Underwater operations in southeastern Lake Michigan near the Donald C. Cook Nuclear Plant during 1974

BENTON HARBOR POWER PLANT LIMNOLOGICAL STUDIES

PART XXII. UNDERWATER OPERATIONS IN SOUTHEASTERN LAKE MICHIGAN
NEAR THE DONALD C. COOK NUCLEAR PLANT DURING 1974

John A. Dorr III
Timothy J. Miller

Under Contract with:

American Electric Power Service Corporation
Indiana and Michigan Electric Company

Special Report No. 44
of the
Great Lakes Research Division
The University of Michigan
Ann Arbor, Michigan

December 1975

PREVIOUS PARTS OF THE REPORT SERIES RELATIVE TO THE
DONALD C. COOK NUCLEAR STATION

Benton Harbor Power Plant Limnological Studies

Part

I. General studies. J. C. Ayers and J. C. K. Huang. April 1967.
31 p.

II. Studies of local winds and alongshore currents. J. C. Ayers, A.
E. Strong, C. F. Powers, and R. Rossmann. December 1967. 45 p.

III. Some effects of power plant waste heat on the ecology of Lake
Michigan. J. R. Krezoski. June 1969. 78 p.

IV. Cook Plant preoperational studies 1969. J. C. Ayers, R. F.
Anderson, N. W. O'Hara, C. Kidd. March 1970. 92 p.

V. Winter operations, March 1970. N. W. O'Hara, R. F. Anderson,
W. L. Yocum, J. C. Ayers. April 1970. 17 p.

VI. Pontoporeia af finis (Crustacea, Amphipoda) as a monitor of radio-
nuclides released to Lake Michigan. C. C. Kidd. 1970. 71 p.

VII. Cook Plant preoperational studies 1970. J. C. Ayers, D. E.

Arnold, R. F. Anderson, H. K. Soo. March 1971. 72 and 13 p.

VIII. Winter operations 1970-1971. J. C. Ayers, N. W. O'Hara, W. L.
Yocum. June 1971. 41 p.

IX. The biological survey of 10 July 1970. J. C. Ayers, W. L. Yocum,
H. K. Soo, T. W. Bottrell, S. C. Mozley, L. C. Garcia. 1971.
72 p.

X. Cook Plant preoperational studies 1971. J. C. Ayers, H. K. Soo,
W. L. Yocum. August 1972. 140 and 12 p.

XI. Winter operations 1971-1972. J. C. Ayers, W. L. Yocum. September
1972. 26 p.

XII. Studies of the fish population near the Donald C. Cook Nuclear
Power Plant, 1972. D. J. Jude, T. W. Bottrell, J. A. Dorr III,
T. J. Miller. March 1973. 115 p.

XIII. Cook Plant preoperational studies 1972. J. C. Ayers and E. Seibel
(eds.). March 1973. 281 p.

XIV. Winter operations 1972-1973. J. C. Ayers, W. L. Yocum, E. Seibel.
May 1973. 22 p.

XV. The biological survey of 12 November 1970. J. C. Ayers, S. C.
Mozley, J. C. Roth. July 1973. 69 p.

XVI. Psammolittoral investigation 1972. E. Seibel, J. C. Roth, J. A.
Stewart, S. L. Williams. July 1973. 63 p.

Ill

XVII. Program of aquatic studies related to the Donald C. Cook Nuclear
Plant. J. C. Ayers and E. Seibel (eds.). December 1973. 57 p.

XVIII. Effect of a thermal discharge on benthos populations: Statis-
tical methods for assessing the impact of the Cook Nuclear Plant.
E. M. Johnston. December 1973. 20 p.

XIX. The seasonal biological surveys of 1971. J. C. Ayers, S. C.
Mozley, J. A. Stewart. December 1974. 181 p.

XX. Statistical power of a proposed method for detecting the effect
of waste heat on benthos populations. E. M. Johnston. December
1974. 29 p.

XXI. Bacteria and phytoplankton of the seasonal surveys of 1972 and
1973. J. C. Ayers. November 1975. 153 p.

Seibel, E. and J. C. Ayers (eds.). 1974. The biological, chemical, and
physical character of Lake Michigan in the vicinity of the Donald C.
Cook Nuclear Plant. Univ. Michigan, Great Lakes Res. Div. Spec.
Rep. 51. 475 p.

Jude, D. J., F. J. Tesar, J. A. Dorr III, T. J. Miller, P., J. Rago and
D. J. Stewart. 1975. Inshore Lake Michigan fish population^ near
the Donald C. Cook Nuclear Power Plant, 1973. Univ. Michigan, Great
Lakes Res. Div. Spec. Rep. 52. 267 p.

Seibel, E., C. T. Carlson and J. W. Maresca, Jr. 1975. Lake and shore
ice conditions on southeastern Lake Michigan in the vicinity of the
Donald C. Cook Nuclear Plant: winter 1973-74. Univ. Michigan,
Great Lakes Res. Div. Spec. Rep. 55. 62 p.

Mozley, S. C. 1975. Preoperational investigations of zoobenthos in
southeastern Lake Michigan near the Cook Nuclear Plant. Univ.
Michigan, Great Lakes Res. Div. Spec. Rep. 56. 132 p.

Rossmann, R. 1975. Chemistry of nearshore surficial sediments from

southeastern Lake Michigan. Univ. Michigan, Great Lakes Res. Div.
Spec. Rep. 57. 62 p.

Evans, M. S. 1975. The 1975. The 1975 preoperational zooplankton

investigations relative to the Donald C. Cook Nuclear Power Plant.
Univ. Michigan, Great Lakes Res. Div. Spec. Rep. 58. In press.

Ayers, J. C. 1975. The phytoplankton of the Cook Plant monthly survey

during the preoperational years 1972, 1973 and 1974. Univ. Michigan,
Great Lakes Res. Div. Spec. Rep. 59. 51 p.

