11› From: Schweiz. Z. Hydrol. 39: 12-45, 1977 1978

FISURIES AND MARINE SERVICE

Translation Series No. 4374

Biology and management of the European lake char (Salvelinus alpinus L.) in Lake Zug (Switzerland)

by Ch. Ruhle

Original title: Biologie und Bewirtschaftung des Seesaiblings 11› (Salvelinus alpinus L.) im Zugersee

From: Schweiz. Z. Hydrol. 39: 12-45, 1977

Translated by the Translation Bureau (VNN) Multilingual Services Division Department of the Secretary of State of Canada

Department of the Environment Fisheries and Marine Service Biological Station St. John's, Mid.

1978

54 pages typescript DEPARTMENT OF THE SECRETARY OF STATE SECRÉTARIAT D'ÉTAT TRANSLATION BUREAU BUREAU DES TRADUCTIONS

MULTILINGUAL SERVICES DIVISION DES SERVICES CANADA DIVISION MULTILINGUES L/ 7/

TRANSLATED FROM - TRADUCTION DE INTO - EN German English

AUTHOR - AUTEUR Ch. Ruhle

TITLE IN ENGLISH - TITRE ANGLAIS

Biology and management of the European lake char (galvelinus capinus L.) in Lake Zug (Switzerland)

TITLE IN FOREIGN LANGUAGE (TRANSLITERATE FOREIGN CHARACTERS) TITRE EN LANGUE ÉTRANGÉRE (TRANSCRIRE EN CARACTÈRES ROMAINS) Biologie und Bewirtschaftung des Seesaiblings (Salvelinus epinus L.) im Zugersee

REFERENCE IN FOREIGN LANGUAGE (NAME OF BOOK OR PUBLICATION) IN FULL. TRANSLITERATE,FOREIGN CHARACTERS. RÉFÉRENCE EN LANGUE ÉTRANGÉRE (NOM DU LIVRE OU PUBLICATION), ,AU COMPLET, TRANSCRIRE EN CARACTÈRES ROMAINS.

Schweizerische Zeitschrift fuer Hydrologie

"EFERENCE IN ENGLISH - RÉFÉRENCE EN ANGLAIS ("Swiss Journal for Hydrology")

PUBLISHER - ÉDI TEUR PAGE NUMBERS IN ORIGINAL DATE OF PUBLICATION NUMÉROS DES PAGES DANS not shown DATE DE PUBLICATION L'ORIGINAL

YEAR ISSUE NO. 12 - 45 VOLUME PLACE OF PUBLICATION ANNÉE NUMÉRO NUMBER OF TYPED PAGES LIEU DE PUBLICATION NOMBRE DE PAGES not shown DACTYLOGRAPHIÉES 1977 39 1 50

REQUESTING DElliViTMENT DFE TRANSLATION BUREAU NO. 1486937 MINISTÈRE-CLIENT NOTRE DOSSIER NO Fisheries Branch, BRANCH OR DIVISION TRANSLATOR (INITIALS) V.N.N. DIRECTION OU DIVISION Nfld. Biological Station TRADUCTEUR (INITIALES)

PERSON REQUESTING Brian Dempson ug 25 BiB DEMANDÉ PAR *t UN ED 0 TR A Pi.".U„ A YOUR NUMBER ;o:.m.7, -;ii:ei on!y VOTRE DOSSIER NO For tn 1 TRADUCTION NON RPVISEE DATE OF REQUEST 17. 07. 1978 Information seulomont iiiiDATE DE LA DEMANDE

SOS-200-10.6 (REV. 2/88) 7030-21-029-5333 • Secretary Secrétariat of State d'Ètat TRANSLATION BUREAU BUREAU DES TRADUCTIONS

MULTILINGUAL SERVICES DIVISION DES SERVICES • DIVISION MULTILINGUES

CITY cuevcs NO. DEPARTMENT DIVISION/BRANCH VILLE N° DU CLIENT MINISTiRE DIVISION/DIRECTION Fisheries Branch D. F. E. St. John's, Nfld Nfld. Biological Station

BUREAU NO. LANGUAGE TRANSLATOR (INITIALS) N° DU BUREAU LANGUE TRADUCTEUR (INITIALES) AUG 25 mu 1486937 German V.N.N.

"Biologie und Bewirtschaftung des Seesaiblings (&alvelinus capinus L.) im .Zugersee," Schweizerische Zeitschrift fuer Hydrologie 39(1), 12 - 35, 1977

Biology and management of the European lake char

(Scavelinus capinus L.) l in Lake Zug (Switzerland) 2

by • Ch. Ruhle From the Institut fuer Gewaesserschutz und Wassertechnologie and der ETH (Eidgenoessische Technische Hochschule) [Institut for Prevention of Water Pollution and Hydrotechnology, Swiss Federal Institute of Technology], Zurich, Switzerland

(Received on 7 March 1977)

Summary - During the past 70 years, yields of European lake char fishery in Lake Zug have dropped from some 100,000 to 5000 fish per year. The present work was aimed ar developing methods for retarding and, perhaps, reversing this downward trend. In order to arrive at a proper base for developing new methods of fish stock management, the biology of the lake char was investigated. It was found that this fish is able to utilize the increased supply of food available in this eutrophie lake, but that the probability of natural reproduction is very low under the environmental conditions presently prevailing in Lake Zug. On the basis of the findings

1 Translator's note: This fish is also know as the European sea trout, a landlocked species found in southern Bavaria, Switzerland, and the Austrian Alps [Scavelinus capinus scavelinus]. 2 This work has been carried out at the Eidgenoessische Anstalt fuer Nasser- versorgung, Abwasserreinigung und Gewaesserschutz [Swiss Federal Institute of Water Supply, Wastewater Purification, and Prevention of Water Pollu- tion] (EAWAG), CH-8600 Duebendorf, Switzerland L5 ;\IEDI T .)- TR /M--i ;2:r ; • I For

'Tf;ADIC.1.1"..);`; NON SEC 5-25T (6/76) .Informailon • - 2 - obtained, the following measures have been recommended for improving lake char yields: (1) Intensified stocking (using yearlings, if possible); (2) use of gill nets with larger mesh size (35 mm); (3) discontinuation of fishing outside of the spawning season; and (4) setting up of new (artificial) spawning grounds in shallow water zones with good oxygenation conditions. The measures for improving the stock of lake char will be expensive. Even with maximum yields, the cost-benefit balance of lake char management will be negative. It is concluded that only the historical significance of European lake char fishery in Lake Zug can justify the great expenditure of public funds involved.

1. Introduction

The Lake Zug lake char is a fish with tradition. It has been mentioned

for the first time in a treaty written in the year 1281, which document

settled an important transaction between the House of Habsburg and the

Austrians (31), and, as in that document, the lake char has been mentioned • in various other documents from the late Middle Ages as tithe or tribute by subordinate courts. In the years 1759 and 1788, the council of Zug had

to deal with this fish (30); these two council matters dealt with the

mutual rights and duties of line-fishermen and net-fishermen, requiring

official regulations for the common practuce of lake char fishing. The

renewal of these regulations led in 1844 to the foundation of a fishermen's

association in Walchwil, which was still in existence one hundred years later.

These rather incomplete data in the role playes by the lake char in

the local history of Zug explain why the people of that region--although

they are now working chiefly in administration, commerce and industry--still

possess a strongly developed "lake char awareness." That awareness not

only finds expression in the fact that this fish has been raised to the

rank of a historical curiosity; it is also expressed in the enactment of • official regulations dealing with the specific promotion of this "typical" fish. And, last but not least, that awareness is reflected in the desire,

above all, of the local government of Zug, but also of many businesses,

associations and individuals to be able to enjoy that historic delicacy

at least once a year during the lake char season.

Around the turn of the century and during the first decades of this

century, the fishermen of Lake Zug were still able to catch relatively large

numbers of lake char. In the fishery lake classification (27; 63), Lake

Zug was listed as one of the characteristic lake char lakes. Yields of

90,000 to 100,000 lake chars per year, representing 85 per cent of the total

catch (58), confirmed the validity of the assignment of Lake Zug to that

lake type, which is distinguished by steno-oligothrophic properties, cor-

responding depth as well as as continuously low temperatures and high oxygen • contents across the entire profile (27). As is indicated by the data plotted in Figure 1, the situation has

greatly changed since then; in the average of the last ten years, only 8400

lake chars have been caught per year; that number of lake chars corresponds

to about two to three per cent of the total catch taken from the Lake.

For some time now, these catches are no longer large enough to satisfy

the demands of the local market, which have been estimated to amount to

approximately 20,000 lake char per year (46). That situation (and the high

proce resulting from the discrepancy between supply and demand) as well

as the conviction of the most important buyers--the restaurant and hotel

owners--that the native fish, for reasons of quality, cannot simply be re-

placed by lake char caught in other lakes have already led to a number of

attempts to revitalize lake char fishery and management in Lake Zug. How- • ever, the goals aimed at have not been reached. For that reason, it became • - 3 -

Figure 1 - Yields (numbers of fish caught) of lake char fishery, 1900 - 1974. Key: 1, Illegible; 2, Year.

• necessary to study the biology of the lake char in Lake Zug within a wider 14

framework than had been done in the past, and to work out management mea-

sures, insitution of which would prevent a further decrease of the yieldd

and, perhaps, even make possible an increase.

2. Description of Lake Zug

2.1. Geography, geology, morphometry, and hydrology

Lake Zug is a lake of the Alpine foothills (middle of its longitudinal

axis: latitude 47 ° 04' north, longitude 8 ° 29' east), located between the

Rigi Mountain (approximately 1800 m above sea level), the Ross Mountain

(1600 m), the Zug Mountain (1000 m), and the foothills of the Root Mountain

(850 m) (Figure 2).

Two peninsulas project into the lake from the west; the bigger one of

these peninsulas, the Kiemen (Chiemen), divides the lake into two, morpho- •

• Figure 2 - Lake Zug.

Table 1 - Morphometric and hydrological data of Lake Zug. Key: 1, Alti- tude above sea level; 2, Maximal length; 3, Maximal width; 4, Minimal width; 5, Maximal depth; 6, Mean depth; 7, Lake surface; 8, Lake volume; 9, Catchment area; 10, Inflow; 11, Inflow into the upper lake; 12, Inflow into the lower lake; 13, Residence time (theoretical); 14, Residence time; 15, Upper lake; 16, Lower lake.

