Status and Trends of Prey Fish Populations
History and Trends
The fish community during 2003 was very different from recent years. Adult alewife abundance during 2003 was extremely low, presumably due to a combination of over winter mortality during 2002-2003 and salmonid predation. However, age-0 alewives were more abundant than at any time since 1992 due to an exceptionally strong year class. Adult rainbow smelt abundance was the lowest observed since 1992, but age-0 rainbow smelt were more abundant that any year since 1998. Adult bloater abundance increased slightly, but age-0 bloaters were ubiquitous. CPE of juvenile bloaters was the highest recorded since 1992, and the 2003 year class may be one of the largest since annual surveys began in 1973. Abundance of most other prey species was stable; however, round gobies continued to increase at southern ports. Prey biomass in U.S. waters increased during 2003, and alewives comprised the bulk of the biomass; however, biomass was composed almost entirely of age-0 fish rather than adults. Monitoring of benthic invertebrates suggests a sequential decline in nearly all benthic invertebrates, especially the deepwater amphipod Diporeia; Diporeia is now absent or declining at even deep (73 m) stations. These declines are associated temporally with increases in quagga mussels Dreissena bugensis but the mechanism is still unknown. These declines reflect the loss of body fat so important to alewife survival and growth. Predators in Lake Huron face potential prey shortages. Although overall prey density was high, there are few adult alewives or rainbow smelt available. Predator feeding conditions during 2004 will depend on alewife overwinter survival and the ability of large predators to subsist on small or non-traditional prey.
Trawl samples are performed annually at five ports in U.S. waters: Detour, Hammond Bay, Alpena,Ausable Point (Tawas), and Harbor Beach. Sampling also occurred at Goderich, Ontario during 1998, 1999, and 2003 using the same trawling regime as at U.S. ports. Data from Goderich are included in this report.
Alewives were abundant during 2003, but catches were dominated almost completely by age-0 fish. CPE of age-0 fish was higher than at any time since 1992. Adult CPE was lower than at any time since 1992, and the 2003 index (49/tow) was less than half the previous lowest value of 112/tow in 1998. Alewife length distribution reflected high density of age-0 fish, and low numbers of adults. Low numbers of 100-130 mm alewives suggested that the 2002 year class experienced almost complete mortality.
The alewife age structure changed dramatically between 2002 and 2003. During 2002, age-1 through age-5 fish comprised about half the catch, but during 2003 trawl catches were dominated completely by age-0 fish from the 2003 year class , presumably due to a combined high over winter mortality and predation on all older age groups.
Adult rainbow smelt were at the lowest level of recorded abundance since 1992. Low adult abundance was probably a result of poor recruitment during 2001 and 2002 combined with high predation from stocked predators. Age-0 rainbow smelt were abundant; the 2003 year class was the second highest since 1992. Length frequency of rainbow smelt was truncated; fish greater than 150 mm TL were rare. Adult rainbow smelt will continue to remain scarce to both salmonids and humans.
Adult bloater abundance in Lake Huron increased during 2003. Unusually high numbers of age-0 bloaters were captured during 2003; this may represent a dominant year class. Juvenile bloaters are pelagic and generally not susceptible to the bottom trawl, so their abundance may not be a reliable index of year class strength. However, age-0 bloaters were captured in every tow, and abundance was higher than any survey since 1992. Bloater length frequencies mirrored high CPE of age-0 fish, and indicated that most adults were between 175 and 225 mm in length.
Sculpins, sticklebacks, and trout-perch
Sculpin abundance in Lake Huron has been highly variable since 1992, but CPE during 2003 suggests that they have been stable recently at low levels. Deepwater sculpins comprise most of the trawl catch, while slimy sculpins are only a minor component of the fish community. Overall sculpin abundance during 2003 was below the average value for the time period, and slimy sculpins were virtually absent from the catch. Abundance of 9-spine sticklebacks increased slightly this year, while trout-perch continue a steady decline that began in 1995.
