Ship Wake Influence on Fish Communities in the Upper St. Lawrence River

Abstract

The St. Lawrence River is home to large vessels that travel between the Atlantic Ocean and the Great Lakes. Ships that travel throughout the waterway generate both primary and secondary waves that travel towards the nearshore ecosystem, disrupting the fish communities. With the increase in novelty of ship hydrodynamics and ecology, this is the first study that incorporates both disciplines into one. The Upper St. Lawrence River is an ideal river for surveying as it spans over 240 kilometres long and up to 7 kilometres wide. The Fish Identification Nearshore (FINS) research team at the St. Lawrence River Institute surveyed over 230 sample locations to perform more than 600 fish surveys. In their database, they contain data for fish surveying through abundance (the total fish count) and richness (total fish species) at each site location, environmental DNA (eDNA) sampling, water quality measurements, habitat and vegetation sampling, and drone imaging. This research uses the FINS database to find correlations between the ships that travel throughout the Upper St. Lawrence River and the data within the database. The primary analysis of this research is to find correlations based on direct exposure to the shipping lane and the distance to the shipping lane from the designated site locations. Secondary analyses consist of exposed site locations within 1 kilometre of the shipping lane for: (1) the coastline geometry classified as straight shoreline or embayment shoreline, and (2) the dominant substrate, and (3) the habitat type classified as wetland or non-wetlands. Four different statistical analyses were used depending on the distribution of fish abundance and fish richness: (1) regression slope analysis for R^2 correlations, (2) analysis of variance (ANOVA) for normal distributions, and nonparametric methods for skewed distributions of (3) Mann-Whitney U testing for categories with two independent groups, and (4) Kruskal-Wallis H testing for categories with more than two independent groups. Probability values where the value was less than 0.05 demonstrated statistically significant results. Effect sizes accompanied the probability values. Results demonstrated the following outcomes: (1) a negative correlation between fish richness and proximity of ships towards the shoreline, (2) higher fish richness at exposed embayment site locations compared to straight shorelines, (3) higher fish richness with site locations primarily consisting of finer grain sizes (sand and clay) and lower fish richness with site locations with site locations consisting of coarser grain sizes (cobble and gravel), and (4) habitat type did not deliver statistically significant results. In summary, sites close to the shipping lane with rocky straight shorelines were found to have reduced fish community abundance and diversity, presumably due to the influence of nearshore wave action.