A Review of Survival Rates ofFish Eggs and Larvae in

Relation to Impact Assessments

MICHAEL D. DAHLBERG

IntroductionPursuant to promulgation of the Fed­

eral Water Pollution Control Act Am­endments of 1972, Section 3l6b, electric

generating stations are required to dem­

onstrate that cooling water intake struct­

ures renect the best technology availablefor minimizing adverse environmental

Michael D. Dahlberg is with the orthern En­vironmental Services Division. N US Corpora­tion, 1910 Cochran Road, Pittsburgh, PA 15220.

ABSTRACT-Enormous fecundities offishes are balanced by high egg and larvalmortalities resulting from natural interactingenvironmental stresses. Survival rates general­ly increased inconsistently with age ofeggs andlarvae. Few published studies provided thedata needed to compare relative mortalityamong the three major developmental stages.Mortality was greatest during the egg stage inthe walleye and striped bass, but during thepostlarval stage in some marine species. Wideranges of egg survival for Atlantic herring,northern pike, rainbow smelt, and walleyedepend on whether egg production is based onfecundity or field counts, and whether survivalis measured to a stage ofdrifting larvae or late

March 1979

impact. The primary types of impact are

impingement of fish on the intake screens

and entrainment of smaller fish and eggsinto the cooling system. The size of theintake screen mesh. usuallyYx inch. and

size of fish determine whether the fish are

entrained or impinged. The impingement

problem was reviewed by Hanson et a!.(1977). The few published studies onentrainment of fi'sh show that millions of

larvae are sometimes entrained daily by aplant during the period of peak abund-

eggs.Amongfreshwater species, hatching success

was low in unprotected eggs and high inspecies which exhibit parental care, constructnests, but do not exhibit parental care, havespecial protective mechanisms (y(!llow perch),and apparently in species which deposit eggs invegetation. Among anadromous species, eggsurvival in striped bass was particularly low incomparison to that in salmon. In the sea,hatching success of demersal eggs was muchhigher than in pelagic eggs. Survival ofyolk­sac larvae was generally higher in marine andfreshwater species than in anadromous spe­cies. Survival of postlarvae was highest infreshwater species in relation to high daily

ance (Edsall, 1975). Impact of entrain­

ment or other perturbations may beassessed by translation of egg and larval

losses to the potential number of adultsthey represent in the absence of entrain­

ment. This is compared with a reference

such as stock size or commercial catch.

Implementation of models requires in­formation on natural survival rates of thespecies of concern, or at a minimum, what

survival rates may be expected among the

various groups of fishes.

survival rates and short developmental per­iods.

The occurrence of brief critical periods ofhigh mortality was generally not supportedwhen data were correctedfor larval extrusion.The potentialfor high mortalin' to be offset bycompensatorv mechanisms is supported byliterature. A direct relationship of survivalrates and development time suggested thathigh mortality rates were an expected mechan­ismfor regulation ofpopulalions having shortdevelopmental periods. The availabilitv andapplicability of survival data to modeling ofimpact is assessed. Many environmental fac­tors should be considered when extrapolatingsurvival data from one site to another.

This paper represents a compilation ofavailable fish egg and larval natural sur­vival rates and discusses problems asso­ciated with interpretation and use of sur­vival data, major sources of mortality,survival rates associated with variousreproductive strategies, and the criticalperiod concept. Effects of humanperturbations and fish culture on survivalrates are not considered.

Interpretation ofSurvival Data

Since survival data are of little valuefor modeling unless they are available foreach of the developmental stages (TableI), it was necessary to construct survivalcurves and designate times of transitionto subsequent stages (Fig. 1-4) when

adequate data were available. Stages areclassified as eggs, yolk-sac larvae (fromhatching to complete absorption of yolk­sac), and postlarvae (from yolk-sac ab­sorption to demersal or fully developedjuvenile).The survival curves are also nec­essary to examine the critical period con­cept, which is dependent on differences ofslope within a curve rather than absoluterates of mortality (Pearcy, 1962). ,Repre­sentat}ve survival data are presented, ei­ther bCy selection of data which appears tobe typical of different years of study or byaveraging data for more than I year asdescribed in the footnotes. However, it isnot possible at this time to quantitativelyaccount for all errors which may resultfrom bias in sampling methodology.

Complete data on postlarvae are avail-

able for relatively few species becauseavoidance of plankton nets increaseswith size of larvae. It was neccessary toassume that postlarval survival rate wasconstant in order to complete the post­larval survival curves for Pacific sardine I

and yellow perch, as described in Table I.This avoidance problem may be resolvedby collection of postlarvae or juvenileswith trawls, as in studies of walleye(Forney, 1976), winter founder (Pearcy1962), and Atlantic herring (Graham eta!., 1972), or with trap nets, as in north­ern pike studies (Forney, 1968).

'Scientific names follow Bailey et al. (1970)except foreign names as listed in Table 4.

Figure I.-Survival curves for eggs and larvae of plaice during abnormal (P-A Y) and typical (P-TY) years. Atlantic mackerel (AM),Japanese sardine (JS), jack mackerel (JM), Japanese anchovy (JA), and Black Sea anchovy (BSA). Incomplete segments are indicated byarrows. Yolk-sac stages indicated by parenthesis. See Tables I and 2 for sources.

