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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.

Map

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).

Tagged Cod

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.


Release Cod
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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