NOAA Technical Memorandum NMFS-AFSC-94

U.S. DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

National Marine Fisheries Service

Alaska Fisheries Science Center

August 1998

by

F. Thrower, R. Martin, and R. Heintz

Effect of Seawater Entry Date on

24-hour Plasma Sodium Concentration

and Survival of Juvenile Spring Chinook

Salmon (Oncorhynchus tshawytscha)

Reared in Marine Net Pens
NOAA Technical Memorandum NMFS

The National Marine Fisheries Service’s Alaska Fisheries Science Center uses

the NOAA Technical Memorandum series to issue informal scientific and

technical publications when complete formal review and editorial processing

are not appropriate or feasible. Documents within this series reflect sound

professional work and may be referenced in the formal scientific and technical

literature.

The NMFS-AFSC Technical Memorandum series of the Alaska Fisheries

Science Center continues the NMFS-F/NWC series established in 1970 by the

Northwest Fisheries Center. The new NMFS-NWFSC series will be used by

the Northwest Fisheries Science Center.

This document should be cited as follows:

Thrower, F., R. Martin, and R. Heintz. 1998. Effect of seawater entry

date on 24-hour plasma sodium concentration and survival of juvenile

spring chinook salmon (Oncorhvnchus tshawvtscha) reared in marine

net-pens. U.S. Dep. Commer., NOAA Tech. Memo. NMFS-AFSC-94,

18 p.

Reference in this document to trade names does not imply endorsement by

the National Marine Fisheries Service, NOAA.
August 1998

NOAA Technical Memorandum NMFS-AFSC-94

by

F. Thrower, R. Martin, and R. Heintz

Effect of Seawater Entry Date on

24-hour Plasma Sodium Concentration

and Survival of Juvenile Spring Chinook

Salmon (Oncorhynchus tshawytscha)

Reared in Marine Net Pens

Auke Bay Laboratory

Alaska Fisheries Science Center

11305 Glacier Highway

Juneau, AK 99801-8626

U.S. DEPARTMENT OF COMMERCE

William M. Daley, Secretary

National Oceanic and Atmospheric Administration

D. James Baker, Under Secretary and Administrator

National Marine Fisheries Service

Rolland A. Schmitten, Assistant Administrator for Fisheries
This document is available to the public through:

National Technical Information Service

U.S. Department of Commerce

5285 Port Royal Road

Springfield, VA 22181

www.nfis.gow
Notice to Users of this Document 

This document is being made available in .PDF format for the convenience of users; however, the 

accuracy and correctness of the document can only be certified as was presented in the original hard 

copy format. 

111

ABSTRACT

On seven dates during the summer and fall of 1987, stream-type chinook salmon

juveniles (8-10 g average weight) were placed in marine net-pens with access to a lowsalinity lens, to be tested for seawater tolerance. Overwinter survival averaged 72 %

(range 27-87%). Plasma concentrations of sodium for fish challenged to 30% salinity

(full-strength) seawater for 24 hours were above critical (170 mmol/l) on all but the late

June challenge date. Plasma concentrations of sodium for fish challenged to 30%

salinity with access to a low-salinity lens were below critical for all dates tested. Survival

to mid-May 1988 and overwinter mortality rate were not correlated with date of entry

into the net-pens or with plasma sodium concentrations 24 hours after entry. The juvenile

chinook salmon demonstrated the ability to acclimate, survive, and grow in an

environment of predominantly full-strength seawater throughout most of the year when

access to a low-salinity environment was provided. Culture of juvenile chinook salmon in

marine net-pens with a low-salinity lens might be a useful rearing strategy for salmon

hatcheries with access to suitable marine sites.
V

CONTENTS

INTRODUCTION ......................................... 1

METHODS ............................................. 2

RESULTS.. ............................................. 4

DISCUSSION ............................................ 6

ACKNOWLEDGMENTS ...................................... 7

CITATIONS .............................................. 9
INTRODUCTION

Many hatcheries in Southeast Alaska supplement traditional freshwater smolt

production by using marine net-pens to produce juveniles for release (Heard and Crone

1976, Martin and Wertheimer 1987, Martin et al. in prep.). Survival during culture in

marine net-pens, however, has varied greatly and may be related to the seawater

adaptability (osmocompetence) of the juveniles when introduced into the saline

environment of a marine net-pen (McGee 1985). For the enhancement program in

Southeast Alaska to maximize the production of chinook salmon, the relationship between

time of seawater entry and survival to release of juvenile chinook salmon (Oncorhynchus

tshawytscha) cultured in marine net-pens must be understood.

