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SURFACE-CURRENT STUDIES
OF SAGINAW BAY

AND LAKE HURON, 1956

SPECIAL SCIENTIFIC REPORT-FISHERIES Na 267

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UNITED STATES DEPARTMENT OF THE INTERIOR
FISH AND WILDLIFE SERVICE

EXPLANATORY NOTE

The series embodies results of investigations, usually of restricted
scope, intended to aid or direct management or utilization practices and as
guides for administrative or legislative action. It is Issued in limited quantities
for Official use of Federal, State or cooperating agencies and in processed form
for economy and to avoid delay in publication .

United States Department of the Interior, Fred A, Seaton, Secretary
Fish and Wildlife Service, Arnie J. Suomela, Commissioner

SURFACE-CURRENT STUDIES OF SAGINAW BAY AND lAKE HURON,

1956

James H. Johnson

Fishery Research Biologist

Great Lakes Fishery Investigations

Bureau of Commercial Fisheries

Special Scientific Report — Fisheries No, 267

Washington, D, C.
December 1958

The Library of Congress catalogue card for this publication
is as follows:

Johnson, James H

Surfacc-cunciit studies of Saginaw Bay and Lake Huron,
1956. AVashington, U. S. Dept. of the Interior, Fish and
AVildlife Service, 1958.

84 p. maps, diagrs., tables. 27 cm. (Special scientific report —
fislieries, no. 267)

Bibliography : p. 27-30.

1. Saginaw Bay. 2. Huron, Lake. i. Title. (Series: U. S.
Fish and Wildlife Service. Special scientific report : fisheries, no.
267)

[SH11.A335 no. 267] Int 59-12

U. S. Dept. of the Interior. Library

for Library of Congress

The Fish and Wildlife Service series, Special Scientific
Report — Fisheries, is catalogued as follows:

U. S. Fish and Wildlife Service.

Special scientific report : fisheries, no. 1-
[Washington, 1949-

no. illus., maps, diagrs. 27 cm.
Supersedes in part the Service's Special scientific report.

1. Fisheries — Research.
SH11.A335 639.2072 59-60217

Library of Congress

Table of Contents

Page

Drift-bottle designs 2

History 2

Drift bottles released in Saginaw Bay and Lake Huron . . 4

Releases and recoveries 7

Wind data 10

Water movements of Saginaw Bay 11

General features of the bay 11

Previous studies 12

Drift-bottle movements in 1956 12

Water movements of Lake Huron 16

Previous studies 16

Drift-bottle movements in 1956 17

Dynamic heights 18

Appraisal of the general pattern 19

Rate of drift 21

Quantitative relationship between surface drift and wind ... 24

Factors influencing drift-bottle movements 25

Saginaw Bay 25

Lake Huron 2 6

Recommendations for study of currents on the Great Lakes ... 26

Acknowledgments 27

Summary 27

Literature cited 27

Appendix 30

ABSTRACT

Surface currents of the waters of Saginaw Bay and
lower Lake Huron area were studied in the summer and
fall of 1956. Drift bottles were used in Saginaw Bay
and drift bottles together with the dynamic-height method
were used in Lake Huron. A total of 2,650 drift bottles
were released; 1,843 (69.5 percent) reply cards from the
recovered bottles were returned.

Correlation appeared to be high in Saginaw Bay
between direction of surface currents that moved these
bottles and direction of winds. In Lake Huron this
correlation was less apparent, although the drift of
bottles was generally from west to east, seemingly under
the influence of the prevailing westerly winds of this
area.

figure 1.— Lake Huron and Saginaw Bay.

SURFACE- CURRENT STUDIES OF SAGINAW BAY AND LAKE HURON, 1956

It is increasingly apparent to students
of aquatic biology that water currents and
movements of large water masses play a para-
mount role in the life cycle of many aquatic
organisms. Water movements influence the
distribution and ultimate survival of eggs,
larvae, and adult aquatic organisms. The
relation is direct when organisms are car-
ried along actively by currents, and indirect
when currents cause changes in environmental
factors such as temperature, salinity, and
other physical and chemical conditions.
Although the direct effects are more obvious,
the indirect influences may play an impor-
tant role in survival and distribution of
aquatic life.

At times movements of water masses can
alter so adversely the habitat of fishes,
especially those that live in a narrow
environmental range, that kills of catastro-
phic proportions occur. The disaster which
overtook the tilefish off the northeastern
coast of the United States in 1882 was due
to a sudden but temporary flooding of cold
polar water into the warmer waters normally
inhabited by this fish (Bigelow and Welsh
1925). An estimated 1 1/2 billion dead
fish were sighted on the surface waters
shortly after this calamitous event. Not
only was fish life affected but certain
invertebrates were exterminated by the cold
mass of water. Outbreaks of red tide off
the western coast of Florida are probably
initiated by water masses which differ in
salinity and chemical characteristics from
the normal water off the Florida coast
(Slobodkin 1953). Slobodkin believed that
prediction of red tides would depend on
more detailed knowledge of coastal drainage
and hydrography, and that prevention of red
tides may be possible, to some extent, by
altering certain coastal drainage patterns.

The adverse effects of movements of
water masses upon fish populations are
probably matched by an equal number of
favorable incidents. The 1904 year class
of herring in the North Sea dominated the
commercial herring fishery in that area
from 1908 to 1919. This year class was
prominent for other species also. Evidence
indicated that the success of this year's
hatch was due to an abnormally intense

inflow of Atlantic water into the North Sea
that carried with it either an abundance of
the actual food required by newly-hatched
fishes or provided certain nutrient salts
resulting in a high abundance of basic food
organisms (Tait 1952). According to Tait ,
there seems little room for doubt that the
essential causes of fishery fluctuations lie
in hydrographic conditions and that adequate
observations of these conditions affords
the surest means of anticipating these
fluctuations. He perceived that the rela-
tionship of hydrography to fisheries is
analogous to that of meteorology to agricul-
ture.

In recent years, certain commercial
fisheries of Saginaw Bay, Michigan, have
deteriorated at an alarming rate. The
annual commercial catch of the walleye
(Stizostedion v. vitreum) has decreased in
the last decade to such an extent that the
economy of this fishery has been greatly
weakened (Hile 1954). Many fishermen attri-
bute the scarcity of the walleye in the bay
to pollution. Production of lake herring
(Leucichthys artedi) and whitef ish (Corego-
nus clupeziformis) is also low. The yellow
perch (Perca f lavescens) , on the other hand,
are at such a high level in numbers that
their growth is stunted (El-Zarka 1958).
A fishery survey conducted with the study
upon which this report is based revealed
an abundance of alewives (Pomolobus pseudo-
harengus) and smelt (Osmerus mordax) but
there is little commercial production of
these species.

The U. S. Fish md Wildlife Service
and the Michigan Department of Conservation
conducted a cooperative limnological survey
in Saginaw Bay and adjacent Lake Huron
waters in the summer and fall of 1956 (fig.
1). The objectives of the study were to
gain basic information on species composi-
tion and species inter- and intra- relation-
ships, and to develop the possible causes
of the fluctuations in the Saginaw Bay
fisheries. As part of this project drift
bottles were used to obtain information on
the current systems and to determine the
amount of water interchange between the bay
jind lake. This report analyzes the drift
bottle movements in Saginaw Bay and Lake

Huron and summarizes briefly the use of
drift bottles by other workers.

DRIFT-BOTTLE DESIGNS

History

Among the first recorded accounts of
the use of drift bottles is that of Bernar-
din De Saint-Pierre who in 1784 recommended
releasing floating bottles from time to time
with each bottle carrying a note telling
the day, latitude, and longitude of release
(Rouch 1954). A French naturalist, Aime',
shortly before the middle of the nineteenth
century released 50 bottles off the Algerian
coast and subsequently obtained returns of
3 of them (Schmidt 1913). An interesting
early record of drift bottles is that
reported by Prince Albert I of Monaco; a
bottle released toward the end of the nine-
teenth century in the Atlantic Ocean south-
west of Ireland was recovered 646 days later
on the coast of Tunis in the Mediterranean
Sea (Schmidt 1913).

Evolution of current indicators since
these experiments have been along two main
lines: indicators of a stationary mechani-
cal type that measure the current at a
certain point; and passive objects carried
along by currents. Since this project
utilized the latter type, the following
report is limited to passive drift units.

In 1892, 1893, and 1894 masters of some
merchant vessels released nearly 5,000
drift bottles at various points throughout
the Great Lakes (Harrington 1895). These
bottles had no ballast or drags and each
contained a reply card. Although the bot-
tles floated low in the water, enough Wcis
exposed above the surface to cause Harring-
ton to remark that the wind may have influ-
enced their movements. He reasoned that
bias to the results wjis not impxartant since
the wind that drifted the bottles would move
the surface water in the same direction.
He did feel, however, that wind caused the
bottles to drift faster than the water but
that the effect was slight.

From the use of plain stoppered bottles,
it was but a short step to reduce the wind
effect by the inclusion of a ballast to make
the bottles float with only a small portion
exposed above the surface. Garstang (1898)
used ballasted "egg-shaped" soda-water

bottles on the English Channel. They were
9 inches long and the upper half was painted
red to make them conspicuous. Ballast con-
sisted of lead shot held stationairy in the
bottle by paraffin to minimize displacement
of the center of gravity. He concluded that
movements of ballasted bottles were princi-
pally due to the force that local winds
exerted upon the surface of the water, sub-
ject, in certain areas, to modification by
tidal currents.

Drift bottles used in the Danish Ocea-
nographical Expeditions to the Mediterranean
Sea in 1908-1910 were ordinary champagne
bottles, well corked, with the mouth dipped
in pitch (Schmidt 1913). Some bottles were
ballasted with sand; others had no ballast.
Any difference in travel between bottles
with and without ballast was not given in
the results of the experiment. Schmidt
believed that the wind had considerable
direct effect upon the bottles. Platania
(1923) in a further report on the Danish
Expeditions concluded that drift bottle
movements in the western Mediterranean did
not reflect true currents, but were influ-
enced primarily by the prevailing winds.

