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Population status and demographics of lake sturgeon (Acipenser fulvescens) in the St. Marys River, from 2000 to 2007
Journal of Great Lakes Research 37 (2011) 47–53
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Journal of Great Lakes Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j g l r
Population status and demographics of lake sturgeon (Acipenser fulvescens) in the St. Marys River, from 2000 to 2007 John M. Bauman a,b, Ashley Moerke a,⁎, Roger Greil a, Brandon Gerig a, Edward Baker c, Justin Chiotti d a
Aquatic Research Laboratory and School of Biological Sciences, Lake Superior State University, 650 W. Easterday Ave, Sault Ste. Marie, MI 49783, USA Michigan State University Fisheries and Wildlife, East Lansing, MI 48824, USA Michigan Department of Natural Resources and Environment, 488 Cherry Creek Rd., Marquette, MI 49855, USA d Department of Natural Resources, Cornell University, Ithaca, NY 14853, USA b c
a r t i c l e
i n f o
Article history: Received 2 December 2009 Accepted 11 November 2010 Available online 15 January 2011 Communicated by R. Marshall Werner Index words: Lake sturgeon Acipenser fulvescens Threatened species St. Marys River
a b s t r a c t The St. Marys River, the sole outflow of Lake Superior, was historically inhabited by lake sturgeon (Acipenser fulvescens); until recently it was unclear whether a population was still present in the river. From 2000 to 2007, the population status of subadult and adult lake sturgeon in the St. Marys River was characterized. Setlines were deployed at multiple water depths (2–20 m) for 3400 setline nights. Biological measurements including total length and weight were recorded and each individual was affixed with unique identification tags before being released. A total of 192 unique lake sturgeon were captured with a recapture rate of 16%. The population size of lake sturgeon in the St. Marys River was estimated to be near 500 individuals. Fish captured exhibited a mean weight of 13 kg (range 2–37 kg) and a mean total length of 125 cm (range 80–175 cm). The mean age of lake sturgeon captured was 20 years (range 7–59 years) and 36 age classes were represented. Lamprey wounds were observed on 23% (N = 53) of sturgeon and nearly 19% (N = 44) of lake sturgeon had visible external parasites classified as Argulus spp. This study suggests that a recovering lake sturgeon population exists in the St. Marys River, however, it remains unclear as to whether this is a self-sustaining population reproducing in the river. Additional information is needed on metapopulation dynamics, habitat use, and younger age classes to assess recruitment success and population status. © 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.
Introduction Historically, lake sturgeon (Acipenser fulvescens) was an abundant species throughout the Great Lakes basin. Populations declined precipitously beginning in the late 1880s because of aggressive commercial harvest, habitat degradation (e.g., shoreline development, logging practices), and construction of dams which prevented access to spawning habitat (Harkness and Dymond, 1961; Rochard et al., 1990). The initial view of sturgeon as a nuisance fish resulted in commercial fishers discarding carcasses ashore. As the market value of lake sturgeon was realized, commercial harvest ensued (Tody, 1974). The largest commercial catches of lake sturgeon in the Great Lakes occurred in the 1880s when an average of 8.6 million pounds was harvested per year, but by the turn of the century lake sturgeon catches had dropped drastically and the Lake Erie population for example declined by over 80% (USFWS, 2008). In addition to overharvest, deforestation and the construction of hydroelectric facilities have degraded the quality and accessibility of spawning
⁎ Corresponding author. E-mail address: [email protected] (A. Moerke).
habitat used by lake sturgeon (Harkness and Dymond, 1961; Auer, 1996a). These factors coupled with unique life history attributes, including late maturity and individual variation in reproduction periodicity make natural recovery of depleted populations a long and difficult process. Currently, lake sturgeon is considered threatened in 20 states and 7 provinces within their native range (Knights et al., 2002). Out of 107 Great Lakes locations where lake sturgeon populations once existed, 59 (55%) are recorded as “small” and 45 (42%) are listed as “extirpated” (Holey et al., 2000). Strategic fisheries rehabilitation goals have been proposed to assist in the recovery of lake sturgeon throughout the Great Lakes. Recently, The Nature Conservancy listed lake sturgeon as a “conservation target” in the St. Marys River (Harris et al., 2009), which further emphasizes the need for local as well as regional rehabilitation efforts. Within the Great Lakes many studies have focused on lake sturgeon to understand their unique life history characteristics in efforts to rehabilitate threatened populations (Harkness and Dymond, 1961; Thomas and Haas, 1999; Fortin et al., 1996; Auer, 1996a,b, 1999a). Despite increased efforts, sturgeon status in many areas of the Great Lakes, including major connecting channels such as the St. Marys River, still remains relatively unknown (Hay-Chmielewski and
0380-1330/$ – see front matter © 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jglr.2010.12.003
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J.M. Bauman et al. / Journal of Great Lakes Research 37 (2011) 47–53
Whelan, 1997; Holey et al., 2000, but see Thomas and Haas, 1999). Since 1975, the Michigan Department of Natural Resources has conducted gill net surveys throughout the St. Marys River to determine trends in the fish community composition at least once every decade (Fielder and Waybrant, 1998). This information has indicated that a sturgeon population exists in the St. Marys River; however, captures were limited and declined from 1975 to 1995 (CPUE = capture per 305 m of gill net per net night: 1975 = 0.99, 1979 = 0.03, 1987 = 0.09, 1995 = 0.00) (Fielder and Waybrant, 1998). The St. Marys River, the sole outflow of Lake Superior, is an important ecological corridor between Lake Superior and Lake Huron. The river and its biota have been impacted by many anthropogenic activities including shipping, sediment contamination, and shoreline development (see Ripley et al., 2011). Understanding the current status of lake sturgeon in the St. Marys River is an essential first step in protecting and recovering sturgeon populations in this area. Also, because lake sturgeon are considered an indicator of ecosystem health and a conservation target for the ecosystem, knowledge gained about the lake sturgeon population will enhance efforts towards conservation of the entire St. Marys River ecosystem. The objective of this study was to characterize the current lake sturgeon population in the upper reaches of the St. Marys River. Study area The St. Marys River connects Lake Superior and Lake Huron through a 112-km waterway. The “rapids” area of the St. Marys River historically was the only hydrological connection between the lakes, but compensating gates and locks now obstruct river passage and the rapids contribute less than 50%, and sometimes less than 10% of the total discharge (Bray, 1996). The river also possesses many large tributaries, including the Garden River, Charlotte River, and Munuscong River, which provide important spawning and nursery habitat for many St. Marys River fishes. During the past century the St. Marys River has been a site of extensive industrialization (see Ripley et al., 2011). The steel and shipping industry, paper processing mills, sewage treatment plants and tanneries have operated on the river and have contributed to the designation of this location as an international Area of Concern (USEPA, 1988). These developments have contributed to the degradation of natural channel morphology, flow regimes, habitat and water quality. Additionally, transoceanic vessels in the Great Lakes have impacted the St. Marys through the introduction of nonnative species and re-suspension of sediment (Gleason et al., 1979; Poe and Edsall, 1982; Mills et al., 1993). Despite vast degradation, the St. Marys River has been listed as “high” in regards to the suitability of maintaining a self-sustaining population of lake sturgeon (Hay-Chmielewski and Whelan, 1997). High habitat heterogeneity offers refuge from environmental disturbance and may be important wintering and feeding habitat (Auer, 1999b). The “rapids” area and some tributaries entering the St. Marys River, including the Garden River, may provide sufficient spawning habitat (e.g., large-cobble substrate, swift current) as characterized in other systems (e.g., LaHaye et al., 1992; Auer, 1996a,b; Chiotti et al., 2008). Reports from local fishermen and Sea Lamprey Control suggest that sturgeon may be spawning in the Garden River and in the main river near Neebish Island. However, natural reproduction by lake sturgeon in the St. Marys River has yet to be documented in the scientific literature. The study site assessed from 2000 to 2007 for lake sturgeon included international waters from the North Channel of Sugar Island to East Neebish Island (Fig. 1). During this study, several attempts were made by Lake Superior State University's Aquatic Research Laboratory (LSSU) to sample lake sturgeon in the shipping channel west of Sugar Island, however, no sturgeon were captured in the shipping channel. Our remaining efforts were focused outside of the
