Effects of Forest Spraying with DDT in New Brunswickon Food of Young Atlantic Salrnon'''

Bv Mrrps H. A. KnoNtnvstnns

F'isheries Research Board' oJ CanodaBiological Station, St. Andrews, l{.8.

ABSTRACT

Food in stomachs of young Atlantic salmon from the Northwest Miramichi River, N.B.,changed following aerial DDT spraying of the surrounding watershed. Before spraying, young

salmon typically ate immature aquatic insects, fry (underyearlings) concentrating on Diptera and

small Ephemeroptera, and parr (overyearlings) on Diptera, Trichoptera, and all sizes of Ephemer-

optera. Reduction of all aquatic insects by DDT was soon followed by resurgence of Chironomidae

and other Diptera, and surviving fry fed heavily on these; parr fed on Diptera but alsoatesnails,

worms, and fish, previously unimportant in their diet. Five years after the last spraying the pre-

spray complexity of young salmon food was being approached. Trichoptera were slowest of the

major fish-food types to reappear in stomachs.

In fry stomachs Ephemeroptera, and in parr stomachs Ephemeroptera and Trichoptera,

were relatively more abundant than in the surrounding stream fauna. Greater availability of these

insects and active selection by fish are discussed as possible causes of these relationships.

INTRODUCTION

YouwC ATLANTIC SALMON in fresh water feed mainly on immature aquatic

stages of insects, particularly Ephemeroptera, Trichoptera, and Diptera (White,

1936 ;E l son , N {S , 1940 ;Carpen te r , 1940 ;A l l en , 1941 ;Hur leY , MS, 1956 ) . Many

of these insects are kil led when DDT insecticide is sprayed on forests and then

enters the rivers in which they l ive (Ide, 1957). After repeated spraying some

species of insects do not return to their pre-spray abundance for several years

(Ide, 1967). Young salmon also are susceptible to poisoning by very low con-

centrat ions of DDT in water (Gagnon, 1958; Keenleyside, 1958), and Langford(1949) has shown that several species of freshwater fish are kil led by ingesting

DDT with their food. Repeated aerial application of DDT since 1952 to control

an outbreak of spruce budworrn in New Brunswick (Kerswi l l , 1967) thus

affected resident young salrnon directly through toxic action and indirectly by

altering their food supply.In the Miramichi River , N.B. , most young salmon spend 3 ) 'ears in f resh

water before going to sea;a few spend 2 or 4 years (Bla i r ' 1935).

The DDT insecticide was applied by low-flying airplanes at a rate of ]lb DDT per + U.S. gal so lut ion (DDT plus o i l ) per acre (Webb, 1959).

Hur ley (MS, 1956) s tudied the ef fects of the 1954 DDT spraying on food

of young Northwest Miramichi River salmon by comparing stomach contents

lReceived for publication December 5' 1966.,The fifth in a ieries of papers on work of the Fisheries Research Board of Canada on effects

of forest insecticides on salmon and aquatic insects.3Present address: Department of Zoology, University of Western Ontario, London, Ont.

807J. Frsr . Rns. Bn. CeNeo.r , 24(4) ,1967.Printed in Canada,

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808 J O U R N A L F I S H E R I E S R E S E A R C H B O A R D O F C A N A D A , V O L . 2 4 , N O , 4 . 1 9 6 7

of fish caught in the same parts of the river in 1953 and 1955. He also comparedthe food of f ish captured in 1955 with aquatic insects collected during the sameyear at locations inside and outside the 1954 spray zone. He found that changesin insect fauna reported by Ide (1957) were reflected in altered diets of the youngsalmon.

The present paper describes changes in the food of young salmon collectedbetween 1953 and 1961 in the Northwest Miramichi River , in an area of NewBrunswick spray'ed with DDT several t imes during that period. For some yearscomparisons are made between food organisms found in fish stomachs and theaquatic insect fauna living in areas lvhere the hsh were collected.

Figure 1 shows the river and the stations where fish and insects werecollected for this study. Parts of the river were within the spray zone in 1954,1956, and 1957. In 1954 all the watershed from the headwaters to an area be-tween stations 7 and 8 was spral'ed. The 1956 spraying covered most of the rvater-shed below station 3; f ish-collecting stations downstream from station 3 wereeither within or immediately downstream from sprayed areas. In 1957 most ofthe watershed below station 4 was sprayed. From 19s7 to 1962 no further spray-ing was done upstrearn from or near station 4.

