Temperature effects on fish production across a natural thermal gradient

Area of Science:

• Ecology
• Climate Change Biology
• Aquatic Ecology

Background:

• Global warming is predicted to negatively impact top predator biomass and survival.
• Understanding exceptions to this trend is crucial for predicting future ecological changes.
• Brown trout (Salmo trutta) in Iceland represent a top predator at the edge of its thermal tolerance range.

Purpose of the Study:

• To investigate the impact of stream temperature on brown trout as top predators.
• To identify the mechanisms driving brown trout success across a temperature gradient.
• To assess the role of diet, trophic position, and resource availability in warmer conditions.

Main Methods:

• A natural warming experiment in Icelandic streams across a temperature gradient (4-25°C).
• A five-month mark-recapture study to assess trout population dynamics.
• Analysis of trout diet, trophic position, and food web efficiency in relation to temperature.

Main Results:

• Brown trout population abundance, biomass, growth rate, and production significantly increased with stream temperature.
• Trout exhibited increased diet selectivity and higher trophic positions in warmer streams.
• Trophic transfer efficiency within the food web improved with increasing stream temperature.

Conclusions:

• Top predators like brown trout can thrive in warmer environments under specific conditions.
• Warming can enhance food web functioning and resource availability for predators.
• These findings offer insights into the complex impacts of climate warming on aquatic ecosystems.