Ecosystem of Cobb Seamount Region

A0057 Vladimir B. Darnitsky Pacific Research Fisheries centre (TINRO-center)

A0058 Mikhail A. Stepanenko

A0059 Vladimir N. Volgdin


The studies of ecosystems of seamounts of North-EEast Pacific coast

include ichtiological, hydrobiological, hydroacoustic and

oceanographic obsevations (Darnitsky, Stepanenko, Vologdin, 2001).

It was detected about 90 species of fishes in region of Cobb seamount

from 1976 to 1988, the majority of which one is part of an inshore

ecosystem of North-East Pacific. The greatest frequentcy species are

resulted in the Table.

Table. Most common species of fish in the Cobb seamount area in 1976

- 1988 (on Russian trawl survey data)

Species Frequency Species Frequency Species Frequency Species Frequency

Sebastes entomelas 231 Sebastes proriger 43 Sebastes alutus 35 Sebastesjordani 20

Trachurus symmetricus 138 Sebastes zacentrus 38 Sebastes helvomaculatus 24 Anoplopoma fimbria 16

Lepidopsetta bilineata 47 Scomber japonicus 36 Lamna ditropis 22 Sebastes miniatus 9

Sebastes melanostomus 46 Brama japonica 36 Sebastes aleutianus 21 Glyptocephalus zachirus 9

The oceanographic surveys have allowed to find availability of

topographic eddies of a density packing near top of the seamount,

which one are a part of integral circulation of waters. Change of

eddy systems was observed with periods from 1 to 7 days. Quite

apparently, that the eddies can be generated directly by Cobb seamount

and also to be caught by it at move of free eddies along North America


The functioning of an ecosystem of Cobb seamount is conditioned by

interaction of inshore fauna and functioning of limited dependent

fauna near to Cobb seamount at the expense of local upwellings

increasing bioproductivity of the initial parts of a food chain. The

biomass of a plankton in an eddy zone was increased up to 852-1735

mg / cubic m as compare to by lower values of surrounding waters.

These values are below of it obtained as a result of statistical

processing of 1984 - 1997 series of Okhotsk sea eddies, biomass in

which one are depending on a season from 1100 up to 2400 mg/cubic m

(Samko et al., 2001). West -East skewness of productivity depends

from background structure and productivity of waters.