瀬戸内海におけるウマヅラハギNavodon modestus (GÜNTHER)の漁況について

On the Catch of Navodon modestus (GÜNTHER) in the Seto Inland Sea

Kakuda Shunpei

広島大学水畜産学部紀要

Journal of the Faculty of Fisheries and Animal Husbandry, Hiroshima University

瀬戸内海におけるウマヅラハギの漁況について,愛媛,広島両県の農林水産統計年報と光,弓削島,仁尾,大浜,箱浦,走島,大飛島,六島,真鍋島,北木島,白石島,福田,北灘の各漁業協同組合などに水揚げされたウマヅラハギ漁獲量の記録とを用いて解析を行ない,次の諸点を明らかにした。
1) 瀬戸内海のウマヅラハギの主たる漁場は伊予灘,安芸灘,燧灘(備後灘を含む)および播麿灘であるが,漁獲量は概して東部よりも西部の方が多い。そして瀬戸内海に隣接する宇和海も良好な漁場である。
2) 主たる漁業種類は伊予灘,安芸灘では小型底曳網,燧灘と播麿灘では桝網であり,宇和海は旋網であるが,各地ともウマヅラハギはこれらの漁業種類以外に刺網,一本釣,船曳網,敷網などによっても漁獲される。
3) 漁期は冬期を除く4～12月であって,盛漁期は春期であるが,秋期の漁獲量も多い。そして豊後水道に近い海域では漁獲量は春期にも多いが夏期,秋期にはさらに多い。
4) 燧灘では4～6月に約500統の大型桝網が操業され,ウマヅラハギを多獲する。この海域では1960～'64年の期間が特に豊漁であったが,この間の年間漁獲量は百数十トンと推定される。桝網の始漁期,盛漁期,終漁期については燧灘の各地区および播麿灘の北灘共にほぼ一致しているが,各地区とも漁獲量の経日変化はかなり大きく,概して漁期の前半において漁獲量が多い。
5) 燧灘の白石島,北木島,真鍋島,六島,走島,大飛島,弓削島,大浜,仁尾および播麿灘の北灘におけるそれぞれの桝網のウマヅラハギ日別漁獲量の1963年と'64年のデータを統計的に処理した結果,日別漁獲量について相似変動が認められ,関連性が強いと考えられるのは燧灘東部の白石島,北木島,真鍋島,六島,走島,大飛島の6地区間においてである。そして弓削島,大浜,仁尾,北灘の相互間において,またこれらの地区と前述の6地区との間においては相似変動が認められる場合と認められない場合があって,必らずしも関連性があるとはいえない。
6) 桝網の操業水域に近い場所で操業された刺網の日別漁獲量と桝網のそれとを比較した結果,両者の間に正の相関関係が認められた。しかし桝網の漁獲量と刺網の漁獲量が極大になる時期には若干のずれがあり,漁期の前半では桝網の漁獲量がより多いのに対し,後半では刺網の漁獲量がより多い。さらに桝網と刺網の盛漁期における漁獲物の性比については,桝網の漁獲物は漁期が進むにつれて雌の比率が大きくなる傾向があるのに対し,漁期の後半における刺網の漁獲物は雄の占ある比率が大きい。
7) ウマヅラハギ漁獲量の経年変化について海域間の関連性を検討するために,愛媛県の燧灘,伊予灘,宇和海の各海域および光,弓削島,大浜,大飛島,六島,福田,北灘そして相模湾の米神の各地区について,相互間におけるSPEARMANの順位相関係数を求めて比較した。その結果,瀬戸内海の西部海域,宇和海および相模湾(米神)の相互間,燧灘の大飛島,六島,弓削島,大浜の相互間(ただし大飛島―六島は除く)においてそれぞれ豊凶の一致性が認められた。しかし前者に属する海域または地区と後者に属する地区との間には,何れの場合も豊凶の一致性は認められない。したがって瀬戸内海におけるウマヅラハギの漁況を経年的にみると,宇和海を含めた西部海域と中部海域とはそれぞれ独立的であるが,それぞれの海域内ではよく類似している。東部海域に関しては結論的なことはいえない。

