JP4605775B2 - Tidal flat covering material, Tidal flat construction method, Tidal flat covering method and Tidal flat covering structure - Google Patents

Description

  TECHNICAL FIELD The present invention relates to an artificial tidal flat or a clam fishing ground tidal flat covering material, a tidal flat construction method, a tidal flat covering method, and a tidal flat covering structure for increasing the amount of clam resources.

  In the clam life cycle (floating larva stage-bottoming stage-juvenile stage-adult clam stage), regarding the bottoming of floating larvae, the bottoming place selection behavior (confirm the bottom sediment conditions with their feet) It is known to perform the action of selecting a landing place, and in particular, there is a report that he prefers coarse sand (particle size: 0.85 to 2 mm) (see Non-Patent Document 1 below). That is, according to Non-Patent Document 1, particularly good results are obtained with coarse sand having a particle size of 0.85 to 2 mm as shown in FIG. The survey method for obtaining the results of FIG. 1 (a) is summarized as shown in FIG. 1 (b). The results of FIG. 1 (a) are classified into 7 particle sizes (0.063 to 4 mm) for clams. It was obtained by investigating the number of individuals on the floor.

  It is thought that the clam floating larvae are prevented from being washed away by tidal currents by spreading a viscous foot consisting of protein and adhering this foot to a substrate such as soil particles after the bottom has settled (Fig. 2). In addition, it is presumed that they prefer sand with a large particle size because they exhibit negative phototacticity in the process of growing from floating larvae to larvae and have a characteristic of seeking a hiding place.

The relationship between the growth environment of the clams and the particle size distribution is summarized as shown in FIG. As shown in FIG. 3, it is considered that growth is impossible at a fine grain content (clay silt content) of 40% or more, and the optimum growth environment estimated from the clam habitat survey is the median particle size D ₅₀ = It is considered to be 0.2 to 0.4 mm and a fine particle content of 20 to 30%.

  As mentioned above, there is a report that the coarse sand (particle size: 0.85 to 2 mm) is preferred for the floating larvae bottoming, but the floating larvae-bottoming stage-juvenile stage-adult shellfish life cycle No knowledge about the most suitable coarse sand content is available.

  The clam prefers coarse sand as a suitable landing site in the process from floating larvae to juveniles, but in the process from juvenile to mature shellfish, it is further submerged for water retention and feeding activities. It is considered that there is a habit of moving to find a suitable place for the growth environment in the process of growing, preferring a finer particle size than coarse sand for ease of action. Adult shellfish show little mobility, but there is a report that it is very mobile during the time of juvenile shellfish and moved about 5m in one month.

  Adult clams and juvenile clams are distinguished by the development of the reproductive organs, and are generally mature (with fertility) at a shell length of 10 to 25 mm. In some cases, younger than 1 year old and less than 15 mm in shell length are distinguished from juvenile shellfish, 1 year old and older, and 15 to 20 mm in shell length and older.

  Fig. 3 shows an example of the particle size distribution of a natural tidal flat (Tokyo Bay) where many clams live, but the particle size distribution of this tidal flat does not match the range of the optimal growth environment. As a means for improving the particle size distribution of the tidal flat to a particle size distribution more suitable for the growth of clams, the idea of adding and mixing fine particles for the purpose of improving water retention and supplying nutrients has been reported.

In addition, depending on the habitat conditions of the desired tidal flat benthic organism, a method of blending any material such as sand, fine particles, organic matter, bacteria, etc. with an optimum blend and utilizing it as a sand covering material (for example, the following patent Reference 1) and a method of utilizing a sand-capping material with a particle size and loss on ignition adjusted according to the desired inhabiting conditions of tidal flat benthic organisms (for example, see Patent Document 2 below) are known. However, Patent Document 1 does not disclose or suggest the optimum growth environment for clams, and Patent Document 2 scores the relationship between clams and sediments in order to prepare an environment suitable for desired tidal flat benthic organisms. However, no attention is paid to the particle size distribution of the sand, particularly the coarse sand content, in consideration of the habits of the clam growth process as described above.
"Selectivity of clam larvae and distribution in Mikawa Bay" Fisheries Engineering Vol.29 (1) 55-59, 1992 JP 2000-314116 A JP 2003-184046 A

  Adult clams can live in various particle size distributions, but in order to maintain clam fishing grounds only by reproduction without releasing larvae, floating larvae-bottoming-juveniles-adult mussels It is considered important to use a sand-capping material with a particle size composition that is most suitable for the life cycle of the season. However, there is currently no clear knowledge about the particle size composition most suitable for the clam life cycle.

Conventionally, in the construction of tidal flats for the development of clam fishing grounds, the median grain size (for example, D ₅₀ = 0) is mainly referred to with reference to the sediment size distribution in the surrounding sea area where clams are found. .2 to 0.4 mm) and fine grain content (for example, content 20 to 30%), we select sea sand and mountain sand to be used as sand-capping material. Does not pay attention. For this reason, in most cases, the coarse sand content of the sand-capping material is less than 20%. This general tidal flat with a coarse sand content of less than 20% is considered to have no problem as a growing environment for clams. However, it is important to increase the amount of clams by promoting the settlement of floating clams. It is hard to say that it is the optimal environment.