CPE of round gobies has increased annually since 1997 (the year when they were first encountered during the survey. Round gobies are now present at Goderich, Harbor Beach, Ausable Point (Tawas), and Alpena, but they have not been collected in the straits.
CPE of adult lake whitefish has decreased since the mid-1990s, and this trend continued during 2003. Assuming that all whitefish less than 200 mm TL were age-0, CPE of juvenile lake whitefish has been consistently low since 1997. Decreased abundance of adult lake whitefish is consistent with lower recruitment since 1997.
Biomass estimates for U.S. waters indicate that total prey biomass was higher in 2003 compared with 2002. Biomass increased for all species but trout-perch, however, the biomass continues to be dominated by alewife. The major change between 2002 and 2003 is that the alewife biomass is now composed largely of age-0 fish from the 2003 year class.
Diporeia, chironomids (midge larvae), sphaerid clams, and dreissenids (zebra and quagga mussels) were the most abundant groups. Between 2001 and 2003, abundance of all species except quagga mussels generally declined. But although quagga mussels increased, we still have not observed high densities found in Lake Michigan. Diporeia was absent at 27 m during 2001 through 2003. At 46 m, Diporeia density decreased between 2001 and 2002, and increased slightly during 2003; however, at 73 m there have been steady decreases in all three years.
The prey fish community has changed considerably since 2002. Last year, large alewives from the 1998, 1999, and 2001 year classes dominated the prey fish community. These fish are no longer present in the population. Alewives continue to dominate an increased prey biomass, but it is now composed almost entirely of age-0 fish from the 2003 year class.
Diporeia continued to decline sequentially from shallow to deeper depths. Diporeia formerly reached high abundance at 27 m; by the time our sampling began in 2001 it had disappeared at 27 m. Diporeia decline occurred at 46 m by 2002, and at 73 m during 2003. Diporeia appears to have been replaced by quagga mussels, but the mechanism responsible for is disappearance is not known. However, it suggests that changes in the benthic community observed in other Great Lakes are now happening in Lake Huron, and we should anticipate changes in diets, growth, or distribution of fishes as this process continues. ˛
Sea Lamprey Management in Lake Huron 2003
· Lake Huron has 1,761 (1,334 Canada, 427 U.S.) tributaries.
· 120 (55 Canada, 65 U.S.) tributaries have historical records of production of sea lamprey larvae.
· 68 (37 Canada, 31 U.S.) tribu-taries have been treated with lampricide at least once during 1994-2003.
· Of these, 46 (24 Canada, 22 U.S.) tributaries are treated on a regular cycle.
· Lampricide treatments were successfully completed in 18 scheduled streams (8 Canada, 10 U.S.)
· Long Lake Outlet in Alpena County was treated for the first time. An infested, upstream section of the river was not treated because of uncooperative land owners.
· The protocol for application of lampricides to streams with populations of young-of-year lake sturgeons (Acipenser fulvescens) was followed during treatment of the Carp River. The protocol limits the concentrations of TFM and Bayluscide to 1.2 times minimum lethal concentration (concentration of lampricide necessary to kill 99.9% of sea lampreys in a 12-hour treatment) to protect young-of-year lake sturgeons.
· The Pigeon River was treated to reduce the population of residual sea lampreys.
· Mortality of non-target fish was minimal in the majority of treatments, with the exception of some mortality to stonecat, a species sensitive to lampricide. A Voluntary Adverse Effects 6(a)(2) report was submitted to the Environmental Protection Agency.
· Bayluscide granules were applied to areas of significant larval sea lamprey density in the St. Marys River by both Service and Department treatment units. In total, 45.2 ha were treated.
· Brown’s Creek, treated in 2002, was added to the stream treatment list after assessment personnel detected a high proportion of large (>120 mm) larvae in assessments conducted in 2003. The 2002 treatment was compromised by a series of beaver dams that prevented treatment of the entire infested area.
