Influence of Historical Exploitation and Recovery of Biological Resources on Contemporary Status of...

ISSN 2079�0864, Biology Bulletin Reviews, 2012, Vol. 2, No. 6, pp. 460–478. © Pleiades Publishing, Ltd., 2012.Original Russian Text © I.N. Bolotov, Yu.V. Bespalaya, A.A. Makhrov, P.E. Aspholm, A.S. Aksenov, M.Yu. Gofarov, G.A. Dvoryankin, O.V. Usacheva, I.V. Vikhrev, S.E. Sokolova,A.A. Pashinin, A.N. Davydov, 2012, published in Uspekhi Sovremennoi Biologii, 2012, Vol. 132, No. 3, pp. 239–258.

460

Freshwater pearl mussel (Margaritifera marga�ritifera L.) is closely connected to Atlantic salmon(Salmo salar L.) via a parasitic relationship [42]. Thelarvae of this freshwater bivalve species (glochidia)develop on salmon gills, as well on the gills of browntrout (Salmo trutta L.) [24]. Previously, the hypothesisof symbiotic interrelationships between freshwaterpearl mussel and salmon was proposed, and glochidiawere proposed as a factor in the life span and cycle ofsalmon [25, 26]. Later, it was proved that there were nosuch relationships between bivalve larvae and fish, andthese relationships were purely parasitic [42]. The sta�tus of freshwater pearl mussel populations in NorthernEurope was discussed in a number of publications thatcovered sites in Russia [7, 10, 24, 43, 49, 79, 85], Fin�land [86, 88, 90], Norway [73], Sweden [72, 74, 78],Denmark [91], Ireland [76], and many other coun�tries. The number of publications on Atlantic salmonand brown trout is also significant [13, 34, 35, 40].Many publications name the specificity of managingand sustaining natural resources as a major complex

factor that affects the status of freshwater pearl musselpopulations. Usually, the decrease in salmonid popu�lations in rivers caused by different reasons is named asa limiting factor [80]. There are some data on positiveeffect of salmon aquaculture on the freshwater pearlmussel population status [7]. Some publicationspresent evidence on the possible consequences of thehistorical management of natural resources, in partic�ular on the effect of pearl fishing on the populationdensity of molluscs [24]. Nevertheless, a qualitativeassessment is usually only made without regard to thepopulation density of the host fish. Archives are alsoinvolved quite obscurely in this type of analysis, butthese sources are necessary when reconstructing his�torical fishery activities, fish farming, and pearl fish�ing. With regard to this type of data, the analysis wasonly performed for the Varzuga River [24, 27] andsome rivers of Karelia [43].

The goal of the present study is to assess the eco�nomic activities linked with managing and sustainingbiological resources on the status of freshwater pearl

Influence of Historical Exploitation and Recovery of Biological Resources on Contemporary Status of Margaritifera margaritifera L.

and Salmo salar L. Populations in Northwestern RussiaI. N. Bolotova, Yu. V. Bespalayaa, A. A. Makhrovb, P. E. Aspholmc, A. S. Aksenova,

M. Yu. Gofarova, G. A. Dvoryankind, O. V. Usachevaa, I. V. Vikhreva,S. E. Sokolovaa, A. A. Pashinina, and A. N. Davydova

a Institute of Environmental Problems of the North, Ural Branch, Russian Academy of Science, Arkhangelsk, Russiab Severtsov Institute of Ecology and Evolution, Russian Academy of Sciences, Moscow, Russia

c Bioforsk�Norwegian Institute for Agricultural and Environmental Research, Svanhovd, Svanwick, Norwayd Knipovich Polar Research Institute of Fisheries and Oceanography, Northern Branch, Arkhangelsk, Russia

e�mail: [email protected]

Abstract—The influence of the historical exploitiation and recovery of biological resources on populationsof freshwater pearl mussel and salmon was studied in the Kozha river (Onega River Basin). The freshwaterpearl mussel was characterized by a low population density (0.09 ind./m2, on the average) and number ofrecruits. The role of the anthropogenic factor in the population is negligible; the effect of the pearl fishing isnot observed. The dramatic decrease in the number of Atlantic salmon in the Onega River Basin in the late20th century is a major reason for the slowed down reproduction of the freshwater pearl mussel. The secondfactor is the reconstruction of the Onega salmon hatchery in 1984, which led to a decrease in the juvenilesalmon population density below the critical level on spawning and nursery grounds. As a result, molluscreproduction has stopped. An artificial increase in the number of recruits must be developed in order to pre�serve the salmon population in the Onega River Basin. It is also necessary to forbid salmon fishing, includingfishing migratory paths (with the exception of trapping for hatchery needs and traditional harvesting per�formed by locals in historical settlements).

Keywords: freshwater pearl mussel, Margaritifera margaritifera, Atlantic salmon, Salmo salar, populations,pearl, fish culture, fishery, nature management, North�Western Russia

DOI: 10.1134/S2079086412060035

BIOLOGY BULLETIN REVIEWS Vol. 2 No. 6 2012

INFLUENCE OF HISTORICAL EXPLOITATION 461

mussel and salmon populations in northwestern Rus�sia with regard to their historical roots. Taking intoaccount the most recent theories [24, 43, 87], as themajor factors, we have chosen the dynamics of thenumber of Atlantic salmon breeders, salmon aquacul�ture, and the history of pearl fishing. The research wasperformed for the Kozha River, one of the tributariesof the Onega River. This river is an important site ofpearl fishing in northwestern Russia, which is reflectedin the significant number of archives and publications.However, the Kozha River plays a huge role in recruit�ing the Onega school of Atlantic salmon [61], andthere is a great deal of historical information aboutsalmon catches in this river and modern data on thesalmon population status; moreover, one of the firstsalmon hatcheries was built here. Only information onthe hydrochemical properties of the river water, dataon bottom sediments, and the freshwater pearl musselpopulation was missing in order to generalize the pat�tern with regard to the historical data. Anthropogenicload (pollutants or consequences of timber�rafting)may have a significant effect on the hydrobionts thatinhabit the riverine ecosystems. The information wasobtained during the international expedition per�formed in September 2010 by the Institute of Ecolog�ical Problems of the North, Ural Branch, RussianAcademy of Science.

REGION OF STUDIES, MATERIAL,AND METHODS

Physical and geographical characteristics of thestudied area. The Kozha River Basin is located west ofthe Onega River on the eastern slope of the VetrenyiPoyas range. The range is constructed with mostly thecrystallized shivers with basalt intrusions and is aPalaeoproterozoic rift belonging to the eastern edge ofthe Baltic Shield (Fennoscandia) [36, 37]; its junctionwith the Eastern European Platform takes over OnegaRiver bed. The studied area belongs to the temperateclimatic zone. Average annual precipitation is 600 mm.January is the coldest month (–12°C), July is thewarmest one (+16°C). The annual temperature differ�ence is 28°C [4, 45]. Firry forests that are typical fortaiga prevail. Kozha River starts from Kozhozero Lakeand belongs to one of the largest left tributaries ofOnega River. The river is 96 km long, and the water�shed area covers 62000 km2 and includes a lot of lakes(Fig. 1). The river is of the mountain type for most ofits length, with a significant number of rifts andgroundsels [47]. The largest groundsels with waterfallsare formed at sites where the water breaks throughbasalt (Padun, Shchurus, and Kyamus waterfalls). Thebeds are mostly sandy pebble, pebble, and stone. Theperiod of snowmelt flooding is 2.5–3.0 months. Theperiod of summer low water lasts from July throughAugust, and the winter low water period starts in Octo�ber–November and lasts for 4.5–6.0 months. InMarch, the flow is minimal.