MATERIALS AND METHODS

Food of young salnon was studied by analyzing stomach contents of twoseries of f ish. The first series was taken from collections made in the late summerof each year from 1953 to 1956, during annual f ish population censuses on theNorthwest Miramichi River (Elson, 1967). Among these were fish examined byHur ley (MS, 1956) wi th addi t ional specimens to make up, wherever possib le,a total of 10 fry and 10 parr from each of several locations each year. Frv used

Frc' 1. Northwest Miran-richi River and its tributaries, shou'ing locations of fish populationcensus statrons.

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KEENLEYSIDE: DD'f UIiIT.EC'I-S oN A-I'L-{NTIC SALAION lJ09

Ior stornach analysis were all underyearling fish and were relatively uniform insize. Parr were selected at random from samples of f ish preserved during popu-lation census work on this river, and fish of various ages were thus used ('IableIV gives age determinations of parr collected in 1959, 1960, and 196I).

The second series of frsh was collected at 2-week intervals between lateMay and ear ly September of 1959, 1960, and 1961 at s tat ions 3 and 4. Eachcollection, whenever possible, consisted of 10 fry and 10 parr from each of thetwo stations. Fry were sometimes not available on the earliest collection datesbecause of their smali size at that t ime. Fish in this series were caught near yard-square strearn cages used for sarnpling emerging adult insects. Insect samplingat stations 3 and 4 was part of the long-term study of effects of DDT sprayingon aquat ic insects ( Ide, 1967). I t was thus possib le to compare the food of thesefish with the insect fauna of the same areas throughout the sumtner.

All f ish were captured with electrofishing gear and a seine (Elson , 1962),and were preserved in 4/6 formalin. Some frsh in the earlier series (1953-56)

lvere stored in formalin for several ).ears before examination. These fish weremeasured (fork length) before stomach analysis but because of dehydrationduring long storage they were not weighed. Fish collected in 1959, 1960, and1961 were weighed and the total length recorded as soon as possible after cap-ture, usually on the same day. Ston-rachs of all f ish were removed and stored in950/6 ethyl alcohol. The esophagus and mouth of each fish were examined beforestomach removal and any food organisms lodged there were stored with thestomach. Only food in the fundr-rs of the stomach was examined, since advanceddigestion usually made food in the pyloric region unidentif iable. Stomachcontents were classified to order (to family in Diptera) in the same manner asthe collections by Ide (1967). Organisms were counted and the volume of thetotal contents was estimated bv the l iouid displacement method.

RESULTS

Fool rN Ynan BBpoRE SPRAYTNG

Fish caught in 1953 provide information on pre-spray feeding conditionsin the river. Parr stomachs contained more and larger food organisms than fry(Table I); the greater mean volume for parr is associated with body size, usuallygreater in parr. Differences in composition of food taken by fry and parr alsocontributed to the differences in total numbers and volume. Chironomid larvaeand pupae (among the smallest organisms eaten by ]roung salmon) made upover 500/6 of fry food, but less than25/6 of parr food (Fig. 2 and 3, upper charts) .Ephemeroptera, Trichoptera, and Plecoptera, which are relatively large insects,formed higher proportions of the food of parr than of fry'.

I, ool rN Ypen op AND rN Ypans AprBn Spn,tvrNc

In 1954 no fry were found in the river dtrring the annual population census,owing to high mortalit ies following DDT spraying in June of that year (Kerswill

and Elson, 1955). Parr samples were collected at seven stations, however,

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810 JOURNAL i . ' tsr IERl l ts RESE'\RCH BO,\RD oF cANr\DA, yoL. 21, No. 4, 1907

T.lnt-B L Food of salmon fry and parr collected in late summer, 19.53-56, in Northwest IVIirami-chi River. F ish col lect ing stat ions shown in l i ig . 1.

