Hatching phenology of the brown shrimp Crangon crangon in the southern North Sea: inter-annual temperature variations and climate change effects

Abstract Crangon crangon is a key species in the southern North Sea and the most valuable target of coastal fisheries. Recruitment and stock development are highly variable. As recruitment is based on larval production, we determined the timing of larval release in relation to the annual temperature course and the winter water temperature. The annual temperature courses over 50 years (1961–2010) showed a strong inter-annual variation but also a continuous increase in winter water temperatures. The share of ovigerous C. crangon females starts to increase in October/November, reaches a maximum in May, and decreases continuously towards September/October. During cold winters (0°C), egg development is strongly retarded and hatching of larvae culminates in a sharp peak in early June. Warm winters (6°C) facilitate embryogenesis and the earliest larvae hatch in January and February. The temperature sums from November to April correlated significantly with the lowest winter water temperatures. Consequently, the lowest winter water temperatures provide a good indication for the appearance of C. crangon larvae and an estimate for the match or mismatch with the spring bloom and the production of microzooplankton, the preferred food of C. crangon larvae.