1 Black croaker can be caught throughout the year, but there are two fishing seasons March to July and October to September, especially we can get a larger quantity in May.
2 The good fishing grounds are divided into three regions-nothern, central and southern and the southern area is the best. (See Fig. 2)
3 The migration, differring in each area and race, is in close connection with oceanic current, namely the northern and southern croakers migrate in the meeting bounds of currents, and the central ones travel in warm current. However, I presume these schools of croaker in the central and southern area migrate and alternate reciprocally their places.
4 The length of fish caught by trawler is 10.5-45.2cm, and the most general size of fish is 19-23cm. Its average length is 22.429±0.056cm. This formation varies according to the fishing ground, sex, season and netting.
5 The lergest fish can be found in the northern fishing ground, and the smallest one in the southern part-the length of fish becomes larger and larger as we advance to the north.
6 The female is 11.7-46.9cm in length, its average length is 22.493±0.093cm-and the, male is 11.2-42.6cm in length, its average length is 22.997±0.094cm, so the female is bigger than the male.
7 The length of fish vary according to each fishing season-the largest in May and June, the next in October and September, and the smallest in August, the next in April. This difference refers to the spawning migration.
8 The length of fish is various in each netting, for school is formed by different ages, sizes, etc.
9 It is presumed that the spawning season continues from April to June.
10 The relative formula of body length (
L) and weight (
W) is shown as follows:
W=0.002 03L
3•40?? The growth rate is high in northern area and in female.
11 The relative formula of body length (
Lcm) and ovarian weight (
Ogr) is shown as follows
O=0.0000154
L5•345 12 When the body length reaches 22-23cm, the number of ova varies from 60, 000 to 550, 000 and it increases in proportion to the length.
13 The water temperature for catch is 12.4-21.8°C, and it is different according to a fishing season. The most favorable temperature for catch being 18.5-20.0°C, and the optimum temperature is 17.5-22.0°C.
14 The fishing depth of water is 45-100 meters, and its proper depth for catch is different in every fishing season; it is deeper in April, October and September, and shallow in May and June.
15 The relation between the moon age and the fishing rate per haul in almost all seasons is concluded as follows: The fishing rate increases at the neap-tide, and decreases at the major tide in Feb., Apr., Aug. and Sept., but the contrary phenomenon is shown in May and June, and this relation does not exist in March and July.
16 Generally speaking, croakers can be abundantly caught in daybreak or twilight, except daytime in October.
17 There is a tendency to find school of black croaker in the benthic region occupied by abundant
Macrura and
Steroidea.
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