shipping channel because previous efforts did not capture sturgeon and freighter traffic in the shipping channel made it logistically difficult to set and retrieve setlines. Methods From 2000 to 2007, lake sturgeon were captured in the St. Marys River by LSSU from early spring to late summer using baited setlines 100 m in length, containing 25 snews each (7/0 saltwater hooks) (Thomas and Haas, 1999). Setlines were deployed for 24 to 48 h intervals at water depths of 2 to 16 m, and baited with a variety of baits. Baits used included lake whitefish (Coregonus clupeaformis), lake trout (Salvelinus namaycush), northern cisco (Coregonus artedi), sucker (Catostomus spp.), brown trout (Salmo trutta), northern pike (Esox lucius), yellow perch (Perca flavescens), chicken livers, earthworms, rainbow smelt (Osmerus mordax) and pickled squid. Setlines were haphazardly placed throughout the study area in the St. Marys River to assess the distribution of lake sturgeon. This approach was used since little information existed on lake sturgeon locations in the St. Marys River. Setlines that did not catch fish for one week were pulled and set at other haphazardly selected locations. Latitude and longitude of all sites were recorded using a portable GPS and imported into ArcGIS (ESRI® ArcMAP(tm)™ 9.3). All sturgeon captured were measured for total length (TL), fork length (FL), weight, and girth. Lake sturgeon were classified as subadults if length at capture was b100 cm or age at capture was b15 years (Auer, 2003). An anterior pectoral fin ray sample was removed for age estimation. For unique identification, lake sturgeon were tagged with alphanumeric passive integrated transponder (PIT) tags inserted under the third dorsal scute and Floy (T-anchor bar) tags inserted posterior to the dorsal fin. Before release, captured lake sturgeon were inspected for any observable abnormalities including lamprey scars and external parasites. In 2006 and 2007, 18 adult lake sturgeon were implanted with sonic transponders with a 4-year battery life (Gerig et al., 2011). Individual yearly capture histories of sub-adult and adult lake sturgeon collected from 2000 to 2007 were used to estimate the population size of lake sturgeon in the St. Marys River. The adult and sub-adult lake sturgeon population estimate was calculated using a POPAN Jolly–Seber model within Program Mark version 5.1 (Crosbie and Manly, 1985; White and Burnham, 1999). Because our sampling took place primarily in the upper St. Marys River and because lake sturgeon emigration and immigration between lakes Huron and Superior and the tributaries are unknown, we considered this an open, mixed population (Fig. 1). In addition to an absolute abundance estimate, the POPAN formulation provides estimates of apparent survival (Φi), recapture probability (pi), and probability of entrance into the population (bi). In the current study the probability of entrance is defined as a measure of recruitment to the gear and immigration into the study area. In order to evaluate the equal recapture probability and survival assumptions associated with Jolly– Seber methods, lake sturgeon were classified as either subadult or adult based on length and age at capture. Lake sturgeon were classified as subadults if length at capture was b100 cm or age at capture was b15 years (Auer, 2003). The recapture probability and survival assumptions between subadults and adults and between sampling occasions were then tested for goodness of fit using program RELEASE within program MARK (Burnham et al., 1987). The constant study area, instantaneous sampling, tag identification, and tag loss assumptions associated with Jolly–Seber population estimates were not evaluated, but nothing in our sampling design would suggest violation of these assumptions. Akaike's information criterion corrected for sample size (AICc) was used to select the most parsimonious model explaining the survival, recapture probability, and probability of entrance parameters (Anderson and Burnham, 2002). Because the analysis of the survival
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Fig. 1. Study area within the upper St. Marys River. Dotted lines represent the upstream and downstream boundaries of the study site. The inset illustrates the location of the St. Marys River within the Great Lakes.
and recapture probability parameters using program RELEASE revealed no significant differences between subadults and adults, models included in the candidate model set did not contain group effects. The candidate model set included variations of constant (.) and time dependent (year) parameters of recapture probability and probability of entrance. Survival of lake sturgeon was assumed to be constant during the study period. These parameter combinations resulted in four models in the candidate model set Φ(.)p(year)b(year), Φ(.)p(.)b(year), Φ(.)p(year)b(.), and Φ(.)p(.)b(.). Constant and time dependent parameters of recapture probability were included in the model set because of variable setline effort throughout the study period. Constant and time dependent parameters of probability of entrance were included in the model set because of unknown spatial and temporal movement patterns of lake sturgeon in the study area and variable setline effort throughout the sampling period. Models were ranked according to Δi (Δi = AICc(i) − AICc(min)). Akaike weights (AICc wi) were used to select the most parsimonious model and provided
strength of evidence for each model in the candidate model set (Burnham and Anderson 2004).
Results During the eight year study, 192 individual lake sturgeon were captured in the St. Marys River and there were 37 recapture events (Table 1). Lake sturgeon were captured throughout much of the area sampled from the North Channel to south Lake George (Fig. 2). Catches were greatest in 2006 and 2007, with 76 and 72 sturgeon collected respectively, and lowest in 2000 with just 2 individuals (Table 1). However, catch rates were related to sampling effort. The mean age of lake sturgeon captured was 20 years and ranged from 7 to 59 years (N = 167) (Fig. 3). Thirty-six age classes were represented, with 64% over 15 years of age (adult) and 36% between the ages of 5–15, which are classified as subadult (Auer, 2003). Back-
Table 1 Setline effort, capture frequency, biological data, and catch-per-unit-effort (CPUE—number of lake sturgeon captured per setline night) for lake sturgeon captured in the St. Marys River, Michigan from 2000 to 2007.
Setline nights N captured N recaptured Mean TL (cm) Mean WGT (kg) CPUE
2000
2001
2002
2003
2004
2005
2006
2007
All years
75 2 NA 122 NA 0.03
659 44 1 128 16 0.07
1214 45 7 122 14 0.04
38 3 1 129 14 0.08
167 8 1 121 14 0.05
156 4 2 133 21 0.03
522 69 7 121 11 0.13
569 54 18 121 10 0.09
3400 229 37 125 (80–175) 13 (2–37) 0.07
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J.M. Bauman et al. / Journal of Great Lakes Research 37 (2011) 47–53
Fig. 2. Location of setline sites and lake sturgeon capture locations within the St. Marys River, from 2000 to 2007.
calculated year class strength of lake sturgeon indicates greatest number of captures from approximately 15 to 25 years ago (Fig. 4). The mean total length and weight of lake sturgeon captured was 125 cm (80–175 cm TL) and 13 kg (2–37 kg), respectively. Regression analysis indicated a strong relationship between total length and weight (R2 = 0.72) (Fig. 5). The mean weight and length of sturgeon in the St. Marys River at 23–27 years of age were greater than or similar to populations within a similar geographic range (Table 2). Fifty-three (23%) lake sturgeon possessed lamprey wounds and 44 (19%) possessed a fish flea ecto-parasite, Argulus spp. There were no records of lamprey still attached at the time of capture, nor were there any known sturgeon mortalities during this survey. Lake sturgeon with parasite occurrences displayed a mean Fulton (Ricker, 1975)
condition factor of Kfulton = 0.602 which was not significantly different than the condition factor of captured sturgeon without the presence of parasites (Kfulton = 0.620; df = 161, P = 0.522). Results from the goodness of fit test in program RELEASE indicated no overall difference in recapture probability and survival between subadults and adults or between sampling occasions (TEST 2 and TEST 3: χ2 = 2.557, df = 10, P = 0.990). The most parsimonious model in the candidate model set was Φ(.)p(year)b(year), suggesting time dependent recapture probability and probability of entrance (Table 3). The estimated population size was 505 subadult and adult individuals (Coefficient of variation = 15%) with 95% confidence intervals ranging from 388 to 692 individuals. Survival probability was estimated at 0.847 (SE = 0.065, 95% CI = 0.675–0.936). The
Fig. 3. Age composition of lake sturgeon captured in the St. Marys River, from 2000 to 2007.
