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.  

In 2005, we learned that our 2004 effort was probably too late as larger, older females from the 1998 year-class were depositing eggs much earlier than we suspected, probably in late May. This resulted in very few egg masses detected in 2004 since the majority of the deposition was by 1998 year-class females. 

In 2008, we searched for 6.3 hours and found only 15 egg masses or 0.52 per 1000 m².  A dramatic drop like this occurred in 2004 but subsequent surveys found more egg masses.  Deposition surveys conducted in 2009 and 2010 will be critical in determining the spawning stock potential of the yellow perch population.

In 2009, we searched for 6.0 hrs and found 222 egg masses which was much higher than observed in 2008.  Poor weather conditions and spring floods in 2008 must have contributed to lower egg masses found during our survey period.  Results from 2009 are lower than other years, probably indicative of the aging of the 1998 year-class of yellow perch.  However, our spring spawning survey detected multiple year-classes of yellow perch which definitely contributed to the number of egg masses found in this year's survey

Yellow Perch Dive Summary

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). Yellow perch were captured, measured to the nearest millimeter and tagged with an individually numbered floy tag. In 1997, a total of 14,474 yellow perch were captured of which only 46 or 0.32% were females. The high percentage of males could be due to the gear selectivity of the fyke nets. WDNR tagged 5,163 yellow perch, considerably more than the 3,000 tagging goal. In 1998, a total of 4,512 yellow perch were captured of which only 221 or 4.9% were females. WDNR tagged only 1,328 yellow perch much lower than our 3,000 fish target. In 1999, a total of 5,867 yellow perch were captured of which only 232 or 4.0% were females. WDNR tagged 3,142 yellow perch just over our 3,000 fish goal. In 2000, a total of 855 yellow perch were captured with only 15% being females. No yellow perch were tagged in 2000 because that phase of the study was concluded.

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.

In 2009, a total of 629 yellow perch were caught in four lifts of 3,500 ft gillnet effort – 465 males and 164 (26%) females. On May 19th, the majority of perch were still green with no spent individuals. The final lift was taken on June 10th when we observed 91% of the males being spent and the remaining were ripe, and 55% of females were spent. Although there were still 32% green females at this time, the spawning activity had peaked. We collected a subsample of 100 age samples (anal spines) during the survey. Age samples of ten males and 10 females from each mesh totaling 50 males and 50 females were analyzed. Age 7 and age 4 yellow perch belonging to the 2002 and 2005 year-classes comprised the majority of perch on the spawning ground followed by age 11 (1998 year-class) and age 6 (2003 year-class).

Wisconsin's Yellow Perch Spawning Assessment

Young-of-the-Year Sampling

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 2005, we saw a dramatic increase in the number of yellow perch collected during this survey. We captured 1,934 or 39 per haul yellow perch.  Similar trends of increase YOY production were detected by other agencies around Lake Michigan.  In 2006, the numbers dropped back down to levels observed throughout most of the 00's at 0.02 yellow perch per seine haul but climbed again in 2007 to 34 perch per seine haul.

In 2008, the number of yellow perch captured in our beach seining survey decreased to only 3.1 per haul.  This amount is more typical of the numbers detected throughout this survey and reflect the difficulties in seining the nearshore areas of Lake Michigan.

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 2008, we fished exclusively 6 and 10mm bar length gill nets and captured 23 perch at two locations over the course of 4 sets. This translated into only 2.6 yellow perch per 100 feet of effort, which is the lowest rate detected during this survey. 

Wisconsin's young-of-the-year gill net assessment

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.

The 1998 year-class of fish continued to dominate the catch in 2006 with 417, 8 year-old yellow perch in caught in the assessment nets.  However, age 4 yellow perch from the 2002 year-class were detected (249) at fairly high levels. 

In the 2007 graded mesh survey, the 1998 year-class was for the first time since 2000 not the dominant year-class. Age 5 yellow perch from the 2002 year-class comprised the majority of the fish caught follow by the 1998 and 2003 year-classes.  The 1998 yellow perch are now 9 years old and are beginning to be represented less in this survey. In addition, the survey indicates that we have at least a 1998, 2002 and 2003 year-class present in the population. 

In the 2008 graded mesh survey, the 2002 and 2005 year-classes dominate the survey at 120 and 159 fish respectively. In addition to these two year-classes we also continued to detect year-classes from 2003 and 1998. The 1998 year-class in this survey are 10 years old and are less dominant than in past years. Because the 2005 year-class of yellow perch appears to be growing slower than the 1998 year-class, we expect this year-class to be fully recruited to the survey in 2009.

In 2009, our graded mesh assessment captured multiple year-classes of yellow perch. The 2005 year-class of yellow perch (age 4) emerged as the dominant group comprising 41% followed by the 2002 year-class (22%). The 1998 year-class is no more the dominant fish in the survey (11%). In addition to the above three year-classes, 2006 and 2003 year-classes also comprised a substantial portion of the survey with 10% and 9%, respectively. In the 2009 survey, the female proportion was greater (60%) compared to previous years. We captured 493 male and 745 female yellow perch in five lifts. The data from the 2008 spawning assessment also indicated decreased male perch in the population. 

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 increased over the last 5 years.  Most of these increases can be attributed to the lower population levels allowing faster growth rates due to decreases in competition for food and habitat.

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.