The Ecology and Distribution of European Bass (Dicentrarchus labrax) in inshore and coastal waters of the U.K.

Abstract

European bass (Dicentrarchus labrax) is a commercially and recreationally important finfish native to the Northeast Atlantic and Mediterranean Sea. The species is targeted throughout its range and represents a significant commercial and recreational fishery, which in the UK are estimated to have a value of £5-6million at first sale, and £100-200 million per year respectively. In 2010, the International Council for Exploration of the Seas (ICES) reported a dramatic decline in the Northeast Atlantic stock (ICES divisions 4.b–c, 7.a, and 7.d–h), which in 2016 declined below “safe biological limits”. In 2019 ICES reported that the Northeast Atlantic stock increased above Blim, however relative to historic levels the population remains in a highly impoverished state and is still below maximum sustainable yield thresholds.

Due to the local economic and social significance of European bass fisheries, the Devon and Severn Inshore Fisheries and Conservation Authority (D&S IFCA) co-funded and co-supervised the current PhD with the University of Plymouth to investigate; the feasibility of localised management/conservation policies to improve local European bass populations. Due to the localized/restricted movement characteristics and estuarine dependence of this species, the PhD project was focussed on identifying; movement, feeding and growth within estuarine habitats, with a particular emphasis on measuring the effectiveness of designated Bass Nursery Areas within the D&S IFCA’s district.

The results from this thesis demonstrate that estuaries and coastal embayments have been subjected to substantial alteration as a result of human activities. This has resulted in an estimated net loss of 2, 482.9km2 of intertidal habitat historically, with this loss estimated to continue at a rate of 0.2% per year. European bass specifically are thought to utilize intertidal habitats e.g. saltmarsh, as a primary feeding habitat within the first year. Analysis of growth variability from three coastal nursery sites, indicated that factors influencing growth within the first year may have important implications for latter growth and corresponding recruitment. It was therefore recommended that the habitat requirements of European bass should be integrated within management policies.

Using acoustic telemetry, European bass were also recorded displaying spatially restricted movement characteristics, and were estimated to occupy an area of <4.7km2 for 42.9-75.5% of the year (depending on tagging location). These results, combined with the wider literature, suggest that a regionalized fisheries management approach may be appropriate for this species.

Presence/absence of European bass within coastal sites in response to environmental variables also demonstrated that site characteristics can fundamentally influence local fish residency characteristics. Notably, within sites with limited freshwater input e.g. coastal rias and/or natural harbours, European bass may maintain residency throughout winter. Therefore seasonal protection/management within designated nursery sites may not be relevant to the behaviour of local European bass populations.