Population Recovery and Natural Recruitment of Lake Trout at Gull Island Shoal, Lake Superior, 1964–1992

doi:10.1016/S0380-1330(95)71095-4

Journal of Great Lakes Research

Volume 21, Supplement 1, 1995, Pages 225-232

https://doi.org/10.1016/S0380-1330(95)71095-4 Get rights and content

Abstract

We documented an increase in the abundance of wild lake trout (Salvelinus namaycush) at Gull Island Shoal in western Lake Superior and examined the relationship between parental-stock size and recruitment of age-0 fish in 1964–1992. Abundance of adult wild female lake trout and densities of age-0 fish both increased during the 28-year period. A significant positive, linear relationship (P = 0.0002) was found between the abundance of wild females on the spawning reef in the fall and density of age-0 lake trout on adjacent nursery grounds in August and September of the following year. The abundance of hatchery-origin females did not explain significant amounts (P = 0.107) of variation in recruitment. We concluded that most recruitment in 1965–1992 was the result of natural reproduction of wild females. After 28 years of recovery the Gull Island Shoal lake trout population appears to have additional capacity to increase because the stock-recruitment relationship is still linear. Therefore, restoration periods on the order of 30 years may be needed for other lake trout populations in the Great Lakes. We recommend that the refuge established to protect this population be maintained to allow further study of the relationship between parental stock and recruitment, and to provide a major source of recruitment to the lake trout population in the surrounding waters.

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Cited by (53)

