Biophysical models reveal the role of tides, wind, and larval behaviour in early transport and retention of Atlantic herring (Clupea harengus) in the Celtic Sea

Fish are adapted to spawn where their larvae will be retained in, or transported to, suitable juvenile habitat. Variability in circulation and behaviour produces variation in larval transport with consequences for recruitment. A biophysical model was used to simulate early larval dispersal of Celtic Sea herring (Clupea harengus) during wintertime in 6 years (2002, 2003, 2004, 2005, 2008, 2010). After 30 days, particles occurred in three areas: inshore Celtic Sea, offshore Celtic Sea, and southern Irish Sea, with the majority (70%–78% on average) of particles retained in the Celtic Sea. Inclusion of tidal forcing increased transport to the Irish Sea and decreased transport offshore, as did release during a spring tide. Retention in the Celtic Sea was increased by diel vertical migration and decreased by horizontal diffusion. Strong and frequent west to southwest winds increased transport offshore, while strong and frequent east to south-southeast winds increased inshore retention in the Celtic Sea and transport into the Irish Sea. The study shows how tides, winds, and behaviour influence larval transport and retention and highlights potential impacts of climate change on population persistence.