The successful osmotic transition of juvenile salmon from fresh water to seawater

is related to time of seawater entry, size at entry, salinity during transition, photoperiod

exposure, and stock. Normally wild, yearling (stream-type) chinook salmon enter

seawater between early April and late June throughout most of their North American

range (Healey 1991). Seawater adaptability of juvenile salmon reared in hatcheries has

been related to changes in gill sodium-potassium ATPase activity and blood

concentrations of thyroid hormones, and follows a seasonal pattern that normally peaks in

spring (Zaugg and McLain 1972, Dickhoff et al. 1978, Lasserre et al. 1978, Ewing et al.

1979). On entering seawater, wild yearling chinook salmon generally are 68-134 mm in

fork length (Healey 1991), or about 5-25 g. Larger juveniles are usually more

osmocompetent than smaller individuals in full-strength seawater ( > 30% salinity)

(Mahnken et al. 1982). Wild juvenile chinook salmon generally migrate from fresh water

into a complex environment of mixed salinities normally found in river mouths or

nearshore marine areas. They can adapt more readily to high-salinity environments when

allowed a short period to acclimate in intermediate-salinity environments (Wagner et al.

1969, Kepshire and McNeil 1972, Gould et al. 1985).

Most research on seawater adaptability has focused on the measurement of various

physiological parameters (e.g., gill sodium-potassium ATPase activity and blood

thyroxine concentration) of fish still in fresh water and the subsequent indexing of those

parameters to performance after static challenges to salinities greater than 28 % . Some

researchers then measure concentrations of sodium in the blood plasma and survival after

24 hours to determine osmocompetence (for reviews, see: Folmar and Dickhoff 1980,

Wedemeyer et al. 1980). Rarely, longer-term growth is used as a measurement of

osmocompetence (Clarke and Shelbourn 1982, Mahnken et al. 1982, Gould et al. 1985).

Normal testing environments are usually homogeneous, with a specific salinity,

and thus are not hydrographically representative of the complex, layered-salinity

environment of most estuaries (Powers 1963, Officer 1976). Upon ocean entry, most

wild and enhanced juvenile chinook salmon encounter a situation that allows them to

move freely between low- and high-salinity environments; this is significantly different

from the environments they have traditionally been tested in. Nevertheless, researchers

have given little attention to the seasonal changes in the adaptability of juveniles to an

environment that allows access to low salinities and to the effects of size on this ability.

Some stocks of chinook salmon migrate seaward outside the normal migration

period (Healey 1991). Juveniles might be able to adapt to a primarily marine
2

environment throughout the year if they have access to a low-salinity zone. The

correlations observed between timing of seaward migration, gill sodium-potassium

ATPase, and blood thyroxine concentration may be related more to the enhanced

probability of survival due to some other factor (e.g., increased seasonal food availability

or predator avoidance) than to the ability to adapt to seawater under natural conditions.

Variation in survival during culture of juvenile chinook salmon in marine net-pens may be

related to variations in time of seawater entry, size at seawater entry, the salinity of pen

environments, or other factors.

In this experiment we challenged unacclimated, underyearling stream-type juvenile

chinook salmon to a full-strength seawater environment that allowed access to a lowsalinity lens. We evaluated osmocompetence by measuring plasma sodium concentration

and survival after 24 hours of exposure to full-strength seawater, in juveniles with and

without access to a low-salinity lens. We evaluated general seawater adaptability of

juveniles with access to a low-salinity lens by measuring survival and growth in marine

net-pens until the time of normal seawater entry in mid-May.

METHODS

The site of the experiment was the Alaska Fisheries Science Center’s Little Port

Walter Biological Research Station on Baranof Island in Southeast Alaska (Fig. 1).