  In view of the problems of the prior art as described above, the present invention maintains an optimum environment in the life cycle of the clam from the floating larva stage to the bottoming stage to the juvenile stage to the adult clam stage, and the floating larvae are settled. An object of the present invention is to provide a tidal flat covering material, a tidal flat preparation method, a tidal flat covering method, and a tidal flat covering structure capable of providing an easy bottom environment.

  In order to achieve the above-mentioned object, the tidal flat covering material according to the present invention is made of sandy sand, which is the optimal particle size for the floating larvae of clams to settle down when constructing artificial tidal flats and clam fishing grounds. To the coarse sand content 20 to 50% after mixing, the passing mass percentage 50 to 80% with a particle size of 0.85 mm, and the passing mass percentage 70 to 100% with a particle size of 2 mm. It is characterized by that.

  According to this tidal flat sand-capping material, coarse sand (particle size 0.85 to 2 mm), which is the optimal particle size for the clam floating larvae to settle, is mixed with sandy soil, and the coarse sand content after mixing By making the content rate 20-50%, passing mass percentage 50-80% of particle size 0.85mm, passing mass percentage 70-100% of particle size 2mm, the clam's floating larva stage-bottoming stage-juvenile stage It is possible to maintain an optimum environment in the life cycle up to the adult clam stage and to create a sediment environment where floating clams of clams are likely to settle. As a result, the most important thing for sustainable clam inhabiting is the formation of new recruitment groups, which can promote the settlement of floating clam larvae, increase the number of clams in the new clad, and increase the amount of clam resources. Increase is possible.

  The reason why the content of the coarse sand after mixing is 20-50% is that the clam prefers coarse sand as a suitable landing site in the process until the clam grows from floating larvae to juveniles, In the process of growing up, because it prefers a finer particle size than coarse sand in order to find more ease of submersible action due to water retention and feeding form, floating larva stage-bottoming stage-juvenile stage- As the most suitable particle size composition for the life cycle of the adult clam, it is not preferable that the content of coarse sand exceeds 50%, and if it is 20% or more, it is sufficient for the settlement of floating larvae It is possible.

  In the tidal flat construction method of the present invention, the coarse sand is mixed with sandy soil, so that the mixed tideland covering sand material has a coarse sand content of 20 to 50% and a passing mass percentage of 50% with a particle size of 0.85 mm. An artificial tidal flat is constructed so that the passing mass percentage with a particle diameter of 2 mm is 70 to 100%.

  According to this tidal flat construction method, coarse sand (particle diameter 0.85 to 2 mm), which is the optimum particle size for the clam floating larvae to settle, is mixed with sandy soil, and the coarse sand content after mixing is contained. By making the rate 20-50%, passing mass percentage 50-80% of particle size 0.85mm, passing mass percentage 70mm-100% of particle size 2mm, the clam's floating larva stage-bottoming stage-juvenile stage- In addition to being able to maintain an optimal environment in the life cycle up to the adult clam stage, it is possible to create a sediment environment in which clams floating larvae can easily settle.

  Another tidal flat construction method according to the present invention comprises mixing coarse sand with sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine particle content of less than 40%. The mixed tideland covering sand material has a coarse sand content of 20 to 50%, a passing mass percentage of 50 to 80% with a particle size of 0.85 mm, and a passing mass percentage of 70 to 100% with a particle size of 2 mm. It is characterized by the construction of artificial tidal flats.

  According to this tidal flat construction method, coarse sand (particle size: 0.85 to 2 mm), which is the optimum particle size for the clam floating larvae to settle, has a coarse sand content of less than 20% and a sand content of Mixed in sandy soil with 60% or more and fine grain content less than 40%, coarse sand content after mixing 20-50%, passing mass percentage of particle size 0.85mm 50-80%, particle size 2mm By setting the passing mass percentage to 70 to 100%, it is possible to maintain an optimal environment in the life cycle from the clam's floating larva stage to the bottoming stage to the juvenile stage to the adult clam stage, and the clam's floating larvae arrive The bottom quality environment that is easy to bottom can be created.

Yet another tidal flats reclamation process according to the invention, coarse sand fraction content of less than 20%, fine fraction content of less than 30%, passing mass percentage 80% to 100% of the particle size 2 mm, and the average particle diameter D ₅₀ = 0. By mixing coarse sand with sandy soil having a size of 15 to 0.6 mm, the mixed tideland covering sand material has a coarse sand content of 20 to 50% and a passing mass percentage of 50 to 50 mm. The artificial tidal flat is constructed so that the passing mass percentage of 70% is 80% and the particle diameter is 2 mm.

According to this tidal flat construction method, coarse sand (particle size: 0.85 to 2 mm), which is the optimum particle size for the clam floating larvae to settle, contains less than 20% of coarse sand and contains fine particles. The ratio is less than 30%, the passing mass percentage with a particle size of 2 mm is 80 to 100%, and the average particle size D ₅₀ is mixed with sandy soil with 0.15 to 0.6 mm, and the coarse sand content after mixing is 20 to 50 %, Passing mass percentage of particle size 0.85mm 50-80%, passing mass percentage of particle diameter 2mm 70-100%, from clam floating larva stage-bottoming stage-juvenile stage-adult clam stage It is possible to maintain an optimum environment in the life cycle of the sea and to create a sediment environment where floating clam larvae can easily settle.

