Spawning Habitat Unsuitability: An Impediment to Cisco Rehabilitation in Lake Michigan?

The cisco Coregonus artedi was one of the most important native prey fishes in Lake Michigan and in the other four Laurentian Great Lakes. Most of the cisco spawning in Lake Michigan was believed to have occurred in Green Bay. The cisco population in Lake Michigan collapsed during the 1950s, and the collapse was attributed in part to habitat degradation within Green Bay. Winter water quality surveys of lower Green Bay during the 1950s and 1960s indicated that the bottom dissolved oxygen (DO) concentration was less than 2 mg/L throughout much of the lower bay, and most cisco eggs would not successfully hatch at such low DO concentrations. To determine present‐day spawning habitat suitability in lower Green Bay, we compared cisco egg survival in lower Green Bay with survival at a reference site (St. Marys River, Michigan–Ontario) during 2009. We also conducted winter water quality surveys in lower Green Bay and the St. Marys River during 2009 and 2010. Cisco egg survival in lower Green Bay averaged 65.3%, which was remarkably similar to and not significantly different from the mean at the St. Marys River site (64.0%). Moreover, the lowest bottom DO concentrations recorded during the winter surveys were 11.2 mg/L in lower Green Bay and 12.7 mg/L in the St. Marys River. These relatively high DO concentrations would not be expected to have any negative effect on cisco egg survival. We conclude that winter water quality conditions in lower Green Bay were suitable for successful hatching of cisco eggs and that water quality during the egg incubation period did not represent an impediment to cisco rehabilitation in Lake Michigan. Our approach to determining spawning habitat suitability for coregonids would be applicable to other aquatic systems.Received May 14, 2011; accepted July 6, 2011Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142025/1/nafm0905.pd

Economies of scale and rural schools

ABSTRAC

The effects of the mechanical performance and alignment of the Atacama Cosmology Telescope on the sensitivity of microwave observations

The Atacama Cosmology Telescope is a six meter, off-axis Gregorian telescope for measuring the cosmic microwave background at arcminute resolutions. The Millimeter Bolometer Array Camera (MBAC) is its current science instrument. Erected in the Atacama Desert of Chile in early 2007, it saw first light with the MBAC on 22 October 2007. In this paper we review its performance after one month of observing, focusing in particular on issues surrounding the alignment of the optical system that impact the sensitivity of the experiment. We discuss the telescope motion, pointing, and susceptibility to thermal distortions. We describe the mirror alignment procedure, which has yielded surface deviations of 31 μm rms on the primary and 10 μm rms on the secondary. Observations of planets show that the optical performance is consistent with the telescope design parameters. Preliminary analysis measures a solid angle of about 215 nanosteradians with a full width at half maximum of 1.44 arcminutes at 145 GHz