Fig. 4. Year class frequency distribution of aged lake sturgeon (N = 167) captured in the St. Marys River, from 2000 to 2007.
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Table 3 Akaike values corrected for sample size (AICc), Δi (Δi = AICc(i) − AICc(min)), Akaike weights (AICc wi), model likelihood, and number of parameters (K) for models included in the candidate model set. Φ = Apparent survival, p = probability of recapture, and b = probability of entrance for time varying (year) and constant (.) models testing these parameters.
Fig. 5. Length-weight power function (y = 2.0 e−9 TL^3.1457) of lake sturgeon captured in the St. Marys River, from 2000 to 2007.
probability of capture over the time period 2001–2006 ranged from 0.015 to 0.502 and the probability of entrance over the time period 2002–2006 ranged from 0.000 to 0.383 (Table 4). Probability of capture could not be estimated during 2000 and 2007 and probability of entrance could not be estimated for 2000, 2001 and 2007. Discussion Eight years of lake sturgeon assessments, along with movement studies (see Gerig et al., 2011), suggest that the St. Marys River contains a localized population of lake sturgeon within the North Channel of Sugar Island and Lake George. Lake sturgeon were captured throughout the sampled area downstream of the Soo Locks and upstream of Neebish Island, with a majority of successful captures in the North Channel and Lake George. The high number of recaptures, along with recent telemetry studies (Gerig et al., 2011), suggest that lake sturgeon likely reside in this area year round. The St. Marys River sturgeon population size is at the lower limits of a self-sustaining population (~500 individuals) based on the Jolly– Seber population estimate. Healthy self-sustaining lake sturgeon populations are defined as those which contain a minimum of 500 to 1500 breeding individuals (Hay-Chmielewski and Whelan, 1997; Auer, 2003; LRBOI, 2008). These estimates were identified as the minimum number needed to prevent over-harvest and maintain genetic diversity within a population. However, approximately 30% of the sturgeon in the study area was immature juveniles less than 15 years old, which suggests that the number of breeding individuals in the population is much less than 500. Age structure characteristics of self-sustaining lake sturgeon populations in Lake Superior have been defined based on age class
Table 2 Mean weight of lake sturgeon for sturgeon with a total length of 100 ± 1.0 cm and mean total length of lake sturgeon aged 23 to 27 years from the St. Marys River, Michigan, and other lake sturgeon populations across 46° latitude (Fortin et al., 1996). Population
Weight (kg)
Total Length (cm)
St. Marys River, Michigan Lower Ottawa River, Ontario Lac des Deux Montagnes, Ontario Lake Sainte-Pierre, Ontario Lake Nipissing, Ontario Menominee River, Wisconsin-Michigan Flambeau River, Wisconsin
6.000 6.437 5.456 6.572 5.460 5.100 5.305
138.2 98.9 114.3 120.0 138.3 132.1 119.1
Model
AICc
Δi
AICc wi
Model likelihood
K
Φ(.)p(year)b(year) Φ(.)p(.)b(year) Φ(.)p(year)b(.) Φ(.)p(.)b(.)
306.2361 349.7642 588.6831 654.7431
0.0000 43.5281 282.4470 348.5070
1.0000 0.0000 0.0000 0.0000
1.0000 0.0000 0.0000 0.0000
13 5 7 3
representation (20 or more adult year classes) and measureable recruitment of age 0 to age 5 fish (Auer 2003). Within the St. Marys River study area, 24 adult year classes of lake sturgeon were represented, but no fish less than 7 years old (80 cm TL) were collected. The underrepresentation of age 0 to 5 sturgeon is likely a function of gear bias toward older, larger fish. It is also possible that we did not sample locations occupied by age 0 to 5 sturgeon. The use of alternative gear types and sampling in other habitats may increase the catch of younger age classes and provide a better understanding of recruitment in the St. Marys River. For example, setlines deployed with smaller hooks and night visual assessments were successful methods used to capture age 0 and age 1 lake sturgeon in the Big Manistee River, Michigan (Chiotti, 2004; Mann, 2008). Recapture probabilities of lake sturgeon were not dependent upon classifications of subadult or adult fish, but did vary over time. This variation in recapture probability can likely be attributed to variable setline effort. For years in which recapture probability could be estimated it was the lowest in 2003, 2004, and 2005 which also corresponded to years with the lowest setline effort. Additional age structure recommendations for healthy lake sturgeon populations include; 70-year old females and 40-year old males, and significant year classes occurring once every 5 years (Holey et al., 2000). During this study, lake sturgeon were not sexed consistently, therefore data used to determine maximum ages by gender and the ratio of females to males for this population are unavailable. However, the oldest individual collected in the study area was 59 and only one additional sturgeon over 50 years of age was collected during the study. Captures of fish representing year classes between 1978 and 1997, and most notably between 1993 and 1997 suggests that recruitment or immigration may have increased in recent years. Recruitment to our gear along with immigration into our study area was evaluated by including the probability of entrance parameter in our models. However, this information should be viewed with caution. The decreased setline effort in 2003, 2004, and 2005 reflects low probability of entrance parameters during these years. We have no reason to suspect immigration to our study area or recruitment to our gear decreased over this time period and highlights the importance for standardized effort when trying to evaluate this parameter. In 2002 and 2006 setline effort was 1214 and 522 nights respectively. During these 2 years the probability of entrance was 0.331 and 0.383 which can be interpreted as 33.1 to 38.3% of the total number of lake sturgeon in the population which were unmarked entered our study area or recruited to our gear. Unfortunately this metric does not allow us to differentiate between recruitment to gear and immigration to our study area. It is unknown what factors are important in determining lake sturgeon year class strength within the St. Marys River, but it is likely a combination of habitat (dredging and sediment contamination) and abundance of spawning adults. The lack of lake sturgeon in the study in excess of 50 years may be related to environmental degradation in the form of chemical contaminants. Lake sturgeon are long-lived
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Table 4 Estimates of yearly recapture probabilities and yearly probabilities of entrance 2001–2006, including standard error (SE) and 95% confidence intervals (CI) calculated under model Φ(.)p(year)b(year) using the POPAN formulation in program MARK. Year
Recapture probability
Recapture probability SE
Recapture probability CI
Probability of entrance
Probability of entrance SE
Probability of entrance CI
2001 2002 2003 2004 2005 2006
0.502 0.186 0.015 0.035 0.021 0.193
0.352 0.062 0.010 0.022 0.015 0.051
0.060–0.941 0.093–0.338 0.004–0.053 0.010–0.114 0.005–0.084 0.111–0.312
NA 0.331 0.000 0.113 0.000 0.383
NA 0.174 0.000 0.240 0.000 0.199
NA 0.096–0.698 0.000–0.000 0.001–0.933 0.000–0.000 0.107–0.762
benthic omnivores which likely increases harmful exposure to and bioaccumulation of contaminated sediments. Sediment contamination peaked in the late 1960s and early 1970s (Kauss, 1991) but has declined over the past 40 years (Keller et al., 2011). More recent progress has come after remediation efforts that followed the USEPA's designation of the St. Marys River as an Area of Concern. The recent increases in abundance of young lake sturgeon may indicate remedial progress for younger age classes, but this has yet to be verified. The estimated population size combined with unknown current and historical harvest rates, suggest the lake sturgeon population in this study area remains vulnerable to further anthropogenic impacts. In 2000, the Michigan Department of Natural Resources prohibited recreational harvest of lake sturgeon. More recently since 2008, lake sturgeon harvest has been regulated under a “zero catch and possession limit” in Ontario waters as administered by the Ontario Ministry of Natural Resources (USEPA, 2009). Currently, Native American and First Nation subsistence fishers are permitted to harvest lake sturgeon throughout the year but current and historical records are unavailable. This information is essential to determine the impacts of current harvest levels on the St. Marys sturgeon population. It is unclear what effect harvest may have had, or currently has, on mortality rates of the St. Marys River lake sturgeon population because data from recreational and subsistence fishers is unavailable for the St. Marys River. However, the probability of survival estimated in the current study suggests that mortality of lake sturgeon in the study area is low and comparable with other studies (Bruch, 1999). Despite the small size of the lake sturgeon population in our study area in the St. Marys River, the individuals collected appear to be in similar health to comparable populations. Lake sturgeon from the St. Marys River were of similar size or larger than comparably aged fish from other populations within similar latitudes. For example, St. Marys River lake sturgeon were approximately 138 cm TL at ages 23 to 27, compared to 120 cm (range 98.9–138.3 cm TL) as reported by Fortin et al. (1996). Additionally, lake sturgeon (at 100 ± 1.0 cm TL) from the St. Marys River were of similar or greater weight (kg) than those from similar latitudes, as reported by Fortin et al. (1996). Parasites and lamprey scarring occurred at a relatively high frequency (19% and 23%, respectively), but the average condition factor of individuals with and without parasites and/or scarring were similar. The condition factors were also comparable to other populations in the St. Clair System (Craig et al., 2005). This study suggests that a small, but likely increasing lake sturgeon population exists in this region of St. Marys River, however, it remains unclear as to whether this is a self-sustaining population. Continued monitoring should help fill knowledge gaps associated with the St. Marys lake sturgeon population and improve our understanding and management of local and Great Lakes sturgeon populations. Also, additional information is needed on habitat use and younger age classes to assess recruitment success, extent of immigration/emigration, and population status. Specifically, identification of spawning, feeding, and nursery habitat for lake sturgeon in the St. Marys River is needed to improve manager's abilities to protect and continue to recover local sturgeon populations.
