Partial diel vertical migrations in pelagic fish.

Area of Science:

• Ecology
• Animal Behavior
• Aquatic Ecology

Background:

• Diel vertical migration (DVM) in aquatic ecosystems typically involves uniform, population-wide movements.
• This contrasts with partial seasonal migrations where individuals adopt resident or migrant strategies based on environmental factors.

Purpose of the Study:

• To investigate if diel vertical migration (DVM) in freshwater zooplanktivorous fish (Coregonus spp.) aligns with partial migration patterns.
• To identify factors influencing the proportion of resident versus migrant fish within the population.

Main Methods:

• Conducted 28 hydroacoustic surveys in Lake Stechlin, Germany, from 2000-2010.
• Collected zooplankton samples from epilimnetic and hypolimnetic layers.
• Analyzed fish from depth-stratified midwater trawl samples to differentiate resident and migrant strategies.

Main Results:

• Demonstrated that freshwater fish DVM resembles partial migration patterns, with 7-33% of fish exhibiting resident behavior.
• The proportion of residents increased with lower zooplankton availability and reduced temperature differences between habitats.
• Observed potential individual differences (size, caloric density) in one species, though further data is needed.

Conclusions:

• The balance between resident and migrant fish in DVM is likely driven by trade-offs between feeding opportunities and migration costs (metabolic, predation).
• Individual traits may play a significant role in the 'decision' to migrate, as fitness consequences for each strategy may differ.