Changing Ocean Temperatures & Atlantic Cod

[ music and rushing water ] [ music ] Hi, I'm Kevin Friedland. I'm a fisheries oceanographer here at the Narragansett Laboratory, which is part of the Northeast Fishery Science Center. I'm here to talk about a new publication that has just come out that deals with changes in thermal properties in the Northeast Shelf related to what's been occurring at the lower trophic levels, which are the base of the food chain, the small animals and plants that are in the water column, and what we believe has been an impact on Atlantic cod in the same area. And what we've found is that as the shelf has been warming in recent years there's been an increase, logically, of the warmest thermal habitat and a decline in the cool water habitats, but the surprise to all this has been a lack of decline, or steady state of the coldest water thermal habitats. They've remained relatively unchanged. As you scan through these figures, they're for January, February, through the course of the entire year and ending up in December.

And the red tones indicate where there's been a positive trend or a trend of increasing temperature, and the blue tones indicate there's been a declining trend in temperature spatially. And you can follow the trace of the northeast coastline, and just keep in mind that the northeast shelf is the region that I'm indicating with my finger out onto Georges Bank and into the Gulf of Maine. These are spatially discreet areas where we've actually seen cooling during this period, and we attribute this to increased flow of the Labrador Current. A number of authors have described how increased ice melt over the last couple decades has intensified this fresher, cooler water flow, and we've actually seen it downstream all the way down into the Northeast Shelf. And it's been associated with a number of different changes to the ecosystem. So part of that overall scenario that we've analyzed is to look at the most important zooplankton species and what we've noticed is that a key species of zooplankton, which are these small little invertebrates that are utilized by fish, is this species called pseudocalanus.

And it's very important to cod. When we look at their trends shelf-wide, we've seen a decline in spatially discreet areas. And we can show this by looking at two maps from two different time periods. So for this first map of pseudocalanus abundance from 1982 to 1986, you can see that pseudocalanus as indicated by the darker tones was relatively in high abundance in the Mid-Atlantic Bight into southern New England and also out on to Georges Bank, and, though not as high, still in some level of abundance in the Gulf of Maine area. We fast-forward a number of years to 2005 to 2009, this second depiction shows that pseudocalanus has now declined in abundance in the Mid-Atlantic Bight, has remained relatively high abundance in southern New England into Mass Bay, but has declined on Georges Bank and is virtually absent from the Gulf of Maine area. The jump to cod, or the linkage to cod, can be seen in this companion figure.

We show here historical distributions of cod where cod was very abundant all through Georges Bank and all through the Gulf of Maine. Again this is the period '68 through '80. We look at the most recent period, 2007 through 2011, we see very low abundances out on Georges Bank, virtually absent in the eastern Gulf of Maine and and still in high abundances in Nantucket Shoals and Mass Bay. And the association we would draw spatially is that it's the areas where pseudocalanus has declined have been also areas where cod has not been doing as well. So the analysis that we've been talking about was one that we focused on the period of 1997 to 2011, but in 2012 the Northeast Shelf went through a tremendous increase in temperature. Temperatures were the highest ever recorded. This dramatic change in temperature would suggest that additional impacts may be occurring to both the fish populations but then also the food webs themselves, so it's an area that we have to continue to monitor and study. .