Acknowledgments We would like to acknowledge the many undergraduates from Lake Superior State University's Aquatic Research Laboratory that provided field assistance and Trent Sutton for early efforts to establish the survey. Financial support for this project was provided in part by Lake Superior State University's Aquatic Research Laboratory, the Soo Area Sportsmen's Club, and the United States Fish and Wildlife Service. We would also like to thank Tracy Galarowicz for assistance with population estimates. References Anderson, D.A., Burnham, K.P., 2002. Avoiding pitfalls when using informationtheoretic methods. Journal of Wildl. Manag. 66 (3), 912–918. Auer, N.A., 1996a. Response of spawning lake sturgeons to change in hydroelectric facility operation. Trans. Amer. Fish. Soc. 125, 66–77. Auer, N.A., 1996b. Importance of habitat and migration to sturgeons with emphasis on lake sturgeon. Can. J. Fish. Aquat. Sci. 53, 152–160. Auer, N.A., 1999a. Population characteristics and movement of lake sturgeon in the Sturgeon River and Lake Superior. J. Great Lakes Res. 25, 282–293. Auer, N.A., 1999b. Lake sturgeon: a unique and imperiled species in the Great Lakes. In: Taylor, W.W., Ferreri, C.P. (Eds.), Great Lakes Fisheries Policy and Management: A Binational Perspective. Michigan State University Press, East Lansing, pp. 515–536. Auer, N.A., 2003. A lake sturgeon rehabilitation plan for Lake Superior. Great Lakes Fish. Comm. Misc. Publ. 2003-2002. Bray, K.E., 1996. Habitat models as tools for evaluating historic change in the St. Marys River. Can. J. Fish. Aquat. Sci. 53, 88–98. Bruch, R.M., 1999. Management of lake sturgeon on the Winnebago System—long term impacts of harvest and regulations on population structure. J. Appl. Ichthyol. 15, 142–152. Burnham, K.P., Anderson, D.R., 2004. Multimodel inference: understanding AIC and BIC in model selection. Sociol. Meth. Resear. 33 (2), 261–304. Burnham, K.P., Anderson, D.R., White, G.C., Brownie, C., Pollock, K.H., 1987. Design and analysis methods for fish survival experiments based on release-recapture. Am. Fish. Soc. Monogr. 5, 1–437. Chiotti, J.A. 2004. Evaluation of spawning habitat, juvenile habitat, and larval drift of lake sturgeon (Acipenser fulvescens) in the Big Manistee River, Michigan. Master's Thesis. Michigan Technological University, Houghton, MI. Chiotti, J.A., Holtgren, M., Auer, N., Ogren, S., 2008. Lake sturgeon spawning habitat in the Big Manistee River, Michigan. N. Am. J. Fish. Manag. 28 (4), 1009–1019. Craig, J.M., Thomas, M.V., Nichols, S.J., 2005. Length-weight relationship and a relative condition factor equation for lake sturgeon (Acipenser fulvescens) from the St Clair River system (Michigan, USA). J. Appl. Ichthyol. 21, 81–85. Crosbie, S.F., Manly, B.F., 1985. Parsimonious modeling of capture-mark recapture studies. Biometrics 41, 385–398. Fielder, D.G. and Waybrant, J.R., 1998. Fish Population Surveys of St. Marys River, 19751995, and Recommendations for Management. Michigan Department of Natural Resources Fisheries Division Research Report. No 2048. Fortin, R., Dumont, P., Guenette, S., 1996. Determinates of growth and body condition of lake sturgeon (Acipenser fulvescens). Can. J. Aquat. Sci. 53, 1150–1156. Gerig, B., Moerke, A., Greil, R., Koproski, S., 2011. Movement patterns and habitat characteristics of Lake Sturgeon (Acipenser fulvescens) in the St. Marys River, Michigan, 2007-2008. J. Great Lakes Res. 37 (Supplement 2), 54–60. Gleason, G.R., Behmer, D.J. and Hook, R., 1979. Evaluation of lake whitefish and herring spawning grounds as they may be affected by excessive sedimentation induced by vessel entrapment due to the ice environment within the St. Marys River system. U.S. Army Corps of Engineers. Contract No. DACW-35-79-M-0561. Harkness, W.J. and Dymond, J.R., 1961. The lake sturgeon; the history of its fishery and problems of conservation. Ontario Dept. of Lands and Forests. Harris, R., Kinder, B., Marino, A., Parker-Greisman, V., Patterson, T., 2009. The St. Marys River conservation action plan summary. The Nature Conservancy, Michigan, p. 10.