• "1 '. Nleereshübe 413 m 2 . Grüsste Lânge 13.4 km 3. Grüsste Breite 4,6 km 4 . Kleinste Breite 0.8 krn 5 • Gri.iste Tiefe- . 198 m .. Mittlere Tiefe ; . ' ; 80 .nt . 7. Seeoberflâche 38.2 km' 8. Seevolumen 3.2 g • Eillzugsgebig.t - „ 4, 412 10 , ZtifhisrS ' - 1,78 mi/sec ' Ziitluss Qb'irSee 2,96 rn3/see ',Zufluss'Untersee 1.!. 4;82 ['Mee' , 13'.,Ânfeniltaltszeit (theor .). . 1:3,t},41ire;, yea:r,s,

• 3,4hre year.s• II) „ .2 , ,. - -yeaf.S" • - 5 - logically different parts, viz. the lower lake (southern part) and the

upper lake (northern part). The deepest site of the lake is located in

the upper lake, which is relatively poor in inlets, and furthest away from

the outlet. Lake Zug is under the civic jurisdiction of three Cantons:

Zug (ZG) (approximately 65 per cent of the surface), Schwyz (SZ) (approx.

25 per cent), and Lucerne (LU) (approx. 10 per cent).

The more important morphometric and hydrological data of Lake Zug are

summarized in Table 1.

2.2. Limnology

Lake Zug became the object of limnological studies only relatively late

[the exception being Brutschy (12)], and is monitored at regular intervals • only since a few years ago. However, its developmental history has been well demonstrated by Wuellig (66) on the basis of drill-core samples from

the sediment. The contents of total phosphorus, total nitrogen, total sul-

fus, sulfide sulfur, organic carbon as well as of both free and bound si-

licic acid determined by the latter author exhibited a certain constancy

up to the turn of the century. The afore-mentioned contents increased

steeply in the sediment horizons for the time after 1900. During that

period (1907 - 1909), Brutschy (12) established the first mass development

of certain planktonic microorganisms. Comparison of transparency (Table 2)

and of lake color (Table 3) provides an idea--even if only a superficial

one--of the development of Lake Zug. These particular data have been taken

from Brutschy (12) and Zeder (65).

The present eutrophic state of Lake Zug is demonstrated when comparing

several limiting-value criteria for the assignment of lakes to the eutro-

phic type and the corresponding values actually obtained in the Lake (Table 4). Table 2 - Transparency of Lake Zug at the turn of the century and during • the past few years. Key: 1, Transparency_(in m; determined using the Secchi disk); 2, Month; 3, Year.

2... Monat Jan. Feb. Mârz April Mai Juni Juli Aug Sep, Okt. '` .;Dez. :.1qarf , ,:May, Ot '12,0 3,8 5,5 • 4,3 4,4 6,2 8,4 ' :i1,8 16,0 11,8 8,9 11,8 62 4,6 4,6 5,3 ' 1968. 14,5 16,1 12,8 4,0 4,8 4,6 46 • 4,6 63 92 111 1909 . .":12,2 3,5 16,5 • 7,4 5,5 1970 .. . 5,8 1,4

Mi7.1 , 6,2 1,6 3,6 • , 1972 .'Jan..41111,Aug.': ea"."5:5. • 1973',' 1,5• 7,3 • 3,8, ■■■■

Table 3 - Color of Lake Zug at the turn of the century and during the piast few years (readings after Forel). Key: 1, Year; 2, Average scale values.

2 Durbhsehnittliehér Skalenwert • , 1, 1907 ' . • 1 „ 1965 1. 6-7 • , 1971-1973... • 10-12 ,

Table 4 - Comparison of various critical values for eutrophic classification with corresponding current values of Lake Zug (calculations based on Zeder [65], page 12). Key: 1, Visibility depth; 2, Nutrient content during circulation; 3, Nutrient supply; 4, Limiting values for the eutrophic state; 5, Actual values found in Lake Zug; 6, Bliographic refer- ences; 7, per year.

2. Nahrstolfgehalt • wiihrend Zirktilatioe:- , .(Gi'énzWe 30 pg, P/1 ..0.67eP/MI:Jài 500 ug NO,-N/1 10,113';.N./m 2 Jalir • 1st-Wert 1,5 m 100pgP/1 10,0gTPY.reJallr Zugersee (M473) 26eugN0,-N1 "50.2g N/m'Jahr • Refèrenz Dobson': "Vôllenweider VoileuWeid,er,.(1969)

2.3. Fishery • situation

As already mentioned in the Introduction, Lake Zug was regarded as a • typical lake char lake still around the turn of the century. There existed a "natural bond" (27) between the construction of the basin and the degree of eutrophication. • -7-

2. 1 1 SEESAIEILINGE 1::::1FELCHEN 80 .q. ifflE1 HECHTE - HARSCHE

r. 1,0 C. F71 KARPFENART1GE w z% e>(.5.`e 40 7. LI. -0 120 ct Lre

8. um 1900 g. um 1950 , tim 1970 , ..,4.(Mittel dei Jahre 1948-55) der Jahre 19e-73)' 10.Z E 1. T

Figure 3 - Changes of species composition of the catches, 1900 - 1975, expressed as percentages of the total catch. Key: 1, Percentages of the total catch; 2, Lake char; 3,‘Whitefish; 4, Pike; 5, Perches; 6, Cyprinids; 7, Other fishes; 8, Around . . .; 9, (Mean value for the years . . • 10, Time.

1001— cp ce 801— ci Ui 601— • e-- <40

'20

1 1955 • 1960 • - 1970 2. JAHR

Figure 4 - Changes in the total yields of Lake Zug fishery, 1946 - 1973. • Key: 1, Total yield; 2, Year. The breaking of that bond by external factors has been reflected in a

change of the species composition of the catches (Figure 3), and in an in-

crease of the total yield of the lake (Figure 4). Both phenomena repre-

sent typical consequences of eutrophication, as we know tham from most Swiss

lakes, with the exception of a few less affected lakes in the Alpine foot-

hills and the Alps.

The change in the species composition in favor of the cyprinids not

much in demand on the market is reflected in a decrease of the average

sales proceeds obtained per unit effort and, assuming that the effort ex-

pended in the landing of different species is identical, in a reduction

of the annual income of the regular fishermen. In the year 1975, fifteen

fishermen were still working on Lake Zug; nine of them worked either full- • time or chiefly in fishery, while six of them had a second occupation apart from fishery. The longterm decrease of the number of professional fisher-

men evident also in the case of Lake Zug is contrasted by an increase of the

importance of sports fishing. During the 1973 - 1974 season, 800 indivi-

duals purchased fishing licences. The public purse received Swiss francs

27,000.00 from the sale of these licences, i.e. 1.7-times more than from

the sale of licences to the professional fishermen. In the average of the

years 1967 to 1972, the share of the sports fishermen in the total [lake

char ?] catch has amounted to about seven per cent.

3. General characterization of the lake char (Salvelinus capinus L.)

In taxonomy, the lake chars [arctic chars] occupy the following position:

Order: Clupeiformes [Isospondyli; Trans1.], the herring-like fishes Suborder: Salmonoidei, Salmon suborder Family: Salmonidea, Salmon family • 9 Subfamily: Salmoninae, Salmon, trouts, and chars (scales small, rounded) Genus: Salvelinus, Chars Species/rassenkreis [rheogameon]: Salvelinus alpinus, Lake char or arctic char

The chars belonging to the Salvelinus aZpinus rassenkreis [definition

of rassenkreis according to Rensch (43): "A complex of intergrading geo-

graphical races or subspecies, representing each other at different geo-

graphical sites, and able to reproduce to an unlimited degree with the race

inhabiting the adjacent biotope"] have circumpolar distribution. They are

found in both the New World and the Old World as well as on the arctic is-

lands (35). They occur as anadromous fish (migrating chars) and as non-

migrating [landlocked] fish (lake char). However, according to Nikolsky

(36), there exist also populations exhibiting behavior with respect to mi- • gration that is not unequivocal. In addition, the latter author has mentioned lake chars that have evolved from anadromous chars only very recently

due to the appearance of artificial or natural barriers.

Various authors attribute unequivocal systematic significance to the

different ways of life of the lake char (8; 10; 34; 35), leading to non-

uniform naming of this fish: Salvelinus alpinus, Salvelinus salvelinus, Salvelinus alpinus sevelinus. In particular, the possibility is still

given at the present time of transforming andromous chars into non-migrating

chars indicates that lake chars and andromous chars are representatives of one complex of races, viz. SaZvelinus capinus. In older publications,

the lake chars have frequently been assigned to the genus Salmo. However,

in contrast to the true salmons, the lake (arctic) char exhibits (10):

(1)Much smaller scales; • (2) Correspondingly more scales along the lateral line (not less than 195, while representatives of the genus Sabi() exhibit 120 to 130); • - 10 - (3)A short vomer bearing a different kind of teeth; and (4)Not more than 50 pyloric caeca (S. trutta, up to 60; S. salar, up to 74).

The chars of the Salvelinus alpinus rassenkreis are found, on the Euro-

pean continent, in Central Europe, on the British Isles, and in Scandinavia

(including Iceland). The present southern limit of occurrence of migra-

tory (anadromous) chars runs approximately along latitude 64 ° north (south

coast of Iceland) (23).

In Central Europe, the lake char is found in the cold, well oxygenated

lakes of the Alps north of the central ridge of the Alps (50). Reportedly,

they occur there up to an altitude of almost 2800 m above sea level (42).

Lake chars are missing on the south side of the Alps. However, toward the • end of the last century, lake chars were introduced into Lake Lugano from Lake Zug (42; 57), and from Lake Lugano in the year 1910 into Lake Maggiore (26).

It appears that the lake char has in the past been represented in most

lakes in northern Alpine Switzerland. However, the extent to which these

populations were autochthonous [generated within these particular habitats]

can no longer be established. There are indications suggesting that the

lake char has been introduced, at least, into Lake Thun and Lake Brienz

(62). Probably, this fish was also absent from Lakes Murten, Pfaeffiker,

Greif, Lunger, Sam, and Hallwill.

The original distribution of this fish in Europe and the southern limit

of occurrence of the migratory chars indicate that both the migratory and

the freshwater char represent cold-stenothermic fish. As salmonids, lake • chars possess a particular high oxygen requirement. • - 11 - 4. Biology of the lake char in Lake Zug

4.1. Nutrition

Free-living, adult lake chars are fished in Lake Zug chiefly during

the spawning season on the spawning grounds. The stomachs of lake chars

almost ready or actually ready to spawn were empty in most cases.

The few lake char examined outside of the spawning season (caught to-

gether with whitefish and perches) exhibited the stomach contents listed

in Table 5.

