旋鋼어업의 操業要因이 정어리漁獲에 미치는 效果 = On the fishing factors affecting catch of the purse seine set for sardine

국문 초록 (Abstract)

한국의 고등어 旋網漁船이 1977年 夜間操業으로 정어리를 漁獲한 227回의 操業記錄에서 操業要因과 操業當漁獲量과의 關係를 細密히 분석하고 정어리의 地理的 分布와 垂直移動에 關하여 考察하였다.
1. 한국 東南部海域의 정어리는 3,4月에는 對馬暖流域에 分布하고 對馬暖流水系의 影響이 對馬島西쪽 海域까지 擴張됨에따라 정어리의 分布도 西쪽으로 擴張되나 6月부터는 한국南岸沿岸水의 影響이 强해짐에 따라 對馬島西쪽의 정어리 分布는 적어진다.
2. 정어리漁群의 垂直分布는 水溫躍層의 發達상태에 따라 다르다. 水溫躍層이 아직 發達되지 않은 3,4月에는 0∼90m 水層에서 정어리가 漁獲되나, 6,7月에 水溫躍層이 發達되면 20∼90m 水層에서는 漁獲되는 回數가 적고 0∼20m 水層과 90∼130m 水層에서 漁獲된 回數가 많았다. 정어리는 水溫躍層에 머물어 있기를 避하는 것 같다.
3. 夜間操業으로 정어리가 漁獲된 回數는 月齡에 따라 다르며 下弦期에 가장 많고 다음에 上弦期에 많다. 上弦期에는 다른 月齡期에 비하여 優良操業의 發生率이 낮다. 投網時刻別 操業回數는 月齡과는 關係가 없고 어느 月齡에서나 總操業回數의 약 80%는 子午以後時刻에 投網되었다.
4. 夜間의 정어리魚群水深은 月齡에 따라 다르다. 정어리의 漁獲水深은 滿月에는 깊고 合朔에는 얕다. 上弦과 下弦에서는 달빛이 비치는 時刻에는 漁獲水深이 깊고 暗黑時刻에는 漁獲水深이 얕다.
5. 右旋回하면서 投網하는 외두리 旋網 漁船의 操業에서 漁獲에 有利한 流向은 投網이 끝난때의 漁船에 대하여 右舷쪽으로 흐르는 流向이다. 右舷쪽 流向일때의 操業에서는 優良操業의 發生率이 높고 不良操業의 發生率이 낮았다.

다국어 초록 (Multilingual Abstract)

The thirteen purse seiner’s detailed logbooks representing the casual 227 night sets for sardine (sardinops melanosticta) were examined to find effects of the fishing factors on sardine catch and some indications of sardine behavior.
1. The sardine in the south-eastern sea of Korea were found within the Tsushima warm current in March and april. The distribution boundary of sardine expanded to the western area of the Tsushima Island in conjunction with the expansion of the Tsushima warm current in May. And then shoals of sardine were found rare in the western boundary area where was under the influence of the south Korea coastal water mass in June and July.
2. The vertical distribution of the sardine changes with the development of thermocline. The sardine were fished from the layers of 0-90m depth when the thermocline is not developed in March and April, while they were fished from the layers of 0-20m depth and also from the layers of 90-130m depth but scarecely from the layers of 20-90m depth, when the thermocline is developed in June and July. It is likely that the sardine pass through the layers of the thermocline in a short time in their upward movement or else remain in the deeper layers.
3. To examine behavior of sardine with regard to the moon’s phase, the days of a lunar month were assigned into four periods of 27th to 3rd, 4th to 10th, 11th to 19th, and 20th to 26th. The four periods were represented with the typical moon’s phase of the new moon, the first quarter moon, the full moon, and the last quarter moon.
More than 70% of the 227 sets on sardire were carried out in the periods of the first quarter moon and the last quarter moon.
The depth layers of sardine in night-time were found to be deeper in the period of full moon than in the period of new moon, and deeper at the before-midnight-time than at the after-midnight-time in both periods.
The depth layers of sardine in night-time were deeper at the before-midnight-time than at the after-midnight-time in the period of the first quarter moon, while the depth layers were shallower at the before-midnight-time than at the after-midnight-time in the period of the last quarter moon, contrary to the period of the first quarter moon.
The puzzle is solved by accounting the daily time-shift of lunar-daytime. In the period of the first quarter moon, the lunar daytime coincides to the before-midnight-time, whereas in the period of the last quarter moon the lunar daytime coincides to the after-midnight-time. Thus the depth layers of sardine are deeper during lunar daytime than during lunar night-time.
4. The favorable current direction in the fishing operation is the “starboard direction ”relative to the boat, or the current directed to the net, when the pursing is commenced.