This research aims to make a contribution to management of the ling bottom long-line (BLL) fishery by: - providing improved understanding of fish bycatch in this fishery by drawing together disparate information on the fishery, incorporating biological, environmental, fishing method and other factors; - examining whether an observer presence affects commercial fishers' behaviour in reporting fish bycatch; - developing a model reporting bycatch quantities using linear regression and extending the model to accommodate observer presence. This will allow the model to be used to identify the significance of the presence of observers and how this affects reported fish bycatch.