The striking predominance of Corethra—which is found mostly in eutro-

phic waters (17), and which in several of the lake char stomachs investi-

gated was present as sole organism in very large numbers (up to 3000)--as

well as the good physical condition of the fish examined indicate that the • lake chars of Lake Zug are able to utilize the supply of food changed due to the eutrophication of the lake.

Young lake chars reared under artificial conditions exhibited a pre-

ference for Cyclops and Bythotrephes. The latter organisms could be demon-

strated in the stomach, even when they represented only a minute fraction

of the food offered. Daphnia was ingested in relatively large numbers

only when the food contained no other organisms or almost no other ones.

Diaptomus was ingested approximately in the same proportion, in which that

organism was represented in the food supplied.

4.2. Growth

The data used in our growth and gain calculations have been obtained • in accordance with the usual standard procedures: • - 12 - Table 5 - Stomach contents of free-living adult lake chars; frequencies of the main food and prey organisms. Key: ',Organisms; 2, Percent of all stomach contents examined, in which organisms were found; 3, Planari- ans and planarian cocoons; 4, Terrestrial insects; 5, Non-identified spawn; 6, Daphnia.

Organismen 2. % aller untersuchten hlageninhalte, in clenn di Organismen gefunden wurden 3.• Phinarien und Planarienkokons _ 30

:. . , 4 Tt:,i-r. Insekten , , .,. . . , ,. , . ,, 5 , :.eltirtntomus 30 ' „ Nieht. identilizierter Laich : 30 Cyclités ., 5 i C'orethia , , 50 : baplutien ': ' 25 . 'itythotrejihes ... 5

(1) Sampling of scales as well as measurements of lengths and weights

chiefly in live (anesthetized) fish;

(2) Interpretation of scales using a projection microscope; and • (3) Retrograde calculations, based on scale size--fish length standard curves after Segestrale, to which the individual scales were fitted with

the aid of a correction factor. The region of the standard curve valid for

small fish was established on the basis of data obtained in post-larval

young fish (fingerlings), juvenile fish hatched during the same year, and

yearlings reared under artificial conditions.

For our growth calculations, we have carried out age determinations

in a total of 389 specimens; 223 of these specimens were females, and 166

were males. According to various authors (4; 25; 37; 42), determinations

of age are difficult to perform in lake char scales. On the other hand,

removal of the internal organs was not possible in our work due to the

high market value of the fish and the custom of selling them alive. The

age determinations were checked against tagged fishes of known ages. These • control examinations revealed no evidence for misinterpretations. • - 13 -

i . 4 9.64(1 -e-0.191(ti -0.239) ) lt

Figure 5 - Age-length relationship. Key: 1, Length (in mm); 2, Oldest ...; 3, Age (in years).

The curve for longitudinal (length) growth, which, according to Von • Bertalanffy (9), is based on the general formula

and, with respect to length, can be converted into

_ e 1-"intax

was calculated with the aid of a program developed by Allen (3). Calcula- 19

tion of the weight gain curve, in the form

v gir a • 12'n. 1 ax

was based on the above-mentioned formula for longitudinal growth and on

the length-weight relationship • - 14 - Figures 5, 6 and 7 illustrate the course of longitudinal growth (length),

the relation between the lengths and the weights as well as the course of

weight increase (including weight gain). Table 6 gives the values used

for plotting the growth (length) curves.

The following results are worthy of note:

On the whole, longitudinal growth of the males and that of the females

differed only a little. Possible differences can be established at best

in the extrapolated region.

At identical length, females are heavier than males.

It then appears that the weight increases of the two sexes differ; the

weight gain maximum is reached by the males about one year earlier than

by the females. • In connection with the question regarding the extent to which employment of very young fish is practical in view of the utilization of the bio-

mass produced at the lower levels of the trophic pyramide, we draw atten-

tion to the low gain performance at that age and to the low utilization

of that biomass based on that performance.

Calculation of courses of length increases of four groups of fish,

which, on the basis of lengths at the end of the first year of life estab-

lished by retrograde calculation, exhibited a very good starting growth

(length at age 1: > 79 mm); good starting growth (69 - 79 mm); moderately

good starting growth (59 - 68 mm); or poor starting growth (< 59 mm), de-

monstrates that these different growth characteristics were retained during • subsequent life. • - 15 -

200 300 .2, L N 1 (mm)

Figure 6 - Length-weight relationship. Key: 1, Weight; 2, Length.

5.3Jahre ZUWACHSMAXIMA.

5 10 "t. .ALTER (JAHRE)

Figure 7 - Age-weight relationship and annual weight increases. Key: 1, • Weight; 2, Increase (gain) maxima at the age of . . . years; 3, Age (years).

- 16 -

Table 6 - Curve parameters of the age-length relationship. Key: 1, Curve value of the growth curve; 2, Standard error; 3, Upper limit of confidence; 4, Lower limit of confidence.

, 1. urieè- ni iat)le S • ()here' .." 'Unkfc Wad v,shm,k un, V crtrauen.grepie' ircr' traut:nNgirçinzt: 0.191147 0.02526 0.191147 • 00,1 7, '0.231.14 0.08366 0,239138

49 641 2(i . 3.02086 49(4 ' I 27

. .

k ,t ':. ,. 0. 21495 ' 11,034'57 0.21495 0,331010 0,068406 0.331010 • 1. , tan ' 47.290175 4.542636 47.290183 160

Table 7 - Age class composition of spawning lake char. Key: 1, Routine catch of spawning char; 3, Nets with a mesh size of 30 mm; 4, Controls; 5, Nets with a mesh size of 5 30 mm.

4 1. 34' 6t

Ord1kher 7,1 59,5 28,6 4,8 141-1,fischfanà 3,2 35,5 8,7 14 suit 2,8 39,5 37,5 13,7 0 niT MW 2,3 18,3 14,8 • % 3,9 4-2,6 35,3 . 24.61 20,0. 144intri?Ile 8 "4. . 30,7 615 ‘. 7,8- 5 1\letzé sun - 13,2 66,0 - 6,6 13,2 ' N1N'i rnm + % - 21,4 64,3 7,1 , :7.2

Table 8 - Lengths and weights of lake chars reared at different temperatures. Key: 1, Date // Control; 2, Lengths, in mm; 3, Weights, dry, in mg.

1.. Dàtum Kontrolle 8°C >.' 10°C 12C. 14°C Argument Î. 2.2 23,8 22 • Ltlàgen 295: 23,8 2,2 23, 2,2 23,8 2,2 23,8 - ' 111171 23. 28,3 2,9 29,5 3,9 29,2 2,8 26,3 4.2 -31,6 , 3.7 . • I& 28,8 3,2 28,8 3,3 31,4 3,1 32,6 ' 3,6 34,4 3,3 2.9. 315 25 34 4 3,3 41,4 4,6 36,6 5,7: 376 15,5 8,3 15,5 . 8,3 15,5 5 2.11 . ,• 32 , 18 34 ,

■•■ • • - 17 - 4.3. Reproduction

In correspondence with their diversiform region of occurrence and their

different ways of life [anadromous versus landlocked], reproduction is non-

uniform in the chars belonging to the Sevelinus alpinus complex.

Distinct differences exist with respect to:

(1) Length of spawning migration, above all, as a consequence of the

different "home ranges" of the anadromous chars and the freshwater lake

chars during the nutritional phase. Among the Salmoninae, the genus Salve-

linus is regarded as the genus with the least marked anadromous habit (Sal- velinus namayeush represents a non-migrating species) (29); nevertheless,

more or less distinct migratory behavior is in evidence also in most land-

locked freshwater lake char populations (lake river, river river, lake • 4 lake) (49); (2) Selection of the spawning waters (standing or running); + + + (3)Age of onset of sexual maturity: 1 to 11 or 12 (2; 25); and

(4)Time required by the eggs to undergo development (that required

by the eggs of anadromous chars apparently is shorter than that required

by those of landlocked freshwater chars).

As common properties we may mention spawning and egg development under

favorable respiratory conditions, usually over gravel bottom [lithophilous

fish (14)]. It appears that chars, in addition, are pluriparous in principle.

The investigations performed with respect to the reproduction of Lake

Zug lake char have dealt with the onset of sexual maturity, development

up to spawning maturity (including sex-specific differences in that deve-

lopment: protandry), fertility and duration of development of the eggs as • well as reproduction under natural conditons in the lake. • - 18 - As has already been mentioned in the Section dealing with nutrition,

lake chars of Lake Zug are caught almost exclusively during the spawning

season and on the spawning grounds. For that reason, it was difficult to

observe gonadal development in the course of the year. It is certain only

that regression of the gonadal glands has been completed in most cases

during May (stage II of maturity after Kiseljowitsch) and that relative

gonadal weight increases steadily to complete maturity during the period

between June and October. A population is regarded ready to spawn if 50

per cent of the captured females are ready to spawn (stage V). In the long-

term average (65 years), that is the case on 15 November (± 4 days).

The first lake chars appear toward the end of October on the spawning

grounds of the upper lake (at the present time, 25 spawning grounds are • still in use at depths between 25 and 80 m); during the feeding phase, these fish are found chiefly in the lower lake, in the littoral and the pelagial

zones. As is indicated by the data plotted in Figure 8, there exists a

considerable difference between the males and females with respect to both

the onset of spawning maturity and arrival of the individuals over the spawn-

ing grounds. That phenomenon (protandry [in the sense that males appear

earlier in the year than females; Transi.] must be attributed--at least,

in part--to the fact that display of courting behavior by the males is

required for several days to elicit ovulation and spawning behavior in the

females (64). This time difference in the maturation of the males and fe-

males can lead to profound, negative consequences in instances where arti-

ficial fertilization is attempted.

Under natural conditions, that shift and the sex ratio--which, with • about 65 per cent females (1973: 71.2%; 1974: 63.5%), deviates rather • - 19 -

10 15 20 25 • 30 3. ZEIT (Tage sell Beginn des Laiclifischfahes)

Figure 8 - Sex-specific differences in times of reaching the spawning grounds. Key: 1, Percentages of the catch; 2, Values obtained during the spawning season of the year ....; 3, Time (days since the start of fishing during the spawning season).

• significantly from the natural sex ratio of about 1:1 (36; 59)--do not have to have the same consequences. It rather appears that the males, under

undisturbed conditions, remain longer over the spawning grounds (20) and

apparently "mate" with several females (21). The early onset of spawning

maturity in the males, thus, is coupled with more prolonged spawning matu-

rity, which overlaps that of the female--a phenomenon, which, of course,

cannot be discerned in a population subjected to intensive fishing during

the spawning season.

Analysis of the age-class composition of the catch landed by commercial

spawning-season fishery during the year 1971 to 1973 yielded the results

summarized in Table 7 (upper part) [page 16 of this Translation].

