The wash zone and habitat use among three benthic fish species in stratified lakes

Mixing processes in lakes are important in determining sedimentation zones
and in setting the so-called “wash zone”, the area of lake bottom in
contact with an oscillating thermocline during wind driven internal seiche
events. The wash zone also aligns with a sharp change in sediment
roughness and hardness. Taken together these rapid changes in temperature
and sediment indicate that the wash zone is a distinctive ecotone in
stratified lakes.  Depth stratified randomized netting was used
to develop count-based habitat use models for three common benthic fish
species as a function of depth or temperature covariates.  Using
data from two lakes with quite different wash zone depths, we show the
wash zone to describe fish habitat for two of three benthic fish species
by utilizing the top 50% of estimated fish abundance as an indicator of
habitat use. White sucker (Catostomus commersoni) habitat use was fully
within the boundaries of the wash zone. Lake whitefish (Coregonus
clupeaformis) habitat was adjacent and within the wash zone. Longnose
sucker (C. catostomus) habitat use was in the deep areas of lakes
dominated by sediment focusing and did not overlap white sucker. Lake
whitefish habitat use overlapped both catostomids, but peak abundance of
both lake whitefish and white sucker overlapped pointing to potential
interactions between these species. Smaller lakes have less vigorous
mixing processes and a narrower wash zone, so with a decline in lake size
the likely area of the wash zone as habitat for benthic feeding fish would
become smaller.