Finding the Unreported Recreational Catch in the Norwegian Lobster (Homarus gammarus) Fishery

Recreational fishing for coastal marine species can be significant, but is often challenging to estimate. Here we present a case study where a probability-based strip transect survey is used to estimate effort in the Norwegian fishery for European lobster (Homarus gammarus). This fishery is conducted by both recreational and commercial fishers, but reliable information on total fishing effort and total catch is lacking. In 2008, we conducted a strip transect sampling survey throughout the lobster fishing season (October-November) along the Agder counties in southern Norway to estimate the number of deployed lobster traps over time. The survey covered a surface area of 471 km² of the coast with depths ≤ 40 meters. Surface buoys marking lobster traps were counted along strip transects placed representatively in the survey area in 5 different weeks from start to end of the lobstering season. Calibration studies were conducted to standardise transect width and to estimate and adjust for detection rates of buoys along transect strips. Mean number of lobster traps per km² and associated variance was estimated by a ratio-estimator using bootstrapping, with transects as primary sampling units. Post-stratification of the counts by depth (by 10 meter depths interval) combined with GIS mapping improved the precision of the estimated density of lobster traps and increased the effective sample size of transects by 22-44 % per week. Catch Per Unit Effort (CPUE) data was obtained independently from volunteer catch diaries, phone interviews and questionnaires. We estimated that recreational catch account for 65 % of the total catch in the study area. Moreover, our study show that only a small proportion (23 %) of the commercial lobster landings are sold through the legal market and documented. In total, the estimated catch of lobster is found to be nearly 14 times higher than the officially reported landings. Our study highlights the need for appropriate data collection of catch in coastal areas and is a warning sign to management authorities of the consequences of ignoring the potential impact of recreational fisheries.