$12\mathrm{.}2.$ A new railway bridge has been proposed for construction across the Wabash River to alleviate traffic congestion on the that construction A primaty concern, however, is erosion of expose the new bridge will cause erat release of oil and soil surfaces, sedimentation, and reles ultimately other construction chemicals that will ultion of lead to a significant depletion of the population of silver carp in the waters traversed by the bridge. Construction is expected to take place in the summer of $2007.$ It has been estimated that every year from the summer to fall season, $2000$ new silver carp hatch out from their eggs and that the total silver carp population in the area is $72,000.$ The average survival rate of the silver carp and their new offspring are $0\mathrm{.}7$ and $0\mathrm{.}45,$ respectively. It has also been estimated that the construction will reduce recruitment rate by $35\%$ and will cause decreases in survival rates of the existing and newborn silver carp by $30\%$ and $35\%,$ respectively. Using the population dynamics model, estimate the change in silver carp population due to the railway bridge project. State any assumptions.