Presentation - Gulf of Maine Research Institute

Spawning site fidelity and fine-scale population
structuring of Atlantic cod in the Gulf of Maine region
Cod Stock Structure Workshop – June 12-14, 2012 – Portsmouth, NH
Douglas Zemeckis 1 , William Hoffman 2 , Micah Dean 2 , Michael P. Armstrong 2 ,
David Martins 3 , and Steven X. Cadrin 1
1
– School for Marine Science & Technology – UMASS Dartmouth, Fairhaven, MA
2
– Massachusetts Division of Marine Fisheries, Gloucester, MA
3
Massachusetts Division of Marine Fisheries – New Bedford, MA

Introduction
• Common assessment techniques and management strategies assume
discrete populations, but management units are typically heterogeneous
and consist of multiple sub-units (Stephenson 1999).
• Metapopulation structuring has been documented within cod management
units off Newfoundland (e.g., Rose et al. 2011), Iceland (e.g., Jonsdottir et al.
2007), Scotland (e.g., Wright et al. 2006), and Norway (e.g., Sarvas and
Fevolden 2005).
– Growing evidence of complex population structuring in U.S. waters
Tagging, genetics, spawning behavior, larval dispersal, growth rates,
morphometry, and productivity patterns (e.g., Runge et al. 2010).
• Maintenance of spawning diversity is critical for sustaining a robust stock.
– Reduce likelihood of recruitment failure (match/mismatch hypothesis)
– Maintain stock productivity and stability

Stock structure in the Gulf of Maine region
• Ames (2004) identified four historic subpopulations based upon 1920’s
data and surveys from retired fishermen.
• Each subpopulation had discrete migration corridors, local cyclical
movements, and partial isolation due to bathymetry.
• Clusters of spawning components were identified within each
subpopulation.

Stock structure in the Gulf of Maine region
• Nearly half of the historic spawning components appear to be inactive,
due to overfishing, coastal pollution, and declines of forage species
(Ames 2004).
– System-wide assessments appear to be unable to detect gradual erosion of
spawning components.
– Inactive spawning sites have not become re-populated once abandoned.
Ames (2004)

Fine-scale population structuring
• Potential mechanisms contributing to fine-scale population structuring:
• Restricted dispersal during early life stages
• Temporal variation in spawning
• Differences in spawning habitat
• Divergent trophic ecology
• Spawning site fidelity
– Return to the same spawning site each year
• Natal homing
– Inferences regarding location where spawned
Wroblewski et al. (2005)

Spawning site fidelity of Atlantic cod
• Robichaud and Rose (2001) investigated the degree of multi-year fidelity to the
Bar Haven spawning ground in Placentia Bay, Newfoundland.
• A total of 48 cod were tagged in 1998.
• Fish were monitored using active tracking
during subsequent spawning seasons.
• All relocated fish were within 10km of
spawning site (most

Spawning site fidelity of Atlantic cod
• Robichaud and Rose (2001) documented straying in cod that were
unobserved during the spawning season.
– Potential genetic exchange among adjacent populations.
• A life history balance appears to exist between homing and straying that
maintains population stability, while permitting recolonization of
inactive spawning sites.
– Accurate and prevalent homing would impede rapid recolonization.

Spawning site fidelity of Atlantic cod
• Skjaeraasen et al. (2011) studied cod on their coastal spawning ground off
western Norway in 2007 using acoustic telemetry.
• Unadjusted rates of spawning site fidelity of at least 55% and 37% were
observed in 2008 and 2009, respectively.
– ‘Extremely’ fine-scale (

Spawning cod in the Gulf of Maine
• Cod in the Gulf of Maine have been suggested to demonstrate spawning
site fidelity/homing behavior based upon conventional tagging data:
– Perkins et al. (1997): Sheepscot Bay, Maine
– Howell et al. (2008): Ipswich Bay spring spawners

Spawning cod in the Gulf of Maine
• Siceloff and Howell (in press) used
stationary receivers and active tracking
to study spawning cod in Ipswich Bay
during the spring of 2006.
– Active tracking for 39 days (5/6 – 6/30)
– Ten stationary receiver stations

Spawning cod in the Gulf of Maine
• Most cod aggregated around raised
bathymetric features Whaleback
• Individuals were typically active in
areas ranging from approximately
17-57 km 2 (mean area of 41 km 2 ).
• Residence time: 8 - 54 + d (mean= 30 d)
• Demonstrates that cod spawning
activity occurs over relatively finescales.
Potential isolation mechanism leading
to fine-scale population structuring.
Individual kernel distribution estimations
(95% volume contours)

