MOVEMENT OF ATLANTIC COD
Atlantic
cod (Gadus morhua), a species with ecological, economic and cultural
significance for New England, is a demersal, omnivorous fish found
throughout the north Atlantic, from the surface to a depth of
600 meters. Cod populations in the Gulf of Maine have been exploited
commercially for several hundred years, and continue to be heavily
exploited today. The fact that cod swim in the ocean is well understood.
Precisely how cod and other fish species move, relative to different
features of the undersea landscape, is much less understood. However,
the successful conservation and management of cod in the Gulf
of Maine, and at the scale of the Stellwagen Bank National Marine
Sanctuary (SBNMS) in particular, is highly dependent on this information.
This
project, a collaboration between researchers at the SBNMS, the
Pfleger Institute
of Environmental Research (PIER) and the National
Undersea Research Center at the University of Connecticut (NURC-UCONN),
used acoustic telemetry technology to quantify cod movement over
different features of the landscape to inform management of the
SBNMS and the greater Gulf of Maine region. Cod were caught and
tagged with coded-acoustic transmitters (each of which emits a
unique ID code, see Figures 1 and 2) then released within the
overlap of the SBNMS and the Western Gulf of Maine Closed Area
(WGoMCA). Movements of tagged cod were recorded by an array of
four acoustic receivers deployed on the seafloor. Data were collected
at the scale of minutes for several months at a time. Preliminary
tracking occurred in the gravel habitat of northeastern Stellwagen
Bank in 2001 (Lindholm and Auster, 2003). From May 2002 through
October 2002 and from September 2004 through March 2005, cod movement
was investigated at four piled boulder reef sites. The locations
of each reef were identified using a sun-illuminated bathymetric
map of the seafloor of the SNBMS and surrounding environs. The
same piled boulder reefs were used in both periods in order to
quantify any influence of seasonality on cod movement behavior.
Combined sun-illuminated topography and acoustic backscatter map
of VR2 receiver sites at piled boulder reefs in the SBNMS. Each
receiver is shown with an estimated radius of detection of 400m
(Figure 1 was prepared by Michael Thompson of Perot Systems using
a map produced by Dr. Page Valentine at the US Geological Survey).
Atlantic
cod with an acoustic transmitter attached externally at the base
of the first dorsal fin. The tagging gun used for insertion of
the T-bar anchor is visible in the lower-center of the image.
Tagged cod about to be returned to the seafloor in a PVC fish
release device.
Three
broad categories of movement behavior were identified at each
of the four piled boulder reefs, across years and across seasons.
Multiple cod showed high site fidelity (present > 90% of the
study) to the boulder reef where they were caught and released
(Table 1). A second set of cod were recorded moving among the
four piled boulder reefs included in the study (including movements
as far as 24 km). A third group of cod were recorded only briefly
at the boulder reef where they were caught and released before
leaving the study area. In each case, cod size (Total Length)
was not a factor in the recorded movement behavior.
The
high site fidelity of many cod to individual piled boulder reefs
suggests that habitat-specific management measures, such as marine
reserves, may offer significant protection to cod within the Sanctuary.
This
project was supported by the National Marine Sanctuary Program
and was conducted under an approved Institutional Animal Care
and Use Committee Protocol at the University of Connecticut.
PUBLICATIONS
Lindholm, J. and P. Auster. 2003. Site utilization by Atlantic
cod (Gadus morhua) in off-shore gravel habitat as determined by
acoustic telemetry: implications for the design of marine protected
areas. Marine Technology Society Journal 37: 27-34.
Lindholm,
J., P. Auster and P. Valentine. 2004. Role of a large marine protected
area for conserving landscape attributes of sand habitats on Georges
Bank (Northwest Atlantic). Marine Ecology Progress Series 269:61-68
Lindholm,
J., P.J. Auster, M. Ruth, and L. Kaufman. 2001. Modeling the effects
of fishing and implications for the design of marine protected
areas: juvenile fish responses to variations in seafloor habitat.
Conservation Biology 15: 424-437.
Lindholm,
J., Auster, PJ. and L. Kaufman. 1999. Habitat-mediated survivorship
of juvenile (0-year) Atlantic cod (Gadus morhua). Marine Ecology
Progress Series 180: 247-255.
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