  Still another tidal flat construction method according to the present invention is a method for forming a surface of a tidal flat composed of sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine particle content of less than 40%. An artificial tidal flat is created by spreading coarse sand to a layer thickness of about 3 cm or less.

  According to this tidal flat construction method, in a calm water area where sandy to mud mud flats, which are generally considered suitable for clams, are formed, there are many cases where there is little rough sand on the surface of the tidal flat. Sand and medium sand often occupy most of the particle size composition, but by spreading coarse sand to a layer thickness of about 3 cm or less on the surface of a tidal flat composed of sandy soil with a low content of coarse sand. In addition, it is possible to make the tidal flat most suitable for the life cycle of floating larva period-bottoming period-juvenile period-adult clam period, and it becomes a sediment environment where floating larvae of clams are easy to settle.

  According to each of the above-mentioned tidal flat construction methods, the most important thing for the sustainable habitat of clams is the formation of new recruitment groups. The tidal flat where the increase of clam resources can be realized can be created.

  The tidal flat covering method according to the present invention comprises a coarse sand (particle size: 0.085 to 2 mm) content of less than 20%, a sand content (particle size of 0.075 to 2 mm) of 60% or more, and a fine particle (grain) (Diameter less than 0.075mm) After preparing the above-mentioned tidal flat covering material by mixing coarse sand with sandy soil having a content of less than 40% using a sand mixing device, dropping it into a predetermined area of the artificial tidal flat It is characterized by.

  According to this tidal flat sand-capping method, the coarse sand content is increased by mixing coarse sand with sandy soil using a sand mixing device, and the sediment environment is suitable for the settlement of floating clam larvae. An artificial tidal flat can be created.

  Another tidal flat sand-capping method according to the present invention is to spread sand on a tidal flat surface layer composed of sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine grain content of less than 40%. The surface of the tidal flat is modified into the above-mentioned tidal flat sand covering material by spraying coarse sand using an apparatus.

  According to this tidal flat sand cover method, in a calm water area where sandy to mud mud flats, which are generally considered suitable for clams, are formed, coarse sand (particle size 0.85) In most cases, fine sand (particle size 0.075 to 0.25 mm) and medium sand (particle size 0.25 to 0.85 mm) occupy most of the particle size composition. The coarse sand content of the tidal flat surface is increased by spraying the coarse sand using a sand spraying device to the tidal flat surface made of sandy soil with a small coarse sand content. It becomes possible to modify to a sediment environment suitable for the bottoming of water.

  According to each of the tidal flat sand-covering methods described above, the most important for sustainable clam inhabiting is the formation of new recruitment groups. You can create a tidal flat where you can increase the population and increase the amount of clams.

  The tidal flat cover structure of the two-layer covered sand type according to the present invention has a coarse sand content (particle size 0.85 to 2 mm) content of less than 20% and a sand content (particle size 0.075 to 2 mm) content 60%. The above is characterized in that it is constituted by spraying coarse sand to a layer thickness of about 3 cm or less in a tidal flat surface layer portion made of sandy soil having a fine particle content (particle size less than 0.075 mm) of less than 40%. And

  According to the tidal flat cover structure of this two-layer covered sand type, in a calm water area where sandy to mud mud flats, which are generally considered suitable for clams, are formed, rough sand is formed on the surface of the tidal flat. In many cases, fine sand and medium sand occupy most of the particle size composition, but the surface of the tidal flat composed of sandy soil with a small content of coarse sand is less than 3 cm of coarse sand. By renovating the tidal flat cover structure spread to the layer thickness, it becomes possible to make the tidal flat most suitable for the life cycle from the floating larva stage to the bottoming stage to the juvenile stage to the adult clam stage, and the floating larva of clams It becomes a sediment environment that is easy to settle.

  The reason why the layer thickness of the coarse sand of the above-mentioned tidal flat cover structure is within about 3 cm is that the clam has a habitat depth of about 1 to 2 times the shell length. It is possible to prepare an optimum environment from the floating larval stage to the bottoming stage to the juvenile stage by using the coarse sand within the range of the habitat depth of less than 15 mm), and the coarse sand content is contained under the coarse sand. Small sand (particle size: 0.075 to 0.25 mm) to medium sand (particle size: 0.25 to 0.85 mm), which is mainly sandy sand, leaves the sandy soil as the main component. This is because the environment can be maintained.

  Another tidal flat covering structure according to the present invention has a coarse sand content (particle size 0.85 to 2 mm) content of less than 20% and a sand content (particle size 0.25 to 0.85 mm) content of 60% or more, And it is comprised by sprinkling coarse sand in several areas in the tidal flat surface layer part which consists of sandy soil with a fine particle content (particle diameter less than 0.25 mm) content less than 40%, and forms several coarse sand pools. It is characterized by that.

  According to this tidal flat cover structure, in a calm water area where sandy to mud mud flats are generally considered suitable for clams, there are many cases where there is little coarse sand on the tidal flat surface, Fine sand and medium sand often occupy most of the particle size composition, but the tidal flat surface layer composed of sandy soil with a small content of coarse sand is sprayed with coarse sand and has multiple coarse sand pools. By remodeling to the sand-capped structure, it becomes possible to make the tidal flat most suitable for the life cycle from the floating larvae settlement stage to the juvenile stage to the adult clam period, and the sediment environment where the clam floating larvae are likely to settle. It becomes.

