•
, I
An Experimental Fishfarm
for Salmon at the
Pacific Biological Station
by W. A. Kennedy
FISHERIES AND MARINE SERVICE
SERVICE DES PECHES ET DES SCIENCES DE LA MER
TECHNICAL REPORT No.
RAPPORT TECHNIQUE N'
1975
543
.+
Environment
Canada
Environnemenl
Fisheries
and Marine
Service
Service des peches
el des sciences
de la mer
Canada
Technical Reports
Technical Reports are research documents that are of sufficient impoltance to
be preserved, but which for some reason are not appropriate for primary scientific
publication. Inquiries concerning any particular Report should be directed to the
issuing establishment.
Rapports Techniques
Les rapports techniques sont des documents de recherche qui revetent une assez
grande importance pour etre conserves mais qui, pour une raison ou pour une autre,
ne conviennent pas une publication scientifique prioritaire. Pour toute demande
de renseignements concernant un rapport particulier, iI faut s'adresser au service
responsable .
a
Department of the Environment
Ministere de l'Environnement
Fisheries and Marine Service
Service desPeches et des Sciences de la mer
Research and Development Directorate
Direction de la Recherche et Developpement
TECHNICAL REPORT NO. 543
RAPPORT TECHNIQUE NO. 543
(Numbers i-456 in this series were
(Les numeros 1-456 dans cette serie furent
issued as Technical Reports of the
utilises comme Rapports
Fisheries Research Board of Canada.
T~chniques
l'office des recherches sur les pecheries
The series name was changed with
du Canada.
report number 457)
Le nom de la serie fut change
avec Ie rapport numero 457)
AN EXPERIMENTAL FISHFARM FOR SALMON AT THE
PACIFIC BIOLOGICAL STATION
by
W. A. Kennedy
This is the 242
de
nd
Technical Report
from the Pacific Biological Station
Nanaimo, British Columbia
April 1975
- ii -
ACKNOWLEDGEMENTS
I welcome this opportunity to thank Messrs. P. Ryan and D. J. Redman
for a great deal of effort in developing plans and supervising construction;
Mr. A. A. Denbigh for the excellent drawings used here; and Mr. W. Griffioen
for some of the photographs used.
-
iii -
ABSTRACT
Kennedy, W. A. 1975. An experimental fishfarm for salmon at the Pacific
Biological Station.
Fish. Mar. Ser. Res. Dev. Tech. Rep. 543: 33 p.
Facilities are described in which 50,000 salmonids can be reared to
market size, in fresh water as fry and in pens in the sea thereafter.
Noteworthy features of the seapens are: hollow concrete floats; the way floats
are connected; anchoring system; a unique method of keeping pens (made of
nylon netting) taut and square. Techniques for changing pens and ror estimating
fish numbers are described.
Kennedy, W. A. 1975. An experimental fishfarm for salmon at the Pacific
Biological Station.
Fish. Mar. Ser. Res. Dev. Tech . Rep . 543: 33 p .
On decrit quelque am~nagements pour l'elevage de 50,000 sa1monides
jusqu' une taille vendable, avec l'eau douce pour les fretins et avec les
cages dans 1a mer quand il sontplus grand. Les cages dans 1a mer sont notables
pour: les radeaux creux en " beton; la facon
joindrent·
., dont les radeaux
,se,
' la
method d'ammarage; une martiere unique pour faire etarque et carre les cages,
qu'on fait avec 1e filet de nylon. On decrit les techniques pour changer 1es
cages et pour evaluer les nombres des poissons.
- 1 -
INTRODUCTION
Facilities for an experimental fishfarm were recently completed at
the Pacific Biological Station, Nanaimo, B.C. Included are the equipment
for hatching sa1monids and rearing them to the smolt stage in fresh water,
plus netpens for holding captive fish in the sea until they reach market size.
Capacities of the freshwater facilities and seapenS are consistent ~ith
producing about 50,000 fish averaging 300 g each (market size) from about
100,000 fertilized eggs.
