The four subregions of the northeast shelf large marine ecosystem. (Photo Credit: NOAA)
Warming sea temperatures drive fish stocks northward
Monday, April 29, 2013, 22:50 (GMT + 9)
Sea surface temperatures in the Northeast Shelf Large Marine Ecosystem during 2012 were the highest recorded in 150 years, according to the latest Ecosystem Advisory issued by the National Oceanic and Atmospheric Administration’s (NOAA) Northeast Fisheries Science Centre (NEFSC). These high sea surface temperatures (SSTs) are the latest in a trend of above average temperature seen during the spring and summer seasons, and part of a pattern of elevated temperatures occurring in the Northwest Atlantic, but not seen elsewhere in the ocean basin over the past century.
According to the advisory's reports on conditions in the second half of 2012, sea surface temperature for the Northeast Shelf Ecosystem reached a record high of 14 degrees Celsius (57.2 °F) in 2012, exceeding the previous record high in 1951. Average SST has typically been lower than 12.4 °C (54.3 F) over the past three decades.
Sea surface temperature in the region is based on both contemporary satellite remote-sensing data and long-term ship-board measurements, with historical SST conditions based on ship-board measurements dating back to 1854. The temperature increase in 2012 was the highest jump in temperature seen in the time series and one of only five times temperature has changed by more than 1 °C (1.8 °F).
The Northeast Shelf's warm water thermal habitat was also at a record high level during 2012, while cold water habitat was at a record low level. Early winter mixing of the water column went to extreme depths, which will impact the spring 2013 plankton bloom. Mixing redistributes nutrients and affects stratification of the water column as the bloom develops.
Temperature is also affecting distributions of fish and shellfish on the Northeast Shelf. The advisory provides data on changes in distribution, or shifts in the centre of the population, of seven key fishery species over time.
The four southern species - black sea bass, summer flounder, longfin squid and butterfish - all showed a northeastward or upshelf shift. American lobster has shifted upshelf over time but at a slower rate than the southern species. Atlantic cod and haddock have shifted downshelf.
"Many factors are involved in these shifts, including temperature, population size, and the distributions of both prey and predators," said Jon Hare, a scientist in the NEFSC's Oceanography Branch.
A number of recent studies have documented changing distributions of fish and shellfish, further supporting NEFSC work reported in 2009 that found about half of the 36 fish stocks studied in the Northwest Atlantic Ocean, many of them commercially valuable species, have been shifting northward over the past four decades.
The Northeast US Continental Shelf Large Marine Ecosystem (LME) extends from the Gulf of Maine to Cape Hatteras, North Carolina.
"Changes in ocean temperatures and the timing and strength of spring and fall plankton blooms could affect the biological clocks of many marine species, which spawn at specific times of the year based on environmental cues like water temperature," Kevin Friedland, a scientist in the NEFSC Ecosystem Assessment programme, said.