Coded-wire-tagged adult chinook salmon, from parents originating from a single

transplant of eggs from the Chickamin River in southern southeastern Alaska in 1976

(Hard et al. 1985), were spawned at the Sashin Creek weir at Little Port Walter in

August 1986. Various lots of eggs were held in ambient, heated, or refrigerated water to

produce juveniles weighing 8-10 g at seven net-pen entry periods in 1987 (13 June; 11

July; 27 Aug.; 15, 16 Sept.; 3, 4 Oct.; 17, 18 Oct.; 6, 7 Nov.). Photoperiod history was

different for each of the three summer trial dates: fish for the June entry date were started

on food in late November; July fish were started in mid-December; August fish were

started in early April. Fish used for the four fall entry dates were started in mid-May.

Size for the fall entry date fish was controlled by manipulation of feeding rates early in

summer to produce four populations that were fed at excess levels the final month of

freshwater rearing.

During each entry period, juveniles were placed into a 3.7 x 3.7 x 3.7 m

polyester net-pen of 9.5-mm mesh with an effective rearing volume of 46.5 m3. Each

entry period had a separate pen or pens, and all pens were surrounded by a Hypalon (rubberized, waterproof material) barrier that extended 1.5 m downward from the water

surface (Fig. 2). The barrier was supported by an aluminum and wood framework extending downward from the flotation collar. About 20 l/min of fresh water was

introduced into the surface of each pen, creating a l-m-deep lens of low salinity (artificial

freshwater lens system [AFLS]). To keep predators out, a l-m-high fence of 25-mmmesh nylon webbing was placed around the pens and bird netting was placed over the

pens. In addition, a standard 12-volt electric fence was placed around the pens to
3

discourage mink (Mustella vison) and river otter (Lutra canadensis). Salinity and

temperature were measured weekly with a Beckman salinometer.

A 510 1 fiberglass tank containing seawater was used for the 24-hour exposure

trials; 20 1/min of seawater was pumped from below 2-m depth of the bay, where

salinities ranged from 29.5 to 30.5% throughout the trials. Fish density in the tank

averaged 1.1 g/l.

During each net-pen entry period, the juveniles were anesthetized with MS-222

and marked by implanting a coded-wire tag in the snout and removing the adipose fin.

The juveniles were then moved directly into net-pens in the AFLS, and a subsample of

45-160 fish was placed into the full-strength seawater container. For each of the three

summer entry periods, 560 fish were placed into net-pens in the AFLS; fish density

averaged 0.1 g/l. For each of the four fall entry periods, 7,560 fish were placed into netpens in the AFLS; fish density averaged 1.7 g/l. To replicate overwinter survival, an

additional lot of 7,500 fish was placed in net-pens in a separate AFLS on each of the four

fall entry dates. Smaller lots of fish were available in summer because of the limited

amount of heated water available for accelerated rearing. Juveniles were bulk-weighed in

lots of 300-400 to determine average weight at entry. All fish were fed BioDiet fish food

at the manufacturer’s specifications throughout the experiment. In mid-May 1988, the

survivors in each pen were counted by hand and 100 fish from each net-pen were

individually weighed and measured.

Sixty fish from the AFLS and all live fish (up to 60) from the full-salinity

container were removed 24 h after entry for each period (for some entry periods, fewer

than 60 fish were available for analysis from the full-salinity groups because of

mortality). They were killed by a quick blow to the head, and the caudal peduncle. was

severed. Blood for plasma sodium analysis was collected from the caudal artery with a

micro-hematocrit tube treated with ammonium-heparin. We collected 0.1 ml of whole

blood from each fish and pooled the blood from three fish. The sample was then

centrifuged for 3 minutes, and the plasma was removed, sealed, and stored at -20°C for

later analysis. Plasma samples were processed on an Orion Model 1020 blood sodium

analyzer. Machine readings were multiplied by 0.941 to make readings comparable with

flame photometric values using a conversion chart (Orion Research Inc. 1983) and with

previously reported serum protein and lipid values for chinook salmon juveniles (Woo et

al. 1978).

