A long-term study of whiting, Merlangius merlangus (L) recruitment and population regulation in the Severn Estuary, UK.

Abstract

Data collected by power station impingement sampling, plus plankton and trawl netting over the last 50 years is used to analyse the dynamics of the whiting, Merlangius merlangus (L.) subpopulation within the Bristol Channel, UK, ecosystem. In Northern Europe, whiting is a dominant member of the inshore community and is commercially exploited. Contemporaneous long-term data for fish and crustacean species gives an exceptional opportunity to explore regulatory interactions for a gadoid fish with high between-year recruitment variability. There is considerable between year variation in whiting recruitment and growth which relates to both biotic and physical variables. However, analysis of a 40-year annual abundance time series detected density-dependent regulation with no long-term trend. Over an extended spawning season, a series of recruitment cohorts travel up estuary to their nursery grounds. The average size at the end of their first year relates to the timing of the dominant cohort within the extended spawning season. Whiting are locked into a web of predator-prey, host-parasite and commensal relationships which act to damp deviations from carrying capacity caused by habitat variability. River flow and seawater temperature change whiting distribution and abundance both directly and via their effects upon prey and predator species. The abundance of two prey, the shrimp, Crangon crangon, and sprat, Sprattus sprattus, positively influence growth and local abundance, conversely, Conger eel, Conger conger, the top predator, has a negative relationship with whiting abundance. During autumn and winter O-group whiting are particularly dependent on C. crangon for food. Whiting appears an ideal candidate for an ecosystem-based fisheries management approach. They are generalist predators eating locally abundant animals smaller than themselves. Carrying capacity likely reflects the total resource base of crustaceans and small fish available.