  The reason why the coarse sand pool is scattered in multiple areas is that the optimum environment from the floating larva period to the juvenile stage (coarse sand pool) and the optimum environment from the juvenile period to the adult clad period ( This is because it is possible to move in search of suitable land in the growth environment in the process of clam growth by interspersing fine sand to sandy soil mainly composed of medium sand with low coarse sand content.

  In the tidal flat covering structure, the plurality of coarse sand pools are preferably formed in an area below the average tide level of the tidal flat surface layer.

  As described above, coarse sand pools are formed on the tidal flats off the average tide level. The clams are low in water temperature and salinity tolerance, and the survival rate in low tide areas where the water temperature and salinity concentration are large. This is because the survival rate after bottoming is increased by placing coarse sand having the optimum particle size for bottoming of clams in places where the water temperature is below the average tide level and where there is little fluctuation in salinity.

  According to each of the tidal flat cover structures described above, the most important for sustainable clam inhabiting is the formation of new recruitment groups. It will become a tidal flat where the number of clams will increase and the amount of clams will increase.

  According to the tidal flat covering material, the tidal flat preparation method, the tidal flat covering method, and the tidal flat covering structure of the present invention, the optimum environment in the life cycle of the clam from the floating larva stage to the bottom stage to the juvenile stage to the adult clad stage It is possible to provide a sediment environment in which floating larvae can easily settle.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  <First embodiment (tidal flat sand covering material)>

  FIG. 4 is a diagram showing an example of a particle size accumulation curve of the tidal flat covering material according to the first embodiment. FIG. 5 conceptually shows the effects of the clam floating larva settlement stage (a), clam juvenile stage (b) and clam adult stage (c) in the artificial tidal flat constructed with the tidal flat covering material of the first embodiment. It is a figure for demonstrating.

  The tidal flat covering sand material according to the first embodiment is coarse sand (particle diameter: 0.85 to 2 mm) having an optimum particle diameter for the clam floating larvae to settle, for example, coarse sand (particle diameter 0). .85-2mm) content rate less than 20%, sand content (particle size 0.075-0.85mm) content rate 60% or more, and fine particle content (particle size less than 0.075mm) content rate less than 40% By mixing with sandy soil, the coarse sand content after mixing is 20 to 50%, the passing mass percentage of particle size 0.85 mm is 50 to 80%, and the passing mass percentage of particle size 2 mm is 70 to 70%. 100%.

  FIG. 4 shows a first embodiment in which the coarse sand content after mixing is 20 to 50%, the passing mass percentage of particle size 0.85 mm is 50 to 80%, and the passing mass percentage of particle size 2 mm is 70 to 100%. The range that satisfies the conditions of the tidal flat sand-covering material is shown by the range A by hatching.

  Moreover, as conditions of the sandy soil of the local soil, for example, the content of coarse particles (particle size 0.075 to 75 mm) is 50% or more and the content of sand (particle size 0.075 to 2 mm) is gravel. The content (particle size 2 to 75 mm) or more and the fine content (particle size less than 0.075 mm) content 40% may be 40%. It shows with. For example, a tidal flat covering material such as the particle size accumulation curve a in FIG. 4 can be obtained using the local soil which is the particle size accumulation curve b in FIG. 4 within the range B of the sandy soil. The sand-covering material is within the range A in FIG.

  The particle size accumulation curve is a curve representing the result (particle size distribution state) obtained by the particle size analysis by the soil particle screening test as a percentage of the proportion of soil particles smaller than a certain particle size and the particle size (logarithm). Say. Each particle size accumulation curve a, b in FIG. 4 was obtained by the “Ground Size Testing Method” (JGS 0131-2000) of the Geotechnical Society standard, and the same applies to FIGS. 6 and 7 described later. is there. Further, the classification of soil particle size (particle size) shown in the lower side of FIG. 4 is based on the Geotechnical Society standards, and the screening standard for obtaining the particle size distribution is shown on the right side of FIG.

  In the artificial tidal flat constructed with the tidal flat covering material of the present embodiment, compared with the rough sand and the local soil, the coarse sand and the sand covering material are used as shown in FIG. As shown in Fig. 5 (b), the number of surviving individuals is large in the order of coarse sand and sand-capped material in the juvenile period, but in the adult period, Fig. 5 (c) As you can see, the surviving population is the largest in sand-capped materials.

  As described above, according to the tidal flat covering material of the present embodiment, it is possible to create an artificial tidal flat in an environment where floating larvae are likely to settle, and in the artificial tidal flat, the clam floating larva stage-bottom stage-larvae The optimal environment can be maintained in the life cycle from the period to the adult shellfish period. For this reason, the most important thing for the sustainable habitat of clams is the formation of new recruitment groups, but it can promote the settlement of clams floating larvae and increase the new recruitment groups of clams. Increasing the amount can increase the amount of clam resources.

  In the tidal flat covering material of this embodiment, the desired tidal flat benthic organisms are limited to clams, paying attention to the content of coarse sand, and further paying attention to the setting location selection behavior of clams Coarse sand can be mixed with small sand-capping material to create suitable land for clams.