5

4

:3

Q:WCD~::::>Z

..~~+----....00 __+

or o

••• Io 0

-:7----__+

~969 P-AY+----+--1:30days

1962

, ,

o •• • AM

o 0

. ........S5days

2

o ...J-..-----r5----IOr-----,r5----Z'0---'Z5----3'O----3T5---'40----4'5----5TO---}55=---"-='=60

DAYS AFTER SPAWNING

Marine Fisheries Review

Determination of survival of yolk-saclarvae generally required interpolationbetween the egg and fully vulnerableyolk-sac stages. This approach is nec­essary because the smallest larvae aregenerally extruded through nets in thesea and are not fully planktonic infreshwater. This approach results in aconstant survival rate for smaller larvaeinstead of a more probable tendency forsurvival to increase during this period.

Egg production was indicated by nurtl­bers of ~ay-old eggs in plaice (Bannisteret aI., 1914) and 1.8·day-old eggs in jackmackerel (Farris, 1961). Actual egg pro­duction was estimated by extrapolationto the spawning date, assuming a con­stant survival rate among the early eggstages.

The use of age-related fecundity datato calculate egg production is a possiblesource of error in the survival data fornorthern pike (Forney, 1968), walleye(Forney, 1976), yellow perch (Clady,1976) and Atlantic herring off Norway(Dragesund and Nakken, 1973). Thismay result in high estimates of egg pro­duction if fertilization is not complete,egg extrusion is incomplete as in salmon(Johnson, 1965), or there are non­spawning adults as in walleye (Forney,1976) and salmon (Johnson, 1965). Clady(1975) indicated that the ratio of eggsdeposited (based on field, counts) andpotential egg deposition (based onfecundity) was low (15-34 percent) in asmallmouth bass population. However,this was possibly a result of egg predation

by red water mites before the eggs weresampled. Comparisons of egg productionbased on fecundity, and water body sam­pling yielded differences varying by a fac­tor of 2.7 in striped bass (Polgar, 1977)and 3-34 in Clyde herring (Saville et aI.,1974). However, these discrepancies werethought to be a result of inadequate eggsampling rather than incomplete eggproduction.

Major Factors WhichInfluence Mortality Rates

The applicability of data from oneregion for another will depend on howsimilar the environmental conditions areduring the developmental periods. Anumber of the major factors whichshould be considered are discussed

Figure 2.-Survival curves for eggs and larvae of northern pike (NP), yellow perch (YP), walleye (W), Pacific sardine (PS), Black Seamackerel (BSM), Atlantic herring in Norway (AH-N), round herring (RH), Atlantic thread herring (ATH), and scaled sardine (SS). Yolk­sac stages indicated by parenthesis. See Tables I and 2 for sources.

4

0:W.,::0:>z

X~YP

PS

'"o-' 2

W-65 DAYS

ATHRH

S5

O,-L--, -,- -,- .---__--,r-____,_----,-------'>fA~H.:...--.:.N:..--____,---__,_, --,, __,_, -,-,D ID 15 20 25 30 35 40 45 50 55 60

DAYS AFTER SPAWNING

March 1979 3

58 -C If D----,--

-----_~C

o

~."'".~~

~"~ ~"I--..

~ ----~ ------ ~S6-P.M-1V

SS-~

D.I -'--TI----,-I----,-I-----,-I-----,-I-----,-1-----,I:---~-_,---_,------r----,--......:=~rrEV----r'o 5 10 /5 20 25 30 35 40 45 50 55 60

DAYS AFTER SPAWNING

5

3

4

Figure 3.-Survival curves for eggs and larvae of striped bass in Potomac River based entirely on net samples (SB-PM-N), in PotomacRiver with egg densities based on fecundity-at-age data (SB-PM-F), in Chesapeake and Delaware Canal (SB-C & D), and in HudsonRiver (SB-HR). Yolk-sac stages indicated by parenthesis. See Table I for sources.

below. Further quantification wouldlend more predictive value to thisinformation. However, this would berather academic for predictive purposessince extent of mortality is a function ofintensity as well as type of perturbation.Quantitative estimates of the magnitudeof mortality due to some factors such aspredation and starvation are almosttotally lacking (May, 1974).

Substrate characteristics innuencedegg survival in salmon (Larkin, 1977),brook trout (HausJe and Coble, 1976),walleye (Johnson, 1961), and herring(Galkina, 1971). Siltation was a source ofmortality in eggs of smallmouth bass(Latta, 1975), lake trout (Youngs andOglesby, 1972), salmon (McNeil, 1966)and Pacific herring (Galkina, 1971).Survival of Pacific herring eggs insubtidal water was about 100 percent

when eggs were deposited on highvegetation and free from silt (Galkina,1971).

Low now or low water levels weredetrimental to survival of eggs of salmon(Warner, 196.1; McNeil, 1966), rainbowsmelt (Rupp, 19(15) and Pacific herring(Soin, 1971), and larvae of northern pike(Hassler, 1970) and striped bass (Stevens,1977). Mortality often resulted fromstranding of the eggs. Mortality ofPacific herring eggs from desiccationincreased from 30 to 100 percent from thelower to the upper intertidal zone, andtotal mortality was 5 percent or less insubtidal areas (Soin, 1971).

