Lake Trout Restoration in the Great Lakes: From Hatchery to Natural Reproduction
Open Access
- Author:
- Salvesen, Kelley Elizabeth
- Graduate Program:
- Wildlife and Fisheries Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- January 15, 2015
- Committee Members:
- Tyler Wagner, Thesis Advisor/Co-Advisor
Meredith Bartron, Thesis Advisor/Co-Advisor - Keywords:
- lake trout
microsatellites
hatchery
great lakes - Abstract:
- Lake trout populations in the Great Lakes began to decline in the late 1800’s as a result of overexploitation, sea lamprey predation and habitat degradation. This decline continued into the 1950’s, when lake trout were thought to be completely extirpated from the Great Lakes, with the exception of Lake Superior and limited areas of Lake Huron. Stocking of lake trout began in the 1960’s in an effort to restore naturally reproducing populations, with stocking relying on remnant lake trout populations as source populations. These source populations from the Great Lakes, the Finger Lakes, and from introduced populations in the western United States provided the ability to produce numerous hatchery strains. Historically, multiple lake trout strains were stocked in various locations throughout the Great Lakes with the intent that natural selection would allow for survival of the strain best suited to each specific habitat. However, stocking has not yet achieved intended recovery targets of restoring basin-wide natural reproduction, and so hatchery supplementation continues. In an effort to further lake trout restoration goals throughout the Great Lakes, this study had three components: (1) evaluate the efficacy of hormone manipulation to increase hatchery production of the Klondike strain (2) quantify the current genetic status of hatchery strains in production; (3) identify hatchery strain of origin for lake trout reproducing in the Niagara River, NY, as well as their offspring, and to quantify adult lake trout movement into and out of the Niagara River. The Klondike strain of lake trout is a humper morphotype native to Lake Superior and the production of broodstock is maintained at Iron River National Fish Hatchery in Iron River, WI. The Klondike strain has very poor eye-up rates compared to other hatchery strains raised in similar conditions (3-33% eye-up rates, compared to >70% of many lean morphotypes). Based on previous studies analyzing potential health and environmental changes possible in a hatchery setting, induction of spawning through the use of gonadotrophin releasing hormone analogues (GnRHa) was explored as a possible hatchery management tool for increasing eye-up rates. The experimental design consisted of two treatment groups of fish (low dose of 10ug/kg body weight and high dose of 20ug/kg bw) and a control group (saline solution injection). Other lake trout, not used in the experiment, but raised in a similar hatchery setting were used for further comparison (i.e., these “baseline” fish were not handled because they did not receive hormone or saline injections). Both the low and high dose injection of GnRHa resulted in similar increases in eye-up rates compared to control fish (~62%) and baseline non-study fish (>98%). Interestingly, the control injection of saline solution also had higher eye-up rates when compared to the baseline group of fish (84% compared to >98% in treatment groups). Beyond an increase in eye-up rates, fish treated with hormones also had a higher number of viable eggs per fish than baseline fish. While this study had some confounding factors that made results for saline-injected control fish difficult to interpret (i.e., hormone injected and control fish were held in the same holding tanks), hormone injection did improve eye-up rates. This improvement in eye-up rate allows the hatchery to produce a greater number of fry, while still maintaining the same number of broodstock fish. Because the Klondike is the only strain of the humper morphotype currently in the federal hatchery system, increased production could result in reaching targeted stocking rates, and possibly allow for increased stocking or stocking in new locations. Currently, there are six different hatchery strains of lake trout in production in the federal hatchery system. These strains each represent a sample of six different lake trout populations and are used to assist in the restoration goal of establishing naturally reproducing lake trout populations throughout the Great Lakes. Because these strains are a sub-sample of the source population, genetic diversity can become limited if not properly monitored. This can be detrimental to establishment of or developing populations, if stocked fry are inbred, genetically similar, or somehow have reduced survival due to lack of genetic diversity. To understand the current status of lake trout hatchery strains, fin clips were taken from at least two different year classes of each strain for genetic analysis (only one year class was available for the Lake Champlain strain; three were available for the Seneca Lake strain). For the Klondike strain, a sample of the source population was available and used for comparison. Using a suite of eleven microsatellite loci, each strain was assessed for genetic diversity. All hatchery strains were found to have similar levels of genetic diversity, even though all are genetically distinct from one another. The Klondike strain, however, showed evidence of loss of genetic diversity, specifically allelic richness, when compared to the wild source population. Continued monitoring of the genetic diversity of the Klondike hatchery strain would be beneficial. Based on sampling by the U.S. Fish and Wildlife Service and anecdotal evidence from recreational fishermen, a naturally reproducing population of lake trout appeared to be using the lower Niagara River for spawning. To better understand movement of this population and to provide further evidence of natural reproduction, fish were captured in the fall 2010 and 2011 before spawning began and implanted with radio transmitters. Tissue samples were also taken to assess hatchery strain of origin of all adults captured. Sampling for naturally reproduced offspring took place in the fall using egg traps, as well as in the spring using nets. Naturally reproduced offspring were genetically sequenced to determine species before microsatellite markers were used to identify hatchery strain of origin. Identical microsatellite protocols were used on adult samples to determine hatchery strain of origin. The majority (86%) of lake trout sampled during this study, adult and offspring, were assigned to the Seneca Lake strain. While radio transmitters were deployed, the data gathered was insufficient for statistical modeling. Based on the findings from this study, the majority of natural reproduction occurring in the lower Niagara River is by stocked lake trout of the Seneca Lake strain.