Mackerel (belonging to family
Scombridae) are found off all British coasts. The family Scombridae
is a large family of marine fishes, containing fish such as
the Tuna. Members of this family are well streamlined for
efficient and fast movement through the water.
Mackerel are predetary fish, primarily feeding
on crustaceans, fish eggs, small fish and even other mackerel
fry.
There are a number of different types of Mackerel
found on either side of the Atlantic Ocean, but only those
found in and around the UK are described here.
Common Mackerel (Scomber
Scombrus)
An important commercial species fished by drift
nets as food fish or for industrial use, but popularly fished
from boats for sport. They grow on average to about 12"
long (30cm) and are coloured blue/green above the lateral
midline and silver below. The also have wavy black vertical
lines covering their backs. The common mackerel has two well
separated dorsal fins with 5 dorsal and anal finlets. Two
keel like fins are also present on the undeside of the fish.
Mackerel winter in deep water (approximately
300m) but return to the shallows around the coast in May-June
to spawn. The fish will then spawn, the resulting eggs released
into the sea in great numbers, up to 90,000 per spawning.
The eggs are between 1 and 1.4mm in size planktonic. They
consist of an unsegmented yolk surrounded by a greeny-black
pigmented oil globule. Hatching occurs after 2-6 days. The
juvenile fish stay offshore for about 2 years until they are
sexually mature. At this time they join the great shoals of
mackerel that form at spawning time.
The shoals of mackerel that form at this time
consist of hundreds of fish. Larger shoals have been estimated
in the thousands. The shoals are constantly on the move, as
the mackerel must keep moving. The common mackerel has no
swimbladder and uses a passive gill ventilation form of breathing.
The fish swim mouth open and the gill chambers expanded, thus
water flows through the gills. (Ramjet effect) This saves
engery which is used by other fish to pump water through the
gills when the mouth closes. Therefore it must move to live,
if the fish is not swimming it will drown. The fish also are
on the move after it's prey, they feed in the summer where
there will be currents, thus around headlands, breakwaters,
piers and beaches that experience a strong tidal flow.
If common mackerel are not caught then they
can live to about 20 years, when they can be 2kg or more in
weight.
Chub or Spanish Mackerel
(Scomber Japonicus)
This mackerel is similar to the common mackerel
but with two differences. The first is that addition of a
swimbladder which enables the fish to hold position off the
bottom of the sea with no mechanical energy. The second difference
is in the markings. The chub mackerel has dark lines or spots
below the laterel midline, with some having darker lines along
the lower flank.
The Chub or Spanish Mackerel are found around from the south
west/west of England and Ireland to the Mediteranean Sea and
the shores of North Africa. The Common Mackerel are also found
in these areas, but their range extends to the North Sea and
up to the northern shores of Norway. The common Mackerel is
also found in the Baltic Sea. |
