Understanding Population Assessments
Population assessments—also known as stock assessments—provide important information for marine resource management.
Population assessments are a key component of marine resource management. These assessments allow us to evaluate and report the status of managed fisheries, marine mammals, and endangered/threatened species under the authorities of the Magnuson-Stevens Fishery Conservation and Management Act, the Marine Mammal Protection Act, and the Endangered Species Act.
To conduct population assessments, our scientists:
The assessment process uses current data and advanced analytical techniques in an effort to provide the best scientific information available for conservation and management decisions.
Fish stock assessments often use catch, abundance, and biology data. These data feed into mathematical models that produce estimates of the fishery management factors needed for managers to make decisions about how to best regulate a fishery.
Scientific review groups advise NOAA Fisheries and U.S. Fish and Wildlife Service on the status of marine mammal stocks within three areas: Alaska, the Atlantic (including the Gulf of Mexico), and the Pacific.
Stock assessments measure the impact of fishing on fish and shellfish stocks. Assessments also project harvest levels to maximize the number of fish that can be caught every year while preventing overfishing, protecting the marine ecosystem, and—where necessary—rebuilding depleted stocks.
These reports provide resource managers with information needed to manage marine mammal stocks protected under Marine Mammal Protection Act. These reports contain valuable information about geographic range, population size and trends, productivity rates, and estimates of mortality to design and implement appropriate conservation measures.
These assessments provide the foundation for evaluating the status of—and threats to—endangered marine mammals, fish, and sea turtles managed by NOAA Fisheries under the Endangered Species Act. Endangered species assessments include synthesis and analysis of scientific information on a species’ or stock’s population structure, life history characteristics, abundance, and threats—particularly those caused by human activities.
Stock assessments are the scientific foundation of successful and sustainable fishery harvest management. Stock assessments measure the impact of fishing on fish and shellfish stocks. They project harvest levels that maximize the number of fish that can be caught every year while preventing overfishing (removing too many fish), protecting the marine ecosystem, and—where necessary—rebuilding overfished (depleted) stocks.
Each stock assessment produces a report that provides fishery managers with a scientific basis for setting sustainable harvest policies under the authority of the Magnuson-Stevens Fishery Conservation and Management Act. Under the Act, we partner with eight regional fishery management councils to manage nearly 500 fishery stocks. NOAA Fisheries provides scientific guidance to resource managers by addressing fundamental questions including:
To learn more about the basics of the fisheries stock assessment process, read our Stock Assessments 101 series:
In addition to commercial and recreational fishery-dependent data sources, many stock assessments use fishery-independent data from surveys. We conduct sample surveys for fishes, invertebrates, and environmental conditions (e.g., temperature, salinity, dissolved oxygen) across the eight regions of the United States exclusive economic zone. We analyze abundance and biological data (e.g., species, length, stomach content) collected by these surveys in stock assessments.
Fishery-independent surveys are managed by our regional fisheries science centers and tracked nationally via the Fisheries-Independent Survey System. This national system characterizes our ocean observation activities and data collection during fishery-independent surveys and provides up-to-date information to fishery scientists, managers, and the public through flexible digital mapping and tabular reporting applications.
Along with our regional, state, and international partners, we conduct an average of 200 stock assessments annually. This includes more than 85 assessments of stocks included in the Fish Stock Sustainability Index, which is used to measure the performance of the most commercially and recreationally important fisheries.
We collect and store fish stock assessment results and related information in the Species Information System. This public portal allows users to view and download stock assessment summaries and results. We also produce National Fish Assessment reports on a quarterly basis with up-to-date summaries on the status of NOAA Fisheries assessment activities for federally-managed fish stocks.
We provide the scientific information that supports the management of approximately 500 fish stocks. However, we only have data and resources to assess about 200 stocks each year. Stock assessment prioritization allows us to work with regional partners to decide which stocks are assessed each year.
Stock assessment prioritization considers stocks managed under federal fishery management plans as well as non-federal stocks that might also be assessed by our regional fisheries science centers. This process considers:
First-time assessments for previously unassessed stocks.
Updating existing assessments using established methods and data types.
Upgrading assessments to use new types of data and methods.
We developed the prioritization process during several years of collaboration with partners. The result is a national framework for prioritizing stocks. Each region uses this framework to help determine assessment targets and priorities to best meet those targets.
The Species Information System database is the central repository for regional and national fish stock information across NOAA Fisheries and includes stock assessment results and related information used to determine stock status. The database includes a species information public portal that provides easy access for anyone to view and download summaries and results of the most recent stock assessments.
Interested in specific regional stock assessments?
Or take a deeper dive and learn more about our stock assessment programs at our science centers:
Alaska Fisheries Science Center|Status of Stocks and Multispecies Assessment Program|Marine Ecology and Stock Assessment Program
Pacific Islands Fisheries Science Center | Fisheries Research and Monitoring Division
Southwest Fisheries Science Center | Stock Assessment Programs
Northeast Fisheries Science Center | Population Dynamics Branch
Southeast Fisheries Science Center | Sustainable Fisheries Division
We are working to advance our stock assessment program to provide fishery managers and the public with more timely, accurate, and complete information on sustainable catch levels and fish stock status. We are updating our Stock Assessment Improvement Plan, first published in 2001, which provides a framework for moving toward a next generation stock assessment enterprise.