Methods of studying freshwater pearl mussel popu�lation. Field studies were performed in September of2010 from the head water of the Kozha River(Kozhozero Lake) downstream to its inflow to theOnega River. The research group traveled by boat andstudied ten river sites, where the probability of fresh�water pearl mussel settlements was high, i.e., by visu�ally assessing the hydrological regime taking intoaccount the experience of the same studies on rivers inRussia, Norway, and Finland). Transects 10–30 mlongs and 1–3 m wide (square of 10–300 m2) werechosen with regard to the current, bottom sediments,and depth. A visual search for molluscs was performedat each transect by diving (P.E. Aspholm, O.N. Bespa�lyi). Some transects on shallow areas were studied withan aquascope (Yu.V. Bespalaya). All of the found mol�luscs were sampled and brought to the shore for mea�suring and weighing. The shell measurements wereperformed according to the standard scheme [24]using the digital beam compass (ShTsTs�1�125, Rus�sia) with an accuracy of 0.1 mm. The molluscs wereweighted on Tefal electronic weighing machine. Atotal of 151 specimens were studied. The molluscswere returned to the sampling site immediately afterthe measurements were finished.

Methods of hydrological studies. Hydrologicalstudied were performed for each transect. The bottomsediments were described visually during the molluscsearching. Video recording was also performed at sev�eral sites using a PPV�1 underwater camera (LRCIndel�Partner, Russia). The rate of areas covered bydifferent bottom sediments was assessed. The types ofbottom sediments were defined by the classificationsdeveloped for salmon�inhabited rivers [13]. The depthof the sampling site was measured by a scale stick withan accuracy of 1 cm; the current velocity was assessedby the standard method with a floater and a stop watch[44]. The relative coverage by aquatic vegetation(macrophytes, bryophytes, and algae) was assessed;the plants were taken for further analysis. The plantspecies was defined by PhD E.Yu. Churakova andPhD O.V. Sidorova (Northern Arctic Federal Univer�sity). Submerged timber was searched at each sam�pling site.

Methods of hydrochemical studies (assessment ofthe anthropogenic load of the water). Sampling sitesnos. 1, 2, 6, and 10 were chosen for hydrochemicalstudies. The water temperature, dissolved oxygen, andpH were measured in the field using an Expert�001probe (Russia). The conductivity was measured at+20°C by a conductometer (HANNA Instruments). Amixed water sample was taken at each site according toGOST state standard R 51592�2000. The subsamplesof each water sample were fixed and stored for the fur�ther analysis of chemical oxygen demand (COD) andheavy metal concentrations. These samples were ana�lyzed at the Center for the Joint Use of ScientificEquipment “Critical Technologies of Russian Federa�tion in a Field of Arctic Ecological Safety (Ural

462


BOLOTOV et al.

Branch, Russian Academy of Sciences) and at theArctic Center for the Joint Use of Scientific Equip�ment of the Northern Arctic Federal University. Themethod of ion chromatography (Stayer�CD, Aquilon

scientific�production company, Russia) and capillaryelectrophoresis (Kapel’�104T, Lumex, Russia) wasapplied). COD (the amount of organic compounds inwater) was measured on a Fluorat�02�3M analyzer

Fig. 1. Schematic map of Kozha River. Spawning and nursery grounds of Atlantic salmon are indicated for different areas of thestream.

Igisha River

Kotel groundsel

Yug groundselRashpur groundsel

Syvtuga River

Myalan

ga River

Nesterukha rift

Kal’tz groundsel Koz

ha R

iver

Kyamus groundsel Chopui groundselSivan’ga groundsel

Zheleznye Vorota groundsel

Shchurus waterfallKobylyak groundsel

Koz

ha R

iver

Koz

ha R

iver

Kobylii groundsel Dedov Prud groundsel

Dolgii groundsel

Kurusskoe Lake

Kozhozero

Lake

Krivoi groundselVilen’ga River

Padun waterfall

Scale, km

Legend

Study sites and their nos.Palings for catching salmon, installed in late 19th to early 20th centuryFish�counting boom of Onega

Distribution of spawning and nursery

61.8

37.8

37.3

35.1

51.5

47.8

58.5

54.663.4

9

61.0

69.3

73.6 57.0

73.3 81.969.5

142.3

71.1

103.2 78.7

158.1124.4

168.1

169.9

10

4

56

7

8

40

40

40

20

20

40

60

60

60

8080

120

100

160

160

140

160

140

160

160

140

100

80

141.1

6.114.919.429.729.9

0 1 2 4 6

hatchery (1933 up to now)

ground coverage, %

34.2

3

2

1



(Lumex, Russia). The concentrations of heavy metalswere measured by atomic absorption at AAS novAA 315(Analytik Jena AG, Germany).

Materials and methods of historical data studies.The search for and analysis of various sources on pearlfishing in the Kozha River and salmon fishery andaquaculture was performed. This work included creat�ing a bibliographical database that comprised publica�tions, scientific reports, and unpublished archivessince the mid�19th century. Archives on pearl fishingwere mostly found in the State Archive of ArkhangelskOblast. The data were systematized and generalizedwith regard to historical and geographical approach,which allowed authentic reconstructing of manage�ment and sustaining of the biological resources ofKozha River. In addition, the data on the biologicalcharacteristics of Atlantic salmon in the Kozha River,its catches at the fish�counting boom of the Onegahatchery, and fry release into the river were providedby the Federal State Department Sevrybvod andSevPINRO.

Statistics. The data of morphometric measure�ments were analyzed by the standard statistical meth�ods. The B : Hm ratio was studied based on the mea�surements of shell gibbosity (B) and maximal shellheight (Hm) of freshwater pearl mussel [60]. The size�dependent variability of the B : Hm ratio was studiedwith regard to the shell length (L). The significance ofdefining the mollusc subpopulations that inhabit dif�ferent river sites based on their morphometric data wasassessed by ANOVA (Statistica v. 6.1 software). Onlythe median and variability limits were calculated forhydrochemical parameters due to the small number ofsamples (n = 4). Two types of assessments of the pop�ulation density of freshwater pearl mussel were usedbased on the weighted average (per square unit) andmedian values.

The age of the youngest mollusc specimens in thesamples were calculated by the equation [56]:

y = (0.275x – 0.206) ± 0.254, (1)where y is the mollusc age (years) and x is the shelllength (≤74.5 mm).

RESULTS

Habitats of freshwater pearl mussel population inthe Kozha River: Hydrological and hydrochemicalcharacteristics. The landscape conditions of theKozha River, which are closely connected to the geo�logical structure of the region, predetermine the spec�ificity of this river, i.e., high water velocity, the domi�nance of stone bottom sediment, and the high numberof rifts and groundsels. The depth of the river at thestudied sites varies from 0.5 to 1.5 m. The aquatic veg�etation is patchy. Bryophyte Fontinalis antypireticumand green algae (mostly Rivularia genus) are foulingon stones. Myriophyllum sp., rarely Potamogeton sp.,Ceratophyllum demersum, and others are macrophytes.

Four major types of freshwater pearl mussel habitatswere defined (Table 1; Fig. 2).

1. Riffles are formed by large boulders and charac�terized by rapid water current; the sandy reaches com�prises 30–50% of total area coverage, pebble sedi�ments comprise up to 10%; the stones are fouled bybryophytes (up to 60% of surface); the aquatic plantsare presented poorly (less than 10% of the coverage atsite nos. 3, 4, 7, and 9).

2. Rifts formed by boulders and pebble and charac�terized by rapid water current, where boulders com�prise approximately 45%, pebble comprises 50%, andsands comprise up to 5%; aquatic plants cover up to40% of the area (site no. 6).

3. Pebble rifts are characterized by a rapid watercurrent; the pebble comprises 90%; sandy reachescomprise approximately 10%; and bryophyte foulingcoverage on the stones comprises up to 60% of surface(site no. 5).

4. Stone–sandy rifts are characterized by slowwater current; the sands comprise approximately 80%;pebble comprises 20%; and aquatic vegetation repre�sented by bryophytes, Myriophyllum sp., and greenalgae covers up to 90% of the surface (site no. 10).

The littering of the bottom by sunken logs, which iscommon for many Russian rivers and is caused byfloating drift, was not found at the studied RK sited.The sunken logs that have appeared in the river due tothe falling of natural wood are rare. The mountain�type current and rapid increase in the water level dur�ing the rise in the stream obstruct the formation ofheaps; the latter are usually formed in the secondarychannels between the river islands beside the mainstream.