The travel of well-designed surface
floaters, when interpreted properly, gives
reasonably reliable information on surface
currents at a particular time and place.
Investigators, however, are frequently
interested also in subsurface currents. To
obtain information on subsurface currents.
Bidder (Carruthers 1927) developed a "bottom
trailer" bottle for use in the North Sea.
The bottom trailer used by Nelson (1922)
was a stoppered glass bottle, the neck of
which carried a straight wire tail pointing
in the direction of the long axis of the
bottle. The bottle was weighted to have a
small negative buoyancy in sea water. When
released it sank to the bottom. Its descent
stopped as the tip of the tail touched the
bottom, and it drifted with the current in
that position. The weight of the bottom
trailer was adjusted so that the bottle
weighed 1.7 grams more than the volume of
sea water (at 8" C. , specific gravity
1.0275) displaced by it. These bottles
were expected to become entangled within
the nets and trawls of fishermen and the
reply cards subsequently to be returned by
them. Carruthers (1947) reported that suc-
cess in the use of "bottom trailers" had
not been great because they "take sanctuary"
between the sand ridges.

Various other methods have been used
to reduce exposure of drift bottles to
winds. Gilson (Carruthers 1930) experi-
mented with coupled systems consisting of
pairs of bottles, one bottle of the pair
with positive buoyancy and the other of
negative buoyancy, linked together by cords
3 meters long. In his experiments in the
North Sea he noted a marked difference in
rate of travel between simple surface float-
ing bottles and his coupled systems. On
occasion simple floating bottles and coupled
bottles released at the same time traveled
significantly different routes and direc-
tions. A similar coupled system was
described by Sverdrup, Johnson, and Fleming
(1942) in which the lower of the two coupled
bottles contained a weak acid which in time
corrodes a metal stopper, thus permitting
sea water to fill the bottle and sink it.
Fishermen are depended upon to return reply
cards from bottles that become entangled in
their nets.

(ballasted and unballasted) , drag-fitted
bottles, and coupled bottles systems.
Drag-fitted bottles were of two kinds:
those with a metal drag suspended from a
surface-floating bottle by a wire 3 feet
long; those with a 9- inch-high, 6- inch-
diameter toffee tin suspended by a 3-foot
wire from a surface-floating bottle. The
toffee tin contained a drift bottle and
both the surface-floating bottle and the
one in the tin contained reply cards. The
coupled system consisted of two bottles,
a bottle of negative buoyancy suspended
from a surface-floating bottle by a 3-foot
piece of stout sash cord. Carruthers found
that in some instances unballasted surface
floaters, ballasted surface floaters, and
drag-fitted bottles put out at the same
time and place showed significantly dif-
ferent movements. Only two replies were
received from the coupled system — not enough
to allow a valid compjirison with the other
returns .

One of the most popular methods of
reducing direct influence of the wind is by
using a metal drag that is suspended from
the drift bottle by a length of wire. This
arrangement not only reduces the surface
area exposed to wind but also causes travels
of the bottle to be affected by currents
between the surface and the depth of the
drag. Length of suspending wire ceui vary
but most workers have used a wire in the
neighborhood of 3 feet long. Mavor (1922),
however, (Bay of Fundy) used drags suspended
by wire 5.5 meters long. Webster and Buller
(1950) in studying ocean currents off the
New Jersey coast used both free bottles and
bottles with drags suspended by a 4-foot
wire. Their bottles released with drags
attained a greater speed of transport than
those without; furthermore, prevailing winds
had little effect upon the direction of
drift. Deason (1932) who released bottles
with a drag suspended 3 feet below the bot-
tle (Lake Michigan) concluded that the
action of the prevailing westerly winds had
much to do with the rate of and direction
of surface currents. In Hudson Bay experi-
ments, Hachey (1935) used a 3-foot galva-
nized wire to suspend a metal drag. He made
no remarks concerning the circulation of
waters other than the general circulation
seemed to be counterclockwise.

Carruthers (1930) experimented with
drift bottles on the North Sea to ascertain
difference in the travels of surface floaters

In recent years drift cards in pis tic
envelopes, as developed by Olson (1951),
have been looked upon with favor by some as
a substitute for drift bottles. Olson used
a polyethylene envelope 0.004 inch thick
with the return card hermetically sealed
within. His Lake Erie experiments indicated
that the travels of these envelopes were not
at the complete mercy of the wind. Some
cards that were returned 18 months after
release were still in good condition. In
remarks on Olson's work, Verber (1953) wrote
that drift cards were better than drift
bottles since the cards are inexpensive and
give greater accuracy in interpreting the
surface flow because they are not exposed
to the wind. He concluded that Olson's
work proved a direct correlation between
wind and surface flow in western Lake Erie
and that the movements of surface water were
wind controlled.

In Georgian Bay, Lake Huron, 3,000
drift cards similar to those developed by
Olson (1951) were dropped from an airplcuie
(Fry 1956). Polyethylene material, however,
was only 0.002 inch thick and proved to be
only moderately satisfactory because pin-
holes developed in the plastic from sand
abrasion.

Drift cards were used by the Fish and
Wildlife Service on Lake Superior in 1953
Eind on Lake Michigan in 1954. Few returns
were obtained from these releases, and of

those cards returned many were found
water-soaked inside the polyethylene enve-
lope. The polyethylene envelope was in
some cases not sealed properly; and since
a number of cards were found on the bottom
off shore, it is possible that many of them
sank before they reached land.

Bougis and Ruivo (1953) added
ballast to the polyethylene-envelope
type of float. Their "siphonophone"
consisted of three parts: a poleth-
ylene envelope of 0.004 inch thick-
ness that floats on the surface; the
reply card within the envelope; and
a drift with ballast. The drift was
a ribbon of polyethylene 1.2 meters
long and 8 centimeters wide attached
to the polyethylene float. About 20
grams of lead ballast were placed at
the lower extremity of the ribbon to
make the drift sink into the water.
Experiments on the Bay Banyuls, with
drift cards only and "siphonophore"
drifts, proved that the former fol-
lowed the course of the wind closely,
whereas the latter traveled at vari-
ous angles with the wind and also
moved much more slowly.

Drift bottles released in

Saginaw Bay and Lake Huron

The drift bottle with metal
drag was the design chosen for the
Saginaw Bay-Lake Huron study in 1956
(fig. 2). It WcLS evident from work
by the Fish and Wildlife Service on
Lake Michigan in 1955 that bottles
with drags resisted direct effects
of wind and presumably gave a better
indication of water currents near
the surface than did the ballasted
bottles. Plastic envelopes were
rejected for reasons already noted.
A disadvantage of a bottle with the
drag suspended several feet below
the bottle is that the drag hits
bottom in the surf zone and resists
being washed ashore by the small
waves characteristics of the Great
Lakes. Observations have revealed
that these bottles can be carried
many miles in the surf, sometimes
against the prevailing offshore
current, before they are washed
ashore. This disadvantage was elim-
inated, for the most part, by

suspending the drag only 1 foot beneath the
bottle instead of the usual 3 to 4 feet.
The change was made after repeated tests
with dye markers showed no discernable dif-
ference, under ordinary conditions, in
water movement between 1 and 4 feet below
the surface.

Water level
Reply card

Brass ring

- P^^^

ron suspension
wire

Metal drag

Figure 2. — Drift bottle as it appeared at time
of release.

Great Lakes Fishery Investigations
Ann Arbor, Michigan, U. S. A.

NOTICE TO FINDER Drift Card No

This card is being used to study currents of the Great Lakes. Please fill in blank
spaces. Mail every card you find. Canadian postage will be replaced. You will be
told the time and place this card was released. Thank you.

a. ni.
-. p. in.

Time of recovery: Date Hour .

Was a metal fin attached to the bottle? Cj Yes; LJ No
Exact location card was found -_

"1
ft

o
n

n
se

D
01

Near

Remarks:

(City)

(County)

(State)

Please print :

(Name) (Address)

U. S GOVERNMENT PRINTING OFFICE 16 — 71459-1

Jigure 3. — Reply card similar to that placed in each bottle.

Reply cards (fig. 3) were placed in
4-ounce Boston-round bottles after which
the bottles were stoppered with corks and
the stoppered ends dipped into beeswax.
Several drops of beeswax were then placed
in the bottle caps and the caps screwed on
the bottle. Drags were squares of 28-gage
galvanized metal (4" X 4") so cut arid
bent that water movement from any
direction struck areas of the three
planes of the drag. During periods
of high winds cind heavy seas the
horizontal fin of the dreig would in-
hibit vertical movement so the bottle
would be under the surface much of
the time.

Studies on Ljike Michigan in 1955
disclosed that many bottles lost
their drags before they were washed
eishore. The comments of finders
indicated that the drags were lost
because the soft iron suspension wire
was broken at the neck of the bottle.
The break was caused, most likely,
by the bending of the wire as the
bottle was moved by the waves. In
the Saginaw Bay-Lake Huron project,
loss of drags was reduced by placing
a brass ring in the suspension wire
at the neck of the bottle (fig. 2).
The bottle could then move freely
without bending the wire. As satis-
factory as this arrangement proved

to be, it did not end loss of drags. Of
1,076 bottles recovered within 29 days
after release, only 18 (1.7 percent) had
lost their drags. Of 523 bottles recovered
after more than 29 days, 168 (33.3 percent)
had lost their drags (table 1). Undoubtedly
some of the 523 bottles recovered after

Table 1. — Loss of drags from drift bottles released in 1956
in relation to number of days between release ajid recovery

Number of days '

Total number

Bottles for which

Bottles that had lost drags

and recovery

recovered

on drags

Number

Percentage

0- 9

510

0.8

10-19

349

0.9

20-29

217

5.2

30-39

147

17.9

40-49

114

38.7

50-59

38.8

60-69

42. C

70-79

46.9

80-89

57.1

90-99

25.0

100-109

37.5

110-119

20.0

> 119

11.8

Not determined

25.0

29 days had actually landed long before
their recovery. The small loss of drags
from bottles out more than 119 days (11.8
percent — table 1) can be explained in part
by the fact that many of these bottles were
recovered at unfrequented places aind may
have landed many days before they were
found. Duck hunters returned a number of
these bottles in the fall from marsh areas.
Even though the time out for the bottles
was around 4 months, total travel from
release point was less than 10 miles.

