Preliminary Investigation Into the Appropriateness of Control Measures and Harvest Control Rules for a Data‐Limited, Sex‐Changing Fish Managed by Harvest Slot Limits

Fisheries assessments require valid life‐history information to evaluate species’ abundance and reproductive potential. Assessing sequential hermaphrodites requires additional information to account for these species’ complex maturation schedules. For data‐limited species, harvest control rules may be applied to inform management decisions on how much fishing should be permitted. Ballan wrasse ( Labrus bergylta ) are data‐limited sequential hermaphrodites used as cleaner fish throughout northern European salmonid aquaculture. In Scotland, harvest slot limits and a seasonal fishery closure were introduced to manage the fishery but the appropriateness of these measures has not been assessed. This fishery has never been formally assessed and management decisions are not currently informed by harvest control rules. This study analysed three years of fishery‐dependent length‐frequency data. Demographic data (sex, gonadosomatic indices , and age) were collected from 620 fish, and an age‐length key was constructed. Ages were assigned to length data, the total mortality rate () was estimated from a catch curve, and the ratio of fishing mortality () to natural mortality () was compared with proximate values for sustainable fishing practices. Landings data were obtained from the Scottish government and harvest control rules were applied. Around 4.4% of landings were outside of harvest slot limits. No males were identified. The maximum observed was 1.54%, suggesting the fishing season does not coincide with the spawning period. (0.58) accounted for 75% of (0.77). There were fundamental incompatibilities between the assumptions of the applied harvest control rules and the limitations of the data, and the use of harvest slot limits to manage this fishery. This research highlights the appropriateness of measures currently used to manage the live ballan wrasse fishery while demonstrating the need to develop a novel assessment framework for fisheries managed by maximum size limits for which only fishery‐dependent data are available.