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- For information on Lake Michigan Fisheries contact:
- Bradley Eggold
YELLOW PERCH RESEARCH
Yellow Perch Project
A large decline in the number of yellow perch surviving their first year of life has caused a reduction in the number of perch in Lake Michigan. Annual surveys of young-of-the-year (YOY) perch using bottom trawls and beach seines in the fall are usually good indicators of the number of fish hatched in a given year that we can expect to see as adults in future years. The number of YOY perch captured lakewide has dropped dramatically since 1988.
The WDNR, along with other agencies and scientists, has used a variety of assessments to analyze the status of the current yellow perch population. These assessments include 1) egg deposition; 2) spawning; 3) mid-water trawling assessment, 4) post-larval perch; 5) young-of-the-year (YOY); and 6) winter graded-mesh. In addition, several other studies have been conducted including an alewife stomach content study, a lakewide mark and recapture study and a reproductive status study. These assessments are detailed below.
Yellow Perch Egg Deposition
Yellow perch egg masses were identified by SCUBA divers at sites that 1) attract spawners, 2) were likely to trap drifting egg masses or 3) were traditional spawning grounds. All egg masses along a 300 meter transect were counted.
The purposes for doing these dives was to identify sites where egg masses were found and to develop an index of relative annual egg densities. During the initial years of the survey, we found very few egg masses. In 1997, divers searched for eggs for 31 hours and 40 minutes and found a total of 9 egg masses on the transects or nets or 0.50 egg masses per 1000 meters2. In 1998, divers searched for 12 hours and 48 minutes and found 0 egg masses or 0.0 egg masses per 1000 meters2. However, since the females from the 1998 year-class have matured we have found good numbers of egg masses distributed on the Green Can Reef starting in 2001 and continuing into 2007.
The trend of few egg skeins continued in 2011, 2012 and 2013 with the dive team finding 55, 37 and 9 egg skeins, respectively despite covering almost 96,311 square meters of lake bottom. As in 2010, the weather and temperature patterns produced a very atypical spring. Very few ripe and spawning males were found during the yellow perch spawning survey which may have lead to the small number of egg skeins found. In addition, egg skeins in 2012 appeared to be well developed by early June and therefore we only conducted one day of diving.
Egg deposition survey conducted on June 16, 2014 showed that the egg density estimate of 1.01 egg mass per 1000 meter square was similar to previous years even though fewer females were present on the reef. A total of 20,700 meter square area was surveyed.
Due to logistical and weather related issues, we were unable to conduct the survey in 2015 and 2016..
Yellow Perch Dive Summary
|Year||Diver Bottom Time (hrs)||Egg masses found (#)||Area covered (m2)||# egg masses per 1000 m2|
Yellow Perch Spawning Assessment
The main objectives of the yellow perch spawning assessment are to collect information on spawning fish including length, weight, sex, condition; collect gametes for scientific studies; determine spawning sites and aid in any other lakewide studies such as tagging and toxicological analysis.
In Wisconsin, adult yellow perch were sampled during the spawning period using 4x6-ft double-ended fyke nets with a 100-ft leader between the two double-throated pots (1997 - 1999), a 6x10 commercial double-ended fyke nets with a 500-ft leader (1998) and with standard 2 1/2 inch commercial and WDNR gill net (1997- present).
In 2006, a total of 1,741 yellow perch were captured which comprised 1,580 males and 161 females. As in previous years, our capture of females during the spawning season remains fairly low. The latest data obtained from 2007 show that we captured a total of 2,132 yellow perch comprised of 2,076 males and 56 females.
Results from this intensive effort were reported by Glover et. al 2008 and concluded that yellow perch prefer rocky substrate in the summer and that there was considerable spatial overlap between yellow perch tagged by different state agencies.
We conducted 2 lifts for yellow perch in 2012, yielding a total of 112 males and 35 females. The catch was composed mostly 7 year-old and 9 year-old perch. Yellow perch spawning seemed to have peaked about 2 weeks earlier than normal so we decided that our 2 lifts would conclude our assessment for the year.
In 2013, the yellow perch spawning assessment was conducted on May 22, 29 and 30 for a total effort of 2,500 ft of gill net set around Green Can Reef. We caught a total of 95 fish, yielding 42 males and 53 females. Compared to the previous years, the number of yellow perch caught during the spawning assessment was very low. Although we caught fewer perch, the general health of yellow perch captured appeared to be fine. Unlike the previous years, males were freely expressing milt, and the gonads appeared fully developed. The ripe females had well developed ovaries. There was no pattern in the number of fish caught or the number of spent female with respect to the depth (deep vs. shallow).
