Program Manager's Update
  July 2003

 

 

 

 

"Many of the papers presented during the symposium will be included in a special issue of The Northeast Naturalist devoted to Mt. Hope Bay, which is due out in Spring 2004."

 

 

 

 

 

"Such a shift [from bottom dwelling fish towards mid-water column fish] can often be indicative of eutrophication effects due to increased nutrient loading."

 

 

 

 

"Although satellite observations can be useful, it is important to remember that they are only capable of measuring the skin temperature of the Bay."

 

 

 

 

 

"Our goal is to develop the Mt. Hope Bay Natural Laboratory as a system for developing process oriented (rather than statistical) estimates of these same cause and effect relationships."

 

Welcome to the Mt. Hope Bay Natural Laboratory website, and this inaugural edition of the update!  Over the course of the coming months and years I hope to use this portion of the website to keep you informed of important information regarding progress in developing and utilizing the natural laboratory.  Through this process, we hope to unravel the complex web of interactions that underpin the MHB ecosystem, and provide information that can be used by interested parties to make strong and effective management decisions.

The Mt. Hope Bay Symposium (NEERS/SNECAFS Joint Spring Meeting)
The complexity of the Mt. Hope Bay system was underscored during the recent symposium on Mt. Hope Bay held on May 10 in Fairhaven, Massachusetts as part of the New England Estuarine Research Society (NEERS) / Southern New England Chapter of the American Fisheries Society (SNECAFS) joint spring meeting.  Presentations during the daylong event, which was hosted by SMAST, initiated discussions on physical processes within the bay, the effectiveness of various fish population models, the state of water quality and dissolved oxygen within Mt. Hope Bay and Narragansett Bay, and the role of natural predators on the local winter flounder population.  During an open discussion period at the end of the day, regulators queried how all of these components might fit together in creating the current state of the Mt. Hope Bay ecosystem.  Although many answers were offered, no general consensus was reached, as the issues at hand are extremely complex and highly dynamic. Many of the papers presented during the symposium will be included in a special issue of The Northeast Naturalist devoted to Mt. Hope Bay, which is due out in Spring 2004.

Increased Nutrient Loading
Based on the variety of papers presented, it was abundently clear that the Bay ecosystem is under stress from a variety of sources. Increased nutrient loading from point and nonpoint sources throughout the watershed can contribute to low dissolved oxygen in bottom waters as shown in talks by Brian Howes of SMAST, and Chris Deacutis of the Narragansett Bay Estuary program.  Both of these talks described data sets identifying periods of critically low dissolved oxygen in bottom waters, a condition that can lead to severe effects for local biological populations.  Rodney Rountree of SMAST presented a review of trawl data from Narragansett and Mt. Hope Bays that show trends in fish abundance within the lower portion of Mt. Hope Bay that are indistinguishable from those throughout the rest of the Narragansett Bay region.  These trends indicated a shift from bottom dwelling fish, such as winter flounder, towards mid-water column fish.  Such a shift can often be indicative of eutrophication effects due to increased nutrient loading. 


Natural Predation
Another direct stressor to fish populations within the Bay is natural predation.  As predator populations are affected through various environmental and management mechanisms, these changes can be passed on to prey populations, such as winter flounder.   An example is the local comorant population, which has increased exponentially over the last few decades.  This bird preys directly on winter flounder and other fish species, with estimated predation rates that are on the same order as mortality rates due to other factors within the Bay,  as shown by Deborah French McCay, of Applied Science Associates (ASA).  The shrimp Crangon Septemspinosa is also a major predator of winter flounder,  directly affecting winter flounder eggs, as described by David Taylor from the University of Rhode Island (URI). 

Satellite Observations and Numerical Models
The impact of the Brayton Point thermal plume on the temperature structure and physics of the Bay was also addressed through satellite observations, as presented by John Mustard from Brown University, and several different numerical models, described by Liuzhi Zhao, SMAST, and Craig Swanson, ASA.  Although satellite observations can be useful, it is important to remember that they are only capable of measuring the skin temperature of the Bay.  Due to the buoyancy of the thermal plume during most of the year and its tendency to occupy only the top meter or two of the water column, focusing on skin temperatures only can provide a skewed perspective of heating effects on the entire Bay.  Numerical models can provide more information about the vertical structure of the temperature field, but require careful calibration and testing to insure that their output is realistic.

Population Models
Several fish population models were presented, each trying to incorporate the effects of these and other stressors, including fishing pressure and losses related to the Brayton Point intake, on fish abundances.  The models were presented in talks by Joseph DeAlteris, of URI, Thomas Englert of Lawler, Matusky and Skelly Engineers LLP (LMS), and Mark Gibson of the Rhode Island Department of Fish and Wildlife (RIDFW).  In many cases, the mortality rates attributable to various stressors within these models are based on statistical correlations between important variables.  While statistical methods can often provide insight into the nature of relationships, it is often difficult to segregate distinct cause and effect relationships in a complex system such as the Mt. Hope Bay ecosystem solely through statistical means.    

The Mt. Hope Bay Natural Laboratory
Our goal is to develop the Mt. Hope Bay Natural Laboratory as a system for developing process oriented (rather than statistical) estimates of these same cause and effect relationships.  We will be able to use the MHBNL to isolate specific factors and evaluate potential ecological effects.  The first step towards this goal is the development of a high-resolution numerical model capable of adequately describing the physics within the Bay.  With this model as a foundation, we can build more complicated processes, such as water quality and biological responses into the system, allowing us to segregate and combine various influences.

Currently, our efforts are primarily focused on improving the MHBNL numerical model through increasing the resolution, which is currently on the order of 100 meters within Mt. Hope Bay.  We hope to increase this resolution to 10 to 50 meters within certain regions of the Bay, particularly in the area surrounding Brayton Point.  Tests of the model’s sensitivity to boundary conditions and comparisons with existing data sets are also an important component of this stage of the model development.  We are also looking forward to conducting field experiments to provide additional data in targeted areas for further model comparison.  We hope to have an adequately resolved, calibrated model by the end of the current year.

We'll keep you informed as things move along.  Check back in the fall for another update.


 -Dan MacDonald
Program Manager
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