Year Col lect ingstat ions

Mean Meannunber volume

Mean length organisms food(range) per stomach per stomach

Stationssprayed

No. offish

F'"y1 9 5 3 1 , 2 , 3 , 5 , 8 , 1 0

1 9 5 4 7 , 2 , 3 , 4 , 5 , 6 , 71 9 5 5 1 , 2 , 3 , 5 , 9 , l 0

1 9 5 6 7 , 2 , 3

5, 9, 1(-)

Parr1953 1 , 2 , 3 , 5 , 8 , 1C)

1 9 . 5 4 1 , 2 , 3 , + , 5 , 6 , 7

1955 1 , 2 , 3 , 5 , 9 , 10

1 9 5 6 1 , 2 , 3

51 9 , 10

None

Alt

None

None

Al l

None

Al l

None

None

Al l

cln

4 . 4( 3 . 6 - s 1 )

( 3 6 - s , 7 )3 . 7

(3. 1-4 4)4 . 1

( 2 . 9 - 4 . 8 )

9 . t )( 6 . 5 - 1 , 1 . 3 )

9 . 8( 6 . s - 1 3 . 4 )

1 1 . 8( i . 2 , 1 6 . 8 )

8 . 2( 6 . 8 - 1 3 . 2 )

7 . 5(6 . r - r3 .2 )

m.l0 . 0 1 8

0 0 1 9

0 028

0 . 0 2 5

0 .083

0 . 0 6 6

o . 2 8 2

0 048

0 063

45

06t)

3n

2 2

5 9

69

6t)

30

29

1 4 . 0

3 4 . 9

r t . . )

1 3 . 9

) t . l

4 7 . 0

3 6 . , 1

3 2 , 1

1 3 . 3

apparently because they were less susceptible than fry to poisoning by DDT.

The mean number of food items found in parr stomachs was more than double

that found in 1953, but the mean volume of th is food per s tomach had decl ined(Table I). Parr stomachs in 1954 contained litt le other than Chironomidae and

other Diptera (Fig. 3).In 1955 the Northwest Miramichi watershed was not sprayed and both

fry and parr were available for stomach analysis. Fry had many more food

organisms per stomach than in the pre-spray year but the average volume of

food per stomach was about the same (Table I). This was because they ate

many more Chironomidae and other Diptera and fewer larger forms, such as

Trichoptera, Ephemeroptera, and Plecoptera (Fig. 2). Parr in 1955 had fewer

organisms per s tomach than in 1954 but more than in 1953 (Table I ) ; the mean

volume of food was higher in 1955 than in any other )-ear of this study (Tables I

and IV). This volume increase in 1955 was partly because of an increase in the

Miscellaneous category, made up of Gastropoda, Oligochaeta, and a few small

f ish (Cyprinidae), and partly because of the large average size of f ish this year,

smaller parr having been shown (Elson, 1967) to be more vulnerable than larger

parr to DDT.

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KEII.NL|YSIDIt: DDT EITITIICTS ON :\TLr\NTIC SALMON

1953

Ec

54 .7e 6 . 9

1954 t95 5

c7 0 . 2

t95 6S t o l i o n s 1 , 2 , 3

I 956S l q l i o n s 5 , 9 , l O

M4 5 . 4

Ftc. 2. Salmon fry food, 1953-56. Numbers are percentages of total number of fooditems. Heavy circle means DDT spraying over collection area that year. C-Chirono-midae; O.D.-other Diptera; E-Iiphemeroptera; T-Trichoptera; P-Plecoptera;

M-M iscellaneous.

Data from fish collected in sprayed and unsprayed parts of the river in1956 are presented separately in Table I and Fig. 2 and 3. In the unsprayedsection (stations l, 2, and 3) the mean number of organisms per fry stomachdeclined in 1956 to slightly below the pre-spray level, but the mean volume was

8 1 1

T -o .7

T3 .9

N o F r y F o u n d

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3 1 2 J oT] I {NAL I i IS I IDIT lES B O l \ I r D ( ) 1 r C ' \ N A D A , V O L . 2 4 , N O . 4 , 1 9 6 7T{I;SI',\RC iI

t953

To . 4F -

o . 2o.D.7.7,

r956S t o t i o n s 1 , 2 , 3

t956Sto t ions 5r9 , lO

c47 .O

F'rc. .j. Salmon parr food, 1953 56. Nurnbers are percentages of total number of fooditerr-rs. Symbols as in Fig. 2.

