The blue mackerel, Japanese mackerel, Pacific mackerel, slimy mackerel, or spotted chub mackerel (Scomber australasicus) is a fish of the family Scombridae, found in tropical and subtropical waters of the Pacific Ocean from Japan south to Australia and New Zealand, in the eastern Pacific (Hawaii and Socorro Island, Mexico), and the Indo-West Pacific: the Red Sea, the Persian Gulf, the Gulf of Oman and the Gulf of Aden, in surface waters down to 200 m (660 ft). In Japanese, it is known as goma saba (胡麻鯖 sesame mackerel). Its length is between 30 and 65 cm (12 and 25.5 in), and weighs a little over 1 kilogram (2.2 lb).
Blue mackerel are often mistaken for chub mackerel. In fact, blue mackerel were believed to be a subspecies of chub mackerel until the late 1980s. Though they are both in the same genus (Scomber), blue mackerel set themselves apart by differing structural genes than those of the chub mackerel. Other, more obvious, characteristics set these two apart, like the longer anal spine of the blue mackerel, and the amount of the first dorsal spines. Mackerels have a round body that narrows into the tail after the second dorsal fin, similar to a tuna fish. The blue mackerel is known as a voracious and indiscriminate feeder, and they devour microscopic plankton and krill, live anchovy, engulf dead cut bait, and strike readily on lures and other flies. When in a school and in a feeding frenzy, they will strike at nonfood items such as cigarette butts and even bare hooks. While relatively small in size, pound for pound, mackerel score high for their fighting ability. Blue mackerel are carnivores, eating smaller fish in their same region of the upper layer of the ocean, the pelagic zone. Due to their eating habits and their diurnal lifestyles, blue mackerel have adapted a higher sensitivity in their retinas, allowing better eyesight even during the night to catch their prey. Another adaptation of blue mackerels is their eye size. They typically have larger eyes than herbivores in their same region.
Throughout the lives of these mackerel, they tend to stay in areas within a few degrees of 10 °C in tropical to subtropical waters. Off the east coast of North America, populations of mackerel have grown to over two million after being depleted in 1982. Blue mackerels can be found from the coast of North America, and as far as Australia and Japan.
Incubation periods range from three to eight days. Periods are shorter when the temperature is higher, and longer when the temperature is lower. In the East China Sea, blue mackerel spawn between February and May, when the water temperatures are ideal. In New South Wales, most spawning occurs 10 km off of the northern shore, in waters that are 100 to 125 m deep. The Eastern Australian Current can carry eggs and larvae away from the original spawning grounds, broadening the area in which blue mackerel are located. However, egg and larvae probability of surviving decreases the further they are carried by the current. A mature blue mackerel is considered to be over 310 mm long. Mackerel can live up to seven years and grow up to 50 cm long, but are most commonly found to be between one and three years of age. Counting the marks on otoliths determines the age of blue mackerel.
The blue mackerel can be flighty and difficult to catch, especially in estuaries and harbors. From 300 to 500 million tons of blue mackerel have been caught annually since the mid 1980s, without many fluctuations from month-to-month catches. Blue mackerel are caught for both commercial and private use, for food as well as bait for tuna and other fish.
While mackerel are often used as cat food, they have a strong-tasting meat which is best for consumption if smoked, grilled, or broiled. The Pacific blue mackerel, while easy to fillet and skin, can be difficult to debone and care must be taken not to damage the soft flesh. Blue mackerel are used as meat binders and as main meat entrees. After being freeze-dried, the protein is extractable and put into other meat products to keep the meat and seasonings tightly together. By using mackerel to bind the meat, cheaper and more appealing products are available to consumers. Not only are products cheaper, but they are also better in flavor, texture, and create larger portions.
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