Marine species can be an excellent indicator of climate change, since many have specific environmental tolerances for temperature as well as diet. Other factors can affect their behavior as well, such as interaction with other species, ocean currents, food availability, the physical (benthic) environment, and the species’ own adaptability. Marine species migration patterns are useful but not uniform indicators of changing conditions in the ocean.
The National Marine Fisheries Service (NMFS), like the National Oceanographic and Atmospheric Administration (NOAA), is part of the Department of Commerce. They conduct annual surveys of fish populations off the US coast (continental, Alaska and Hawaii) by trawling at regular intervals. Using their the trawl counts they estimate fish and benthic population distributions by “center of biomass”. That is, with the survey results scientists at these agencies estimate population densities across a range of areas, which also produces overall population estimates.
These estimates of population and range are used by the NMFS to establish fishing quotas—the main reason that agency is despised by commercial fishers—but over the years, successive surveys can be combined to show geographic trends. The centers of biomass, as estimated by the trawl surveys, are not stationary. Over the decades, on the east coast, they have trended northward and deeper, indicating that water temperature and other important factors are likewise changing. The trend is much more moderate in the Bering Sea than in the Atlantic, however.
It must also be borne in mind that the species charted here are harvested commercially, so density trends are also a function of fishing pressures. These biomass estimates can be valuable tools to illustrate a changing marine environment, but are not diagnostic climate indicators. Surveys of non-commercial marine species, outside of marine mammals, are comparatively rare, however.
Tomorrow: oceanic heat content.
Be brave, and be well.
No comments:
Post a Comment