水研センター研報，第32号，51−60，平成22年
Bull. Fish. Res. Agen. No. 32, 51‑60, 2010

Introduction of Isoyake Recovery Guideline (Fisheries Agency, Japan)
Hisami KUWAHARA＊1, Osamu HASHIMOTO＊2, Akito SATO

＊2and Daisuke FUJITA＊3

Abstract : Reduction of seaweed beds called isoyake has become a serious problem inmost of coastal prefectures in Japan. To restore seaweed beds, Fisheries Agency carried out
a national project in cooperation with 16 prefectures and 19 specialists from fiscal 2004 to2006. Isoyake Recovery Guideline was published in February 2007. Main users are fishermen
who should be at the core of the restoration. Main theme is the control of intensive grazing
by sea urchins and herbivorous fishes. Major topics are as follows.: (i) adaptive management
to lead to successful reforestation through adaptive learning and feedback, (ii) flow chart for
selecting techniques through 6 simplified categories which minimize trial and error, (iii) organized cooperation to support fishermen by volunteers, citizens, enterprises, specialists andlocal governments, (iv) useful viewpoints for detecting decrease of seaweeds and finding critical factors in recovering seaweed beds, (v) explanation of each technique systematized as aflow chart, (vi) promotion of effective use of herbivores to remove them from the habitat andso on.
Key words : guideline, barren ground, isoyake, adaptive management, herbivorous fish, sea
urchins

Isoyake recovery project

was published in February 2007 (Fisheries Agency,2007).

Seaweed beds provide marine life with foodsources and habitat, including breeding and nursery

Concept of guideline

grounds, thus they are important communities tomaintain fishery resources. However, reduction of

It has long been said that there are various

seaweed beds called isoyake has become a serious

factors causing isoyake including elevation of water

problem in most coastal prefectures in Japan. It

temperature, and decrease of nutrients. (Kuwahara

is said that the area of seaweed beds that have

2006a). According to the questionnaire survey

disappeared are more than thousand hectares.

to local government in 2005, reduction of seaweeds

To restore seaweed beds, Fisheries Agency

was reported from most of the coastal prefectures

carried out a national project in cooperation withand overgrazing by herbivores (sea urchins and/or

16 prefectures and 19 specialists from fiscal 2004 to

herbivorous fishes) is the most common causative

2006. This project reviewed restoration attempts

agent of isoyake (Kuwahara

for isoyake reported in previous literatures, andthe major theme of the guideline is how to control

tested them with some newly developed techniques

grazing by herbivores.

, 2006b). Therefore,

in the field. In addition, various issues on isoyake

Fig. 1 illustrates the situation of isoyake inwere discussed at 2 national conferences and 2 local

Japan. When grazing on seaweeds by herbivores

committees in a year. As a summary of the review

exceeds the growth of seaweeds, the balance will

and these meetings, the Isoyake Recovery Guideline

incline clockwise leading to isoyake. The clockwise

2010年 月 日受理（Received on July 1. 2010）＊1
National Research Institute of Fishery Engineering, Fisheries Research Agency, 7620-7 Hasaki, Kamisu, Ibaraki 314-0804, Japan＊2
Fisheries Agency, 1-2-1 Kasumigaseki, Chiyoda, Tokyo 100-8907, Japan＊3
Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato, Tokyo 108-8477, Japan

Hisami KUWAHARA, Osamu HASHIMOTO, Akito SATO and Daisuke FUJITA
movement of the balance may be strengthened

some practical techniques are selected. with the aid

by other changes in backgrounds such as globalof a systematic flow chart of techniques. In section

warming and anthropogenic destruction ofF, restoration is carried out using the techniquemarine resources. In the unbalanced situations,on the target barren ground. The techniques

disappearance of seaweeds and the consequentshould be selected considering social contexts inbarren state will enlarge and maintain for a

the fishermen s community because of easiness tolong time. Though the algal growth and grazing

repeat. After the action, as denoted in section G inshould be rebalanced essentially by improving