These results must be questioned, a priori, due to the selectivity of

the minimum mesh size of 30 mm prescribed by law. The results obtained in • control catches using a more finely meshed net are presented in the lower • - 20 -

!.... , 2200 (.) N.462.15+3.16.91 I: n.:293.et 095I

1800

k -, 1406

‹,

1 I. • 1 1 1 i 200 .,.' :300:,..'•.. 400 • ' "100 -" .i.. 300: ' .,, „ . ., . _:600:;2; -t :.".‘e.. ; .'' ,-.; 61'.. `‘,. . at.,. 2';.L:ffi'egf.... —„ itriii.n).—i s :, •3 •GWICHT • ::.(à) ,e,•. : . ;:. it, Al.,11:07,;;.,(„lahré)

Figure 9- Relationship between egg number and total length, weight, and age of fish, respectively. Key: 1, Number of eggs; 2, Length (mm); 3, Weight (g); 4, Age (years).

• part of that Table. (Taking into consideration the facts just outlined with respect to the sex ratio) we are permitted to draw the following conclusions

regarding the age of the lake chars at the onset of sexual maturity: Onset

of sexual maturity at the age of 1 + : excluded with great probability; 2 + :

possible, specifically in the case of males; 34. : probable; 44. : possible

specifically in the case of females.

Suworow (59) has defined the fertility of fishes with the number of

eggs deposited. That definition does not agree with other ones, based on

the number of maturing or mature eggs (6). Suworow's definition has been

used [in the present work], in particular, because it was not possible to

kill fish in really adequate numbers. Fertility of the lake chars of Lake

Zug was determined in 87 females. Forty eggs of 55 of these females were

measured. The r-sults of our fertility determinations are plotted in Fi- • gure 9. .8 • - 21 - As was to be expected, the number of eggs increased with increasing

fish length. The non-linear function is expressed by the general formula b F = a x L , where F is fertility or egg number. In general, the exponent

b would possess a value of around 2 [Kisselewitch, quoted after Suworow

(59)]. Bagenal (7) has found values between 2.34 and 5.28. The low expon-

ent of 1.4 calculated by the present author must be attributed in the first

instance to the fact that too few large and old females were included in

the evaluation. Relative fertility (number of eggs/kg female) can be de-

termined on the basis of the linear relationship existing between body

weight and egg number. In the case of Lake Zug lake chars, that fertility

amounts to 7782.83. The difference between the egg numbers of the females

of different ages is of statistical significance. • The egg measurements revealed that egg size does not change with increasing fish size. For that reason, we were unable to investigate the

question whether large eggs produce bigger and stronger offspring than

small eggs (7; 13).

Under artificial incubation conditions, Lake Zug lake chars hatch after

about 380 day-degrees; the difference between eggs incubated at relatively

high temperatures and low temperatures is small: 12 °C: 384 day-degrees,

and 3 ° C: 381 day-degrees. According to Bigelow (10), egg development of

(anadromous?) chars takes 270 to 315 day-degrees.

It is worthy of note that the different water temperatures affect the

individual phases of development in non-uniform fashion: Development up

to the eyed stage takes 2.8 times longer in water of 3 ° C than in water of

12 ° C; that factor mnounts to 6.5 for the development from the eyed statge

to the larva (hatching); and to 1.9 from the time of hatching to yolk sac

absorption. • - 22 - The question whether and to what extent the lake char are still able

to reproduce naturally in Lake Zug is of decisive importance for lake char

management. Determinationof that question was relatively simple with re-

gard to one of the two functions of spawning grounds, viz , to attract the

fish to the spawning grounds for spawning. Already the large yields ob-

tained during the spawning season on some of the spawning grounds still

being fished at the present time demonstrate with certainty that, at least,

these spawning grounds correspond with respect to gravel composition to

the requirements of the spawning lake char. According to Fabricius and (\ Gustafson (21), 92 of 100 lake chars preferred spawning grounds of fine

gravel (n = 6), of coarse gravel (n = 53), of rubble (n = 23), and stones

embedded in sand (n = 11) for spawning to other, finely structured grounds.

This preference for coarse gravel bottoms was observed also in the case

of Lake Zug lake char. It is reflected in a relatively distinct dependence

of the number of fish arriving over the spawning grounds (expressed as the

number of fish caught per unit of fishing effort under comparable conditions)

on the condition of these spawning grounds (determined in the present work

by photographic means: cf. Figures 10 and 11) (Figure 12).

Several difficulties arose in connection with the question whether lake

char eggs reach the spawning grounds naturally and, above all, whether they

are able to undergo development under the conditions prevailing in the eu-

trophic Lake Zug. The minimum numbers of the eggs spawned in the Lake dur-

ing the years 1973 and 1974 were estimated to have amounted to 200,00 and

70,000, respectively. That assumption was based on the examination of

5127 captured females (1973: 3385; and 1974: 1742), of which 44.16 and • 31.[illegible: .1 or .4) per cent, respectively, were "empty." That at - 23 -

Figure 10 - Underwater camera, mounted on tripod with iron feet, perpendi- cular, and manometer. least one third of these "empty" females had spawned under natural conditions, and had not simply lost their eggs as a consequence of being captured or due to improper handling by the fishermen, is indicated by the fact showing that the regression line between the percentages of spent females (determined every day) and the time past since the start of fishing for spawning lake char exhibited during the two years under consideration practically identical curves and a comparable determinant; the level of that percentage, thus, is not influenced to any significant degree by external influences (fishery).

Direct testing of the proper functioning of the spawning grounds with regard to the incubation of deposited eggs was attempted in three different ways:

(1)Employment of a sledge-type dredge (15);

(2) Removal (by means of digging) of spawning grounds [as done, for example, by Roth and Geiger (44)]; that work was carried out in the Lake by divers; and • - 24 -

Figure 11 - Photograph of a coarse-gravel spawning ground. The position of the perdendicular indicates an extremely steep spawning ground. •

qFrire'. I I t • I • 20 40 , 60 80 ,100 2 (Anteil kiesiges Ma'le>rial • • ZlI STAND 0E8 'LAIÉHGRUNDES in der Oberflâche; %)

Figure 12 - Relationship between fish attraction capacity of the spawning grounds (expressed as catch per unit fishing effort) and the condition of the spawning ground (percentage of coarse gravel on the bottom surface). Key: 1, Yield (catch per unit of fishing effort); 2, State of the spawning ground (percentage of coarse gravel material on the bottom surface); 3, Limit of confidence.

(3) Employment of a small trawl net (54) prior to the release of arti-

ficially incubated and reared young fish for detection of lake chars developed • under natural conditions. • - 25 - The results obtained using these three procedures did not permit us

to draw definite conclusions regarding the proper functioning of the lake

char spawning grounds as medium for the development of eggs. More success-

ful was the employment of Vibert-like cages (60), into which fertilized

eggs were placed, whereupon the cages were lowered to the bottom of the

spawning grounds. In one of these submerged cages, we were able to demon-

strate a breeding success (incubation success) of at least one per cent.

In all other cages, the eggs had died, and were coated with a black layer

of organic sediment apparently degraded under poor oxygen conditions. In

order to establish with certainty that these losses were not due to metho-

dical factors, we have carried out a number of different control experi-

ments (incubation of the same spawn material in a breeding sieve; use of • the Vibert-like cage under favorable respiratory conditions in a trough, in the free water of Lake Zug, and in Lake Walen). The results obtained

in these control experiments, however, have confirmed the results of the

main experiment, which results actually are not surprising considering the

particular oxygen conditions prevailing both in the water above the bottom

and (in the case of eggs deposited naturally, resting in the lake bottom)

in the interstitial water as well as the particular oxygen requirements of salmonid eggs:

(1)According to data reported by Aldridge et al. (1), the oxygen re-

quirement of salmonid eggs increases with advancing development. At the

conclusion of egg development, the critical oxygen content (i.e. the oxygen

content, at which undisturbed development is still assured) amounts, for

example, in the case of O. [Oncorhynehus] keta, to 7 mg/L.

(2)Hayes and Macauley (28) have found that oxygen depletion of the

sediment by the overlying water amounted to 11 mg/dm2 /day in a lake classi- fied as being meso- to eutrophic. • - 26 - (3) According to Provoni (39), oxygen uptake from the water resting

above the bottom depends less on the trophic conditions than on the oxygen

content of that water (and the temperature). At a content of 5 mg/L, de- 2 pletion, according to the latter worker, amounts to about 20 mg/m /h or 2 4.8 mg/dm /day.

(4) The average mean depth of lake char spawning grounds amounts to

50 m in Lake Zug. At that depth, oxygen contents of 5 to 7 mg/L are the

rule during the spawning season and the the weeks following that season.

However, lower contents (3 to 4 mg/L) have frequently been measured [at

these spawning grounds].

These facts alone explain already the low breeding (incubation) successes

in the case of the eggs submerged inside our cages. In connection with the • development of naturally deposited eggs embedded in the bottom of the spawning grounds, we must give consideration also to both the oxygen content

of the interstitial water and the rate of replacement of the interstitial

water depending on the fraction:

(1)According to Eltringham (16) [Based on (11)], we must count on a

reduction of the oxygen content of the interstitial water to ten per cent,

if the fine-sand fraction amounts to only about 15 per cent (oxygen-saturated water above the bottom = 100%).

(2)According to Glass and Poldoski (24), the oxygen content of the

interstitial water of the upper 2.5-cm thick sediment layer of Lake Superior

decreases from 12.7 to 5.3 mg/L. The ratio of oxygen content of intersti-

tial water : oxygen content of water above the bottom amounts to 0.4.

(3)Even very high oxygen concentrations in the water above the bottom • cannot compensate both the reduction of the rate of flow brought about by • - 27 - the high fine-sand fraction and the consequences of that reduction of the

flow rate (52; 53).

(4) According to Rukhlov (48), 75 to 100 per cent of the deposited O.

gorbuscha eggs die, if the sand fraction of the bottom of the spawning

ground exceeds 20 per cent; more than 50 per cent of the embedded O. keta

eggs die if the bottom of the spawning ground contains more than 22 per

cent sand. The investigations carried out by Phillips et al. (38) have

yielded similar results. The two latter data are valid in the case of

running waters; in lakes, the results could at best be equal to the latter

results considering the circulatory conditions prevailing there.

If we, in connection with the results obtained in the case of the sub-

merged eggs, take into consideration the aspects just outlined, we can only • conclude that the probability for undisturbed development of lake char eggs deposited in natural fashion in Lake Zug, perhaps, does not equal zero,

but certainly is not very great. The rather considerable number of spawned

(and fertilized) eggs, thus, cannot contribute to any noticeable extent to

the reproduction of the population.

