Example
From GeoClasses
Contents |
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Presence or absence of fish species in New Zealand lakes
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Research Hypothesis
- background: land-locked species of fish are those that can establish freshwater populations even though normally they would migrate between the sea and rivers (to spawn) during their lifetime
- there must be a lake downstream suitable for raising young fish, similar to the conditions of the sea
- Question: many rivers in New Zealand are being dammed for human consumption of water - how is this affecting the fish?
- Question:if residence time is low, does the fast flow cause larvae to wash out or lose its food source?
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What does a graph of lake volume versus residence time tell us?
- bottom left corner = small lake, low residence time = fast water flow
- lower middle of graph = small to medium size lake with medium residence time = moderate water flow
- upper middle of graph = medium to large size lake with medium residence time = sluggish water flow
- upper right corner = large lake with high residence time = water flow very very slow
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What do we know from the fish?
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koaro
- require well shaded tributaries for spawning
- larvae are good swimmers and are found throughout the water column in lakes
- where would you expect to see them?
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common bully
- must compete for nutrients against the koaro and sometimes are predated by koaro
- larvae are restricted to the top 5-20 meters of lake
- where would you expect to see them?
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common smelt
- have not been artificially stocked in large lakes (usually done to provide a food source for trout)
- larvae are good swimmers and are found throughout the water column in lakes
- where would you expect to see them?
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What do the lakes tell us?
- small lakes are primarily water storage reservoirs with shaded tributaries in the catchment
- if residence time is low in a small lake, then water must be moving very fast through these lakes = strong currents
