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Allison DeLong


Allison DeLong

Grinnell College
BA Mathematics

Humboldt State University
MS Mathematical Modeling option of the Environmental Systems graduate program

Marine Research Associate
University of Rhode Island
Graduate School of Oceanography

Fish provide an important source of protein in the U.S. and the world. It is important to manage the oceans well so that we can maximize the amount of fish that can be sustainably harvested. History has proved how challenging it is to do this, as several stocks of the most desirable fish species have been reduced to very low levels from commercial exploitation; for example some stocks (and subsequently catches) of haddock and flounder off the northeast U.S. were severely reduced in early 90s. Several Pacific salmon stocks are considered threatened and endangered. This situation is not unique to the United States. Scientists and resource managers are trying to determine how to rebuild these stocks, and even whether it is possible to do so. The people who look into these questions have a solid understanding of such topics as ecology, biology, statistics, dynamic systems, and linear algebra--just to name a few. It is very common for individuals with backgrounds in both applied mathematics/statistics and biology/ecology to pursue this field.

Since June 1997, I have been working as a Marine Research Associate at the University of Rhode Island's graduate school of oceanography. I am employed by a professor to work on projects related to fisheries stock assessment and population dynamics of exploited fish stocks. I am funded through grants we apply for from such institutions as the National Oceanic and Atmospheric Administration, National Marine Fisheries Service, and state agencies, such as the Alaska Department of Fish and Game (ADF&G). These agencies are charged with sustainably managing the aquatic resources and habitat in the areas under their jurisdiction and our findings aid them in their mission.

One of the projects I recently completed was to extend and hopefully improve the model currently used by the ADF&G to estimate several king crab stock abundances. The ADF&G permits the retention of crabs that are larger than a certain size. This size cutoff is set to be greater than the size at sexual maturity, so that crabs will have an opportunity to reproduce at least once. Managers set a commercial quota each year to be a proportion of these legal sized crabs, if the stock biomass is above a threshold value. If it is below the threshold, the fishery is closed for the year. Furthermore, they do not allow the quota to exceed a set proportion of the mature stock. This management policy requires estimates of both the mature and legal stock abundances. The model as previously formulated was not able to estimate the mature catch, so we extended this model to do this. We then thoroughly tested and compared this new model to the earlier version with Monte Carlo simulations and other statistical tests. This new model is to be used to help set the 1998 quotas for several king crab stocks.

We were all brought up to believe that big fish eat little fish, so that a lot of fish die just from being eaten by other fish. It is logical to suspect that the relative mixture of fish within the marine ecosystem influences individual species abundances. However, most exploited stocks are managed on a species by species basis. Another of our ongoing projects is to develop a dynamic model that attempts to describe the stock growth and decline as a function of both commercial exploitation and predation, with the hope of better understanding this relationship. We are examining the mathematics of the resulting model to determine if there are multiple stable equilibria and whether this may influence the ability of the system to return to its pre-fished state.

I chose to pursue this field in graduate school when I learned how interesting quantitative ecology can be and how vital this information is to regulators as they attempt to manage the resource. The ocean presents another level of complexity as it is difficult to observe the resource being managed. I plan to continue in this field because the challenges are endless and I collaborate with some very intelligent individuals to answer some interesting questions.