Energy Content of Rainbow Smelt (Osmerus mordax) in Lake Huron, and a Comparison between Lake Huron and Erie

Abstract

Rainbow smelt (Osmerus mordax) is major planktivorous fish species in Lake Huron, providing important energy and nutrient pathways for piscivores. The main objective of this study was to identify current status of energy content of rainbow smelt under declining lake productivity in Lake Huron. Rainbow smelt were sampled by bottom and mid-water trawls on research vessels in Lake Huron and Lake Erie from April to September in 2017. A total of 1603 rainbow smelt were later processed and measured in the laboratory. Overall, before spawning in April, female rainbow smelt from Lake Huron had 9.2% higher energy density than males, and also had increasingly higher total energy content at larger TL. Energy density of rainbow smelt decreased 10% from April to June after spawning, then increased 3.6% from June to July and 9.9% from July to September. Energy density in September was 3.5% higher than that in April. Energy density of rainbow smelt from Lake Erie was up to 60.3% higher for small rainbow smelt (< 90 mm) and up to 36.5% higher for large fish ( 90) than that from Lake Huron. Within Lake Huron, energy density of rainbow smelt from North Channel was slightly higher than that from other regions. Rainbow smelt from Georgian Bay generally had the lowest energy density. Across 6 sites in both lakes, chlorophyll a concentration had a strong positive correlation with energy density for both small (r = 0.99) and large (r = 0.99) rainbow smelt. Rainbow smelt started to become mature at 80 mm in total length and all fish became mature when longer than 120 mm in total length. Results in this study showed that energy density of rainbow smelt in Lake Huron was 4-31% lower than historical data from studies before 2004.