Remarks made by persons returning cards
from bottles with lost drags indicate that
the second weakness of the unit is in the
attachment of the suspension wire to the
drag. The weight of the drag and the stress
imposed during the bottle's journey even-
tually cut through the wire. Because
bottles in this study moved relatively short
distances, the percentage of drags lost was
small. In an experiment where bottles might

be expected to be out for an average of
over 30 days, the weakness in the suspen-
sion of the drag should be remedied.

The question often arises whether or
not a reward should be paid for return of
Ccirds. A reward might increase the prob-
ability of the return of a reply card that
has been found, ajid might encourage active
searches for bottles. On the other hand,
in projects where a large number of bottles
are released the cost of rewards becomes
prohibitive. Although the data (table 2)
are far from conclusive, it appears that
where rewards have been offered, the re-
turns have not been consistently (12 to 57
percent recovery, average 29.0) greater
than in experiments where rewards were not
offered (3 to 67 percent, average 28.6).
This may not, however, be an entirely fair
comparison. Poor returns are to be expected
in some experiments and those on which
rewards were offered may have been this type.

Table 2. --Comparison of numbers of "bottles' released and percentage
return for each of several areas

Investigator

Area

Number
released

Percentage
i-eturn

Type of
drift unit

Reward

Alme 1845 1/

Mediterranean

. . . .2/. . .

None

reported

Ayers et al. 1956

Lake Huron

1,641

Plastic toothbrush

containers

None

Carruthers 1925

North Sea

1,275

Bottles plain

None

reported

Carruthers 1927

English Channel

500

Bottles bottom-trailing
and bottles plain

None

reported

Daniel and Lewis 1930

Irish Sea

1,180

. . . .2/. . .

None

reported

Deason 1932
Fry 1956
Garstang 1898

Lake Michigan
Georgian Bay
English Channel

283

3,000

430

64
10
27

Bottles with drags
Drift cards
Bottles ballasted

None
None
None

reported
reported

Hachey 1935
Harrington 1895
Mavor 1922

Hudson Bay
Great Lakes
Bay of Fundy

500

5,000

396

5
14
18

Bottles with drags
Bottles plain
Bottles with drags
and bottles plain

None reported
None reported

25 cents

Platania 1923

Mediterranean

515

Bottles ballasted
and bottles plain

None

reported

Ruschmeyer, Olson,

Lake Superior

1,000

Bottles ballasted

None

reported

and Bosch 1957
Schmidt W13

Mediterranean

200

Bottles ballasted
and bottles plain

None

reported

Tait 1930
Tibby 1939
Uda 1932
Waldichuck

and Tabata 1955

North Sea
Pacific Ocean
Wakasa Bay
Strait of Georgia

4,825

5,943

740

237

23
3

31
57

Bottles ballasted
Bottles ballasted

. . . .2/. . .
Bottles ballasted

None
None

None reported
Small monetary
award 3/

Webster and Buller 1950

Atlantic Ocean

489

Bottles with drags
and bottles plain

50 cents

Wright 1955

Lake Erie

Bottles with drags

None

reported

1/ Reported by Sclunidt 1913; not seen by me
2/ Type of drift unit not specified
3/ Exact amount of reward not stated

No monetary rewards were offered in
this study since remarks on returns of cards
released in Lake Michigan in 1954-55 clearly
indicated that finders were more interested
in learning when and where bottles were
released than in remuneration. Inquiry in
shore areas showed that once a bottle was
found word spread fast in the vicinity and
searching for them quickly became a loccil
pastime, merely for the satisfaction of
finding a bottle that had drifted from an
unknown point and for the feeling of parti-
cipating in a scientific study. Business
reply cards were used in this study so no
postage was required when they were mailed
in the United States. Where return of a

STATUTE MILES

Figure 4. — Drift bottles released at 42 stations in
Saginaw Bay and Lake Huron during 1956 and rela-
tive abundance of recoveries along the shoreline.
Triangles indicate stations where 30 bottles were
released, squares 40 bottles, X*s 80 bottles, zuid
circles 160 bottles.

card was at the expense of the finder, as
viftien these cards were mailed in Canada, the
sender was returned the postage due him. A
letter was sent to the finder of every bot-
tle telling of the time, place, and purpose
of release. Any postcige due the finder,
was included with this letter.

RELEASES AND RECOVERIES

From June 5, 1956, until November 14,
1956, during nine cruises of the Fish and
Wildlife Service research vessel Cisco,
2,200 drift bottles were released at 27 dif-
ferent stations on Saginaw Bay and adjacent
areas of Lake Huron. In addi-
tion, on three synoptic sur-
veys of Saginaw Bay on June 7,
August 10, and October 30, 1956,
the Fish and Wildlife Service
research vessel Musky and a
Michigan Department of Conser-
vation patrol boat dropped an
additional 450 bottles at 15
different stations. Altogether,
2,650 bottles were released at
42 stations (fig. 4). In Sagi-
naw Bay the distance from any
one point to a release point
did not exceed 6 miles. Re-
leases were more widely spaced
in the adjacent waters of Lake
Huron. It was not the intent
of the investigation to make
an intensive study of Lake
Huron proper; rather we wished
to study Saginaw Bay and its
relation to the lake.

It is common in drift-
bottle work to receive reply
cards from bottles recovered
months and even years Eifter
the date of release. The value
of a recovery in the determina-
tion of currents decreases the
longer the bottle is out in
excess of actual drifting time.
In areas where ice forms yearly,
the possible effects of the
spring ice breakup upon bottle
movements preclude sensible
analysis. To eliminate the
latter problem and to eliminate
other questionable records,
bottles recovered after Febru-
ary 28, 1957, were not used in
analysis. As of that date.

StClair
River

Figure 5. — Location of recoveries of drift bottles found after

February 28, 1957.

returns had been received on
1,603 bottles; 60.5 percent of
the total released. By Decem-
ber 1, 1957, an additional 240
reply cards had been returned
(fig. 5) giving a total return
of 69.5 percent--a very high
percentage in comparison with
returns in other studies
(table 2). The percentage re-
turn of bottles released during
any one cruise in this investi-
gation decreased as the season
progressed (table 3).

Recoveries of bottles were
for the most part highest over
weekends (table 4). This trend
was especially noticeable in
late summer and early fall.
During June, July, and August,
the beaches and shores of the
lake were apparently well
covered throughout the week.
After the vacation season ended,
however, the shores were visited
more frequently on weekends.

Table 3, — Returns of bottles released in 1956 from each of nine
different cruises of the Cisco and from three cruises each by
the Musky and Michigan Department of Conservation Patrol Boat

[Returns from bottles recovered after February 28, 1957,
are not included]

Cruise

Date

Number of
bottles released

Number
returned

Percentage
return

li/

June 3-11, 1956

350

262

74.9

June 19-July 2, 1956

310

232

74.8

III

July 11-23, 1956

240

171

71.3

ivi/

July 31-August 13, 1956

460

299

65.0

August 21-September 2, 1956

240

155

64.6

September 11-24, 1956

310

145

46.8

VII

October 2-15, 1956

240

125

52.1

villi''

October 23-November 5, 1S5G

460

211

45.9

November 13-21, 1955

7.5

Total

2,650

1,603

...
1

1/ Cruises during which the Musky and Michigan DeparLiiient of Conservation
patrol boat participated

Recoveries before February 28, 1957,
were made from a point 5 miles north of
Sturgeon Point on the western shore of Lake
Huron down through Saginaw Bay, the lower
lake area, and up the eastern shore of Lake
Huron to Cape Kurd (fig. 4). Several areas,
however, yielded surprisingly few recovei)-
ies. Returns were especially light from
the southeasterly corner of Lake Huron
(fig. 4).

Table 4.^ — Percentage distribution of recoveries of bottles
within the week, in the various months of recovery in 1956

Day

June

July

August

September

October

November

December

Monday

9.0

6.3

10.8

4.7

11.7

2.1

12.9

Tuesday

15.7

8.8

7.7

6.3

3.9

5 . 3

12.9

Wednesday

12.4

9.2

7.0

9.0

7.8

3.7

9.7

Thursday

15.7

10.1

9.2

8.6

9.7

17.0

16.1

Friday

11.4

33.7

22.1

11.4

7.0

7.6

9.7

Saturday

19.4

16.2

20.6

27.9

35.9

34.0

2.6

Sunday

16.3

15.8

22.7

32.0

24.0

30.3

36.1

Total

recoveries

196

246

314

293

305

200

The number of returns from any pstrti-
cular area depends on two major factors.
First, of course, bottles must actually wash
ashore. The numbers that do are determined
by water moyements and shore configuration.
Second, the bottle must be seen and picked
up. Apparently all shore areas were covered
to some extent, especially during the vaca-
tion period, but the distribution of resorts
and beaches is by no means uniform. Conse-
quently, the recovery records
do not give a precisely accu-
rate measure of actual landings.
I believe, however, that within
reasonable limits they are
quantitatively dependable, at
least for central and southern
Lake Huron.

Five returns made after
the "cut-off date" of Febru-
ary 28, 1957, are of particular
interest because the recovery
points were so far removed from
the rest. All five were re-
leased during the fall of 1956.
Apparently, travel of these
bottles was influenced by water
circulation resulting from the
strong southeaist, east, and
southwest winds that blew during

the fall which would account
for their travel to Drununond
and Manitoulin Islands (fig.
5). It is conceivable that a
number of bottles landed on
these and other islands that
rim the northern boundaries of
Lake Huron, but because the
shores are so little frequented
only a few were found.

WIND DATA

After many years of work
on the North Sea, Carruthers
(1947) emphasized the impor-
tance of keeping suitable
records of wind for use with
studies of water movements.

