Estimation and comparison of connectivity measures for the dispersal of Lepeophtheirus salmonis sea lice among Atlantic salmon farms in new Brunswick, Canada

Atlantic salmon aquaculture sites in the Bay of Fundy, New Brunswick (NB), share a common coastal body of water, which potentiates the exchange of free-swimming stages of the parasite Lepeophtheirus salmonis among sites, where each site is an aggregation of salmon hosts for the attached and mobile stages of the parasite. The measure of seaway distances among sites is commonly used to capture some of the effects of connectivity and transmission patterns among sites. However, we propose novel measures to quantify connectivity, some with the use of bathymetry data to improve on seaway distances, but without extensive hydrodynamic modelling. We compared seaway distance at differing grid resolutions, topographical distance, percent surface area of water along seaway path, and volume of water along seaway path directly and indirectly. These connectivity measures were indirectly compared through the external infestation pressure (EIP) of the model for the abundance of adult female L. salmonis from empirical data stored in the Fish-iTrends database from 2009 to 2018. The percent surface area of water along seaway path improved the model fit as compared to the seaway distance with 100 m grid resolution. An estimate of dispersal distance of 7-10 km was produced through the comparison of optimal model fit with EIP using the Akaike information criterion (AIC), supporting the continued use of area-wide parasite management in the Bay of Fundy, NB.