Echosounder derived metrics from small-scale coastal surveys

Echosounder surveys are appealing for monitoring benthic rocky reef fishes
like rockfish (Sebastes spp.) as they cover large areas quickly and are
non-destructive, but they are rarely used due to difficulties ensonifying
benthic fish in rocky habitats.  We conducted echosounder and
remote operated vehicle (ROV) surveys at 39 sites in Mowachaht/Muchalaht
territory (Nootka Sound, BC, Canada) in August 2023.  We examined
correlations between an echosounder biomass proxy (nautical area
scattering coefficient (NASC)) and ROV benthic fish density using
generalized linear models. Increases in the fish biomass proxy (NASC)
within 10m of the bottom was correlated with increasing benthic fish
density (deviance explained 52%), suggesting NASC helps predict benthic
fish hotspot locations.  We compared echosounder and ROV habitat
metrics using Spearman’s rank correlation tests and found rugosity and
slope were comparable across methods with reduced analyst variability in
echosounder metrics. This study provides a new and efficient method for
identifying rocky reef fish hotspots in near-shore areas that can help
fishers avoid non-target species and act as a guide for marine protected
area (MPA) site selection.