4.4. Parasites and predators

The following list is based on incidental observations made in the fish

subjected to measurements and in the course of incubating and rearing lake

chars as well as in experimental material. That list does not claim to be

complete.

Parasites - Infestation of eggs: Fungi resembling fish-skin fungi; pla-

narians; fish leech (Piscicola geometra). ---- Juvenile stages: Fungi

• resembling fish - skin fungi, Myxosoma cerebralis, Chondrococcus or Cytophaga • - 28 - columnaris, Argulus foliaceus. Adults: Fungi resembling fish-skin fungi, Ichtyotaenia longicollis.

Predators of eggs: Lota iota (burbot), and of adults: Esox lucius (northern pike).

S. Management of the lake char

I regard managing as an activity aimed at influencing the production

of an economic commodity in a fashion ensuring that a certain economic goal

(set usually by external factors, i.e. the market place) is realized on a

permanent basis and with an effort as little as possible. In the case of

Lake Zug lake char management, we then have to work out optimal methods

enabling us to satisfy, on a regular basis, the demands of the local market • estimated to amount to 20,000 fish per year. (The negavtive balance of Lake Zug lake char management already outlined permits one to think only of

giving satisfaction to the demands of the local market; working with

that negative balance requires support of the public purse [i.e. of the

Cantons of Zug, Schwyz and Lucerne]. That support is provided in the

form of maintenance subventions, which must be justified by extra-economic

factors; these factors are based on purely local historical considerations.)

Two secondary or marginal conditions are of importance in the case of

Lake Zug lake char management:

(1)The population can be maintained only by artificial means; and

(2) The reproductive matter employed in artificial reproduction of the

population must be obtained from fish caught in Lake Zug: Employment of

foreign spawn material or of spawn material derived from pond fish would • deprive this type of fishery performed exclusively during the spawning • - 29 - season (because of local custom) of its legal base. (Fishing [for other

fish] is prohobited during the spawning season; it may be permitted under taking certain conditions for the purpose of samples of reproductive products,

i.e. we are dealing with a prohibition with permission granted in special cases.)

Employment of foreign spawn material with simultaneous protection of

the local fish stock as measure for promoting a hard-pressed population

will not be discussed in the present paper, although that approach might

be used under certain conditions also in the lake char management of Lake

Zug. The close relations existing between these two marginal conditions

and the desire to realize the economic goal in rational and permanent

fashion not only makes necessary the employment of optimal stocking elem- • ents, but also demands the institution of population-stabilizing fishery measures. The desire to operate expensive lake char management in rational

fashion, finally, requires technical measures aimed at promoting both ar-

tificial and natural production conditions.

5.1. Stocking measures

Stocking measures will be optimally effective if the relation of costs

associated with the production of fish for stocking and their stocking value

tends toward minimal. In the present case, optimization, thus, means re-

duction of the production costs (related to unit of effort/cost) and increase of the stocking value.

5.1.1. Calculations of stocking value

On the basis of stocking numbers and catch results (41) as well as on

the basis of an age-class composition of the catches determined in sample • - 30 - catches, we have determined the stocking value of hatchlings (hatchlings

were used for stocking up to the year 1957) and of post-larval young fish

[fingerlings] (used for stocking between 1958 and 1970). The correlation

of all catches with the releases, without question, is wrong for the early

years when hatchlings were stocked; that correlation was based on the er-

roneous assumption that already at that time no natural contribution was

made to population reproduction. However, the magnitude of the coefficient

of correlation for the relation between the time and the quotient of catch

and stocking (= stocking value) makes it possible to estimate the extent

of that error. With r = 0.65 (P = 99%), that coefficient is twice as high

as it has to be in the case of a correlation to be regarded as being signi-

ficant. It then appears to be proper to regard the calculated stocking • value as correct in the case of the last two years under consideration. For the last ten years during which hatchlings were released for stocking,

we have obtained for stocking fish of that age a stocking value of 0.0041

(meaning that 4.1--0.41%--adults were caught per 1000 hatchlings released

for stocking); for the post-larval young fish released during the years

1958 to 1970, the stocking value amounted to 0.026 (i.e. 2.69% of the re-

leased post-larval young fish were caught).

Calculation of the stocking value of yearlings was based on a marking

experiment (for the tags used, cf. Figure 13), which can as yet not be re-

garded as having been concluded. Since the tagged fishes with respect to

their size did not correspond to the average fish (on the basis of retro-

grade ca;cu;ation to the same age) of the population, but were bigger, the

calculations of the reports of catches still expected had to be based on • a modified age-calss composition taking into consideration these different • - 31 -

Figure 13 - Tagged lake char, age 1 4". Tags are made of stainless steel and individually numbered (manufactured by Presadom, Brive, France).

2,LANGENVERG1EICH 3. GEWICHTSVERGLEICH q. ahs Haufigkeden Haufigkeilen 100 -300.. 50 100 150

• ' 35

• / 16 30

/1 • 14 / • E u , */. - —

10 r ' . • 5 fliae12.99 Z , 1 9

4% A •

. „. 1 1 • 25 1 15 2 •••:' 5. s. Zedpki • Marlderung Mark erung • >. . , L•T E. ALTER (Jr\FIRÈ) •

, • _ , .,Langen-Véitedung..„ 4. Gewichls - Verted ung der. mark Fische • der milk, Fische 1. Wachslunisverlauf der : •,,—;-''‘Vidisidinsverlaut der Gesamtpopulalion Gesaildpopedim 43. Wachstoinsvoilati1 der. Tedpopulation sehr igulerii . Jugendwachslum

Figure 14 - Age-length and age-weight relationships of the fish used in the tagging experiment compared to 'standard fish' of equal age. Key: 1, Length (mm); 2, Age-length relations; 3, Age-weight relationship; 4, Absolute frequencies; 5, Time of tagging: Age (in years); 6, Lengths distribution among the tagged fish; 7, Growth course of total population; 8, Growth course of partial population with very good juvenile growth; 9, Weight distribution among the tagged fish; 10, Growth course of the total population. • - 32 - different growth characteristics (Figure 14) and the resulting appearance

over the spawning grounds at different ages.

We furthermore had to take into consideration (1) that tagging- (clipp-

ing-) caused losses did occur, as have also been observed following the

use of jaw-tags by Stauffer and Hansen (55) as well as by Knecht (32), and

(2) that the fishermen did not pay attention to the tagged fish despite

the reward of Swiss francs 2.00 offered. + At the age of 6 the last tagged lake chars probably will have been

caught. The recapture frequency may be estimated to amount to 0.085 to

0.205 taking into consideration the factors just mentioned. The great span

between these two numerical values must be attributed to the fact that the + frequency of reporting of fish released during the summer at age 1 into • the lower lake (where the majority of lake chars dwells during that season) differs greatly from the frequency of reporting of fish released into the

upper lake. This particular difference between the frequencies of reporting

of these two groups is of statistical significance. In the case of con-

sequent release of l + fish into the lower lake, we would then be permitted

to count on a stocking value of 0.205 for fish of that age.

5.1.2. Production of fish for stocking

The first artificially incubated lake chars were released inti Lake

Zug during the year 1883 (62). The methods for producing fish for stocking

used at that time were maintained until the year 1968, and at that time

were modified only to the extent that the fish were no longer stripped

("skimmed") by the fishermen with the eggs brought by them to the hatchery; • since 1968, a fisheries technician visits the individual fishermen and there looks after the business of removing the reproductive products and • - 33 - their transportation to the hatchery. The incubation successes had been

poor in particular during the last years, amounting to only 60 per cent.

An expenditure of at least four hours was required each day for taking

care of the spawning material (removal of dead eggs, etc.).

The suggestion arose to ascribe these unsatisfactory results to

unsuited incubation temperatures in the hatchery. For that reason, we made

a preliminary attempt to determine the temperature optimal for incubating

eggs of Lake Zug lake chars. For that purpose, we have used a reconstructed

incubator, in which each one of the ten breeding (incubating) sieves could

be supplied with water of different temperatures between 3 ° and 12 ° C. The

success was judged, first, on the basis of the losses suffered, and, se-

condly, on that of the weights and lengths of the hatchlings determined • at the time of completed yolk sac absorption. The results are illustrated in Figures 15 and 16.

It is surprising that the fish that, on the basis of the losses suffered,

must be regarded as having been incubated under optimal conditions exhibited

the lowest, or almost lowest, weights. That phenomenon can be explained

only on the basis that fish incubated under favorable conditions are more

active than other ones, and turn over a correspondingly greater fraction

of their reserves in maintenance metabolism. In consequence, the time of

measurement at the conclusion of yolk sac absorption (which, in the first

instance, can be determined only with difficulty) must be regarded as be-

ing unsuited for the purpose of measurements. Weighing at the time of

hatching would, possibly, have yielded more appropriate results. This un-

certainty with regard to the quality of water of different temperatures • for incubation caused by the difficulties associated with the interpretation - 34 -

• - .ds Aunpunt t

-Apghngs'rriiiii:ma•

11' 12

Figure 15 - Hatchery losses in relation to incubation temperature. Key: 1, Losses; 2, Up to onset of larval stage; 3, Up to onset of eyed stage; 4, Loss minima.

• 9

• • '•

Figure 16 - Length ( ) and weight ( ) of lake chars at the end of yold sac absorption following incubation at different temperatures. Key: 1, Weight (dry); 2, Length; 3, Weight.

of the results forced us to continue our experimental work over a period of

rearing of three months. The results of that control experiment (Figures 17

and 18), however, have confirmed that optimal incubation conditions prevail

for eggs of the Lake Zug lake char at water temperatures of around 6 ° C.

The results obtained in these two experiments lead to the conclusion

that the great losses mentioned further above cannot have been caused by • the incubation conditions existing in the hatchery, where the water during the period of incubation exhibited temperatures between 5 and 6°C. • - 35 -

3 5 6 7 8 TEMPERATURE ( °C) •

Figure 17 - Losses during a three-month rearing period under lake-like conditions in dependence on egg incubation temperature. Key: 1, Losses

• It••• 8 •

.0 5(-) ¢ 4 ' ANGEN iis •

Lu. 2 . 4 n • i I 6 7 8 9 10 11 12 '...TEMPfi.lATUREerC)

Figure 18 - Length and weight increases during a three-month rearing period. Key: 1, Weight increase (dry weight); 2, Increase maxima; 3, Length increase; 4, Weight increase.