relatively high, even though fry stomachs contained virtually nothing butChironomidae and Ephemeroptera. Parr from unsprayed stations in 1956 had

more items per stomach than before spraying began, but the mean volume of

this food u'as lov,', because of the preponderance of Chironomidae and Ephemer-

optera. Snails and worms, which lvere so conspicuous in parr stomachs of 1955,'were scarce in those of 1956.

| 954

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KI tnNl - l tYS l l )F i : D .D" l ' l i l r l rE( ] l S ( )N A ' l l -AN ' i '1 ( l l iALNI ( )N

Stomachs of fry from stations sprayed in 1956 contained about the samenumber and volume of food items as those fron-r the upper, unsprayed sections(Table I). However, there were differences in food composition between fryfrom the two areas (Fig. 2). In the sprayed area Chironomidae and Ephemer-optera were proportionately scarcer and the Miscellaneous items rluch moreabundant, the latter because of large numbers of Collembola in fish from station10. The stomachs of parr from stations spral'ed in 1956 contained fewer foodorganisms than those of parr from unsprayed areas; the mean volume of foodper stomach, however, was greater among the former (Table III). This rnayhave been caused by the smaller proportions of Chironomidae and Ephemer-optera and the greater proportion of Trichoptera in stomachs of parr fromsprayed stations (Fig. 3). Trichoptera larvae, usually highly susceptible toDDT poisoning (Ide, 1957), were relatively more numerous in stomachs ofboth fry and parr from stations sprayed in 1956 than in fish from unsprayedstations the same year (Fig. 2 and 3).

Foon DunrNG INSECT RBcovpny pnon DDT

Information on the food of young salmon during 3-7 years after sprayingwas obtained at two stations (Tables II-IV, Fig.4-6). Fry and parr werecollected in the summers of 1959-61 in an area sprayed only in 1954 (station 3)and in another sprayed only in 1954 and 1956 (stat ion 4) . in 1956 the upstreamspray boundary was between stations 3 and 4 and the latter may not havereceived much DDT; in 1957 the spray zone was downstream from station 4.Data on emergence of adult insects into stream cages were obtained at the twostations in 1959-61 (Fig. a-6).

TenrB II. Food of salmon fry collected thi"#rqi;Hl.lifigl"* of 1e5e-61 at stations 3 and 4,

E l 3

Collectine No. ofYear station- fish

l lean length Mean rveight(range) (range)

Mean number Mean volumeorganisms food

per stomach per stomach

1 959

1960

53

cln

4 . 6(3 .0-s . 8)

5 . 2( 3 6 - 7 . 0 )

4 . 0(2 . s-6. s)

. f l

(2 .3-7 . +)3 . 5

(2 . s-4.7)3 . 6

( ) )-< ')\

g1 . 3

0 . s - 2 . 1 )1 . 8

(0. s-3 .7)0 . 9

( 0 . 2 - 2 . 2 )t . 7

(0 . 1 - .1 .3 )0 . 4

( 0 . 0 1 , 1 . 0 )0 . 7

(0 2-1 s)

mtr0 .009

0 . 0 1 2

0 .027

0 . 0 2 7

0 . 0 1 0

0 . 0 1 1

9 " '2

1 6 . 9

1 6 . 0

J 1 l

1 0 . 2

8 . 340

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E 1 - 1 J O U R N A I , l ' l s i l E l r l t t s R I t S E A R C I I J O , \ I { D o t i c : \ N : \ D A , \ ' o L . 2 . 1 , N o . 4 , t 9 o 7

In the 3 years 1959-61, salmon fry collected at station 4 were slightlylonger and heavier than those from statior-r 3 (Table II). This may have beencaused by slightly higher sulrlrner water temperatures prevail ing at station 4,which is about 7 river miles downstrearn from station 3. Parr from station 4 werealso larger than those from station 3, but this was at least partly because of thehigher average age of parr collected at station 4 (Table III).

In 1959, salmon fry and parr collected at station 4 had a higher meannumber and volume of food organisrls per stomach than those from station 3(Tables II and III). Strearn cage coilections at the two sites in 1959 (Fig. a)showed that Chironomidae and Epherneroptera were relatively more abundantin the insect fauna at station 3 than at station 4, while' lr ichoptera, Piecoptera,and other Diptera were relatively rnore nulnerous at station 4, although atboth locations Chironomidae and other Diptera made up almost 75o/o of. theinsects collected.