On the June and July entry dates, plasma sodium concentration was also

measured in 60 fish removed directly from the freshwater raceway and anesthetized,

tagged, and returned to the freshwater raceways for 24 hours, as freshwater controls.

Overwinter survival for each entry period was determined by dividing the

number of live fish in the spring by the number placed in the net(s). Overwinter

mortality rate (r) was calculated to compensate for the differing number of days of culture

by r = 1n (overwinter survival)/days of culture.

Linear regression analysis was used to compare 24-hour plasma sodium

concentrations with total overwinter survival and with daily overwinter mortality rate in

juveniles challenged to full-strength seawater and in those exposed to the AFLS (four
4

regressions). Linear regression analysis was also used to compare total overwinter

survival and daily overwinter mortality rate with date of AFLS entry (two regressions).

Two-way analysis of variance was used to examine the interaction of date of entry with

plasma sodium levels of juveniles exposed to seawater or in the AFLS.

Overwinter growth rates were calculated by r = ln(w,lw,)lt, where r is equal

to percent body weight gain per day, w1 is equal to the average weight of a fish in the

population at the end of culture,. w,, is equal to the average weight of a fish in the same

population at seawater entry, and t equals the number of days of culture.

Initial data analysis revealed patterns within the 24-hour plasma sodium data

that were further examined by linear regression of plasma sodium concentration by time

of entry for both environments and by analysis of covariance of those data.

Data caveats were 1) If a substantial number of smaller fish of a given

population died, then the actual overwinter growth rate could be overestimated because

smaller juveniles are generally less osmocompetent than larger ones. Comparisons of

differences in growth rates between entry periods are limited because water temperature

changes seasonally and affects growth rate. 2) Mortality influenced 24-hour plasma

sodium concentrations of fish in full-strength seawater. Substantial mortality occurred on

two entry dates. Survivors probably had lower plasma sodium concentration than those

that died, resulting in artificially low concentrations for those entry dates; these results

should be viewed as minimums. 3) Although we attempted to maintain similar sizes of

fish for all entry periods, some variability occurred. Entry sizes were smallest in midSeptember (8.0 g) and in mid-October (8.6 g), which could have resulted in higher

plasma sodium concentrations than in fish 1.5-2.0 g larger. 4) Two weeks after seawater

entry, an outbreak of Vibrio anguillarum was diagnosed in the July entry group, resulting

in substantial mortality.

RESULIS

Salinity in the AFLS remained relatively constant, averaging 30% between 1.5

and 4.0 m depths. The upper 1 m of the AFLS varied most: the average surface salinity

was less than 5 % and salinity at 1 m averaged 8 % (Fig. 3). Freshwater temperatures

varied normally: a high of 15°C in late July and a low of 1.5oC in February (Fig. 4).

Seawater temperature varied substantially less: a maximum of 11.5oC in July and a

minimum of 4.5 oC in January.

For all entry periods, 24-hour plasma sodium concentrations were higher in

juveniles in full-strength seawater than in those in the AFLS (Fig. 5). Plasma sodium

concentrations were below 170 mmol/l for all entry periods for the juveniles in the AFLS

and above 170 mmol/l for all entry periods except mid-June for those in full-strength

seawater. Plasma sodium concentrations were lowest in mid-June and highest in midOctober for both environments.

Overwinter survival in the AFLS averaged 72% (range, 27-87%) (Table 1).

Survival was lowest for juveniles placed in net-pens in July and highest for those placed
5

in August. Compensation for length of culture in the AFLS confirmed the survival

pattern: mid-July had the highest mortality rate and late August had the lowest.

In the AFLS, 24-hour survival after entry was 100% for each entry period. In

full-strength seawater, 24-hour survival was lowest (8%) for the mid-September entry and

highest (100%) for the mid-June, late August, and early October entries.

Overwinter growth in the AFLS was good: fish in all groups at least doubled

their initial weight. Growth rates ranged from an average of 0.98% body weight gain per

day for the summer entry groups to an average of 0.38% for the fall entry groups.

