Other things related to echosounder data: [[,echosounder-method,
  [[<-,echosounder-method,
  as.echosounder,
  echosounder-class,
  echosounder, findBottom,
  plot,echosounder-method,
  read.echosounder,
  summary,echosounder-method
Other functions that subset oce objects: subset,adp-method,
  subset,adv-method,
  subset,amsr-method,
  subset,argo-method,
  subset,cm-method,
  subset,coastline-method,
  subset,ctd-method,
  subset,lobo-method,
  subset,met-method,
  subset,oce-method,
  subset,odf-method,
  subset,rsk-method,
  subset,sealevel-method,
  subset,section-method,
  subset,topo-method