Wind data for this investigation were taken
from Coast Guard Stations on Lake Huron and
Saginaw Bay. (Other stations were held to
be too far distant for the records to be
useful in this study.) At no time were
bottles dropped more than 50 miles from a
source of wind information. The Tawas
Point, Bay City, and Harbor Beach Coast
Guard Stations submitted wind data consist-
ing of six observations daily, that is, an
observation every 4 hours. The wind direc-

Table 5. — July 31 j 1956, wind data from Coast Guard Stations
on Saginaw Bay and Lake Huron

Hour

Tawas Point

Bay City

Harbor Beach

0400

S 5

NNW 18

S 16

0800

S 10

NW 16

SE 10

1200

SW 5

NW 10

Calm

1600

SE 2

N 6

SE 16

2000

N 2

N 12

S 5

2400

NW 5

N 6

NW 5

HARBOR BEACH

TAWAS POINT

lOmph

tion~and velocity were recorded for each
observation at each station and a prevail-
ing wind vector for the day at each station
determined. A wind track based on these
vectors was used in interpreting drift-
bottle movements.

Even though the area studied lies
within the belt of prevailing westerlies,
frequent wind changes occur with the pas-
sage of the racuiy pressure systems through
the lakes cireas. These changes are
of paramount importance in affecting
surface-water flow. In addition,
there may be some tendency for off-
shore breezes at night and onshore
breezes during the daytime. Because
of these frequent wind changes,
local winds at stations no more than
50 miles apart may be blowing from
nearly opposite directions at the
same time (table 5). These differ-
: ences in wind direction among the
■ stations are more common during
periods of light, variable breezes.
During strong blows and gales the
wind direction is less likely to
differ between stations.

BAY CITY

Figure 6. — July 31, 1956, wind vector at the
Tawas Point, Bay City, and Harbor Beach,
Michigan Coast Guard Stations.

Although the prevailing winds
can differ between stations (fig.
6), the wind tracks in 1956 taken
over periods of a month, were simi-
lax (fig. 7). Similarity among
stations was greatest for August,
September, October, and November
and least in June and July when winds
were usually light. This seasonal
trend has prime significance in

31 OCTOBER

TAWAS POINT

10 OCTOBER

BAY CITY

10 OCTOBER

31 OCTOBER

HARBOR BEACH

10 OCTOBER

Figure 7. — Prevailing wind vectors for October 1956,
at Coast Guard Stations bordering Lake Huron.

determining the procedure to be
followed in the interpretation
of effects of wind on water move-
ment. The direction of the wind
and direction of the movement of
a bottle were correlated over
periods of several weeks, regard-
less of the station for which
the track was used. On the other
hand, for study of short-term
movements, it is desirable to
use wind data from the station
closest to the path of drift.
It may be of some significance
that movements of bottles that
agree least with wind movements
were those dropped farthest from
any source of wind information.

WATER MOVEMENTS OF
SAGINAW BAY

General features of the Bay

According to the Great Lakes
Pilot, 1956, "Saginaw Bay, the
largest indentation along the
west shore of Lake Huron, has a
width at its entrance between
Pointe aux Barques and Au Sable
Point of 26 miles, and from this
line southwesterly to its head
at the mouth of Saginaw River the
distance is 51 miles. Its mini-
mum width is 13 miles, between
Sand Point on the east and Point
Lookout on the west in the outer
portion of the bay; but, owing
to the very shallow bank extend-
ing from the easterly shore to
beyond the Charity Islands, and
to the shoal projecting from
Point Lookout, the deep channel
at this point of least width is
contracted to a width of about
1 3/4 miles. The water level in
Saginaw Bay is subject to sudden
changes due to the wind, a north-
east gale driving the water into
the bay so as to raise the level
at the mouth of Saginaw River 3
to 4 feet sometimes in less than
as many hours , while a southwest
wind lowers the level at times
sufficiently to cause large ves-
sels to ground in the channel."

Of the several tributaries

to Saginaw Bay, the Saginaw River at the
southwestern end is the largest. It follows
that the net flow of water must be from the
southwestern end of the bay northeastward
into Lake Huron.

north side and a similarly distributed
outflow on the south side. They thought
that the winter circulation might be the
same as that in the spring or fall.

The greater portion of the bay is less
than 20 feet deep. It is only near Lake
Huron at the mouth of the bay that a well-
formed, persisting thermocline is present
in the summer and early fall. Temporary
stratification does, however, occur within
the bay during the Rummer. In 1956 a ther-
mocline developed in certain inner areas
but it was ill-defined and temporary.
Approximately 25 percent of the total area
of the bay became stratified and almost all
of this area was at or near the mouth.

Previous studies

Both Harrington (1895) and Ayers et al .
(1956) were concerned primarily with circu-
lation in Lake Huron proper, although the
latter released "bottles" in the bay, and
both had recoveries here. According to
Harrington (1895) the most marked feature
of the drift in Lake Huron is the stream
passing southward along the west shore and
crossing the mouth of Saginaw Bay. The few
bottles that entered the bay during his
investigation landed in the northwestern
and southeastern sections. He did not com-
ment on circulation within the bay.

The Saginaw Valley Project is of inter-
est here even though no current studies
were made (Adams 1937). For the summer and
fall of 1935 and the summer of 1936, it is
apparent from the study that there was
little or no correlation between chloride
concentrations in different areas of the
bay and wind direction.

Ayers et al. (1956) noted changes in
circulation at the mouth of the bay in
different months. They believed that in
June 1954 there was inflow on the north
side and outflow along the south side.
Some inflow in July was thought to be sub-
surface with outflow spread over much of
the surface. Conditions in August were
held to be similar to those of July. They
conjectured from their limited data that
Saginaw Bay may behave like a simple estu-
ary of the same geographical orientation;
hence, in the autumnal circulation there
would be inflow at all levels along the

Drift-bottle movements in 1956

In our investigations, analysis of the
drift-bottle returns from releases in Sagi-
naw Bay confirms the belief of Ayers et al.
(1956) that no one stable surface-current
pattern exists within the bay. In fact,
results disclose more variability of the
surface currents than their studies were
able to show. It appears that the dynamics
of the bay are closely related to the highly
variable meteorological conditions of this
area and that the surface currents are in
a continuous state of change. For this
reason, we must state specifically under
what conditions any particular surface-
current pattern was found.

It is possible in Saginaw Bay for com-
pletely different current patterns to exist

Figure 8. — Typical surface-current flow
for Saginaw Bay in the summer of 1956.

on succeeding days. In the summer of 1956
surface currents did at times approach a
state that might be called "typical" for
the bay (fig. 8). Yet this system was in
a continuous state of readjustment to chang-
ing winds and no single surface-current
pattern persisted over an extended period.
Movements of bottles, released on August 10,
give a good indication of surface currents
under fairly stable westerly winds (fig. 9).
Of 230 bottles released on this day only
one was recovered on the western shore.
Its travel cannot be determined since it
was out 99 days before recovery. Very
likely it first traveled easterly under the
west winds, became entangled in marsh weeds
along the eastern shores and then was re-
floated by strojqg easterly winds and carried
across the bay to the western shore.

Under the influence of prevailing
easterly winds, surface currents travel
westerly in the bay as is demonstrated by

the recoveries from bottle releases on
October 12 and 13 (fig. 10). Although
releases were made at fewer stations on
these dates than on August 10, it is clear-
ly evident from the recoveries that south-
east, east, and northeast winds caused a
general westerly surface drift.

To indicate more clearly the relation-
ship between local winds and drift-bottle
travel, the release and recovery points of
the drift bottles have been plotted, along
with the winds that blew a short time prior
and subsequent to release (Appendix). As
exajnples, three typical stations in the
bay have been chosen [an inner-bay station,
fig. 11; mid-bay station, fig. 12; and
outer-bay station, fig. 13 (see pages 14
and 15)], and drift-bottle travel will be
discussed on the basis of information from
releases at these stations.

Nineteen recoveries were made from the

STATUTE MILES

"Figure 9. — Surface currents in Saginaw Bay
determined from travel of drift bottles
released on August 10, 1956, during a
period of moderate westerly winds.

Figure 10. — Surface currents in Saginaw Bay
determined from travel of drift bottles
released on October 12-13, 1956, during a
period of strong southeast-northeast winds.

30 relejises at the inner-bay station (fig.
11). It is apparent that no single surface
circulation could have existed throughout
the summer and fall seasons to give such a
pattern of recoveries. On the June 7 (fig.
21 A) and August 10 (fig. 43 A) releases,
the direction of drift was to the northeast,
presumably resulting from prevailing south-
west winds at these times. Two days after
10 bottles were released on October 30
(fig. 68 A), moderate northeast winds caused
currents that carried all but 3 of the bot-
tles ashore to the southwest.

The 27 recoveries from the 30 releases
at a mid-bay station show a greater disper-
sion than those recovered from the releases
at the inner-bay station (fig. 12). Subse-
quent to June 7, at which time 10 bottles
were released, the net wind vector was to
the north. The resulting water movement
accounts for the recovery of the 2 bottles

found to the north of the release point
(fig. 23 B). The 7 bottles recovered at
least 49 days after release to the east and
southeast appear to have drifted in this
direction because of the net winds to the
southeast for the period of time they were
adrift (fig. 23 B). The 8 recoveries from
the 10 releases on August 10 were to the
east and southeast (fig. 45 B). The net
wind vector for the period of time these
bottles were drifting was to the east. The
10 bottles released on October 30 landed to
the northwest of their release point (fig.
69 C). Apparently these bottles were car-
ried with water moved by the winds that
blew the day of and the day after release.

The 60 recoveries of 80 bottles re-
leased from ein outer-bay station substan-
tiate the theory that surface-current flow
was unstable during this study (fig. 13).
Recoveries from releases at this station

41 MILES

ABOVE PORT

HURON

STATUTE MILES

Figure 11. — Location of 19 recoveries from
30 drift bottles released at an inner
Saginaw Bay station. Ten releases were
made on June 7, Aigust 10, and October 30,
1956. A triangle shows release point;
X's mark recovery points.