Reduction of oxygen to a critical levelcan cause mortality, e.g., salmon eggs(McNeil, 1966), brook trouteggs(Hausleand Coble, 1976), carp eggs (Nikolskii,1969), and Baltic cod larvae (Grauman,

1973). Lethal dissolved oxygen levelswere caused by high egg concentrationsin Atlantic herring (Jones and Hall, 1974),Pacific herring (Hempel, 1971), rainbowsmelt (McKenzie, 1947), and salmon(Johnson, 1965).

Adverse effects of low water temper­ature on eggs have been shown withsmallmouth bass (Kramer and Smith,1962), rainbow smelt (Rothschild, 1961),and northern pike (Hassler, 1970). Lowwater temperatures apparently reducedthe rate of larval development andcaused prolonged exposure to predationin plaice (Bannister et aI., 1974), Pacificsardine (Murphy, 1961), Atlantic herring

(Graham et aI., 1972), northern anchovy(O'Connell and Raymond, 1970), andwalleye (Busch et aI., 1975). Colton( 1959) reported mass mortali ty of mari nefish larvae due to natural warming. A

4 Marine Fisheries Review

4

~

~3

,~a: '" ~UJ

~CD:l::::>

2z

'"0 \ -------------+~-'

\ r '\ t +WF

\ / \\ / \

\ / \\PH-J

\1 \\ PH-B

00

20 30 40 50 60 70 80 90

DAYS AFTER SPAWNING

Figure 4.-Partial survival curves for larvae of winter nounder (WF). Atlantic herring off Maine (AH-M), Pacific herring offJapan (PH-J), and Pacific herring off British Columbia (PH-B). Approximate days after spawning are indicated. See Tables Iand 2 for sources.

rapid rise in water temperature adverselyaffected embryonic and larval survival in

herring (Rannak, 1971).Storms and wave action caused

mortality of herring larvae (Wiborg,

1976) and cod eggs (Rollefsen, 1930).Wave action caused stranding of I percent

of the yellow perch eggs in a lake (Clady,1976) and along with low temperaturewas responsible for failure of largemouth

bass nests (Kramer and Smith. 1962).Egg loss from nonfertilization is

generally minimal and has been reported

as about I percent in salmonids (Warner,

1963) and 0.2-0.4 percent in Baltic herring(Rannak, 1971). Egg loss from predation

has been reported in many species,including Atlantic herring (Dragesund

and Nakken, 1973), Pacific herring

(Soin. 1971), small mouth bass (Latta,1975), and rainbow smelt (Rothschild,

1961). Predation and cannibalism were

significant sources of larval mortality in

March /979

Black Sea anchovy (Dekhnik et aI.,

1970), Black Sea mackerel (Dek hni k,(964), Japanese anchovy (Nakai et aI.,1955), Pacific sardine (Murphy, (961),northern anchovy (O'Connell and

Raymond, 1970), winter flounder(Pearcy, 1962), walleye (Forney, 1976),

yellow perch (Tarby, 1974), northernpike (Forney, 1968), pink salmon(Johnson, 1965), and sockeye salmon(Hartman et aI., (962). Occasional highrates of predation on eggs and larvae ofroach, rainbow trout, and other

freshwater species were noted by Paling( 1971).

The hypothesis that lack offood causeslarval mortality (Hjort, 1914) has been

supported by studies of Atlanticmackerel (Sette, (943), plaice (Bannister

et aI., 1974), Japanese sardine (Nakai and

Hattori, 1962), Atlantic herring (Graham

et aI., (972), pilchard (Karlovac, 1967),

and Japanese anchovy (Nakai et aI.,

1955). Dekhnik et al. (1970) noted that

postlarvae survive 10-18 days withoutfood and concluded that " ... the foodfactor cannot be considered a cause of themortality of fish larvae in the Black Sea."However, inadequate food increases

vulnerability to other stresses and itseffect on survival is mainly indirect(Nikolskii, (969).

Relationship of Survival Ratesto Reproductive Strategies

I n addition to specific environmental

factors cited above, it is possible to makesome generalizations regarding thesurvival rates of fish eggs and larvae in

relation to different reproductive

strategies and habitats.

Survival of Fish Eggs

Hatching success of eggs is often low in

freshwater species which do not guard

the demersal eggs. As little as 3 percent

survival from egg to migrant larvae has

5

been reported for the white sucker (Scottand Crossman, 1973). Forney (1976)noted less than I percent walleye survivalthrough the swim-up stage in OneidaLake, with most of the loss probably inthe egg stage. Walleye survival fromrecently spawned eggs to a prehatching"eyed" stage was 2.4-25 percent onvarious natural substrates (Johnson,1961). High egg mortality also occurs inthe rainbow smelt: Rothschild (1961)reported 24 percent egg survival (to 1-15days before hatching) and 0.5 percentsurvival to the drifting yolk-sac stage;McKenzie (1947) found that the hatchingrate was usually 0.8-1.8 percent; andRupp (1965) reported a mean hatch of 1.1percent in lakeshore spawners of thisspecies.