The food of fry collected at the two stations in 1959 differed l itt le in percent representation of insect groups. Chironornidae and Ephemeroptera rnadeup over 900/6 of. fry food items at both stations (Fig. 4). Food of parr in 1959reflected more closel-v than that of fry the differences in relative abundance of

J.Lnr-r IIL Food of salmon parr collected throughout the summers of 1959-61 at stations 3(sprayed in 1954) and 4 (sprayed in 1954 and 1956), Northwest Miramichi River.

CollectingYear station

Ag" Per(years) cent

No. offish

Meanlength(range)

NIeanweightlrange)

Mean Meannumber volume

organisms f oodper stomach per stomach

1959cln

8 . 9( 5 . 3 - 1 2 . 2 )

1 0 . +( s . e - 1 6 . 4 )

8 . 7(4 .+ -12 .6 )

r 1 . 2(8 .0-1e .0)

8 . 8r i J - 1 ? l )

9 . 6( 6 . s - 1 3 . 7 )

c8 . 0

( 2 . 4 - r 7 . r )

1 1 . 9(2 .4 -27 . s )

7 . 9( 1 . 0 - 2 0 . 1 )

16 .2(s .8 -36 .1 )

/ . J

( 2 . o - 1 7 . 6 )

9 . 9( 2 . 6 - 2 7 . s )

1 4 6 . 52 14.23 9 . 31 1 6 . 02 6 6 . 73 1 6 . 04 1 . 31 7 3 . 02 2 + . 73 2 . 2I J J . U

2 3 8 . 83 6 . 31 1 t .4'2 41 .+3 1 7 . 11 3 0 . 02 54 .33 1 5 . 7

ml0 .033

0 .058

0 0,18

0 .058

0 .0 )9

(:) . (1,11

1 5 . 0

3 1 . 5

3 7 . 3

3 0 . 0

2 l . 9

2 .1 ,6

/.)

t96 i

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Sf ot ion 3

KEENLEYSIDII: DD1' It l ' l ' l tLlTS Or\ A'I 'LAN'f IC SALMON

CAGESP

4.3

Et9 .5

c6 2 . 9FRY

Po.D.l t ' 5

PARRP MM

t 6T2 3

c5t o

E44.O

c44'OE

44 .4

CAGESP

8.5

Stotion 4E

l o . o c53 's PAR R

c38.s

E2 4 4

s4 oD.220

Frc' 4. Insect fauna and food of young salrnon at stations 3 and 4 in 1959. Numbers are percent-ages of total number of organisms. Symbols as in Fig. 2.

c397

oD.1 . 6

FRYP

P

T 0 3

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l J l6 JoURNAL TTISI tE t { IES 1{DSDt I tc I l l l oAI t l ) ( )1 " ( l ' \ - \ ' \D- \ , \ ' ( )L 1 .1 ' No. t l , 190 i

insect groups at the two stations (as measured by cage collections). Chirono-

midae and Ephemeroptera were relatively rnore nunrerous in parr from station 3

than in parr from station 4; Trichoptera and other Diptera wefe relatively

more numerous in parr from station 4. Plecoptera and Miscellaneous items were

found in almost identical proportions in stomachs of parr frorn the two stations(Fig. a) .

Forage ratios (per cents, by numbers, of insect groups in food divided by

per cents of same insect groups in cage coliections) were calculated for fry and

parr co l lected at both stat ions in 1959, 1960, and 1961 (Table IV) . A forage

ratio greater than one rneans the insects rvere found in greater relative abundancein fish stomachs than in cage collections frorn the same area. Among fry examined

in 1959, forage ratios greater than one occurred only rvith Ephemeroptera.

For parr in the same year forage ratios over one occurred with'frichoptera and

Ephemeroptera at both stations and with other Diptera at station 4.