  <Second Embodiment (Tidal Flat Formation Method)>

  FIG. 6 is a diagram showing an example of the particle size accumulation curve of the tidal flat covering material in the tidal flat construction method according to the second embodiment.

  In the tidal flat formation method according to the second embodiment, coarse sand is mixed with sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine particle content of less than 40%, After mixing, the tidal flat covering sand material has a coarse sand content of 20 to 50%, a passing mass percentage of 50 to 80% with a particle size of 0.85 mm, and a passing mass percentage of 70 to 100% with a particle size of 2 mm. To create artificial tidal flats.

  FIG. 6 shows a range A1 by hatching that satisfies the conditions of the tidal flat covering material in the tidal flat construction method according to the second embodiment. Moreover, the said conditions of the sandy soil of local soil are shown by range B1 shown with the broken line of FIG. For example, a tidal flat covering material such as the particle size accumulation curve a1 of FIG. 6 can be obtained using the local soil which is the particle size accumulation curve b1 of FIG. 6 within the sandy soil range B1. The sand-covering material is within the range A1 in FIG. 6 and satisfies the conditions of the tidal flat sand-covering material.

  According to the tidal flat construction method described above, coarse sand (particle size: 0.85 to 2 mm), which is the optimal particle size for the clam floating larvae to settle, contains less than 20% coarse sand content and contains sand. Mixed in sandy soil with a rate of 60% or more and a fine particle content of less than 40%, the coarse sand content after mixing is 20-50%, the passing mass percentage of particle size 0.85 mm is 50-80%, the particle size By setting the passing mass percentage of 2 mm to 70 to 100%, it is possible to maintain an optimum environment in the life cycle of the clam from the floating larva stage to the bottoming stage to the juvenile stage to the adult clam stage, and the clam floating larvae It is possible to create a bottom environment that is easy to bottom.

  Next, another tidal flat creation method according to the second embodiment will be described with reference to FIG. FIG. 7 is a diagram showing an example of the particle size accumulation curve of the tidal flat covering material in another tidal flat construction method according to the second embodiment.

Another tidal flats reclamation method according to the second embodiment, the coarse sand fraction content of less than 20%, fine fraction content of less than 30%, passing mass percentage 80% to 100% of the particle size 2 mm, and the average particle size D ₅₀ = By mixing coarse sand with sandy soil of 0.15 to 0.6 mm, the mixed tideland covering sand material has a coarse sand content of 20 to 50% and a passing mass with a particle size of 0.85 mm. The artificial tidal flat is constructed so that the percentage is 50 to 80% and the passing mass percentage with a particle diameter of 2 mm is 70 to 100%.

  FIG. 7 shows a range A2 by hatching that satisfies the conditions of the tidal flat covering material in another tidal flat construction method according to the second embodiment. Moreover, the said conditions of the sandy soil of local soil are shown by range B2 shown with the broken line of FIG. For example, a tidal flat covering material such as the particle size accumulation curve a2 of FIG. 7 can be obtained using the local soil which is the particle size accumulation curve b2 of FIG. 7 within the sandy soil range B2. The sand-covering material is within the range A2 in FIG. 7 and satisfies the conditions of the tidal flat sand-covering material.

According to this tidal flat construction method, coarse sand (particle size: 0.85 to 2 mm), which is the optimum particle size for the clam floating larvae to settle, contains less than 20% of coarse sand and contains fine particles. The ratio is less than 30%, the passing mass percentage with a particle size of 2 mm is 80 to 100%, and the average particle size D ₅₀ is mixed with sandy soil with 0.15 to 0.6 mm, and the coarse sand content after mixing is 20 to 50 %, Passing mass percentage of particle size 0.85mm 50-80%, passing mass percentage of particle diameter 2mm 70-100%, from clam floating larva stage-bottoming stage-juvenile stage-adult clam stage It is possible to maintain an optimum environment in the life cycle of the sea and to create a sediment environment where floating clam larvae can easily settle.

  In addition, FIG. 16 shows a particle size accumulation curve of sandy soil (local soil) of tidal flats in various parts of the country shown in FIG. A range B2 that satisfies the soil condition is shown. It can be seen from FIG. 16 that the particle size accumulation curve of the sandy soil in the tidal flats throughout the country falls within the range B2 that satisfies the conditions of the sandy soil in FIG.

  In the tidal flats constructed by the tidal flat construction methods of the second embodiment described above, the most important for the sustainable habitat of clams is the formation of new recruitment groups. It is possible to increase the number of clams and increase the number of clams. Each of the tidal flat creation methods described above can be executed by the tidal flat covering method of FIG. 8 or FIG. 9 described later.

  <Third Embodiment (Tidal Flat Covering Method)>

  FIG. 8 is a diagram for explaining a tidal flat sand covering method (pre-mixing method) according to the third embodiment. FIG. 9 is a diagram for explaining another tidal flat sand covering method (in-situ spraying method) according to the third embodiment.

  The tidal flat covering method of FIG. 8 is a method for creating an artificial tidal flat composed of the above-mentioned tidal flat covering material, and the content of coarse sand (particle size: 0.85 to 2 mm) is less than 20%, and the sand content (grain) Coarse sand (particle size 0. 2mm) using a sand mixing device for sandy soil with a content of 60% or more and a fine fraction (particle size less than 0.075mm) content of less than 40%. This is an artificial tidal flat sand covering method in which the above-mentioned flat tidal sand covering material is prepared by mixing 85 to 2 mm) and then dropped at a predetermined position.