Egg survival was generally high infreshwater species exhibiting parentalcare (Breder and Rosen, 1966) and infreshwater and anadromous salmonidswhich cover the eggs with gravel (Table3). Parental care was a factor in the 49-94percent survival of white crappie eggs(Siefert, 1968), 26-33 percent survival toemergence in smallmouth bass (Clady,1975; Latta, 1975), and 94 percentsurvival of smallmouth bass eggs in astream (Pflieger, 1966). However, only44-55 percent of smallmouth bass nestsproduced fry in large natural lakes(La tta, 1975).

High egg survival has been reported inthree freshwater species which spawn invegetation: 60-95 percent for northernpike (Franklin and Smith, 1963), 80-94

percent at high oxygen concentrationsfor carp (Nikolskii, 1969), and 34-90percent for carp-bream (Nikolskii, 1969).Forney (1968) reported 77 percentviability of northern pike eggs in aregulated marsh but found thatrecruitment to pelagic yolk-sac larvaewas only 16-19 percent. Protectionafforded by the unique egg massenvelopes contributes to high survival ofyellow perch eggs: Clady (1975) observedthat viability was generally over 95percent.

Survival of unguarded demersal eggsof three marine species (Atlantic herring,Pacific herring, and capelin) wasgenerally considered to be over 90percent (Baxter, 1971; Soin, 1971;Rannak, 1971; Gj«lsaeter and Saetre,

Table 1.-Survival rates of eggs and larvae 0' marine, freshwater, and anadromou5 fishes. Footnotes are cross-referenced to Figures 1~5.

Eggs Yolk sac larvae Postlarvae TotalSurvival Survival Survival Survival

Fishes SurvIval Days per day Survival Days per day SIJrvival Days per day Survival Days per day

MarineAtlantic r.erring 1 0030 21 0.846 0.175 14 0.884 0050000 90 0.967 0.000263 125 0936

Atlantic mackerel' 0300 9 0.875 0.200 8 0.818 0.000067 60 0.852 0.000004 77 0.851

Atlantic thread herring3 0.660 0.8 0.595 0.400 4.9 0.830

Black sea anchovy 4 0.060 2.5 0.325 0.383 1.5 0.527

Jack mackerels 0.132 3.5 0.560 0.100 4.5 0.600 0.002182 49 0885 0.000024 57 0.830

Japa.nese sardine6 0.270 4 0.721 0.333 4 0.760 0.003333 62 0.913 0.000300 70 0.893

Pacific sardine7 0.360 3 0.712 0667 4 0.904 0008333 43 0.896 0002000 50 0883

Pla;cea 0.118 22 0.907 0.678 9 0958 0.00012.5 99 0.914 0.000010 130 0915

Round herring9 0.380 2 0.616 0.250 8 0.841Scaled sardine'o 0.120 0.8 0.071 0.106 7.5 0742

FreshwaterNorthern pike l1 0180 13 0.880 0572 8 0.931 0.291262 22 0.945 0.030000 43 0922

Walleye 12 0.005 24 0.800 0.132 9 0800 0.333333 31 0965 0.000060 64 0859

Yellow perch 13 0.259740 ~O 0.956 O.O~OOOO 55 0.931

AnadromousStriped bass 14 0.009 2 0095 12 0.726 0.014000 41 0.901 0000003 55 0.793

Striped bass!S 0.003 2 0055 0.021 12 0.726 0.014000 41 0.901 0.000001 55 0.778

Striped bass 16 0.100 2.5 0.398 0.100 12.5 0.832 0.100000 75 0.870 0.001000 90 0.926

Striped bass l1 0.100 2.25 0.360 0.150 6 0.728 0.030000 52 0.935 0.000450 60 0.879

'Dragesund and Nakken (1973). Means of egg survival (0.01-0.05) and YOlk· saclarva survival (0.05-0.30). Egg survival based on fecundity-at-age data. (Fig. 2).Postlarva data from Gushing (1974). Average values for 6-year study. limited to first90 days (Fig. 4)2Sette (1943). Planktonic survival was 1x10-6 to 1x10-s, but 4x10-6 in his Figure 17Apparent net avoidance in older larvae. (Fig. 1)JHoude (1977bL Means of survival to 5.5 mm yolk-sac larvae and 15.5 mm earlypostlarvae. (Fig. 2)'Dekhnik (1963). Nikolskii (1969). Egg survival also given as 58 peroent (Dekhnik,1960) and 19-40 percent (Pavlovskaia. 1955). (Fig. 1)sFarris (1961). Means of data for 3 years. Survival for first month was approxim::ately01 percent all 3 years. Eight day period of yolk nutrition (Farris, 1960). (Fig. t)'Nakai and Hattori (1962. Table 6). Means of data for 3 years (Fig. 1)'Lenarz (1972) for abundance by length and Ahlstrom (1954) for ag~-Iength

relationship. Samples collected at night and corrected for extrusion (Lenarz.1972). Egg survival (0.36) from Smith (1973). Four-day yolk-sac larva period(Ahlstrom. 1954). Daily survival rate for days 30-35 assumed to be constantthrough day 50. (Fig. 2)'Bannister et al. (1974). Data for typical year (1962). Yolk-sac larva period tollowsRyland (1966) (Fig 1)'Houde (1977a). Means of survival to 5.5-mm yol'-sac larvae and 15.5-mm earlyoor,tlarvae. (Fig. 2)

