Biology and fishing of the mackerel

Biology and reproduction:

• The mackerel is a species with external fertilization, and its reproduction takes place from spring to early summer.

• Sexual maturity generally occurs at the end of the third year in the Celtic Sea, and between 3 and 4 years of age in the North Sea.

• Growth is very rapid during the first year, remains significant up to 3 years, and then slows down considerably.

Feeding and migrations:

• The diet is essentially planktonic (copepods in the spring) and diversifies in the summer/autumn with small fish (clupeids, gadoids).

• The migratory cycle includes a demersal winter phase (fasting in deep water) and a pelagic phase (spring/summer) linked to nutrition and reproduction.

Stocks and populations:

• The study distinguishes several populations (Celtic Sea, Northern North Sea/Utsira, and Dogger Bank) that exhibit different physiological characteristics and spawning grounds.

• The Celtic Sea population appears to be clearly separated from that of the North Sea.

Environmental conditions:

• Salinity mainly influences spawning grounds, while temperature conditions overwintering and summer dispersal in coastal waters.

• The location of trophic concentrations (feeding areas) is strongly correlated with the abundance of animal plankton.

Fishing:

• Trawling is the primary fishing method for fishermen from Boulogne, using gear similar to that used for herring.

• There is a distinction between the areas exploited by trawlers (feeding concentrations) and those exploited by drift nets (linked to sexual maturity).