In order to clarify various features of the catch of the file-fish, Navodon modestus (GÜNTHER), in the Seto Inland Sea, the commercial catching data of this species were collected and analysed statistically. The data upon which this study is based are compiled from the published records of Ehime Prefecture from 1963 onward and Hiroshima Prefecture during the period 1950-1963 and from the unpublished records obtained from several Fishermen's Cooperative Associations in the Seto Inland Sea. General conclusions obtained in this study are summarized are follows:

1) The file-fish, N. modestus, has always been a common fish of commercial value in the Seto Inland Sea. Generally the catch of this species is more abundant in the western region than the eastern of the Sea in recent years. The main fishing grounds of N. modestus in the Sea are Iyo-nada, Aki-nada (western), Hiuchi-nada (central) and Harima-nada (eastern) (Fig.1). In the western region of the Sea almost all the commercial catch of this species is made with the Kogata-sokobiki-ami (a small beam trawl) and in the central and eastern regions half of the catch with the Masu-ami (a small set net) (Figs.2, 3). N modestus is captured commercially by the Sashi-ami (a gill net), the Maki-ami (a surrounding net), the Ipponzuri (the angling) and the Funabiki-ami (a boat seine), too (Figs.2, 3). While the fishing season of the Kogata-sokobiki-ami lasts from April until December, landing in most abundant in June or July and that of the Masu-ami lasts from April until June, the landing is most abundant in May (Figs. 4, 5).

2) In Hiuchi-nada, central region of the Sea, almost all the commercial catch of N. modestus is hawled in by the Masu-ami during the three months from April to June. This species was very abundant during from 1960 to 1964 in this region, and its annual catch hawled in by about 500 nets of Masu-ami seems to have been 120～150 metric tons (Fig.6). The beginning, the peak and the end in fishing of the Masu-ami are the same in all the fishing grounds in Hiuchi-nada including Kitanada in Harima-nada (Fig.7). The daily catch by the Masu-ami of N modestus shows a considerably sharp fluctuation, a similar fluctuation was observed in each of the other six fishing grounds of Shiraishi-shima, Kitagi-shima, Manabe-shima, Mu-shima, Hashiri-shima and Ohi-shima, eastern part of Hiuchi-nada in 1963 and 1964. But in the four fishing grounds of Yuge-shima, Ohama, Nio and Kitanada, we had only a slight or no significant fluctuation in the same years 1963 and 1964 (Table 1).

3) Two patterns of seasonal variations of the Masu-ami and the Sashi-ami operated near the Masu-ami show nearly the same fluctuation (Fig.8). The abundance of the daily catch of the Masu-ami seems to have a highly significant correlation with the abundance of the Sashi-ami catch operated near the Masu-ami as the result of calculating the correlation coefficient between the two. The sex ratio in N. modestus is likely to be 1: 1, but males are more abundant than females in the samples captured by the Sashi-ami and females are slightly more abundant than males in the samples captured by the Masu-ami during the latter half of the fishing season (Table 2).

4) The annual catch of N. modestus shows irregular and sharp fluctuations in the different fishing grounds (Figs.9, 10). But it is noticed that the annual variation patterns of the catch can be classified into two types in general. One is that the catch was abundant in the first half of the 1960's and about 1970, and the other is that the catch has been abundant from 1969 onward (Fig.12). Moreover, the correlation of variation patterns of the annual catch in the regions of the Seto Inland Sea was examined with the aid of the SPEARMAN'S rank correlation. By the examination it must be concluded that the western region of the Sea including Uwa-kai and the central region of the Sea are independent of each other for the similarity in abundance of the catch. The variation patterns of the western region of the Sea bear a close similarity to those of Sagami Bay (Tables 3, 4).

Fishing industry. Fisheries [ 660 ]

jpn

広島大学水畜産学部

[ISSN] 0440-8756

[NCID] AN00213563

[NAID] 40003288828