Use of the AFLS by the juveniles varied seasonally and diurnally. During the

day in summer and fall, the fish schooled and swam in a circle in the pens at the interface

of the fresh and saltwater layers, whereas in winter and spring they remained in the

seawater near the bottom of the pens. During darkness, the fish tended not to school and

distributed throughout both fresh and seawater layers. In all seasons, the fish moved into

the freshwater layer for feeding.

Plasma sodium concentration after 24 hours in juveniles in each environment

was not related to overwinter survival or overwinter mortality rate. Mean plasma sodium

concentration was not significantly related to overwinter survival (seawater r2 = 0.135, P

= 0.267; AFLS r2 = 0.096, P = 0.355) or overwinter mortality rate (seawater r2 =

0.016, P = 0.709; AFLS r2 = 0.002, P = 0.897) within either treatment.

Survival, as determined by total overwinter survival or daily overwinter

mortality rate, was not related to date of seawater entry. Date of net-pen entry was not

significantly related to total overwinter survival (r2 = 0.251, P = 0.117) or overwinter

mortality rate (r2 = 0.119, P = 0.299).

Two-way analysis of variance on 24-hour plasma sodium concentrations in

juveniles in either seawater only or the AFLS over the three summer and four fall entry

dates indicated significant differences (F1,222 = 641.55, P < 0.001) between treatments.

Juveniles in the AFLS had substantially lower plasma sodium concentrations (Table 1,

Fig. 5). The two-way analysis also revealed a significant effect of time across treatment

(F6, 222 = 56.69, P < 0.001): for both treatments, plasma sodium concentrations were

lower in June and higher in the fall.

Further analysis of the effect of entry date on 24-hour plasma sodium

concentration by linear regression indicated significant positive relationships between date

of entry and plasma sodium concentration (AFLS r2 = 0.498, P < 0.001; seawater r2 =

0.441, P < 0.000l), which indicates a trend of generally increasing plasma sodium

concentration over time. The analysis of covariance indicated significantly different

slopes F6,222 = 18.58, P < 0.001) and intercepts (F6,222 = 35.90, P < 0.000l), with a

proportionately greater change over time and a substantially higher intercept (153 mmol/l

vs. 135 mmol/l) for the fish exposed to full-strength seawater.
6

DISCUSSION

Our results indicate that juvenile stream-type chinook salmon weighing 8-10 g

can adapt to a high-salinity marine environment throughout much of the year when low

salinity water is available. This finding appears to contrast with the seasonality of osmocompetence indicated by previous measurements of gill sodium-potassium ATPase activity

of juvenile chinook salmon (Ewing et al. 1979) and blood thyroxine concentrations

(Dickhoff et al. 1982) and by previous indirect measurement of timing of

osmocompetence and normal smolt migration (Wagner et al. 1969).

Plasma sodium concentrations and survival after 24 hours of exposure to fullstrength seawater indicated generally deteriorating osmocompetence from late June

through early November. This result supports the evidence of Dickhoff et al. (1982) and

Gould et al. (1985) of periodicity in osmocompetence upon direct exposure to fullstrength seawater. Wagner et al. (1969) showed an opposite trend, with increased 30-day

survival from spring through late winter of juvenile chinook salmon exposed to fullstrength seawater; however, those juveniles grew so rapidly throughout the experiment

that the effects of size confounded the influence of time on osmocompetence.

Photoperiod history is known to have a substantial effect on osmoregulatory ability in

stream-type chinook salmon (Clark et al. 1989, 1992). The good seawater tolerance

shown by the June and, to a lesser degree, the July entry fish probably relates to their

short day-exposure history.

Fish in the AFLS had some seasonal increase in sodium concentration;

however, sodium concentrations were generally well within the osmocompetent range and

the lack of 24-hour mortality in all entry periods confirms their osmocompetence.

Plasma sodium concentration and short-term mortality can be important in

determining osmocompetence and swimming performance (Brauner et al. 1992) at that

time. However, they may not be useful predictors of longer-term growth and survival of

fish released into the natural environment or of captive fish in an AFLS. For fish in an

AFLS until May, we found no significant relationship between 24-hour plasma sodium

concentrations, total survival, or overwinter mortality rate up to release several months

later. All populations at least doubled their average weight over winter, indicating no

significant impairment of growth. In contrast, Clarke and Shelbourn (1982) found an

inverse relationship between growth and 24-hour plasma sodium concentrations in

juvenile coho salmon (Oncorhynchus kisutch) reared without a freshwater lens.