  As shown in Fig. 8, on the trolley, in the local soil supply line, the local soil collected in the artificial tidal flat construction area is transported by a ship carrier and sent to the quantitative feeder by the backhoe. Carry it by ship and send it to the quantitative feeder with backhoe, mix the local soil and coarse sand from each quantitative feeder with a kneader (sand mixing device) so that the content of coarse sand will be 20-50%, then flow Move to the input location with the tapping conveyor and input.

  As described above, in FIG. 8, the tidal flat covering material obtained by mixing the local soil and coarse sand with the local soil supply line, coarse sand supply line and kneading machine on the trolley is placed at the artificial tidal flat formation position. An artificial tidal flat is created by moving and dropping.

  The tidal flat sand covering method in FIG. 9 is a method of creating artificial tidal flats or modifying natural tidal flats by spraying the above-mentioned tidal flat sand covering materials on site, and has a coarse sand content of less than 20% and sand. The surface of the tidal flat is covered with the above-mentioned sand by spraying coarse sand on the surface of the tidal flat composed of sandy soil having a fine content of 60% or more and less than 40%. It is a sand-capping method that modifies materials or constructs artificial tidal flats.

  As shown in Fig. 9, on the trolley, coarse sand is carried by an earth ship and supplied to a jet conveyor (sand spreader) by a backhoe, and coarse sand is sprayed to the original position (reformation target position or artificial tidal flat formation position). To do. In this way, in FIG. 9, coarse sand is sprayed on the natural tidal flat or artificial tidal flat from the top of the trolley, so that the tidal flat surface part is modified to the above-mentioned sand covering material or the artificial tidal flat is formed.

  As described above, according to the tidal flat covering method of the present embodiment, it is possible to create an artificial tidal flat in an environment where floating larvae are easy to settle, or to improve a natural tidal flat into an environment where floating larvae are easy to settle. At the same time, in the tidal flat, the optimum environment can be maintained in the life cycle of the clams from the floating larval stage to the bottoming stage to the juvenile stage to the adult clam stage. For this reason, the most important thing for the sustainable habitat of clams is the formation of new recruitment groups, but it can promote the settlement of clams floating larvae and increase the new recruitment groups of clams. Increasing the amount can increase the amount of clam resources.

  <Fourth Embodiment (Tidal Flat Covered Structure)>

  FIG. 10 is a sectional view for explaining a tidal flat covering structure of a double layer covering type according to the fourth embodiment. FIG. 11 is a cross-sectional view for explaining another tidal flat covering structure (having a coarse sand pool) according to the fourth embodiment. FIG. 12 shows an example of planar arrangement (at low tide) of the tidal flat cover structure (having a coarse sand pool) in FIG. 11, a dotted type (a), a right angle type (b), a parallel type (c), and a lattice type (d). It is a top view for demonstrating. FIG. 13 conceptually illustrates the effects of the clam floating larval stage (a), clam juvenile stage (b) and clam adult stage (c) in the tidal flat having the tidal flat covering structure of the fourth embodiment. FIG.

  The tidal flat covering structure of the double layer covering sand type shown in FIG. 10 has a coarse sand content (particle size 0.85 to 2 mm) content of less than 20% and a sand content (particle size 0.075 to 2 mm) content 60. %, And coarse sand that is the optimal particle size for the clam floating larvae to settle on the tidal flat surface layer composed of sandy soil with a fine particle content (particle size less than 0.075 mm) of less than 40% (Particle diameter 0.85 to 2 mm) is formed by spraying the entire surface with a layer thickness of about 3 cm or less.

  In the tidal flat cover structure of the double layer cover type of FIG. 10, the floating larva 1 having a shell length of about 0.25 mm settles on the rough sand on the surface of the coarse sand layer B, and the juvenile shellfish 2 has a shell length of about 0.25 mm. When growing in coarse sand and growing to a shell length of about 15 mm, the coarse sand is submerged into sandy soil composed mainly of fine sand to medium sand (submersible sand), and the adult shellfish 3 is grown in sandy soil. The clams move vertically as they grow.

  It is said that the clam has a habitat depth of about 1 to 2 times the shell length. By setting the layer thickness of the coarse sand to within 3 cm, the depth of the clams from the surface of the tidal flat to the habitat depth of juvenile shells 2 with a shell length of less than 15 mm Since the range can be rough sand, the optimum environment from the bottom of floating larvae 1 to the growth of juveniles 2 can be prepared. In addition, by leaving a sandy soil mainly composed of fine sand (particle size 0.075 to 0.25 mm) to medium sand (particle size 0.25 to 0.85 mm) having a small content of coarse sand under the coarse sand. The optimum environment from the growth of the juvenile shell 2 to the growth of the adult shell 3 can be maintained.

  In addition, when it is difficult to finish the tidal flat cover structure of FIG. 8 by sea construction, after calculating the predetermined amount of soil that the rough sand thickness of the whole tidal flat is within about 3 cm, It can be constructed by spreading in each plane arrangement as shown in FIG. 12 and taking time until it is evenly distributed using natural erosion effects such as tides, waves, and rainfall.