Incubation of the spawning material separated in accordance with the individual fishermen who had supplied that material then demonstrated

that the treatment accorded the parental fishes between the actual catch 32

and the stripping ("skimming") was inappropriate in the cases of certain

• fishermen (daily removal from the containers for checking the state of - 36 -

• maturity; checking whether the fish destined for the market had already been stripped; returning of the fish into the containers; etc.). By

means of the type of stripping performed today right after the catch in

the hatchery, which is passed by most fishermen after hauling in of the

nets, it became possible on a number of occasions to reduce the losses to

less than ten per cent.

In 1941, Steinmann (56) recommended the employment of post-larval young

lake chars; his recommendations have been followed since 1958. The pro- TM duction of post-larval young fish is carried out in round Eternit troughs.

However, the rearing results hitherto obtained are very poor; in the year

1973, the success amounted to only 13 per cent (33). In the round troughs,

the lake chars exhibited the same behavior described by Roth and Geiger • (45) in the case of trout. The fish remain at the bottom of the trough among food rests and exrement; there, they are attacked by parasites; be-

come indifferent; and show lack of appetite. The most obvious therapy--

viz. to give more food--leads to deterioration of the situation, with block-

ing of the gills in extreme cases, and, frequently, bacterial gill dis-

ease (Cytophaga columnaris). Roth and Geiger (45) have proposed the use

of sieve-drawers, which, floating in the round troughs, adapt the fish kept

in the sieves to swimming and feeding in the free water. A preliminary

experiment carried out in the Walchwill hatchery using that type of sieves

did initially give the desired results. However, that experiment had to

be discontinued prematurely: The algal coat formed on the underside of the

sieve-dish prevented circulation and, thus, washing away of excrement and

food rests. Employment of the sieve-dishes in filtered water (a filter • was installed in 1975) may lead to better results. • - 37 - As in the case of incubation, we made an attempt to determine the ideal

water temperature also in the case of rearing of post-larval young fish.

That particular experiment was carried out in 40-L containers, in which

the water, using thermostats, could be kept at desired temperatures (8,

10, 12, and 14 ° C; control: the working temperature of the hatchery water,

viz. 5 to 7 °C). As is indicated by the data presented in Table 8 [page 16

of this Translation], the young fish exhibited maximal growth gain per-

formance in the 10 ° C-basin. The loss minimum (added up) was observed in

the 12 ° C-basin.

Temperatures around 10 ° C correspond to the working temperature of the

Weesen hatchery used during lake char rearing (5) and to that of the St.

Moritz hatchery used during trout rearing (40). Swedish rearing experi-

ments have yielded similar optimal temperatures for lake char rearing (19).

In principle, it is possible to mix water of that temperature in the Walch-

wil hatchery: The hatchery is equipped with to suction inlet tubes (the

inlet openings of which are located in the lake at depths of 1 m and 30 m,

respectively), through which relative warm and cold water can be obtained.

The pumping system, however, would have to be modified for the purpose of

mixing the two kinds of water.

In addition to the use of sieve-dishes and the adaptation of the water

temperature to the requirements of the fishes, feeding with artificial

food might result in a further improvement of the rearing successes ]in

the largest government-owned hatchery in British Columbia, Canada, located

in Wardner (Kootenay Trout Hatchery), all salmonid stocking fish produced

there are fed exclusively artificial food; losses up to the day of release

as fingerlings: approximately 20 per cent). In hatcheries in which good

production conditions are maintained (for example, Faulen Lake, BE), rear-

ing successes of 80 per cent are obtained regularly. - 38 -

Since the fall of 1972, the fisheries administration of the Canton

of Zug has available a net-enclosed fish rearing station; the two net pouches 3 have a volume of 48 m (each); the mesh sizes are 4.25 and 6 mm, respectively. Since three years ago, lake char yearlings are being reared in these

enclosures. The rearing successes hitherto obtained (starting with the post-larval age) amount to 85 per cent. Each section of that net enclosure can hold up to 20,000 post-larval lake chars: The level of losses is affected only to a small degree by the stock density; however, at greater densities, growth perforamce is considerably reduced (total length of 101 mm and weight of 9.9 g at 8 L of water per fish versus total length of 57.2 mm and weight of 1.42 g at 1.5 L of water per fish; recording dates: 20 and 24 April, respectively).

5.1.3. Production costs and cost-benefit comparison

Table 9 summarizes the results of our analyses of production costs performed in connection with fish released for stocking at different ages.

Data that could not be determined by the present author have been taken from Frei (22) and from Roth and Geiger (45). Table 10 gives the benefit- cost relations for the hatchlings, post-larval young fish, and yearlings produced under different conditions. Both Tables illustrate clearly the extent to which incubation and rearing successes can affect the expenditures associated with stocking measures.

5.2. Fishery measures

Lake char fishery in Lake Zug must be operated in a way ensuring that

(1) fishes, which were unable to reproduce effectively, remain excluded from the catch made outside of the spawning season, and • - 39 - Table 9 - Production costs for lake char. Key: 1, Production costs for . . . (in Swiss francs); 2, Procedure, production success, and remarks; 3, 1000 Hatchlings (fry); 4, Conventional skimming procedure, 60% rearing success; hatchery half-full (5 x 10 5 eggs); 5,Conventional skimming procedure, 60% rearing success; hatchery full (10 6 eggs); 6, Optimized skimming procedure, 90% rearing success, hatchery half-full; 7, Optimized skimming procedure, 90% rearing success, hatchery full; 8, 1000 Post- larval young fish; 9, Rearing procedure used hitherto, 60% represents the minimal rearing success aimed for (theoretical); 12, 1000 Yearlings; 13, Rearing success: 85%; 14, (in the costs reported, we have included the costs of production for the starting material of the next, higher production level).

Produktionskosten fin* 2 . Verfahren, Produktionserfolge, Bernerkungen 3.. '1000 Brtitlinge 37.93 4 . Herkiimmliches Streifverfahren, Bruterfolg 60% Brutanstalt halb voll (5 x 10 5 Eier) 29.93 5. HeiUmmliches Streifverfahren, Bruterfolg 60% Brutanstalt %;Cii1"(10 6 Eier) 19.73 6. Optimiertes Sireifverfahren, Bruterfolg 90% Brutanstalt halb voll , 7 .- Optimiertes,Streifverfahren, Bruterfolg 90%, Brutanstalt volt 1000 Vorsiimmerlinge> . 1, 351.17 9. Bisheriges Aufzuchtverfahren, Aùfzuchterfo!ge,2e,.1,, (Ist) 74.32 10. Optimiertes Aufitichtverfahren, Minimeangestrebtek , • Aufzuchterfolg 60% (Soli) ,•,, 49.55 11.' Bei idealem Aufzuchterfolg von 90% 525.50 13 Aufzitchterfolg 85% pt.' (in den genannten Kosten sind die ProdUktionskOsten fur das Ausgangsmaterial der nitchst 110heren Produk tiongstufe bertickSichtigt)

(2) a fished population consisting of at least two reproductive year

classes is built up.

Re. the first demand: Ultimately that demand leads to discontinuation

of all lake char fishing outside of the spawning season: even if lake chars

do spawn in Lake Zug under natural conditions, they--according to the con-

clusions drawn in the Section dealing with lake char reproduction—do not

contribute to population reproduction; that is the case only if their re-

productive products are utilized under favorable conditions established by

artificial means. Lake char fishery in Lake Zug—as operated at the pres- • ent time--does not produce fish with reproductive products unusable due to age-associated factors.

• - 40 - Table 10 - Cost-benefit relations for lake char released at different ages and produced by different methods. Key: e, Efficiency; 1, Fish used for stocking; 2, Production costs, stocking value; 3, Production costs per "harvested" fish, in Swiss francs; 4, Rank; 5, Hatchlings (fry); 6, Cqn- ventional skimming procedure; 7, Hatchery full; 8, Hatchery half-full; 9, Optimized skimming procedure; 10, Hatchery full; 11, Hatchery half-full; 12, Post-larval young fish; 13, Previous rearing procedure; 14, Optimized rearing procedure; 15, Yearlings; 16, Production using juveniles reared under conventional conditions; 18, Released at random sites; 19, Released at ideal stocking sites (lower lake); 20, Production using juveniles reared under optimized conditions; 22, Released at random sites; 23, Released at ideal stocking sites (lower lake).

B'esatzfisehe 2. Produktions- 3. Produktionskosien 4 Rang kosten pro «geernteten»l:iSeh e— Ilesatzwert 5 . Brlittinge • • , 6 . a) lierkeinunliches Streifveifahten • Ilaitanstalt ' 0,02993/0,0041 - 7.30 8 ; t'.13nitanstall IaIb,voII • 0,03793/0,0041 — 9.25 9.. .14'.(1Ptiertes SWeifverfaliien : 1 .0 ,: ltritianStu lt w41, . 0,0144/0,0041 — 3,51 11. IiiiIIvoII 0,01973/0,0041 — 4.81

13:`' Atifiticlovvrtithren 0;15117/0.0.hi —11,51 14. 10.0p(iiiiielies Aulint litverfallien 0.0/412/i , 15. jt/hilinge ' 16.. .8)"..Produktion mit Vors6itouérlingen

18. irgendwo 0,931u5'0,085 10.9h 19 . .u.inNalze an idealen Einsatzorlen ((1ntersee) 0.93 1(0, 0,205 — 4.54 20. 1)) Produktion nut VorsOninterlingen aus optiinierter _ .- Aufzucht 22. - liins1itze irgendwo 0,5255/03085 .1 ,6.18 23. - Ii,ts.Itzc an' ideate) Einsatzorten (Untersee) 0,5255/0,205

Re. the second demand: The age-class composition of the spawning-fish

catch of 1971 demonstrated that the population--at least, in transitory

fashion--consisted chiefly of fish ready to spawn for the first time + + + + + + (2 : 5.88%; 3 : 77.64%; 4 " 7.06; 5 : 5.88%; 6 : 2.35%; and 7 : 1.18%). In

lakes, in which the production conditions for lake char are close to pessi-

mal, it can be imagined that the consequent succession of younger year • classes' is interrupted. Various reasons may be responsible for that

• - 41 - Table 11 - Calculated relative frequencies of the different age classes in the catches with nets of different mesh sizes (catches made during the spawning season). Key: 1, Age classes (during spawning time); 2, Mesh sizes, in mm.