● A total of 15,114 spawning-phase male sea lampreys were transported to Hammond Bay Biological Station from trapping operations in the Cheboygan River (4,916), Ocqueoc River (182), Trout River (114), Echo River (1,139), Thessalon River (2,384), Koshkawong River (39), Au Sable River (582), East Au Gres River (115), Tittabawassee River (197), Carp Lake Outlet (1,007), and St. Marys River (4,439). An additional 15,866 were obtained from tributaries of three other Great Lakes.
● A total of 27,963 sterilized male sea lampreys from all sources were released in the St. Marys River. The estimated population of unsterilized spawning-phase sea lampreys in the St. Marys River was 27,011 (17,835 males). Assessment traps removed 9,220 sea lamprey (6,088 males), an estimated reduction of 33% from trapping. The ratio of sterile males to unsterilized male sea lampreys remaining in the St. Marys River was estimated at 2.3:1 (27,963 sterile: 11,959 estimated untreated males extant).
● The theoretical reduction in reproduction from trapping and enhanced sterile male release was estimated at 80% during 2003. The average theoretical reduction from trapping and enhanced sterile male release was 89% during 1997-2002. Prior to enhancement (1991-1996) the theoretical reduction in reproduction averaged 58%.
● The release of sterile male sea lampreys, combined with the removal of lampreys by traps, reduced the theoretical number of effective fertile females in the river from 9,176 to 1,860 during 2003.
● In the St. Marys River Rapids, 11 sterile and 5 untreated male sea lampreys (ratio of 2.2:1) were observed on 9 of 109 nests located and probed for eggs. Egg viability was 21% for the 10 nests yielding final samples for this index. Average egg viability (weighted by nests per year) during 1997-2002 was 26%.
Nineteen barriers have been built or modified on Lake Huron streams with the specific intent of blocking the upstream movement of spawning phase sea lampreys.
● A new seasonal stop log barrier was constructed in Greene Creek during 2003.
● New construction projects are in various stages of development on the Black Mallard and Au Gres rivers and Schmidt Creek.
● OMNR undertook a restoration of the Thornbury Dam on the Beaver River. A nature-like fishway was installed as part of the project. Department staff also completed the design of a sea lamprey trap for the same structure, and plans to install and operate the trap for the 2004 season.
Rainbow Trout Management Summary
In Duluth Area stream assessments, the numbers of young-of-the-year, YOY, and one-year-old rainbow trout and brook trout sampled throughout the summer of 2003 were consistently lower than the mean numbers sampled during previous years. Lower catch rates were attributed to severe winter conditions in 2002-2003 when many streams froze to the bottom.
On bothe the Baptism and Split Rock rivers, numbers of one-year-old steelhead were very low, while YOY catch rates were about average. Stocking upstream of the index stations took place in both streams. Electrofishing in streams around the Grand Marais area showed good numbers of healthy YOY steelhead in larger streams, but few one-year-old fish indicating severe winter conditions occurred along the entire shore.
The spring anadromous creel survey covered 17 tributaries. Clerks measured 116 Kamloops, 11 hatchery-reared steelhead, and recorded 56 unclipped steelhead caught and released. Angler catch rates were stable along the upper shore, but fell for anglers fishing the lower shore. Shorewide, anglers caught one unclipped steelhead for every 18 hours fished. Catch rates for Kamloops have remained relatively stable with anglers catching a Kamloops strain rainbow trout on average every 5.5 hours.
The Lake Superior creel survey recorded 17 unclipped steelhead. No Kamloops or clipped steelhead were sampled in this summer’s creel.
The fall creel survey recorded only 3,908 angler hours of fishing effort at seven tributaries. The survey recorded a total of seven unclipped steelhead, three hatcher-reared steelhead, 17 Kamloops and six Chinook salmon.
Fry – Unclipped steelhead from the Knife River produced 24,676 fry, which were also stocked into the Knife River system. Approximately 45,000 fry from unclipped steelhead were started on feed to produce yearlings or “smolts” that will be returned to the Knife River in spring of 2004. These fish will be stocked without an adipose clip and will not be legal to harvest. Unclipped steelhead from the French River produced 117,596 fry, which were stocked back into the French River. Clipped steelhead returning to the French River produced 108,248 fry, which were stocked in various short-run streams. A portion of this number, 4,306 fry, were stocked into the Sucker, Stewart, and Encampment rivers to evaluate the importance of woody debris in the production of juvenile steelhead.
