Veliger monitoring
Veliger monitoring is a sampling program to verify the presence of zebra mussel larvae in Lake Massawippi. Sampling takes place between mid-May and early November at 3 separate sites, one to three times a month. Some sampling is duplicated in order to send samples for analysis to Fisheries and Oceans Canada (DFO).
The results obtained then enable us to compare veliger densities between different months, and thus gain a better understanding of veliger population dynamics. Comparisons between years also enable us to detect whether there is any demographic growth in populations.
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As planktonic organisms, veligers float in the water column. To collect them, water samples are collected using a plankton net and stored until laboratory analysis.
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Using a microscope, veliger beetles are identified and counted according to a protocol standardized by DFO.
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The analysis of samples collected in 2022 (left), 2023 (right), and 2024 (bottom) led to the development of the image below contrasting the three years. Between 2023 and 2024, veliger densities slightly increased, in contrast to the sharp decline observed between 2022 and 2023. The 2023 decline was partially attributed to the July floods of that year, which resulted in significant water inflow. At the time, it was challenging to assess the impact of control efforts compared to that of environmental factors. Thus, the absence of a drastic increase in 2024 may reflect the effectiveness of Blue Massawippi’s actions. The observed increase likely corresponds to the natural population growth of zebra mussels.
Figure 1. Veliger concentration in Lake Massawippi between the years 2022 and 2023. Veliger concentration is measured as the number of individuals per cubic metre at three sampling stations over the last two field seasons.