link to AFSC home page

link to AFSC home page link to NMFS home page link to NOAA home page

Status of Stocks & Multispecies Assessment Program

Update on Groundfish Stock Assessments for the 2013 Fishery (cont.)

Research Reports
Oct-Nov-Dec 2012
ABL Reports
FMA Reports
NMML Reports
RACE Reports
REFM Reports
Complete Rpt. (pdf)
Quarterly Index
Quarterly Home

Bering Sea/Aleutian Islands (BSAI)

In the BSAI region, full assessments for 24 stocks or stock groups were completed. Since new primary groundfish survey data were available for the Aleutian Islands, full assessments for the rockfish stocks were presented to the Council (in years where no survey occurs, a summary update is conducted for long-lived species).  For the region, the sum of the ABCs for 2013 is about 2.64 million t, up slightly from the 2012 totals (2.51 million t).  The largest component is the EBS pollock ABC (1.375 million t for 2013 compared to 1.22 million t in 2012).  The EBS 2013 pollock TAC increased by 4%  to 1.247 million t from the 2012 TAC of 1.2 million t. The 2013 Pacific cod TAC increased by about 18% to 307,000 t from 261,000 t in 2012. 


Figure 1.   NMFS survey biomass trends (in t) for the main groundfish species observed in the Aleutian Islands region, 1980-2012. Click to enlarge.


Figure 2.   NMFS survey biomass trends (in metric tons) for the main rockfish species groups in the Aleutian Islands.  Click to enlarge.


Figure 3.   NMFS acoustic-trawl and bottom trawl survey results for 2012.  Vertical lines and contours represent relative biomass of pollock as observed in the different surveys. Click to enlarge.


Figure 4.   EBS pollock CPUE (shades = relative kg/hectare) and bottom temperature isotherms of 0º, 2º, and 4º Celsius from NMFS summer bottom-trawl surveys, 2005-2012. Click to enlarge.


Figure 5.   Atka mackerel Aleutian Islands survey biomass estimates by area and survey year. Bars represent 95% confidence intervals based on sampling error. Click to enlarge.


A synopsis of the Aleutian Islands survey trends by main groundfish stock groups indicates a mixture of declines and increases between species with the overall total being about average in 2012 (Fig. 1).  Examining just the main rockfish stocks indicates mostly above-average stock sizes, particularly for Pacific ocean perch and northern rockfish (Fig. 2).

Most of the BSAI groundfish stocks continue to be above target spawning biomass levels.  Two stocks are projected to be below Bmsy in 2013: Aleutian Islands pollock (by about 2%) and Greenland turbot (by about 44%). Age 3+ pollock biomass estimates are projected to be 8.14 million t in 2013 whereas Pacific cod projections are for about 1.51 million t. The flatfish show generally increasing trends and due to recent high recruitments, Greenland turbot is projected to increase by about 17% in the coming year. The biomass of Atka mackerel for 2013 is estimated at 289,000 t, down 29% from the 2012 level.

EBS Pollock:  As noted above, the MACE group within the RACE Division completed an extensive acoustic-trawl survey in summer 2012 that indicated about 22% of the mid-water pollock biomass (~500,000 t) they observed occurred within the Russian zone.  The abundances in mid-water (being comprised mainly of pollock aged 1-4 years) were considerably shifted to the northwest portion of the survey compared to the generally older pollock (ages 4-15+) observed in the bottom trawl survey (Fig.3).  The occurrence of mid-water pollock in the Russian zone was also considered unusual because the bottom temperatures were very cold with a very extensive “cold pool.”  Even within the U.S. zone, concentrations of pollock extended well into the cold pool which, when compared to other years, they tended to avoid (Fig. 4).

The new data on age composition from the fishery and the surveys resulted in estimates for the 2008 year class that were considerably higher than last year (and well above average) and that the next most recent strong year class (2006) was estimated to be of lower strength than estimated in 2011. In response to requests from the Council, a new form of decision table for considering future pollock fishing levels was presented which considered factors affecting fishing conditions (i.e., CPUE (catch per unit effort)), proximity of stock status to threshold levels, and indicators on the diversity of ages within the spawning population. This work generated some lively discussion and provided direction for more management-strategy evaluation studies.

BSAI Pacific Cod:  The EBS shelf survey biomass estimate was nearly the same (less than 1% change) in 2011 and 2012 and 15% above the 1982-2012 mean value.  The stock is increasing due to the fact that the six most recent year classes include four of the top nine year classes of all time (2006, 2008, 2010, and 2011). The female spawning biomass is estimated to be above Bmsy levels (about 47% of unfished) and the projected near-term outlook is for further increases. The Council also discussed the presentation of splitting the AI region from the EBS (a preliminary analysis was presented) and the expectation (if the Council proceeds) is that the TAC would be split in 2014 (to allow for further developments of the assessment approach).

BSAI Flatfish:  Yellowfin sole is one of the most abundant flatfish species in the EBS and the projected female spawning biomass estimate for 2013 is 582,000 t (well above the Bmsy value of 353,000 t) with a stable trend which may increase due to an above-average 2003 year class.  The northern rock sole model indicates a 2013 age-6+ biomass estimate of just under 1.5 million t, and the relatively low harvest rates suggest further increases for the next few years.  Alaska plaice and flathead sole models indicate that the 2013 spawning biomass estimates are well above Bmsy levels and that exploitation rates remain relatively low (catches are about one-third of ABCs).  Arrowtooth flounder and Kamchatka flounder stocks commenced being treated separately in 2011.  Presently, the models for both of these assessments are in the process of being refined for application in 2013.  The catches have remained well below the ABC limits.

BSAI Greenland Turbot:  Recent trawl surveys of the EBS shelf trawl survey indicate positive signs of recruitment to the population.  The assessment model and data for Greenland turbot was completely revised in 2012.  This included updated weights-at-age and selectivities and a correct to the projection model inputs.  This affected the stock status determination (estimated to be at about 21% of “unfished” in 2013) and subsequently reduced the recommended ABC to about 26% of last year’s estimate. Fortunately, there appears to be strong 2008 and 2009 year classes based on both the survey and fisheries size composition data.  These two year classes are expected to be larger than any other recruitment event since the 1970s and will begin to have an increasing influence on spawning stock biomass starting in about 2014.

BSAI Atka Mackerel:  Due to a very low survey estimate in 2012 the catch projections for Atka mackerel have been revised downwards from previous estimates. Survey estimates in all areas declined from the 2010 values, especially for the eastern Aleutian Islands area (including the southern Bering Sea segment of the survey; Fig. 5). This assessment is characterized by having considerable uncertainty in the survey biomass index but fairly consistent age composition information over time from both surveys and the fishery. Model results indicate that the abundance of Atka mackerel has decreased after a peak in 2005 due to four back-to-back strong year classes (1998-2001). The projected female spawning biomass for 2013 is 103,000 t, which is 37% of unfished levels.  Atka mackerel is thought to be the most common prey item of the endangered western Steller sea lions within the AI region. NMFS has closed Atka mackerel fishing in areas around Steller sea lion haulouts and rookeries and also has used fine-scale time-area ABC allocations in attempts to maintain sufficient prey for Steller sea lions.  Other regional closure measures have reduced the amount of allowable catch, which should promote future increases in the stock.

By Jim Ianelli

<<< previous

next >>>

            Home | FOIA | Privacy | | Accessibility      doc logo