In the summer and autumn, despite of high con�centration of humic acids, the pH of river water variesfrom 6.9 to 7.3 (Table 2) due to underground waterseeps [55]. The water is characterized by relatively lowtotal mineralization and the water conductivity is 27–34 μS/cm. COD is relatively high, i.e., 30.5–35.9 mgO2/L. Taking into account the low water mineraliza�tion, these high COD values are preconditioned by anelevated concentration of organic compounds (humicacids mostly). The average dissolved oxygen concen�tration is 9.3 mg/L, which refers to an oxygen satura�tion of 85.8–92.7%. The water type may be defined ascalcareous (Ca2+ and Mg2+ cations, 5.1–6.2 mg/L and3.2–3.6 mg/L, respectively) and hydrocarbonate(hydrocarbonates 12.2–15.9 mg/L) by anionic�cat�ionic classification. The ammonium cation concentra�tion varies highly from 0.31 up to 1.04 mg/L, similar tothe concentration of nitrates (0.05–1.38 mg/L). Thewaters of the Kozha River are enriched by Fe cations(0.43–0.52 mg/L). The concentrations of phosphatesand Mn are extremely low; the concentrations of someanthropogenic heavy metals (copper, zinc, cadmium,and lead) were lower than the analytic detection limitswe used.

464


BOLOTOV et al.

Freshwater pearl mussel population density andmorphometric characteristics of molluscs. The popula�tion density of freshwater pearl mussels in the KozhaRiver depends on the sampling site and varies from 0.013up to 1.417 ind./m2 (Table 1); average weighted density is0.09 ind./m2; and the median density is 0.05 ind./m2.The mollusc biomass (wet weight) is 0.85–113.92 g/m2; the average weighted biomass is 7.0 g/m2;and the median biomass is 3.9 g/m2. The molluscswere absent at three sites, i.e., two sites upstream of thePadun waterfall (sites nos. 1 and 2) and at one site inthe middle stream of the river (site no. 8). The distri�butional pattern of freshwater pearl mussel strictlyrefers to the locations of salmon spawning and nurserygrounds.

The shell size of freshwater pearl mussel decreasedsignificantly from the riverhead downstream (Table 3).This characteristic is tracked for all shell parameterswhen the shell length decreases by 13.4%, the maximalshell height decreased by 11.8%, the shell gibbositydecreased by 17.9%, and the ligament lengthdecreased by 21.2%. The ratio between the shell gib�bosity and maximal shell height (B : Hm), which usu�

ally serves as one of the taxonomic parameters infreshwater pearl mussels [71], also decreases signifi�cantly by 6.5%. In addition, the samples of freshwaterpearl mussel taken from different sites on the KozhaRiver are characterized by high variability of this ratio(Fig. 3). In particular, only two specimens (4.4%)sampled from the upper stream, four specimens fromthe middle stream (7.8%), and fourteen (37.8%) sam�pled from the lower stream were characterized by B :Hm ≤ 0.56, i.e., may be defined as Margaritifera mar�garitifera according to Bogatov et al. [71]. About 50%of specimens in samples taken from the upper andmiddle stream, and 27% of specimens in samples fromthe lower stream were classified as Margaritifera elon�gata (B : Hm = 0.58–0.62). Finally, 24% of molluscssampled in the upper stream, 20% in the middlestream, and 11% in the lower stream may be charac�terized as Margaritifera borealis (B : Hm ≥ 0.65).

The smallest specimen in the total sample was 52.6 mmlong, while the largest was 120.8 mm long. The mol�luscs sampled in the upper stream were the largest(56% of the specimens were 101–110 mm long); con�versely, on average, the molluscs that inhabit sites in

Table 1. Characteristics of studied sites on the Kozha River and population density of freshwater pearl mussels

Site no. S, m2 D1, km D2, km Habitat Bottom type Aquatic vegetation

Total relative coverage by aquatic veg�etation, %

Mollusc population

density, ind./m2

Biomass (wet weight) of molluscs,

g/m2

1* 50 0.0 87.8 Reach Silt and sand

Sagittaria sagitifolia, Comarum palustre, Equisetum fluviatile, Nuphar lutea

70 0.000 0.00

2* 100 4.7 83.1 Rift Boulders and sand

Fontinalis antypireticum

50 0.000 0.00

3 80 8.6 79.2 Groundsel Boulders and sand

F. antypireticum 60 0.563 49.65

4 80 18.4 69.4 Rift Boulders and sand


5 80 20.6 67.2 Groundsel Pebble F. antypireticum 60 0.013 0.85


F. antypireticum, Potamogeton sp., Ceratophyllum demersum

40 0.060 5.91



8 100 37.6 52.2 Rift Pebby and sand



F. antypireticum, Ranunculus sp., Myriophyllum sp.

60 0.034 1.87


F. antypireticum, Myriophyllum sp., Rivularia sp.

90 0.100 7.20

Note: S is square of the studied site; D1 is distance from riverhead; D2 is distance to Syvtuga River influx. Sites indicated by an asteriskare located upstream of the main spawning and nursery grounds of salmon (upstream Padun waterfall), where the freshwater pearlmussels were unlikely to be found.



the lower stream were the smallest (38% of specimenswere 71–80 mm long) (Fig. 4). Molluscs with shelllengths of 91–100 mm dominated in the middlestream of the Kozha River.

DISCUSSION

Status of freshwater pearl mussel population in theKozha River. The average population density of fresh�water pearl mussels in the Kozha River is lower than inother rivers. For example, in the Solza River and itstributary, the Kazanka River, the average populationdensities of mollusc are 1.75 and 1.36 ind./m2, respec�

tively [7]. The data available for assessing the popula�tion of freshwater pearl mussel in the Kozha River arescarce. According to Zyuganov et al. [24], the distribu�tion pattern of freshwater pearl mussel locations coin�cides with areas of salmon spawning and nurserygrounds. The total coverage of spawning and nurserygrounds in the Kozha River varies from 1.46 km2 [35]to 1.48 km2 [61], with an average of 1.47 km2. Assum�ing that the median population density of molluscs is0.05 ind./m2, we can assume that there are 70000 speci�mens (1.47 km2 × 0.05 ind./m2); if the averageweighted density is used, the population is assumed tobe about 130000 specimens (1.47 km2 × 0.09 ind./m2).

(a)

(b)

Fig. 2. Several sites of freshwater pearl mussel locations in the Kozha River: (a) site no. 3 (mainstream), (b) site no. 9 (channelalong the island).

466


BOLOTOV et al.

If the average of these two assessments is calculated,the average population of freshwater pearl mussels inthe Kozha River is about 100000 specimens. This isnot the highest number compared to the populationsthat inhabit other rivers of northwestern Russia. Forexample, the population of freshwater pearl mussels ina small river located in the Leningrad oblast’ comprisesabout 40000 specimens [85]; for conservation reasons,the authors do not indicate the location of the river. Thelargest population of freshwater pearl mussels in theworld is located in the Varzuga River (140 million indi�viduals), followed by the population in the Keret’River, which is 6 million individuals [24].

The following three criteria were suggested toassess the status of freshwater pearl mussel population:

(1) the total population must be 500 individuals ormore;

(2) 20% of young specimens must be 50 mm orlonger;

(3) the population must comprise specimens withshell lengths of less than 20 mm [89].