TABLE OF CONTENTS

PREVIOUS PARTS OF THE REPORT SERIES RELATIVE TO THE

DONALD C. COOK NUCLEAR STATION iii

ABSTRACT ix

ACKNOWLEDGMENTS x

INTRODUCTION 1

METHODS 1

OBSERVATIONS 4

Dive No. 1, 16 April, North Control Station 4

Dive No. 2, 17 April, Middle Intake Structure 7

Dive No. 3, 19 April, Riprap Area Surrounding

North Intake and Discharge Structures , . . 7

Dive No. 4, 20 May, Middle Intake Structure 7

Dive No. 5, 21 May, South Intake Structure 9

Dive No. 6, 22 May, North Discharge Structure 12

Dive No. 7, 13 June, South Intake Structure 13

Dive No. 8, 13 June, North Discharge Structure 14

Dive No. 9, 13 June, 6.1 m Contour Directly

South of the South Discharge Structure 15

Dive No. 10, 13 June, South Intake Structure 16

Dive No. 11, 14 June, North Discharge Structure .... 17

Dive No. 12, 14 June, South Intake Structure 18

Dive No. 13, 26 June, South Intake Structure 20

Dive No. 14, 22 July, 6.1 m Contour Directly

South of the South Discharge Structure 20

Dive No. 15, 23 July, 9.1 m Contour Directly

South of the South Intake Structure 21

Dive No. 16, 24 September, North Discharge Structue . . 22

Dive No. 17, 23 October, Middle Intake Structure .... 23

Dive No. 18, 24 October, North Discharge Structure ... 25

DISCUSSION 26

CONCLUSION 29

1975 PROGRAM OBJECTIVES 30

REFERENCES 32

Vll

UNDERWATER OPERATIONS IN SOUTHEASTERN LAKE MICHIGAN NEAR
THE DONALD C. COOK NUCLEAR PLANT DURING 1974

Abstract. Underwater operations in the vicinity of the Donald C. Cook
Nuclear Plant began in 1973 and continued in 1974 and 1975. These under-
water surveys permitted visual examination and handsampling of the area,
which in turn may be correlated with mechanical sampling of the area.
Eighteen dives were performed between April and October 1974 at locations
within and without the riprap zone. Ten species of fish were observed:
sculpin, johnny darter, alewife, yellow perch, lake trout, burbot,
emerald shiner, channel catfish, black bullhead and carp. Slimy sculpin
eggs were collected in the study area during May; spottail shiner eggs
were collected in June. In both cases, samples of each species of egg
were retained in the laboratory, where limited hatching subsequently
took place. Crayfish and one species of snail, Physa Integra y were
frequently observed in the riprap zone, never outside it. Samples of
algae and periphyton were collected from the study area; 39 species of
algae and diatoms were identified in samples taken from the riprap zone.
However, only one algae (Spirogyra) was collected outside the riprap
zone. This algae was unattached and possibly washed into this area.
Diversity of fish species, abundance and activity levels of fish, snails
and crayfish, and the density of algae were found to be higher within
the riprap zone. Increases are attributed primarily to the presence of
underwater structures and riprap surrounding these structures. Bio-
logical diversity, abundance and activity levels were much higher at
night than during the day. Most areas of the bottom were free of
decaying material. Macrophytes were not observed. The 1975 diving
program objectives are outlined and include an intensification of the
effort to quantify observations.

IX

ACKNOWLEDGMENTS

We are greatly indebted for the support and guidance given to us
by Erwin Seibel, who has been instrumental in the development of the
diving program at the Great Lakes Research Division. Lee H. Somers
deserves our appreciation for the hours he has spent training many of
our departmental divers. We would like to extend special thanks to
Jon Barnes for his assistance at the Cook Plant and during several of
the dives. We are grateful for the time and effort expended by
Marybeth M. Bowman during her analysis of the periphyton samples.

Special recognition is deserved by our fellow divers, Frank Tesar,
David Jude and Gregg Gitschlag, who often endured unpleasant diving
conditions, and without whose assistance living operations at the Cook
Plant would have been impossible.

INTRODUCTION

Underwater operations were conducted in the vicinity of the Donald
C. Cook Nuclear Plant during 6 months of 1974. Eighteen dives to col-
lect scientific data were made during April, May, June, July, September
and October. The 1974 underwater survey program produced substantive
results which permitted a comparison of 1973 and 1974 observations.

Data obtained through visuaJ observations and handsampling were
used to supplement and correlate with mechanical sampling data.

METHODS

Open circuit SCUBA was used for all dives, and a 16 ft Boston
Whaler served as the primary support vessel. Although the- 1974 field
schedule originally called for 5-6 dives per month from April through
November, inclement weather, limited visibility and problems associated
with equipment and operational logistics forced a reduction of the
diving schedule nearly every month. However, portions of the intake
and discharge areas were examined in April, May, June, September (dis-
charge area only) and October, thus establishing some spatial and
temporal continuity.

Standard monthly observations were made at permanent stations
located within the riprap zone (Fig. 1). The north discharge structure
and either the middle or south intake structure were examined regularly.
Swims were conducted around the top and base of the structure and a
section of riprap 2-3 m wide surrounding the structure. Sampling and
swims farther out onto the riprap were intermittently conducted. Ob-
servations were also made at a control station outside the riprap area.
This station is located halfway between the intake and discharge struc-
tures at a depth of approximately 7.6 m, and covers an area parallel to
shore 2-3 m wide (dependent upon visibility) extending for a distance
of 200 m northward from the north range pole. Supplemental dives were
performed on seven occasions, three at non-permanent locations; these
dives are discussed in the observations section.

MIDDLE INTAKE
STRUCTURE (9.1m)

SOUTH INTAKE
STRUCTURE (9.1m)

SOUTH DISCHARGE
STRUCTURE (6.1m)

NORTH INTAKE
STRUCTURE (9.1m)

LAKE
MICHIGAN

NORTH CONTROL
STATION SWIM (7.6m)

unni

■NORTH DISCHARGE
STRUCTURE (6.1 m)

-RIPRAP ZONE

SOUTH
RANGE POLE

DONALD C.COOK
NUCLEAR PLANT

NORTH
RANGE POLE

MICHIGAN

METER«>
I 1 1

200

FIG. 1. Map of the Cook Plant study area in southeastern Lake Michigan
in 1974.

Observations were made by John A. Dorr III, Gregg R. Gitschlag,
David J. Jude, Timothy J. Miller, and Frank J. Tesar. During the dives,
observations were written on slates or committed to memory and trans-
cribed on the surface. In all cases, observations made by participating
divers were combined and summarized in a dive report.

Because visual observations tend to be subjective, the following
terms or phrases used in the report are defined: few = 1-10, many =
10-50, numerous = 50-100, and abundant = more than 100. For the sake
of brevity the terms "apart," "high" and "length" were used to describe
ripple marks. "High" refers to the trough-to-crest distance, and "length"
refers to the distance from one end to the other of an individual ripple
mark. Ripple mark direction (the direction from which they were generated)
was determined with an underwater compass. "Riprap" refers to the broken

stone surrounding the various intake and discharge structures. "Floe"
refers to the loose accumulation of fine particulate material (con-
sisting primarily of sediment, some periphyton and diatomaceous material)
which in this area often covers the bottom with a thin (3-10 mm) layer.
"Organic debris" refers primarily to terrestrial vegetation such as trunks
and branches of trees, roots, leaves, dune grass, etc. An attempt was
made to describe the behavior of observed fish. Unless schooling or
other social behavior is noted, all fish were solitary individuals;
unless specifically noted as juveniles, all fish were adults. The value
given for horizontal visibility is an estimate which can vary to ±20%,
depending on the distance estimated. Current direction was determined
with a compass. Rate of flow was estimated by timing the horizontal
transport of suspended material past stationary divers. Surface temper-
ature was taken within 1 m of the surface and bottom temperature within
1 m of the bottom. All times are Eastern Standard Time.

As in 1973 (Dorr 1974) observations were occasionally taken from a

predetermined (transect swims) location for the purpose of quantifying

2
visual data (number s/m ) and calculating densities, testing equipment

and methods, and training personnel to quantify their underwater obser-
vations.

During Dives Nos. 5, 6 and 11, a transect 1 m wide and 10 m long

2
(10 m ) was swum along the bottom beginning at the north, south, east

and west sides of the indicated structure; each transect began at the
base of the structure and extended outward, perpendicular to the struc-
ture. Observations were made by two divers, each observing one half of
the transect width. The data from each diver's observations were then
pooled and summarized. It should be noted that these transect counts
represent numbers of easily visible organisms only. Since the bottom
(riprap) was not examined from all angles nor was it overturned, higher
actual densities might well be expected. Although exact densities can-
not be calculated reliably, the method of observation and bottom type
remained similar for all transect swims, thus allowing some relative
density comparisons.

OBSERVATIONS

Tables 1 and 2 summarize the standard monthly and supplementary
dives performed in southeastern Lake Michigan at the plant in 1974.
Observations made during each dive are presented in this section. The
dives are presented in the order in which they were performed. Occa-
sionally, limited discussion focusing on a specific observation is also
presented in this section, for the purpose of retaining and clarifying
the connection between the observation and subsequent interpretation,
and to avoid reiteration of observational data which would be neces-
sitated if the discussion were to be presented in a later section of
the report.