In 1960, stomachs of fry from station 4 contained a higher mean number

of food organisrns than those frorn station 3, but an identical mean volume(Table II). Parr from station 4 had f ewer food items but a greater volume of foodper stomach than those from station 3 (Table iII). The differences in per cent

representation of rnost insect groups between the two series of cage collections

were smail; Plecoptera, however, were relatively nlore abundant at station

3 (F ig . s ) .As in 1959, Chirononidae and Ephemeroptera made up most of the food

of fry in 1960 at both collecting stations (Fig. 5). Parr in 1960 also concentratedlargely on Ephemeroptera and Chironomidae. Plecoptera, which were abun-

dant at station 3, were rarely uti l ized as food by either fry or parr.

T. leLu lV. Forage rat iosa for young salmon col lected dur ing 3 _ye.ars at . s tat ions 3 (sprayed

t" tt"r ..a - ,.tr.

YearPlecop- Trichop- Ephemer- Chirono- Other

Station tera tera optera midae Diptera

1959

l9ol)

1961

Fry

Parr

F- r.r

Parr

liry

Parr

0 .050 . 0 20 . 0 50 . 0 40 . 0 50 .400 "020 .950 .030 . 0 40 . 1 50 .04

o . 6 70 . 3 51 . 2 81 . 7 0n 1 1

0 . 2 82 . 1 3| . 2 2z . l J

0 . 5 8+ . J i

3 . 3 9

2 . 2 85 . 1 22 2 6o t t

1 . 6 82 7 8I . J J

2 . O 30 . 7 00 . 9 22 . 1 52 . 0 5

+

,1

i

5

q

?

I

cn

0 8 1 0 . 1 40 7 4 0 . 2 60 7 0 0 7 00 7 1 1 , 1 2| . 0 2 0 . 2 60 3 6 0 2 10 9 9 0 6 . 50 . 5 3 0 4 81 . 3 3 0 . 2 10 . 9 5 0 9 00 , 3 7 0 . 9 00 . 1 2 0 . 2 7

aPercentages, by numbers, of insect groups in food divided by percentages of same insectgroups in cage collections.

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KEENLEYSIDE: DDT EFI -ECTS ON ATLANTIC SALMON

CAGES

Pt 2 . 9

c3 6 ' 9

8 1 7

Stqt ion 3

E5 2 . 9

S tqt ion 4

FRYP

FRYP

T o . e Mo 5----- 1 --ot

E3 t ' 4

M0 . 6

E2 8 . O

c15.4

PARRP

o 3 Mo '7T

3.7

o.D.t 7 ' 2

E4 8 r

c43-2

PARRP

T3'2

37.8

c3 6.7

CAGES

T2.2 c

23.12 5 . O

n nt 2 l

E E56.77 7 .9

Iirc. .5. Insect fauna and food of young salmon at stations 3 and 4 in 1960. Numbers are percent-ages of total number of organisms. Symbols as in Fig. 2.

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818 JoURNAL FISHERIES RESEARCH I to . \RD o ! - CANADA, vor ' . 24 , No. 4 , 1967

Forage ratios for fry and parr in 1960 (Table IV) indicate that severalinsect groups were relatively more abundant in fish stomachs than in cage

collections. Ephemeroptera for fry and Ephemeroptera and Trichoptera forparr are the most consistent examples.

In 1961 the mean numbers and volume of fry food organisms at station 3

had declined to about the 1959 level, while at station 4 they were the lowest

in this 3-year intensive sampling program (Table II). The latter was at leastpartly due to unavailabil it] ' of salmon fry at station 4 on two collection dates in

August. N{ean numbers and volume of parr food organisms in 1961 were l ike-

wise lower at both stations than in 1960 (Table III). Cage collections of emerg-

ing insects (Fig. 6) showed Chironomidae and other Diptera were relativell '

more abundant at station 3 than at station 4, while Ephemeroptera and Plecop-

tera were relatively more numerous in the fauna at station 4.In general in 1961, Chironomidae and Ephemeroptera again made up the

largest percentage by number of food items of fry and parr at both stations(Fig. 6). One exception occurred: at station 4, parr ate very few Chironomidae.

In 1961, fry forage ratios greater than one occurred only for Trichopteraand Chironomidae at station 3; Trichoptera and Ephemeroptera were relativelymore nulnerous in parr stomachs than in the local fauna at both stations (Ta-

b le IV ) .