6

"Houde (1977c). Means of survival to 5.5-mm prolarvae and 15.5-mm earlypostlarv.e. (Fig. 2)II Forney (1968). Means of data for 2 years. Assume transformation to juvenile at 35mm and 43 days .fter spawning (Franklin and Smith, 1963). Actual egg survival wasbetween the observed 77 percent viability and 18 percent survival to pelagic YOlk­sac larvae. (Fig. 2)12Forney (1976). Mean values for 3 years in which cohorts Which were notaugmented with yolk-sac larvae Survivors~ip of yolk-sac larvae (13.2 percent)estimated from relative numbers of 1- to 3-day-old larvae and 10-day-old larvae byassuming that differences in numbers of 10-day-old larvae in augmented andunstocked cohorts resulted fro'1"' stocking Egg production based on fecundity.Trawled juvenile data used to complete the postrarvae ,urviv.1 segment (Fig. 2)"Noble (1975). Survival values for davs 25 to 45 in 3 years. assumed to be constantto demersal age (55 days). Survival and duration of earlier stages from Glady(1975). (Fig 2)"Polgar (1977. Table 2) Assumed exponential age distribution. Net samples only.through post-finfold (late PQstlarva) stage. (Fig, 3)"Polgar (1977). As above. but with egg production based on fecundity-at-age data.(Fig. 3)"Portner (1975). Assumed 0.100 survival for each stage. (Fig. 3)"LMS (1975). Swartzman et al. (1977) Net samples only. through juvenile I (lateposllarva) stage. (Fig. 3)

Marine Fisheries Review

Table 3.-Survlval rates 01 salmonids Irom egg tohatching and emergence in nature.

bass (Tables 1-3). Daily survival rateswere 53-96 percent, 80-93 percent, and73-83 percent, respectively. Survival ofyolk-sac larvae of Danubian shad wasless than 10 percent (Dekhnik et a!.,1970). Thus, there are no obviousdifferences in survival rates among thegroups with the possible exception of lowsurvival in the anadromous species.

Survival of Postlarvae

Postlarval survival (Table I) wasconsiderably higher In the three

0.92'0.59, '0.79

0.91

Egg toemergence

001-0.25"0.26-0.54,"0.14-0.54

Less than 0.13"0.03-0.21"0.01-0.25"042-0.92"0.20. "0.085"040

"0-0.79nO.86

Over 150.80

Hatching

0.93'0.80-0.93.'0.84

Atlantic salmon'Brook trout

Cutthroat trout '3Lake whitefish 14

Pink salmon

Brown troutrainbow trout andchinook salmon' 0.71-0.97

Brown trout '0.89. '0.98Chum salmon' Over 0.80Coho salmon '0.35-0.85

'°0.850.25-040

Species

Rainbow troutSockeyeSteelhead

Survival of Yolk-Sac Larvae

Survival of yolk-sac larvae ranged from2.3 percent (winter flounder) to 68percent (plaice) in marine species, 13to 57 percent in two freshwater species,and 2.1 to 15.0 percent in striped

Survival of pelagic cunner eggs wasestimated as 5 percent by Williams et a!.(1973). Survival of pelagic Baltic(Atlantic) cod eggs varied from I to 21percent in relation to dissolved oxygen,buoyancy (resulting from salinity) andegg quality (based on size and fatcontent) (Grauman, 1973). Survival ofpelagic Argentinean anchovy eggs was 7­13 percent (Ciechomski and Capezzani,1973). There are additional observationson viability of pelagic eggs, whichprobably exceed actual survival rates,e.g., viability of pelagic pilchard eggs was50 percent off England and 48-87 percentin other studies (Southward and Demir,1974). Very low survival (0.3-10 percent)was also reported for the semi buoyanteggs of anadromous striped bass (TableI).

1974). Lower survival from spawning onless suitable substrates or from densepacking of eggs has been reported, butthis is probably of little consequence incomparison to predation on eggs(Hempel, 1971). Dragesund and Nakken(1973) concluded that egg loss frompredation was 15-40 percent, andmortality from hatching to recruitmentinto the plankton was 83-95 percent inone herring population. An assumed 10percent hatch of demersal winterflounder eggs (Hess et a!., 1975) has notbeen verified.

Data in Table I indicate that survivalof pelagic eggs in the sea was relativelylow (6-66 percent, mean 26 percent)although Murphy (1977) concluded that

demersal eggs were more vulnerable topredation. However, survival of BlackSea anchovy eggs has also been reportedas 58 percent (Dekhnik, 1960) and 19-40percent (Pavlovskaia, 1955). Survival ofpelagic Japanese anchovy eggs was 70percent (Hayasi, 1967). Survival of pelagicsole eggs was 0.05 percent and 4.35 percentat two locations off England (Riley, 1974).