The experimental fishfarm is expected to play an important part in
establishing commercial fishfarming as a viable industry on the west coast of
Canada. Information resulting from rearing sizeable numbers of fish under
simulated commercial conditions should be very useful to anyone weighing the
pros and cons of becoming a fishfarmer. At the same time the experimental
fishfarm should serve as a means both of developing suitable rearing techniques
and of demonstrating those that have been developed.
Techniques for hatching sa1monids and rearing them in fresh water
have been developing for more than a century and are well established. On the
other hand salmon have only recently been reared on a large scale in seapens.
It therefore seems appropriate to report in greater detail on the marine
facilities than on the freshwater.
HISTORY
Starting in 1968, a common interest in maricu1ture led to a series of
informal meetings of several biologists at the Pacific Biological Station
(Brett et a1. 1972). One result was that 1 undertook to develop a design for
a flotation system for supporting pens etc. in or on which marine organisms
could be reared. With the help of a local engineering firm a tentative design
was developed but no further action was taken at that time. When, in early
1973, approval was given to establish the experimental fishfarm at the Patific
Biological Station, it became necessary to plan and construct a flotation
system to support the seapens contemplated. Using elements from the earlier
design, but with many modifications and improvements, Mr. Peter Ryan, an
engineer with Fisheries and Marine Service, Environment Canada, designed and
supervised construction and assembly of the ferroconcrete floats, of the
bridges that connect them and of the stiff1egs and cables that anchor the
whole system. Engineering aspects are reported in detail in a separate report
(Ryan 1975).
1 designed the netpens using as a general pattern the crib part of the
type of poundnet used on the Great Lakes (Kennedy 1966). Considerable adapta~
tion was necessary because Great Lakes poundnets are designed ' for a tideless
condition. A major objective was to design a netpen that would require using
neither divers nor ponderous equipment for servicing.
2
The sea pens became operational in May 1974. Most of the freshwater
facility was operational by the end of 1973 but part was not finished until
November 1974.
HATCHING AND FRESHWATER REARING
Facilities for hatching salmon eggs and for rearing young salmon in
fresh water (or in pumped sea water if required) are located in the basement
of the Taylor Building, Pacific Biological Station. Floors and ceilings are
of concrete, and walls are either concrete or painted plywood, all being
readily cleanable. Entry to the hatching and rearing area is through an
anteroom where outdoor clothing is left, hands washed, and special footwear
and lab. coat put on before proceeding.
A widely used, commercially produced incubation tray is used for
hatching eggs; there are three stacks of them, eight trays per stack.
Normally water passes once through the stack but, should the supply fail,
an emergency pump is activated and recycles water.
There are eight fiberglass troughs for rearing alevins and early fry.
They are 365 X 40 cm by 20 cm deep (12 ft X 16 in X 8 in) usually holding
about 13 cm (5 in) of water. The troughs and supports were made from molds
developed at the Freshwater Institute, Winnipeg. Water height is controlled
by an adjustable downstream standpipe.
Ten fiberglass tanks are available for rearing fish from fry to
smolts. They are oval, 230 X 180 cm by 120 cm deep (9 X 7 X 4 ft) and usually
are filled to the 90 cm (3 ft) level at which they hold 4,500 liters (1,000
gal). Incoming water is directed tangentially, which, together with the nearly
round shape of the tank, plus central drain, causes it to rotate and gradually
spiral into the centre thereby making the tank largely self-cleaning. The
tanks are supported about 90 cm (3 ft) above the floor so that modifications
can be easily made (recirculation of used water is contemplated). A wooden
false floor about 120 cm (4 ft) above the real floor facilitates servicing
·the tanks.
Fresh water and
heated are piped to each
fresh water are piped to
raise water temperatures
sea water, each both at ambient temperatures and
tank and trough. Both ambient temperature and heated
the incubation tray stacks. Thus it is possible to
in order to promote faster growth.
The freshwater supply is Nanaimo city water that has been decholoriated
and aerated. The seawater supply is pumped locally, the intake being about 18 m
(60 ft) below the sea surface at low tide. It is passed through a rapid sand
filter that removes much of the plankton. Fresh water and sea water are heated
electrically in separate heaters and in each case the heated water is stripped
of excess dissolved nitrogen and aerated before delivery.
