Assessment of Top-Down and Bottom-Up Controls on the Collapse of Alewives (Alosa pseudoharengus) in Lake Huron

Abstract

Food web models are powerful tools to inform management of lake ecosystems, where top-down (predation) and bottom-up (resource) controls likely propagate through multiple trophic levels because of strong predator-prey links. We used the Ecopath with Ecosim modeling approach to assess these controls on the Lake Huron main basin food web and the 2003 collapse of an invasive pelagic prey fish, alewife (Alosa pseudoharengus). We parameterized two Ecopath models to characterize food web changes occurring between two study periods of 1981-1985 and 1998-2002. We also built an Ecosim model and simulated food web time-dynamics under scenarios representing different levels of top-down control by Chinook salmon (Oncorhynchus tshawytscha) and of bottom-up control by quagga mussels (Dreissena rostriformis bugensis) and nutrients. Ecopath results showed an increase in the relative importance of bottom-up controls between the two periods, as production decreased across all trophic levels. The production of non-dreissenid benthos decreased most, which could cause decreases in production of pelagic prey fishes feeding on them. Ecosim simulation results indicated that the alewife collapse was caused by a combination of top-down and bottom-up controls. Results showed that while controls by Chinook salmon were relatively constant before alewife collapse, controls by quagga mussels and nutrients increased jointly to unsustainable levels. Under current conditions of low nutrients and high quagga mussel biomass, simulation results showed that recovery of alewives is unlikely regardless of Chinook salmon biomass in Lake Huron, which implies that the shrinking prey base cannot support the same level of salmonine predators as that prevailed during the 1980s.

Influence of invasive quagga mussels, phosphorus loads, and climate on spatial and temporal patterns of productivity in Lake Michigan: A biophysical modeling study

“…In Lake Huron, biomass of alewives, the preferred prey of stocked Pacific salmon, collapsed between 2002 and 2003, resulting in declining recreational harvests of salmon. Statistical analysis did not identify a clear cause of the crash (Bunnell et al ), while food web and fisheries models suggested a combination of top‐down and bottom‐up causes (He et al ; Kao et al ).…”

Food‐web structure and ecosystem function in the Laurentian Great Lakes—Toward a conceptual model

“…Drivers of offshore fish community production He et al (2015); Kao, Adlerstein, and Rutherford (2016); Riley et al (2008) Ecological models…”

“…Implications of density-dependent top-down effects of planktivore grazing and piscivore predation on ecosystem function and adaptive capacity Negus, Schreiner, and Halpern (2008); Kao et al (2016) Ecological models Drivers of changes in zooplankton community structure and impacts of these changes on food-web structure and adaptive capacity of the system Barbiero et al (2012); Barbiero, Lesht, and Warren (2014) (Casini et al, 2009;Daskalov, Grishin, Rodionov, & Mihneva, 2007);…”

Piscivore Diet Shifts and Trophic Level Change after Alewife Establishment in Lake Champlain

“…; Kao et al. ). In Lake Huron, the Alewife population collapse was likely due to predation by stocked Pacific salmon Oncorhynchus spp.…”

“…Understanding salmonid and Walleye Sander vitreus predation on forage fish has become an important research topic because of concern regarding declining forage fish populations in some lakes and because many salmonids are stocked and predator numbers can, to some extent, be manipulated to be in balance with the prey supply (Kitchell et al 1994;Riley et al 2008). Declining forage fish populations, and specifically Alewife Alosa pseudoharengus populations, have become a concern in the Laurentian Great Lakes over the past several decades, following the collapse of Alewife populations in Lake Huron in the early 2000s (Dettmers et al 2012;Kao et al 2016). In Lake Huron, the Alewife population collapse was likely due to predation by stocked Pacific salmon Oncorhynchus spp.…”