Table 2.-Survlval rates 01 Iish larvae and various larva and egg combinationsnot shown In Tables 1 and 3. Footnotes cross-relerenced to Figures 1-5.

Species

Winter flounder'

Pacific herring 2

Pacific herring3

Pilchard·Northern anchovy5Chub mackerel 6

Japanese anchovy 7

Black sea mackerel 6

Smallmouth bass'Smallmouth bass lO

Stage

Yolk-sac larvaePostlarvae10-15 mm postlarvae15-18 mm post larvae18-28 mm postlarvae10-28 mm postlarvaePostlarvaePostlarvae2-20 mm larvae3-16 mm larvaeEggs and larvaeEggs and larvaeEggsYolk-sac larvaeEggs to fry emergenceEggs to fry emergence

Survival

0.0230.3190.1200.0170.5000.00090.00050.0250.0040.0070.0050.00090.2070.05602860.941

Days

172814

819402011

23311.16

1010

Survivaleer day

08000.9600.8600.6010.9640.8390.6840.715

0.7210.7990.2390.6180.8820.994

'Warner (1963). Survival to late eyed stage and emergence.'Shetter (1961). Typical range.'Hausle and Coble (1976).'Brasch (1949). Upwelling favorable to survival.'Hobbs (1940). New Zealand.'Allen (1951) and Braum (1971).'Kramer and Smith (1965).'McNeil (1966). Typical emergence values.'Cloern (1976). Typical range. but 0-0.014 in Wisconsin."Briggs (1953)."Moring and Lantz (1975)."Koski (1966)."Ball and Cope (1961)."Van Oosten (1956)."McNeil (1966).16Hanavan and Skud (1954). Tidal waters"McNeil (1966). Typical values"Bjorn (1966). Planted eggs."Krogius (1951).wJohnson (1965). Survival to entry into nursery ground<"Hartman et al. (1962). Survival to fry Qutmigration."Briggs (1953)."Coble (1961).

'Pearcy (1962). Data excludes 2.3-3.5 mm larvae. Translocation was minorcomponent of total 105585. Survival curve extrapolated to complete transformationage in Figure 4.<'lizuka (1966). Data for postlarvae in 1959, representing three distinct survivalslopes. Complete recruitment at 60 days after spawning. (Fig. 4)'Stevenson (1962). Bimodal curve represents two broods of larvae. (Fig. 4)'Karlovac (1967). 2-20 mm larvae (Fig. 5).'Lenarz (1972). 3-16 mm larvae. Night samples corrected for losses through 0.55­mm mesh. (Fig. 5).'Watanabe (1970). Spawning to day 23. Also called Japanese common mackerel'Nakai et al. (1955). Survival from spawning to day 31. Mean of 3 years. (Fig. 1).'Dekhnik (1964). From his table 3. (Fig. 2).'Clady (1975). Data for 3 years. Ten-day duration from Allan and Romero (1975).Survival also reported as 27.6 percent (Latta, 1963)."Pflieger (1966) Stream population. Duration from Allen and Romero (1975).

Table 4.-Usl of common and scientific names ot foreignIIshes cited In this paper.

Common name Scientific name

Argentinean anchovy Engraulis anchoitaBlack sea anchovy Engraulis encrasicholusBlack sea mackerel Trachurus mediterraneusCarp-bream Abramis bramaDanubian shad A/osa a/osaJapanese anchovy Engraulis japonicaJapanese sardine Sardinops me/anostictaPilchard Sardina pi/chardusRoach Rutilus ruti/usSole Solea solea

March /979 7

100

XNA ·P-AS

0.1 -+--r--,--,----r--,--,--,.--r---.--,--

o 6 8 10 12 14 16 16 20

LENGTH (mm)

Figure 5.-Partial larval survival curves ofAdriatic Sea pilchard (P-AS) and northernanchovy (NA) in terms of percent of total larvaeVS length. See Table 2 for sources.

days (10-12 mm) (Dragesund and:\Iakken. 1971. May 1974) and 70-95percent in 14 days (9-13 mm)( Dragesundand Nakken, 1973). The delay of a highmortality period (98 percent in 8 days) toa size range of 15-18 mm in Pacificherring postlarvae in Japanese waters(lizuka, 1966) may be attributable totheir retention in a bay. The relativelyconstant survival rate of yolk-sac andpostlarval Atlantic herring in the Gulf ofMaine (Graham et aI., 1972 as modifiedby Cushing, 1974) suggests thatobservation of high mortality in otherpopulations of herring may result fromoffshore drift or errors caused by netavoidance. Offshore drift as a majorcause of death was postulated for Pacificherring in British Columbia (Stevenson.1962) although the extent of mortality atsea was not determined.

Observations representing catastroph­ic mortality may be confused withcritical periods. Catastrophic mortalityin the early larval stages of herring wasdocumented by Soleim (1942). Marr(1956) and May (1974) suggested that thenet in this study was contaminated withherring larvae of previous hauls. Wiborg(1976) and Nikolskii (1969) citedevidence that such mass mortalities resultfrom storms.