Taking into account the first criterion, the popula�tion of freshwater pearl mussels in the Kozha Riverexceeds the minimal population number by two orders

of magnitude; however, the ratio of young molluscshere is extremely low. We define “young” molluscs asspecimens with shell lengths of 70 mm or less [7, 24].This criterion was used for the comparative analysisperformed for freshwater pearl mussel populationsthat inhabit several Russian rivers. When comparingthe population that inhabits the Kozha River to otherrivers of the White Sea Basin, the status of freshwaterpearl mussels that recruit in this river is close to crucial(Fig. 5). It has been reported that the largest popula�tions of freshwater pearl mussel in Varzuga and Keret’rivers are characterized by a significant ratio of juvenilemolluscs and may be characterized as successfullyrecruiting molluscs [24]. The size class distribution ofmolluscs in these rivers is uniform. The populations offreshwater pearl mussel in the Solza and Kazanka riv�ers (a tributary of the Solza River) are characterized bya shift to the right part of the class spectrum, i.e., by adecreased ratio of juvenile molluscs compared to theVarzuga and Keret’ rivers (Fig. 6). In the Kozha River,almost 80% of specimens are characterized by shelllengths of 81–110 mm and only one young specimenin the sample was smaller than 70 mm (0.7%). Theaverage calculated age of the youngest ten specimensin the Kozha River is the highest among the studiedsites at 19.5 ± 0.5 years, compared to 16.8 ± 0.42 yearsin the Kazanka River and 16.0 ± 0.73 years in theSolza River (ANOVA: F = 8.4; d.f. = 2, 27; p = 0.001)(Fig. 7). The youngest specimens were 14.5, 13.4, and9.1 years, respectively. Therefore, the population offreshwater pearl mussels in the Kozha River may bedefined as growing old, and its recruiting is now quiteslow.

All three major morphotypes of freshwater pearlmussel (margaritifera, elongata, and borealis) and thetransition forms were found at each study site of theKozha River based on the B : Hm ratio (see Fig. 3).These three morphotypes were given a species statusby V.V. Bogatov [50, 71] in accordance to the circum�flexion of the frontal profile of the shell. These speciesare Margaritifera margaritifera (Linnaeus, 1758),M. elongata (Lamarck, 1819), and M. borealis (West�erlund, 1871). Since we have performed a large num�ber of morphometric measurements of live freshwaterpearl mussels, the B : Hm ratio was used to define themollusc morph. It was previously proved statisticallythat the constant angle of the logarithmic spiral inbivalve molluscs is strictly predetermined by the gib�bosity of the shell valve to the shell valve height [31].The ratio of morphs in the freshwater pearl musselpopulation depends on the river site (Fig. 3). In addi�tion, 98% of the total sample (Σn = 133 individuals atthe sites nos. 3, 7, and 9) were presented by molluscswith a shell length of 7–11 cm, which were used to cal�culate the B : Hm ratio [8: p. 498]. Modal values of thisparameter are similar to the arithmetic means, i.e.,0.62 (upper stream, site no. 3), 0.61 (middle stream,site no. 7), and 0.58 (lower stream, site no. 9); in allcases, these values refer to the elongata morph. Taking

Table 2. Hydrochemical composition of Kozha River (n = 4)

Parameters Median min–max

Temperature, °C 12.3 11.8–13.5

pH 7.3 6.9–7.3

[O2], mg/L 9.3 9.1–10.1

Conductivity, µS/cm 29.4 27–34

Chemical oxygen demand (COD), mg O2/L

35.7 32.3–35.9

mg/L 15.6 12.2–15.9

mg/L 1.6 1.4–1.6

[Cl–], mg/L 1.8 1.5–2.2

[Ca2+], mg/L 5.6 5.1–6.2

[Mg2+], mg/L 3.5 3.2–3.6

[Na+], mg/L 1.7 1.7–2.0

[K+], mg/L 0.72 0.66–0.75

mg/L 0.26 0.05–1.38

mg/L 0.37 0.31–1.04

[Fetotal], mg/L 0.47 0.43–0.52

[F–], mg/L 0.02 0.02–0.02

[Mn2+], mg/L 0.02 0.01–0.05

Note: The concentrations of some trace metals were lower than thedetection threshold of the method, i.e., Cu (<0.01 mg/L),Zn (<0.05 mg/L), Cd (<0.01 mg/L), and Pb (<0.01 mg/L).

HCO3–

[ ],

SO42–

[ ],

NO3–

[ ],

NH4+

[ ],



into account Bogatov’s recommendations [8, 50, 71],the freshwater pearl mussel population in the KozhaRiver must be defined as belonging to Margaritiferaelongata (Lamarck, 1819) species, despite the variabil�ity of the shell shape and the presence of transitionalforms. This approach seems to be quite disputable andis widely discussed now in the scientific publications[8, 57]. Professor A.A. Shileiko tends to define thisdiscussion as being “…theologically based, since eachscientist agrees or disagrees whether the comparativeapproach suggested by Logvinenko and Starobogatov[39] is reliable in species definition.” Indeed, thisproblem of defining an individual species (taxonomi�

cal structure of Margaritifera genus representativesinhabiting Northwestern Europe) covers the basic pos�tulate of Russian malacological science. During recentlast years, the discussion of comparative methods hasintensified, and new powerful talking points have beenput forth against the use of this approach in species

systematics [15, 31, 75]1. One must also consider the

fact that defining three “species” of freshwater pearlmussel contradicts the data on mitochondrial DNAanalysis [11].

Economic activities, and hydrochemical character�istics of the Kozha River. The watershed area of theKozha River belongs to a poorly inhabited area cov�ered by natural taiga. The Kozhozerskii Monastery issituated on the coast of Kozhozero Lake; the history of

1 Unfortunately, some authors have failed when it comes to thelogic of discussing this extremely complicated problem. Forexample, upon perusal, the review by Rizhinashvili [54] appearsto be a mosaic of contradictory text fragments. The author con�cludes that “…the major problem of Bivalve systematics is notthat there are two contradictory approaches (conditionallycalled “traditional” and “comparatory”) to defining the numberof taxa, but rather in the scarce data on these animals, their biol�ogy, and ecology” (p. 375). Therefore, despite the dozens of newtaxa described by the circumflexion of the frontal profile of theshell, the problem does not refer to the comparatory method(even though the followers of this method start to revise the taxawith the large�scale combination of genera and taxa, e.g., [9]),but rather refers to the weak examination of the parameters ofthe studied objects! This seems to be a dead�end, but Rizhinash�vili [54] has developed a brand new approach to solve the taxo�nomical problems, i.e., “…one can puzzle out this mess if he orshe studies the species composition and the population densityof bivalve molluscs in bodies of water with regard to the environ�mental conditions of the studied sites” (p. 375). We provide nocomments here. We would only like to note that this idea, whichhas enriched the modern taxonomical science, is given with ref�erence to [53].

Table 3. Average morphometric characteristics of freshwater pearl mussels sampled at different sites of the Kozha River

Parameters

Headstream (site no. 3; n = 45)

Middle stream (site no. 7; n = 51)

Lower stream (site no. 9; n = 37)

M ± SEM min–max M ± SEM min–max M ± SEM min–max

Shell length (L), mm 98.9 ± 1.7 52.6–112.7 95.3 ± 1.6 71.5–120.8 85.7 ± 1.7 71.2–109.9

Distance between the shell forefront and apex (A), mm

41.6 ± 1.0 24.2–56.7 34.1 ± 0.8 21.1–45.2 26.7 ± 0.7 17.6–37.7

Height above the apex (H), mm

38.6 ± 0.7 21.2–45.3 36.7 ± 0.7 25.8–46.1 34.0 ± 0.8 26.4–45.0

Maximal distance between the dorsal and ventral edges of the shell (Hm), mm

46.5 ± 0.8 26.2–55.4 44.6 ± 0.7 34.1–55.5 41.0 ± 0.7 31.6–49.8

Shell gibbosity (B), mm 29.1 ± 0.5 14.4–33.5 27.1 ± 0.5 20.8–33.8 23.9 ± 0.5 18.6–29.6

B : Hm 0.62 ± 0.00 0.54–0.70 0.61 ± 0.01 0.48–0.74 0.58 ± 0.01 0.51–0.68

Ligament length (Llig), mm 51.8 ± 1.4 26.0 + 76.6 51.1 ± 1.1 32.9–75.4 40.8 ± 1.3 28.6–62.2

Wet weigh of live mollusc, g 88.3 ± 3.8 12–130 80.4 ± 4.0 34–148 54.6 ± 3.6 27–115

Note: The differences between all the studied sites are significant for each parameter (ANOVA: F > 10; d.f. = 2, 130; p < 0.0001). M ± SEM—arithmetical mean and standard error; min–max—limits of variability.

