Summary: A total of 232 lake sturgeon were collected from the St. Clair River and Lake St. Clair in 2000. Sturgeon were collected with bottom trawls and baited setlines. Pectoral fin ray sections were used to age 801 fish captured from 1997 to 2000. Ages ranged from 1 to 74 years and included 50 year classes. Mean length at age data indicated that these sturgeon grew faster as juveniles, compared with lake sturgeon in Michigan's inland waters. A total of 217 sturgeon were tagged with serial numbered monel cattle ear tags and released in 2000. An additional 160 sturgeon have been tagged and released through September 1, 2001. In total, over 1000 lake sturgeon have been captured, tagged, and released in Lake St. Clair and the St. Clair River since this study began in 1996. Tag recoveries have been rare. Only eighteen recaptures have been made with survey gear, while another 15 have been reported by sport or commercial fishermen.
The Mt. Clemens Fisheries Research Station began an investigation into the distribution and abundance of lake sturgeon in the St. Clair River and Lake St. Clair in 1996. Since 1997, the study has been funded through the Federal Aid for Sport Fish Restoration program. The objectives of this study are (1) to determine spawning period, areal distribution of spawning activity, and characterize spawning habitat for lake sturgeon in the St. Clair River, (2) to determine early (juvenile) life history of lake sturgeon in the St. Clair River and Lake St. Clair, and identify habitat requirements of lake sturgeon, (3) to document lake sturgeon population parameters for Lake St. Clair and the St. Clair River, including estimated abundance, exploitation, age composition, growth rate, and age/sex composition of the spawning stock.
Capture of juvenile and adult lake sturgeon to collect biological data and mark with monel tags - Sturgeon were collected with two gear types in 2000. A total of 82 sturgeon, including three recaptures, was caught in 72 overnight sets using setlines in the North Channel of the St. Clair River, between May 8 and May 25. Total length of sturgeon caught on setlines ranged from 744 mm to 1,887 mm. Ages ranged from 6 to 74 years. All fish were tagged with monel cattle ear tags and released.
A total of 150 lake sturgeon, including two recaptures, was captured with 10m headrope bottom trawls from June through October on Lake St. Clair. Total length of sturgeon captured ranged from 859 mm to 1,849 mm. Ages ranged from 6 to 59 years. All fish were tagged with monel cattle ear tags and released. One of the two fish recaptured with trawls in 2000 was a fish previously tagged in the opercle, but the tag had been lost. A scar was clearly evident on the opercle and the left pectoral fin ray had clearly been removed. This is the first documented case of tag loss during this study.
Overall, the age distribution of lake sturgeon captured from 1997 through 2000 appeared well balanced, with a total of 50 year classes represented by the 801 lake sturgeon sampled for age (Figure 1). This sample reveals consistently good recruitment from 1973 to 1993. It may not be coincidental that this period of recruitment followed the federal Clean Water Act of 1972. The strongest year-classes were produced in 1993, 1991, 1985, 1979, and 1977. The 1995 to 1998 year classes were poorly represented in the sample. This could be due to gear selectivity, juvenile distribution, or poor recruitment in recent years. Since lake sturgeon are known to be capable of exceeding 50 years in age (Scott and Crossman 1973), year-classes prior to 1965 appeared under-represented in the catch. This could be an indication that recruitment prior to 1965 was poor, but has improved dramatically since that time. Alternatively, those year-classes may have experienced high exploitation rates in the past, particularly during the 1970’s and early 1980’s, prior to the closure of sturgeon season during the spawning period in May and June for these waters in 1983. A third alternative explanation for the low representation of pre-1961 cohorts is that the longevity of lake sturgeon in the St. Clair system is now, and always has been, less than 50 years for nearly all individuals in the population.
Growth of lake sturgeon in the St. Clair ecosystem was good, with some fish attaining a total length of 1 m as early as age 8. A mean length of 1,270 mm is attained by age 19 (Table 1). In contrast, lake sturgeon in Michigan's inland waters grow slower, particularly from age 1 to age 15, and attain a mean length of 1270 mm at age 22 (Baker 1980). Based on age and growth data collected during this study, the MDNR implemented new regulations for sturgeon sport fishing on Lake St. Clair and the St. Clair River in 1999. The regulations included a “slot” size limit, with a minimum length limit of 1,067 mm (42 inches) and a maximum length limit of 1,270 mm (50 inches), a season bag limit of 1 fish, an open season from July 16 to September 30, and mandatory registration of harvested sturgeon at designated check stations. This “slot” limit allows a limited harvest to continue, while protecting sexually mature female fish and potentially allowing older fish to increase in abundance.
Characterization of adult spawning habitat and juvenile habitat, based on catch distribution, using underwater video, sidescan sonar, doppler flow meter, temperature and oxygen profiles - While good sidescan images of the site have been obtained from the Seascan PC system, signal returns from cinder substrate are not obviously different from the surrounding clay and gravel substrates. River currents tend to make the towfish unstable, resulting in distorted images. Also, steep bottom contours typical of the St. Clair River shorelines make it difficult to use the sidescan sonar effectively. Consequently, a quick reliable way to search the St Clair River and it’s many deltaic channels for additional spawning sites has not been found. Since researchers from the USGS Great Lakes Science Center undertook an investigation of suspected sturgeon spawning locations in 2001, we have directed our efforts towards other issues.
