Visual sensitivity of deepwater fishes in Lake Superior

Abstract

The predator-prey interactions in the offshore food web of Lake Superior have been well documented, but the sensory systems mediating these interactions remain unknown. The deepwater sculpin, (Myoxocephalus thompsoni), siscowet (Salvelinus namaycush siscowet), and kiyi (Coregonus kiyi) inhabit low light level environments. To investigate the potential role of vision in predator-prey interactions, electroretinography was used to determine visual sensitivity for each species. Spectral sensitivity curves revealed peak sensitivity at 525 nm for each species which closely corresponds to the prevalent downwelling light spectrum at depth. To determine if sufficient light was available to mediate predator-prey interactions, visual sensitivity was correlated with the intensity of downwelling light in Lake Superior to construct visual depth profiles for each species. Sufficient daytime irradiance exists for visual interactions to approximately 325 m for siscowet and kiyi and 355 m for the deepwater sculpin during summer months. Under full moon conditions, sufficient irradiance exists to elicit ERG response to light available at approximately 30 m for the siscowet and kiyi and 45 m for the deepwater sculpin. Visual interactions are therefore possible at the depths and times when these organisms overlap in the water column indicating that vision may play a far greater role at depth in deep freshwater lakes than had been previously documented.

Figure 1. The main food web of the offshore waters of Lake Superior.

The relative depth is plotted on the y axis with fish distribution shown both day (left) and night (right). Arrows indicate predation on particular species.

Figure 2. An electroretinogram with amplitude of the b-wave (mV) plotted vs time.

The ERG was recorded from kiyi in response to 550 nm light. The open rectangle indicates the onset and offset of the 200 ms flash.

Figure 3. The average irradiance (1/photons cm⁻²s⁻¹) needed to invoke the criterion response is plotted versus wavelength (nm) for kiyi (black circles), siscowet (open circles), and deepwater sculpin (triangles).

Lines connecting the symbols are for illustrative purposes only. Error bars = 1 SE.

Figure 4. The depth at which 1% of surface irradiance occurs under spring summer (k_PAR = 0.1) conditions (solid line) and fall (k_PAR = 0.3) conditions in Lake Superior.

Figure 5. The maximal depth at which sufficient downwelling irradiance is available to elicit an ERG under full sun conditions is plotted versus depth (m) for kiyi (black circles), siscowet (white circles), and deepwater sculpin (black triangles) for (A) spring/summer (k_PAR = 0.1) and (B) fall (k_PAR = 0.3) conditions in Lake Superior.

Figure 6. The maximum depth at which sufficient downwelling irradiance is available to elicit an ERG under full moon conditions is plotted versus depth (m) for kiyi (black circles), siscowet (white circles), and deepwater sculpin (black triangles) for (A) spring/summer (k_PAR = 0.1) and (B) fall (k_PAR = 0.3) conditions in Lake Superior.