0.75

0.70

0.45130120110100806050 70 90

0.65

0.60

0.55

0.50

Shell length (L), mm

B : Hm

‘borealis’

‘elongata’

‘margaritifera’

Site no. 3 Site no. 7 Site no. 9

Fig. 3. Size structure of freshwater pearl mussel sampled atdifferent sites of Kozha River assessed by B : Hm index andshell length (L). Horizontal lines show values of B : Hmindices, which are used for the diagnostics of three fresh�water pearl mussel species according to V.V. Bogatov et al.[17].

468


BOLOTOV et al.

this settlement is thoroughly described in [51]. Beforethe October Revolution in 1917, the monastery was alarge settlement. Eleven villages, eight mills, four saltfurnaces, and the best salmon fisheries along OnegaRiver and the seacoast belonged to the monastery,which covered more 17600 dessiatins of land (approx�imately 160 km2). The monastery had one herd of cat�tle (more than 200 cows) and 50 horses. In 1917,20 monks and eight novitiates, including up to 30 pil�grimages and up to 45 freelance workers lived in themonastery. After the October Revolution, the monas�tery was closedby the Soviet Union, but was reopenedagain in 1997. Five to ten people (monks, pilgrimages,and workers) lived in the monastery during 2006–2010. Therefore, there is currently no significantanthropogenic load that may have a negative effect on

the water quality along the stream of the Kozha Riverand in the vicinity of the Kozhozero Lake. Histori�cally, the forest procurement and drift floating wastotally absent in this area. The riverbed is clear and isnot littered by wood materials.

The problem of the water quality and the effect ofsome pollutants on the population of freshwater pearlmussel were studied earlier [70, 73, 83, 92]. It wasfound that the normal living of freshwater pearl musselis possible in a specific range of some hydrochemicalcharacteristics; however, the data on these limits arescarce and fragmentary. Glochidia and juvenile mol�luscs are reported to be the most vulnerable life stagesto water quality [93]. The low concentration of bio�genic compounds, nitrites, phosphates, high conduc�tivity, low concentrations of heavy metals, and pH val�ues close to neutral are characteristics of waters whereMargaritifera margaritifera lives (Table 4). The resultsof an analysis of the water sampled in the Kozha Rivershow that the major water characteristics (pH, con�ductivity, oxygen saturation, heavy metals’ concentra�tions) belong to optimum ranges that are common forrivers inhabited by freshwater pearl mussels. The ele�vated concentration of the organic compounds is theonly exception [24, 77] observed in the Kozha River.The high COD (median value of 36 mg O2/L) exceedsthe maximum concentration limit for bodies of watersignificant to fisheries, just as elevated concentrationsof nitrites and ammonia ions do at some sites of theriver. High concentrations of organic compounds werealso registered in the Solza River Basin [7]. Mostlikely, the high oxidation susceptibility of waters pre�conditioned by a significant number of swamps in thewatershed area is a characteristic of the habitats offreshwater pearl mussel in the northwestern margins ofits geographic range. Here, the high concentration oforganic compounds does not limit the population

60

50

40

30

20

10

051–60 61–70 71–80 81–90 91–100 101–110111–120 121–130

Rate of specimens, %

Size classes of shell length (L), mm

no. 3

no. 7

no. 9

Fig. 4. Size classes of freshwater pearl mussel sampled at different sites of Kozha River according to shell length.

40

35

30

25

20

15

10

5

0


Kozha Kazanka Solza RiverRiver River

Keret’ River

Varzuga River

Fig. 5. Ratio of young specimens (≤70 mm) in differentpopulations of freshwater pearl mussel that inhabit rivers ofnorthwestern Russia.

35.4

17.3

10.86.7

0.7



density of freshwater pearl mussels, which allows us toexpand the tolerance range of this species. The lowconcentration of calcium cations in the Kozha River iscommon for areas inhabited by freshwater pearl mus�

sel [81]. Even the minimal concentration of ammoniaions exceeds the upper limit (0.16 mg/L) for thesalmon�inhabited rivers of Europe [82]. Elevated con�centrations of nitrates (sometimes more than 1 mg/L)

40

0

35

30

25

20

15

10

5

11–1021–30

31–4041–50

51–6061–70

71–8081–90

91–100101–110

111–120121–130

131–140141–150

Size classes of shell length (L), mm

Kazanka River

Solza River

Varzuga River

Kozha River

Keret’ River


Fig. 6. Size structure of freshwater pearl mussel sampled in different rivers of the White Sea basin, according to its shell length.Number of sampled molluscs: Varzuga River, n = 192 [24]; Keret’ River, n = 214 [24]; lower stream of Solza River, year of 2005,n = 185; Kazanka River, n = 208 [7]; Kozha River, n = 151.

25

15

10

5

0

20

1 2 3 4 5 6 7 8 9 10

Age, years

Rank of specimen by age in sample

Solza River

Kazanka River

Kozha River

Fig. 7. Rank distribution by mollusc age for ten youngest specimens of freshwater pearl mussel in samples taken from Solza,Kazanka [7], and Kozha rivers. Ages of molluscs were calculated according to Eq. (1).

470


BOLOTOV et al.

may affect adult specimens of freshwater pearl mussels[70]. The concentration of phosphates in the KozhaRiver is lower than the lower limit of 0.03 mg/Lreported by some researchers [70, 84]. Elevated con�centrations of heavy metals may deteriorate the func�tioning of the proteins and DNA in molluscs [83];however, their concentrations in the Kozha River isextremely low.

Salmon as hosts of glochidia of freshwater pearlmussel: Biology and abundance of Atlantic salmon. TheAtlantic salmon is the key salmonid species in theKozha River, and is a major host for freshwater pearlmussel glochidia. The Atlantic salmon penetrates farto the upper stream of the Kozha River, successfullysurmounting the large Shchurus (middle stream) andPadun (upper stream) waterfalls. Other salmon spe�cies, i.e., brown trout (Salmo trutta) and pink salmon(Oncorhynchus gorbuscha), which were introduced tothe White Sea, are rare. These species enter the river,but do not penetrate farther than the Shchurus water�fall, which is situated 22 km from the estuary. Onlybrown trout may serve as the host for glochidia [24].

Data on the age, size, and biomass of juvenile anddwarf males of the population of Atlantic salmon thatinhabit the Kozha River are presented by Ustyuzhin�skii et al. [63]. It is known that salmon juvenilesmigrate to the sea from the Kozha River at the age of2+ to 3+; only one juvenile was 4+ years old [35]. Thescale structure demonstrates the growth period of theAtlantic salmon in freshwater areas of the Onega Bayof the White Sea; only after this do the fish migrate tothe Atlantic Ocean [34]. The summer generation ofOnega Atlantic salmon spends a year in the sea, whilethe autumn generation spends 2–3 years [35, 64]. Thelatter spawns in the Kozha River and overwinters inthe reaches of the Onega River upstream of the Porogsettlement [28]. The salmon migrates to the KozhaRiver and Syvtuga River in late May [35]. The Onegapopulation of Atlantic salmon is characterized by a

large size; its average body weight varies from 7.6 to 9.6 kgin different years [35]. The average body mass of theAtlantic salmon caught in 2002–2004 was signifi�cantly lower, i.e., 4.2, 3.8, and 4.4 kg [61, 62, 65]. Inthe 19th century, the salted salmon caught in theOnega River was given the name “Porog”; this salmonsupposed to be the most delicious compared to thosecaught in other rivers [32].

The Kozha River, as well as its tributary, the Syv�tuga River, is one of the major salmon spawning areasin the Onega River Basin, possibly even the mostimportant one [28, 35, 61, 67, 68]. Currently, theKozha and Syvtuga rivers are two of the three tributar�ies of the Onega River, where wild juveniles of Atlanticsalmon were caught [61, 62]. Unfortunately, thesepublications do not provide data on the abundance ofjuveniles in the Kozha River. The spawning grounds areaof Atlantic salmon covers 16 ha in the Kozha River and8.7 ha in the Syvtuga River; nursery grounds cover 132 hain the Kozha River and 45 ha in the Syvtuga River [35].Other studies reported that spawning and nurserygrounds cover 1.46 km2 in the Kozha River and 0.48 km2

in the Syvtuga River [61]. Spawning and nurserygrounds of the Kozha River are rifts and riffles formedby pebbles and boulders and 0.3–0.8 m deep. About60% of their coverage is located within 79–40 km fromthe estuary (Fig. 1). No spawning and nursery groundsof Atlantic salmon were found downstream of the Syv�tuga River (11 km from the Kozha River estuary) andupstream of the Padun waterfall.

