Influence of Total Phosphorus Variability on the Fishery Resources in the Bay of Quinte

The restoration efforts were successful in controlling the external nutrient loading, thereby initiating a “re-oligotrophication” process in many sites of the Great Lakes. Emerging evidence suggests that the Great Lakes experience an “offshore desertification”, whereby the low ambient phosphorus levels undermine pelagic ecosystem integrity. We examined the hypothesis that the mitigation control of eutrophication in nearshore areas is likely to induce similar shifts in fish productivity and biomass. Based on the Bay of Quinte, an Area of Concern (AOC), we use a combination of Bayesian statistical techniques (dynamic linear modelling, hierarchical piecewise regression) to draw inference about the strength of the relationship between fish biomass and total phosphorus in time and space. Our analysis suggests that the relationship between the two variables was quite strong during the period when the system was eutrophic (early 1970s), but the signature of phosphorus on fish biomass became distinctly weaker during recent years. The posterior estimate of the breakpoint value when the shift in the fish-total phosphorus relationship occurred corresponds to an approximate level of 35 ug/L. Our study concludes with a discussion of the ecological factors that could conceivably shape the future trajectory of the fish population in the Bay of Quinte AOC.