SAE staff contributed advanced statistical analyses for an Environment Canada study of seabird abundance and behaviour around commercial gillnet fishing vessels to evaluate net entanglement risk in coastal BC.
Our analyses focused on rhinoceros auklets (Cerorhinca monocerata), the most abundant seabird detected during at-sea transects. Auklets are epipelagic foragers, diving for long periods to retrieve fish, including juvenile salmon (Onchorhyncus spp.). This foraging behaviour puts them at risk of becoming entangled in salmon gillnets. As seabird by-catch is suspected to be under-reported in the study area, we used indirect measures to evaluate risk. Auklet counts and behaviours were recorded during at-sea transects in commercial fishing areas and point count surveys at active gillnet vessels.
Results of the study confirmed that patterns of relative auklet effort-adjusted density and behaviour change near gillnet fishing vessels, likely due to attraction. Advanced zero-inflated modeling techniques used to estimate probability that diving birds were present during surveys, but missed, revealed a higher probability of unrecorded diving birds closer to fishing vessels. Finally, site, time of day, tide height, and distance from shore were important environmental predictors of auklet densities, while net depth and mesh size were significant parameters that predicted auklet densities near gillnets.
Results have important implications for mitigating potential impacts of coastal gillnet fisheries on this species and other alcids with similar foraging traits.