Tuesday, July 31, 2007

Dolphin food fact sheet

Dolphin food: Sardines and Mackerel 


Sardines and mackerel, are a small schooling fish that make up part of the diet of the dolphins in the Azores, such as common dolphins and Atlantic spotted dolphins. Both sardines and mackerel are pelagic and always form large schools. Both are fished off the Portuguese coast and in the Azores they are caught by commercial fishing boats across networks (seine with heaving line, balcony of Art) and through lines and hooks (hand line). They are often also used as bait to catch larger fish such as tuna.

Sardines belongs to the Clupeidae family. They are usually small, reaching a length of 10 to 15 cm (maximum 25 cm) and a weight of 1.5 kg. They have only a dorsal fin without spines, a forked tail and their mouth is toothless. They feed on small things such as plankton and can live to 7 years old.

Mackerel belong to the Carangidae family. The species that dolphins in the Azores (mainly common dolphins and Atlantic spotted dolphins) primary feed on are bluejack mackerel (Trachurus picturatus), Atlantic horse mackerel (Trachurus trachurus) and Atlantic chub mackerel (Scomber colias).

  • The blue jack mackerel (Trachurus picturatus) is a small fish with an elongated fusiform body. They are generally small, reaching 20 to 25 cmin length (maximum 60 cm, breeding size about 25 cm) and can weigh 2.9 kg. Mackerel feed on small planktonic crustaceans (noteably copepods) and small fish. They can live to be 10 years old and are found in open ocean, coastal areas and around oceanic seamounts. The adults can be found in depths of up to 370 m, while juveniles live in shallower waters. Blue jack mackerel are often found in large shoals or schools, especially in the Azores where it is one of the most abundant species. It is estimated that the minimum time for the population to double in size is fewer then 4.4 years.
  • The Atlantic horse mackerel (Trachurus trachurus) is also known as saurel or scad. They are pelagic fish, forming big schools in coastal areas, and feed on smaller fish, crustaceans and cephalopods. They can lay as many as 140 000 eggs which hatch into 5 mm larvae. Adults can reach a length of 21to 30 cm, with a maximum length of 70 cm, and can weigh up to 2 kg.
  • The Atlantic chub mackerel (Scomber colias) has an elongated fusiform body that is covered in many small scales. The colour of ventral surface is silver and the dorsal ranges from tones of brilliant blue to blueish green. They can reach a length of 64 cm and weigh 2.9 kg. They can live to be 8 to 10 years old (breeding age 2 to 3 years). They feed on small fish, cephalopods, crustaceans and other zooplankton. Their range extends from temperate to subtropical waters and they can be found from surface waters down to depths of 300 m. Atlantic chub mackerel form large schools which are commonly encountered in the Atlantic Ocean, the Black Sea and also in the Mediterranean Sea.
  • Garfish or sea needle (Belone belone) is a long and slender fish reaching a length 50 to 75 cm and they have a blueish-green dorsal and silverish ventral colour . The jaws are elongated and full of sharp teeth. They are pelagic fish that live close to the surface water. Garfish feed on smaller fish and free swimming crustaceans. They are oviparous and the eggs are often found attached to objects. 

School of horse mackerel



Feeding time! 
Swimming with dolphins - watching the dolphins surrounding a concentrated ball of horse mackerel




A school of mackrel seen underwater during a swimming with dolphins tour



Common dolphin with a mackerel in its mouth

Juvenile gull trying to steal a fish (horse mackerel) off a Cory's shearwater








Lunch anyone?
Some of us, both crew and clients, ate this type of fish for lunch later.
This individual fish went back into the ocean and swam away

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