Evaluating spatio-temporal variability in the habitat quality of Atlantic cod (Gadus morhua) in the Gulf of Maine

Reduced abundance and contracted spatial distribution of Atlantic cod, Gadus morhua, in the Gulf of Maine (GOM) may indicate large spatio-temporal variation in their habitat quality. Season-specific Habitat Suitability Index (HSI) models were developed to quantify such variation in the offshore GOM management area. Data used were non-zero cod catch rates with calibrations from the Northeast Fisheries Science Center (NEFSC) spring and fall bottom trawl surveys over the period 1982-2013 and key physical environmental variables including depth, bottom temperature, bottom salinity and sediment types. Significant declines were found in the average HSI across the study area in the springs of early 2000s and 2010s. These low average HSI values coincide with reduced age-1 recruitment of GOM cod stock after the mid1990s. Moreover, the western coastal areas of the GOM generally exhibited higher average HSI values than the eastern coastal areas, whereas the offshore areas always had the lowest average HSI. Relatively higher cod survey catch rates in the western GOM may imply positive influences of environmental controls on the distribution of GOM cod.