Midwater Assessment & Conservation Engineering (MACE) Program
Winter Surveys in the Gulf of Alaska and the Southeast Aleutian Basin
Figure 3. Relative backscattering (NASC) (m2 nm-2)
attributed to pollock observed to within 0.5 m off bottom along tracklines surveyed during the 9-19
February 2005 echo integration-trawl survey of the Shumagin Islands and Sanak Trough in the
Gulf of Alaska.
Scientists from the Midwater Assessment and
Conservation Engineering (MACE) Program conducted echo integration-trawl
(EIT) surveys of the Shumagin Islands and Sanak Trough in the Gulf of
Alaska 9-19 February (Fig. 3 above), and of the Bogoslof Island area in the
southeastern Aleutian Basin, 7-12 March 2005 (Fig. 4 below) aboard the NOAA
ship Miller Freeman. The surveys provided data on the abundance,
distribution, and biological composition of spawning walleye pollock (Theragra
chalcogramma). Echo integration and trawl data were collected 24
hours per day. A total of 16 trawl hauls were made in the Shumagin
Islands and Sanak Trough regions, and 19 trawl hauls were conducted in
the Bogoslof Island region. With a few exceptions, pollock dominated the
trawl catches. The most notable exceptions were rockfish captured during
the southeastern Aleutian Basin survey between Umnak Island and Unalaska
Figure 4. Relative backscattering (NASC) (m2 nm-2)
attributed to pollock observed to within 0.5 m off bottom along tracklines surveyed during the 7-12
March 2005 echo integration-trawl survey of the southeastern Aleutian Basin near Bogoslof Island.
Transect numbers are underlined and the Central Bering Sea (CBS) Specific Area boundary is marked.
For the Gulf of Alaska surveys, the densest pollock
aggregations were located off Renshaw Point in the Shumagin Islands, and
in the southern part of Sanak Trough (Fig. 3). The pollock size
composition was unimodal in each of the two areas. Most of the pollock
in the Shumagin Islands measured between 46 and 48 cm fork length (FL),
and most of the pollock in Sanak Trough were between 48 and 49 cm FL.
The unweighted maturity composition of female pollock with lengths
greater than 40 cm, was 64% mature, 5% spawning, and 23% post-spawning
(spent) in the Shumagin Island area, and 70% mature, 7% spawning, and
17% spent in Sanak Trough.
In the southeastern Aleutian Basin survey, pollock were concentrated
in two main locations: northeast of Umnak Island, off Cape Idak, and
just north of Samalga Pass, between the Islands of Four Mountains and
Umnak Island (Fig. 4). Although pollock ranged between 37 cm and 73 cm
FL for each of the two regions, pollock off Cape Idak were
predominately 42-45 cm FL, while most of the pollock in the Samalga Pass
area were about 59-63 cm FL. The reproductive condition of female
pollock was observed as 68% mature, 5% actively spawning, and 14% spent.
By Denise McKelvey
Acoustic Testing of NOAA Ship Oscar Dyson
Alex De Robertis of the MACE Program participated in
sonar-self noise testing of the new NOAA ship Oscar Dyson from 10
to 13 December. The vessel underwent acoustic testing conducted by the
U.S. Navy and NOAA personnel to confirm that sounds produced by the
vessel do not interfere with the onboard scientific echosounders used
for fisheries work. During the tests, De Robertis took measurements from
onboard Simrad EK60 echosounders and SM2000 multibeam sonars, which will
be compared to measurements from hull-mounted hydrophones to identify
sounds produced by the vessel, and their influence on acoustic data
By Alex De Robertis
The Conservation Engineering Program continued
cooperative work developing salmon excluders for the Alaska pollock
fisheries. Carwyn Hammond travelled to Dutch Harbor in February to
provide camera and sonar systems to fishers with these devices installed
in their trawls and to train crews to use the observations systems.
In March, Craig Rose participated in tests of the excluders aboard the FV
Destination. Those tests were one of four such trips authorized
under an exempted fishing permit issued to industry partners.
The latest version of the excluder continued to allow significant salmon escape
with little loss of pollock. Modifications alleviated most problems
involving accumulation of animals and partial blockage at the excluder
associated with high catch rates or jellyfish concentrations. Further improvements
in exclusion rates and performance will be the goal of continuing work.
By Craig Rose
AFSC Quarterly Research Reports Jan-Mar 2005