How Many Fish?

Human Impacts—How Many Fish?

Summary: How many fish do humans harvest, and can we harvest as many as we can and still expect fish populations to remain stable over time? Through hands-on modeling activities, students explore issues of population ecology and stock management issues in the Pacific Northwest. All of the activities presented here lead to stewardship activities that are listed in the Finding a Balance topic guide.

Concepts to teach: Renewable and non-renewable resources, population ecology, fisheries management, sustainability

Goals: The ocean’s resources are vast but not unlimited. With the help of scientific research and modeling, fisheries managers make rules about fishing so that the industry will remain (or become) sustainable.

H.3S.1, H.3S.2, H.3S.3

Specific Objectives:

  1. Recognize that fish populations remain stable when life history characteristics, ecological relationships, and harvesting practices are in balance.
  2. Explain how technology changes success in fishing.
  3. Demonstrate how fisheries managers use scientific research, models, and math to determine how many fish can be harvested.

Activity Links and Resources:

  • From the Alaska Fisheries Science Center:
    • Population Estimation—This narrated learning module introduces the concept of population estimation and then provides five examples using different species to describe the various methods AFSC scientists use to estimate population sizes.
    • Fish Fetch—This activity helps students understand how to estimate population size from samples.
  • Use the NOAA Fisheries: Office of Science and Technology website to download actual data on fish caught from year to year. The site allows you to sort for a specific species such as “salmon, sockeye” and for a location, “Oregon.” Use the data for graphing, finding mean and median, comparing, and other math exercises.
  • NOAA Fisheries Northwest Regional Office School Curricula highlight how scientific evidence and stakeholder input help NOAA Fisheries policy makers and manager to decide on regulations and other actions to conserve and manage the resources for which the agency is responsible.
  • Population Dynamics – Selena Hepell, Associate Professor in Fisheries and Wildlife at OSU, developed these lesson plan for undergraduates.
    • Population Estimates—Students conduct a mark-recapture experiment, estimate population size using two different mark-recapture techniques (in both a closed and open system), and learn how to construct a histogram of population estimation data.
      Lab Printable | Answer Sheet
    • Trends—Learn some Excel basics, create graphs of population size through time, fit a trend line to the data, and determine if the trend is significant.
      Lab Printable | Answer Sheet
    • Logistic Model—In this lab, students explore the logistic equation, its behavior under stochastic conditions, and some basic harvest simulations. Includes Answer Sheet.
      Lab Printable | Answer Sheet
    • Potential Biological Removal (PBR) for Whales—Students calculate limits to the allowable human-caused mortality of cetaceans and pinnipeds. Lab Printable
  • Impacts of Invasive Species on marine species populations
    • Olympia Oyster—This library-research lesson from Ocean and Coastal Interdisciplinary Science (OACIS) focuses on the effect a non-native Pacific Oyster has on populations of Olympia Oyster in the Puget Sound region.


  • Assessment worksheets and other tools are included in the NOAA Fisheries curricula.