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Rethinking the Global Fisheries Crisis

Dr. Olaf Jensen
Rutgers University, Department of Marine and Coastal Science

The global human population is anticipated to reach nine billion by the year 2050, begging the question of how to feed so many people. This concern raises new questions for the sustainability of the world’s fisheries, which are generally considered to be already stressed beyond recovery. Or are they?

On Tuesday, June 11, 2013, Olaf Jensen, Ph.D., of Rutgers University’s Institute of Marine and Coastal Science, spoke about “Rethinking the Global Fisheries Crisis” as part of Metcalf Institute’s annual public lecture series at the University of Rhode Island Graduate School of Oceanography. Predictions of global fish collapse have been based on fish landings, not on the number of fish that are actually in the water. Jensen described how meta-analysis, a method that pools datasets from researchers and agencies around the world, is used to compile a massive database of marine fish populations. Meta-analyses are also used to describe general trends in the state of fish stocks, create new hypotheses about fisheries health and management, and challenge existing assumptions about the state of our global fish stocks.

The database that Jensen and his colleagues have compiled, the RAM Legacy Stock Assessment Database (, is the first database of global stock assessments, containing information on more than 350 stocks of 147 fish and 16 invertebrate species. Jensen noted that stock assessment data are very useful to better explain the status of fisheries because they show fisheries’ responses to regulatory actions, instead of just the catch data. Unfortunately, most of the world’s ocean lacks these stock assessment data. The Jensen team uses the database to compare present-day population sizes of various commercially important fisheries to what researchers think are the optimal population, or “stock” sizes. Jensen referred to the popular fisheries management concept of a “maximum sustainable yield,” which he described as akin to a fish bank account. With a small principle in the bank account, a person could expect to gain only a small amount of interest. The goal of fisheries management is to identify catch rates that will leave an intermediate stock size and maximize interest (the number of remaining fish).

Jensen explained that 63% of global fisheries stocks are below the Maximum Sustainable Yield, indicating lower population numbers than would be ideal. These indicators are improving, however, with recoveries underway for over 50% of overfished populations. Jensen went on to debunk several commonly held assumptions about fish stocks based on the findings of their meta-analyses.

Assumption 1: Fish stocks are bad and getting worse. The results from Jensen’s meta-analysis demonstrate that two-thirds of fish populations are low compared to where they ought to be. However, because excessive fishing is beginning to be controlled, many locations are starting to recover.

Assumption 2: Large, top trophic-level predators are the most vulnerable to collapse. It is widely assumed that initially aim to catch the top-value and/or largest fish first. Once the populations of top-level species are depleted, fishermen then move to catch the next marketable species down the food chain. This process has been referred to as “fishing down the food web.” The reality, said Jensen, is that the first fisheries to develop were those that yielded the greatest value for the least effort. Commercial fishing operations targeting lower trophic level species (e.g., lobster) developed concurrently with those catching top predators. The meta-analysis findings showed that a species’ trophic level is not a good indicator of the status of a fishery. (See more about this here:

Assumption 3: Most fish stocks are depleted and unrecoverable. Jensen and colleagues challenged this assumption by asking what decides the recovery rate of fisheries that have shown improvement. The results of the meta-analysis led them to conclude that there is no point beyond which fisheries cannot recover. In fact, some fish populations that have been fished at high but consistent rates over long periods of time have adapted mechanisms to aid in the speedy recovery of the population. According to Jensen, fishing pressures determine the recovery rate, suggesting that careful fishing practices may improve recovery.

Jensen argued that many fish stocks are overfished, and overfished species are vulnerable to collapse regardless of trophic level. However, he added that the causes and consequences of overfishing are not as simple as they are often portrayed. Jensen noted that commercial fisheries are moving to waters owned by countries with more relaxed regulations, which may be worrisome if fishing pressures exceed sustainability. He concluded by referring to a final common assumption: those people who care about the environment should avoid eating fish. Jensen disagreed with this argument, recommending instead that consumers choose their fish carefully and buy local, since 91 percent of seafood consumed in the U.S. is currently imported from these nations with poor environmental oversight.

Lecture Summary prepared by Al Nyack, Ph.D.

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