Fig. 2, it is necessary to monitor the successional

the background conditions, we have few specificchanges on the treated barren ground. Results

methods for the improvement at present. Therefore,

obtained from monitoring are assessed throughthough restoration of seaweed beds should besection H where the data is compared with the goal

started from accessible areal size such as 100m ×of the plans in section C. If the achievement of the100m, this guideline shows the effective and efficient

goal is confirmed, the new goal should be aimed

methods to recover seaweed beds by decreasing

by starting from section C. If the goal has not been

herbivores and by increasing seaweed production.

achieved yet, restarting from section B is needed
to clarify the reason of the failure. After the reason

Adaptive management in recovery from isoyake

was clarified, the new approach can be started.

In this guideline, adaptive management isadaptive learning and feedback control in theintroduced. This approach consists of eight sections

restoration of seaweed beds, and they give us

from A to H (Fig. 2). In section A, the occurrence

valuable information on further management forof the isoyake is detected and diagnosed. If therocky shore ecosystems.

Cycles of trials and monitoring to establish thecharacter of isoyake is enumerated, we proceed toSection B where the factor(s) inhibiting seaweed

Flow chart of processes in isoyake recovery

bed formation is identified using simple experiments
or surveys in the field. In section C, the goal of theFig. 3 shows a flow chart of processes sections

recovery is set with the reference of records offrom A to H. This flow chart helps us to findseaweed bed distributions in the past. In section D,techniques to minimize the cost and labor ofmethods to remove or alleviate the inhibiting factor
identified in section B are examined. In section E,

Fig. 1. Situation of isoyake in Japan.

Fig. 2. Adaptive management in isoyake recovery

Introduction of Isoyake Recovery Guideline (Fisheries Agency, Japan)

Fig. 3. Flow chart of processes in isoyake recovery

Detection of isoyakerequired for trial and error. The techniques werecategorized into 25 groups according to theircharacteristics;. These techniques were extracted

Fig. 4 shows section A that proposes twofrom a database with more than 1000 papers indiagnostic methods for isoyake. The first method

domestic journals on restoration of seaweed beds

is the detection from benthic seascapes recorded

published from 1970 to 2005 (Kuwahara2006c).

at the fixed monitoring site every year. The pair ofThe flow chart is composed of two main branches;

photos (Fig. 4a, b) taken in Ofunato district, Iwate

reduction of grazing by herbivores and stock

Prefecture, is an example that shows isoyake caused

enhancement of seaweeds. The former main branch

by sea urchins. Photos taken on the sea area will

was divided into two branches, for sea urchins andgive us valuable information about not only thefor herbivorous fishes, which are comprised of 10

presence or absence of isoyake but the process

and 7 techniques, respectively. In each branch, theof deterioration of the seaweed bed. The second

techniques are categorized into 3 groups, removal,

method is the use of statistical data of seaweed

dispersion and defense. The latter main branch isand/or and the related herbivores. The figure (Fig.

composed of 8 techniques categorized into 4 groups,4c) shows the relationship between catch yields

planting, reducing sedimentation, fertilization andof a canopy forming kelp,deploying substrates.

abalones (andspp.) in Hainan district, Shizuoka

Prefecture. Catch yields ofdecreased in

the 1990ʼs and followed by the depletion in catchyields of abalone. However, each fluctuation cannotHisami KUWAHARA, Osamu HASHIMOTO, Akito SATO and Daisuke FUJITA
1. Using data of benthic landscapesa)(Ofunato district in Iwate Prefecture)

bed before deforestation(October, 2001)b) Persistence of urchin barren(October, 2003)

2. Using statistic of catch amount(Hainan district in Shizuoka Prefecture)c) Relationship betweenand abalone

Fig. 4. Two methods for detection of isoyake

be easily reverted as shown in the Fig. 4c.
Specification of limiting factor for reforestation
In section B, the factors inhibiting growth ofseaweeds should be specified. At first, basic fieldsurveys should be carried out using cross-shore
observations and the profile of sea bottom,
characteristics of sediment, spatial distribution,
species composition, coverage of seaweeds anddensity of herbivores (the top figure of Fig. 5).
Through the survey, the limiting factor can bespeculated. Otherwise manipulative experiments
should be planned. The bottom figure of Fig. 5
shows an example of a cage experiment. Twogroups of seaweeds are transplanted on theexperimental barren ground; one is protected fromgrazing by herbivores with the cage, the other is
exposed to the grazers. If seaweeds in the cageremain while seaweeds outside disappear, grazing

Fig. 5. Specification of limiting factors

Introduction of Isoyake Recovery Guideline (Fisheries Agency, Japan)
by herbivores can be one of the inhibiting factors.

defense and dispersion.