Àllers1:1:*5en 2 . blaschenweiten in rim) 2=1 26 28 30 32 34

% , . 6194 55,79 49,77 • 5,37 29,92 1920 3' 28,32 31,07 37,27 33,42 40,61 43.62 ,, 39.47 34,53-

' . 8,07 10,47 11,01 19e, :22,22 28.20 3533 • 37,20 5' 1,73 2,67 1 ;95 ; (• 55 7,25 • '8,972 • 14.30 ,

Total ' 100 11/1) UN) 11}0 1 (X), 1(/() 2. l(g)1(10 . , • „ ' '

// /.. • >,, , , -,... li■ b. d -» e e-P3:.. Melleill3r4-■ , 'e 11111illik iWader 4S1‘41 I1..41.7:41111411011r.l .. . .. ''.' , i''. • 3 0 . . . I I0 derA I Lei I IVr 8 1. MASCHENWEITE 1 11111Pr', Allifflibb... - (mm) '411111reillirdellaire; 6 Ille. 4* 5+ . ' • (2,ALTER -

Figure 19 - Relationships between mesh size, age of the fish, and catch percentage (roughly estimated values). Key: 1, Catch percentage; 2, Age; 3, Mesh size (in mm).

interruption: Poor conditions during the fishing for spawning fish; break-

downs of the incubating and rearing devices; unfavorable conditions during • release of fish for stocking; poorly selected release sites; etc. The permanent realization of the economical goal then requires a stable popu-

lation, which can be obtained more readily with increasing number of repro-

ductive year classes being present in that population (the breakdown of a • - 42 - population depends on the age of the reproductive animals; on the number

of repreducing generations; and on the number of successive year classes

without offspring or with only a few offspring). This requirement is met

if an adequate fraction of the fishes ready to spawn for the first time

and, in principle, liable to be captured is excluded from the catch.

Determination of the mesh size, contributing, perhaps, to the realiza-

tion of the second demand, was based on both sample catches using nets with

varying mesh sizes and calculation of the age-length relations. The re-

sults of these particular investigations yielded the calculated relative

frequencies of the different age classes in the catches using nets of dif-

ferent mesh sizes (Table 11), and the relationships between mesh size, age

of fish and catch percentage (Figure 19). + + • Since a balanced 2 : 3 ratio corresponding to the second requirement cannot be realized, the fished population consisting of two reproductive + + generations must be built up of 3 and 4 fishes. Partial preservation + 3 fishes of the can be attained by using nets with 35 to 36 mm mesh size.

Partial preservation of fishes ready to spawn for the first time and their

catch at a higher age lead "automatically" to an increased yield of spawn;

the desire of the consumer (in my view irrelevant in this critical situa-

tion) for fishes of a small size, unfortunately, cannot be met.

5.3. Technical measures

Technical measures are defined as arrangements aimed at the improvement

of both natural and artificial production conditions with the goal of mak-

ing lake char management more rational (more economocal). Among these • measures are all improvements in production devices recommended in the • - 43 - course of the present investigations and, in part, have already been carried

out (net enclosures for rearing yearlings; sieve-drawers for rearing post-

larval young fish; modification of the pumping system for water processing;

filtering device for preventing formation of algal coats on trouhgs and

sieve-drawers used for incubation; etc.). Among them are also measures

aimed at preventing pollution of the lake water; it is hoped that these

particular measures will improve the state of the lake water permitting '

a more natural management of the lake char (the predictions of attaining

that goal within a reasonable period of time, however, are not very real-

istic due to both the particular hydrological conditions and the present

stand in the construction of pollution-preventing devices).

One technical measure of a particular kind is found in the gravel surfac-

ing of (dumping of gravel onto) the spawning grounds. That procedure has

been practised with certainty already in 1844 [1844: the year of the foun-

dation of the Walchwil Fishermen's Association; one of the goals of that

Association was the dumping of gravel onto the spawning grounds, which

could be done better on a cooperative basis (31)], and demonstrates an

understanding of fishery-biological aspects surprising for that time. Since,

at that time, there still existed the conditions required for natural egg

development (66), that undertaking must be regarded as a measure aimed at

improving fishing (concentration of the fishes over a small area easily

fished) and as means used by the fishermen not belonging to the Association

to create the foundation for catching lake char (by establishing their own,

new spawning grounds) (31).

With the regulation of the mountainstreams (reduction of the rate of

water flow; stabilization of the mountainsides and the bottom; reduction

of introduction into the lake of large boulders and rubble; etc.) and since - 44 -

• the eutrophication-induced intensification of autochthonous sedimentation, that measure [the dumping of gravel] represents--as is illustrated by Fi-

gure 12--an elementary prerequisite for catching spawning lake char.

On the basis of photographic investigations, it was possible to in-

validate the frequently mentioned fear that gravel surfacing on very steep

slopes could not lead to stable spawning grounds [cf. also Doerfel (14) on

spanning grounds on slopes with inclinations of about 30 degrees]. The

steepest slope, on which a stable spawning ground was photographed [by us],

exhibited an inclination of 63 ° 30".

Because of the different circulation and sedimentation conditions [pre-

vailing at the different sites in the Lake], it was not possible to estab-

lish a general gravel surfacing frequency. Unnecessary gravel dumping on • spawning grounds still in good condition probably can be prevented only by means of periodic determination of the state of these grounds with the aidof

photography, as has been done within the framework of the present study

in all spawning grounds. Hitherto, the spawning grounds still in existence

at the present time have been covered with fresh gravel at intervals of

about three years independent of their actual state. On these occasions, 3 about 20 to 30 m gravel, particle size 3 to 8 mm, are dumped--shovel-by-

shovel--from an anchored boat over the spawning grounds exactlyplotted with

the aid of fixed points on land. Gravel surfacing of spawning grounds

from hopper barges did not lead to the desired results. Gravel surfacing

of one spawning ground using the traditional method costs about Swiss

francs 750.00.

For some time now, the lake chars have been avoiding spawning grounds, • in part, still in good state. That phenomenon must be attributed to the • - 45 - fact that the water over the spawning grounds exhibits inadequate oxygen

concentrayions if fall circulation is ineffective. Shifting of the spawn-

ing grounds to zones with better oxygen conditions (avoiding the metalimnic

oxygen minimum still in existence occasionally in rudimental fashion during

the spawning season) may reverse that trend (47). However, construction

of new spawning grounds on bottoms as yet not stabilized would be very ex-

pensive, and would with certainty lead to questions regarding the sense

of continuing lake char fishery in Lake Zug.

5.4. Balance of lake char management

The overall expenditure in lake char management is composed of the costs

associated with stocking measures, fishery measures, and technical measures. • The magnitude of that expenditure is determined, above all, by the costs of the fish used for stocking and by the gravel surfacing of the spawning

grounds, i.e. that expenditure, thus, depends to a significant extent on

the difference between actual production conditions and optimal production

conditions in the Lake. The exploitation costs, on the other hand, vary

little in dependence on the production conditions. The expenditures vary

between Swiss francs 40,000 and 290,000, depending on which goal [formulated

economical goal (20,000 fish/year) or the average yield of the last ten

years (8400 fish/year) or optimal utilization of the production capacity]

is envisaged, and which production procedures are employed.

The total yield amounts to about Swiss francs 50,000.00, if the aimed-

for goal is realized. It reaches only Swiss francs 21,000.00, if the same

yields are obtained as harvested during the last ten years.

In any case, the balance is negative (in the red). If an attempt were

to be made to realize the aimed-for goal using stocking fish produced under • - 46 - optimal conditions, we may expect that 72.3 per cent of the expenditures

will be covered by income (100% representing Swiss francs 69,000.00). If

fishes produced using the traditional procedures are used as stocking ele-

ments in a number ensuring that the average yield of the last ten years

will be realized in the future, that share amounts to only 16 per cent

(100% representing Swiss francs 131,000.00). The deficit is made up largely

by public funds, and only the historical significance of lake char fishery

in Lake Zug can justify this considerable expenditure of public funds (18).

Acknowledgements - The present work is based to a large extent on a Doctoral Thesis prepared during the years 1971 to 1976 at the Institut fuer Gewaesserschutz and Wassertechnologie der ETH und der EAWAG (cf. footnote on page 1 of this Translation). I am indebted, above all, to Dr. W. Geiger • and Professor Dr. W. Stumm of the EAWAG; Professor Dr. H. Leibundgut, In- stitut fuer Waldbau [Institute for Forestry], ETH; Mr. E. Geuz and Dr. H. Schwarzenbach, Schweizerische Stiftung fuer Alpine Forschungen [Swiss Foundadtion for Alpine Research]; and Mr. R. Keiser, fisheries supervisor in Walchwil. All these individuals have contributed greatly to the success of this work.

•

- 47 -

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Étcf.* ' 10. Stuttgart - 19,0;,;,„, ....`:. :',`, - ;2,-,,,y»i:; i' • ' ,'''' •':: .,' " ,', , • ,,• .; ' ' :\ :', ; ' i 4 ' •.:: . : .:,:',.,' • % • ...,',,..; ' ,' , water over 28 . . 1-layes,',ÉlR.',..• .. ünd. - MacaulaY,',NIÀ::4Ëàke,water.and. . .. , -Seklitnent,',. y: OXYgen conSuMed in sediment 'cores,. Lininol. DceariOgr:.4.(3);',291 --297 (1959), -,:- V ,, . • . - •-',,, , 29 :- H'O'ar,.-'WS:::•S.niolt -transforination::eVOlution; behaviour a:41phy:iiolpgy...1..Fish..Res..B,ci .Canada '33: . ' (5), 12341252,(1976)...: -; -'.».•,:. -,'.:-':- •-• ''' :-'-''' ' , :,•,•,,,'„,,!. ,,,-;\.,,,,,. .; ''-',:.r.,': 30 t. hemaligen Fiseliereirechte der Stadt Zug. hit.ftigersee...-spi4- Freiburg .K.art-Zehri4n; ,.-- .,, ''-.': .,- o.„-•,..: ,.., .r` : ••'-, ', -‹••:-. ' .. '• .. .,:.--.•'•':',-.: --;'. Ziig,1920.•2./' • - ,.' . ••••. , '.- - . ,-, .,.s.„...;., '.-..;-:;--:'....„'-`• 2---,:',-:-.,- ;:, ...., '. 2 •--: - 1 31:: lien, À.: Die Rdtelfischerel itO,Zugersee.b.unz i,pfliffikiin'1,933.-',....:2,-,•,...... ,..:. ,,, ; , -;..,`,,,', ' .... -:-...e: , .. . .,. .32'',..o.Ktieeht," À.: Der Einfluss vori'Nlarkiertingen:atif'dirS' WachitUm von, FiSehert bei. . . tintérSelnedfiChént:-., . • . -.... FutterangebOti unveràffentlieht(1974). ' .. ...

