Smooth Bottom Net Trawl Fishing Gear Effect on - New England ...

successional stage reflecting the long term ambient disturbance frequency. An inspection of the
benthic species list reveals that two of the faunal dominants (Prionospio steenstrupi and Unciola
inermis) are important food items for bottom fish and that overall faunal density is slightly
higher in the trawled lanes than in the controls. What if the trawling frequency was doubled or
tripled? Would this frequency of “pulsing” be accompanied by enhanced productivity of both
the invertebrate prey species and increased net catch?
4.4 A Modeling/Simulation Approach
Field experiments involving manipulated pulsed disturbances and associated ground-truth
sampling can be very expensive. For this reason, we recommend that before such a field effort is
made, modeling/simulation studies be conducted to provide insight into the pulse frequency to
maintain or optimize secondary benthic productivity. Examples of such modeling exercises are
given in McCall (1975, 1977), Rhoads, McCall, and Yingst (1978), Whitlach, Lohrer, and
Thrush (2003), and Zajac (2001). This type of modeling is based on knowledge of the dominant
colonizing species life history attributes, literature values for known recolonization rates, and
seasonal affects on somatic/population growth rates and recruitment.
We suggest that the STELLA graphical program used by Whitlach, Lohrer, and Thrush (2003) to
simulate the recovery time for benthic systems colonized by larval and non-larval recruitment
may serve as a platform for the modeling and simulation proposed here. Some additions and
reconfigurations would be required in their STELLA program to address the critical trawling
frequency problem. The model (or family of models) would need to address a wide range of
management scenarios. For example, the simulation should be sensitive to the targeted fish
population (s) and hence the preferred benthic prey species eaten by the fish populations interest.
The input variables to the simulations would include how frequently the system is impacted by
natural disturbances known to be important in restructuring the benthos such as storm reworking,
seasonal hypoxia, or major fluctuations in salinity. The response of benthic prey to such
disturbances will also depend on the candidate species pool that can populate the site. This
includes the method and frequency of each species’ mode of reproduction, dispersal, and
fecundity. Finally, the model must consider the effect of seasonal water temperatures and
primary production cycles that drive recruitment and growth.
For this initial modeling effort, we suggest that the simulation be run for two sites representing
end members in terms of ambient disturbance. The first would be Little Tow/Mud Hole
representing a naturally disturbed bottom (seasonal storm induced bed load transport). This
simulation will rely on data already in hand in our 2001 and 2002 trawling impact studies. A
second simulation would be run representing a low kinetic energy site in Massachusetts Bay (off
Gloucester per Alan Michael’s suggestion or a high successional stage mud site in central Mass
Bay where several years data from the MWRA study is available). The two simulations would
provide insight into the critical pulse disturbance in areas naturally affected by storm reworking
(Little Tow and Mud Hole) versus a low kinetic energy bottom which is maintained in a high
order successional stage. Seasonality factors would be able to be held constant given the
proximity of the two sites.
The product of such a modeling exercise would be bivariate graphs of disturbance frequency
versus secondary productivity over an annual cycle for both sites. Based on this simulation
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