Elevated gill ATPase activity and increased thyroxine concentrations in juvenile

salmon in fresh water are related to seaward migration and, ultimately, seawater

adaptation. However, they may not indicate whether juvenile salmon, particularly

chinook, can adapt osmotically to a marine existence during much of their normal

freshwater development, when the salinity regime of their environment is more

representative of the natural, layered-salinity environment common in estuaries. Access

to a low-salinity environment appears to allow juveniles that are not generally
7

osmocompetent to survive and grow in a high-salinity environment by periodically using

the lens for osmotic relief.

Our results indicate that 8-10 g stream-type chinook salmon can be cultured

successfully overwinter in marine net-pens with an artificial freshwater lens. The timing

of AFLS entry is highly flexible, but problems associated with summer entry (e.g.

disease) indicate the fall entry period is most suitable. High rates of overwinter survival

should be possible at almost any marine site with access to small amounts of fresh water.

Although the juveniles produced with the AFLS appeared normal at release, the return of

adults to the hatchery and their presence in harvests will be the final proof.

ACKNOWLEDGMENTS

We are indebted to Karen Lipson (Alaska Department of Fish and Game) for

field assistance in the care of the fish populations and to three anonymous reviewers for

help with the manuscript.
9

CITATIONS

Brauner, C. J., J. M. Shrimpton, and D. J. Randall. 1992. Effect of short-duration

seawater exposure on plasma ion concentrations and swimming performance in

coho salmon (Oncorhynchus kisutch) parr. Can. J. Fish. Aquat. Sci.

49:2399-2405.

Clarke, W. C., and J. E. Shelbourn. 1982. Growth and smolting of underyearling coho

salmon in relation to photoperiod and temperature. In Proc. North Pacific

Aquaculture Symp., Alaska Sea Grant Rep. 82-2, p. 209-216. University of

Alaska Fairbanks.

Clarke, W. C., J. E. Shelbourn, T. Ogasawara, and T. Hirano. 1989. Effect of initial

daylength on growth, seawater adaptability and plasma growth hormone levels

in underyearling coho, chinook, and chum salmon. Aquaculture 82:51-62.

Clarke, W. C., R. E. Withler, and J. E. Shelbourn. 1992. Genetic control of juvenile

life history pattern in chinook salmon (Oncorhynchus tshawytscha). Can. J.

Fish. Aquat. Sci. 49:2300-2306.

Dickhoff, W. W., L. C. Folmar, and A. Gorbman. 1978. Changes in plasma thyroxine

during smoltification of coho salmon (Oncorhynchus kisutch). Gen. Comp.

Endocrinology 36:229-232.

Dickhoff, W. W., L. C. Folmar, J. L. Mighell, and C. V. W. Mahnken. 1982. Plasma

thyroid hormones during smoltification of yearling and underyearling coho

salmon and yearling chinook salmon and steelhead trout. Aquaculture

28:39-48.

Ewing, R. D., S. L. Johnson, H. J. Pribble, and J. A. Lichatowich. 1979. Temperature

and photoperiod effects on gill (Na+K)-ATPase activity in chinook salmon

(Oncorhynchus tshayytscha). J. Fish. Res. Board Can. 36:1347-1353.

Folmar, L. C., and W. W. Dickhoff. 1980. The Parr-smolt transformation

(smoltification) and seawater adaptation in salmonids. A review of selected

literature. Aquaculture 21: l-37.

Gould, R. W., A. N. Palmisano, S. D. Smith, C. V. W. Mahnken, W. S. Zaugg, and E.

F. Prentice. 1985. Seawater acclimation of premigratory (presmolt) fall

chinook salmon: a possible new management strategy? In C. J. Sidermann

(editor), Proceedings of the Eleventh U.S.-Japan Meeting on Aquaculture,

Salmon Enhancement, p. 15-19. Tokyo, Japan, October 19-20, 1982. U.S.

Dep. Commer., NOAA Tech. Rep. NMFS 27.