Compressed air and oxygen are piped to each of the taLks and troughs.
A steam hose is available by which any part of the hatching and rearing area
can be steam cleaned . The area is windowless and the lights (partly fluorescent,
partly incandescent) are turned off and on by time switches in a variable preset
- 3 -
pattern.
troughs.
Time-controlled feeders of various types are used on both tanks and
MARINE REARING
Flotation system
As noted above there is a separate detailed report on the flotation
system that supports the seapens. Briefly, flotation is provided by three
hollow floats made of reinforced concrete.
As indicated in Fig. 1 and 2 the
floats are held in fixed relationship to one another by steel bridges, the
long axes of the floats being parallel to one another, the bridges being at
right angles to the long axes. Rubber washers on the bolts that join bridge
to float allow flexibility so that each float responds independently to wave
action.
Two steel stifflegs, with universal joints at either end, join the
inner corners of the central float to steel pedestals that are fixed to the
bedrock of Brandon Island. Two cables join the inner corners of the central
float to two more widely separated pedestals also fixed to the Island. The
stifflegs prevent the whole from moving perpendicularly to the shoreline
(except for a slight, controlled, movement with tides) while the cables prevent
movement parallel to the shoreline. Log booms between the ends of the outer
float and the Island divert floating debris. A small building on the central
float houses a field laboratory and storage space.
Netpens
Netpens, for containing fish in the sea, are hung in each of the
spaces framed by floats on two sides and bridges on the other two, all four
sides of each netpen being close to either a float or a bridge. The netpens
are boxlike, with four sides and a bottom, the open top of the "box" being
above the water surface. All are formed of 210/10 (210 denier X 10 threads),
knot less nylon netting, dyed green but not otherwise treated. Three of the
netpens are 4.6 X 4.6 m by 6 m deep (15 X 15 X 20 ft) of 19 mm (3/4 in) mesh,
stretched measure. The other two are of 7.6 X 7.6 m by 6 m deep (25 X 25 X 20
ft) of 25 nun (1 in) mesh. In the latter the corners are "rounded" by inserting,
at each corner, a panel Df netting 90 em (3 ft) wide from top to bottom at an
angle of 45 0 to each adjacent side, making the net octagonal (4 short sides,
4 long sides) in plan. On all netpens, ropes are seamed to the netting along
the upper edge of each side, along each junction of side and side, and along
each junction of side and bottom.
To make a netpen take the required boxlike shape the corners are
pulled outward from the centre. Each top corner is attached at the junction of
a bridge and float; by tightening the attaching ropes the upper edges of net pen
sides are pulled taut and square. Each bottom corner is pulled down and
sideways towards a 100 kg (220 lb) weight that hangs in a po&::'tion appropriate
for that purpose as indicated in Fig. 3. As Fig. 3 shows, one end of a length
of rope ("downhaul") is tied to each bottom corner, and its bight passes
through a ring on the weight so that a pull on the other end (at the float)
- 4 -
draws the bottom corner towards the weight. The weight hangs on a separate rope
at a fixed distance below the float, and clear of the sea bottom at all stages
of the tide. When downhauls are slacked off it becomes easy to manipulate the
netting in order to concentrate live fish, or to recover dead fish, or to
inspect and repair the netting, or for whatever purpose. Divers are never
required for servicing or operating these netpens, although divers are used
for related scientific studies.
It is considered very important that the "box" be kept square and
taut. This ensures that the maximum volume of water is enclosed and that the
meshes are fully extended thus promoting maximum exchange of water. It is
considered particularly important to have the bottom fully extended. Otherwise
ropes and netting relax into folds in which any fish that die tend to collect.
There is reason to believe that dogfish, Squalus acanthias, inadvertently make
holes in netpens while eating dead fish that lie in folds of netting, but that
a taut net bottom prevents such damage. Weights hung on bottom corners would
keep sides taut and square but would not exert the horizontal forces needed to
keep bottoms taut that downhauls and independently suspended weights provide.