In 2014 we sampled spawning yellow perch at two locations – Green Can Reef and Milwaukee inner harbor. Contrary to previous years, the majority of the female perch caught in the nets were still green even as late as mid-June. Perhaps extreme cold winter delayed peak spawning this year.
In both 2015 and 2016, we caught extremely low numbers of yellow perch despite good gill net effort spread over many days. In both cases, catches were very low and comprised mainly of female fish. This continues a trend of decreasing number of yellow perch seen in our surveys over the past 3 to 5 years.
Wisconsin's Yellow Perch Spawning Assessment
|Year||# of males caught||# of females caught||# of unknowns caught||Total caught||Number tagged|
Young-of-the-year yellow perch abundances have proven to be a relatively effective predictor of future year-class strength. To improve the utility of YOY abundances as a predictor, index stations were added to the Michigan shoreline where none existed before and were compared with the relative efficiencies of beach seines and bottom trawls, the two most commonly used types of gear, so that all agencies can contribute to lakewide abundance data. Until recently, YOY yellow perch have consistently appeared in shore seines in fall when littoral trawling has failed to find them. A review of work in inland lakes suggests that post-larval perch move nearshore during the day which emphasizes the need to trawl different depths nearshore to track movements of fish.
In Wisconsin, we have used a 25-ft bag seine to sample 18 - 22 index stations between Sheboygan (north) and Kenosha (south). Two 100-ft pulls were made directly toward shore or parallel to shore depending on wave conditions since 1989. In 1989, WDNR caught 18.2 yellow perch per unit of effort. This number dropped to 0 in 1994 and was 0.05 in 1997. In 1998, the CPE rose to 3.02 indicating a detectable, yet weak year class of yellow perch. In 1999 the CPE fell to 0.0 with no yellow perch caught during the entire assessment.
The number of index stations were reduced to 14 starting in the summer of 2002 due to decreased water levels, increased Cladophora and suitable access.
Catch Per Unit Effort of Yellow Perch in Wisconsin Beach Seines
In 2012, a total of 4,900 ft of seine hauls were conducted at fourteen sites capturing 24 YOY yellow perch yielding a catch per effort (CPE) of 0.5 YOY yellow perch per 100 foot seine haul. All 24 YOY yellow perch were caught at two locations – Milwaukee and Sheboygan. The average size of the YOY yellow perch in 2011 was 62.4 mm, ranging from 45 to 89 mm. The majority of the yellow perch in this year's survey were larger than 60mm probably due to the warm weather and increased water temperaturs.
In 2013, fourteen stations were sampled from Sheboygan to Kenosha (Sheboygan – 3, Ozaukee – 2, Milwaukee – 5, Racine – 2 and Kenosha – 2). Seining conditions were generally good in the Sheboygan sites in the first round of seining, yet we caught very few fish. Most of the sites south of Sheboygan all the way down to Bender Park beach, Milwaukee Co., were very difficult to seine due to cladophora clogging the net. Further south, Racine and Kenosha sites had good seining conditions with little cladophora and calm waters. We caught two YOY yellow perch (50mm, 62m) in Meyers Park in Racine. In the second week of seining, we caught three YOY yellow perch (48mm, 51mm, and 54mm) at Doctors Park. The density of cladophora varied from station to station during much of the season depending on the prevailing winds making conditions unpredictable. A total of 12 species of fish were captured during the seining survey (Table 1). Young-of-the-year and juvenile alewife dominated the catch followed by Spottail shiner and round goby.
Beach seining and micromesh gill net surveys in 2014 summer showed very low numbers of YOY yellow perch, with a CPE of 0.16 YOY per 100 ft. of beach seine, and 0.22 YOY per 100 for of gill net. The numbers have been similar since 2011. The surface water temperature remained much cooler near 50 F during much of the sampling period. The average size of the YOY yellow perch was much lower than previous years probably due to the extended cold weather coupled with poor plankton production.
Micromesh Gill Nets
In addition to the typical seine hauls, the Wisconsin DNR has used monofilament gillnets to increase the sampling area in nearshore waters (since 2002). The gills nets consisted of 6.25 mm, 8 mm, 10 mm and 12 mm bar length mesh sizes each 10 feet long. Each gill net was therefore 40 feet long. We set out 2 to 3 nets at each major seining site and fished them for one night.
In 2012, we used a 100-foot gang of 12 mm stretch mesh gill net. Two index stations, Shoop Park (Racine Co.) and Doctors Park (Milwaukee Co.), were selected for setting micromesh gill net. At each site we conducted two lifts of 200 ft of net. A total of ten species of fish were captured in these nets with spottail shiners dominating the catch. Only one YOY yellow perch were caught at Doctors Park location. The catch per 100 ft of gillnet was only 0.13 YOY yellow perch (CPE=0.13).