The occurrence of a critical period inAdriatic pilchard (Karlovac, 1967; May,1974) is not strongly supported byKarlovac's data. Samples were collectedat monthly intervals during the spawningseasons, and larval densities weretabulated by size. A plot of larvalnumbers as percent of total larvae VSlengths (Fig. 5) following the procedureof Lenarz (1972), does not provide anyevidence of a critical period. However. nocorrection for variation in growth ratewas made.

Data on striped bass of the PotomacRiver, Chesapeake and Delaware Canal,and Hudson River (Table I, Fig. 3) revealvery high mortality of eggs (90-99.7percent). Highest egg mortality ofPotomac River striped bass is apparentwhen egg production is based onfecundity-at-age data. The markeddifferences in the striped bass survivalcurves for the three study areas areinfluenced by the use of hypotheticalsurvival rates for the Chesapeake and

and 2 indicate that mortality is greatest inthe postlarval stages of the marine speciesand also in the Hudson River stripedbass. Therefore, the environmentalconditions existing during the relativelylong postlarval periods may be morecritical to the determination of year-class'strength than the egg and yolk-sac larvaenvironments.

Critical periods have been postulatedfor many species. Larval survival curves,presented as percent of larvae VS length,for Pacific hake, jack mackerel, Pacificsardine, and northern anchovy (Lenarz,1973) revealed some evidence for earlycritical periods, but there was also somedegree of extrusion through the 0.55-mmmesh net. Survival curves of pacificsardine (Fig. 2) and northern anchovylarvae (Fig. 5) did not provide anyevidence of a critical period whendensities were corrected for loss of smalllarvae through the mesh (Lenarz, 1972).

Survival curves of herring larvae donot follow a consistent pattern (Fig. 2,4).Mortality rates of Norwegian herringlarvae were estimated at 94 percent in 6

Enormous fecundities of fishes arebalanced by high mortality rates. Theoccurrence of most mortality during ashort period in early development is thecritical period concept. Total losses areundoubtedly highest during egg or yolk­

sac larva stages (Farris, 1960, Dekhniket aI., 1970). If a critical period can beidentified, then it is likely that theconsequences of human perturbationswould be much greater if they occurredafter the critical period rather thanbefore.

Critical period may also be viewed interms of relative survival rates among thedevelopmental stages. Data in Tables I

freshwater species (26-33 percent) than inthe 10 examples of marine species (0.01­31. 9 percent, mean 4.09 percent). Thismay be attributable to higher dailysurvival rates and shorter postlarvalperiods (22-31 days). An intermediaterate of survival is apparent for the 41-75day postlarval periods in the striped bass.

Observations on PossibleCritical Periods

x

10.x

-' x...t-ot-

...0

1.0 X

8 Marine Fisherie.\ Re\'ie\\'

to larva survival. Other models requireadditional data on survival rates of larvaeand juveniles, population size, larvalproduction, compensatory reserve, etc.Such information is available for a verylimited number of species and must be

used cautiously in predictive modeling.Data collected at one site may not be

applicable to another if there aredifferences in natural factors, such assubstrate characteristics, disease, waterlevel, dissolved oxygen, watertemperature. wave action, predation,cannibalism, food supply, carryingcapacity. and condition of spawnersInteraction of more than one stress hasbeen frequently observed It has beenpruposed that low water temperaturessignificantly prolong development andexposure to predation. several stressesmay act slmu!w.neously as in small mouthbass (Latta. 1975). yellow perch ((lady,1976), salmun (Jurnson, 19(5), andmarine fishes (M'IY. 1974) Skud (1973)concluded I.hat environmental factorshad a "random inOuence" in pink salmonsince egg and larv'll sliP/Ivai was highest

when the sp'lwners were lalge andspawned early. First year survival 01'smallmouth bass was pr0bab lydetermined by carrYing capacity \0 astream (Pllieger, 1975).

!\;atllral stresses cause high mortalityof eggs In those freshwater speCics whichbroadcast the eggs and have no specialprotective mechanisms. This strategypOints to prC'dation as a chronic sourceof the high mortality in walleye andrainbow smell. The importance ofpredation by Invertebrates. considered tobc the main predators on fish eggs andlarvae (Nikolskii. 1969). has receivedlittle attention. l.arval and nymphalInsccts and leeches feed on rainbow smelteggs (Rothschild. 1961),

High egg survival has been reported infrC's!.water species which cover the nestedeggs with gravel (salmonids), depositeggs In vegetation (carpbream, carp,northern pike), have unique egg massenl-elup,:, (vcllow p';rch) or guard thcncsts (centrarchJd.s) "vbny stud!':s haveshuwn ()\t:r l.)() perC"'nt survllal ufdemers,,1 egg, of m:;rlne specie, whichbroadcast the q~gs and have n"f,rotcctllC mecranl\ms Howcver mo,t ofthese slL'dws protnhl) JicJ not account

~H

'*PL

Discussion

compensatory mechanISm, functioningto maintain egg and larval populationsthrough longer devell)pm~ntalperiods inmanne fish. LImited data make a ,il11 ilarassessment With freshwater oranadromous fishes difficult. However.data on chinook salmon (Johnson. 19(5)support the hypothesis. A daily survivalrat~ of 99 percent was calculated for aposslole 9-month dnelopment period