Steelhead fry stocking in Minnesota waters.
Location Number Stocked
French River 117,596
Main Branch Knife River 28,314
Little Knife River 14,973
McCarthy Creek 13,307
Sucker River 1,797
Stewart River 1,311
Silver Creek 50,079
Encampment River 1,198
Gooseberry River 53,863
Yearlings – A total of 42,481 hatchery-reared steelhead yearlings were stocked into the Knife River system. All stocked yearlings were given a fin clip to identify them as hatchery fish. If the total number, 22,828 were stocked below the Knife River trap. A total of 104,375 Kamloops-strain rainbow trout were stocked, with 42,504 yearlings into Lester River and 61,871 into the French River.
Fingerlings – 4,841 steelhead fall fingerlings of Knife River parentage were stocked into the west branch of the Knife River.
French River trap – The DNR captured 102 unclipped steelhead, 267 clipped steelhead and 1,351 Kamloops. The number of unclipped steelhead returning to the French River was around the five-year average of 104 fish.
Main Knife River trap – Spring 2003 totals included 367 unclipped steelhead, 116 hatchery-reared (clipped) steelhead, and 72 Kamloops. Unclipped steelhead were transported to the French River facility to supply eggs for fry stocking programs and then returned to the lake. Kamloops were not passed above the trap and were returned to the lake. Most unclipped steelhead were passed upstream so they could reproduce naturally, however 68 were taken to the hatchery and spawned to produce fish for the yearling program.
Little Knife River trap – Ten female and 13 male clipped steelhead were put upstream of the trap in 2003. This was the second year that clipped fish were passed upstream to evaluate natural reproduction of clipped fish above the Little Knife weir. The presence of 681 YOY moving through the smolt trap and the presence of YOY at Little Knife River index stations may be evidence of successful reproduction or fry stocking. The relative contribution of each will be determined through genetic work. ˛
Lake Superior Fisheries
Chinook Salmon Update
The number of returning adult Chinook salmon to the French River Trap was down significantly from last year. The catch in fall 2003 was 53 fish compared to a catch of 106 in 2002. Forty-four out of the 53 Chinook were marked with a left rear clip indicating they were from the Lake Huron strain stocked from 1999-2002. These fish were stocked in an attempt to revitalize the Minnesota Chinook program after declining returns to the French River of Minnesota strain fish made the program unsustainable. Criteria to evaluate this program include having enough fish return to enable spawning of 75 pairs of disease-free fish. This criterion will be applied in each year, 2003-2006.
In 2003, the run size limited spawning to 15 pairs of fish, of which, two pair had bacterial kidney disease (BKD) and their eggs had to be destroyed. The 13 pair remaining produced approximately 28,000 eggs. Relatively poor eye-up or development to eyed-egg stage of 57% resulted in 14,556 fingerlings, which are currently being reared at the French River coldwater Hatchery. These fish will be stocked back into the French River in spring 2004.
Despite the low return of stocked fish to the French River, the catch rate for Chinook salmon in the summer trolling fishery has shown an increase over the last 10 years. Information collected from the anglers catch indicates the majority of Chinook salmon being caught in Minnesota are naturally reproduced. ˛
Ruffe – region wide
Background and history
Ruffe are presently in the St. Louis River Estuary (SLRE), MN/WI, where they were originally introduced during the mid 1980s. Ruffe were also discovered in Thunder Bay Harbour, Ontario, in 1991. Due to potential competition for food and space, ruffe pose a threat to native fish populations.
Research conducted by the U of Minnesota-Duluth revealed that ruffe consume a significant amount of benthic macroinvertebrate energy. However, a statistical analysis conducted by USGS showed no significant relationship between an increasing ruffe population and declining native fish populations in the St. Louis River, MN/WI. In three Wisconsin tributaries just east of the St. Louis River, 1995-2002 trawl data suggests that yellow perch abundance declines in years that ruffe abundance increases.
