Proceedings: Short Papers
Field Research on Atlantic Cod, Gadus morhua L. in Canada
Susan B. Fudge(1) and George A. Rose(2)
(1) Fisheries Conservation Chair, Fisheries and Marine Institute, Memorial
University of Newfoundland, 155 Ridge Road, PO Box 4920, St. Johns,
NF Canada, A1C 5R3 firstname.lastname@example.org.
(2) Senior Chair of Fisheries Conservation, Fisheries and Marine Institute,
Memorial University of Newfoundland, 155 Ridge Road, PO Box 4920, St.
Johns, NF Canada, A1C 5R3 email@example.com.
The Atlantic cod is a very important commercial fish in Newfoundland and
Atlantic Canada and has been a part of the culture for centuries. In the
past ten years, cod stocks have been drastically depleted. In Newfoundland
waters, cod is found from the coast to the continental shelf in water
temperatures ranging from approximately 0.5 0C to 8.5 0C. They are
broadcast spawners and typically spawn in large aggregations (Robichaud,
2002). The spawning season typically occurs in the spring but varies by
area and is influenced by environmental factors, such as temperature (Scott
and Scott, 1988). Spawning begins in the north as early as February and
ends in the south as late as December. The depth at which spawning occurs
varies among stocks; some may spawn in water as shallow as 20m, while
others at depths over 300m (Rose, 1993). Differences in spawning behaviours
among sub-stocks and among ages and sexes have been reported (Robichaud,
2002). Laboratory studies have shown that cod have elaborate courtship
behaviours with males being very territorial and more aggressive males
having the most success at spawning. Cod are also known to detect and
produce sound and this observation has long been recognized by lab experiments
(e.g. Brawn, 1961). This study is the first attempt in Canada to document
the sounds made during spawning and to relate them to spawning behaviour
in order to link active and passive acoustic research in behavioural field
Previous and future
research on Atlantic cod behaviour
Two of the largest spawning components of Atlantic cod in Newfoundland
waters have been studied using active acoustics for several years. These
include Placentia Bay, located on the south coast of Newfoundland (NAFO
regulatory area 3Ps), and Trinity Bay, located on the north east coast
(NAFO regulatory area 3L). Annual acoustic surveys using SIMRAD EK 500
echo sounders, along with the analyses of the data using FASIT (Fisheries
Assessment and Species Identification Tool) (Lefeuvre et al., 2000) have
provided insights into stock migrations and spawning behaviours. The echogram
in Figure 1 is from April 2000 in Placentia Bay, Newfoundland, showing
some of the pelagic behaviour easily observed using an echo sounder. Cod
in this area have a peak spawning period between April and June. This
spawning aggregation was found in a trench, over 300m deep. The image
in the bottom corner is an enlargement of the echogram where single cod
targets (white arrow) are resolved.
1: Echogram of a spawning cod aggregation in Placentia Bay, Newfoundland
|Figure 2: Cod
spawning column in Placentia Bay in 1997
The use of active
acoustics has lead to observations of different spawning aggregation structures.
Figure 2 is an echogram of spawning columns observed in shallow waters
of Placentia Bay in 1997 at a depth of approximately 50m (Rose, 1993).
In section A, several columns are shown. Section B is an enlargement of
one of these columns, which extends approximately 20m off the ocean floor.
Throughout their range, cod occur in distinct stocks as well as sub-stocks,
and spawning behaviour within specific sub-stocks is of interest. Sonar
tagging studies have been conducted to investigate the homing ability
of Atlantic cod to specific spawning grounds. Long-term sonar transmitting
tags (Lotek CAFT16_3 Acoustic Transmitters) were implanted in female and
male cod at a spawning ground in Placentia Bay, Newfoundland in April
1998. Homing of cod back to the spawning ground from which they were taken
was observed. Approximately 50% of the tagged cod returned to the same
spawning ground (capture site) in subsequent years and 25% of the tagged
cod returned 3 years in a row (Robichaud and Rose, 2001). This study provides
some of the first direct evidence that cod undertaking long-distance feeding
migrations may home to a specific spawning location in consecutive years.
