1. Geographical location of Miyajima-numa
- Location: Omagari 2-ku, Bibai-cho, Bibai-city, Hokkaido, Japan
2. Dimensions etc.
3. Environmental and geographical features
- ｛Reference from *1, Data in square brackets, [ ] from *2. Data in parentheses,
( ) are practical values.}
Altitude: 13m, Circumference: approx 2.7km 〔3.0m〕,
Lake area: 0.36km2 (Water Surface Area: approx. 30ha)
Depth: Nominal Max 2.4 m, Average 1.7 m [1.6 m]
(Actual Measurement: Max 1.23 m, Average 0.86 m ～Recorded August 29-30,
1994, by Tanabe and others)
Quality of Water: Phosphorous 0.055 mg/l, Nitrogen 1.2 mg/l, COD 10.5 mg/l,
Chlorophyll a 12 μg/l Humus type nutritious lake
Origin: Officially unknown
(It is thought that it is one of a number of bodies of water left after
the Ishikari River flooded its banks.)
- It is located 500 m east of the Ishikari River which is at the western
edge of Bibai city. It is part of the old Bibai wilderness of peat, in
a wet, low-lying area where there is some high-grade, but mostly low-grade,
peat. (The former Bibai wilderness was a special area that consisted of
approximately 50% high-grade sphagnum peat. For reference, Kushiro had
5%, and Sarobetsu 10%.)
The banks of the marsh have no artificial protection devices and its natural
state is maintained. Wild rice grows thickly in the reeds. Apart from the
north where a copse of various trees remains, most of the surrounding area
of the marsh is used for rice farming.
*2 [Naturally growing trees: 21.62%, Other undisturbed land: 18.92%, Cultivated
land: 21.62%, Land used for other purposes 37.84% = Artificial lake shore.]
- Settlement of the area around the marsh began in 1890 (Meiji 26), and the
name "Miyajima-numa" was derived from the name of Miyajima Farm,
which was beside it.
- Deep high grade peat hindered development of the area, and cultivation
of the land around the marsh did not take place until 1950, after World
- It is said that when settlement began in the Meiji period, geese eggs were
taken and used as food, but this has not been confirmed. It is also said
that many geese covered the fields during the spring plowing season at
the beginning of the Showa period (circa 1930), but it is not known if
these geese were white-fronted or bean geese.
- Since about 1971, when all wild geese were designated a special national
treasure, the dry fields around the lake were converted to rice fields
because the irrigation system was well established and demand for rice
had increased. In addition to the wide and shallow marsh, which is a particularly
good place to roost, the geese were blessed with plenty of food in the
form of fallen rice. This resulted in a rapid increase in the numbers of
geese. Furthermore, the white-fronted geese which had until then roosted
at Ishikari bay some 40 km away and used the marsh as a feeding ground
began to use Miyajima-numa as a roost in 1978 (*reference for 3).
5. Use of the lake by geese etc.
- Almost all of the wintering white-fronted geese gather and stay throughout
April. Their number is far greater than the number wintering in Japan,
but migration from the continent has not yet been confirmed. No legal measures
to protect wildlife at Miyajima-numa have been taken. Voluntary restrictions
on shooting have been exercised since autumn 1989, after it was discovered
that many birds had died in spring of that year due to lead poisoning.
As a result, white-fronted geese stay throughout October with ducks and
so on before flying south.
- The geese that gather at Miyajima-numa are white-fronted geese only. Only
a few hundred オオヒシクイ stop at Miyajima on the way to lakes and marshes in
Sarobetsu wilderness. A few カリガネ、コクガン、シジュウカラガン and 亜種ヒシクイ are also make
rare appearances amongst the other birds.
- Over ten thousand whistling swans pass through in early spring and gather
at Lake Kussharo on the Okhotsk coast near Wakkanai. Several hundred whooper
swans also stay for a few weeks on their way to lake Tofutsu-ko. Wild ducks,
mainly オナガガモ, come to the lake but they are displaced to the Ishikari river
and their numbers appear low when the number of geese increases in the
6. Vermin Damage of Agricultural Produce by Waterfowl
Crop damage to rice by waterfowl before harvesting has largely been eliminated
due to the development of rice farming techniques. However, damage to malt
by white-fronted geese has recently started to occur.
- Through national agricultural administration changes, the rice fields that
had been feeding grounds for the geese became wheat fields planted in the
autumn. The white-fronted geese came to their established feeding grounds
after the winter snow had melted, but with no rice they began to eat the
green malt. As many as 40% of the fields were changed, and the crop damage
became obvious. Following that, agricultural administration restrictions
on crop rotation were eased, the fields were restored and “vermin damage
disturbance” faded out. In the mid 1990s, the WTO Uruguay Round Agreement
resulted once again in the rice paddies becoming dry fields, and the problem
of damage to the crops by geese recurred. The problem of crop damage by
geese will be dealt with in another section.
7. Lead poisoning of waterfowl
- It was at Miyajima-numa in Japan that it first became clear that lead
shot for duck hunting scattered at the bottom of lakes was being taken
as small stones by waterfowl to aid their digestion, but resulting in their
death by lead poisoning. This problem and its occurrence at the marsh
will also be dealt with in another section.
- "Hokkaido no Kosyo" Hokkaido Kogai Boshi Kenkyu-jo
- "Hokkaido Shizen Kankyo Joho (Shizen Hogo Nenpo)" Hokkaido Shizen
Hogo Kyokai 1985
- "Gan to Hakucho no Setai (Ishikari shuhen no Kansatsu Yori)" K.
Hoshino 1990, Published Independently
"Miyajima-numa Oyobi Sono Shuhen ni Okeru Mizudori-rui no Dotai Shokuse-to
ni Kansuru Chosa Kenkyu Hokoku-sho (Yoyaku-ban) " Takugin Sogo Kenkyu-jo
"Hokkaido chuo-bu no Bibai ni Okeru Chorui-so" H.Masatomi, S.Kusano,
"Journal of Hokkaido College, Senshu University 26, extra number" 1993
"Gan no Sato Miyajima-numa" S. Kusano Hokkaido Terebi Mamehon
"Magan" T.Ikeuchi 1996 Bunichi Sogo Shuppan
"Bibai to Sono Shuhen ni Okeru Tancho-chi" I. Tanabe 1997, Independently
"Gan no Tayori" Gan wo Hogo Suru Kai Kaiho
"GOOSE STUDY" Gan wo Hogo Suru Kai
"Miyajima-numa Tsushin" Miyajima-numa no Kai Kaiho 1994.6-