Comparison of catches of two pound nets located at different distances from the shore

　内湾に設置された桝網について，その設置場所と漁獲物組成との関係を明らかにするために，瀬戸内海の小内湾である笠岡湾の桝網群の中より，岸に近い網と，同一漁場の沖側の網とを選び，1961年6月から1年間冬期を除いて毎週1回，それらの網の全漁獲物について調査を行ない，次の結果を得た.
1) 桝網の漁獲物は葎類数，尾数，漁獲量の何れにおいても，設置場所により，叉季節によって可成り変動した.
2) 岸の網の漁獲物の種類数は一般に沖の網のそれよりも多く，季節的には夏季が最も多かった.
3) 漁獲物の尾数の点については岸の網より沖の網が多かった.然し，漁獲量では非常に多量のマルアジが沖の網でのみ漁獲された8月と9月を除くと，漁獲尾数と反対に，沖の網より岸の網が多く，両網聞の漁獲尾数についても，叉漁獲量についても相関々係は非常に有意であった.
4) 桝網漁獲物の中では比較的魚体が大きく，重要魚と考えられるクロダイ，ボラ，メナダは主として岸の網によって漁獲された.然しこれらの魚種は一度に多数漁獲されることはなかった.
5) 主として沖の網によって漁獲されたものは，マルアジ，カタクチイワシ，イシモチ，テンジクダィ，ヒイラギ等の魚体の小さい魚，若しくは若年魚群であった.漁獲尾数で第1位に位したマルアジはその99%が沖の網で漁獲された.
6) 湾内に群をなして来治する魚種としてカタクチイワシ， トカゲエソ， トウゴロイワシ，アカカマス，マルアジ，スズキ，イシモチ，メイタガレイ，マコガレイ等が考えられる.

The whole daily catches by the two masu-ami (a kind of the pound net) operated in Kasaoka Bay were investigated, with reference to the species and size composition, at about weekly intervals during the one-year period from June, I96I through June, I962, for the purpose of clarifying the difference between the catches. These nets, which were selected as the sample out of the many masu-ami operated in this region, were located off Terama village of Konoshima, one 60 m. and the other 350 m. from the shore. Water depths at the locations of these nets were 3.5 and 5.5 m. below the mean water level respectively. There was no significant difference in such hydrographic conditions as water temperature, chlorinity and dissolved oxygen between the locations of the two nets. From comparison of the catches of the two nets, the following results were obtained:

1) The species composition of the catches of these masu-ami showed considerable seasonal variations and local differences.
2) The catch of the nearshore net was, in general, richer in species, greater in weight and fewer in number of individuals than that of the offshore net. The correlation coefficient between the catches of the two nets either in weight or in number of individuals, was highly significant except in August and September.
3) The number of the captured species was relatively numerous in July and August when water temperature was high. Thereafter, it gradually decreased with the falling water temperature, and remained nearly constant during November and December. The species composition of catches of the two nets, however, always differed from each other.
4) The fishes, larger in size and higher in market value in the catches of masuami, such as Mylio macrocephalus Mugil cephalus and Liza haematocheila except Platycephalus indicus were mainly caught by the nearshore net and seldom came into the offshore net. The number per haul of these fishes was usually small.
5) A large number of young Decapterus maruadsi were caught almost exclusively by the offshore net, practically none of them appeared in the catch of the near shore net. They occurred in Kasaoka Bay in large schools from July through October.
6) There was an indication that small-sized or young fishes are taken more numerously by the offshore net than the nearshore net.
7) The following fishes were presumed to come into Kasaoka Bay in schools. They are Engraulis japonia, Saurida elongata, Allanetta bleekeri, Sphyraena pinguis, Lateolabrax japonicus, Argyrosomus argentatus, Limanda yokohamae and Kareius bicoloratus.