Efforts to identify habitat requirements of juvenile lake sturgeon have been impeded by our inability to consistently collect young lake sturgeon. Less than 1% of the sturgeon captured through 2000 were younger than age 3 (smaller than about 500 mm total length). Efforts to capture Age 0 lake sturgeon in littoral areas with a 4.8m headrope trawl have been unsuccessful. Potentially, Age 0 lake sturgeon in the St. Clair system may inhabit deep channel areas of the St. Clair delta. However, sampling in these areas is extremely difficult. We examined one of the deep channel areas with underwater video during fall 2000. However, the search was ineffective due to camera instability resulting from current turbulence. Alternative methods of collecting juveniles will be explored in 2002. Smaller scale setlines or small minnow trap devices are possible sampling options yet to be investigated. Additional catch data from collections over the next few years may also help identify juvenile habitat based on the geographical distribution of juveniles in the catch.
Collect and analyze tag recovery data - Tag recovery data remain sparse. Through 2000, only 29 lake sturgeon tagged and released during this study had been recaptured. Eleven have been recovered during the setline survey portion of this study in the North Channel, while three have been recovered while survey trawling. Seven recoveries were reported in 1998 and 1999 by sport anglers in the North Channel. Eight recoveries have been reported from the Ontario commercial trap-net fishery in southern Lake Huron, approximately 70 kilometers from the tag site. All other recaptures have occurred within 10 km of the tag sites. These data suggest that sturgeon movement between the St. Clair system and southern Lake Huron is common. Furthermore, it suggests that sturgeon spawning in the Michigan waters of the St. Clair River, experience considerable fishing exploitation in the Ontario waters of southern Lake Huron. These factors should be recognized in future sturgeon management strategies on these waters.
Lake sturgeon movements are unrestricted by human or natural barriers in the St. Clair system. The potential for free immigration and emmigration makes it difficult to estimate abundance based on mark-recapture techniques. However, it is possible to produce some estimates of numerical abundance based on the mark-recapture data available from our survey gear. Using the SCHNABEL method (Ricker 1975) we estimated the abundance of lake sturgeon in the St. Clair system was 39,952 (95% CI=20,719-557,481). Using CAPTURE software (White et al 1978) we estimated the abundance of lake sturgeon in the St. Clair system was 45,506 (95% CI=24,230-86,190). Despite the problems associated with the potential violation of various assumptions regarding these estimation techniques, we believe the magnitude of these estimates suggests subadult and adult sturgeon abundance in the St. Clair system exceeds 20,000 fish.
Brief 2001 Update
In 2001, we caught a total of 52 sturgeon, including 3 recaptures, with setlines in 56 overnight sets. An additional 120 sturgeon, including 2 recaptures, were captured with trawls on Lake St. Clair through Sept. 1. Passive integrated transponder (PIT) tags were applied to all sturgeon captured and released in 2001. The PIT tag is inserted under a dorsal scute and will allow us to evaluate tag loss of the monel tags. Diet samples were collected from 10 fish in late August, using a non-lethal stomach pumping technique. The volume of gut contents collected from several of the fish was substantial and will require considerable lab processing time. Preliminary examination of the gut contents indicated zebra mussels, snails, mayfly nymphs, and chironomid larvae were all present. In fact, live mayflies, zebra mussels, and chironomid larvae were collected from the stomachs of several of the fish. Processing of fin rays for age analysis for sturgeon captured in 2001 is underway.
We plan to continue the study in 2002, with additional effort made to document the diet of lake sturgeon in the high density sturgeon area of Lake St. Clair. Further effort to determine the distribution of young (age 2 or younger) lake sturgeon in the system will also be made.
Baker, J.P. 1980. The distribution, ecology, and management of the lake sturgeon (Acipenser fulvescens Rafinesque) in Michigan. Michigan Department of Natural Resources, Fisheries Research Report No. 1883, Ann Arbor.
Scott, W. B. and E. J. Crossman. 1973. Freshwater Fishes of Canada. Bulletin 184. Fisheries Research Board of Canada. Ottawa.
Ricker, W.E. 1975. Computation and interpretation of biological statistics of fish populations. Bulletin of the Fisheries Resources Board of Canada 191: 382 pp.
White, G.C., K.P. Burnham, D.L. Otis, and D.R. Anderson. 1978. User’s manual for program CAPTURE. Utah State University Press, Logan, Utah.
Table 1.–Mean length at age for all lake sturgeon sampled for age from the St. Clair River (SCR) and Lake St. Clair (LSC) for 1997-2000 and standard error (SE) compared to mean length from Michigan’s inland lakes (Baker 1980).
Mean length (mm)
Figure 1. Year class frequency for lake sturgeon captured in the St. Clair River and Lake St. Clair from 1997 to 2000 (n=801). Ages based on pectoral fin ray section interpretation.
Prepared by: Michael V. Thomas and Robert C. Haas
Date: September 30, 2001