ABSTRACT-Coastal eutrophication has been identified as an important ecological problem in many regions. Yet simple, generalizable models, such as those available for the management of lake eutrophication, do not exist for estuaries. As a first step in the development of estuarine eutrophication models, we generated chlorophyll anutrient regression models for 15 estuaries in Prince Edward Island, Canada. Total phosphorus and total nitrogen account for 65 and 72 % of the variance in chlorophyll (chl), respectively. However, when these models are compared to similar models for lakes, the yield of chl per unit nutrient is between 1 and 2 orders of magnitude lower in estuaries than in lakes. As herbivory and turbidity are likely contributors to this low yield, we used a mass-balance approach to model phytoplankton biomass as a function of primary production and losses due to flushing, sedimentation and herbivory In the 6 estuanes with mussel aquaculture, 45 to 88% of the chl deficit could be accounted for by herbivory In the remaining 9 estuaries, t u r b~d~t y accounted for 35 to 75% of the chl deficit. Considering both herbivory and turbidity, the mass-balance accounted for on average 68?;, of the chl d e f~c~t for the 15 estuaries. We also generated an empir~cal model predicting the deficit as a function of herb~vory and turb~dity; this model accounted for 50'41 of the variat~on in the deficit. The analysis suggests that ch1:nutnent relations can be generalized across fresh and estuarine aquatic systems if turb~dity and herbivory are considered.

Although infrequent recruitment of new individuals into the adult spawning populations of Lost River suckers (Deltistes luxatus) and shortnose suckers (Chasmistes brevirostris) limits recovery of these species in Upper Klamath Lake, it is not clear that populations are recruitment limited in Clear Lake Reservoir (hereafter Clear Lake). Specifically, some evidence indicates that shortnose suckers may regularly recruit to the adult spawning population in Clear Lake. Therefore, a study of early life history patterns and recruitment dynamics in Clear Lake may lead to a better understanding of what is limiting recovery of suckers in both lakes. Adult suckers in Clear Lake migrate up Willow Creek and its tributaries to spawn in some years, but low flow in Willow Creek may inhibit spawning migrations in other years. It is unclear whether spawning is successful, larvae survive, or how frequently juveniles persist to adulthood. Environmental variables associated with successful spawning or young-of-year survival have not been identified, and early life history for these populations is poorly understood. The U.S. Geological Survey, in cooperation with the U.S. Fish and Wildlife Service, initiated a study in 2011 to better understand juvenile sucker life history in Clear Lake, and to identify constraints in the early life history that may limit recruitment to the adult spawning populations. The relative weights of shortnose suckers from Clear Lake and Upper Klamath Lake were compared to examine differences in condition. However, it is unclear whether the disparity in relative weights between the populations reflects differences in condition, phenotype, or both. Approximately 80 percent of juvenile suckers in Clear Lake are shortnose suckers with some morphologic features similar to Klamath largescale suckers (Catostomus snyderi), whereas juvenile suckers in Upper Klamath Lake can be clearly classified as either shortnose or Lost River suckers. The presence of juvenile suckers age-3 and older indicate that production, larval survival, and juvenile survival are at least periodically sufficient to lead to recruitment into the adult population of shortnose suckers in Clear Lake.