The Ruffe Control Program was drafted in 1995 with a revision in 1996 after ruffe were discovered in Lake Huron in 1995. The goal of the Ruffe Control Program is “to prevent or delay the spread of ruffe in the Great Lakes and inland waters.” Surveillance was one of eight objectives designed into the program to achieve this goal.
In 2002, major ruffe range expansion was detected. Ashland FRO discovered ruffe in Lake Michigan near Escanaba, MI, and in the Keweenaw Waterway, Lake Superior, 101 km east of the Ontonagon River, MI, the previous eastern boundary of the ruffe range along the south shore of Lake Superior. In the Ontonagon River, although trawling indicated a decline in ruffe abundance from 2001, the overall trend in ruffe abundance continues to increase. No ruffe expansion was detected in Lake Huron, and no ruffe were captured in trawls within the ruffe range in Lake Huron.
In 2003, only minor ruffe range expansion was detected in Thunder Bay Harbour, ON, Lake Superior, and in Little Bay de Noc, Lake Michigan. However, ruffe CPE in trawls increased significantly in Thunder Bay Harbour from 78/hr. in 2000 to 569/hr. in 2003. In addition, round goby (Neogobius melanostomus) and white perch (Morone americana) were discovered in Thunder Bay Harbour, the second confirmed location for round goby in Lake Superior.
The primary objective of surveillance activities is to locate new populations of ruffe and describe their age and/or size composition.
Lake Superior Surveillance in 2003
Thunder Bay Harbour, Ontario – A total of 1,139 ruffe were collected over 15 transects and one trap site. One ruffe was captured in a baited modified Windermere trap set in the Kam River, 3 km upriver from the junction with the Mission River. The majority of the total catch was composed of spottail shiner (35%), ruffe (21%), and trout-perch (14%). Ruffe were first discovered here in 1991.
St. Louis River & Estuary, MN/WI
A total of 8,215 ruffe were captured, and ruffe dominated the total catch followed by yellow perch (136/ha), and trout-perch. Ruffe were discovered here in 1986, the initial sighting in North America.
Amnicon River, WI
Twelve species were captured with trout-perch dominating the total catch followed by ruffe (177/ha), yellow perch (6/ha). A total of 93 ruffe were collected, which consisted primarily of sub-adults. Ruffe were first discovered here in 1988.
Iron River, WI
Eleven species were captured with ruffe dominating the total catch followed by trout-perch, spottail shiner. A total of 23 ruffe were collected, which consisted of a 50:50 ratio of sub-adults and adults. Ruffe were first discovered here in 1991.
Flag River, WI – Thirteen species were captured with trout-perch dominating the total catch followed by yellow perch, ruffe, spottail shiner. A total of 56 ruffe were collected, which consisted primarily of sub-adults. Ruffe were first discovered here in 1992.
Ontonagon River, MI
Thirteen species were captured with trout-perch dominating the total catch followed by ruffe, yellow perch. A total of 18 ruffe were collected, which consisted of a 50:50 ratio of sub-adults and adults. Ruffe were first discovered here in 1994.
Lake Huron Surveillance in 2003
Ruffe were not captured from any new locations in Lake Huron, however, they continue to persist in the Thunder Bay River, MI, where they were first discovered in 1995. In order to decrease the spawning ruffe population, ruffe population reduction was conducted in the Thunder By River for the second year.
Region-wide surveillance in 2003Additionally, surveillance was conducted in the major ports and tributaries of the Great Lakes by FWS survey crews. No ruffe were found. FWS crews from all FRO Great Lakes offices participated in the many Surveillance trips conducted and/or coordinated by Region 3 USFWS and Mark Dryer, station chief Ashland, WI FRO and Chairman, Ruffe Control Committee. The Great Lakes Sport Fishing Council has been an active member and participant of the Ruffe Control Committee since its founding in 1994.