The vision of this “next generation” enterprise is to improve timeliness and efficiency of assessments while maintaining their utility to fishery management, prioritizing work relative to available resources, expanding the scope of stock assessments to be more holistic and ecosystem-linked, and using innovative modeling and data collection techniques. When finalized, the updated Stock Assessment Improvement Plan will better guide us toward our vision of resilient ecosystems, communities, and economies for future generations.
View our Stock Assessment Improvement Plan
We also support the development of future and current stock assessment scientists. Programs focused on training the next generation of scientists in stock assessment and other relevant career fields include the QUEST Program and NOAA Fisheries-Sea Grant Fellowship Program. We also provide current stock assessment scientists with opportunities for continued education and training in the evolving skills necessary for next generation stock assessments through in-person and online workshops.
We publish marine mammal stock assessment reports, which contain information about geographic range, population size and trends, productivity rates, and estimates of mortality. Marine mammals under our jurisdiction include whales, dolphins/porpoises, and seals/sea lions. The reports are prepared in consultation with one or more of three regional scientific review groups, and drafts are available for public review and comment.
Each year, we review reports for strategic stocks of marine mammals. For non-strategic stocks, we review reports every three years, or when new information becomes available. If the reviews show that the status of the stock has changed or can be assessed more accurately, we revise the report in consultation with the scientific review groups and after public review and comment.
The U.S. Fish and Wildlife Service also prepares stock assessment reports for marine mammals under their jurisdiction including manatees, polar bears, sea otters, and walruses. Some reports include information on multiple stocks.
NOAA Fisheries and U.S. Fish and Wildlife Service prepare reports only for marine mammal stocks that occur in waters under U.S. jurisdiction, as stated in the Marine Mammal Protection Act. We do not prepare reports for marine mammal stocks worldwide.
Data collection, analysis, and interpretation are conducted through marine mammal research programs at each of our regional fisheries science centers and by other researchers. Data are collected in a variety of methods, including aerial and ship-based surveys, acoustic monitoring, photo identification studies, biopsy sampling for genetic studies, and tagging.
The Marine Mammal Protection Act provides only general descriptions of the kinds of information that must be included in stock assessment reports. For example, the reports require a "minimum population estimate," which means we have "reasonable" assurance there are at least the estimated number in the population.
Each marine mammal stock assessment report includes:
The first stock assessment reports prepared in 1995 included about 165 reports on marine mammal stocks in U.S. waters:
The number of reports may vary from year to year because stock identification is subject to change. Marine mammal stocks may be added or removed from the regional list of compiled reports due to changes in distribution.
We use marine mammal stock assessment reports to:
For marine mammal stock assessments, the Marine Mammal Protection Act provides only general guidance on assessment methods and on the content of the reports. To include values for the required elements in the reports, NOAA Fisheries and U.S. Fish and Wildlife Service translated qualitative concepts into quantitative terms. After building a scientific foundation through simulation modeling, we proposed guidelines for selecting specific values to include in the reports. The guidelines received review and comments by the public and scientific review groups.
View the Guidelines for Assessing Marine Mammal Stocks for information on the background, decisions, and default values that go into developing the stock assessment reports.
Additionally, we work with partners to develop and evaluate analytical products and applications to improve population assessments.
To disseminate results and increase national coordination and collaboration in conducting assessments, we support and organize protected species assessment workshops biennially. Other workshops address specific technical topics and advance various protected species science initiatives with direct relevance to management actions. Similarly, various dedicated working groups encourage dissemination of best practices and latest advances in the field.
Population assessments provide the foundation for evaluating the status of and threats to marine mammals, sea turtles, and fish protected under the Endangered Species Act and to plan and implement species recovery and conservation actions.
Marine resource managers require accurate and precise information on a species or stock’s population structure, life history characteristics and vital rates, abundance, and threats (particularly those caused by human activities). This information informs agency decisions related to:
Information included in endangered species population assessments is vital to how we support and advise state and tribal-managed coastal areas. It also allows us to provide scientific and policy leadership to regional and international bodies such as multi-state marine fishery commissions, U.S. fishery management councils, international fishery management organizations, and the Convention on International Trade in Endangered Species of Wild Fauna and Flora.
We provide funding support to our agency scientists as well as university, federal, and state partners to improve sea turtle population assessments through a competitive, peer-reviewed process. Funds are awarded based on relevance to management concerns and scientific research priorities.
For assessing acoustic impacts on endangered species, we also provide funding through a competitive, peer-reviewed process to support research conducted by NOAA scientists and partners.
We have established the National Protected Species Toolbox Initiative to support the development of analytical products and applications that aim to investigate impacts and consequences of human and environmental disturbance on endangered and threatened marine life and other protected species.
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We study the size and age composition of fish populations throughout New England and the Mid-Atlantic. We do this in order to: Monitor the abundance of fish stocks. Measure the impact of fishing activity. Evaluate biological aspects