J.M. Bauman et al. / Journal of Great Lakes Research 37 (2011) 47–53 Hay-Chmielewski, E.M. and Whelan, G.E., 1997. Lake Sturgeon Rehabilitation Strategy. Michigan Department of Natural Resources Fisheries Division Special Report 18. Holey, M.E., E.A. Baker, T.F. Thuemler, and R. Elliot. 2000. Research and Assessment Needs to Restore Lake Sturgeon in the Great Lakes: Great Lakes Fishery Trust, Lansing, Michigan. Kauss, P.B., 1991. Biota of the St. Marys River: habitat evaluation and environmental assessment. Hydrobiologia 219, 1–35. Keller, B.J., Back, R.C., Westrick, J., Werner, M., Evans, B., Moerke, A., Zimmerman, G., Wright, D., Grenfell, E., Courneya, J., 2011. Sediment quality at select sites in the St. Marys River Area of Concern. J. Great Lakes Res. 37 (Supplement 2), 12–19. Knights, B.C., Vallazza, J., Zigler, S., Dewey, M., 2002. Habitat and movement of lake sturgeon in the Upper Mississippi River System, USA. Trans. Amer. Fish. Soc. 131, 507–522. LaHaye, M., Branchaud, A., Gendron, M., Verdon, R., Fortin, R., 1992. Reproduction early life history, and characteristics of spawning grounds of the lake sturgeon (Acipenser fulvescens) in Des Prairies and L'Assomption rivers, near Montreal, Quebec. Can. J. Zool. 70, 1681–1689. LRBOI, 2008. Nme (Lake sturgeon) Stewardship Plan for the Big Manistee River and 1836 Reservation. Natural Resources Department, Special Report 1, Manistee. Mann, K.A. 2008. Life history of reared and wild juvenile lake sturgeon, Big Manistee River, Michigan. Master's Thesis. Michigan Technological University, Houghton, Michigan. Mills, E.L., Leach, J.H., Carlton, J.T., Secor, C.L., 1993. Exotic species in the Great Lakes: a
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history of biotic crisis and anthropogenic introductions. J. Great Lakes Res. 19 (1), 1–54. Poe, T.P., Edsall, T.A., 1982. Effects of vessel-induced waves on the composition and amount of drift in an ice environment in the St. Marys River. Admin. Rep. 82-6. U.S. Fish and Wildlife Service, Great Lakes Fishery Laboratory. Ricker, W.E., 1975. Computation and interpretation of biological statistics of fish populations. Bull. Fish. Res. Board Canada 191, 1–382. Ripley, M.P., Arbic, B., Zimmerman, G., 2011. Environmental history of the St. Marys River. J. Great Lakes Res. 37 (Supplement 2), 5–11. Rochard, E., Castelnaud, G., Lepage, M., 1990. Sturgeons (Pisces: Acipenseridae); threats and prospects. J. Fish Biol. 37 (A), 123–132. Thomas, M.V., Haas, R., 1999. Capture of lake sturgeon with setlines in the St. Clair, River, Michigan. N. Am. J. Fish. Manag. 19, 610–612. Tody, W.H. 1974. Whitefish, sturgeon and the early Michigan commercial fishery. Pages 45-60 in Michigan Department of Natural Resources. Michigan Fisheries Centennial Report 1873-1973. Michigan Department of Natural Resources, Management Report 6, Lansing. USEPA, St. Marys River Area of Concern. 1988. http://www.epa.gov/glnpo/aoc/stmarys. html. 2009. USEPA, State of the Great Lakes. 2009. http://www.epa.gov/solec/sogl2009/. 2009. USFWS, Lake Sturgeon Biology and Population History in the Great Lakes, http://www. fws.gov/midwest/sturgeon/biology.htm Updated 10/30/2008. White, G.C., Burnham, K.P., 1999. Program MARK: survival estimation from populations of marked animals. Bird Study 46, 120–139.
Contents lists available at ScienceDirect
Journal of Great Lakes Research j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / j g l r
Population status and demographics of lake sturgeon (Acipenser fulvescens) in the St. Marys River, from 2000 to 2007 John M. Bauman a,b, Ashley Moerke a,⁎, Roger Greil a, Brandon Gerig a, Edward Baker c, Justin Chiotti d a
Aquatic Research Laboratory and School of Biological Sciences, Lake Superior State University, 650 W. Easterday Ave, Sault Ste. Marie, MI 49783, USA Michigan State University Fisheries and Wildlife, East Lansing, MI 48824, USA Michigan Department of Natural Resources and Environment, 488 Cherry Creek Rd., Marquette, MI 49855, USA d Department of Natural Resources, Cornell University, Ithaca, NY 14853, USA b c
a r t i c l e
i n f o
Article history: Received 2 December 2009 Accepted 11 November 2010 Available online 15 January 2011 Communicated by R. Marshall Werner Index words: Lake sturgeon Acipenser fulvescens Threatened species St. Marys River
a b s t r a c t The St. Marys River, the sole outflow of Lake Superior, was historically inhabited by lake sturgeon (Acipenser fulvescens); until recently it was unclear whether a population was still present in the river. From 2000 to 2007, the population status of subadult and adult lake sturgeon in the St. Marys River was characterized. Setlines were deployed at multiple water depths (2–20 m) for 3400 setline nights. Biological measurements including total length and weight were recorded and each individual was affixed with unique identification tags before being released. A total of 192 unique lake sturgeon were captured with a recapture rate of 16%. The population size of lake sturgeon in the St. Marys River was estimated to be near 500 individuals. Fish captured exhibited a mean weight of 13 kg (range 2–37 kg) and a mean total length of 125 cm (range 80–175 cm). The mean age of lake sturgeon captured was 20 years (range 7–59 years) and 36 age classes were represented. Lamprey wounds were observed on 23% (N = 53) of sturgeon and nearly 19% (N = 44) of lake sturgeon had visible external parasites classified as Argulus spp. This study suggests that a recovering lake sturgeon population exists in the St. Marys River, however, it remains unclear as to whether this is a self-sustaining population reproducing in the river. Additional information is needed on metapopulation dynamics, habitat use, and younger age classes to assess recruitment success and population status. © 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.
Introduction Historically, lake sturgeon (Acipenser fulvescens) was an abundant species throughout the Great Lakes basin. Populations declined precipitously beginning in the late 1880s because of aggressive commercial harvest, habitat degradation (e.g., shoreline development, logging practices), and construction of dams which prevented access to spawning habitat (Harkness and Dymond, 1961; Rochard et al., 1990). The initial view of sturgeon as a nuisance fish resulted in commercial fishers discarding carcasses ashore. As the market value of lake sturgeon was realized, commercial harvest ensued (Tody, 1974). The largest commercial catches of lake sturgeon in the Great Lakes occurred in the 1880s when an average of 8.6 million pounds was harvested per year, but by the turn of the century lake sturgeon catches had dropped drastically and the Lake Erie population for example declined by over 80% (USFWS, 2008). In addition to overharvest, deforestation and the construction of hydroelectric facilities have degraded the quality and accessibility of spawning
⁎ Corresponding author. E-mail address: [email protected] (A. Moerke).
habitat used by lake sturgeon (Harkness and Dymond, 1961; Auer, 1996a). These factors coupled with unique life history attributes, including late maturity and individual variation in reproduction periodicity make natural recovery of depleted populations a long and difficult process. Currently, lake sturgeon is considered threatened in 20 states and 7 provinces within their native range (Knights et al., 2002). Out of 107 Great Lakes locations where lake sturgeon populations once existed, 59 (55%) are recorded as “small” and 45 (42%) are listed as “extirpated” (Holey et al., 2000). Strategic fisheries rehabilitation goals have been proposed to assist in the recovery of lake sturgeon throughout the Great Lakes. Recently, The Nature Conservancy listed lake sturgeon as a “conservation target” in the St. Marys River (Harris et al., 2009), which further emphasizes the need for local as well as regional rehabilitation efforts. Within the Great Lakes many studies have focused on lake sturgeon to understand their unique life history characteristics in efforts to rehabilitate threatened populations (Harkness and Dymond, 1961; Thomas and Haas, 1999; Fortin et al., 1996; Auer, 1996a,b, 1999a). Despite increased efforts, sturgeon status in many areas of the Great Lakes, including major connecting channels such as the St. Marys River, still remains relatively unknown (Hay-Chmielewski and
0380-1330/$ – see front matter © 2010 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.jglr.2010.12.003