In addition, this experiment provides us some otherRemoval includes capture by divers, collecting

useful information. If seaweeds never deteriorate

from boat, baskets and pump. Removal by diving isafter transplantation, one can infer that ambient

the most efficient among the 4 techniques, but it also

water conditions including nutrients and light haverequires much labor and cost. Removal by boating

hardly affect growth of the seaweeds. Furthermore,

and basket needs skill and is difficult to remove sea

if juveniles of the target seaweed appear withinurchins hiding under stones. Removal by pump is

the cage, supply of seaweed spores can be

to be developed because of its easiness for handlingconfirmed. It is important to find out the limiting

and low cost.

factors for seaweeds before one decides immediate
countermeasures for isoyake.

Defenses include rope, fence, increase of flow
velocity and improvement of substrata. The
suspended rope is effective along exposed coasts

Techniques to control grazing by sea urchinsbecause sea urchins are shaken off by wave action.
For enclosure, fence such as loosely folded or buoyed

Fig. 6 shows techniques to control the density

gill nets are used. Furthermore, changing their(hence grazing pressure) of sea urchins. Theseposition is also the way that destabilize footholds

techniques are categorized into 3 groups, removal,for sea urchins. But biofouling and destruction byFig. 6. Techniques to control density of sea urchinsHisami KUWAHARA, Osamu HASHIMOTO, Akito SATO and Daisuke FUJITA

Fig. 7. Techniques to control grazing by herbivorous fishes

Fig. 8. Techniques for stock enhancement of seaweeds

waves disable long-term use of this method. Theurchins and help seaweed grow. The relationshipelevation of the bottom level using blocks or stones

between the wave action and feeding activity ofenhances the wave action on them. Enhancedsea urchins is discussed by Kawamata in this issue.

wave motions suppress feeding activity of sea

The improvement of substrata is a way to modify

Introduction of Isoyake Recovery Guideline (Fisheries Agency, Japan)

Fig. 9. Examples of effective use of herbivores

the surface microtopography of stones or blocks towith other species. According to information fromincrease the refuge of seaweed juveniles.

divers, herbivorous fishes feed much more on

Dispersion is used to decrease the density of sea

seaweeds in uni-algal population than in multispecies

urchins by loosening their aggregations by feeding

communities. Studies about selectivity on seaweed

harvested seaweeds.

species in herbivorous fishes were started recently.
Dispersion is a method that keeps fish away fromTechniques to control grazing by herbivorous fishes

the seaweed bed by generating blast noises in thewater. Wakayama Prefecture Fisheries ExperimentFig. 7 shows techniques to control grazing by

Station is developing this method (Yamauchi

herbivorous fish. Removal includes capturing with2006). Browsing by herbivorous fish has been known

gill net, fixed shore net and fishing. Herbivorousfor more than a century but has become serious

fishes have often been recorded among the by-catchonly recently in Japan. Ecological information is notin net fishing (Akiyama, 2007). Recently, the active

enough to develop effective control of herbivorous

removal of herbivorous fishes has been started byfishes. The latest information on herbivorous fishes

fishing. Defenses include fences, increase of flow

is shown by Yamaguchi in this issue.

velocity and combination. Seaweeds in the fence
are protected from browsing by fishes. However,Techniques for stock enhancement of seaweeds

the seaweed beds cannot extend out of the fence.
Therefore, further improvement is needed to enable

Fig. 8 shows techniques for stock enhancement

seaweeds to grow outside the fence. The combinationof seaweeds. Planting includes transplantation ofis a trial to transplant the target on seaweed species

adult seaweeds, supply of spores and embryos andHisami KUWAHARA, Osamu HASHIMOTO, Akito SATO and Daisuke FUJITA

Fig. 10. Examples of the activity by Shiriya Fisheries Cooperative inAomori Prefecture.