- 48 -

• ;•‘33 •Konkordatsberichte, atich: Berichte•Bber2.-die.'KeenkOrdzdtiSelierei;• anett'i:.Beriehte“.der: Aufsicl •• konunissifin über die KonlcorBatSfiScherei, pOlyeopiert (1889L 1975); , • "..„ • 34'Muus.B.J., und Dahlifroein, P.: , •SiissWasserlikliel,BLV, Mfincilen .1968: •• • • • Nikolkky, G.Y.: SpezieBe FiSeliktmde„.. VE13' Deuts.cher.Y.criztg - dei'.WiSSenliaften; Berlin 1957. , . 36- .1•11kolskY; 37 1Slordene On . S"Pi&i,,'iifiig,fieipieneïdefertitinedfiiin4des'and:othi)1if:;:'Ny-tt Mag. :: • L.; Clziii'e, 2 E.W.,::tind, Mori'ng. J. IL.: Some etlecfs -'of'grz'iveftniXtUres 'On ' • -.einergenee'of Çoho salmon and Steelhead ..trOitt,iy›;,. •Trans.'Am. Fish. ( 197,5). 39 Provoni, i.: Sediment rkspiration.ify;six Italiaii;lakeS• in different trop14.•`iiciitil,iiiOrts...f-Vt.- int. • ,. • • ridindliche .Mitteitting. Eiseherei-iAnfSeher,: Kurs, 1975. . . 41 Kigier.iingsrat. des Kantons Zug: IteeitenSchaftsberiehte. SftizitSkanilei;`Zti. g:(b1s.'.1974),. .42 .K.t:isinger, E.: Zum Saiblingsproblern. Carintbia.:1C63 (2), 74-102'(1953), 43 It'ensch, 13.: Dais Prinzip geographischer Rassenkrekie und das ,Problemtier- 'ft,itbilditnetlerlin:1929. : und Geiger, W.: Die in't Bach und Ztg., Sep. 2 1-3 (1961). , - •45 Itotli, J I., und Geiger, W::'Aideuelit ijt;If BesailiSchen in Trbgen. Ver. cdg1 Ami Um el u. Fisci,. 4 = IrPI). 25 (1968)., ‘ »uhlé,'Clt::..: Die •BewirtSchaftung , des,,SeesaiblingS7(S!i/i.ilinns. (*inus L.) int Zügersec. • 58(19,2.21•S:-Aku-FotOdrtk-;-"Ztirielf 1976.. , 1, • 47- de la population des ombles chevaliers (alveliniii:iilpinus L.) dans k lac dc Zoug par l'entretien artificiel des frayères et Dar >des repeuplements de.'poiSsons d'âges.divcis..Actes du Deuxième Congrès Européen des là-ithyolOgiste:, paris, 8-14 septernPièt1976. • . 48 12iikjdoli,F.1\1.: Materials characterizing texture and;the:rnaterials in the.SPawing grounds adredds ---,of the. Pink 'salmon 10en.(irltynchus lOneorItyp,chsuiletet,, .,•;, • (Walh.)I of Sakhalin. Prohl. !chili. 9 (5), 635-644 '( le(!9).. 2 • • tIlar 49 Savvaitova, ,K.A.: Homologous varianon• ii .„ „. of the., gener:C.Vaive/iniis'-:(Nilssok).. (;iIl pytilele11111::,./..18.33 (196)) .:; _ 50 Sàtindler', sch c. yeitigshtichhandl ting,`2SinnU ' • • • . , • • ()her skalintelri sch,.. ttes.ttn;,»,),tit',4s It iteaten waeh stunt,... be, I-

it tea I (1 ,)33) . . . réà , ::'_.,.. . . . . ›, si,,„‘. I) t . \v,,,,,,,, (•-,,r . t,,,,t rt,,,t,,,,, tr, (2. , Itt`tfti,:;te,..-,,,,(- ,,„,‘ .,,,ti ,-,,,t,scittrat ,ott .itut ni%,,).etnent on the gulwth ot"..Steelhead tiout and éo'..11:‘:•sa.li-tion',cint.,nos.- nàii, Am ›t:,1,. S, ,.., t 41.. i-i • Ix; t Iqc,.ti 53• .!--iilvcr..1-',...1.•: „-Warren..- ..':C.,-E,„, ; ninl - piiilOroff,n. -C:: 1)isso1yet..1. oxygen': teqb1r-er-ii-ents: of.:.de ,>clopping ■ ' !. •., ' . . t.t.,l'.- If': it m I i rolli ant;' .. 1 .-C1 inttn).,' 1.....'h .,.‘ ..inon s :.p• '1_)rit» ; • ‘.a t ,t.Ft)* i tn.'- - it :v...ta ..t_ -r'v „ . ...t 1't'_ t,, k Y: tts., .'1 ----,'-'. ;_ 4's_. ".'. ,n). À . I:*v.11.. ' Si th... .,)' -,...... 37.„2 3.13 .(11Y „. . ,.„31: ' . . 54':;.%■'llit1iw:1 Ft1;.:A:1.:. 111wroved metit,od.,of.sainiding piit -,Ifir■ial.young ,fisb arid niYkri:±plank tun, J. ut ai-. ■ ■■ , , •• , in,')1.' A:S.'„1, :.1:,. -50.'(, 9 '712 t 1970i.....f. :, - .--.. .: ''••• ' -.• '.- .... ,- •...,•••=--.. - !....,.,.,, , --; .••••..--m,z,..,....•,-„-.:•,..2 ,, - N orvivat Dpil.. £.4*.i)y.li} .'i4'..:'iv,;:..1:1,.tted ,an d ii rt' 5•••,.•:•ii:iii-ili.' F. t+.1.; und flaw:en. hl ...1.:. ., -, ht.. • irk, . retention.... - .ettpud.i,tinbo\v,t,ii ■iit. Ttai),.i:A1!),r,llisAi ,'Soc:,. -,9...Y., 21-7-5.',?.21.). .( .191,9 /.!-:' :- '''''-":',:..-.•:.. ein inanh'. -P,•4 1bei 'Veili‘ésseningen iu der Iiiitelenelit.'Siél;c KintkOfretaINI)e.-Te4,;(1941).---::' "•'' . • - -.- t-56.. . -St ..... , — • '51,- Stelitinaiin.:P.: 1:\ ilé.iiiiienielle -Unici'sileiningen,.tiber die -WfieliNigkcit (le_ss.Scc›.aililing:i. Sékveik,- „> ":,:- .1„i.s0.1"...-..i.ig.' 9, i '9*(1942):'' - ..... , ... . . . . . • .. -. ...: ,. , ,•., . 55 ':,:iiiibeck. G.:lit:Wag:nu 1: contnis 'i.ki:'1 .;iselièrèive11):iltnissc. .iristZuger.see.-..Selywirii.: - FiSC , . . . . .. . , -.:- . .. ,... . , ,., .• 9:1....:'Sti■‘'..ort)yr,',..1:,g,•::,-.Allgen'teine,Fischkuritle.Nri-E,11.,1).etttscher, Verlag•dcr•Wissensdneften. Berlin,.1959:.'• . ,. "Sittninitts.•.piir„F.-•43-1-1c d'alev'in;ige.: ilitlf.' ,'6()- ."....•••i'i. -lii,-It•-.•:• :K'i:il•iiiiiiti,., ., .. . _ ,t..1iYitiqti,du,re. -p1;1.1'11. ie"tiint',i•iii't-rti'itis,'t. *i- •• , • , ..... ,..•••-, .."‘•()IT. Int. Con.•Sup. 1.'45:11i, h:o.,37,,,iy,(.1‘95,5)...‘,,,...;:.: . . ;..:.; .,. ;;•_ , .-- .",..-..',..-; 11;: - F•ini:k .iiinn .SeiS;itibling.,-(,tlttlitial.1,':5.7.•:, . ,, ,, . - , , . . .93-7102:,(t4t5):• . .wal?e.er. c.:: i),..resee; ■ibliwg.,..sellwciÉT,80;:?..■i... S,cp.:(189fi)i:.,','-:,;-...-'.,: -.Walter.; als'Nebenbet,rich-deS„l'ant4iinteS.nruJistm,anncs.,:lettri)ann,,f11endaluin .. • •:...., . ' ' '' "•'' , of • the • -p,06$.h..ittnn'In -(irr-ritiiii.s-=

rrytit:d2; - ir411:11Mal'racierit:ei; tu ilt e I:Li n t:6 t)tt r tit pi ittitàiy 19 (i5):.! i)5•

8.;:' .66 ZÜltij. .' V V • 5-144 (1956), ' • .:.••••-• V ' 4 • -49 - Translation of foreign-language titles

12. Monographic studies of Lake Zug. 14. Investigations of the problems faced by the lake char (&alvelinus. alpinus L.) populations in Lake Ueberling (Lake Constance). 15. A sledge-type dredge. 17. Life in pond, brook, and fishpond. 18. Expert group appointed by the Swiss Federal Council: General investigation of Swiss Federal subventions. 19. Faber-Ewos, Feedstuffs, personal communication. 22. Approximate expenditures for lake char and pike rearing; unpublished. 27. Fishery biology of the Alp lakes. In. , The inland waters, Vol. 10. 30. The fishing rights formerly held by the City of Zug in Lake Zug. 31. Lake char fishery in Lake Zug. 32. Effects of tagging on the growth of fishes under different food supply conditions; unpublished. 33. Concordat reports; cf. also: Reports on concordat fishery; furthermore: Reports of the supervisory commission on concordat fishery; mimeographed. • 34. Freshwater fishes. 35. Ecology of fishes. 40. Personal cimmunication. 41. Executive council of the Canton of Zug: Financial report. 42. The lake char problem. 43. The principle of geographic rassenkreise [rheogameons] and the problem of speciation. 44. Reproduction of the trout in the river and in the hatchery. 45. Rearing of stocking fishes in troughs. 46. Management of the lake char (Salvelinus alpinus scavelinus) in Lake Zug; Doctoral Thesis. 50. Native freshwater fishes. 51. Scalimetric methods for determining linear growth of fishes. 56. Improvements in lake char rearing. Cf. concordat reports (1941). 57. Experimental investigations of the growth characteristics of the lake char. 58. Contribution to the knowledge of the fishery situation in Lake Zug. 59. Ecology of fishes. • 61. Aspects concerning the lake char. ' • - 50 - 62. The lake char. 63. Fishery as secondary occupation of farmers and foresters. 65. Report on the investigation of Lake Zug and its inlets by the Zug Cantonal Laboratory; mimeographed. 66. Sediments as expression of the state of a body of water.

Address of the author: Dr. clipl.. Forsting. F.TU . Seenform..Ining.slabora. tofiunt der

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