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The Fisheries subgoal measures the sustainability of wild-caught
seafood harvests, with the aim of maximizing the amount that can be harvested year after year. Each year's catch must not take so much from the population that future catches will decline.
The status of a fishery is usually measured by the current abundance of a stock(s), expressed as biomass of fish in the water, in comparison with a reference point. For example, the UN Food and Agriculture Organization (FAO) categorizes stocks as 'overexploited', 'fully exploited' or 'underexploited' depending on whether the current biomass is less than 40 percent, 40-60 percent, or greater than 60 percent, respectively of the 'pristine' (unfished) biomass (Ye 2011).
The Ocean Health Index uses estimates of biomass to assess stock status, with the reference point that the biomass of all stocks should be at the level that provides maximum sustainable yield.
Stock status can also be judged by spawning potential, catch trend and size-age composition. Spawning potential is measured as the ratio of the total biomass of sexually mature fish in the stock ('spawning stock biomass') to the number of fish large enough to be caught that 'recruit' to the population each year through growth or migration. Ratios of less than 20 percent, 20-40 percent and greater than 40 percent indicate stocks that are 'overexploited', 'fully exploited' and 'non-fully exploited', respectively. Catches that drop significantly without reduction of fishing effort or that are less than 50 percent of the maximum (after 5-year smoothing) indicate an overexploited stock, as does an unstable size-age composition. Catches that remain at or close to peak values for the past 5-10 years and/or have stable size-age composition indicate a fully exploited stock. Catches that increase with increased effort without any change in size-age composition are non-fully exploited (Ye 2011).
How Was It Measured?
The Ocean Health Index bases its status assessments on current biomass (B) in relation to the biomass that would produce maximum sustainable yield (BMSY). Overall Fisheries status is calculated as the geometric mean of the status of
each fisheries stock, weighted by that stock's contribution to the overall catch. Learn more about what that means and how it was measured by scrolling down this page.
Stocks, Catches and Landings
Fisheries stocks. A 'stock' is the management unit of a
population of fish. Species with broad geographical distribution usually
comprise a number of smaller sub-populations within which reproduction takes
place. Sub-populations may differ
slightly in size, coloration or behavior owing to genetic variation or local
fishing pressure. Separate management plans are typically created for each
sub-population. Managed sub-populations
are referred to as 'stocks'. The UN Food
and Agriculture Organization (FAO) tracks approximately 600 seafood stocks.
Catches and landings. Data for evaluating fish stocks comes from catches and landings. ‘Catch’—sometimes called ‘harvest’ or ‘yield’-- is the total amount of whole fish captured and removal from the ecosystem. ‘Landings’ is the portion of catch brought to market on shore. The weight of landings is frequently less than the weight of catch, because guts are thrown overboard if fish are cleaned at sea; and some of a vessel’s catch may be eaten by the crew, used for bait or discarded overboard because it was undersized, spoiled or of the wrong species. Countries annually report their fish landings to the UN Food and Agriculture Organization (FAO). The FAO database covers about 70 percent of commercially exploited stocks. The remaining 30 percent are considered insignificant to world fisheries production.
Stock Status (B/Bmsy)
Stock status (B/BMSY). A stock’s status is expressed as the
ratio between its population biomass (B)--live weight in the ocean-- and the
biomass that can produce the maximum sustainable yield (MSY). MSY is the largest amount that can be caught
from the population year after year. The
goal is for all stocks to have B within 5% of the value that produces MSY (BMSY).
Scores are penalized for overfishing (B
> BMSY) and underfishing (B < BMSY) with increasingly penalties for larger departures of B from BMSY. Underfishing
is penalized only half as much as
B/BMSY is measured in different ways depending on what information is available, as described below.
1. Stocks with Formal Assessments
Formal stock assessments
gather detailed time-series data on catches from a fish stock. Data on size,
weight and age of fish caught as well as the species reproductive
characteristics are used to produce reliable models of B/BMSY. B/BMSY data for approximately 100 formally assessed
stocks were obtained from the RAM legacy database.
For stocks that have not been formally assessed, B/BMSY is estimated using data from the FAO, but in different ways for stocks identified to species and for others.
2. Stocks Identified to Species Level
For stocks identified to species, a modified version of Martell and Frœse’s (2012) “catch-MSY’ method is used. That model uses data on the reported catches over time, plus a series of estimated values for rate of population increase (r) and environmental carrying capacity (K) to estimate the biomass at the end of a time series. Using Rosenberg et al.’s (2014) modification, a biomass time series is computed for each ecologically relevant pair of r and K values, and values for B and BMSY are drawn from the arithmetic mean of those series. Modeling varied slightly for well-managed versus poorly-managed stocks, which are distinguished by calculating a ‘stock resilience score.’ The method for well-managed stocks is used for those with resilience scores of 0.6 or higher.
The resilience score is calculated as the mean of the fisheries resilience score used within the resilience dimension of the fisheries goal calculation (see Table K) across all the regions where the stock was caught, weighted by the stock’s relative mean catch in each of the regions. For a stock (or portions thereof) in a high seas area, a regional fisheries management organization(s) (RFMO) with an explicit mandate to manage that species received a score; without that mandate it scored 0. Factors included in RFMO scores are presence of harvest controls (such as setting of MSY, gear management measures or strategies for rebuilding stocks); harvest monitoring measures (such as maintaining a record of vessels and IUU vessels or having vessel monitoring systems); data reporting on catch, effort, gear, and bycatch; and making information available via a Web site, minutes of meetings or other means. For species managed by more than one RFMO within a given FAO major fishing area, the stock’s score is the mean of the individual RFMO scores, weighted by the relative area they respectively cover within that FAO region.