  Next, the tidal flat cover structure shown in FIG. 11 is a tidal flat surface layer composed of sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine particle content of less than 40%. It is configured to have a plurality of coarse sand pools by spraying a plurality of areas with coarse sand having an optimum particle size for the clam floating larvae to settle at the section.

  In the tidal flat cover structure having a coarse sand pool in FIG. 11, the floating larva 1 having a shell length of about 0.25 mm settles on the coarse sand in the coarse sand pool C, and the juvenile shell 2 has a coarse sand from a shell length of about 0.25 mm. When growing in the reservoir C and growing to a shell length of about 15 mm, the coarse sand reservoir C moves to sandy soil mainly composed of fine sand to medium sand, and the adult shell 3 grows in sandy soil, The clams move horizontally as they grow.

  By dispersing the coarse sand pool C in multiple areas, the optimal environment (floating sand pool) from the bottom of the floating larva 1 to the growth of the juvenile 2 and the growth of the juvenile shell 2 in the same sea area 3 can be interspersed with the optimal environment (fine sand with a small content of coarse sand to sandy soil mainly composed of medium sand) until the growth of No.3. it can.

  In addition, the tidal flat covering structure which has a rough sand reservoir of FIG. 11 can be constructed by, for example, spraying rough sand in a limited area by the tidal flat covering method (original position spraying method) of FIG.

  Further, as shown in FIGS. 12 (a) to 12 (d), the coarse sand pool in the tidal flat cover structure of FIG. 11 has a high tide level (HWL) shore side and a low tide level (LWL) based on the average tide level (MWL). ) On the tidal flats on the shore and shore.

  The coarse sand pools are arranged in a plane as shown in FIG. 12 (a), arranged almost perpendicular to the shore as shown in FIG. 12 (b), or as shown in FIG. 12 (c). They can be arranged almost parallel to the shore or arranged in a lattice shape as shown in FIG.

  In addition, as shown in FIGS. 12 (a) to 12 (d), the coarse sand pool can be provided in various patterns throughout the tidal flat in terms of construction, but the most promising effect is provided in an area below the average tide level. That is. In other words, by forming a coarse sand pool in the tidal flat surface on the offshore side with reference to the mean tide level (MWL), the coarse particle size that is optimal for the settlement of floating clam larvae in places where there is little fluctuation in water temperature and salinity. Sand can be placed, and the survival rate after landing is high.

  In the tidal flat with the tidal flat cover structure of the present embodiment, compared to the rough sand and the local soil, during the floating larval period of clams, as shown in FIG. There are many bottom individuals, and clams have a large number of surviving individuals in the order of coarse sand and main cover sand structure as shown in Fig. 13 (b) during the juvenile period, but as shown in Fig. 13 (c) during the adult period. In addition, this surviving sand structure has the largest number of surviving individuals.

  As described above, the tidal flat covering structure of the present embodiment can maintain an optimum environment in the life cycle of the clam from the floating larva stage to the bottoming stage to the juvenile stage to the adult clam stage, and the floating larvae can be worn. The bottom quality environment that is easy to bottom can be maintained. For this reason, the most important thing for the sustainable habitat of clams is the formation of new recruitment groups, but it can promote the settlement of clams floating larvae and increase the new recruitment groups of clams. Increasing the amount can increase the amount of clam resources.

  In the tidal flat cover structure of the present embodiment, the desired tidal flat benthic organisms are limited to clams, and by focusing on the choice of the landing location of clams, by utilizing the coarse sand effective for floating larva settlement, An optimal environment can be provided in the clam life cycle.

  Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to the examples.

  This example is a demonstration experiment conducted in an actual sea area. In other words, we set up tidal flat sand-covering materials with different particle sizes in the actual sea area, and conducted demonstration experiments to clarify the particle size selectivity of clams floating larvae.

  The respective particle sizes of Examples 1 to 6 of the experimental cases are shown in the following Table 1, and the particle size accumulation curves of Examples 1 to 6 are shown in FIG. In addition, the local soil of Example 6 used the sand of the tidal flat where many clams actually live.

The experimental results are shown in FIG. From the experimental results shown in FIG. 15, the number of juvenile shells per cm ^{3 of} covered sand was confirmed to be the largest in the coarse sand of Example 4 (particle diameter: 0.85 to 2 mm). (Particle size 0.85 to 2 mm) is considered to be the optimum particle size for the bottom of the clam floating larvae. Also, regarding the settlement of floating larvae, it was found that sand collected from tidal flats where a lot of clams actually live is not always optimal.

  As described above, the best mode for carrying out the present invention has been described. However, the present invention is not limited to these, and various modifications are possible within the scope of the technical idea of the present invention. For example, the planar arrangement of the coarse sand pool is not limited to the shapes shown in FIGS. 12A to 12D, but may be other planar arrangements.

