Hammerhead shark

by S.Y.

Introduction

image00A common Hammerhead shark is living the coast of the warm seas of the world. And they are living the sea of Kochi. I touched Hammerhead shark with a neighboring fishmonger for the first time in the days of a high school. I was fascinated what attractive. Hammerhead shark is called “Shumokuzame” from the form of the head such as wooden bell hammer ringing Japanese musical instruments in Japan, and in English, the form of the head is likened with a hammer and it is called “Hammerhead shark”.

Description & Taxonomy

Hammerhead shark is a generic name of a shark belonging to order Carcharhiniformes family Sphyrnidae. Nine kinds are known all over the world. Full length is 5 meters, and the big thing becomes 6 meters. Since the head spread horizontally like a hammer and it is sticking out, Hammerhead shark can be recognized immediately. The body back is gray and brown, yellowish-brown, and the ventral is white, there are not the fleck outstanding in particular.

Range & Ecology

Hammerhead shark lives the sea to 100 meters of depth of the water and sometimes sink to 300 meters of depth of the water. They live the offing mainly, but live the coast, a reef, and the estuary. They chase food and may come near a shore. Since eyes stick the both ends of the head, they have a view larger than other sharks, and food can be looked for easily. Hammerhead shark is a strong predator, and they feed not only fish and a cuttlefish and an octopus and Crustacea but also other sharks and prey on one another. Their favorite food is Dasyatis akajei, and they eat to the sting of a caudal fin. They move to high latitude sea area in summer, and come back to the tropical zone when it is winter. Although the life is unknown, probably about 30 years are presumed. Hammerhead shark forms a group uniquely as a shark, and acts. Occasionally the number may amount to hundreds of them.

Use & Conservation

Hammerhead shark is processed into the dried fish called “Maira” and “Tetsuboshi” in Kochi. It matches rice well. The things which is the most terrible for Hammerhead shark is fishery and indiscriminate hunting. It is said that the shark killed by human being becomes from 50 million to 100 million of them a year. In this situation the sharks become extinct. The important thing is Hammerhead shark is only one animal alike other animals, and everyone understands that they are by no means atrocious killer. Hammerhead shark is kept in many aquariums, and their mysterious shape attracts the eyes of many people. And it’s may appeal for the need of the conservation of the shark.

Viewing

If you want to meet Hammerhead shark in Kochi, let’s go to Niyodogawa after the heavy rain. They come to the mouth of a river of Niyodogawa after the heavy rain. Hammerhead shark is one of a few sharks attacking the human being, but is not ferocious as a rumor because they becomes rarely aggressive. If you come across Hammerhead shark in the sea, please read the action exactly calmly. The probability attacked by a shark is hard to happen than being struck by lightning than being stung by the hornet.

Ayu: Plecoglossus altivelis altivelis

In summer, if you go to upper reaches of a river, you may see many anglers who have very long fishing rods. Probably, they are Ayu fishing. Ayu is famous in Japan. Most Japanese know Ayu live clean rivers at least.

Ayu have many relations. First, we eat Ayu. For esample, Sioyaki, Tempura, Segosi, Sabazusi and Uruka. But Ayu may have parasitic which are called Yokogawakyuutyuu. So if you eat Ayu, you should not eat it raw. In addition to this, it is Ayu fishing. There are caught by decoy and fry-fishing. But there are closed season for fishing from May to November and we must buy license fishing. And goods are very expensive.

Ayu’s scientific name is Plecoglossus altivelis altivelis. They belong to Osmeriformes like smelt and Japanese smelt. They are related to koukakugyorui.

Ayu fry live in sea and downriver. They eat plankton and insect which live or fall in the water. They hatch from two weeks and they are clear in body so we can their beating heart and air bladder. When they become ten millimeters, they begin to be fragrant like watermelon or Oriental melon. On April and May, they get color and the teeth become like spit. And they go up river.

Adult Ayu live in middle and upper reaches of rivers and eat algae. They are gray and green. Young Ayu swim together but bigger Ayu make territory in places where there are many diatom. This territory is one meter in every direction and if others enter the territory, they deliver an attack by bodily impact. In fall, they become orange and black. It is nuptial coloration. From February to September they swim down river. Then they lay eggs in shallows where there are many pebble stones and sand in group and die. So they end their lifetimes in one year.

Much Ayu live in Kochi rivers because Kochi’s river are clean. Rivers which Ayu live in Kochi are Shimanto River, Yoshino River, Niyodo River, Monobe River and Kagami River. So if you are interested in Ayu, go to the upper reaches of a river and fish Ayu.

Ayu have a relation with people from old times. But wild Ayu are decreasing by people impact. Ayu cannot live in muddy rivers because algae cannot photosynthesize in muddy rivers. Releasing Ayu into the river is done in Japan. It is good thing. But I don’t like this because it may mix alien species and origin. So I think we must keep clean river. If wild Ayu are not seen river, it is very lonely.