Taking into account the productivity of the KozhaRiver is no less than the productivity of the Megra River,which is located significantly northeast (14000 salmonsmolts per 1 km2), as well as that about 5% of fishreturn to the river after the sea growing period [59],one can easily calculate that more than 1000 breedersmust return to the Kozha River each year in the case ofthe optimal use of the spawning grounds. This numberrefers to the catches of Atlantic salmon in the Kozha

Table 4. Limiting hydrochemical parameters for freshwater pearl mussels and their values in the Solza [7] and Kozha rivers

ParametersLimits of variability

Solza River Kozha River[84] [70] [27]

mg/L <1.0 <0.50 No data 0.21 0.05–1.38

pH 6.5–7.2 No data 6.6–7.8 6.6–6.7 6.9–7.3

Conductivity, µS/cm <100 <70 30–77 No data 27–34

[Ca2+], mg/L <10 2 2–21.6* 10.0 5.1–6.2

Dissolved [O2], % 90–110 No data 86–106 79.1–82.8 85.8–93.4

Note: asterisk* indicates the data recalculated under water hardness.

NO3–

[ ],



250

150

100

50

0

1980

20019

81

1982

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

0.6

0.4

0.3

0.1

0

1980

0.5

1981

1983

1984

1987

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

2010

0.2

1982

2011

Catches, ind.Natural

reproduction of M. marga�

Dramatic decrease in number of M. margaritifera recruits (less than 1% juveniles)

Interruption of M. margaritifera reproduction (the juveniles do not appear)

Natural reproduction of M. marga�

Dramatic decrease

M. margaritifera recruits (less than 1% juveniles)

in number of Interruption of M. margaritifera reproduction (the juveniles do not appear)

1 2 3

Population density of juveniles, ind./m2

(a)

(b)

Fig. 8. (a) Catches of Atlantic salmon breeders in the Kozha River and (b) calculated population density of the farm�reared juve�niles of salmon species on spawning and nursery grounds according to data presented by Sevrybvod (Northern Fishery Depart�ment): 1–2, Atlantic salmon (1–2�year�old fish, 2, less than 1 year old); 3, Brown trout. Double vertical lines are marginsbetween major phases of population development of freshwater pearl mussels with regard to the status of salmon population andfishery technology. Dotted horizontal lines indicate minimal population density of salmon juveniles needed for a successful num�ber of recruits of freshwater pearl mussels [24]. Data on catches in 1983–1988 and juvenile population density in 1985–1986 and1988–1990 are absent in Sevrybvod (they were lost in 1990s). Calculations of juvenile population density were performed accord�ing to data of released farm�reared fry (for 2�year�old juveniles of salmon we have used the correction of ×0.4, since about 60%of them quickly migrate to the sea) and according to the area of the hatching�growth ground, which was assumed to be 1.47 km2.

Rec

on

stru

ctio

n o

f th

e O

neg

a h

atch

ery

ritifera

ritifera

472


BOLOTOV et al.

River 100 years ago. It is known that, in the beginningof the 20th century, about 540 fish (in average) werecaught in the Kozha River each year by stakes; somefish were sampled by fishing on the spawning grounds[1]. The number of breeders sampled for aquaculturein the Onega hatchery varied greatly from year to year,but according to the fishery reports, a long�termdecreasing trend was obvious (unfortunately, somereports were lost). In 1947, the highest number ofbreeders (370) was used for aquaculture purposes.After 1962, less than 300 fish were caught per year, andafter 1965 less than 200–220 individuals were caught.A dramatic decrease in the catches was observed in1980–1990s with an absolute minimum in 1995, whenonly 13 fish were caught, which corresponds to the ageof the youngest freshwater pearl mussel in our samples(Fig. 8a).

The similar tendency was tracked for reared fryreleased to the Kozha River. Fries are usually releasedby aquaculture farms in March (data courtesy ofSevrybvod), and more than 60% of juveniles are usu�ally released 7 km upstream of the Shchurus waterfall, theother fish is released nearby Petrovskaya village. In 1980–1983, the hatchery released 337000–824000 salmonjuveniles per year (including young�of�the�year fish),which makes the estimated population density of parrs0.23–0.56 ind./m2 (Fig. 8b). This is a rather high valuefor a salmon�inhabited river and is close to the num�bers for the Varzuga River [24]. After the reconstruc�tion of the Onega hatchery in 1984, the rearing tech�nology was changed and the fish were released at theage of 1+, so the number of the released juveniles wassignificantly lower; in some years, fish were notreleased into the Kozha River (1984, 1994–1998). In2011, brown trout juveniles (40900 individuals) werefirst released together with Atlantic salmon juveniles(53600 individuals) into the Kozha River. The averageabundance of salmon juveniles released into theKozha River per year was 38500 individuals in 1984–2011. In addition, about 60% of parrs (1+ age)released in March migrate to the sea in May, while therest stay in the river and migrate to the sea the next yearspring. That is why the correlation coefficient wasestablished to be ×0.4 in order to calculate the averagepopulation density of fish aged 2+ on the spawning andnursery grounds of the Kozha River; this leads to an aver�age estimated density of 0.01 ind./m2. The minimal pop�ulation density of salmon fry needed to successfullyrecruit freshwater pearl mussels (glochidia survival and

growth) must be no less than 0.03–0.05 ind./m2 [24].2

Accordingly, the population density of farm�reared fry

2 According to [24], juveniles aged 0+ make up a major age classof salmon that are not immune to glochidia invasion; the otherages were previously attacked by glochidia and, as a result,became immune to them (p. 22). However, with regard to farm�reared fry, the invasion of glochidia makes sense if the river waterentering the circulation system of the aquaculture farm carries asignificant number of glochidia. The latter was not observed forthe Onega hatchery.

in the Kozha River has been lower than or close to thecritical level since 1984, which led to the deteriorationof freshwater pearl mussel recruitment (Fig. 8b).

Before the October Revolution of 1917, the salmonstake was located 4 versts (appr. 4.25 km) upstream ofthe Petrovskaya village [68]. Since 1933, salmonbreeders have been caught in the vicinity of the Bere�zovye Islands, i.e., 52–53 km downstream of the river�head, which is significantly upstream of the old stake.Therefore, the decline of catches compared to thebeginning of the 20th century is somehow precondi�tioned by the location of the fish uptake; i.e., they donot catch fish that spawn at the site between BerezovyeIslands and the old salmon stake. However, even ananalysis of the data provided in the hatchery reportsreveals the dramatic decrease (by several times) inAtlantic salmon catches in the Kozha River. The totalabundance of Atlantic salmon also decreases by thesame order of magnitude. An artificial increase in thenumber of recruits must be developed to preserve thesalmon population in the Kozha River and OnegaRiver Basins. It is also necessary to forbid salmon fish�ing, including on migration pathways (except catchingfor hatchery needs and traditional harvesting per�formed by locals in historical settlements).

The history of the hatchery. The Kozha River playsa significant role in the history of Atlantic salmonbreeding. In just 1913, a notable public figure in fish�ery, V.R. Aleev, proposed establishing a pioneer hatch�ery station on the Kozha River during the Meeting onFisheries at the Department of Agriculture [1]. Theproposition was accepted on the Meeting, but theWorld War I (1914) and the October Revolution (1917)obstructed the foundation of the hatchery, and it wasnot opened until 1922 on Zimnyaya Zolotitsa River(White Sea Basin).