DIVE NO. 1, 16 APRIL, NORTH CONTROL STATION

The horizontal visibility at working depth was 0.6 m. The Secchi
disc reading of 1.2 m was below average for the area, probably caused by
three days of northwest winds and waves 3 m high which increased the
amount of material suspended in the water. Water temperature at the
surface and bottom was 1.6 Cj air temperature was 7.2 C. There was no
noticeable current, the lake was calm, there was little wind and the sky
was clear.

The bottom was quite homogeneous and consisted of well-sorted sand.
Areas of gravel or silt were not observed. The floe layer that covered
the sand was unusually heavy, 8-10 mm thick, and easily placed into
suspension. Ripple marks were noted to be running from the northwest.
They were 15 cm apart and 2-5 cm high, and were cross-hatched by smaller
ripple marks running from the southwest.

The troughs of the large ripple marks contained a thin layer of

organic detritus which consisted primarily of dune grass, wood chips,

and plant stems. Empty sphaeriid (fingernail clam) shells were abundant

2
(an estimated 50 to several hundred per m ) and many live individuals

were observed. One live crayfish was noted, and when disturbed swam

away from the divers. Fish, macrophytes and other macroscopic biota

were not observed.

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DIVE NO. 2, 17 APRIL, MIDDLE INTAKE STRUCTURE

Horizontal visibility at working depth was 0.8 m. The low Secchi
disc reading of 1.0 m was related to both relatively high turbidity and
the loss of light as evening approached. Water temperature was 7.1 C
at the surface and 7 . 3 C at the bottom, air temperature was 12.8 C.
There was no noticeable current, the lake was calm, there was little
wind and the sky was clear.

The riprap was covered with a layer of floe 10 mm thick, again
unusually heavy for the area. The riprap was free of inorganic scrap
(pipe, cable, sheet metal, scrap metal, bottles or cans, scour cloth,
plastic, etc.) as well as any appreciable amount of organic debris.

One live crayfish was seen. Fish, gastropods, macrophytes and
other biota were not observed. A macroscopic examination of the struc-
ture and surrounding riprap disclosed no apparent growth of Ctadophora^
in contrast to the luxuriant summer growth observed during 1,973 on both
the top of the structure and the surrounding riprap.

DIVE NO. 3, 19 APRIL, RIPRAP AREA SURROUNDING NORTH INTAKE AND DISCHARGE
STRUCTURES

Horizontal visibility at working depth was 0.8 m. The Secchi disc
reading was 1.0 m. Water temperature at the surface and bottom was 6.7
C, air temperature was 15.6 C. There was no noticeable current, and
weather conditions were calm and clear.

The purpose of this dive was to attach buoy markers to the north
intake and discharge structures. The surrounding riprap area between
these two structures was examined briefly. Again a heavy, 10 mm thick
layer of floe was noted. Very little inorganic or organic debris was
seen on the riprap. Fish, molluscs, crayfish and macrophytes were not
observed.

DIVE NO. 4, 20 MAY, MIDDLE INTAKE STRUCTURE

Horizontal visibility at working depth with underwater lights was
3.0-4.5 m. The water temperature at the surface and bottom was 10.0 C,
air temperature was 21.1 C. There was no noticeable current, the lake

was calm, and the sky was hazy. Diving conditions were excellent, and
underwater visibility was unusually high.

The floe layer was not as thick (less than 10 'mm) as observed
during the April dives. Very little inorganic or organic debris was
observed on the riprap.

Periphyton was noted on top of the structure, with Ctadophora growing
along the outside edge. Since Ctadophora was not observed on either the
structure or the riprap during the April 1974 dives, it is possible that
this algae does not become available as a fish spawning substrate until
May.

A few crayfish were seen among the riprap. They were solitary, in-
active and hiding in crevices. Snails (JPhysa integra) were very abundant.
In one area of the riprap, 10 were counted in an area of approximately
0.1 m^ (1 sq ft).

The following fish species and their behavior were observed: "

Species

Number

Location

Burbot

1 adult

Top of structure

Channel catfish

1 juvenile

Top of structure

Emerald shiner

1 adult

Top of structure

Carp

1 adult

Riprap near base
of structure

Yellow perch

20-30

Near or resting

adults

on riprap

Johnny darter

100-200

Top of structure

adults

and resting on
riprap

Sculpin

Several

Top of structure

hundred

and resting on
riprap

Behavior

Resting motionless
Resting motionless
Solitary, slow

random swimming
Slow swimming

Solitary, slow

swimming or

motionless
Solitary, active

and alert

Solitary , s tat ionary
and alert

A burbot approximately 45 cm in length was grasped and squeezed, but
exuded no sex products. The carp was swimming steadily and passed by
the divers quickly. Most yellow perch appeared to be "resting" or
"sleeping" and could be touched or grasped. Johnny darters were very
abundant and were seen resting on top of or between the riprap; they

were active, alert and easily frightened. Sculp in were by far the most
abundant species of fish; they were solitary and alert. As noted during
the 1973 diving operations, burbot, catfish, shiners and perch appeared
quiescent at night. Sculpin and darters seemed to be diurnally and
nocturnally active. However, they tended to remain concealed among the
riprap during the daylight hours.

None of the fish were seen to swim near the sides of the structure
or through the intake grids, nor was any schooling behavior observed.
It is interesting to note that only one (yellow perch) of the five
species of fish most common to the area (alewife, spottail shiner,
yellow perch, rainbow smelt and trout-perch) was observed during May
1974 diving operations. In particular, alewives were very abundant
inshore during this time of the year, and no explanation can be
given at this time concerning the absence of this species at the dive
site.

The divers then swam west across the riprap and 10 m onto the sand.
No significant biological changes were noted between the areas of riprap
and sand examined.

Many pieces of riprap were overturned by the divers but fish eggs
were not observed, nor were macrophytes.

DIVE NO. 5, 21 MAY, SOUTH INTAKE STRUCTURE

Horizontal visibility at working depth was 3.5 m. Water temperature
at the surface was 13.3 C, 11.1 C on the bottom. Air temperature was
24.5 C, the lake was calm and there was little wind. There was no
noticeable current.

A portion of the riprap adjacent to the structure was examined and
found to be covered with a thin (3 mm) layer of floe. Periphyton, but
no Cladophora^ grew sparsely on the riprap.

The top of the structure was also covered with a 3 mm layer of floe.
Cladophora was not growing in the central portion of the top of the crib.
Along the extreme edges of the crib it grew sparsely to a length of 4 cm,
wrs green and free of silt. Diving observations have shown that when

Cladophora first appears in the spring, it is initially observed on the
upper outside edges of the intake structures. The combination of direct
exposure to sunlight, relatively shallow depth (4.6 m — allowing greater
light penetration) and beter-than-average water circulation around this
projecting edge may stimulate early growth of Cladophora at this
location.

Upon analysis, a sample of periphyton taken from the top of the
structure was found to contain Cladophora ^ the attached diatom Gomphonema
and the protozoan Vortioella.

Transect swims were conducted as described in the methods section

and results are summarized in Table 3. The bottom composition remained

homogeneous (riprap) throughout all four transect swims. With the

2
exception of the 8.1 snails/m on the north side transect, densities of

2
the organisms observed were usually less than 1/m in each of the four

transects. The high snail density on the north side cannot be explained

at this time. However, uneven distribution of snails has been noted

upon several other occasions. All snails observed were Physa integra.