Figure 12. — Location of 27 recoveries from
30 drift bottles released at a middle
Saginaw Bay station. Ten releases were
made on June 7, August 10, and October 30,
1956. A triangle shows release point;
X's mark recovery points.

were made not only from widely scattered
areas in Saginaw Bay but also from many
points along the shore of Lake Huron. All
10 bottles released from this station on
June 7 were recovered from the Tawas Bay
area to the northwest within a short dis-
tance of one another (fig. 24 B). After
release of these bottles, winds were vari-
able for 3 days; next the wind was to the
northeast for 3 days; the wind to the
southwest a week after release ^parently
caused the bottles to land in and around
Tawas Point. Bottles released on June 29
were recovered for the most part on the
eastern side of the Michigan Thumb (fig.
30 B). The net wind to the southeast most
likely caused currents that Ccirried the
bottles to this cirea. The widely scattered
points of the 7 recoveries from the 10
releases on July 18 follow well, with one
exception, the wind track (fig. 36 B). The
only logical explanation for the recovery

STATUTE MILE5

Figure 13. — Location of 60 recoveries from
80 drift bottles released at an outer
Saginaw Bay station. Ten releases were
made at 8 different times from June
through October 1956. A triangle shows
release point; X's mark recovery points.

on the Michigan Thumb after 27 days is the
influence of a current entering Saginaw Bay
from Lake Huron. The recoveries from
releases on August 10 (fig. 46 B) and Au-
gust 30 (fig. 52 B) indicate that surface
currents flowed toward the east in August
and September. Westerly winds prevailed
these months. Bottles recovered from
releases on September 21 (fig. 59 B) and
October 12 (fig. 63 A) apparently were car-
ried by currents caused by east and south
winds, respectively. The recoveries from
October 30 releases (fig. 70 A), although
scattered widely, correspond well with wind
direction. Apparently the bottles drifted
into the bay where one was deposited on the
west shore. A reversal in wind direction
then drove the bottles over to the Michigan
Thum where they landed near the mouth of
the bay.

It is evident from the foregoing dis-
cussion that the surface currents of Sagi-
naw Bay are closely related to the winds
cind consequently are highly variable. This
dependence of currents on wind wzis closest
for the inner reaches of the bay. Near the
mouth of the bay a few bottles were found,
the movement of which could not be explained
by local wind action (fig. 33 B). Wind
direction here at the time of release was
to the northeast. The 3 bottles that landed
within a day of release, however, traveled
to the southeast at least 90° to the right
of the wind vector. This variation most
probably was brought about by a strong
current entering the bay from Lake Huron,
causing the bottles to drift at right angles
to the wind. Additional variations were
noted around Tawas Point and the area north-
east of Sand Point.

Surface currents in the bay apparaitly
orient to changing winds in a short period
of time. For 2 days prior to release and
on the day of release of 10 bottles north-
east of Point Lookout, winds were from the
south (fig. 32 B). The day after release
the south winds diminished and chcinged to
north. Surface currents had to reorient to
the north winds in a very short time in
order to cause the bottles to land as indi-
cated. For 4 days prior to release of 10
bottles south of Point Au Ores on October 30,
strong southerly winds blew (fig. 69 A).
The day after release the south winds moder-
ated and the second day after release
changed to north. The surface currents had
to reorient rapidly to the north wind to

cause southwest drift of bottles, one of
which was recovered 4 days after release.

The time required for the current to
orient to the wind is dependent, of course,
upon the strength of the wind and the
existing flow pattern. In an area such as
Saginaw Bay where a consistent current
pattern does not exist, it seems possible
that a surface current might change in
response to a rapidly changed strong wind
in a matter of hours.

No attempt was made to study subsur-
face currents. The Ekman spiral (Sverdrup,
Johnson, and Fleming 1942) is frequently
mentioned in explanations of surface and
subsurface currents. According to this
theory, surface currents on the northern
hemisphere are directed 45° to the right
of the wind, while at greater depths the
current turns more to the right and the
velocity decreases. Near the bottom of the
friction layer the currents are low in velo-
city and move opposite to the wind direc-
tion. This theory, however, presupposes
conditions of equilibrium, a state that is
not reached in Saginaw Bay because of the
influence of variable winds. Thus it would
seem that the theory of the Ekman sprial
does not apply. The relative shallowness
of the basin also would seem to be an ad-
verse factor. Because of the prevalence
of shallow water and the consequent transi-
tory thermocline development, I suspect
that subsurface currents are highly influ-
enced by surface currents and may be
similar in direction to them.

Modifying factors exist in the bay to
complicate the simple wind-dependent sur-
face flow. Outflow of the streams and
rivers in the area must have some effect
upon surface currents. The largest of
these, the Saginaw River, enters the south-
ern end of the bay. Some of this river
water must diffuse into the bay water but
a discrete mass of water has been found to
follow the eastern shore of the bay out
into Lake Huron proper (Adams 1937). This
mass well might be the flow of Saginaw
River water.

A theory proposed by Steele (1957)
interprets the hydrography of the northern
North Sea in terms of the possible effects
of lateral eddy diffusion. This diffusion
depends upon the principle "that when a jet
issues into a motionless fluid there is

turbulent mixing along its edges malting
the jet gradually spread out. An important
feature is that as a result of this mixing,
the jet draws in fluid from its surround-
ings." If this theory holds true for the
North Sea and other bodies of water, it may
apply to Saginaw Bay also, especially if
all the streams and rivers entering the bay
and currents entering from Lake Huron be-
have as jets drawing in water laterally.

Circulation at the mouth of the bay
must be affected to a large extent by move-
ments of Lake Huron water. Harrington's
(1895) work indicated that a strong current
flows down the western shore of Lake Huron
across the mouth of Saginaw Bay. The pene-
tration of Lake Huron water into the bay is
still a matter to be resolved through chemi-
cal and physical data collected during this
study.

WATER MOVEMENTS OF LAKE HURON

Previous studies

The first account of drift-bottle work
upon Lake Huron was that by Harrington
(1895). He recognized a variability in
surface currents of the lake when he stated,
"While the winds from the Great Lakes are
westerly in their prevailing direction,
this is the region of variable weather, and
the actual directions of the wind change
from day to day. There will, consequently,
be considerable variation in the currents
from time to time, and this undoubtedly
causes a wayward motion of the current
bottles." He found that the courses taken
by the bottles in Lake Huron exhibited a
somewhat more complicated drift than did
bottles released in Lake Superior and Lake
Michigan.

Ayers (1956) adapted the oceanogra-
phers' dynamic-height method of determining
currents to freshwater conditions. Find-
ings on Lake Huron in 1954, based on this
method, seemed to be in good agreement with
results obtained by other methods (Ayers
et al . 1956). Analysis of the data from
three synoptic runs in 1954 revealed dis-
tinct differences in surface circulation
at the times (spring, summer, and fall) of
the runs. They concluded, further, "The
fundamental surface circulation pattern in
the upper and central portions of the lake
appeared to be counterclockwise. In the

lower end of the lake outflow to the St.
Clair River appeared to consist of a mean-
dering surface current, near or east of the
midline of the lake, which approached the
entrance of the river from the northeast."

Drift-bottle movements in 1956

In the present investigations, only
one bottle was found below the head of the
St. Clair River that flows out of Lake
Huron. Of the many bottles that rounded
the Michigan Thumb, most landed on the east-
ern side of the Thumb before reaching the
river mouth. These recoveries lend some
support to Ayers' contention that outflow
to the St. Clair River was from the north-
east.

Recoveries of 416 bottles from 760
releases along 3 transects in the southern
part of the lake (fig. 4) are considered in

the analysis of Lake Huron water movements.
A striking feature of the returns from
these releases was the scarcity of recover-
ies from the Saginaw Bay area (fig. 14).
Only 16 bottles were found within the bay
and none of these had penetrated more than
10 miles. Penetration into the bay was
correlated with easterly winds during the
time the bottles were adrift. As Harrington
(1895) and Ayers e_t al. (1956) have indi-
cated, however, a strong current may at
times pass down the west shore of Lake Huron
and set up counterclockwise rotation at the
mouth of Saginaw Bay. Had bottles been
released near the west shore above Au Sable
Point, it is possible that many would have
been carried into the bay by such a current.

The remainder of the recoveries from
the Lake Huron shores were scattered widely.
The tendency was marked, however, for the
bottles to drift to the east (fig. 15).
All recoveries from stations 2-8 were from
the Michigan Thumb area, mostly on the
..northern and Ccistern sides and from the

STATUTE MILES

Figure 14. — Location of 16 drift-bottle re-
coveries in Saginaw Bay from 760 releases
on Lake Huron. Eighty bottles were re-
leased each at stations 1-6 and 40 each at
stations 7-13. X's mark recovery points.

Figure 15. — Location of 45 recoveries from
80 drift-bottle releases at a Lake Huron
station. Triangle marks release point;
X's mark recovery points.

eastern shore of LaJce Huron. All recoveries
from 200 releases at stations 9-13 were from
the eastern shore of Lake Huron. Apparently
the surface current on Lake Huron during
the summer and fall of 1956 had a net circu-
lation from west to east.

Although the direction and intensity
of local winds were important in explaining
surface drift in Saginaw Bay, they appear
less significant in Lake Huron proper (fig.
42 D) . On August 3, 20 releases were made,
10 at each of the indicated stations, within
2 1/2 miles of one another. The large dif-
ference in direction of drift from the two
stations of bottles that were out approxi-
mately the same length of time and released
at nearly the same time indicates forces
other than wind at work in the formation of
currents.

Certainly, wind conditions play a
prominent role in formations of surface
currents in Lake Huron. However, the rela-
tionship between wind and currents is not

STATUTE MILES

Figure 16. — Location of 22 recoveries from
40 drift-bottle releases at a Lake Huron
station. Triangle marks release point;
X's mark recovery points.

nearly so obvious as in Saginaw Bay.
According to Millar (1952) the energy input
into a lake from a day's wind may not be
completely dissipated until 12 days later.
If this relation holds in Lake Huron, the
prevailing winds assume a prominent role in
formation of the general surface current
pattern in the lake.