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Whelan, 1997; Holey et al., 2000, but see Thomas and Haas, 1999). Since 1975, the Michigan Department of Natural Resources has conducted gill net surveys throughout the St. Marys River to determine trends in the fish community composition at least once every decade (Fielder and Waybrant, 1998). This information has indicated that a sturgeon population exists in the St. Marys River; however, captures were limited and declined from 1975 to 1995 (CPUE = capture per 305 m of gill net per net night: 1975 = 0.99, 1979 = 0.03, 1987 = 0.09, 1995 = 0.00) (Fielder and Waybrant, 1998). The St. Marys River, the sole outflow of Lake Superior, is an important ecological corridor between Lake Superior and Lake Huron. The river and its biota have been impacted by many anthropogenic activities including shipping, sediment contamination, and shoreline development (see Ripley et al., 2011). Understanding the current status of lake sturgeon in the St. Marys River is an essential first step in protecting and recovering sturgeon populations in this area. Also, because lake sturgeon are considered an indicator of ecosystem health and a conservation target for the ecosystem, knowledge gained about the lake sturgeon population will enhance efforts towards conservation of the entire St. Marys River ecosystem. The objective of this study was to characterize the current lake sturgeon population in the upper reaches of the St. Marys River. Study area The St. Marys River connects Lake Superior and Lake Huron through a 112-km waterway. The “rapids” area of the St. Marys River historically was the only hydrological connection between the lakes, but compensating gates and locks now obstruct river passage and the rapids contribute less than 50%, and sometimes less than 10% of the total discharge (Bray, 1996). The river also possesses many large tributaries, including the Garden River, Charlotte River, and Munuscong River, which provide important spawning and nursery habitat for many St. Marys River fishes. During the past century the St. Marys River has been a site of extensive industrialization (see Ripley et al., 2011). The steel and shipping industry, paper processing mills, sewage treatment plants and tanneries have operated on the river and have contributed to the designation of this location as an international Area of Concern (USEPA, 1988). These developments have contributed to the degradation of natural channel morphology, flow regimes, habitat and water quality. Additionally, transoceanic vessels in the Great Lakes have impacted the St. Marys through the introduction of nonnative species and re-suspension of sediment (Gleason et al., 1979; Poe and Edsall, 1982; Mills et al., 1993). Despite vast degradation, the St. Marys River has been listed as “high” in regards to the suitability of maintaining a self-sustaining population of lake sturgeon (Hay-Chmielewski and Whelan, 1997). High habitat heterogeneity offers refuge from environmental disturbance and may be important wintering and feeding habitat (Auer, 1999b). The “rapids” area and some tributaries entering the St. Marys River, including the Garden River, may provide sufficient spawning habitat (e.g., large-cobble substrate, swift current) as characterized in other systems (e.g., LaHaye et al., 1992; Auer, 1996a,b; Chiotti et al., 2008). Reports from local fishermen and Sea Lamprey Control suggest that sturgeon may be spawning in the Garden River and in the main river near Neebish Island. However, natural reproduction by lake sturgeon in the St. Marys River has yet to be documented in the scientific literature. The study site assessed from 2000 to 2007 for lake sturgeon included international waters from the North Channel of Sugar Island to East Neebish Island (Fig. 1). During this study, several attempts were made by Lake Superior State University's Aquatic Research Laboratory (LSSU) to sample lake sturgeon in the shipping channel west of Sugar Island, however, no sturgeon were captured in the shipping channel. Our remaining efforts were focused outside of the
shipping channel because previous efforts did not capture sturgeon and freighter traffic in the shipping channel made it logistically difficult to set and retrieve setlines. Methods From 2000 to 2007, lake sturgeon were captured in the St. Marys River by LSSU from early spring to late summer using baited setlines 100 m in length, containing 25 snews each (7/0 saltwater hooks) (Thomas and Haas, 1999). Setlines were deployed for 24 to 48 h intervals at water depths of 2 to 16 m, and baited with a variety of baits. Baits used included lake whitefish (Coregonus clupeaformis), lake trout (Salvelinus namaycush), northern cisco (Coregonus artedi), sucker (Catostomus spp.), brown trout (Salmo trutta), northern pike (Esox lucius), yellow perch (Perca flavescens), chicken livers, earthworms, rainbow smelt (Osmerus mordax) and pickled squid. Setlines were haphazardly placed throughout the study area in the St. Marys River to assess the distribution of lake sturgeon. This approach was used since little information existed on lake sturgeon locations in the St. Marys River. Setlines that did not catch fish for one week were pulled and set at other haphazardly selected locations. Latitude and longitude of all sites were recorded using a portable GPS and imported into ArcGIS (ESRI® ArcMAP(tm)™ 9.3). All sturgeon captured were measured for total length (TL), fork length (FL), weight, and girth. Lake sturgeon were classified as subadults if length at capture was b100 cm or age at capture was b15 years (Auer, 2003). An anterior pectoral fin ray sample was removed for age estimation. For unique identification, lake sturgeon were tagged with alphanumeric passive integrated transponder (PIT) tags inserted under the third dorsal scute and Floy (T-anchor bar) tags inserted posterior to the dorsal fin. Before release, captured lake sturgeon were inspected for any observable abnormalities including lamprey scars and external parasites. In 2006 and 2007, 18 adult lake sturgeon were implanted with sonic transponders with a 4-year battery life (Gerig et al., 2011). Individual yearly capture histories of sub-adult and adult lake sturgeon collected from 2000 to 2007 were used to estimate the population size of lake sturgeon in the St. Marys River. The adult and sub-adult lake sturgeon population estimate was calculated using a POPAN Jolly–Seber model within Program Mark version 5.1 (Crosbie and Manly, 1985; White and Burnham, 1999). Because our sampling took place primarily in the upper St. Marys River and because lake sturgeon emigration and immigration between lakes Huron and Superior and the tributaries are unknown, we considered this an open, mixed population (Fig. 1). In addition to an absolute abundance estimate, the POPAN formulation provides estimates of apparent survival (Φi), recapture probability (pi), and probability of entrance into the population (bi). In the current study the probability of entrance is defined as a measure of recruitment to the gear and immigration into the study area. In order to evaluate the equal recapture probability and survival assumptions associated with Jolly– Seber methods, lake sturgeon were classified as either subadult or adult based on length and age at capture. Lake sturgeon were classified as subadults if length at capture was b100 cm or age at capture was b15 years (Auer, 2003). The recapture probability and survival assumptions between subadults and adults and between sampling occasions were then tested for goodness of fit using program RELEASE within program MARK (Burnham et al., 1987). The constant study area, instantaneous sampling, tag identification, and tag loss assumptions associated with Jolly–Seber population estimates were not evaluated, but nothing in our sampling design would suggest violation of these assumptions. Akaike's information criterion corrected for sample size (AICc) was used to select the most parsimonious model explaining the survival, recapture probability, and probability of entrance parameters (Anderson and Burnham, 2002). Because the analysis of the survival
J.M. Bauman et al. / Journal of Great Lakes Research 37 (2011) 47–53
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Fig. 1. Study area within the upper St. Marys River. Dotted lines represent the upstream and downstream boundaries of the study site. The inset illustrates the location of the St. Marys River within the Great Lakes.
and recapture probability parameters using program RELEASE revealed no significant differences between subadults and adults, models included in the candidate model set did not contain group effects. The candidate model set included variations of constant (.) and time dependent (year) parameters of recapture probability and probability of entrance. Survival of lake sturgeon was assumed to be constant during the study period. These parameter combinations resulted in four models in the candidate model set Φ(.)p(year)b(year), Φ(.)p(.)b(year), Φ(.)p(year)b(.), and Φ(.)p(.)b(.). Constant and time dependent parameters of recapture probability were included in the model set because of variable setline effort throughout the study period. Constant and time dependent parameters of probability of entrance were included in the model set because of unknown spatial and temporal movement patterns of lake sturgeon in the study area and variable setline effort throughout the sampling period. Models were ranked according to Δi (Δi = AICc(i) − AICc(min)). Akaike weights (AICc wi) were used to select the most parsimonious model and provided
strength of evidence for each model in the candidate model set (Burnham and Anderson 2004).
Results During the eight year study, 192 individual lake sturgeon were captured in the St. Marys River and there were 37 recapture events (Table 1). Lake sturgeon were captured throughout much of the area sampled from the North Channel to south Lake George (Fig. 2). Catches were greatest in 2006 and 2007, with 76 and 72 sturgeon collected respectively, and lowest in 2000 with just 2 individuals (Table 1). However, catch rates were related to sampling effort. The mean age of lake sturgeon captured was 20 years and ranged from 7 to 59 years (N = 167) (Fig. 3). Thirty-six age classes were represented, with 64% over 15 years of age (adult) and 36% between the ages of 5–15, which are classified as subadult (Auer, 2003). Back-
Table 1 Setline effort, capture frequency, biological data, and catch-per-unit-effort (CPUE—number of lake sturgeon captured per setline night) for lake sturgeon captured in the St. Marys River, Michigan from 2000 to 2007.