Many snail egg cases (probably P. integra) were observed, some
containing eggs. Johnny darters were the most frequently observed fish
during this daytime dive, contrary to the previous (night) dive when
sculpin were most commonly seen. One black bullhead was observed when a
piece of riprap was overturned. No other species of fish were noted.
All fish were resting on the bottom; pelagic fish were not observed.

At the end of the dive, a piece of riprap bearing a clump of slimy
sculpin eggs attached in a mass to its undersurface was overturned. The
riprap, with eggs attached, was transported to the laboratory in an
85 liter ice chest filled with lake water, where a hatch of several
hundred larvae took place over a period of 10 min to several hours. The
larvae were later Identified as slimy sculpin {Cottus oognatus) . During
the remainder of the dive approximately 100 more pieces of riprap were
overturned but additional eggs were not found.

Macrophytes were not observed. Little organic debris covered the
riprap, and no large sticks, logs or accumulations of terrestrial
vegetation were seen.

10

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DIVE NO. 6, 22 MAY, NORTH DISCHARGE STRUCTURE

Horizontal visibility at working depth was 3.0 m. The Secchi disc
reading was 3.7 m. Water temperature was 12.0 C at the surface and
11.1 C on the bottom, air temperature was 21.1 C. There was no notice-
able current. During the dive, a storm developed from the southwest
which generated 1 m surface waves. However, with the exception of a
pronounced decrease in light levels, no effect (current, swells, etc.)
of the developing storm was noticed on the bottom.

The riprap surrounding the structure out to a distance of 4.6 to
6.1 m was carefully examined. The riprap on the slot discharge side of
the structure varied in diameter from 20 to 90 cm. There was no notice-
able accumulation of floe in this area, although a few small (less than
0.6 m diameter), thin (less than 15 cm thick and underlain by riprap)
patches of sand were evident. Large patches of sand, troughs or mounds
in the riprap were not seen. Pieces of inorganic scrap were common and
were scattered randomly over the area. The riprap on the back side of
the structure, opposite the slot discharge, was much more homogeneous,
with diameters ranging from 15 to 40 cm. There was a light layer of
floe covering this riprap, but patches of sand were not observed. The
primary differences noted between the riprap surrounding the north dis-
charge structure and that surrounding the south intake structure examined
the day before were: the discharge riprap was coarser, had less floe
covering it, and patches of sand were not observed anywhere in the intake
area.

Transect swims were conducted. During the north swim, many empty

snail shells (Goniobasis sp.) and one severely decayed yellow perch were

noted. Twelve caddisfly larvae were counted during the west transect

swim. The outer 5 m of the east transect swim extended beyond the riprap

onto the sand, therefore the change in bottom composition may have

affected the distribution and subsequent count of organisms. Again,

uneven distribution of snails is evidenced by the density variation

2
between the north transect swims on 21 May (8.1/m ) and 22 May (0). In

this case, the difference in location may account for some of the density

variation.

12

During a general examination of the riprap area surrounding the dis-
charge structure, one dead sculpin and one unidentifiable dead fish were
noted.. Dead fish have been seen during diving operations on only one
other occasion, a dive made 8 km south, off Warren Dunes State Park on
18 June 1973, but never in the vicinity of the Cook Plant. Caddisfly
larvae were numerous, and snail shells were common. Snails were more
frequently observed during both the previous day and night dives (Nos. 4
and 5) in the vicinity of the south intake structure than during this
dive in the area of the north discharge structure. No explanation can
be offered for this difference in distribution. Free-swimming (pelagic)
fish were not observed; fish seen were all solitary adults resting on
the bottom.

The structure and riprap were examined for Cladophora or other
attached algal growth, but none were noted. A large section of a tree
(the stump and a portion of the trunk) approximately 12 m in length with
a trunk base diameter of 1 m was found lying within 3 m of the north
side of the structure, with the stump pointing northwest. The tree had
no apparent macroscopic biota attached to it and remained firmly in
position until July when it was removed mechanically by a crane. Branches
and debris from terrestrial plants were scattered sparsely over the rip-
rap. Macrophytes were not observed.

As in the previous dive, 75-100 pieces of riprap were overturned and
examined for fish eggs. One piece had a small clump of sculpin eggs
attached to the underside. These eggs were transported to the laboratory
in a manner similar to that described in Dive No. 5. However, hatching
did not occur. Microscopic examination of the eggs did show that several
stages of embryonic development had taken place.

DIVE NO. 7, 13 JUNE, SOUTH INTAKE STRUCTURE

Horizontal visibility at working depth was 3.0 m. The Secchi disc
reading was 3.5 m. Water temperature at the surface was 15.3 C and
IS.O C on the bottom, air temperature was 24.0 C. The lake and the wind
were calm. A slight current to the northeast was detected. The bottom

13

was not examined carefully, but a floe layer of average (5-8 mm) thick-
ness was noted.

Cladophora was growing on the edges of the structure, the
top of the ice guard and in isolated patches on the central portion of
the top of the structure. One snail (Physa integra) was noted on the
riprap, and 5-10 crayfish were seen hiding between the rocks.

More than 50 johnny darters were counted, randomly dispersed and
resting on the riprap. Twelve yellow perch were seen randomly swimming
beside the structure and behind the oblique ice guards. Eight-to-ten
slowly swimming, solitary alewives were observed within 3 m of the
bottom. Sculp in were not observed, which was unexpected since they are
very abundant in the area.

Thousands of spottail shiner eggs were observed attached to

Cladophora growing on the top of the structure. Where the Cladophora

2
grew densely, egg counts reached 1-2/cm (approximately 10/sq in),. Most

of the eggs were clear, unbroken and not fungused, indicating viability.

Samples of these eggs were collected during two subsequent dives (refer

to Dives 12 and 13 for further discussion) .

DIVE NO. 8, 13 JUNE, NORTH DISCHARGE STRUCTURE

Horizontal visibility at working depth was 3.0 m. The Secchi disc
reading was 3.5 m. Water temperature at the surface was 15.3 C and
15.0 C on the bottom. Although the upper 2 m of the water column was
only 0.3 C warmer than the underlying water, this temperature differ-
ential was readily detectable to the divers* hands and faces. It is
possible that even such a slight thermal stratification could be detected
by and affect the vertical orientation of thermally sensitive organisms.
The air temperature was 23.9 C and weather conditions were calm. There
was no noticeable current.

Two johnny darters were observed resting on the riprap; no other
fish were observed. The purpose of this dive was to orient new divers
and to test a small centrifugal pump designed to sample planktonic
organisms and fine sediment on or immediately above the bottom. This

14

method of sampling might be applied to areas where near or on bottom
sampling is desirable, but where conditions (rocks, logs, weeds, etc.)
prevent effective use of conventional sampling devices (plankton nets,
sleds, or ponar grab samplers). The pump was effective and may be in-
corporated into future sampling operations.

DIVE NO. 9, 13 JUNE, 6.1 M CONTOUR DIRECTLY SOUTH OF THE SOUTH DISCHARGE
STRUCTURE

Horizontal visibility at working depth was 3.0 m. The Secchi disc
reading was 3.5 m. Water temperature at the surface was 15.3 C and
15.0 C on the bottom. Air temperature was 23.9 C, weather conditions
were calm, and there was no noticeable current. The area examined con-
sisted of a transect 3 m wide by 160 m long. The transect began directly
out from the south range pole (Fig. 1) in 6.1 m of water and proceeded
south along the bottom. The purpose of the dive was to e^tamine tjie
fishing position and entrapment mechanism of a 2 m x 160 m multifilament,
nylon-twine, sinking gill net, and to investigate the bottom area immedi-
ately adjacent to it.