As was true in Saginaw. Bay, location
of Lake Huron returns from a particular
station can vary widely throughout the
season. The wide scatter of the 45 returns
from 80 bottles released off Harbor Beach
(10 bottles each at 8 different times from
June through October 1956) is strong evi-
dence of the instability of the lake cur-
rents (fig. 15). The drift throughout the
investigation from some stations, however,
could be much more stable (fig. 16).

Dynamic heights

The use of the dynamic-height method
of determining current flow depends upon
the availability of a subsurface reference
plane at which currents are absent. Ayers
et al . (1956) has indicated that Lake Huron
has certain characteristics concerning
circulation that are psuedo-oceanic. In
calculating the relationship between wind
and depth of mixing for oceans, Sverdrup,
Johnson, and Fleming (1942) derived the

formula D = 7.6

where D is

^~Sl

the depth in meters, W the wind velocity in
meters per second, and v the latitude for
which the calculation is made. If 44° (the
approximate average latitude for southern
Lake Huron) is substituted for <f and 6.7
meters per second (a common wind velocity
over Lake Huron during the summer) is sub-
stituted for W, D, or the depth of the layer
that is stirred up by wind becomes approxi-
mately 60 meters. Mortimer (1954) believed
that mixing (water movement or currents)
may occur in some Icikes to depths three
times that of the thermocline. The average
depth of the thermocline in south-central
Lake Huron during the summer of 1956 was
50 feet. In order to lessen the probability
of currents below the base, a depth of 60
meters (somewhat more than 3 times the 50-
foot level of the thermocline) was taken as
a reference plane for dynamic-height calcu-
lations.

Use of this method to determine
currents was limited because records were
available from only one transect for any
one day. For best results a large number
of stations over an area should be avail-
able so that dynamic-height contours can
be drawn with the Kinimura of uncertainty.
The dynamic heights at points along the
transect gave only an approximation of the
initial direction of flow of current. For
instance, if the dynamic heights indicated
a northerly component, current flow could
actually be northeast, northwest, or even a
mere fraction of a degree north of east or
west. The use of this method in conjunction
with drift bottles was of some value in
determining possible surface-current flow
in the lake (figs. 17 A-D, see page 20).
This analysis indicates that surface-current
patterns may be much more complicated than
has been realized.

The dynamic-height method in surface-
current calculations might not be applicable
in and around the littoral zone. On two
occasions off Canadian shores, August 3,
1956 (fig. 17 B), and October 27, 1956 (fig.
17 D) , calculations indicated currents near
shore to be to the south but bottles re-
leased in the area on these dates drifted
to the north. The possibility exists, how-
ever, that the bottles at first drifted to
the south but later their direction of drift
was reversed.

topography of the free surface but may show
a number of features which, instead of
being associated with the general distribu-
tion of mass, are brought about by the
presence of internal waves. In view of
this circumstance which, so far, has not
received great attention, conclusions as to
general currents based on charts of geopo-
tential topography should be used with even
more reservation than has been previously
emphasized." However, in support of the
dynamic-height method of determining cur-
rents they remjirk that, "So mamy reserva-
tions have been made that it may appear as
if the computed currents have little or no
relation to the actual currents. Fortu-
nately, however, most of the assumptions
made lead only to minor errors, and currents
can be correctly represented in the first
approximation by means of the slopes of a
series of isobaric surfaces relative to one
reference surface."

Appraisal of the general pattern

Although no one characteristic current
system is indicated for Lake Huron, the
following general remarks concerning surface
circulation in Lake Huron in 1956 seem per-
tinent: There is a general but highly
variable west-to-east drift; the most highly
developed west-to-east drift occurs during
August and September; there is some inflow

The rate of change in the
dynamic heights is still a mat-
ter of conjecture. Prominent
changes over a period of appro-
ximately 5 weeks resulted in
new current patterns as shown
by figure 17 (A-D). Variation
from one day to the next was
so small that no significant
change in current pattern re-
sulted (table 6). Over a
period of days, however, the
total of these small differ-
ences produced the prominent
changes noted between cruises.

What effect internal
waves in the Great Lakes have
upon the geopotential topo-
graphy should be resolved.
According to Sverdrup, Johnson,

and Fleming (1942), " charts

of geopotential topography may
not represent the average

Table 6. — Dynamic heights In meters (reference level 60 meters)
for stations on the Harbor Beach, Mlchigan-Goderich, Ontario,
transect on successive days during three months of 1956

Statute miles
from Harbor
Beach

Date

June 22

June 23

August 3

August 4

September 15

September 16

3.0

59.992

59.995

60.016

60.030

5.0

59.996

60.018

60.032

7.0

59.998

60.019

60.027

60.033

60.025

12.0

60.003

60.008

60.022

60.034

17.0

59.996

60.000

60.020

60.034

22.0

59.999

60.000

60.018

60.026

60.029

27.5

59.992

59.995

60.028

60.024

60.033

32.5

59.994

59.996

60.021

60.018

60.033

37.0

59.999

59.997

60.012

60.005

60.028

60.027

41.5

60.000

60.005

60.006

60.021

60.018

44.0

60.004

60.005

59.998

60 . 002

60.020

60.018

Figure 17. — Surface-current flow in Lake Huron determined from dynamic
heights (solid lines) and drift-bottle movements (broken lines).
Dynamic heights calculated and drift bottles released on June 22,
1956 (A), August 3, 1956 (B) , September 15, 1956 (C) , and Octo-
ber 27, 1956 (D).

of surface water into Saginaw Bay; a strong
southerly littoral current flows at times
along the eastern coast of the Michigan
Thumb area (figs. 18 A-C, see page 22).

RATE OF DRIFT

Reliability in computing rate of drift
of bottles is impaired by a lack of knowl-
edge of how long a bottle was ashore before
it was discovered, and by a lack of informa-
tion on the course a bottle followed from
its release point to the recovery point.
Effects of the first of these two factors
might be minimized by using in calculations
only those bottles that are actually ob-
served washing ashore or those found still
drifting in the water. However, comparisons
of records for bottles from the same lot
that traveled similar courses revealed that
many discovered still floating or washing
ashore exhibited a lower rate of drift than
those recovered from the shore. Most prob-
ably some of the former had actually been
beached and refloated by changes in winds,
water level, and wave actions. For this rea-
son computations of rate of drift were not
restricted to recoveries of bottles found
still floating or washing ashore.

The second factor, lack of any means
of determining the exact course of a bottle
from its release point to its recovery point,
is not to be eliminated. The straight-line
distance from release point to recovery
point has been used in calculating the rate
of transport.

Saginaw Bay crossed the lake east to the
Canadian shore at a minimum average rate of
0.95 miles per day, the lowest averate rate
of bottles that crossed the lake for all
the cruises (table 7). The average rate of
movement increased for bottles that were
released at the mouth of Saginaw Bay on
Cruises II and III and later recovered in
Canada. During Cruise II, however, only
one bottle made this crosEing--not enough
to give a fair value for this cruise. The
number of bottles crossing the lake that
were released during Cruises IV and V was
more than twice the number that crossed from
releases of the six other cruises. During
August and the first weeks of September
when bottles released on Cruises IV and V
were adrift, the prevalence of westerly
winds was greater than at any other time
during the investigations. Recovery of
bottles from Cruises VI, VII, and VIII that
crossed the lake was low and no trend is
apparent in the average drift rate. Cover-
age of shore area and consequently returns
from these last cruises were much lower
than for the earlier ones. Had better
coverage existed, perhaps, more bottles
would have been found on the Canadian shores.

Rapidly moving bottles, those drifting
at an arbitrarily chosen 3 miles per day
cuid faster (10 percent of the bottles re-
covered) have been used to give some indi-
cation of actual drift rates approached
along assumed straight-line courses (figs.
18 A-H, see pages 22 and 23). The large
number of rapidly drifting bottles recovered

A bottle exhibiting a high
rate of drift along a course
should be a better indicator of
the actual drift rate than the
average of the rates of all of the
bottles traveling this course.
The average rate might include
bottles that were on the shore
many days before they were found.
The average drift rate can be
of value, however, not in indicat-
ing actual speed, but in making
certain comparisons between
cruises (table 7).

During and for a short time
after Cruise I in June 1956,
winds were variable but they
did display some tendency to be
from the west. Six bottles of
110 dropped at the mouth of

Table 7. — Number of bottles released at stations at the mouth of

Saginaw Bay each cruise in 1956, total number of recoveries of

these bottles crossing Lake Huron, and the average minimum

rate of drift bottles made in the crossing

Cruise

Dates of

Number of

Number of bottles

I
Average minimum

release

bottles

recovered that

rate of drift in

released

crossed to Canada

miles per day

June 5-7

110

0.95

June 21-29

110

1.73

III

July 13-18

110

1.89

August 2-10

110

1.95

August 24-30

110

2.35

September 13-21

110

2.07

VII

October 5-12

110

VIII

October 27-30

110

2.07

CRUISE I-JUNE J-11,1956

CRUISE n- JUNE 19- JULY 2, 1956

CRUISE 21- JULY 11-23,1956

CRUISE 12- JULY 31-AUGUST 13,1956

STATUTE MILES

Figure 18, — Release, recovery points, and tracks of bottles traveling
at least 3 miles per day along straight-line courses.
Trianglesshow release points. Drift rate indicated by

CRUISE Y- AUGUST 21-SEPTEMBER 2, 1956

CRUISE ra- OCTOBER 2-15,1956

CRUISE am- OCTOBER 23- NOV. 5, 1956

STATUTE MILU

number to the nearest tenth of a mile per day. Whole numbers in
parenthesis show number of bottles traveling at indicated rate.

from the releases on Cruises I, II, and III
consistently show a strong current down the
eastern shore of the Michigan Thumb (figs.
18 A-C); rates were as high as 12.7 miles
per day for bottles released on Cruise III.
During and for a short period after these
cruises in June and July 1956, the winds
over the lake were largely from the north
and the west. A temporary reversal of the
strong surface current clockwise around the
tip of the Michigan Thumb is indicated by
the travel of bottles released during Cruise
IV (fig. 18 D). Apparently this reversal
was caused by strong east winds that blew
during the first week of August. Of the
bottles released on Cruise IV (fig. 18 D)
sind V (fig. 18 E), the general direction of
those moving 3 miles per day and faster was
to the east. This easterly drift coincided
with prevailing westerly winds during
August and September 1956. Of the bottles
released on Cruises VI, VII, and VllI (figs.
18 F-H) only two crossed to the Canadian
shore at a rate in excess of 3 miles per
day. The remainder of the "rapid drifters"
traveled to the north (figs. 18 G-H) . Dur-
ing the time that these bottles were adrift,
the prevailing winds were from the south.

