Changing sea surface temperatures and water circulation patterns affecting food supply for young Atlantic cod

NOAA's Northeast Fisheries Science Center: Changing ocean water temperatures and circulation patterns have profoundly affected key Northeast U.S. Continental Shelf zooplankton species in recent decades, and may be influencing the recovery of Atlantic cod and other fish stocks in the region.

NOAA researcher Kevin Friedland and colleagues looked at the distribution and abundance of important zooplankton species, sea surface water temperatures, and cod abundance. They found that zooplankton species critical for the survival of Atlantic cod larvae have declined in abundance in the same areas where Atlantic cod stocks have struggled to rebuild after an extended period of overfishing.

“Temperature is a governing factor in the growth, reproduction and distribution of marine organisms. Shifting temperature distributions, whether triggered by natural or human factors, can cause the redistribution of plankton communities on regional and basin-wide scales,” said Friedland, lead author on the study and a scientist at NOAA's Northeast Fisheries Science Center (NEFSC).

The change in thermal habitats has had biological consequences on multiple levels in the food chain, according to the study in press in the journal Progress in Oceanography (available online).

“The geographic and depth distributions of fish and shellfish populations can also change based on their preferred thermal habitats. Future changes in thermal conditions are expected to lead to further shifts in the distributional ranges of species by, in many cases, the loss and gain of local populations,” said Friedland.

Friedland and his colleagues found that ocean water temperatures of the Northeast Continental Shelf have increased in recent decades, but these changes have not been uniform over the entire ecosystem.  Warm water habitats (16 to 27 C, 60 to 80 F) have increased and cool water habitats (5 to 15 C, 41 to 59 F), historically the core habitats in the ecosystem, have declined; however, the coldest habitats in the ecosystem (1-4 C, 34-39 F) have either stayed the same or increased slightly during the study period 1982-2011. This discontinuity is attributed to changes in circulation in the northern Gulf of Maine associated with the Labrador Current....

Eight boxes represent index areas for long-term sea surface temperature (SST) trends for the Northeast Shelf ecosystem; annual mean, minimum, and maximum SST for the period 1854-2011 was calculated for the index area. The grey shaded area of the Northeast Shelf was used in the calculation of thermal habitat distribution for the ecosystem. Credit: Kevin Friedland, NEFSC/NOAA