The bottom consisted of well-sorted sand with no noticeable floe
covering it. Large ripple marks 15-20 cm apart, 2.5 cm high and 50-90 cm
in length were running from the northwest and were cross-hatched by
smaller asymmetric ripple marks running from the west and southwest.

Loose algae (Spirogyra) had accumulated in patches 2.5-7.5 cm in
diameter with a frequency of 2-5 patches/m . Clumps had been collected
during the previous few days in seines, trawls, gill nets and plankton
nets. Aggregations of this algae had not been noticed during previous
dives in the area. Since the algae was unattached, it may have been
washed into the area. Macrophytes and organic debris were not observed.

Observations pertaining to the fishing position and entrapment
mechanism of the described net were:

1) Tangles or twists in a 2 m high net can render a 2-3 m section in-
effective.

2) The use of spreaders at each end of the net greatly increased the
width and effectiveness of the first 3 m of the net.

15

3) Algae accumulation on the netting mesh greatly increased the visi-
bility of the net.

4) Close mesh sections (1.3 cm bar mesh) of the net were visually more
prominent than the large mesh sections (10.2 cm bar mesh).

5) Direction of fish entry, i.e., direction of their movement, was
easily determined; 75% of the fish entered from the west side (the net
was set north to south, parallel to shore).

A total of 683 alewives, 9 yellow perch and 8 spottail shiners were
taken in this net, primarily in the first three of 11 panels of progres-
sively increasing mesh size. The net was set from 0610-1830 hr (12 1/4
hr) and the dive was made during the last 2 hr. Two points should be
noted: first, the efficiency of the panels in which the fish were caught
was greatly reduced by the end of the set. The panels, which contained
alewives, were very conspicuous to the divers because the fish were
actively twisting and turning. Second, although fish were obviously
present in the area of the dive and visibility was good, free-swimming
fish were not observed. This suggests that failure to observe fish does
not exclude their presence from the area of observation. Most likely,
diver estimates of pelagic fish abundance are quite rough. The fish
probably sense the divers' presence and retreat from the area before
they are visible to the divers. Observations of fish in our study area,
where the visibility seldom exceeds 4 m, can best be made at night with
underwater lights and when the visibility is 3-4 m. Once in the water,
if the divers remain immobile they will reduce the tendency for their
movements to disturb fish in the area. Our observations indicate that
many of the fish in our study area appear to be less sensitive to stimuli
(movement, vibration, etc.) at night.

DIVE NO. 10, 13 JUNE, SOUTH INTAKE STRUCTURE

Horizontal visibility at working depth with underwater lights was
2.3 m. Water temperature at the surface was 15.3 C and 15.0 C on the
bottom. Air temperature was 15.6 C, the lake was calm, there was little
wind and the air was cool. No noticeable current was present.

16

A few crayfish were seen hiding among the riprap. Snails (P.

integra) were very abundant although, as has been noted consistently

during both transect swims and general observations, their distribution

was uneven. The density of snails at one location was estimated to be

2
100-150/m (10-15 sq ft). Snail egg cases were very abundant, but their

distribution was also uneven.

During the observation period, many fish were seen on top of the

structure. Spottail shiners were abundant, with a density in the first

3
meter of water above the top of the structure estimated to be 10/m .

These fish appeared to concentrate near the top of the structure and

none were seen while descending or ascending.

The spottails were swimming randomly, not schooling or spawning,
and when captured and squeezed did not exude gonadal products. Spottail
shiners were not observed at a level below the top of the structure. It
appeared that sculpin were less abundant than during the previous night
dive. Eight johnny darters were noted, all resting on the riprap.

Approximately 20-30 alewives were observed scattered throughout the
4.6-9.1 m depth interval, all adults, solitary and not observed to remain
stationary or approach the riprap. The infrequency of observed alewives
was unexpected because, during fishing operations in the area the night
before, extremely large numbers of alewives were seen "jumping" and
schooling on the surface. However, if the alewives were concentrating
at the surface, they might not be observed in large numbers at the depths
(4.6-9.1 m) where we were diving.

The primary intent of this dive was to contrast day/night levels of
species diversity, abundance and behavioral activity. As noted on
previous occasions, the species diversity and abundance of fish and the
number of snails observed was much higher at night than during the day.

DIVE NO. 11, 14 JUNE, NORTH DISCHARGE STRUCTURE

Horizontal visibility at working depth was 3.0 m. The Secchi disc
reading was 3.5 m. Water temperature at the surface and bottom was
15.0 C. Air temperature was 22.2 C, the lake was calm and there was
little wind. A slight current to the northeast was present.

17

The bottom in the vicinity of the slot (jet) discharges was examined
for scour; none was observed. Inorganic scrap was scattered lightly over
the riprap on the slot side of the structure. On the north side of the
structure, the riprap extended outward 5 m at which point the sand bottom
began. The sand/riprap boundary was located a similar distance from the
structure on the northeast side. The large tree stump described in Dive
No. 6 appeared to have maintained its position. There was no evidence of
Ctadophora growth on either the structure or the riprap.

Transect swims were conducted. The number of snails observed in
the south transect was higher this month than during the preceding month
(Dive No. 6) and johnny darters were seen less frequently in all four
transects. Many snail egg cases were noted during the east transect swim.
Five empty snail shells (P. integra) were counted during the west tran-
sect swim, as well as five juvenile alewives and one adult carp.

A fragment of a large (5-6 diameter cm) gastropod shell was collec-
ted ; not enough was present to make an identification. Johnny darters were
numerous in certain areas of the riprap, and alewives were observed
swimming in small schools of less than 50 fish. The observation of the
large fish, a carp approximately 60 cm in length, was unusual, as large
fish in this area are seldom seen by divers. Biological activity was
higher this year than observed at this location and time during the
previous year (17 June 1973).

Two samples of periphyton were collected, one from the riprap and
one from the top of the structure. A qualitative analysis of the samples
is summarized in Table 4. Four species of green algae and 13 species of
diatoms were found in the sample taken from the riprap. Five species of
green algae, one species of blue-green algae and 14 species of diatoms
were found in the sample taken from the top of the structure.

DIVE NO. 12, 14 JUNE, SOUTH INTAKE STRUCTURE

Horizontal visibility at working depth was 3.5 m. The Secchi disc
reading was 3.5 m. Water temperature at the surface was 15.0 C. Air
temperature was 22.2 C, the lake was calm, there was no wind and the sky
was overcast. A slight current to the northeast was present.

18

TABLE 4. Algae and diatoms observed in qualitative analysis of peri-
phyton collected in southeastern Lake Michigan near the Donald C. Cook
Nuclear Plant during 1974 diving operations. ND = North Discharge
Structure, MI = Middle Intake Structure.

Sampling location

Riprap

Top of
structure

14 Jun

ND

23 Oct

24 Oct

MI

ND

24 Jun

ND

23 Oct

MI

Green algae
Ctadophora sp.
Clostevtopsis sp.
Oocystis sp.
Pediastvwn duplex
Pediastrum tetras
Soenedesmus quadricauda
Sp-irogyra sp.
Utothrix sp-

Blue-green algae
Oscillatoria sp.

