004 was about 13% lower than average condition during 1984-1994. In addition, alewife weightat-age decreased during the late 1990s (Madenjian et al 2003). The decrease in alewife growth and condition during the 1990s has been attributed to a decline in Diporeia, spp.…”

“…The decrease in alewife growth and condition during the 1990s has been attributed to a decline in Diporeia, spp. abundance (Madenjian et al 2003 An analysis of USGS bottom-trawl data has shown that survival of alewives to age 3 has been influenced primarily by salmonine predation and secondarily by spring and summer water temperatures during an alewife's first year (Madenjian et al 2005b). These results corroborated the contention that the decline in alewife abundance during the 1970s and early 1980s was driven by salmonine predation.…”

Chinook Salmon Foraging Patterns in a Changing Lake Michigan

“…Recent exotic species invasions by zebra mussels Dreissena polymorpha and quagga mussels D. bugensis (hereafter referred to as dreissenids), Round Goby Neogobius melanostomus, and the spiny water flea Bythotrephes longimanus have coincided with large-scale ecosystem change in the Great Lakes, including reduced primary production and offshore nutrient transport due to filter feeding by dreissenid mussels (Hecky et al 2004;Depew et al 2006), declines in native zooplankton and benthic invertebrate populations (Nalepa et al 2006;Barbiero et al 2009), reduced growth and condition of fishes through indirect bottom-up food web interactions (Madenjian et al 2003;Rennie et al 2009), and reduced abundance of native fishes through direct species interactions (Lauer et al 2004). In Lake Huron, such changes have been implicated in the recent Alewife population collapse and offshore fish community shift (Riley et al 2008), though increasing native and naturalized salmonine predator abundance in Lake Huron (Johnson et al 2010) suggests that the Alewife collapse was more likely the result of top-down pressure.…”