In 1930, the Northern Regional Land Authorityprovided special funds to the Ichthyologic Institute(currently the State Research Institute of Lake andRiver Fishery, GosNIORKh) to study SevernayaDvina and Onega rivers for the possibility of Atlanticsalmon aquaculture activities at those regions. Thereport on these expeditions may be found in the publi�cation by Isachenko [28]. He concluded that theKozha River is the only river in Onega River Basinwhere a significant number of breeders needed toestablish a fish aquaculture might be caught. Since alist of important, but still unstudied issues in the biol�ogy of Atlantic salmon existed at that time, he alsoproposed primary research for modeling Atlanticsalmon reproduction using Zhukovskii chambers.Therefore, additional research did not yield any newdata. Surprisingly, Isachenko’s publication [28] doesnot provide an analysis of the 10 years of operation ofthe Atlantic salmon hatchery on the ZimnyayaZolotitsa River and V.R. Aleev’s work on fish aquacul�ture and Atlantic salmon biology. One must also notethat the experiences of newly opened Atlantic salmonfarms were not analyzed by the scientists, and the



farms that had been working for decades in an experi�mental regime.

In 1932–1934, according to Decree no. 228 bycomrade A.I. Mikoyan, issued at September 14, 1932,the Pinezhskii, Onega, and Soyanskii hatcheries wereestablished (Report on the fish aquaculture activity bySevrybvod, 1949, p. 69). The construction of a net�work of hatcheries in northern Russia was aimed atcompensating for the negative effects of overfishing,wood floating, and water engineering on the Atlanticsalmon population, and was part of the Soviet politicsof industrialization. It was assumed that salmonaquaculture would be based on blue pasture technol�ogy, which has been widely used in the rivers of theBaltic Sea Basin. However, the implementation ofinnovative know�how faced a number of serious prob�lems that were preconditioned by scarce data of thebiological peculiarities of Atlantic salmon.

In particular, the technology for rearing Atlanticsalmon used at that time included fry release; it wasassumed that the natural spawning of the Atlanticsalmon was ineffective and accompanied by high eggmortality. Farm rearing had to fill this gap in the repro�duction of Atlantic salmon and, thus, to significantlyincrease the fish recruitment. However, the naturalspawning of Atlantic salmon is quite effective, evendespite the years when the eggs perish due to freezingor drying.

Taking into account these peculiarities, Nusen�baum [48, p. 125] concluded that, “We can state nowthat our choice of the rivers for establishing the hatch�ery, the job content, and the locations of farm build�ings did not take into account our knowledge of Atlan�tic salmon biology. As a result, the Atlantic salmonaquaculture appeared to be a displacement of the nat�ural recruitment of this species in areas where it wasnaturally successful, e.g., on the Soyana, Onega, andVarzuga rivers.”

After the hatcheries were built, it was found thatblue pastures were located far from the coasts of theSoviet Union in the North Atlantic Ocean [20].Therefore, the probability of salmon dying of naturalcauses is quite high during the long passage to thesepastures and back. In addition, breeders of Atlanticsalmon are caught by fishermen in both Russian andforeign waters [14].

Until now, many Russian ichthyologists were surethat breeders of Atlantic salmon might spawn en massein rivers where they did not hatch. These ideas becamepractice, and the collection of eggs from several riverswas performed to reduce the fry at one hatchery. How�ever, the number of breeders that return to the “sec�ondary” river decreases dramatically if such technol�ogy is applied [2].

The data on these collections and their conse�quences were reviewed and analyzed [3]. The changesin the genetic structure of Atlantic salmon populationthat inhabits the Onega River was induced by the

transport of fish from other rivers to this area [41].Currently, the replacement of juveniles from other riv�ers to the Onega River has nearly stopped.

The Kozha River, where most of the spawning andnursery grounds of the Onega population of the Atlan�tic salmon are situated, is located far from large settle�ments and is hard to reach. This has led to a dead�endsituation when many problems arose after the hatch�ery was built on this river, i.e., the supply of the farmand the workers was quite difficult to organize and,when a hatchery was built near Onega city, there wasthe problem of releasing farm�reared juveniles.

The hatchery was built 10 km upstream of theOnega River estuary and was supplied by water takenfrom Sheleksa spring. The eggs were collected in theKozha River and its tributary, the Syvtuga River (in1937, also in Nimenga River). The fry were released tothe Onega (13 km upstream the farm) or Kozha (Fish�ery Reports by Sevrybvod) Rivers; for several years, allfish farming was performed at the Kozha River [33].

For a long time period, fish farmers asked for helpfrom scientists in solving the problems that arose at thefarms [33]. Finally, after the study performed byVNIORKh (now GosNIORKh), it was recommendedto reconstruct the Onega hatchery, i.e., “…to move itto an area where it would be possible to sample breed�ers and store eggs…” and “…to build incubation tanks,Basins for fry rearing, and residential buildings…” [46,p. 124].

Obviously, it was difficult to build all of these con�structions in a far taiga, so the hatchery was reopenedat the same place as earlier. However, in 1964–1970,the farm was reconstructed, the basins for fry rearingwere enlarged, the growth ponds were constructed,and the farm began to rear juveniles. The method ofhigh�abundance rearing was developed in cooperationwith colleagues from GosNIORKh; this methodallowed for the release of extra juveniles [19]. These frywere mostly released in the Onega River, since it passesby the hatchery. However, the release of extra fry intoa restricted growth area was criticized [5]. It was rec�ommended to reconstruct the farm so Atlantic salmoncould be reared to the age of parr, which are large juve�niles that can immediately migrate to the sea and donot depend on river food resources [29], and theproject of farm reconstruction was ordered. In 1984,the new hatchery was nearly finished at the other loca�tion, the Anda River, where it is still in operation.Unfortunately, new problems arose for fish breeders.

The hatchery “…faces continuous problemsbecause the ineffective planning of the water supple�ment system, which is linked to a small lake. This lakeeutrophicates, especially during the summer, andwater is not suitable for rearing Atlantic salmon juve�niles. When the summer is hot, a significant number offry die. It is necessary to perform an experimental workto justify the release of juveniles with body masses of0.5–1.0 g to the most food�supported areas of riverswhere salmon spawn” [21, p. 192–193]. Therefore, it

474


BOLOTOV et al.

was again recommended to release the fry. Since fishfarmers follow the recommendations of the scientistscarefully (they cannot change the technology by them�selves), it seems that the same story is repeated. On theother hand, the release of 0+ fish will allow for thefreshwater pearl mussel population to be recruited [7].

History of pearl fishing. It is known that pearl fish�ing in the basin of the Onega River began long ago,when the Onega District was part (county) of theArkhangelsk Province since at least the 18th century[66]. A list of rivers that were inhabited by freshwaterpearl mussels is provided in historical documents andincludes the Onega, Vaiga, Syvtuga, Yarega, Sara,Ivenga, Simbo, Kozha, and Khain�Ruchey rivers [12,23, 52, 58]. Here, pearl fishing was performed mostlyby nonlocals. In 1863, one of the travelers pointed thisout and explained this phenomenon by the loss ofpearl fishing habits by locals, since several previousgenerations worked for an English employer,Mr. Gomm, at his sawmills and shipyards [6]. In the1860s, these manufacturing units were closed and thelocals (men) started to leave the area for seasonalwork. This tendency continued in the early 19th cen�tury. Travelers in the province passed through villageswhere only women and children lived during the sum�mer months [30]. Therefore, pearl fishing was forgot�ten for the only season when it was possible. As aresult, newcomers from Karelia and exiles, who wereprohibited to leave the province, were the main pearlfishers [12].