DISCUSSION

The presentstudy has largely confirmed the conclusions of Hurley (NIS' 1956)

that DDT spraying of the Northwest N{iramichi River in 1954 had pronounced

effects on the insect fauna and as a result, on the food of resident young salmon.However, this more extensive study shows that the effects of DDT spraying

on salmon food are somewhat more complex than he suggested.The following observations support the suggestion that a direct relation

exists betrveen size of f ish and size of their food (Lindstrom, 1955). While bothfry and parr feed on a wide variety of insect types (Carpenter, 1940; Allen,1941) Nll iramichi fry concentrated on smaller forms, particularly Clhironomidae,other Diptera, and small Ephenreroptera. Parr generally had a diet consistingof large Ephemeroptera and Trichoptera, although on occasion thel' fs4 heavil l-

on smal l Diptera.Because Chironomidae recover soon after spraying with DDT and emerge

in large numbers ( Ide, 1957), f ry which have not been k i l led are able to capi ta l izeon their resurgence. Because larger insect types are slower to recover, parr atsuch times eat small insects, as they did in 1954 (Fig. 3), but even large numbersof Chironomidae made up a relatively small volume of food in parr stomachs

that year (Table I). Generally, in such cases parr fed on a variety of organisms

which are not normally important in their diet, such as aquatic snails andworms.

The second spraying of the Northwest N1[iramichi, in June 1956, appearsto have had less drastic effects on the aquatic fauna than the first spraying in

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KEENLEYSIDE: DDT EI I I IECTS ON ATLANTIC SALMON

C AGES

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Frc. 6. Insect fauna and food of young salmon at stations 3 and 4 in 1961. Numbers are percentages of total number of organisms. Syrnbols as in Fig. 2.

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8 2 0 J O U R N A L F I S H E R T E S R E S E A R C H B o A R D o F C A N A D A , v o L . 2 4 , N o . 4 , 1 9 6 7

1954. Nloderate numbers of Trichoptera iarvae, usually extremely sensitive toDDT (Ide, 1957), rvere found in 1956 in the stomachs of fry, more of whichsurvived than after the 1954 spraying (Kerswill and Elson, 1955), and also in

those of parr (Fig. 2 and 3). Probably the complete coverage of the NorthwestMiramichi headwaters during the 1954 spraying resulted in a relatively largeamount of DDT entering the river. In 1956 the upper parts were not sprayedand partial coverage of the iower stretches may have put less insecticide intothe rvater.

The intensive sampling at stations 3 and 4, beginning in 1959, was expectedto yield information about recovery of important f ish food organisms. Collectionsof emerging insects indicated that, in terms of relative numbers of kinds, theaquatic fauna at these stations was diversif ied by 1959, especially at station 4

where Trichoptera and Plecoptera were relatively numerous (Fig. a).In 1960 continued recovery from the effects of DDT was evident among

some but not a l i groups of insects (F ig.5) . Ephemeroptera made up a largershare of the cage collections at both sites than in 1959, but Trichoptera declinedin relative abundance, especiaily at station 4. Plecoptera also were relativelyless numerous at station 4 in 1960, but showed an increase at station 3.

Changes in uti l ization of aquatic insects as food by fry did not appear tofollow any clear trends during 1959, 1960, and 1961 (Fig. a-6). Fry concentratedmainly on Diptera and Ephemeroptera in all 3 years. They occasionall5r 31sTrichoptera in small numbers but seldom ate Plecoptera, which are relativelylarge insects.

The only clear trends in the feeding habits of sahnon parr over the 3-yearrecovery period were the increasing relative importance of Ephemeroptera,and the decreasing relative importance of Chironomidae. In general this followedsimilar trends in abundance of these two insect groups in the stream fauna.Trichoptera made a small contribution to parr food ir-r all years, while Plecopterawere seldom eaten, even when numerous in the area (Fig. 6).

The forage ratio data (Table IV) show the types of insects most frequentlyeaten by young salmon, relative to the insect's abundance in the local streamfauna. With fry, the forage ratios for Ephemeroptera were most frequentlygreater than one;with parr both Ephemeroptera and Trichoptera forage ratioswere always over one. Ratios for other insect groups were generally n.ruch lessthan one.

