Originally from: lina
                        
When fish are foulMigrating salmon transport
pollutants from the sea to their freshwater spawning
grounds | By Stuart Blackman

Salmon are famous for their mass migration from the
sea to their freshwater spawning grounds. Sockeye
salmon (Oncorhynchus nerka) live most of their lives
in the North Pacific Ocean, where they accumulate 95%
of their biomass. On reaching reproductive age, they
can migrate as far as 1000 km up North American rivers
to spawn in lakes, dying soon afterward and
subsequently releasing their constituents into the
freshwater ecosystem. In a brief communication the
September 18 Nature E.M. Krümmel and colleagues at the
University of Ottawa report that this complicated life
history means that sockeye salmon can act as bulk
transport vectors for pollutants from the ocean to
freshwater systems (Nature, 424:255–256, September 18,
2003).

Krümmel et al. focused on polychlorinated biphenyls
(PCBs), which are produced by industrial processes
such as waste incineration and which can be dispersed
directly into the atmosphere or can be washed into
aquatic environments. Seawater typically contains 1 ng
of PCBs per liter; 1 gram of salmon body fat can
contain 2500 ng. The authors analyzed sediment from
eight Alaskan lakes and showed that the PCB
concentration and accumulation rate in lake sediments
correlated strongly with the density of spawning
salmon. PCB concentrations in Frazer Lake—which has
annual salmon returns of 11,700 fish per km2—were 10
times those of Spiridon Lake, which does not receive
spawners. In addition, the PCB signature from Frazer
Lake corresponded to that found in the tissues of the
salmon. The PCBs from Spiridon Lake, however,
consisted mainly of lighter forms, which are readily
deposited from atmospheric sources.

"Returning sockeye salmon act as 'biological pumps' by
transporting contaminants upstream, where pollutants
may affect their offspring and/or predators such as
bears, eagles and humans. Whether these contaminants
affect juvenile salmon survival is yet unknown, but
they are suspected of causing immunosuppression.
Ironically, the marine-nutrient pump, which
historically has increased successful recruitment, may
now pose a risk to some of these populations,"
conclude the authors.

Links for this article
Sockeye salmon http://www.nmfs.noaa.gov/prot_res/species/fish/sockeye_salmon.h
tml

E.M. Krümmel et al., "Delivery of pollutants by
spawning salmon," Nature, 424:255–256, September 18,
2003.