Exercise: Gone Fishing
Goals -
- analyze annual fish landing, mortality, and biomass data;
- explain what caused the collapse of ground fish populations in New England;
- define the terms overfishing and overfished;
- understand how MPAs can be effective management tools for preventing and reviving overfished populations;
- and examine your role as a consumer in aiding the sustainability of fish in our oceans.
Background
For as long as people have lived near water, people have fished. Sadly, in many instances, the history of fishing is paralleled by a history of overfishing. According to the 2006 Report of Status of U.S. Fisheries, 20% of U.S. fish stocks with known overfishing status are subject to overfishing and 25% of stocks with known overfished status are considered to be overfished. An additional four stocks currently classified as not overfished are approaching overfished status. Contributing factors to the current level of overfishing include:
- technological advances that have made large-scale fishing easier;
- too many fishing boats on the water;
- international partnerships that allow foreign fleets to overfish in the waters of developing countries;
- illegal fishing that violates fishing laws or agreements;
- large amounts of bycatch of juvenile fish and non-target species; and
- the shortcomings of fisheries conservation and management efforts.
The impacts of declining fish catches are being painfully felt by many coastal fishing communities around the globe. Jobs are lost and food is scarce. Impacts are also felt in the oceans as other marine species are left with fewer fish to eat. Overfishing affects the entire marine food web. But how do know when overfishing is occurring or when a stock is overfished? More importantly, can these conditions be reversed?
Part 1: Overfishing in Georges Bank
Georges Bank is an underwater bank situated along the eastern edge of the Gulf of Maine between Cape Cod and Nova Scotia. This region is one of the most biologically productive marine areas on the eastern seaboard, historically accounting for a large percentage of New England's commercial fish landings. The Georges Bank fishery is particularly well-known for its ground fish-species such as cod, haddock, and flounder that feed near the bottom of the ocean.
Look at the graph on the next page of trends in Georges Bank haddock catch and mortality from 1969 through 2004.
- The histogram shows the annual haddock landing-the amount of fish that are caught and kept to sell.
- The red line shows the fishing mortality rate, F-the rate at which fish are removed from a population due to fishing (as opposed to removals due to natural causes such as disease or predation). F can also be thought of as the percentage of a population that die in one year due to fishing.
(1) Describe the trends you see in the Haddock landings from 1969-2004. Are there steady trends or distinct turning points?
(2) Calculate the difference between the greatest and least landing values. What percentage of the maximum yield was the minimum yield? In what years did these extremes occur?
(3) Look carefully at the years 1985-2000. What does it mean for the fishing mortality to be consistently "high" while landings were consistently "low"?
Overfishing is the consequence of removing fish from the oceans faster than they can replenish themselves. This occurs when fishing mortality exceeds the Maximum Fishing Mortality Threshold (MFMT, or FTHRESHOLD). This value is normally equivalent to FMSY, where MSY (maximum sustainable yield) is the maximum catch the stock can sustain without impairing its ability to replenish itself through reproduction. Therefore, MSY is a measure of how many fish can be taken from the sea without causing the stock to become depleted.
(4) According to stock assessments by the Northeast Fisheries Science Center, the value of FMSY for Georges Bank haddock is 0.26. During which years was Georges Bank haddock subject to overfishing?
(5) Was Georges Bank haddock subject to overfishing as of 2004?
Part 2: Overfished in Georges Bank
Legend has it that Atlantic cod were once so abundant on the Georges Bank that men could scoop them from the sea with baskets. Unfortunately, this is no longer the case. Over the last several decades, Georges Bank has experienced significant declines in fish catch as a result of overfishing and ecosystem degradation by certain types of fishing gear. Do these declines in catch mean that fish species in this region are overfished?
For a species to be considered overfished, the population size must be below a level determined by scientists to be healthy. Look at the graph below of Georges Bank Atlantic Cod recruitment and biomass.
- Recruitment is the number of young fish that are just starting to be caught in fishing gear in a given year, or the number of fish that are reaching a particular size or age.
- Biomass is the total weight of a population of fish.
- Spawning Stock Biomass (SSB) is the total weight of all sexually mature fish in the population.
- NOTE: Stock biomass values along the y-axis are reported in 1,000s of metric tons (mt).
(6) Describe the trends you see in Georges Bank Atlantic Cod Spawning Stock Biomass from 1978-2004. Are there steady trends or distinct turning points?
(7) What do you think are the long-term consequences of declining Spawning Stock Biomass?
Read the History of the groundfishing industry in New England to learn about the many factors contributing to the overfishing and overfished status of New England groundfish species.
(8) Summarize how the ground fishing industry in New England changed over the course of the 20th century.
Part 3: Gone Today, Here Tomorrow?
Any stock that has previously been listed, or is currently listed, as overfished is required to have a rebuilding program until the stock has been rebuilt to levels consistent with supporting MSY on a sustainable basis. In many locations, such as Georges Bank, this rebuilding plan includes the establishment of Marine Protected Areas.
Read the WWF article, Protecting Fish and Fishermen: Marine Reserves in the United States Demonstrate Major Benefits to Fisheries. Answer these questions:
(9) What actions were taken to rebuild Georges Bank groundfish stocks in 1994?
(10) How were fishing zone closures enforced?
(11) How did groundfish species respond to protection?
(12) Besides the groundfish species targeted for rebuilding, what other species were affected by the closure of Georges Bank fishing grounds?
The article you read was written in 2003 and references Georges Bank fisheries data only through 2001. Examine the combined landings and biomass graphs below, which include data through 2005.
(13) Describe the trends in annual landings and biomass for Georges Bank haddock and Atlantic cod since 1994.
(14) Do you think the 1994 closures had long-term success for both species or do you think additional measures need to be taken to ensure the sustainability of Georges Bank groundfish? Explain.