Mass‐Marking Reveals Emerging Self Regulation of the Chinook Salmon Population in Lake Huron

Abstract

All Chinook salmon Oncorhynchus tshawytscha stocked in Lake Huron during 2000–2003 were marked with oxytetracycline (OTC), fin clips, or a combination thereof to determine the relative contributions of natural reproduction and stocking to recruitment. Oxytetracycline administered in feed proved to be an effective, low‐cost method of marking spring fingerling Chinook salmon. Vertebrae proved to be suitable tissue for OTC detection, meeting standards for accuracy and reproducibility. Vertebrae were not suitable as aging structures, perhaps due to the slow somatic growth of Lake Huron's Chinook salmon during this study. Based on lakewide recoveries from recreational and commercial fisheries, we estimated that nearly 80% of Chinook salmon from the marked year‐classes were from natural reproduction. Wild‐origin Chinook salmon constituted 96% of open‐water samples from Georgian Bay; 82, 80, and 68% of those from the central, southern, and northern portions of the main basin; and 64% of those from the North Channel. The percentage of wild‐origin Chinook salmon in some tributaries in the Ontario watershed of Lake Huron approached 100%. There was less variation in wild recruitment between years than between lake areas. This Chinook salmon population was introduced in the late 1960s and until recently had been widely viewed as hatchery dependent; our findings suggest otherwise. A self‐sustaining predator population would represent a paradigm shift from an era when predation rates could be manipulated by adjusting salmonid stocking (i.e., 1968 to about 1995). These findings should help managers to critically review the effects of stocked Chinook salmon on Lake Huron's fisheries and ecosystem, including prey consumption demand, and to assess future needs for propagated Chinook salmon in Lake Huron.

Joint analysis of stressors and ecosystem services to enhance restoration effectiveness

“…4 C and D) requires further research to determine if these services would benefit from restoration or are sufficiently resilient to stress that restoration is unnecessary. However, beach closings (17), sport fishery declines (18), and other types of foregone recreational opportunities suggest that stressor mitigation could indeed enhance service provisioning. For example, a number of studies have found that improvements in water quality result in increased benefits (19), consistent with estimates that Great Lakes restoration efforts could yield returns in excess of $50 billion beyond their costs (11).…”

Seasonal zooplankton dynamics in Lake Michigan: Disentangling impacts of resource limitation, ecosystem engineering, and predation during a critical ecosystem transition

“…Predation on alewives by Chinook salmon in Lake Michigan has apparently increased during the 2000s, and this increased predation was likely responsible for the reduced adult alewife abundance observed during (Madenjian et al, 2010. A new source of wild Chinook salmon recruitment to Lake Huron, and presumably Lake Michigan as well, was activated sometime during the late 1990s or early 2000s (Johnson et al, 2010). In addition, the reduction in alewife energy density during the late 1990s was also expected to increase the predation rate on alewives by Chinook salmon in Lake Michigan during the 2000s .…”

Chinook Salmon Foraging Patterns in a Changing Lake Michigan

“…Adlerstein et al (2007) found that 6% of coded-wire-tagged Chinook Salmon from Lake Huron were recovered in Lake Michigan during 1993-2001, whereas Adlerstein et al (2008) found no evidence of Lake Michigan Chinook Salmon recoveries in Lake Huron. Since wild Chinook Salmon production has remained high after the Alewife population collapse that occurred in Lake Huron soon thereafter (Johnson et al 2010), there is some concern that substantial numbers of Chinook Salmon are crossing the Straits of Mackinac into Lake Michigan to forage. Wild reproduction of Chinook Salmon also occurs in Lake Michigan, and though highly variable, in some years it has exceeded stocking levels .…”

“…As previously mentioned, the decrease in Lake Michigan Alewife energy density, which probably occurred during the mid or late 1990s, could potentially lead to a substantial increase in the rate of Alewife consumption by Chinook Salmon . Finally, the surge in production of wild Chinook Salmon smolts originating from one tributary or set of tributaries to Georgian Bay of Lake Huron during the late 1990s or early 2000s, as documented by Johnson et al (2010) and Marklevitz et al (2011), may have led to a substantial increase in Chinook Salmon abundance in Lake Michigan between the 1994-1996 and 2009-2010 periods.…”

“…In Lake Huron, such changes have been implicated in the recent Alewife population collapse and offshore fish community shift (Riley et al 2008), though increasing native and naturalized salmonine predator abundance in Lake Huron (Johnson et al 2010) suggests that the Alewife collapse was more likely the result of top-down pressure. Due to similarities in species invasions throughout the Great Lakes, changing lower trophic level community structure, and apparent bottom-up forcing, there is some indication that similar community shifts may also occur in other lakes.…”