Setline nights N captured N recaptured Mean TL (cm) Mean WGT (kg) CPUE
2000
2001
2002
2003
2004
2005
2006
2007
All years
75 2 NA 122 NA 0.03
659 44 1 128 16 0.07
1214 45 7 122 14 0.04
38 3 1 129 14 0.08
167 8 1 121 14 0.05
156 4 2 133 21 0.03
522 69 7 121 11 0.13
569 54 18 121 10 0.09
3400 229 37 125 (80–175) 13 (2–37) 0.07
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J.M. Bauman et al. / Journal of Great Lakes Research 37 (2011) 47–53
Fig. 2. Location of setline sites and lake sturgeon capture locations within the St. Marys River, from 2000 to 2007.
calculated year class strength of lake sturgeon indicates greatest number of captures from approximately 15 to 25 years ago (Fig. 4). The mean total length and weight of lake sturgeon captured was 125 cm (80–175 cm TL) and 13 kg (2–37 kg), respectively. Regression analysis indicated a strong relationship between total length and weight (R2 = 0.72) (Fig. 5). The mean weight and length of sturgeon in the St. Marys River at 23–27 years of age were greater than or similar to populations within a similar geographic range (Table 2). Fifty-three (23%) lake sturgeon possessed lamprey wounds and 44 (19%) possessed a fish flea ecto-parasite, Argulus spp. There were no records of lamprey still attached at the time of capture, nor were there any known sturgeon mortalities during this survey. Lake sturgeon with parasite occurrences displayed a mean Fulton (Ricker, 1975)
condition factor of Kfulton = 0.602 which was not significantly different than the condition factor of captured sturgeon without the presence of parasites (Kfulton = 0.620; df = 161, P = 0.522). Results from the goodness of fit test in program RELEASE indicated no overall difference in recapture probability and survival between subadults and adults or between sampling occasions (TEST 2 and TEST 3: χ2 = 2.557, df = 10, P = 0.990). The most parsimonious model in the candidate model set was Φ(.)p(year)b(year), suggesting time dependent recapture probability and probability of entrance (Table 3). The estimated population size was 505 subadult and adult individuals (Coefficient of variation = 15%) with 95% confidence intervals ranging from 388 to 692 individuals. Survival probability was estimated at 0.847 (SE = 0.065, 95% CI = 0.675–0.936). The
Fig. 3. Age composition of lake sturgeon captured in the St. Marys River, from 2000 to 2007.
Fig. 4. Year class frequency distribution of aged lake sturgeon (N = 167) captured in the St. Marys River, from 2000 to 2007.
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Table 3 Akaike values corrected for sample size (AICc), Δi (Δi = AICc(i) − AICc(min)), Akaike weights (AICc wi), model likelihood, and number of parameters (K) for models included in the candidate model set. Φ = Apparent survival, p = probability of recapture, and b = probability of entrance for time varying (year) and constant (.) models testing these parameters.
Fig. 5. Length-weight power function (y = 2.0 e−9 TL^3.1457) of lake sturgeon captured in the St. Marys River, from 2000 to 2007.
probability of capture over the time period 2001–2006 ranged from 0.015 to 0.502 and the probability of entrance over the time period 2002–2006 ranged from 0.000 to 0.383 (Table 4). Probability of capture could not be estimated during 2000 and 2007 and probability of entrance could not be estimated for 2000, 2001 and 2007. Discussion Eight years of lake sturgeon assessments, along with movement studies (see Gerig et al., 2011), suggest that the St. Marys River contains a localized population of lake sturgeon within the North Channel of Sugar Island and Lake George. Lake sturgeon were captured throughout the sampled area downstream of the Soo Locks and upstream of Neebish Island, with a majority of successful captures in the North Channel and Lake George. The high number of recaptures, along with recent telemetry studies (Gerig et al., 2011), suggest that lake sturgeon likely reside in this area year round. The St. Marys River sturgeon population size is at the lower limits of a self-sustaining population (~500 individuals) based on the Jolly– Seber population estimate. Healthy self-sustaining lake sturgeon populations are defined as those which contain a minimum of 500 to 1500 breeding individuals (Hay-Chmielewski and Whelan, 1997; Auer, 2003; LRBOI, 2008). These estimates were identified as the minimum number needed to prevent over-harvest and maintain genetic diversity within a population. However, approximately 30% of the sturgeon in the study area was immature juveniles less than 15 years old, which suggests that the number of breeding individuals in the population is much less than 500. Age structure characteristics of self-sustaining lake sturgeon populations in Lake Superior have been defined based on age class
Table 2 Mean weight of lake sturgeon for sturgeon with a total length of 100 ± 1.0 cm and mean total length of lake sturgeon aged 23 to 27 years from the St. Marys River, Michigan, and other lake sturgeon populations across 46° latitude (Fortin et al., 1996). Population
Weight (kg)
Total Length (cm)
St. Marys River, Michigan Lower Ottawa River, Ontario Lac des Deux Montagnes, Ontario Lake Sainte-Pierre, Ontario Lake Nipissing, Ontario Menominee River, Wisconsin-Michigan Flambeau River, Wisconsin
6.000 6.437 5.456 6.572 5.460 5.100 5.305
138.2 98.9 114.3 120.0 138.3 132.1 119.1
Model
AICc
Δi
AICc wi
Model likelihood
K
Φ(.)p(year)b(year) Φ(.)p(.)b(year) Φ(.)p(year)b(.) Φ(.)p(.)b(.)
306.2361 349.7642 588.6831 654.7431
0.0000 43.5281 282.4470 348.5070
1.0000 0.0000 0.0000 0.0000
1.0000 0.0000 0.0000 0.0000
13 5 7 3
representation (20 or more adult year classes) and measureable recruitment of age 0 to age 5 fish (Auer 2003). Within the St. Marys River study area, 24 adult year classes of lake sturgeon were represented, but no fish less than 7 years old (80 cm TL) were collected. The underrepresentation of age 0 to 5 sturgeon is likely a function of gear bias toward older, larger fish. It is also possible that we did not sample locations occupied by age 0 to 5 sturgeon. The use of alternative gear types and sampling in other habitats may increase the catch of younger age classes and provide a better understanding of recruitment in the St. Marys River. For example, setlines deployed with smaller hooks and night visual assessments were successful methods used to capture age 0 and age 1 lake sturgeon in the Big Manistee River, Michigan (Chiotti, 2004; Mann, 2008). Recapture probabilities of lake sturgeon were not dependent upon classifications of subadult or adult fish, but did vary over time. This variation in recapture probability can likely be attributed to variable setline effort. For years in which recapture probability could be estimated it was the lowest in 2003, 2004, and 2005 which also corresponded to years with the lowest setline effort. Additional age structure recommendations for healthy lake sturgeon populations include; 70-year old females and 40-year old males, and significant year classes occurring once every 5 years (Holey et al., 2000). During this study, lake sturgeon were not sexed consistently, therefore data used to determine maximum ages by gender and the ratio of females to males for this population are unavailable. However, the oldest individual collected in the study area was 59 and only one additional sturgeon over 50 years of age was collected during the study. Captures of fish representing year classes between 1978 and 1997, and most notably between 1993 and 1997 suggests that recruitment or immigration may have increased in recent years. Recruitment to our gear along with immigration into our study area was evaluated by including the probability of entrance parameter in our models. However, this information should be viewed with caution. The decreased setline effort in 2003, 2004, and 2005 reflects low probability of entrance parameters during these years. We have no reason to suspect immigration to our study area or recruitment to our gear decreased over this time period and highlights the importance for standardized effort when trying to evaluate this parameter. In 2002 and 2006 setline effort was 1214 and 522 nights respectively. During these 2 years the probability of entrance was 0.331 and 0.383 which can be interpreted as 33.1 to 38.3% of the total number of lake sturgeon in the population which were unmarked entered our study area or recruited to our gear. Unfortunately this metric does not allow us to differentiate between recruitment to gear and immigration to our study area. It is unknown what factors are important in determining lake sturgeon year class strength within the St. Marys River, but it is likely a combination of habitat (dredging and sediment contamination) and abundance of spawning adults. The lack of lake sturgeon in the study in excess of 50 years may be related to environmental degradation in the form of chemical contaminants. Lake sturgeon are long-lived