Changing netpens
Except at low temperatures, netting left in the sea soon becomes
heavily coated with a great variety of marine organisms living and dead. It
is therefore necessary to periodically replace netpens that have become fouled
with marine growth with clean ones. A technique for changing netpens, that
allows the fish to be transferred with no handling, is described below. To
facilitate description, one side of the netpen is called "inner," the opposite
side "outer," and the other two sides "bridge"; the netpen to be replaced is
called "old," its replacement "new"; the rope seamed along the upper edge of
any side of the netpen is called "rimlip.e."
1.
The new netpen is laid-out, bottom up, on the float adjacent to the inner
side of the old netpen.
2.
All downhauls are slackened.
3.
The two inner corners of the old netpen are untied, then retied to leave a
space between netpen and inner float (Fig. 4).
4.
A length of galvanized iron pipe is placed from bridge to bridge along the
outer side of the old netpen (Fig. 5 and 6). The two ends of the pipe are
advanced by stages along the respective bridges towards the inner side,
netting being pulled over the pipe at each stage (Fig. 7, 8 and 9). As the
bottom corners of the old netpen come to the surface, the downhauls are
untied from them and transferred to the corresponding corners of the new
netpen, being careful to avoid tangling them.
5.
Finally the fish are concentrated between pipe and inner side of old
netpen (Fig. 10).
6.
The new net pen is put into the water in the space provided by Step 3
(Fig. 11). The downhauls are pulled but not fully tightened. The two
inner corners are fastened at intersections of bridges and inner float,
the inner rimline being pulled taut.
- 5 -
7.
The outer rimline of the new netpen is worked under the part of the old
netpen where the fish are concentrated. Pulling on the outer downhauls
greatly facilitates the maneuver.
8.
The top outer corners of the new netpen are hauled up, then opposing pulls
on them stretch the outer rimline taut immediately under the pipe (Fig. 12).
The two bridge side rimlines are bunched up until fishproof.
9.
At this point the new netpen,only partly extended but fishproofed, surrounds
the part of the old netpen in which fish were concentrated in Step 5.
10.
The inside rimline of the old netpen is dropped and the fish are herded
gently from the old netpen to the new (Fig. 13).
11.
The old netpen is removed (Fig. 14) and the new one is extended fully.
12.
The old net pen is hung to dry (Fig. 2). Usually sea water from a high
pressure hose is used to clean off most of the marine growth, but cleaning
is not essential. When dry, the netpen is ready for re-use.
Stock assessment
Apparently North American fishfarmers who rear salmonids in sea water
often cannot satisfactorily determine how many fish are on hand. It is said to
be not uncommon to find, when a group of fish are killed for market, that the
number on hand is less than half the number expected on the basis of known
initial number minus known losses. Overestimating numbers can lead to overfeeding (hence reduced profits) as well as other problems.
With the type of net pen described here, the number of fish on hand
can be assessed easily and fairly accurately.
If a count is required the net pen changing procedure is modified at
Steps 9 and 10. As noted, at Step 9 the fish are concentrated in a long
narrow part (Fig. 11) of the old netpen which in turn is surrounded by the new
netpen. The netting is manipulated to divide the long narrow space at its
longitudinal midpoint. Since the space is symmetrical, this must necessarily
divide the concentrated fish into two approximately equal lots. One lot is
herded into the new net, the other is retained. rhe long narrow space
(diminished laterally) is restored and the retained fish are allowed to
re-distribute themselves evenly in it. The fish are again divided and again
one lot is herded into the new net, the other is retained. The process is
repeated as often as necessary. After, for instance, 5 splits, approximately
1/32 of the original fish are still retained. If they are counted and the
count multiplied by 32 then the resulting value is an estimate of the number
of fish in the netpen.
- 6 -
EXPERIENCE WITH THE EXPERIMENTAL FISHFARM
As this is written, the flotation system for netpens has been in
place for over a year and the netpens themselves have been in use for almost
a year. The complex has been highly satisfactory. The flotation system has
withstood severe winter storms without visible damage. The described system
of operating netpens has been quite satisfactory. The described techniques for
changing nets and for assessing numbers have been used repeatedly with success.