Non-Patent Document 1 (“Selection field of clam larvae and distribution in Mikawa Bay” Shigeaki Yanagibashi, Fisheries Engineering Vol. 29 (1), pp. 55-59, 1992) It is the figure (b) for demonstrating the graph (a) which shows a survey result, and the number-of-bottom population survey of a clam larva. It is a figure which shows a mode that a clam juvenile stretches a foot thread and affixes it on a soil particle. It is a figure for demonstrating the relationship between the growth environment of a clam and a particle size distribution which the present inventors put together with reference to the conventional research example. It is a figure which shows the example of the particle size accumulation curve of the tidal flat covering sand material by 1st Embodiment. It is a figure for demonstrating the effect of the clam floating larva stage (a), clam juvenile stage (b), and clam adult stage (c) in the artificial tidal flat constructed with the tidal flat covering material of 1st Embodiment. . It is a figure which shows the example of the particle size accumulation curve of the tidal flat covering material in the tidal flat formation method by 2nd Embodiment. It is a figure which shows the example of the particle size accumulation curve of the tidal flat covering material in another tidal flat formation method by 2nd Embodiment. It is a figure for demonstrating the tidal flat covering method (pre-mixing system) by 3rd Embodiment. It is a figure for demonstrating another tidal flat sand covering method (original position spraying method) by 3rd Embodiment. It is sectional drawing for demonstrating the tidal flat covering sand structure of the double layer covering sand type by 4th Embodiment. It is sectional drawing for demonstrating another tidal flat covering structure (it has a coarse sand pool) by 4th Embodiment. As a planar arrangement example (at low tide) of the tidal flat covering structure (having a coarse sand pool) in FIG. 11, a dotted type (a), a right angle type (b), a parallel type (c), and a lattice type (d) will be described. FIG. It is a figure for demonstrating the effect of the clam floating larva stage (a), clam juvenile stage (b), and clam adult stage (c) in the tidal flat which has the tidal flat cover structure of 3rd Embodiment. is there. It is a figure which shows each particle size accumulation curve of Example 1 thru | or 6 in a present Example. It is a figure which shows the experimental result in a present Example. It is a figure which shows the particle size accumulation curve of the sandy soil (local soil) of the tidal flat of the whole country.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Floating larva 2 Larvae 3 Adult shellfish B Coarse sand layer C Coarse sand reservoir

Claims (14)

  By mixing coarse sand with sandy soil, the coarse sand content after mixing is 20-50%, the passing mass percentage of particle size 0.85mm is 50-80%, and the passing mass percentage of particle size is 2mm. A tidal flat covering material characterized by 70 to 100%.   The tidal flat sand covering material according to claim 1, wherein the tidal flat sand covering material is suitable for clam growth.   By mixing coarse sand with sandy soil, the mixed tideland covering sand material has a coarse sand content of 20 to 50%, a passing mass percentage of 50 to 80% with a particle size of 0.85 mm, and a particle size of An artificial tidal flat is constructed so that the passing mass percentage of 2 mm is 70 to 100%.   By mixing coarse sand with sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine-grain content of less than 40%, the mixed tideland covering sand material becomes coarse sand. An artificial tidal flat is constructed so that the content ratio is 20 to 50%, the passing mass percentage is 50 to 80% with a particle size of 0.85 mm, and the passing mass percentage is 70 to 100% with a particle size of 2 mm. Tidal flat construction method. For sandy soil having a coarse sand content of less than 20%, a fine particle content of less than 30%, a passing mass percentage of 2 mm in particle size of 80 to 100%, and an average particle size D ₅₀ = 0.15 to 0.6 mm By mixing coarse sand, the mixed tideland covering sand material has a coarse sand content of 20 to 50%, a passing mass percentage of 50 to 80% with a particle size of 0.85 mm, and a passing mass with a particle size of 2 mm. A tidal flat construction method characterized by constructing an artificial tidal flat so that the percentage is 70 to 100%.   Coarse sand is sprinkled on the surface of the tidal flat composed of sandy soil with a coarse sand content of less than 20%, a sand content of 60% or more, and a fine grain content of less than 40%. To create an artificial tidal flat.   The method for creating a tidal flat according to any one of claims 3 to 6, wherein the artificial tidal flat is suitable for clam growth.   The coarse sand is mixed by using a sand mixing device with sandy soil having a coarse sand content of less than 20%, a sand content of 60% or more, and a fine particle content of less than 40%. A tidal flat sand-capping method comprising preparing a tidal flat sand-capping material and dropping it into a predetermined area of an artificial tidal flat.   Use a sand spraying device to spray coarse sand on the tidal flat surface layer composed of sandy soil with a coarse sand content of less than 20%, a sand content of 60% or more, and a fine grain content of less than 40%. The tidal flat covering method is characterized in that the tidal flat surface layer is modified to the tidal flat covering material according to claim 1.   The tidal flat construction method according to claim 8 or 9, wherein the tidal flat by the tidal flat covering method is suitable for clam growth.   Coarse sand is sprinkled on the surface of the tidal flat composed of sandy soil with a coarse sand content of less than 20%, a sand content of 60% or more, and a fine grain content of less than 40%. A tidal flat cover structure in the form of double-layer cover sand.   Coarse sand is spread over multiple areas on the tidal flat surface layer composed of sandy soil with a coarse sand content of less than 20%, a sand content of 60% or more, and a fine grain content of less than 40%. A tidal flat covering structure characterized by forming a coarse sand pool.   The tidal flat sand-covering structure according to claim 12, wherein the plurality of coarse sand pools are formed in an area below the average tide level of the tidal flat surface. The tidal flat covering structure according to claim 11, 12 or 13, wherein the tidal flat by the tidal flat covering structure is suitable for clam growth.

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