It might seem that the bottles that
had lost their drags would predominate in
those classed as "rapid drifters". Without
drags bottles presumably come more under
the direct influence of wind. However, of
the 168 bottles of these studies that
drifted at a rate of 3 miles per day or bet-
ter, only 9 had lost their drags.

It should not be assumed from these
remarks and figures that no speeds of drift
greater than those given were attained.
Also, most certainly other bottles would be
included as "rapid drifters" if the exact
tracks of the bottles as well as their
exact landing times were known.

QUANTITATIVE RELATIONSHIP BETWEEN
SURFACE DRIFT AND WIND

Garstang (1898) believed the relation-
ship between winds and surface currents
were so precise that he worked out a quan-
titative relationship between the two. He

developed the formula R ~ ^ — where

D is the distance traveled in miles and Pn

is the resultant pressure in pounds per
foot determined from n observations daily.
The accuracy of this method depends on the
assumption that the velocity of drift
varies as the pressure of the wind and not
directly as its velocity. Pressures were
obtained from the following set of values:

Force, Beauiort scale 0 1 2 3 45678 9 10 11 12

Velocity, miles per hour 3 8 13 18 23 28 34 40 48 56 65 75 90

Pressure, pounds foot 0.05 0.3 0.8 1.5 2.5 4 6 8 11.5 15 21 28 40

Pressure-equivalents were computed from the
velocities by multiplying the squares of
the velocities by the factor 0.005 and ex-
pressing the results in whole numbers.
Garstang did not give proof that these com-
putations were valid but remarked that the
table had been authorized by the Metero-
logical Office in 1875. He admitted that
the pressure-ratio is only an approximation
to the true law of drift. However, his
calculated and empirical travels of drift
bottles were fairly close. But he wrote,
"Some further examination, however, is
necessary before the reliability of my
method can be depended upon, because the
estimated results depend upon the assump-
tion of open water, and this cannot always
be conceded."

R. Witting (Carruthers 1927) decided

1/2
that the formula, V = MW ' , could be

used to show wind-surface drift relation-
ship where V is the velocity of drift in
centimeters per second, W is wind speed in
centimeters per second, and M is a constant.
In observations at Finnish lightships,
Witting computed the value of M to be 0.44;

1/2
the equation then became V = 0.44W

Carruthers in using the same formula with
V and W expressed in miles per day, arrived
at an M value of 0.45 for the English
Channel. Daniel and Lewis (1930) in work
on the Irish Sea, expressing V and W in
miles per day, arrived at values of M from
.04 to 1.29 for different sectors. In
later work on the English Channel, Car-
ruthers (1930) worked out the formula
S = 1/18 W for the wind-surface drift rela-
Tionship where ^ is bottle travel in miles
per day and W the wind speed in the same
units. Days of similar wind conditions,

with little day-to-day variation, enabled
him to work out this relationship. He was
quick to point out, however, that this
relationship was not necessarily applicable
to waters other thantthose he studied. He
inferred that it would be foolish to seek
any equation other than a simple one because
of the many variables involved.

Welch (1952) wrote that in large lakes
such as the Great Lakes surface velocity is
claimed to be about 5 percent of that of
the wind causing it but that the percentage
was less than 5 in smaller lakes. This
statement is in agreement generally with
Stromsten (1929) who found that a wind of
800 feet per minute produced a surface cur-
rent of 25 feet per minute on Lake Okoboji,
Iowa. Expressed in percentages, the surface
current there was about 3 percent of the
wind velocity. According to Whipple (1927),
Ackermann found the surface current to be
3 percent of a wind velocity of 5 miles per
hour and 1 percent of a wind velocity of
30 miles per hour on Owasco Lake, New York.
Velocity at a depth of 10 feet was about
60 percent of the surface velocity and at
20 feet it was 25 percent.

In this study no attempt has been made
to correlate quantitatively wind velocity
and surface drift. To do so accurately
would require knowledge of the characteris-
tics of reasonable steady winds from any
one direction, knowledge of the exact time
of bottle travel, and an accurate track of
the bottle drift. At no time could we be
certain of the true course of bottle drift.
It was seldom that wind velocity remained
fairly stable for several days after the
releases and occasions when bottles were
actually seen to land were rare. At no
time did the two conditions, necessary for
accurate computation, exist simultaneously.
When steady wind conditions did prevail for
several days, no bottles were seen to land
that had completed their entire travels
under this wind.

Another major difficulty in determin-
ing the relationship between water current
and wind velocity in regions of variable
winds is the lack of information on the
exact rate at which surface currents adjust
to a changing wind. Once this problem is
solved, we shall be in a better position
to compute the relationship quantitatively.

FACTORS INFLUENCING
DRIFT-BOTTLE MOVEMENTS

Surface currents in Saginaw Bay and
Lake Huron are extremely variable and are
dependent largely upon wind conditions.
However, the effects of winds on the two
bodies of water differ to a large extent
because of dissimilar morphometry of the
basins. Saginaw Bay is shallow, long, and
narrow, whereas Lake Huron is much deeper
and larger.

Saginaw Bay

In Saginaw Bay changes in the local
winds will alter surface currents in a very
short time as the energy accumulation in
currents in Saginaw Bay is far below that
of currents in Lake Huron. Because the
surface currents in the bay are so depend-
ent upon local winds, any pattern described
should be related to the winds producing
it if results are to be meaningful.

Forces other than winds which modify
the surface currents in the bay result from
inflows of streams and rivers and possibly
ground water. Lake Huron water also alters
current patterns as it enters or leaves the
bay. Lake Huron water enters principally
along the western area of the bay.

The shoreline in the lower reaches of
the bay, especially the eastern, is ill-
defined. Extensive areas in this region
are covered with emergent aquatic vegeta-
tion. It is apparent that currents in this
portion of the bay are relatively moderate.
However, it was here that direction of wind
and direction of bottle travel were most
closely correlated.

Shore areas in the outer half of the
bay indicate much stronger eroding action
from currents. Although surface currents
flowed outward at some time at different
points at the mouth of the bay, the princi-
pal outflow was along the eastern shore and
thence around the tip of the Michigan Thumb
area. The correlation between wind direc-
tion and direction of bottle drift in the
outer half of the bay broke down at times,
most likely because of the influence of the
currents entering from Lake Huron. A
general counterclockwise circulation with

inflow along the western shores and outflow
along the eastern shores was observed
several times during the sununer and fall.

Lake Huron

indicate that in open waters surface
currents also are variable. Apparently,
movement of water from west to east in
Lake Huron does not follow a straight line,
but direction changes several times before
it reaches the Canadiain shores.

In Lake Huron the prevailing winds are
more important than local winds in forming
current patterns. The energy input intp
the lake by the prevailing wind is not dis-
sipated by temporary wind shifts. Currents
on any one day reflect the wind input of
the previous days (at least 12, according
to Millar 1952). The general drift in Lake
Huron was from west to east; it was caused
presumably by the prevailing westerly winds.
This finding seems to support Millar's
theory. On the other hand, bottles under
the influence of strong local winds moved,
at times, against the prevailing pattern.
The most marked of these exceptions to
pattern was the drift of bottles from east
to west around the tip of the Michigan Thumb
area where there is normally a strong cur-
rent in the opposite direction. Other
examples of this reversal against the pre-
vailing pattern were noted in the Tawas
Point-Au Sable Point area. Millar's state-
ment to the effect that the energy input
is not dissipated for several days might
not apply to the surface water; at least it
would seem not to apply in the above-cited
reversals.

The effects of stratification upon
currents present an unsolved problem in
Lake Huron. The depth to which currents
are present in stratified lakes is still a
subject of much study. As Mortimer (1954)
has found, subsurface currents are, most
likely, present in water much deeper than
was formerly realized and, consequently,
are of some significance.

Ayers' (1956) method of using dynamic
heights has contributed a new concept in
calculating surface currents of large in-
land lakes. But as he has suggested, this
method should always be checked by means of
other parameters to determine whether it is
giving valid results. His method may be
limited in some degree by the high ratio of
shoreline to surface-water area and the
confined nature of some areas of inland
basins. The shoreline, if appears, plays
an important role in conforming currents
into some pattern regardless of the dynamic
heights. Dynamic-height calculations

RECOMMENDATIONS FOR STUDY OF CURRENTS
ON THE GREAT LAKES

Current-pattern determination on the
Great Lakes is still in its earliest state
of development. The few studies available
leave much to be desired. Just what the
subsurface currents are and what their
relation to surface currents is remains a
matter of conjecture. Surface-current
observations have not extended over long
enough periods to support conclusions
regarding seasonal patterns. If the true
nature of currents in the Great Lakes is
to be determined, a program must be carried
out that will include the following points:

1. Study one lake or one area of a
lake for a period of several years through-
out all seasons. Such a project should
disclose what forces are at work in forma-
tion of currents, and thus lay the founda-
tion for predictions of currents.

2. Employ various methods in deter-
mining currents and check each method
against others and against known conditions
whenever possible. The relisibility of each
method could be ascertained and the limita-
tions of each determined.

3. Study the degree of correlation
between meteorological conditions and
current patterns. Present methods of
recording wind data over the lake should
be refined. Recent evidence indicates
that large variations in the winds occur.

4. Develop new equipment and methods
auid use devices other than drift bottles.
The transponding drift buoy as described
by Bumpus et^ aS. (1957) appears to hold
much promise as a current indicator. The
tracking of radio signals emitted from this
free floating buoy makes it possible to
determine its movement precisely. Investi-
gate the use of the radioactive isotope as
an aid in determining movements of water
masses. Recently, the City of Los Angeles
employed isotopes to determine the path of
the flow of sewage into the Pacific Ocean.

