How the cormorant finds and catches fish and the cuts on the fish marked with its beak

Abstract

Although there are numerous birds which feed on fish, the method of catching fish varies greatly. Cormorant is one of the animals which catch fish diving into the water. It has a shape very suitable to catch fish diving into the water. The method of fishing with Cormorant practiced on the River Nagara, Gifu Pref. is widely known abroad, and the Cormorant used for that purpose is called Temminck's Cormorant Phalacrocorax capillatus (Temminck et Schlegel) which is domesticated and trained.
Cormorant, when diving into the water, turns skillfully right and left following the fish, and finally catches it with its beak. Cormorant usually attacks the vital spot of the fish at a stretch, and therefore, it hardly fails to catch it unless otherwise the fish is extremely large or its skin is too smooth.
The fishing period on the River Nagara is for five months, May 11 up to October 15 of the year, and the majority of the Cormorant's catch is Ayu Plecoglossus attivelis Temminck et Schlegel, and it comes to 70% of the total catch.
The biting marks left by Cormorant greatly differ from those effected by other birds and they resemble the marks out with scissors, and their position are as shown in Figure No. 1. The marks. in the case of Ayu, are invariably made from the attacks from the top, and its epidermis is torn and scales come off. When it bites the fish too strongly, however, its dorsal fin is sometimes broken, or it bleeds under the skin. When the wound is serious, its muscles are cut and its viscera comes out (Ref. to Figure No. 1). Figure No. 2 shows the difference between the marks left by Cormorant's upper chap and those left by its lower one. (Left-by upper chap, right-by lower chap.) As regards the distribution of the biting marks left on the skin of Ayu, if it is divided into 8 parts as in Fig. No. 4, they are centered on parts 2 and 3, and it appears to be because its important internal organs are therein. If it is divided as in Fig. No. 5, the majority of the biting marks are left on part two, just as in the case of Fig. No. 4.