3. Stocks Not Identified to Species Level
Catch-MSY can only be
used stocks identified to species. Unfortunately, landings from many countries are variously identified at
six progressively less informative taxonomic levels: (6) species, e.g. Clupea harengus (Atlantic herring); (5) genus, e.g. Clupea; (4) family, e.g. Clupeidae; (3)
order, e.g. Clupeiformes; (2) subclass or subphylum, e.g. Neopterigii or
Vertebrata, respectively; or (1) coarsest level identification, e.g.
‘finfishes’ or ‘pelagic fishes.’ B/BMSY
for stocks not identified to species was estimated as follows.
First, the median value of all B/BMSY estimates for stocks that were identified to species within the same fishing area and year is computed. That median value is then assigned to all other stocks, but penalized by 10%, 20%, 50%, 75% and 99% for identification to genus, family, order, subclass/subphylum or coarsest level of identification, respectively. Penalties are applied because the ability to manage stocks properly is increasingly compromised by poorer ability to identify them.
4. Regional Fisheries Status Scores
Once B/BMSY values for all of the stocks in a region are estimated for a particular year, the overall status of wild caught fisheries in the region for that year is calculated as the geometric mean of
the B/BMSY values for each stock weighted by its relative contribution to
Finding the regional stock status values requires spatial allocation of catches from the FAO’s 19 major fishing areas to those smaller areas, which include EEZs, areas beyond national jurisdiction (High Seas) and Antarctica. Allocations maintained the relative proportion of stocks per EEZ per fishing area published by Sea Around Us in 2006 based on the species’ known geographic ranges and other factors, but used data from more recent years to update values for total biomass per taxon per major fishing area and update taxonomic resolution of catch reports where possible.
Benefits, Limitation and Caveat
Benefit: The B/BMSY method provides stock status scores that vary continuously from 0 to 1, which is useful because different management systems differ in the criteria they use for categorizing stocks as 'overexploited', 'fully exploited' or 'underexploited.'
Benefit: Use of the geometric weighted mean gives small stocks that are doing poorly more influence on the overall score than they would have using an arithmetic weighted mean. Improving the status of a poorly performing stock is rewarded more than improving a well-performing stock, because it requires more effort and can have more important effects on the system than making a species that is already abundant even more abundant.
Limitation: The model does not account for interactions between fish species, such as competition and predation, though use of the geometric mean could incorporate some of them.
Caveat: The catch-MSY model is applied to stocks of non-fish seafood (invertebrates such as shrimp, scallops, clams, etc.) though Martell and Froese (2012) developed it and tested it only for fish. Invertebrates represent 12 of the top 17 species for global caught biomass and are the dominant stocks in many EEZs, but models for assessing their status are poorly developed.
What Are The Impacts?
Overfishing has caused significant decreases in catches for many of the world’s fisheries, negatively impacting ecosystem health and the sustainability of stocks.
Accurate assessment of Fisheries Status is crucial to avoiding unacceptable harm to fish stocks, habitats, and ecosystems caused by overfishing.
HUMAN HEALTH IMPACT
Human food supplies have been reduced due to overfishing and the resulting decline in catches for many of the world’s fisheries.
A product of the fishing industry, fish oil is an important source of omega-3 fatty acids, which can provide nutritional benefits to humans. Over-exploited fisheries may be unable to sustainably supply increased amounts of fish oils. Production levels have decreased in recent years.
In 2009, total fish oil production by the five main exporting countries (Peru, Chile, Iceland, Norway, and Denmark) was 530,000 tonnes, 100,000 tonnes less than in 2008 (FAO 2010).
Accurate assessment of Fisheries Status is crucial to maximizing human food benefits both now and in the future. Sustainable food provision from ocean ecosystems is likely to be an increasingly important diet component for the growing human population.
Overfishing and decreased overall catches in fisheries threaten the social and economic sustainability of fishing communities worldwide.
Properly managed sustainable fisheries could provide additional global net economic benefits of $50 billion each year (World Bank and FAO 2009).
Accurate assessment of Fisheries Status is crucial for maintaining the long-term economic health of livelihoods in the fishing industry and of the coastal communities providing those livelihoods.
Get More Information
Food and Agriculture Organization of the United Nations (FAO)
Fishery Fact Sheets Collections
ASFIS List of Species for Fishery Statistics Purposes
Developed at the WorldFish Center in collaboration with the Food and Agriculture Organization of the United Nations (FAO) and many other partners, this global information system provides detailed information on almost all of the known world fish species and aquatic living organisms (marine and freshwater), and is searchable by country and species.
The Sea Around Us Project
The Sea Around Us project investigates the impact of fisheries on the marine ecosystems of the world, and offers mitigating solutions to a range of stakeholders. The project is a scientific collaboration between the University of British Columbia and the Pew Environment Group that began in July 1999. The Sea Around Us project conducts a catch reconstruction program, the results of which improve the accuracy of estimates of catch, stock exploitation status, and other key factors for fisheries management.
Martell, S. and R. Froese. (2013). A simple method for estimating MSY from catch and resilience. Fish and Fisheries 14(4): 504-514. DOI:10.1111/j.1467-2979.2012.00485.x
World Bank and FAO. 2009. The Sunken Billions: The EconomicJustification for Fisheries Reform. World Bank. Washington, DC.