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J.M. Bauman et al. / Journal of Great Lakes Research 37 (2011) 47–53
Table 4 Estimates of yearly recapture probabilities and yearly probabilities of entrance 2001–2006, including standard error (SE) and 95% confidence intervals (CI) calculated under model Φ(.)p(year)b(year) using the POPAN formulation in program MARK. Year
Recapture probability
Recapture probability SE
Recapture probability CI
Probability of entrance
Probability of entrance SE
Probability of entrance CI
2001 2002 2003 2004 2005 2006
0.502 0.186 0.015 0.035 0.021 0.193
0.352 0.062 0.010 0.022 0.015 0.051
0.060–0.941 0.093–0.338 0.004–0.053 0.010–0.114 0.005–0.084 0.111–0.312
NA 0.331 0.000 0.113 0.000 0.383
NA 0.174 0.000 0.240 0.000 0.199
NA 0.096–0.698 0.000–0.000 0.001–0.933 0.000–0.000 0.107–0.762
benthic omnivores which likely increases harmful exposure to and bioaccumulation of contaminated sediments. Sediment contamination peaked in the late 1960s and early 1970s (Kauss, 1991) but has declined over the past 40 years (Keller et al., 2011). More recent progress has come after remediation efforts that followed the USEPA's designation of the St. Marys River as an Area of Concern. The recent increases in abundance of young lake sturgeon may indicate remedial progress for younger age classes, but this has yet to be verified. The estimated population size combined with unknown current and historical harvest rates, suggest the lake sturgeon population in this study area remains vulnerable to further anthropogenic impacts. In 2000, the Michigan Department of Natural Resources prohibited recreational harvest of lake sturgeon. More recently since 2008, lake sturgeon harvest has been regulated under a “zero catch and possession limit” in Ontario waters as administered by the Ontario Ministry of Natural Resources (USEPA, 2009). Currently, Native American and First Nation subsistence fishers are permitted to harvest lake sturgeon throughout the year but current and historical records are unavailable. This information is essential to determine the impacts of current harvest levels on the St. Marys sturgeon population. It is unclear what effect harvest may have had, or currently has, on mortality rates of the St. Marys River lake sturgeon population because data from recreational and subsistence fishers is unavailable for the St. Marys River. However, the probability of survival estimated in the current study suggests that mortality of lake sturgeon in the study area is low and comparable with other studies (Bruch, 1999). Despite the small size of the lake sturgeon population in our study area in the St. Marys River, the individuals collected appear to be in similar health to comparable populations. Lake sturgeon from the St. Marys River were of similar size or larger than comparably aged fish from other populations within similar latitudes. For example, St. Marys River lake sturgeon were approximately 138 cm TL at ages 23 to 27, compared to 120 cm (range 98.9–138.3 cm TL) as reported by Fortin et al. (1996). Additionally, lake sturgeon (at 100 ± 1.0 cm TL) from the St. Marys River were of similar or greater weight (kg) than those from similar latitudes, as reported by Fortin et al. (1996). Parasites and lamprey scarring occurred at a relatively high frequency (19% and 23%, respectively), but the average condition factor of individuals with and without parasites and/or scarring were similar. The condition factors were also comparable to other populations in the St. Clair System (Craig et al., 2005). This study suggests that a small, but likely increasing lake sturgeon population exists in this region of St. Marys River, however, it remains unclear as to whether this is a self-sustaining population. Continued monitoring should help fill knowledge gaps associated with the St. Marys lake sturgeon population and improve our understanding and management of local and Great Lakes sturgeon populations. Also, additional information is needed on habitat use and younger age classes to assess recruitment success, extent of immigration/emigration, and population status. Specifically, identification of spawning, feeding, and nursery habitat for lake sturgeon in the St. Marys River is needed to improve manager's abilities to protect and continue to recover local sturgeon populations.
Acknowledgments We would like to acknowledge the many undergraduates from Lake Superior State University's Aquatic Research Laboratory that provided field assistance and Trent Sutton for early efforts to establish the survey. Financial support for this project was provided in part by Lake Superior State University's Aquatic Research Laboratory, the Soo Area Sportsmen's Club, and the United States Fish and Wildlife Service. We would also like to thank Tracy Galarowicz for assistance with population estimates. References Anderson, D.A., Burnham, K.P., 2002. Avoiding pitfalls when using informationtheoretic methods. Journal of Wildl. Manag. 66 (3), 912–918. Auer, N.A., 1996a. Response of spawning lake sturgeons to change in hydroelectric facility operation. Trans. Amer. Fish. Soc. 125, 66–77. Auer, N.A., 1996b. Importance of habitat and migration to sturgeons with emphasis on lake sturgeon. Can. J. Fish. Aquat. Sci. 53, 152–160. Auer, N.A., 1999a. Population characteristics and movement of lake sturgeon in the Sturgeon River and Lake Superior. J. Great Lakes Res. 25, 282–293. Auer, N.A., 1999b. Lake sturgeon: a unique and imperiled species in the Great Lakes. In: Taylor, W.W., Ferreri, C.P. (Eds.), Great Lakes Fisheries Policy and Management: A Binational Perspective. Michigan State University Press, East Lansing, pp. 515–536. Auer, N.A., 2003. A lake sturgeon rehabilitation plan for Lake Superior. Great Lakes Fish. Comm. Misc. Publ. 2003-2002. Bray, K.E., 1996. Habitat models as tools for evaluating historic change in the St. Marys River. Can. J. Fish. Aquat. Sci. 53, 88–98. Bruch, R.M., 1999. Management of lake sturgeon on the Winnebago System—long term impacts of harvest and regulations on population structure. J. Appl. Ichthyol. 15, 142–152. Burnham, K.P., Anderson, D.R., 2004. Multimodel inference: understanding AIC and BIC in model selection. Sociol. Meth. Resear. 33 (2), 261–304. Burnham, K.P., Anderson, D.R., White, G.C., Brownie, C., Pollock, K.H., 1987. Design and analysis methods for fish survival experiments based on release-recapture. Am. Fish. Soc. Monogr. 5, 1–437. Chiotti, J.A. 2004. Evaluation of spawning habitat, juvenile habitat, and larval drift of lake sturgeon (Acipenser fulvescens) in the Big Manistee River, Michigan. Master's Thesis. Michigan Technological University, Houghton, MI. Chiotti, J.A., Holtgren, M., Auer, N., Ogren, S., 2008. Lake sturgeon spawning habitat in the Big Manistee River, Michigan. N. Am. J. Fish. Manag. 28 (4), 1009–1019. Craig, J.M., Thomas, M.V., Nichols, S.J., 2005. Length-weight relationship and a relative condition factor equation for lake sturgeon (Acipenser fulvescens) from the St Clair River system (Michigan, USA). J. Appl. Ichthyol. 21, 81–85. Crosbie, S.F., Manly, B.F., 1985. Parsimonious modeling of capture-mark recapture studies. Biometrics 41, 385–398. Fielder, D.G. and Waybrant, J.R., 1998. Fish Population Surveys of St. Marys River, 19751995, and Recommendations for Management. Michigan Department of Natural Resources Fisheries Division Research Report. No 2048. Fortin, R., Dumont, P., Guenette, S., 1996. Determinates of growth and body condition of lake sturgeon (Acipenser fulvescens). Can. J. Aquat. Sci. 53, 1150–1156. Gerig, B., Moerke, A., Greil, R., Koproski, S., 2011. Movement patterns and habitat characteristics of Lake Sturgeon (Acipenser fulvescens) in the St. Marys River, Michigan, 2007-2008. J. Great Lakes Res. 37 (Supplement 2), 54–60. Gleason, G.R., Behmer, D.J. and Hook, R., 1979. Evaluation of lake whitefish and herring spawning grounds as they may be affected by excessive sedimentation induced by vessel entrapment due to the ice environment within the St. Marys River system. U.S. Army Corps of Engineers. Contract No. DACW-35-79-M-0561. Harkness, W.J. and Dymond, J.R., 1961. The lake sturgeon; the history of its fishery and problems of conservation. Ontario Dept. of Lands and Forests. Harris, R., Kinder, B., Marino, A., Parker-Greisman, V., Patterson, T., 2009. The St. Marys River conservation action plan summary. The Nature Conservancy, Michigan, p. 10.
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