In 2013, gill net sampling was conducted from 8/27/13 to 10/8/13. A total of twelve species of fish were captured in these nets with round goby, alewife and spottail shiners dominating the catch. Only two YOY yellow perch were caught, one at Doctors Park and the other at Shoop Park (Table 3). The catch per 100 ft of gillnet was only 0.11 YOY yellow perch.
Wisconsin's young-of-the-year gill net assessment
|Year||Number of sets||Total effort||Number of Yellow Perch caught||Catch per 100 feet of effort|
Winter Graded-mesh Assessment
The major objectives of the winter graded-mesh assessments are to assess the year-class strength, sex ratio, age, growth and mortality of the yellow perch population in Lake Michigan. We conduct 5 graded-mesh gill net sets offshore near the Green Can Reef in Milwaukee and use these data to estimate the year-class strength of the yellow perch population in Wisconsin waters of Lake Michigan.
Recruitment of younger yellow perch has been very poor since 1990. This is reflected in the graded mesh assessment by poor representation of smaller (younger) yellow perch in the smaller mesh panels of the net. The mesh sizes vary from 1 to 3 inches in 0.25 increments.
An analysis of the distribution of yellow perch in different mesh sizes during the 2001 graded mesh assessment indicated a relatively higher proportion of yellow perch from the 1998 year-class which are represented by age 3 fish in this year's assessment. The 1998 year-class is the strongest since 1989 and contributed to the sport harvest starting in 2000 and continuing to 2008. In addition, the large numbers of egg masses deposited on spawning reefs in 2001 to 2005 were mostly from females from the 1998 year-class. The sex ratio of yellow perch caught in 2001 was the same observed in 2000 at 36% males and 64% females. This ratio is much different than prior years (1990-1995) when the exploitation rate from commercial and sport anglers was much higher.
Although the total effort, index sites and sampling period remained consistent, the 2011 winter graded mesh survey produced fewer perch compared to the other years. Water clarity was generally poor, although the nets were not heavily infested with cladophora. Cold temperatures in early December caused ice formation in the harbor as well as floating ice on the lake. Changing wind directions caused ice to move in and out of the assessment area which may have impacted fish movement and may have contributed to the poor catch of only 283 yellow perch. In general, very few perch were caught in less than 2 inch mesh, and none in 1 and 1.25 inch mesh. Consequently, there were no perch less than 4 years old in the sample. Age was determined using anal spines sampled from 239 yellow perch. Age 6 perch (2005 year-class) dominated the catch representing 43% of the catch followed by age 8 perch (2003 year-class) with 13% and age 9 perch (2002 year-class) with 11%. Age 4 and age 5 perch comprised 10% each. The oldest perch (13 years) from the 1998 year-class made up less than 4% of the catch. Sex ratio was skewed toward female with 76% female and 24% male. The largest yellow perch captured this season was a 379 mm, 11 year-old female and the smallest yellow perch was a 146 mm, 4 year-old male.
In December 2011, the total number of yellow perch caught during the survey was 300 which, though small, was similar to the previous sampling year. Nearly half of all yellow perch caught (48.6%) belonged to the 2005 year-class (7 years old), followed by the 2003 (10%) and 2006 (9%) year-classes. Very few younger yellow perch (age 2 and age 3) were present in the sample. Female perch dominated the catch comprising 76.6%. Among female perch from different year-classes, the 2005 year-class comprised 56% of the females, and among male perch 24% were from 2005 year-class.
In December 2012, the total number of yellow perch caught during the survey was 79 which is the fewest fish caught in this assessment since 2005. Nearly half of all yellow perch caught (39.2%) belonged to the 2005 year-class (8 years old). Very few younger yellow perch (age 2 and age 3) were present in the sample. Female perch dominated the catch comprising 75.0%. Among female perch from different year-classes, the 2005 year-class comprised 46% of the females, and among male perch 15.8% were from 2005 year-class.
In early December 2013, the air and water temperature started dropping very quickly. Hence the captain and the crew tried to move quickly so that the assessment could be completed in a short time. Ideally we would prefer to sample over several weeks if conditions are good. However, due to the severe cold temperatures, and for safety of the vessel and the crew, the assessment was cut short with only two lifts, one on 12/6 and the other on 12/7. We lifted six boxes of gill net on 12/6 and eight boxes of gillnet on 12/7. The total number of yellow perch caught in this year's survey was all time low (10 perch). The catch per 1000 ft. was 0.89 yellow perch (for all meshes combined). Most perch were caught in the larger size meshes (Table 1). There were two males, 294mm and 309mm, and eight females which ranged from 239mm to 362mm. The perch ages ranged from 2 to 13, with the majority of them being age 9 (2005 year-class).
