Download Fishery Stock Status: Biomass – February 2014

Northeast Groundfish Interim Findings: Ecological Indicators
Version: February 2014
Fishery Stock Status - Biomass
This indicator measures the abundance of fish stocks as a component of fishery stock status (Fishery Stock
Status: Introduction).
Additional charts provided below. The images in this downloadable fact sheet may not show all the components
within each indicator. To work with an interactive display of the data underlying this indicator, go to:
http://catchshareindicators.org/indicators/northeast/fishery-stock-status-biomass/
Key Terms and Definitions:
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Biomass (B): The total weight or volume of a stock of fish.
BMSY : The biomass that would provide the highest long-term average catch (or maximum sustainable yield,
MSY) of a fish stock.
B/BMSY : For a particular fish stock, the ratio of observed biomass to the biomass that would provide maximum
sustainable yield. When B/BMSY = 1, then biomass equals BMSY. If B/BMSY falls below 1, biomass is too low to
provide maximum sustainable yield. For example, if B/BMSY = 0.5, then biomass is only 50% of that needed
for maximum sustainable yield.
Northeast: Fishery Stock Status - Biomass
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Overview
Over the past decade, biomasses of groundfish stocks have fluctuated without clear, discernible trends.
Average biomass has generally increased from a low point in 2005, while the percent of stocks with
biomass levels less than 50 percent BMSY has declined, also since 2005. BMSY is the biomass that would
maximize long-term average catches. There is no apparent trend in the percent of stocks having biomass
less than BMSY, which has been relatively constant around 71 percent since 2005. With only one year of
data available for the catch share program, it is too early to see any trend. Biomass indicators, like many
other ecological indicators, may take many years to show patterns of change since they are subject to
many different influences. The appearance of a decline in average biomass in 2010 is because of the fact
that biomass data were not available for two abundant stocks (pollock, Gulf of Maine winter flounder). We
expect those data to be available in the second half of 2014.
Baseline Period
Where B/BMSY = 1, the given stock biomass would be equal to the BMSY value, the biomass that would
maximize long-term average catches. During the baseline period of 2002 through 2009, the average
biomass ratio of fish stocks initially declined from roughly 0.45 to 0.35 in 2005.
During the baseline period of 2002 through 2009, the average biomass ratio (B/BMSY; BMSY is the
biomass that would maximize long-term average catches) of fish stocks initially declined from roughly
0.45 to 0.35 in 2005. They then rose continuously until reaching 0.46 in 2009 (where B/BMSY = 1, the
given stock biomass would be equal to the BMSY value). This means that the average biomass across all
surveyed species was between 35 and 45 percent of the level that would produce maximum sustainable
yield (MSY). Two stocks—Gulf of Maine (GOM) winter flounder and GOM haddock—had biomasses that
exceeded BMSY for the entire baseline period. In contrast, six stocks had biomasses that were less than 50
percent of BMSY (overfished) for the entire baseline period. Trends in the biomass of individual stocks
showed no consistent patterns, with one-half of stocks showing an increasing trend and the other half
showing a declining trend.
The number of stocks deemed to have “low biomass” or to be “overfished” during the baseline period did
not demonstrate notable trends. In this case, “low biomass” is defined as any stock biomass below BMSY
and “overfished” as any biomass less than half of BMSY. In 2004 and 2005, nine out of 14 of the assessed
groundfish stocks had biomass levels that were less than one half of the value that produces MSY. But this
number declined to 50 percent by the end of the baseline period, meaning fewer stocks were overfished. In
any given year of the baseline period, between two and five of the individual stocks had biomass levels
that exceeded MSY, while the majority of stocks had low biomass levels (less than BMSY). Three stocks
showed improvement in status, increasing from a “low biomass” level to a level above the biomass
reference point during the baseline period. Those stocks were Acadian redfish, Atlantic pollock and
Western Georges Bank (GB) haddock. American plaice stock showed improvement from “overfished” to “low
biomass,” while GOM haddock declined, shifting from above BMSY to “low biomass” during the baseline
period. Meanwhile, witch flounder deteriorated from “low biomass” to “overfished” over the same period.
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Both GB and GOM cod showed slight improvement in biomass beginning in 2006, although both stocks
remain overfished.
Catch Share Program
The average biomass ratio continued its slight upward trend in 2010, following a similar trajectory from
the post-2005 baseline years. Both the percentage of stocks with low biomass and the percentage of
stocks considered overfished remained relatively unchanged in the first year of the catch share program.
One stock (white hake) exhibited an improvement in stock status from “overfished” to “low biomass”, but
no other stocks exhibited a change in status during the first two years of the sector program. This lack of
dramatic change matches expectations, since we would not expect biomass of stocks to change abruptly
because of the implementation of the catch shares program or the imposition of annual catch limits (ACLs).