This pattern was the norm for the Kozha River. Insecond half of the 19th century, all of the settlementson this river were located in the lower stream betweenthe Igisha and Onega rivers. This area comprises sev�eral villages, including Petrovskaya, Sidorovskaya, Efi�movskaya, Filimonovskaya, Semenovskaya, andMakar’inskii Pogost. According to the demographicdata (year of 1872), most of the men in these villages leftthe area for seasonal work [16]. Up to 50% of men leftthe Petrovskaya, Sidorovskaya, and Filimonovskaya vil�lages. Weaving was the major craft. Each family had aherd that required daily tending. Clearing wood foragriculture took a lot of time and effort. Pearl fishingcan only turn a profit if the fisher has significant expe�rience and equipment. The countrymen and the coun�trywomen, who were especially busy with everydaywork, had no time to study the secrets of the pearl fish�ing. Therefore, it is no surprise that pearl fishers in theKozha River were mostly newcomers. The only localwho regularly fished for pearls in the tributaries of theOnega River was a countryman of Kem’ county, AntonLipkin. In particular, he valued the Syvtuga and KozaRivers, since they were the most inhabited by thefreshwater pearl mussels in the whole Onega District[18]. In 1869, Anton Lipkin and six of his friends weregiven by 150 roubles for 20 pearls, which were takenfrom the Kozha River and presented as a gift to theGrand Princess. One year later, he and Ilya Kond�rat’ev, also a countryman from Onega District, were

given 120 and 180 roubles, respectively, for 39 pearls[17]. The fact that the pearls were gifted to the GrandPrincess was evidence of the high quality of the pearls.In 1871, Anton Lipkin brought 70 pearls to theEmpress Maria Alexandrovna, which he considered tobe “very lucky,” since he was rewarded with 400 rou�bles [18]. Pearl fishing by locals was less lucky, as IvanKuritsyn, from the same district, had also sent thepearls to the court, but they were sent back [66].

The sampling gear was primitive. If the bottom wasnot covered with too many stones, then a scrape wasused. Of course, in this case, all of the sampled shellswere opened and no conservation efforts were made.Fishing from the raft was more selective. The descrip�tion of this raft is given in the article about pearl fishingin Kem’ county [38]. The raft is made from four–sixfir logs about 1 sagene (fathom, 2.1336 m) long. A holeabout 4 vershoks (1 vershok = 4.445 cm) in diameterwas made on one edge of the raft. A tube made frombirch bark was placed into the hole, and the fisherlooked through it for molluscs on the river bottom.The mussels were brought to the surface by using a six�ended brush made from steel rods. Using this technol�ogy, one fisher with five mates could not bring toomuch harm to the freshwater pearl mussel populationin the river.

Most likely, this situation of pearl fishing was main�tained for the next years. According to the reports onthe 1928 expedition headed by E.V. Terent’eva, theshells of the freshwater pearl mussels were frequentlyfound along the coast of the Kozha River, and the chil�dren who lived in the Petrovskaya village often foundthem on the shore [22]. The conservation of the fresh�water pearl mussel population was only possiblebecause of the low level of economic activity on theriver. Here, settlements were rare and there were nosawmills here at all, so there was no floating wood; fur�thermore, Atlantic salmon was not actively caught bylocals. All of these factors combined lead to successfulfreshwater pearl mussel recruiting.

Currently, there are some cases of illegal fishing forfreshwater pearl mussels by tourists. We have found areport on the Internet about tourists rafting along theSyvtuga River (a tributary of the Kozha River) in 2002.The author of the report carefully describes attempts atillegal pearl fishing by himself and other participantsof the group at a site located 700–800 m downstreamof the Padun waterfall, and even shows a photo of amollusc being opened with a knife (http://land�lost.narod.ru/dnevniki3.html). We have not found anysuch reports for the Kozha River. However, taking intoaccount the increasing number of these tourists as wellas the low level of ecological culture in the population,we cannot exclude the risk of such senseless poaching.

CONCLUSIONS

The population of freshwater pearl mussels in theKozha River is characterized by a low population den�



sity and extremely low level of recruiting; its abun�dance may be assumed to be 100000 individuals. Largemolluscs dominate, 79% of which are characterized byshell lengths of 8–11 cm, while 56% of which haveshell lengths of 9–11 cm. The ratio of juvenile mol�luscs is less than 1%, and the average age of the tenyoungest specimens is about 20 years. According to themodal values of the B : Hm ratio (the ratio between theshell gibbosity and the maximal shell height), this pop�ulation of freshwater pearl mussels belongs to theelongatamorphotype, even though other morphotypeswere also found with relatively high frequency.

The Kozha River Basin is poorly used, and the eco�nomic activity is extremely low. Historically, settle�ments and sawmills have been absent for the most ofthis area, floating wood was not found, so the riverbedis clean and is not littered with wood debris. There areno sources of anthropogenic load for water resources;thus, all major hydrochemical parameters refer to thewater standard and natural environment. Currently,the population of locals from Kozhozero Lake to thePetrovskaya village does not exceed 20 people, whichis significantly lower, even compared to the 19th cen�tury population, when a large monastery was develop�ing on the coast of Kozhozero Lake. Therefore, here,the anthropogenic load and its effect on the freshwaterpearl mussel population is negligible.

The effect of pearl fishing on the current state offreshwater pearl mussel population is also minor andunobvious. Most of the locals preferred to leave thisarea for the seasonal work in the late 19th century. Thehistorical evidence on pearl fishing in the Kozha Riverand in other rivers of Northern Europe are quitescarce. It was found that only one countryman fromKem’ county, Anton Lipkin, and five of his colleaguesfished for pearls here in 1860–1870s. They used quiteprimitive sampling gear, so it is unlikely that they couldhave exhausted the population of freshwater pearlmussel in the river. On his own, Anton Lipkin found aconsiderable number of freshwater pearl mussels in theKozha River and noted that he could sample more ifthe equipment were better [18]. There are data that indi�cate that pearl fishing ended in 1880, i.e., 130 yearsbefore our study. This time period is close to the max�imal life span of freshwater pearl mussels, since onlysingle specimens may reach this age or older [69].Therefore, most of the freshwater pearl mussel mod�ern population appeared here after pearl fishing wasfinished. Furthermore, pearl fishing activities in the19th century might have had a minor effect on thefreshwater pearl mussel population and the number ofjuveniles. We cannot exaggerate the effect of poachingdue to modern tourist activities, since most groups arethere to go rafting, not to catch freshwater pearl mus�sels in cold and rapid river streams.

The reason for the low recruitment of freshwaterpearl mussels is the dramatic decrease in Atlanticsalmon in the Onega River Basin in the late 20th cen�tury. The reconstruction of the Onega hatchery in 1984

and the release of juveniles at the age of 1+ is a secondnegative factor. These factors led to the breakdown ofmollusc recruitment because the population density ofsalmon juveniles at spawning and nursery groundsbecame smaller than the lower limit. However, due tothe long life span of this species, a significant numberof adult breeders of freshwater pearl mussel are stillalive in the river; these individuals may produce suc�cessful offspring if the population density of 0+ juve�niles at spawning and nursery grounds is sufficient.The release of about 150000–300000 salmon into theriver per year is sufficient to cover the essentialdemand for freshwater pearl mussel recruitment. Thisnumber of juveniles will allow their density at spawn�ing and nursery grounds to be 0.1–0.2 ind./m2, i.e., itwill exceed the lower limit by two to four times. Theother possible scenario is the artificial infection offarm�reared juveniles by glochidia during the aquacul�ture period and according to technology [24]. Onemust consider the hatchery at the Solza River, whichsupports successful freshwater pearl mussel recruit�ment by releasing juvenile Atlantic salmon into thisriver and its tributary, the Kazanka River [7].

Currently, the Kozha and Syvtuga Rivers are two ofthe three rivers of the Onega River basin where wildjuvenile Atlantic salmon are registered. This may pos�itively affect the successful recruitment of freshwaterpearl mussels. Historically, the natural spawning ofAtlantic salmon in the Kozha River has been sufficientto maintain a significant number of smolts forglochidia attachment based on the abundance offreshwater pearl mussels in this river. The artificialincrease in the number of recruits must be developedto preserve the salmon population in the Kozha Riverand Onega River Basin. It is also necessary to forbidsalmon fishing, including fishing on migratory path�ways (except for the catching for needs of the hatcheryand for traditional harvesting performed by locals inhistorical settlements).

ACKNOWLEDGMENTS

The study was supported by the Russian Founda�tion for Basic Researches (grants nos. 10�04�00897,10�04�10125, 11�04�98815, and 12�04�00594�a),interdisciplinary project of the Ural Branch of RussianAcademy of Sciences “Landscape�Climatic Condi�tions and Biodiversity of Invertebrates in the EuropeanNorth”, Federal Target Program “Research and Ped�agogical Cadre for Innovative Russia” for 2009–2013,and by the Russian Federation President grant forYoung Doctor of science (MD�4164.2011.5).

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