Boom in boarfish abundance: insight from otolith analysis

The boarfish Capros aper is a pelagic shoaling species widely distributed along the Northeast Atlantic continental shelf. In recent years, this species has experienced a dramatic boom in abundance in the Bay of Biscay and Celtic Sea. This study aims at resolving the mechanisms responsible for this increase in stock size.

Based on annual otolith growth increments, we developed a growth chronology as a proxy for stock fecundity. Growth patterns were similar between geographically separate areas west and south of Ireland, with distinct years of good and bad growth. Good growth was observed in 2004 and 2008, while 2005 was exceptionally bad.

In the northernmost areas, growth was significantly influenced by autumn temperatures and food availability, while growth south of Ireland was only influenced by summer temperatures. These months are the primary growing season of the boarfish. Year‐class strength was not correlated with growth in the same year.

However, year‐class strength was significantly correlated with adult growth the previous year, together with temperature during the months following spawning. The age structure shows that this species is very long lived (>30 years), but that a considerable proportion of fish are only aged 4–6 years.

These age classes correspond to the year with exceptionally high recruitment. This study has demonstrated that both adult growth as a proxy for reproductive potential and environmental conditions favouring early life stage survival may be the cause for the boom in boarfish abundance