All about the bass

Biology and ecology

The European sea bass (Dicentrarchus labrax) is an iconic and fascinating species, highly valued by commercial and recreational fisheries that contribute culturally, socially and economically to coastal communities. They also represent an important aquaculture species in mainland Europe, particularly in the Mediterranean Sea. Sea bass is a highly mobile species which is distributed widely across the northeast Atlantic and the Mediterranean.

They are relatively slow growing and late maturing fish that feature a complex life cycle that includes both inshore and offshore habitats (see image below). Adult bass can grow up to about 9kg – once mature, they can reproduce for 20 years, with the oldest bass ever recorded having reached 28 years old.

Migration and spawning

Adults migrate between feeding and spawning areas – migrating south during the late autumn and winter, down the west coast of the UK, and along the south coast of the UK, aggregating into large shoals as they prepare to make their overwintering/pre-spawning grounds at the western end of the English Channel.  The trigger for this migration seems to be falling water temperatures, since a temperature of more than 9˚C is needed for successful spawning. After spawning eggs and larvae drift in the currents before settling in estuaries and shallow embayments. Fish will remain in nursery areas for 4-6 years in the UK (typically 2-3 in Portugal) before reaching maturity and joining the adult population. They spend each summer and early autumn on the same inshore feeding grounds, exhibiting socalled ‘site fidelity’. 

Resilience and threats

Bass have been around for millions of years and have evolved various strategies to cope with changing environmental conditions. Year-to-year survival and growth are highly variable, affected by factors such as currents, temperature, storms, food supply, habitat availability, disease, pollution and predation. We are increasingly aware that most of these factors are also affected by human activities and human caused climate change. Sadly, much of the nearshore nursery habitats used by juvenile bass such as salt marsh and biogenic reefs have been lost over the last 150 years or suffer from poor water quality due to industry and urbanisation. Surveys of adult and juvenile sea bass in UK waters have shown rapid declines in abundance due to poor recruitment (low juvenile survival) and high fishing mortality.

UK bass management and policy

Bass support important commercial and recreational fisheries that contribute culturally, socially and economically to coastal communities. They also represent an important aquaculture species in mainland Europe, particularly in the Mediterranean Sea. However, a combination of overfishing and poor year class strength (the number of individuals born in any given year) saw a sharp decline in bass stock levels from 2010 to 2018. In response, in 2015 the UK and EU implemented a joint management approach, which has been amended annually. 

Current measures include:

• a minimum conservation reference size (currently 42cm)
• closed seasons (currently February and March for both commercial and recreational fishers)
• recreational bag limit of 2 fish per day
• a catch limit for hooks and lines, gill nets and other gears for commercial fishers

Since these measures were introduced, there has been an increase in spawning stock biomass (SSB) – although recruitment levels remain low.

For further information about the stock status, management measures read the UK Fisheries Management Plan.

Other useful resources

• Defra (2022) Fisheries management plan for sea bass in English and Welsh waters
• Kieran Hyder, Callum Scougal, Elena Couce, Lenka Fronkova, Adam Waugh, Mary Brown, Lucille Paltriguera, Lisa Readdy, Bryony Townhill, and Mike Armstrong (2018) Presence of European sea bass (Dicentrarchus labrax) and other species in proposed bass nursery areas (.PDF) 
• Britton J.R., Harrison A., Andreou D., Dominguez Almela V. and Pinder A.C. (2023) Review and synthesis of current evidence on the biology, ecology and fisheries for sea bass and assessment of evidence gaps. BU Global Environmental Solutions (BUG) report (BUG2931a) to Cefas. 95 pp (available in Proposed Fisheries Management Plan for Sea bass in English and Welsh Waters Annexes PDF)
• All About the Bass speaker biographies and talk abstracts
• All About the Bass talks on Youtube
• All About the Bass speaker slides