Network of nearshore protected areas provides important benefits to lake whitefish in the Apostle Islands region of Lake Superior
2024, Journal of Great Lakes Research
Aquatic protected areas are commonly used for fish conservation, restoration, and management and a spectrum of protection levels exist in the Great Lakes. Using fishery-independent survey data over 43 years, we evaluated whether lake whitefish (Coregonus clupeaformis) population dynamics differed among nearshore partially protected areas (PPAs; commercial fishing prohibited or severely limited), offshore no-take refuges, and unprotected areas in the Apostle Islands region of Lake Superior. Lake whitefish biomass and recruitment to the spawning stock increased at faster rates in nearshore PPAs and offshore refuges than unprotected areas during the initial phase after protected areas were established (1980–2000). Recruitment and biomass stabilized in all management areas in the post-rebuild phase (2002–2022), and mortality was lower in the nearshore PPAs. Mean size of adults decreased within protected areas as abundance increased but not in unprotected areas, suggesting a density-dependent growth response and spillover to the fishing grounds, which was reflected in commercial catch rates. However, nearshore PPAs still harbored larger, faster-growing, and earlier-maturing lake whitefish, likely due to underlying habitat differences. Tag recaptures indicated greater minimum distances traveled near an offshore refuge compared to a nearshore PPA, suggesting habitat gradients may influence boundary porosity. PPAs provided protection and benefits for lake whitefish in areas of higher vulnerability where ceasing all fishing was not reasonable. Great Lakes managers should consider implementing networks of protected areas across multiple habitats as tools for conserving spawning biomass, maintaining diverse population demographics, and preserving portfolio effects to enhance recruitment and population stability.
Influence of protected riparian areas on habitat structure and biodiversity in and at small lakes managed by recreational fisheries
2022, Fisheries Research
Citation Excerpt :
Beyond protection offered to fish, small-scale protected areas assigned to serve fisheries may have unintended effects on nontarget habitats and taxa of lower interest to fisheries and thereby indirectly contribute to conservation more generally (Cucherousset et al., 2007; Langlois and Ballantine, 2005). The key influence of protected areas, especially of no-take protected areas, is excluding fishing as a source of fish mortality as well as reducing disturbances of habitats from fishing gear and boating (Cambray, 2002; Hilborn, 2016; Hilborn and Sinclair, 2021; Sanyanga et al., 1995; Schram et al., 1995). Therefore, it can be expected that the fish biomass and the length of fish increase in protected areas relative to open areas if the size of the protected area is large enough relative to the movements of the fish beyond the protection borders (Lester and Halpern, 2008; Ohayon et al., 2021).
Protected areas are a common management tool to conserve habitats and species by controlling access and disturbances by humans. Whenever protected areas result in restricting access to riparian zones in lakes, they may have positive effects on habitats and taxa beyond fish by lowering influences of trampling or boating on plants, by reducing the degree of human-induced disturbances to sensitive taxa such as birds, and by reducing fishing effort. However, especially in small freshwater systems knowledge about the functioning of protected areas that cover only parts of the lake shorelines is limited. We studied small gravel pit lakes in Germany where recreational fishing clubs have voluntarily assigned no-access riparian protected areas on parts of the lake shorelines and examined outcomes for habitat quality, plants, fish and bird populations. A total of 15 lakes were sampled, and we assessed habitat structure and abundance of plants, and fish within and outside protected areas and bird abundance at the lake scale, relying on standardized sampling methods. After controlling for confounding environmental factors related to lake morphology, age, nutrients, and land use, we detected positive contributions of small-scale riparian protected areas on habitat structure, riparian vegetation, local fish abundance and abundance of sensitive songbirds at the lake-scale, but we found no effects on aquatic vegetation and on disturbance-sensitive waterfowl species. Scale-restricted riparian protected areas voluntarily assigned by recreational fishing clubs can have positive outcomes for habitat quality and biodiversity, particularly by reducing trampling and access to anglers and other recreationists. Moreover, through provision of key habitat for young fish, small-scale riparian protected areas can also benefit fish abundance and in turn recreational fisheries.
Effects of lake trout refuges on lake whitefish and cisco in the Apostle Islands Region of Lake Superior
2016, Journal of Great Lakes Research
Citation Excerpt :
The two refuges were created to aid recovery of lake trout populations in Lake Superior (Hansen et al., 1995; Stanley et al., 1987; Swanson and Swedberg, 1980). Gull Island Shoal Refuge and Devils Island Shoal Refuge were designated to encompass areas historically important for lake trout spawning (Coberly and Horrall, 1980)—areas that had also been heavily fished prior to establishing a refuge around the Gull Island Shoal (Schram et al., 1995; Swanson and Swedberg, 1980). This first refuge was established in 1976 to protect an important remnant spawning stock of lake trout (Hansen et al., 1995; Schram et al., 1995; Stanley et al., 1987; Swanson and Swedberg, 1980).
Lake trout refuges in the Apostle Islands region of Lake Superior are analogous to the concept of marine protected areas. These refuges, established specifically for lake trout (Salvelinus namaycush) and closed to most forms of recreational and commercial fishing, were implicated as one of several management actions leading to successful rehabilitation of Lake Superior lake trout. To investigate the potential significance of Gull Island Shoal and Devils Island Shoal refuges for populations of not only lake trout but also other fish species, relative abundances of lake trout, lake whitefish (Coregonus clupeaformis), and cisco (Coregonus artedi) were compared between areas sampled inside versus outside of refuge boundaries. During 1982–2010, lake trout relative abundance was higher and increased faster inside the refuges, where lake trout fishing was prohibited, than outside the refuges. Over the same period, lake whitefish relative abundance increased faster inside than outside the refuges. Both evaluations provided clear evidence that refuges protected these species. In contrast, trends in relative abundance of cisco, a prey item of lake trout, did not differ significantly between areas inside and outside the refuges. This result did not suggest indirect or cascading refuge effects due to changes in predator levels. Overall, this study highlights the potential of species-specific refuges to benefit other fish species beyond those that were the refuges' original target. Improved understanding of refuge effects on multiple species of Great Lakes fishes can be valuable for developing rationales for refuge establishment and predicting associated fish community-level effects.
Loss of genetic diversity and reduction of genetic distance among lake trout Salvelinus namaycush ecomorphs, Lake Superior 1959 to 2013
2016, Journal of Great Lakes Research
North America's northern lakes are undergoing major changes. Lake Superior is the coldest and northernmost of the Laurentian Great Lakes. Here, we present an extension of a long-term data set that monitors genetic and phenotypic diversity of lake trout Salvelinus namaycush in Lake Superior. Hypotheses were investigated pertaining to loss of genetic diversity and genetic homogenization among three lake trout ecomorphs in Lake Superior during their recovery several decades after a major fishery collapse in the early 1960s. Comparison of a contemporary (2004–2013) microsatellite DNA data set to a previously published, post-collapse recovery period data set (1995–1999) indicated substantive losses in genetic diversity. Allelic richness decreased by 5.7%, 12.3%, and 6.8% at Isle Royale, Stannard Rock, and Klondike Reef, respectively. A 60.7% reduction in genetic distance among ecomorphs since the 1990s was detected. Comparisons with a third data set of samples collected during the fishery collapse (1959) indicated an overall 18.2% loss in allelic richness at Isle Royale. The amount of introgression among ecomorphs has likely increased over time. Apparent losses in genetic diversity could be a consequence of historical fishery harvests (early 1900s) exacerbated by intensive stocking (1950s–1980s) and invasions of non-native species (1960s–1990s). Overlap in foraging and breeding areas may have contributed to increasing levels of hybridization among ecomorphs. Knowledge of these processes will help to identify impediments and strategies for the maintenance of lake trout biodiversity in northern Great Lakes, and their re-establishment in the Laurentian Great Lakes.
Maternal characteristics versus egg size and energy density: Do stocked lake trout in Lake Ontario experience premature reproductive senescence?
2008, Journal of Great Lakes Research
Observations from September 1994 and 1997 collections of hatchery-origin, mature female lake trout (Salvelinus namaycush) from Lake Ontario indicated that egg mass decreased with age, fueling the notion that stocked fish experienced premature reproductive senescence. Supplemental collections during September 2002 and November 2002-2004 were combined with the 1994 and 1997 samples to examine whether sample date or maternal age, body mass, condition (K), egg count, or strain were related to egg mass or energy content (percentage dry mass [%DM]). Body mass was correlated with egg mass for age ≥ 8 lake trout sampled in September, and egg count was correlated with egg mass for September age-6 lake trout only. Within each month, egg mass was not related to K or egg %DM, however, egg %DM was 1.52% greater (P ≤ 0.0247) in November than in September which is equivalent to a 110 cal/g difference. Samples were grouped for the three most abundant strains (Seneca, Superior, and Ontario) after finding no strain or year effects from our 1994 and 1997 samples and based on life history data from the literature and our assessment sampling. Further analysis indicated that September egg masses were greater for fish ages ≤ 6 than for fish ages ≥ 8. The age effect disappeared in November when mean egg mass across all ages (0.078 g) was greater than September means (P < 0.0005) for ages-5 (0.054 g), -6 (0.057 g) and ≥ 8 (0.041 g). Our results indicate that the decrease in egg mass with female age in September was not due to senescence, but to oogenesis being closer to completion in young age-5 and -6 fish than in older individuals.
Spatial and ontogenetic variability of sea lamprey diets in Lake Superior
2008, Journal of Great Lakes Research
Invasive sea lamprey (Petromyzon marinus) remain an important source of fish mortality in the Laurentian Great Lakes, yet assessing their impact is hindered by lack of quantitative diet information. We examined nitrogen and carbon stable isotope ratios (δ¹⁵N and δ¹³C) of sea lamprey and host species in six ecoregions of Lake Superior, mainly in 2002–2004. Data implied that most sea lamprey fed primarily on upper trophic level species, including forms of lake trout (Salvelinus namaycush). However, in Ontario waters, particularly semi-enclosed Black Bay, sea lamprey relied heavily on lower trophic levels, such as coregonines (Coregonus spp.) and suckers (Catostomus spp.). Sea lamprey δ¹⁵N and δ¹³C generally increased with sea lamprey size, implying dependence on higher trophic levels later in life. Most parasitic sea lamprey that we captured were attached to either lean lake trout (35% of observed attachments), lake whitefish (Coregonus clupeaformis; 25%), or cisco (C. artedii; 25%); the latter sea lamprey were typically < 15 g. Survey- and fishery-dependent wounding rate data compiled from 1986–2005 suggest that lean and siscowet lake trout were selectively parasitized by sea lamprey, which is consistent with our stable isotope data. Our results largely support the notion that lake trout are the principal host species in Lake Superior. However, stable isotope evidence that sea lamprey feed at lower trophic levels in some regions argues for comprehensive monitoring of sea lamprey impacts throughout the fish community in systems that sea lamprey have invaded.