The food selection-availabil ity problern l.ras been discussed at length in

the l iterature. Carpenter (1940) studied the food of salmon parr in the DeeRiver for 2 years and concluded that ". .. the fishes are indiscriminately carniv-orous, and that their food varies strictly in accordance with the number andrelative accessibil i ty of species present in the rivers." Allen (1941) presented

statistical evidence that young salmon shorv no selection when food is scarce,or when they are feeding l ightly, but show increasingly more selection as theyfeed more heavily. Other workers have discussed predator-prey relations be-

tween salmonid fish and freshwater organisms (Neil l, 1938; Morgan and Waddell,i 9 6 1 ) .

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KBENLEYSIDE: DDT EFFECTS ON ATI ,ANTIC SALMON 821

The present study was not designed to investigate the availabil ity-selection

problem as applied to the feeding of young salmon. The following tentative

conclusions are drawn, however, regarding vulnerabil ity of potential food

organisms to them: Ephemeroptera are highly vulnerable to predation by all

sizes of young salmon, even when they form only a small proportion of the

stream insect fauna; Trichoptera are also vulnerable, especially to larger

young salmon; Plecoptera are seldom eaten, even when abundant; Chironomidae

and other types of Diptera are eaten by young saltnon of all sizes although,

because these insects are vefy small, large numbers must be eaten to equal in

volume a smaller number of larger insects. In the absence of immature aquatic

insects young salmon can live on other organisms such as snails, worms, and

small f ish. Parr eat a greater variety of these than do fry, possibly because they

can forage farther and more persistently than the smaller fry'

ACKNOWLEDGMENTS

Thanks are extended to those people who contributed to this study by

doing much of the laborious field work. NIr E. J. Schofield and his assistants of

the Fisheries Research Board of Canada office at Chatham, N.B', collected the

samples of young salmon at regular intervals during three summers. Several

students, employed by the Board as summer assistants in the Miramichi River

area, made the cage collections of insects and analyzed the stomach contents of

f ish. These inc luded R. J . Gibson, D. A. G' N' I ick le, C. D' Grant , and F ' W'

Clark. The assistance of Dr F. P. Ide, University of Toronto, in the planning

of this project is also gratefully acknowledged. Finaily I wish to thank Dr C. J.Kerswill for crit ically reading the manuscript and making valuable suggestions

for its improvement.

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Brarn, A. A. 1935. Ages at migration of Atlantic salmon (Satmo salar) in Miramichi River.

J. Biol. Bd. Canada, l : 159-169.

Ca,nlnNren, K. E. 1940. 'fhe feeding of salmon parr in l:he Cheshire Dee. Proc. Zool. Soc.London, A ,110: 81-96 .

Er.sow, P. F. MS. 1940. Atlantic salmon and trout investigation-s, 19-10. Iiood of salmon,troutand eels in Goldmine Brook. Fish. Res. Bd. ( 'anada, MS ltept. Ser. (Biol.) . No. 210.1 o p .

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InB, F. P. Ig57. Effect of forest spraying with DDT on aquatic insects of salmon streams.Trans. Am. Fish. Soc.. 86: 208-219.

1967. Effects of itiest sprayitrg with DDT on aquatic insects of salmon streams inNew Brunswick. J. Fish. R-es. Bd. Canada, 24(4):769-805

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I{onswrrr-., C. J.,-+ND P. F. Elsoll. 1955. Preliminary observations on effects of 1954 DDTspraying on Miramichi salmon stocks. Fish. Res. Bd. canada, Atlaniic progr. Rept. No.62. p. 17-24.

LeNcrono,-R. R. 1949. The effect of DDT on freshrvater fishes. Biol. Bull. Res. Div., ontDept. Lands and Forests, 2: 19-37.

l , tNlsrnoM,.T., 1955. 01 the relat ion f ish size - food size. Rept. Inst. Freshwater Res.,Drottningholm, 36 : 133-747 .

Moncex, N. C.,,aNn A' B. W.uner-1. 1961. Insect emergence from a small trout loch and itsbearrng on the food supply of fish. Freshwater Salmon-Fish. R"r.,'S.oiiu"a, zS,-i_gS.-

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wnrrn, H. c. 1936. Thefood of salmon fry in eastern canada. J. Biol. Bd. canarla, 2: 499-506.

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