X
X
X

X
X

X
X
X
X
X

Diatoms

Amphipleura pellucida
Amorpha ovalis
Amorpha sp-
Asterzonella formosa
Coooonesis sp.
Cymatopteura solea
Cyclotelta ocellata
Cymbella ventricosa
Cyrribella sp.

Diatoma tenue v. elongation
Diatoma tenue
Fragilaria crotonensis
Gomphonema sp.
Gyrosira sp.
Melosiva gvanulata
Melosira varians
Melosira sp.
Navicula sp.
Nitzschia sp.
Ehizosolenia eriensis
Rhoicosphenia curvata
Stephanodiscus niagavae
Stephanodiscus minutus
Stephanodiscus tenuis
Stephanodiscus sp.
Surirella angusta
Surirella ovata v. pinnata
Synedra ulna
Synedra sp.
Tabellaris fenestrata

X
X
X

X
X

X
X

X

X

X
X

X
X

X

X
X

X
X

X

X

X
X
X

X
X

X
X

X

X

X

X

X
X

X
X

X
X

X

X

19

The purpose of this dive was to collect samples of fish eggs
attached to Ctadophora growing along the top edges of the structure.
Egg samples were collected and incubated in the laboratory. Five spot-
tail shiner larvae were hatched. This identification was based upon
measurements of egg diameters, knowledge of the concurrent distribution
and gonad condition of fish species in the area, use of fish identifi-
cation keys and comparison of the hatched larvae with specimens of
known identity.

Alewives and yellow perch were observed swimming around the top
and sides of the structure. The base of the structure and surrounding
riprap were not examined.

DIVE NO. 13, 26 JUNE, SOUTH INTAKE STRUCTURE

Horizontal visibility at working depth was 1.8 m. The Secchi disc
reading was 2.7 m. Water temperature at the surface was 15.0 C and
13.5 C on the bottom. Air temperature was 14.0 C and weather conditions
were calm. Although there was no noticeable current, surface wave action
was quite evident on top of the structure.

The purpose of this dive was to collect additional samples of fish
eggs observed during previous dives in the area (Dives 7, 10 and 12).
These eggs were first observed 13 days prior. By the time of this dive,
the number of eggs attached to the Ctadophora was greatly reduced. Also,
the majority of the eggs were now either empty shells or covered with
fungus. The Ctadophora was growing in uniform density along the top edge
of the structure and was approximately 7.5 cm in length. One adult
yellow perch was observed.

DIVE NO. 14, 22 JULY, 6.1 M CONTOUR DIRECTLY SOUTH OF THE SOUTH DISCHARGE
STRUCTURE

Two core samples were taken at each of five stations located along
the 6.1 m depth contour. The first station was 100-200 m south of the
discharge area, and each of the following four stations was approximately
100 m south of the preceding one. Besides taking core samples, the
divers had an opportunity to observe the lake bottom at locations outside

20

the riprap area. Analysis of the core samples showed both the presence

2
and wide variation in density per m of fish eggs, probably alewife.

Analysis and discussion of these core samples can be found in Mozley

(1975).

Horizontal visibility at working depth was 1.5-1.8 m. Water tem-
perature at the surface was 15.6 C, 15.0 C on the bottom. The water was
unusually cold for this time of the year as the result of an upwelling
accompanying offshore winds. Air temperature was 17.2 C, and there was
a slight northerly current.

The bottom consisted of well-sorted sand which varied from station
to station in mean grain size and degree of compactness. At some of the
stations, the coring tubes were easily pushed into the bottom (depth of
the core was 15 cm) while at other stations the tubes were forced into
the bottom with some difficulty. Ripple marks at the five stations were
constant in size, 10 cm apart, 4 cm high and 60-90 cm in length, running
from the northwest. Silt pockets were not observed. Although a few
empty shells and shell fragments were noted in the troughs of the ripple
marks, no live molluscs were seen. Live fish were not observed; one
dead alewife was seen. Algae, macrophytes and organic debris were not
observed.

DIVE NO. 15, 23 JULY, 9.1 M CONTOUR DIRECTLY SOUTH OF THE SOUTH INTAKE
STRUCTURE

This dive was similar to Dive No. 14. Two core samples were taken
at each of five stations located along the 9.1 m depth contour. The
first station was 100-200 m south of the intake area, and each of the
following four stations was approximately 100 m south of the preceding
one. Two other locations in the area were examined, and two 100 m swims
were conducted during the course of the dive.

Horizontal visibility at working depth was 1.5 m. Water temperature
at the surface was 15.6 C, 7.8 C on the bottom. The thermal interface
was v€iry well-defined, but the depth at which it occurred was not
determined. A noticeable current to the southeast was present. Cold-
wate^ upwelling, poor visibility and rough surface conditions combined
to make diving conditions poor.

21

At the five coring stations and two other locations, as well as
during the two 100 m swims, the bottom type varied more than had been
observed during previous dives in this area south of the riprap zone.
The increase in variability may have resulted from the larger number of
observation stations and the greater alongshore distance covered,
compared to previous dives such as No. 9 when only 160 m was swum.
Bottom types encountered included: 1) hard, fine sand; 2) hard, fine
sand with patches of loose algae and organic debris present (patches

were 2.5-7.5 cm in diameter and occurred with a frequency of approxi-

2
mately 1/m ); 3) soft sediment 2.5-5.0 cm thick, overlying hard sand;

4) coarse sand displaying large ripple marks. This final bottom type

was encountered at the location furthest from the plant — approximately

2000 m. The large ripple marks were 20 cm apart, 3 cm high and running

from the northwest. Ripple marks observed at all the previous locations

examined were 10 cm apart, 1.5 cm high and running from the norttiwest.

As in the previous dive, live molluscs were not observed although

shell fragments were present at several locations. No live fish were

observed. Four dead alewives were counted. Macrophytes were not

observed.

DIVE NO. 16, 24 SEPTEMBER, NORTH DISCHARGE STRUCTURE

Horizontal visibility at working depth was 1.8 m. The Secchi disc
reading was 1.5 m. Water temperature at the surface and bottom was
17.0 C. Air temperature was 23.9 C, and the sky was partly cloudy. A
current to the north was noted.

Both the top of the structure and the riprap were covered with a
thin layer of floe (3 mm) . The riprap surrounding the structure was
examined for scour, but none was observed. The bottom area to the north
and northwest of the structure was examined out to the riprap /sand
boundary. This area appeared to be the same as when last examined (June,
Dive No. 11). Limited water pump circulation from the plant had taken
place between July and September.

Cladophova was growing on top of the structure to a length of 3-4 cm.
Growth was uneven but extensive and extended at least 1.8 m inward from

22

the edge of the structure. This was the first occasion in 1974 during
which Ctadophora was observed to be growing on this structure.
Cladophora was not observed growing on the riprap surrounding the
structure. Relatively large (1-3 m diameter) loose aggregations of
organic debris (planks, tree branches, small stumps, leaves and dune
grass) were randomly scattered over the bottom on the south and east
sides of the structure. Macrophytes were not observed.

Snails (P. integra) were abundant on the riprap. Gastropod (P.
integra and Goniobasis sp. or Pleurocera sp.) and sphaeriid shells had
accumulated in abundance on small patches of sand adjacent to the base
of the structure.

Sculpin and crayfish were abundant but were hiding beneath the rip-
rap and were frequently not observed unless the stone was overturned.
Two johnny darters were seen on the sand north of the riprap; none were
seen on the riprap. Pelagic fish were not observed.