Hard, J. J., A. C. Wertheimer, W. R. Heard, and R. M. Martin. 1985. Early male

maturity in two stocks of chinook salmon (Oncorhynchus tshawytscha)

transplanted to an experimental hatchery in southeastern Alaska. Aquaculture

48:35 l-359.

Healey, M. C. 1991. Life history of chinook salmon (Oncorhynchus tshawytscha). In

C. Groot and L. Margolis (editors), Pacific salmon life histories, p. 311-393.

University of British Columbia Press, Vancouver.
10

Heard, W. R., and R. A. Crone. 1976. Raising coho salmon from fry to smelts in

estuarine pens, and returns of adults from two smolt releases. Prog. Fish-Cult.

38: 171-174.

Kepshire, B. M., Jr., and W. J. McNeil. 1972. Growth of premigratory chinook

salmon in seawater. Fish. Bull. 70: 119-123.

Lasserre, P., G. Boeuf, and Y. Harache. 1978. Osmotic adaptation of Oncorhynchus

kisutch Walbaum. I. Seasonal variations of gill Na-K ATPase activity in coho

salmon, O-age and yearling, reared in fresh water. Aquaculture 14:365-382.

Mahnken, C., E. Prentice, W. Waknitz, G. Monan, C. Sims, and J. Williams. 1982.

The application of recent smoltification research to public hatchery releases: an

assessment of size/time requirements for Columbia River hatchery coho salmon

(Oncorhynchus kisutch). Aquaculture 28:251-268.

Martin, R. ‘M., and A. C. Wertheimer. 1987. Survival of coho salmon (Oncorhynchus

kisutch) cultured in fresh water and in estuarine net pens. Aquaculture

61: 181-191.

Martin, R. M., A. C. Wertheimer, and F. P. Thrower. In prep. Overwinter survival for

six broods of chinook salmon during culture in estuarine net-pens or fresh

water at Little Port Walter, southeastern Alaska. Available Auke Bay

Laboratory, Alaska Fish. Sci. Cent., Natl. Mar. Fish. Serv., NOAA, 11305

Glacier Hwy., Juneau, AK 99801-8626.

McGee, S. (Compiler). 1985. Evaluation of chinook mitigation hatchery proposals: a

planning report. Southeast Alaska Chinook Technical Planning Team, Private

Nonprofit Program. Alaska Dep. Fish and Game, 71 p.

Officer, C. B. 1976. Physical oceanography of estuaries (and associated coastal waters).

John Wiley & Sons, New York, 465 p.

Orion Research, Inc. 1983. Instruction manual: model 1020 sodium/potassium analyzer.

Orion Research Inc., 840 Memorial Dr., Cambridge, MA 02139, 42 p.

Powers, C. F. 1963. Some aspects of the oceanography of Little Port Walter estuary,

Baranof Island, Alaska. Fish. Bull., U.S. 63:143-164.

Wagner, H. H., F. P. Come, and J. L. Fessler. 1969. Development of osmotic and

ionic regulation in two races of chinook salmon Oncorhynchus tshawytscha.

Comp. Biochem. Physiol. 29:325-341.

Wedemeyer, G. A., R. L. Saunders, and W. C. Clarke. 1980. Environmental factors

affecting smoltification and early marine survival of anadromous salmonids.

Mar. Fish. Rev. June: 1-14.

Woo, N. Y. S., H. A. Bern, and R. S. Nishioka. 1978. Changes in body composition

associated with smoltification and premature transfer to seawater in coho

salmon (Oncorhynchus kisutch) and king salmon (0. tschawytscha [sic]). J.

Fish Biol. 13:421-428.
11

Zaugg, W. S., and L. R. McLain. 1972. Changes in gill adenosinetriphosphatase

activity associated with Parr-smolt transformation in steelhead trout, coho, and

spring chinook salmon. J. Fish. Res. Board Can. 29:167-171.
Table 1 .--Culture information for juvenile chinook salmon in 30% salinity seawater or seawater with an artificial freshwater lens

(AFLS). FW = fresh water; SD = standard deviation.
14

Figure l.--Location of National Marine Fisheries Service Little Port Walter Biological

Research Station, Baranof Island, Alaska.
15

Figure 2.--Schematic diagram of an artificial freshwater lens system with space for

nine 3.7 m X 3.7 m net-pens.


