Geographic distribution and biology
Northeast Atlantic mackerel spawns over a large area from outside Portugal to the North Sea. The stock has been considered to consist of three components (southern mackerel, western mackerel and North Sea mackerel), but recent analyses indicate that northeast Atlantic mackerel is one component with inter-annual variation in geographic distribution. Most of the individuals migrate after spawning northward to feed in the North Sea and the Norwegian Sea.
Mackerel spawn in the surface layer. The larvae are 3,5 mm long when hatching in the spring, but grow to be 20 cm long the following autumn. Mackerel do not have a swimbladder and needs to constantly swim to avoid sinking. It is a typical plankton feeder, swimming with the mouth open and filtrating zooplankton through the gill rakers. It also uses particulate feeding on fish larvae and small fish. Mackerel prefers waters warmer than 6 °C. It is spawning for the first time when it is around 30 cm long.
Mackerel migrate into the North Sea and the Norwegian Sea after spawning to feed. There has been an historical expansion of mackerel the last years, and mackerel is found west to Greenland, north to the Barents Sea and up to Svalbard, and east into Skagerrak in the summer. Mackerel stay in these areas throughout the autumn before migrating towards the spawning areas early in the winter.
Mackerel is a pelagic and fast-swimming schooling fish that is easily recognized due to its round, torpedo-shaped body. The back (dorsal side) is covered with green, black and blue stripes. The body is soft to touch, but covered with small scales. Mackerel can reach the age of 25 years and a size of 70 cm and 3.5 kg, but are seldom larger than 50 cm and 1 kg. It is a typical plankton feeder.
There are three time-series used in the stock assessment for mackerel; a triennial spawning egg survey, an annual pelagic trawl survey and an annual bottom-trawl survey. The spawning survey measure egg production and is a collaboration between several EU-countries, Iceland and the Faroese Isles. The pelagic trawl survey is a collaboration between Norway, Iceland, the Faroese Isles and Greenland. This survey covers the Nordic seas in July-August. The bottom-trawl survey covers the waters around the northern British Iles. This is used as an indicator on recruitment (year class strength). These three surveys are together with data from the commercial fishery used to calculate the size of the mackerel stock.
Total landings of mackerel have been higher than recommended by ICES the last years. The main reason is substantial disagreement between the countries participating in the fishery on how to share the quotas. In 2015 there was a management agreement between EU, Norway and the Faroese Isles. Iceland did not agree with the other countries, and together with Russia and Greenland all these three countries have set their own unilateral mackerel quota the last few years outside the management arrangement.