Although the use of isotopes is expensive,
it is believed that in the near future the
cost will decrease greatly.

5. Investigate littoral currents more
thoroughly and determine the relationship
between lake morphometry and currents.

6. Undertake the determination of
subsurface currents and the relationship
between subsurface and surface currents.

Costs of such a program would be high
both in money and time. It will, however,
be necessary if the true nature of currents
is to be found and predictions of currents
made possible.

ACKNOWLEDGMENTS

The following agencies and individuals
contributed to this study: the crews of
the U. S. Fish and Wildlife Service research
vessels Cisco and Musky assembled and re-
leased drift bottles; the crews of the
Michigan Department of Conservation Patrol
Boats Nos. 2 and 3 assisted in releasing
drift bottles; the U. S. Coast Guard made
wind records available; many, many persons
returned the cards from the bottles; Mr.
William Cristanelli drafted the figures;
James Moffett, Ralph Hile, and Stanford
Smith of the Great Lakes Fishery Investiga-
tions and John Ayers of the Great Lakes
Research Institute made suggestions in the
preparation of this manuscript.

SUMMARY

1. The U. S. Fish and Wildlife Service
and the Michigan Department of Conservation,
in a cooperative project, conducted a com-
prehensive liranological survey in Saginaw
Bay and adjacent Lake Huron waters in the
summer and fall of 1956. As a part of this
project in order to gain information on
surface currents, drift bottles were used

in Saginaw Bay, and drift bottles together
with the dynamic-height method were used in
lower Lake Huron area.

2. The drift bottle consisted of a
4-ounce Boston round bottle corked, sealed
with beeswax, and fitted with a metal drag
suspended 12 inches below the neck of the
bottle by a piece of black iron wire. The
purpose of the drag was to reduce the direct

influence of the wind upon bottle movement.
For the most part drags appeared to func-
tion properly up to at least 30 days, after
which time many broke away from their drift
bottles.

3. A total of 2,650 of these units
were released from the U. S. Fish and Wild-
life Service research vessels Cisco and
Musky and Michigan Department of Conserva-
tion Patrol Boats Nos. 2 and 3. Subsequent-
ly 1,843 (69.5 percent) reply cards from
the recovered bottles were returned. Of
these, 240 were returned after the cut-off
date of February 28, 1957, and were not
used in studies of surface currents.

4. Recovery of bottles during the
summer and fall was greatest over weekends
with this becoming more pronounced after
August. Percentage return of bottles re-
leased from any one of the nine cruise
periods decreased as the season progressed.

5. Wind records at the Tawas Point,
Bay City, and Harbor Beach, Michigan Coast
Guard stations were used in drafting wind
tracks .

6. There appeared to be a high corre-
lation in Saginaw Bay between direction of
surface currents that moved these bottles
and direction of winds. In Lake Huron this
correlation applied to a lesser extent
although the drift of bottles was generally
from west to east, apparently under the
influence of the prevailing westerly winds
of this area.

7. Use of the dynamic-height method
in Lake Huron was restricted because of the
paucity of stations covered. It appeared,
however, from results using this method
along with drift bottles that the surface
currents in Lake Huron are much more com-
plicated than has been suspected.

8. Greatest rates of drift were
obtained from bottles drifting clockwise
around the top of the Michigan Thumb,
thence south along the east coast of the
Thumb.

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195(5. A dynamic height method for the

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APPENDIX

Figures 19-27 contain the release and
recovery points of drift bottles floated in
the 1956 Saginaw Bay-Lake Huron study.
Meanings of numbers and symbols used are as
follows :

A bottle recovered on the day it was
released was considered to have been adrift
zero days. If it was recovered the day
after release, the drift period was one
day.

1. Triangle - release point.

2. Dot - recovery point.

3. Plain number - number of days

between release and recovery.
Drift unit intact.

4. Number circled - same as No. 3

except unit without drag when
recovered.

The wind track
station nearest the
bottles is included
wind track includes
days prior to releas
as the time interval
might be influencing
Numbers on the wind
indicate the end of

from the Coast Guard
drift paths of the
on each page. The
the wind vectors 4-10
e of bottles as well
during which the wind
bottle movement.
track are dates and
a 24-hour period.

5. Number enclosed by square or

rectangle - same as No. 3 except
loss or retention of drag not
indicated.

6. Number enclosed by hexagon - same

as No. 3 except reply card only
was found.

7. Question mark - number of days

between release cind recovery not
known.

INT.-DUP. SEC. WASH., D.C. ueOJ2

ST*T<JTC MILEi

Figure 19. — Recovery points of drift bottles released June 5, 1956.

STATUTE MILES

Figure 20. —Recovery points of drift bottles released June 5, 1956.

STATUTE MILES

Figure 21. — Recovery points of drift bottles released June 7, 1956.

Figure 22. — Recovery points of drift bottles released June 7, 1956.

Figure 23. — Recovery points of drift bottles released June 7, 1956.

STATwTC MILtS

Figure 24. — Recovery points of drift bottles released June 7, 1956.

STATUTE MILES

Figure 25. — Recovery points of drift bottles released June 10, 1956.

10 20

STATUTE MILES

Figure 26.— Recovery points of drift bottles released June 20, 1956.

Figure 27. — Recovery points of drift bottles released June 21, 1956.

STATUTE MILES

Figure 28.— Recovery points of drift bottles released June 21, 1956.

Figure 29. — Recovery points of drift bottles released June 22, 195^.

Figure 30. —Recovery points of drift bottles released June 29, 1956.

5 0 10 ?0 30 40 50

STATUTE MILES

Figure 31. — Recovery points of drift bottles released June 29, 1956.

STATUTE MJLES

Figure 32. — Recovery points of drift bottles released July 1, 1956.

Figure 33, — Recovery points of drift bottles released July 12, 1956.

Figure 34. --Recovery points of drift bottles released July 13, 1956.

WIND TRACK — HARBOR BEftCH

5T*TyTC MILES

Figure 35. — Recovery points of drift bottles released July 13, 1956.

Figure 36. — Recovery points of drift bottles released July 18, 1956.

10 5 O 10 20

STATUTE MILES

Figure 37. — Recovery points of drift bottles released July 18, 1956.

Figure 38. — Recovery points of drift bottles released July 22, 1956.

STATUTt MltES

WIND TRACK— TAWAS POINT

Figure 39. — Recovery points of drift bottles released August 1, 1956.

3 SEPTEMBER

10 SEPTEMBER

29 AUGUST

WIND TRACK — TAWftS POINT

10 20

STATUTE MILES

Figure 40.— Recovery points of drift bottles released August 2, 1956,

STATUTE MILES

Figure 41. — Recovery points of drift bottles released August 2, 1956.

Figure 42. — Recovery points of drift bottles released August 3, 1956.

so 10 20

5TAT-UTE MILES

Figure 43. — Recovery points of drift bottles released August 10, 1956.

10 20

STATUTE MILES

Figure 44. — Recovery points of drift bottles released August 10, 1956.

STATUTE MILti

Figure 45. — Recovery points of drift bottles released August 10, 1956.

Figure 46.— Recovery points of drift bottles released August 10, 1956.

STATWTC MILE4

Figure 47. — Recovery points of drift bottles released August 10, 1956.

10 20

STATUTE MILES

Figure 48.— Recovery points of drift bottles released August 12, 1956.

Figure 49. — Recovery points of drift bottles released August 22, 1956.

STATUTE MILES

Figure 50. --Recovery points of drift bottles released August 24, 1956.

Figure 51. — Recovery points of drift bottles released August 24, 1956.

Figure 52. — Recovery points of drift bottles released August 30, 1956.

STATUTE MILES

Figure 53. — Recovery points of drift bottles released August 30, 1956.

15 OCTOBER

WIND TRACK— HARBOR BEACH

^24 SEPTEMBER

STATUTE MILES

Figure 55. — Recovery points of drift bottles released September 12, 1956.

STATUTE MH.ES

Figure 56. --Recovery points of drift bottles released September 13, 1956.

30 40 50

STATUTE MILES

Figure 57. --Recovery points of drift bottles released September 13, 1956.

10 20 30 40 50

STATUTE MILCS

Figure 58. — Recovery points of drift bottles released September 15, 1956.

STATUTE MILES

Figure 59. — Recovery points of drift bottles released September 21, 1956.

B SEPTEMBER J^^^ ^ OCTOBER , 21

23 SEPTEMBER

lOmph
WIND TRACK— TAWAS POINT

STATUTC MILES

Figure 60. — Recovery points of drift bottles released September 23, 1956.

STATUTE MILES

Figure 61. — Recovery points of drift bottles released October 3, 1956,

Figure 62.— Recovery points of drift bottles released October 4, 5, 1956.

STATUTE MILES

Figure 63. — Recovery points of drift bottles released October 12, 1956.

Figure 64. — Recovery points of drift bottles released October 13, 1956,

WIND TRACK — TflWAS POINT

20 OCTOBER

STATUTE MILES

Figure 65 .--Recovery points of drift bottles released October 25, 1956.

STATUTE MILCS

Figure 66. — Recovery points of drift bottles released October 27, 1956.

30 OCTOBER

WIND TRACK — HARBOR BEACH

Figure 67. — Recovery points of drift bottles released October 27, 1956.

STATUTE MILES

Figure 68. — Recovery points of drift bottles released October 30, 1956.

Figure 69. — Recovery points of drift bottles released October 30, 1956.

STATUTE MILES

Figure 70. — Recovery points of drift bottles releaised October 30, 1956.

30 NOVEMBER

10 20

STATUTE MILES

10 30 30 40 M

STATUTE MILES

Figure 71. — Recovery points of drift bottles released November 3, 1956.

30 NOVEMBER

WIND TRACK-TflWAS POINT

9 NOVEMBER

Figure 72. — Recovery points of drift bottles released November 14, 1956.

INT.-DUP. SBC., WASH., D.C. 4,9022

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