Catch Per Effort and the Percent of Each Sex of Yellow Perch Caught in Graded Mesh Gill Nets
Mean length at age for both female and male yellow perch have decreased or leveled out the past 5 years. Most of these changes can be attributed to the lower population levels and lower amounts of available food.
Alewife Stomach Content Sampling
Alewife predation on yellow perch larvae has been demonstrated in studies on other Great Lakes. No attempt to quantify the influence of alewife predation in Lake Michigan has been undertaken since the 1970s. We sampled adult alewife in an attempt to quantify the proportion of yellow perch larvae lost due to predation by alewife.
Adult alewife were sampled using a graded mesh gill net (1 to 2 1/2 inch stretched mesh). Nets were fished at sunset for 30 minutes. Alewife were measured and their stomachs removed and immediately preserved in 95% ethanol. In addition, a plankton net collected available food sources for the alewives. In 1997, a total of 340 alewife stomach samples were obtained from adult alewife in Lake Michigan during 6 nights of sampling. Not surprisingly, no larval fish were found in any of the alewife stomachs. Copepoda dominated the diet of alewives, comprising by number 95% of the diet. A plankton net collected available food items. Again, copepoda were the dominant prey available. In 1998, one night of fishing was conducted. Due to the low to zero numbers of larval yellow perch in the neuston nets, this was our only set in 1998.
Lakewide Mark and Recapture Project
Data from surveys conducted lakewide by agencies in each state have indicated that production of young-of-the-year (YOY) yellow perch in Lake Michigan has been minimal since 1989. This recruitment failure has resulted in a 90% to 95% reduction in assessment catches in Wisconsin and Indiana waters, and an 86% decline in Illinois. In addition, the average age of yellow perch captured in assessment catches has steadily increased. Without vital information about lakewide movement, spawning site fidelity and the abundance of the spawning population, management strategies implemented to protect existing yellow perch stocks and enhance population recovery may be ineffective or could adversely affect the restoration and sustainability of the yellow perch fishery.
To effectively manage any sport or commercial fishery, estimates of population size and mortality rates are needed. Although a number of yellow perch tagging projects have been conducted in Lake Michigan and its embayments in the past, these efforts have been conducted independently of one another and only one was known to have included an objective to estimate perch abundance. By conducting a collaborative lakewide tagging study which incorporates standardized mark and recapture methods along with enhanced recovery efforts, we will be able to generate estimates of local perch population abundance that will be comparable among jurisdictions.
Results from this study can be read from:
David C. Glover, John M. Dettmers, and David F. Clapp. 2008. Lake-wide mark and recapture investigation of Lake Michigan yellow perch: evaluation of interstate movements, spawning site fidelity, spawning population abundance, and sources of mortality. Can. J. Fish. Aquat. Sci. 65:1919-1930.
Reproductive Status and Health of Ovaries and Testes of Adult Yellow Perch from Lakes Michigan and Mendota
After spawning, the sex organs of mature female fish recover and fish begin to invest energy into developing oocytes (eggs) and milt (sperm) for the next spawning season. Ovaries and testes develop over the summer and winter until these sex organs are again ready for spawning. The sex organs of a fish can be examined to indicate how ready the fish is to spawning, also referred to as their reproductive status. The health of the ovaries and testes are important to the success of spawning and survival of hatchlings and young-of-year (YOY) fish. Other parameters, such as hormone and protein levels in blood, can also provide information on the reproductive status and health of the fish.
The objective of this study was to examine the reproductive health of yellow perch
from Lake Michigan and the exposure of these fish to pollutants. Yellow perch from Lake Michigan and a reference site, Lake Mendota
Wisconsin, were collected in winter 1996, at spawning in 1997 and in fall 1997. Endpoints included stage and histopathology of ovaries and testes, plasma hormones and vitellogenin, liver mixed function oxygenase activity (EROD),
indicators of pollutant exposure, and other parameters. Analysis of variance was conducted to test for the significance of site,
sex, year class (age), and gross gonad stage.
Yellow perch from Lake Michigan had higher concentrations of PCBs in all seasons, higher concentrations of p,p'-DDE in the winter (depending on age) and in the fall. In winter, Lake Michigan fish had lower mercury burdens while spring results showed interactions (site*sex and age*stage) to be significant. Lake Michigan fish exhibited higher EROD activities compared to Lake Mendota fish in the spring.
Reproductive parameters differed between sites in some seasons but other main effects and interactions were also significant. In general, Lake Michigan females had vitellogenin levels comparable to males. A greater percentage of Lake Michigan fish were at earlier stages of gametogenesis at each season. Also, a higher percentage of males from Lake Michigan exhibited testicular neoplasms.