Present tagging work that has begun this year also will involve the identification
of distinct spawning populations using acoustic surveys; cod have been
released within their "home" populations as well as within other
groups. Results of this study hope to provide valuable insight into the
Atlantic cods homing properties.
Using active acoustics in surveys and sonar tagging studies, we have learned
a great deal about cod spawning aggregations and migratory behaviour.
As spawning is the first step towards recruitment and rebuilding cod stocks,
there is a continuing interest in the specific behaviour of spawning.
Brawn (1961) documented many interesting features of cod spawning behaviour.
Cod are known to have specific social behaviours related to spawning.
Brawn (1961) observed distinct courtship behaviours performed by males
toward females, as well as aggressive behaviour of males toward males.
Both sexes in cod have been observed to produce sound, although it is
the males whose sound production is thought to play an important role
in spawning, such as attracting females and holding territories (Brawn,
1961). In cod, the drumming muscles surrounding the swim bladder are thought
to be related to sound production.
Present field studies will observe the acoustic properties of spawning
aggregations over two spawning seasons. These studies are interested in
both the production and reception of sound by cod, its role in spawning
behaviour, and also the influence of ambient noise in the ocean environment
on these behaviours. We have chosen two main research areas, which have
been studied for the past number of years using active acoustics and sonar
tracking. Placentia Bay and Trinity Bay both have relatively large coastal
spawning populations. However, Placentia Bay is becoming increasingly
industrialized while Trinity Bay is not. With use of a small vessel specially
equipped for the work, cod spawning aggregations will be located using
a Biosonics DE 70 kHz echosounder with digital data storage. Once located
sounds from the aggregation are detected, they will be recorded using
a hydrophone (ITC 8212) with a Stanford Research System pre-amplifier
(model SR560). Data will be in the form of WAV files and stored on a hard
drive of a lap-top computer and analyzed using Avisoft SASLab Pro software.
Video recordings will be made using an underwater video camera (J.W. Fishers
MFG. Inc., TOV-1). A parallel study will be conducted on fish from the
same stocks kept in the lab at the aquaculture facility at Memorial University
This study is the first of its kind in Canada, and is attempting to document
the sounds that cod make during spawning at sea and to relate these to
spawning behaviour. The work attempts to link active acoustic research
with passive acoustics and to use real-time video to study cod spawning
behaviour. From past acoustic research, we have learned much about the
state of cod stocks, spawning aggregations, migrations, and homing. With
the addition of passive acoustic tools, we hope to learn more about the
spawning behaviour of individual cod.
Several people were instrumental in past and present studies. We would
like to thank Dave Robichaud, Wade Hiscock, Matt Windle, the crews of
the CCGS Teleost and CCGS Shamook. Danny Boyce of the Aquaculture Facility
at Memorial University and all the participants and sponsors of the International
Workshop of Passive Acoustics in Fisheries.
Brawn, Vivien M. 1961. Aggressive behaviour in the cod (Gadus callarias
L.). Behaviour 18: 108-145.
Brawn, Vivien M. 1961. Reproductive behaviour of cod (Gadus callarias
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Brawn, Vivien M. 1961. Sound production by the cod (Gadus callarias L.).
Behaviour 18: 239-245.
Chapman, C.J. and A. D. Hawkins. 1973. A hearing study in the cod, Gadus
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Lefeuvre, P., G.A. Rose, R. Gosine, R. Hale, W. Pearson, and R. Khan.
2000. Acoustic species identification in the northwest Atlantic using
digital image processing.Fisheries Research 47: 137-147
Nordeide, J.T. and E. Kjellsby. 1999. Sound from cod at their spawning
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Robichaud, D. 2002. Homing, population structure and management of cod,
with emphasis on cod spawning at Bar Haven in Placentia Bay, Newfoundland.
Ph. D. thesis. Biology Department, Memorial University of Newfoundland.
Rose, G.A. 1993. Cod spawning on a migration highway in the north-west
Atlantic. Nature 366: 458-461.
Scott W.B., and M.G. Scott. 1988. Atlantic Fishes of Canada. University
of Toronto Press, Toronto.
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