Growth and maturity of sprat (Sprattus sprattus) in the Kattegat and Skagerrak, eastern North Sea

Information on fish biology, as growth and reproduction, is an essential first step for a sound assessment and management of a fishery resource. Here we analyzed the annual cycle of body condition factor (K), gonadosomatic index (GSI) and maturity of sprat from the Skagerrak and Kattegat as well as from the Skagerrak inner fjords (Uddevalla fjords). The results show an inverse yearly pattern for K and GSI in both areas, K being the highest in autumn and lowest in spring, while the GSI index was highest in spring and lowest in autumn. The annual highest proportion of spawning fish was recorded from May to July, indicating the late spring and early summer as the main spawning period for sprat in these areas. Male sprat reached maturity at a higher size in the Uddevalla fjords compared to Skagerrak and Kattegat, while negligible differences were shown by females. The K, GSI and size-at-age were the lowest in the Uddevalla fjords, while K and GSI were the highest in the Skagerrak, potentially related to the different environmental conditions encountered in the different areas. All in all the present results furnish important information about the biology of the sprat in the area that is highly relevant in stock assessment and management. The potentiality for the sprat inhabiting the Uddevalla fjords to be a different sub-population should be addressed through further investigations.