Spawning cod in the Gulf of Maine
• Zemeckis et al. (in progress) have been studying spawning cod in
northern Massachusetts Bay since 2009.
– Spring Cod Conservation Zone (SCCZ): Closed annually April 16 – July 21

Spawning cod in the Gulf of Maine
• Cod were monitored on the spawning site using a stationary Vemco
VR2W Positioning System (VPS).
• Acoustic transmitters have been released annually since 2009.
– 2009: n = 7
– 2010: n = 52
– 2011: n = 4
– 2012: in progress

Spawning cod in the Gulf of Maine
Spawning site fidelity : 2009 Releases
• Three of the seven fish tagged in 2009 returned to the spawning site in
2010 (43%).
– Two of these same fish also returned in 2011.
– One of which has also returned in 2012.
• Documentation of extremely fine-scale (

Spawning cod in the Gulf of Maine
Spawning site fidelity : 2010 Releases
• A total of 15 of the 52 cod tagged in 2010 returned to the spawning site in 2011.
Unadjusted rate of 29%
• A total of 13 of the 52 cod tagged in 2010 were recovered in the fishery.
25% minimum fishing mortality rate
20% natural mortality
• Adjusted rate of spawning site fidelity = 74%
– Does not account for skipped spawning or tag failure rate, and includes a minimum
rate of observed fishing mortality (tag non-reporting rate).
• Residence times in 2011 ranged from 4 - 106 days (mean = 36 days).
• At least four fish have returned in 2012 to confirm multi-year fidelity.

Spawning cod in the Gulf of Maine
• Evidence of connectivity among
coastal spawning sites:
• < 100% adjusted rate of spawning
site fidelity
• Tag recaptures from other spawning
sites: Whaleback & Eagle Ridge
• 2012 acoustic telemetry data
• Connectivity among coastal spring
spawning sites corroborates genetic
findings (Kovach et al. 2010).
• Rates of recolonization are expected
to be low given the prevalent
homing behavior.
Recapture locations of SCCZ tag releases

Synthesis of Stock Structure
• The expression of spawning site fidelity supports the hypothesis of complex
population structuring and significant intra-stock diversity in the Gulf of
Maine region.
• The biological stock structure in the Gulf of Maine region is reflective of a
metapopulation.
– Multiple spawning components that experience partially independent dynamics
with some degree of connectivity.
• The fine-scale population structuring is not consistent with the current largescale
management units that assume discrete populations.
– Threat of continued declines in spawning diversity
– Continued difficulties in rebuilding are expected
• Potential management options include restricted fishing during the spawning
season (e.g., spawning closures) and trip limits to prevent the extirpation of
additional spawning components.

Future Research
• The following research is required to better inform recommendations
on the most likely stock structure in the Gulf of Maine region:
– Documentation of spawning site fidelity in other locations
– Further investigation of fine-scale spawning behavior
– Investigation of the connectivity among spawning sites
– Identifying potential mechanisms for the recolonization of inactive
spawning sites
– Determining the effectiveness of spawning closures
– Studying the seasonal migration patterns of each spawning
component

Acknowledgments
• This research has been funded in part by the US Fish and
Wildlife Services through the Sportfish Restoration Act, and the
Massachusetts Marine Fisheries Institute (MFI).

References
Ames, E.P. 2004. Atlantic cod stock structure in the Gulf of Maine. Fisheries 29(1), 10-28.
Howell, W.H., Morin, M., Rennels, N., and Goethel, D. 2008. Residency of adult Atlantic cod (Gadus morhua) in the
western Gulf of Maine. Fisheries Research 91, 123-132.
Jonsdottir, I. G., G. Marteinsdottir and S. E. Campana. 2007. Contribution of diverent spawning components to the
mixed stock fishery for cod in Icelandic waters. ICES Journal of Marine Science, 64: 1749-1759.
Kovach, A.I., Breton, T.S., Berlinsky, D.L., Maceda, L., and Wirgin, I. 2010. Fine-scale spatial and temporal genetic
structure of Atlantic cod off the Atlantic coast of the USA. Marine Ecology Progress Series 410, 177-195.
Perkins, H.C., Chenoweth, S.B., and Langton, R.W. 1997. The Gulf of Maine Atlantic cod complex, patterns of
distribution and movement of the Sheepscot Bay substock. Bull. Natl. Res. Inst. Aquacult. Suppl. 3, 101-107.
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Rose, G.A., Nelson, R.J., and Mello, L.G.S. 2011. Isolation or metapopulation: whence and whither the Smith Sound
cod?. Canadian Journal of Fisheries and Aquatic Sciences 68, 152-169.

References
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