Do biomass indices from Icelandic groundfish surveys reflect changes in the population of female lumpfish (Cyclopterus lumpus)?

Abstract

The female portion of the population of lumpfish (Cyclopterus lumpus) in Iceland is currently monitored using a biomass index calculated using catch data from the Icelandic spring groundfish survey (referred to as the spring survey). This has been controversial among lumpfish fishers who insist that the behaviour and variations in the migration of lumpfish make the use of this survey inappropriate for assessment. To evaluate whether changes in the biomass index from the spring survey adequately reflect changes in the population, the spatial and depth distribution of catches of lumpfish from this survey are compared with the total coverage of the survey. The biomass index from the spring survey is also considered alongside data from two other surveys (gillnet survey and autumn groundfish survey) and catch per unit effort (CPUE) from the female lumpfish fishery. In the spring survey, female lumpfish were predominantly caught at depths shallower than 300mand within 100 km of shore, while the survey extends to a depth of 500m and 227 km from shore, indicating that survey coverage was fitting for this species. The changes in the biomass index from the spring survey were similar to that of the gillnet survey, and also to changes in CPUE of the fishery. A decrease in the biomass index of large lumpfish (???45 cm) caught during the survey was correlated with the decreasing use of large mesh sizes in the fishery indicating that changes in size distribution in the population could be detected using the spring survey. These results indicate that the use of the spring survey to monitor changes in lumpfish population in Iceland is justified. The use of data from bottom trawl surveys to track lumpfish populations in other regions is discussed.