Figure 5.--Mean 24-h (+SD) plasma sodium concentrations for juvenile chinook salmon exposed to full-strength seawater or

seawater with a freshwater lens. Dashed line represents maximum levels for osmocompetent juveniles.
RECENT TECHNICAL MEMORANDUMS

Copies of this and other NOAA Technical Memorandums are available from the

National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22167 (web

site: www.ntis.gov). Paper and microfiche copies vary in price.

AFSC93

92

91

90

89

88

87

86

85

84

83

82

81

80

79

78

MURPHY, J. M., N. E. MALONEY, and B. L. WING. 1998. Distribution and abundance of zooplankton

in the north Pacific Subarctic Frontal Zone and adjacent water masses, 31 p. NTIS number pending.

FRITZ, L. W., and S. A. LOWE. 1998. Seasonal distributions of Atka mackerel (Pleuroarammus

monootervoius) in commercially-fished areas of the Aleutian Islands and Gulf of Alaska, 29 p. NTIS NO.

PB98-153703.

WING, B. L., and J. J. PELLA. 1998. Time series analyses of climatological records from Auke Bay,

Alaska, 90 p. NTIS No. PB98-149206.

PACUNSKI, R. E., P. A. LIVINGSTON, and B. S. MILLER. 1998. Food of flathead sole hippoglossoides

elassodon in the eastern Bering Sea, 27 p. NTIS No. PB98-148679.

WILKINS, M. E., M. ZIMMERMANN, and K. L. WEINBERG. 1998. The 1995 Pacific west coast bottom

trawl survey of groundfish resources: Estimates of distribution, abundance, and length and age

composition, 138 p. plus Appendices. NTIS No. PB98-136252.

FRITZ, L. W., A. GREIG, and R. F. REUTER. 1998. Catch-per-unit-effort, length, and depth distributions

of major groundfish and bycatch species in the Bering Sea, Aleutian Islands, and Gulf of Alaska regions

based on groundfish fishery observer data, 179 p. NTIS No. PB98-139298.

SINCLAIR, E. H. (editor) 1997. Fur seal investigations, 1996, 115 p. NTIS No. PB98-131790.

SINCLAIR, E.H. (editor). 1997. Fur seal investigations, 1995, 188 p. NTIS No. PB98-131808.

KINOSHITA, R. K., A. GREIG, and J. M. TERRY. 1998. Economic status of the groundfish fisheries off

Alaska, 1996, 91 p. NTIS No. PB98-126170.

LAAKE, J., D. RUGH, and L. BARAFF. 1998. Observations of harbor porpoise in the vicinity of acoustic

alarms on a set gill net, 40 p. NTIS No. PB98-117641.

RUTECKI, T. L., M. F. SIGLER, and H. H. ZENGER JR. 1997. Data report: National Marine Fisheries

Service longline surveys, 1991-96,64 p. NTIS No. PB98-108822.

MARTIN, M. H. 1997. Data report: 1996 Gulf of Alaska bottom trawl survey, 235 p. NTIS No. PB98-

103930.

LAUTH, R. R. 1997. The 1996 Pacific West Coast upper continental slope trawl survey of groundfish

resources off Washington and Oregon: Estimates of distribution, abundance, and length composition,

156 p. NTIS No. PB97-208912.

LAUTH, R. R. 1997. The 1995 Pacific West Coast upper continental slope trawl survey of groundfish

resources off southern Oregon and northern California: Estimates of distribution, abundance, and length

composition, 110 p. NTIS No. PB97-208920.

LAUTH, R. R., M. E. WILKINS, and P. A. RAYMORE JR. 1997. Results of trawl surveys of groundfish

resources of the West Coast upper continental slope from 1989 to 1993, 342 p. NTIS No. PB97-208904.

HILL, P. S., D. P. DEMASTER, and R. J. SMALL. 1997. Alaska marine mammal stock assessments,

1996, 150 p. NTIS No. PB97-203277.