Fig. 11. Examples of the restoration activity by Nagoya Fisheries
Cooperative in Oita PrefectureIntroduction of Isoyake Recovery Guideline (Fisheries Agency, Japan)
Practice of Isoyake recovery guideline

cultured juveniles. In the transplantation of adultseaweeds, fixed adult seaweeds with adhesive
anchors on the bottom. The simpler method is to

Our project team travelled all over the country to

throw adult seaweeds with weights from the sea

inform people about the guideline and to encourage

surface. Cultured juveniles are transplanted withthem to practice the procedures given in theropes or plates where embryos of seaweed grow.

guideline. The core of this activity is giving adequate

Supply of spores or embryos includes mesh bag withtechnical support to fishermen who are trying toadult seaweeds, middle layer net with seaweeds

start restoration of seaweed beds in isoyake area.

and catcher of drifting seaweeds floated near theThis activity has been carried out in about 15 areas,sea surface. This method is explained by Yatsuya

where fishermen positively work on recovery fromin this issue. The influence of sedimentation and/orisoyake. In each area, a local consultation groupsuspended particles has been reported in some bay

was organized to decide the plan. In this group,

and inland waters, and is becoming more serious

practitioners of local government and scientificrecently. Removal of suspended particles may be

experts were included. We started new attempts

needed to decrease light attenuation in the water,in which that fishermen work together with people

but the sources and pass way of the particles shouldfrom other sectors such as universities and highbe clarified to reduce the inflow.

schools. This practice is explained by Taino in thisissue.

Effective use of herbivores

Fig. 10 shows an example of the activity by
Shiriya Fisheries Cooperative in Aomori Prefecture.

Utilization of herbivores caught by fishermen is

In this area, 1-3 hectares per year of kelp

very important for the effective and sustainable(management of the wild and restored seaweed beds.

since professional divers employed by fisherman

The left of Fig. 9 is an example of simple pen-culture

carried out removal of sea urchins. In 2008,in a fishing port for sea urchins removed fromfishermen manifested the removal of sea urchins forurchin barrens. This example has been carried out

themselves. Therefore, they were trained to use dry

at Setana district in Hokkaido. At the beginningsuits and to practice removal of sea urchins. Theyof the culture, sea urchins are fed with meat ofmanaged to implement a large-scale sea urchinfishremoval project.

caught abundantly in) beds have been recovered

this region, and then cultivated kelps are givenFig. 11 shows the case of Nagoya Fisheries

to enhance their flavor. Sea urchins reared in

Cooperative in Ohita Prefecture. Seaweed bed in this

this method mature faster than wild individuals;

region has been heavily grazed by both sea urchins

therefore their gonads can be sold at a good priceand herbivorous fish. The fishermen made cages

early in the season.

to protect seaweed from fish grazing and fences toIn Japan, custom of eating herbivorous fishes areprotect from herbivorous fish. In this area, there arelimited to local areas. The right of Fig. 9 shows aa lot of fishermen divers because they use SCUBAparty for sampling the taste of rabbit fishdiving gears in their daily jobs. Therefore, they. In general, rabbit fish is disliked becauseof the distinctive smell of the fish meat and a toxic

could complete sea urchin removal by themselves
and they set nets and cages on the sea bottom.

spine in their dorsal fins. However, the dishes ofReferences

rabbit fish had good evaluation when cooked wellwithout damaging the viscera in the sampling party.
To popularize the taste for its commercialization,
more sampling parties should be organized.

Fisheries Agency, 2007: Isoyake recovery guideline.
213 pp. (in Japanese)
Akiyama S. (2007) Discards in Large-Scale Set Net inTateyama Bay, Nippon Suisan Gakkaishi, 73(6),1103‑1108.

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