Hypotheses
Interested in seeing current hypotheses from the literature? Below is some information that we have found in papers. If you are interested in only a brief overview, there are some visuals below.
Current Hypotheses in the Literature
Ice Cover Concentration/Duration
Ice reduces physical disturbances in nearshore egg incubation habitats (wave actions and wind impacts are reduced for eggs) so the more ice the better for larval coregonines. Ice cover can also impact light penetration which can affect egg incubation dynamics.
​
Ice cover may have impacts on spring water temperatures and hatch timing which can influence conditions for developing coregonines.
Spawning Stock Size
While the relationship between recruitment and spawning stock biomass is not necessarily strong, there does appear to be a minimum spawning stock biomass for Cisco and Lake Whitefish.
​
This loosely means that if there is low SSB, this could mean that there is some minimum threshold that may limit subsequent recruitment.
Piscivorous Predators
Lake trout in Lake Superior may be rehabilitated and near capacity. This may affect predation on Cisco. Ultimately leading to impacts on Spawning Stock Biomass.
​
Non-native fish such as Rainbow Smelt, Alewife, and other invasives like zebra mussels may be having an impact on the recovery of Cisco in Superior. With the decline of Smelt and Alewife in recent years, this may not be as prominent in our later time series data.
Water Temperatures
Water temperatures can affect time at hatch and may result in a zooplankton prey availability mismatch.
​
Cisco prefer to spawn in incredibly cold water in late November and early December. If water temperatures are not ideal moving forward, it may affect their hatching and spawning times.
Storms, strong wind events
Strong storms and the resultant water currents can disperse larvae into habitats that can be either beneficial or detrimental for hatchling Cisco. this movement could determine their growth and survival.
​
In terms of impacts on their egg stage specifically, a physical disturbance may be more impactful for Lake Whitefish that spawn in Lake Superior in shallower areas compared to Cisco. Cisco appear to be spawning in deeper reaches compared to LWF, but still a valuable piece of information to know.
Competition with Zooplanktivores
Localized depletion of zooplankton fields or shift in zooplankton prey community composition has been a result of the invasion of rainbow smelt. The quantity and quality of zooplankton, a food source of Cisco, has declined.
​
Spiny water flea in Lake Superior could be a large scale driver of availability of native zooplankton community through predation and results of their invasion may have impacts on larval and juvenile Cisco. This has been found to be more impactful to Cisco compared to LWF.
​