Indirect assessment of fisheries response to water-level management using network properties of macroinvertebrate food webs in Voyageurs National Park, MN

Water levels in reservoirs are often regulated to increase fisheries production, but assessing the impact of water-level management decisions directly on fisheries can be difficult. We used a network approach to investigate how responses of benthic invertebrate communities to a change in water-level management could be linked to potential impacts on fisheries. We analyzed 23 spatially distinct food webs within two reservoirs at Voyageurs National Park, both before and after a change affecting the magnitude of winter drawdown and the timing of spring refill in one of the reservoirs (the impact system), but not the other (the reference system). We found an increase in the complexity of food webs overall and longer food chains from basal resources to fish associated with the change in water-level management regimes. Our method has potential for assessing impacts in other cases where direct monitoring of fisheries and other vertebrates is difficult.