The critical period i, a relatl\'e conceptand d~pends mor~ on the differ'ences ufslope in a surVival cun'r rather thanabsolute rates of mortality Pearcy ( 19(2)concludcd that thiS concept has limitedusefulness. p:-trticularly If compen,atorymechanisms actlvelv rcsp'lnd to pel"lodsof high mortality 1he pr<:valence ofcompensation in fi-,hes was revlcwed byMcFadden (1977)

Current federal regulati,'ns "I'tennecessitate entrainment impact modelingIn the absence of complete or site-specificdata. In the simplistic equivalent adultsmodel (Horst. 1975). larva to adultsurvilal IS est Imated from data onfecundity. annual survival rates, and·,.gg

w-J; X•~ X

JM<S>

XX

NP YP• •

1.0

0.6

0.9

~ .eM-:: 0.7

>­

"a o.aa:...Q.

10 20 30 40 50 60 70 60 90 100 liD 120 130TOTAL DAYS OF DEVELOPMENT

Figure 6. Relationship of daily survival roles anu length, ofdevelopmental period in striped ba" (X), chub lll<Jckcrd(eM), Japanese anchovy (')i\). northern pike ('\iP). Pacificsardine (PS), yellow perch (Y Pl. jack mackerellJ M). walleye(W). Japanese sardine (JS), Atlantic mackerel (AM), plaice(PL), and Atlantic herring (AH). Diamond figure indicate,marine species. See lables I and 2 for sour~e:'.

Delaware Canal population, and bydifferences in sampling and I or datainterpretations, and therefore do notprovide strong evidence tor a criticalperiod.

Maintena nce of stock Sl7e dependslargely on egg production and rate ofsurvival through egg and larval stages. Itfollows that species having short perIodsof egg and larval development willexhibit higher daily mortality rateswhich may be Interpreted itS cnticalperiods. To investigate the relationshipof daily egg and larval surVival rates withtotal time of egg and larval development.these data (Tables I. 2) were plotted farspeCies represented by relativelycomplete survival data (Fig. 6). Dailysurvival rates ranged from 72 percent inchub mackerel to 94 percent in Atlanticherring and a general correlation ISapparent. However. the low survivalratcs of chub macknel and Japaneseanchovy are strongly inOuC'ncr:d by theabsence of larger larvae. A trend ofincreaSing surVIval with time ofdevclopment IS apparent with theremaining marine species. Higher dailysurvival rates apparentlv represent i'

J111rc!1 /97')

for predation which resulted in 15-40percent mortality in one herring study(Dragesund and Nakken, 1973). Theratio of swim-up larvae and depositedeggs does not provide a reliable measureof egg survival because mortality duringthe period of hatching and recruitmentinto the plankton may be high (Forney,1968; Dragesund and Nakken, 1973).Furthermore, the youngest yolk-saclarvae often associate with the bottomand are not fully vulnerable to planktonsampling gear in freshwaters. Mortalityof pelagic eggs has been determined fromratios of various egg stages, but this istenuous when of short duration such as Ior 2 days. Polgar (1977) indicated thatstriped bass eggs were not adequatelysampled during the daytime because thisspecies spawns at night. Thesemi buoyant nature of the eggs may alsoresult in low estimates when sampledwith plankton gear. Selection ofrepresentative egg survival values isparticularly important in the equivalentadults model because of the proportionalinverse relationship with the projectedadult loss. Because of the samplingproblems and natural variability,application ofa possible range ofsurvivalvalues is recommended.

Yolk ·sac larvae are the most difficultof the three developmental stages tosample because they are frequentlyextruded through the net in marinestudies and are in a transition between ademersal and pelagic existence in mostfreshwater species. Thus, survival ofyolk-sac larvae is generally based onsurvival curves which exclude data forthe smallest larvae or have incorporatedcorrection factors (Lenarz, 1972). Earlierobservations of possible critical periodsin marine fishes generally reflect thissampling error. Such data gaps do notpreclude impact modeling and mayrepresent a minor factor in relation to thevarious assumptions that are requiredand the minimal information availableon compensatory reserve in fishes.

Development of survival data islagging far behind the modeling state-of­the-art in impact assessment. As a result,important decisions are being madefrom incomplete data. A need for furtherevaluation of models is also evident in theliterature. As an example, a series of

10

models for entrainment of striped bass inthe Hudson River yielded conflictingresults. Major differences in predictionswere related to definition of life stages,whether fishing mortality and mortalityof larvae and juveniles were density­dependent or density-independent,method of computing recruitment ofyoung-of-the-year fish, and majordifferences in values of parameters suchas egg production, population size, andsurvival probabilities (Swartzman et a!.,1977).

Acknowledgments

Compilation of fish egg and larvalsurvival data has heen encouraged bys.c. Marcy, Jr. and other NUS staff whowere concerned with power plant impactstudies, under the direction of P. V.Morgan, Vice President and GeneralManager of Ecological SciencesDivision. I thank W. J. B. Johnson fordrafting the figures. Critical reviews wereprovided by B. C. Marcy and E. P.Wilkins of NUS Corporation and by S.Gregory and J. Andreasen of the U.S.Fish and Wildlife Service.

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Marine Fisheries Re"iew