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Journal of Great Lakes Research

Abstract

References (23)

Hatching, dispersal, and bathymetric distribution of age-0 wild lake trout at the Gull Island Shoal complex, Lake Superior

J. Great Lakes Res.

Density-independent survival of wild lake trout in the Apostle Islands area of Lake Superior

J. Great Lakes Res.

Recovery of an offshore lake trout (Salvelinus namaycush) population in eastern Lake Superior

J. Great Lakes Res.

Lake trout (Salvelinus namaycush) populations in Lake Superior and their restoration in 1959–1993

J. Great Lakes Res.

The study of stock and recruitment

Bathymetric distribution of fish in the Apostle Islands Region

Lake Superior. Trans. Amer. Fish. Soc.

Rehabilitation of lake trout in the Apostle Islands region of Lake Superior

J. Fish. Res. Board Can.

Loss of exploited indigenous populations of lake trout, Salvelinus namaycush, by stocking of hatchery-reared, non-native stocks

Can. J. Fish. Aquat. Sci.

Fish Stock Assessment: A Manual of Basic Methods

Cited by (53)

Network of nearshore protected areas provides important benefits to lake whitefish in the Apostle Islands region of Lake Superior

Influence of protected riparian areas on habitat structure and biodiversity in and at small lakes managed by recreational fisheries

Effects of lake trout refuges on lake whitefish and cisco in the Apostle Islands Region of Lake Superior

Loss of genetic diversity and reduction of genetic distance among lake trout Salvelinus namaycush ecomorphs, Lake Superior 1959 to 2013

Maternal characteristics versus egg size and energy density: Do stocked lake trout in Lake Ontario experience premature reproductive senescence?

Spatial and ontogenetic variability of sea lamprey diets in Lake Superior