Two men can change a 4.6 X 4.6 m net in about 1 hr and three can change a
7.6 X 7.6 in slightly longer. Assessing fish numbers adds from t hr to 1 hr
to the time required.
REFERENCES
Brett, J. R., J , R. Ca1aprice, R. J. Ghelardi, W. A. Kennedy, D. B. Quayle, and
C. T. Shoop. 1972. A brief on mariculture. Fish. Res. Board Can. Tech.
Rep. 301: 46 p.
Kennedy, W. A. 1966. A history of commercial fishing in inland Canada.
Res. Board Can. MS Rep. (BioI.) 871: 38 p.
Ryan, P. 1975. A raft for five mariculture nets.
Tech. Rep. 544.
Fish.
Fish. Mar. Ser. Res. Dev.
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Fig. 1. Sketch (not to scale) of marine part of experimental fishfarm. Three rectangular floats, central
one with small building, lie parallel to a shoreline (foreground). Four bridges connect nearest float
to central one; three connect farthest float to central one. Two stifflegs join two inner corners of
central float to shore, as do two cables (only partly shown). Note two logbooms (only partly shown) to
divert debris. Netpens hang in the five spaces enclosed by floats and bridges.
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Fig. 2. Photograph of marine part of experimental fishfarm; compare with Fig. 1. Note stiffleg and part
of cable in foreground. Previously used netpens hang drying in left foreground and beyond building.
11 -
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Fig. 3. Diagram of a netpen showing how it is kept taut and square. Top
corners are pulled out and fastened to divergent fixed points. Each
bottom corner is pulled downward and outward towards an independently
suspended weight by means of a rope from corner, through ring on weight,
to float above.
- 13 -
Fig. 4. Photograph showing Step 3 in netpen changing. Upper corner of old
netpen has been untied and operator is retying it to leave gap between it
and float for introducing new netpen. Note stiffleg behind operator and
bridge on which he kneels. The netting behind operator is part of a system
for interc ppting floAting debris.
I--'
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Fig. 5. Photograph showing start of Step 4 in netpen changing. Operator is maneuvering a length of pipe
between netpen and float. Note how top corner of netpen is attached at junction of bridge and float.
Small building in centre of background houses connections at the end of an undersea power supply cable.
17 -
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Fig. 8.
Photograph showing Step 4 in netpen changing.
Pipe has been pulled
along but netting has not yet been manually hauled over it.
Dog discourages
predators and trespassers.
-
23 -
Fig. 9. Photograph showing Step 4 in netpen changing.
Pipe in same position
as in Fig. 8 but netting has been manually hauled over it.
-
'2 5 -
Fig. 10. Photograph showing Step 5 in netpen changing. Note new netpen laid
out on float (left), gap between float and rimline of old net (c e ntr e ), and
long narrow space in which fish are concentrated between rimline and pipe
(from beside operator to right foreground).
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Fig. 11. Diagram showing Step 6 in netpen changing. Fish have been concentrated in part of old netpen.
Men 'at left pull on downhauls attached to bottom corners of new netpen (at right). New netpen, which
was laid bottom-up on the float, is becoming bottom-down as it enters the water. In actual practice
new netpen is put into water manually before downhauls are tightened.
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Fig. 12. Photograph showing Step 8 in netpen changing.
Operator is pulling on rope attached to outer
corner of new netpen thereby pulling outer rimline taut under pipe (from operator to upper right corner).
Note inner rimline of old netpen (bottom left corner); fish are enclosed in part of old netpen between
it and pipe .
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Fig. 13. Diagram showing Step 10 of netpen changing. Old netpen is as in Fig. 11; new netpen in water, but
not fully extended, below and to right of old. New netpen encloses that part of old where fish are
concentrated. Operator manipulates old netpen to herd fish into new . The diagram indicates an
alternative to the te x t-d e scribed method of fishproofing a partially ex tended netpen.
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