DIVE NO. 17, 23 OCTOBER, MIDDLE INTAKE STRUCTURE

Horizontal visibility at working depth was 1.2 m with underwater
lights. Water temperature at the surface and on the bottom was 13.0 C.
Air temperature was 16.7 C; the lake and the wind were calm. Almost
constantly for 5 weeks prior to this dive, the weather was inclement and
seas had been rough. During this dive, both a current to the north and
surface wave action were noticeable.

The floe layer on the top of the structure and the riprap was of
average thickness, 5 mm. This was somewhat unexpected, since after 5
weeks of increased water mixing and sediment suspension, either an
unusually heavy settling out of floe or removal of floe from the area
might have been expected.

Cladophora 2-4 cm in length was growing on top of the structure and
sparsely on the sides of the ice guards. The upper surface of the rip-
rap was also covered by Cladophora 1-2 cm in length. The algae on the
structure and the riprap was examined for fish eggs; none were observed.
Numerous pieces of riprap were overturned but fish eggs were not ob-
served among the stones. However, bryozoa were growing on the sides of

23

two pieces of riprap. The combination of high oxygen levels, clear
water, dim light and a relatively silt-free surface (sides of riprap)
apparently constituted a suitable habitat for bryozoa. This was the
first observation of this organism. Upon casual examination, bryozoan
colonies such as these could be mistaken for snail egg masses, so care
will be taken in the future to distinguish between the two. Little
organic debris was encountered. Macrophytes were not observed.

One piece of riprap collected from the southwest side of the
structure was covered with a thin mass of freshwater sponge. This was
the first time that sponge was observed by divers, although it had been
collected previously from the intake forebay of the plant during en-
trainment sampling procedures.

Even when the riprap was overturned, crayfish were not observed.

This was contrary to summertime observations, when crayfish were often

quite abundant. Snails (P. integra) were very abundant but uneverj in

their distribution. In one area, counts indicated an approximate

2
density of at least 80 snails/m , with the true density possibly being

much higher. Other areas appeared devoid of snails.

Approximately 10 large sculp in were counted on top of the structure.

They could be approached to within a few centimeters without being

disturbed. When disturbed, they swam only a meter or so before coming

to rest. The density of sculp in on top of the structure was estimated

2
at 0.5 fish/m . Several sculpin were seen resting on the oblique sides

of the ice guards, and 50-75 were seen between the riprap. As with the

2
snails, the density of sculpin varied from zero to several fish per m .

One large and one medium sized adult lake trout were observed
briefly as they swam slowly through the range of the underwater lights.
The sighting of large fish, particularly salmonids, was unusual; perhaps
these trout may have been attracted to the underwater lights. No other
species of fish were observed.

A qualitative analysis of the periphyton samples collected from
both the top of the structure and the riprap is presented in Table 4.
Compared with the other samples presented in the table, the sample
taken from the riprap contained relatively few species of algae and
diatoms.

24

DIVE NO. 18, 24 OCTOBER, NORTH DISCHARGE STRUCTURE

Horizontal visibility at working depth was 3.5 m. The Secchi disc
reading was 4.0 m. Water temperature at the surface and the bottom was
13.0 C. Air temperature was 21.1 C, the lake was calm and there was no
wind. A very slight current to the northeast was present. As noted in
Dive 17, the weather preceding this dive had been inclement.

Both the top of the structure and the riprap were covereid with a
relatively heavy layer of floe 5-8 mm thick. The riprap surrounding the
structure was examined carefully, and a trough was noted on the east
side of the structure, running perpendicularly outward. Beginning 1 m
from the base of the structure, it was 3 m long, 1 m deep, 2.5 m wide
at the top and 1.2 m wide at the base. The bottom of the trough con-
sisted of sand and the sides of 7-15 cm diameter riprap. The sand
extended up to the base of the structure, and at one point midway along
the trough a diver dug 30 cm into the sand bottom but failed to encounter
riprap. Indications of riprap scour were not observed on the south,
west, or north sides of the structure. A swim of approximately 400 m
was conducted from the south side of the north discharge structure to
a point 100 m southwest of the south discharge structure. Nothing
unusual was observed.

Cladophora was growing on top of the north discharge structure and
was considerably longer and more luxuriant than that observed on the top
of the middle intake structure (Dive No. 17). During the 400 m swim,
Cladophora was also seen growing on the riprap. In general, the
Cladophora growth was longer and more luxuriant in the discharge area.
Dive No. 18, than in the intake area. Dive No. 17.

Snails (P. Integra) were abundant on the riprap adjacent to the
south and east sides of the structure. Again distribution was uneven.
One crayfish was observed while overturning pieces of riprap. Four
sculp in were seen hiding among the riprap.

Small (0.3-1.0 m diameter) scattered patches of organic debris
consisting of leaves, roots, branches and dune grass were noted on the
riprap to the west and south sides of the structure. Macrophytes were
not observed.

25

A qualitative analysis of a periphyton sample collected from the
riprap is presented in Table 4. No sample was taken from the top of
the structure. One species of green algae and 15 species of diatoms
were identified.

DISCUSSION

1) Table 5 summarizes the species of fish observed during 1973
and 1974 diving operations.

TABLE 5. Summary of fish species observed during 1973 and 1974 diving
operations in southeastern Lake Michigan, near the Donald C. Cook
Nuclear Plant. Species are listed by location and date in order of
descending frequency of observation.

Location

1973

1974

Area of intake

structures (riprap)

Area of discharge
structures (riprap)

Areas outside the
riprap zone

Sculpin
Johnny darter
Alewife
Yellow perch
Spottail shiner
Trout-perch
Not observed
Not observed
Not observed
Not observed
Not observed
Not observed

Sculpin
Johnny darter
Yellow perch
Not observed
Not observed

Johnny darter

Sculpin
Johnny darter
Alewife
Yellow perch
Not observed
Not observed
Carp

Lake trout
Burbot

Emerald shiner
Channel catfish
Black bullhead

Sculpin
Johnny darter
Not observed
Alewife
Carp

Not observed

26

A total of twelve species have been observed during the two field
seasons. In 1974, one species of fish very common to the area, spot-
tail shiner, was not seen. Rainbow smelt have never been observed by
our divers, probably because the adult fish spawn inshore in the early
spring prior to the commencement of diving operations and then migrate
offshore, remaining there past the end of the diving season.

Large fish are seldom observed by divers. Demersal fish, such as
darters and sculp in, are more frequently observed by divers than pelagic
fish. When a diver's presence is sensed, pelagic fish tend to retreat
from the area, whereas demersal fish hide on the bottom or between the
riprap. Fishing efforts have shown that in this area lake trout con-
centrate inshore during the fall and are most active at night. Although
only one night dive (No. 17) was performed during the fall, two lake
trout were observed. Prior to this, lake trout had never been observed
by our divers. Additional data from fall nighttime diving should
continue to document the known inshore concentration of these fish
during this time of the year, and their predominantly nocturnal activity.

2) Fish eggs were observed during two months of diving activity.
In May, slimy sculp in eggs were collected from riprap in both the intake
and discharge structure areas. During June, spottail shiner eggs were
collected from Cladophora growing on top of the south intake structure.
In both cases the eggs were attached, not pelagic, and larvae were
hatched from them in the laboratory. Two conclusions may be drawn from
these observations. Since the eggs were attached (not pelagic),
spawning of slimy sculpin and spottail shiners does occur in the area
with Cladophora and riprap serving as substrates. This observation is
supported by observations made in June 1973, when our divers saw spottail
shiners spawning in the Cladophora attached to the south intake structure
and collected samples of their eggs. Second, based on the advanced stage
of embryonic development of the slimy sculpin eggs and the number of
empty spottail shiner egg shells observed, it can be safely assumed that
in this area the eggs of these two fish species incubated and hatched
successfully during 1974.