Rather, it may take one or more fish generations (at least 5 years) to see improvements in biomass levels.
Biomass data for 2011 were available only for four stocks, three of which—GB cod, GB yellowtail flounder,
and SNE/MA yellowtail flounder—were overfished. We will monitor changes in biomass regularly as stock
status information is updated.
Data Gaps and Limitations
Data for this indicator came from the most recent fisheries stock assessments for 14 of the 16 stocks
allocated in the Northeast Multispecies Sector Program. Eastern GB cod and Western GB haddock are not
included in this analysis because assessment documents did not include an estimate of BMSY. For GOM
winter flounder and Atlantic pollock, the most recent assessment provides biomass estimates only through
2009. We did not attempt to extrapolate biomass levels for these stocks in order to fill in any missing
values.
Focusing on average biomass on a stock-by-stock basis allows equal weighting of the different stocks,
regardless of their overall biomass. Furthermore, we used the geometric mean of the biomass ratios rather
than an arithmetic mean to ensure a proper comparison of species that were above or below the
BMSY threshold.
It is important to remember that responses in stock biomass to changes in management or other factors
take considerable time to realize. The response time varies from species to species based on generation
time. Furthermore, the response may be partially or entirely masked by other factors, such as
environmental conditions and predation. It may take a number of years of data to properly identify
relevant trends.
Information Sources
Brooks, E.N., Sutherland, S., Van Eeckhaute, L., and Palmer, M.C. 2012. Georges Bank Haddock Assessment
Update. Northeast Fisheries Science Center Groundfish Assessment Updates 12-06.
Group, N.D.W. 2010. Stock Assessment of Pollock in US Waters for 2010. Northeast Fisheries Science
Center Stock Assessment Workshop 10-17.
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February 2014
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Legault, C., Alade, L., Emery, S., King, J., and Sherman, S. 2012a. Cape Cod-Gulf of Maine Yellowtail Flounder
Groundfish Assessment Update. Northeast Fisheries Science Center Groundfish Assessment Updates 12-06.
Legault, C., Alade, L., Stone, H.H., and Gross, W.E. 2012b. Stock Assessment of Georges Bank Yellowtail
Flounder for 2012. Transboundary Resources Assessment Committee.
Miller, T.J. 2012. Gulf of Maine-Georges Bank Acadian Redfish. Northeast Fisheries Science Center
Groundfish Assessment Updates 12-06.
Northeast Fisheries Science Center. 2011. 52nd Northeast Regional Stock Assessment Workshop (52nd
SAW): Northeast Fisheries Science Center Reference Document 11-17.
Northeast Fisheries Science Center. 2012a. Gulf of Maine Atlantic Cod (Gadus morhua) Stock Assessment for
2011, Updated through 2010. Stock Assessment Workshop 12-05: 1–369.
Northeast Fisheries Science Center. 2012b. Southern New England Mid-Atlantic Yellowtail Flounder
(Limanda ferruginea) Stock Assessment for 2012, Updated through 2011. Stock Assessment Workshop 1218: 1–246.
Northeast Fisheries Science Center. 2013a. Stock Assessment of Georges Bank Atlantic Cod (Gadus morhua)
for 2012. Stock Assessment Workshop 13-11: 1–206.
Northeast Fisheries Science Center. 2013b. Gulf of Maine Atlantic Cod (Gadus morhua) Stock Assessment
for 2012, Updated through 2011. Northeast Fisheries Science Center Stock Assessment Workshop 13-11.
O’Brien, L., and Dayton, J. 2012. Gulf of Maine-Georges Bank American Plaice Assessment for 2012.
Northeast Fisheries Science Center Groundfish Assessment Updates 12-06.
Palmer, M.C., Sutherland, S., and Brooks, E.N. 2012. 2012 Update of the Gulf of Maine haddock
(Melanogrammus aeglefinus) stock assessment: an update of the resource through calendar year 2010.
Northeast Fisheries Science Center Groundfish Assessment Updates 12-06.
Shepherd, G., Sosebee, K., and Brooks, L. 2013. Gulf of Maine/Georges Bank White Hake (Urophycis tenuis)
Stock Assessment for 2013, Updated through 2011. Northeast Fisheries Science Center Reference
Documents 13-10.
Van Eeckhaute, L., Brooks, E.N., and Hansen, S.C. 2012. Assessment of Eastern Georges Bank Haddock for
2012. Transboundary Resources Assessment Committee.
Wang, Y., and O’Brien, L. 2012. Assessment of Eastern Georges Bank Atlantic Cod for 2012. Transboundary
Resources Assessment Committee: 1–88.
Wigley, S.E., and Emery, S. 2012. Witch Flounder. Northeast Fisheries Science Center Groundfish
Assessment Updates 12-06.
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Charts
Proportion of Stocks with Low Biomass
Biomass for Allocated Stocks
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February 2014
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