27

3) Crayfish were observed during every month of diving. As
indicated by observations in the individual dive reports, the abundance
of crayfish varied greatly over both space and time.

4) Physa integra was the most frequently observed gastropod and
was seen during all months that diving operations were conducted.
Shells from either the genus Goniobasis or Pleurooera were collected.
However, poor condition prevented identification at the species level.

5) Sphaeriid (fingernail clam) shells were frequently observed.
Live specimens were not often seen, probably because only the exposed
surface of the bottom was examined, not the underlying strata.

6) Macrophytes were not observed on any occasion.

7) Eight species of green algae, one species of blue-green algae
and 30 species of diatoms were noted in samples collected in the
vicinity of the Cook Plant (Table 4) . Only one green algae (Spirogyra
sp.) was observed outside the riprap area.

8) Cladophora was not seen on the south intake structure in April
but was present by May and remained through the last dive of the field
season (October). Cladophora was not observed on the north discharge
structure in April, May or June. Dives were not performed in this area
during July or August. Cladophora was first noted on the north discharge
structure in September and remained through the last dive of the field
season. It was observed only sporadically on the riprap in the intake
and discharge areas; growth was unusually sparse and occurred pre-
dominately during the summer months. Generally, the growth of Cladophora
in this area appears to reach a seasonal maximum length and density
between late June and July. This maximal growth level is maintained
through early September. It then probably tapers off in late fall as
temperatures fall and light levels diminish, reaching a minimum in late
winter or early spring. Refer to Dive No. 4 for a discussion of the
seasonal availability of Cladophora spawning substrate.

9) The floe layer (consisting primarily of sediments, organic
detritus and diatomaceous material) varied from less than 3 mm to

28

approximately 10 mm in thickness, depending upon the location and the
date; 5 mm represented a layer of average thickness. The floe layer was
much lighter outside the riprap area than within it.

10) Dead fish and patches of organic debris were occasionally
observed. However, during the annual late-spring alewife dieoff, dead
fish were still only infrequently observed on the bottom.

11) With the exception of Dive No. 18, no scour or other significant
disturbances of the riprap were observed.

12) As the divers swam along the bottom, the intensity of reflected
light noticeably decreased as they passed from sand to riprap. Pelagic
organisms might be attracted to or repelled from an area such as the
riprap, where bottom reflected light levels are lower than the surrounding
area.

13) The distribution of snails, crayfish and other biota often
appeared uneven (Table 3). It may well be that the distribution of many
biota (speaking primarily of demersal organisms in the case of diving
observations) is uneven. Also, the methods, area examined and frequency
of observations (including all diving observations) may have been in-
sufficient to determine any overall patterns of unevenness or continuity.

14) During any monthly series of dives, observed biological activ-
ity and diversity was higher at night than during the day and was much
higher within the riprap area than outside it.

15) Transect studies (Table 3) were conducted for the purpose of
developing methodologies for quantifying observations. Although monthly

and seasonal (comparing Table 3 with 1973 transect observations) vari-

i,
2

2
at ion occurred, density expressed as number of organisms /m remained

between 0-10/m

CONCLUSION

The seasonal trend in biological activity and diversity, as observed

29

by divers, appears to begin with a sharp late-spring increase (between
early April and mid-May) , reaching a maximum during the summer months
and then tapering off gradually in the fall, probably between mid-
September and late-November. In general, this observed pattern is
supported by concurrent sampling studies. Compared to the surrounding
inshore zone of the lake (30 m or less), the riprap area appears to
attract fish and invertebrates, possibly because it offers greater
shelter, an increased supply of food or simple physical attraction.
This attraction which concentrates fish and invertebrates was observed
during 1973 and again in 1974. The end result is the establishment of
a small ecosystem which is atypical of the surrounding area.

1975 PROGRAM OBJECTIVES

A standard series of five monthly (April-November) observational
dives is scheduled. They will include day and night observations in
the areas of the south intake and discharge structures and at control
stations outside the riprap. Operations, observations and analysis
will include:

1) Observations for:

Scour and general status of the riprap

Suspended material and floe deposition

Inorganic and organic debris and decaying material

Attached algae/periphyton - visual analysis and

monthly sampling
Macrophytes

Crayfish, molluscs and other macro-invertebrates
Fish, fish eggs and fish larvae

2) Limited observations in the plume in an area to the north and
outside of the riprap area.

3) Supplemental sampling operations such as coring, if such sampling
is warranted.

4) An attempt will be made to quantify observations whenever possible,
for the purpose of facilitating comparisons in space and time.

30

Quantification efforts will be emphasized in planned transect swim
studies. An example of the recording format to be used during ob-
servations is presented in Figure 2, for the purpose of illustrating
the manner and direction towards which our quantification efforts
are proceeding.

5) Day-night comparisons in faunal diversity, abundance and activity.

6) Comparison of floral and faunal diversity, abundance and activity
in the areas of the intake structures, discharge structures and

TEMP.

. VISIBfUTY (HORIZ. AT WORKING DEPTH)

. GRAVEL SAND MUD.

. CURRENT: NO .

. DIR. .

»OnOMCOIV\P.r»)j ROCK

RIPPLE AAARKS; NO 01 R. FROM LENGTH HEIGHT NOTES.

OTHER .

SCOURi INDICATIONS
LOCATION

INORGANIC DEBRIS: NO .

. AMT. & AREA SIZE ,

LOCATION & OESCR

ORGANIC DEBRIS: NO AA\T. L AREA SIZE .

LOCATION & DESCR

SUSPENDED MATERIAL: NO DESCR

MACROPHYTES: NO LOCATION & DEPTH

ALGAE. NO LOCATION DEPTH ,

PEWPHYTON: NO-

. LOCATION ,

ClAAAS: # LIVE & AREA SIZE .

SNAILS: # LIVE & AREA SIZE .

CRAYFISHi # LIVE i AREA SIZE

FBH EGGt LOCATION

riSH SPECIES SIZE

. DEPTH .

. AREA SIZE .

.DESCR.
.DESCR.,

. LENGTH .
. LENGTH .

i SHELLS i AREA SIZE .

, # SHaLS & AREA SIZE -
, LOCATION

? SPECIES-
. BEHAV. «

. DEPTH NATURE OF DEPOSIT .

#1. AREA SIZE DEPTH

LOCATION

BEHAVIOR

FIG. 2. Underwater data-recording format to be implemented during
1975 diving operations in southeastern lake Michigan near the Donald
C. Cook Nuclear Plant.

31

control stations. Comparisons will be made on a diel, monthly
and seasonal basis.

7) General visual analysis of the physical and biological status of
the area near the Cook Plant.

REFERENCES

Dorr, J. A. III. 1974. Underwater operations in southeastern Lake

Michigan near the Donald C. Cook Power Plant during 1973, p. 465-
475. In E. Seibel and J. C. Ayers (eds.). The biological, chemical
and physical character of Lake Michigan in the vicinity of the
Donald C. Cook Nuclear Plant. Univ. Michigan, Great Lakes Res.
Div. Spec. Rep. 51. 475 p.

Mozley, S. C. 1975. Preoperational investigations of zoobenthos in
southeastern Lake Michigan near the Cook Nuclear Plant. Univ.
Michigan, Great Lakes Res. Div. Spec. Rep. 56. 132 p.

32