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.
Since 1993, 1-3 day old perch larvae have been captured in large numbers at one site in Illinois and one site in Michigan. Sites were sampled based on historic catches in these areas and produced large numbers even when very few YOY's were captured at these sites later in the season. Since 1994, the number of yellow perch larvae at the Illinois site has been severely reduced. Data from one site however cannot be used to predict what has happened lakewide. The loss of larvae may have been due to something that is very specific to that one site.
Therefore, the WDNR, along with other agencies and scientists, have used a variety of assessments to analyze the status of the current yellow perch population. These assessments include 1) egg deposition; 2) spawning; 3) post-larval perch; 4) young-of-the-year (YOY); and 5) 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. This changed in 2005, when we observed egg masses from the 1998 year-class females as well as females from the 2001 and 2002 year-classes. We searched for 6 hours and found 493 egg masses or 11.74 per 1000 m2. In 2007, we again had an early start to our survey. We searched for about 5.5 hours over 8 dives and found 378 egg masses or 10.81 per 1000 m2.
Yellow Perch Dive Summary
| Year | Diver Bottom Time (hrs) | Egg masses found (#) | Area covered (m2) | # egg masses per 1000 m2 |
|---|---|---|---|---|
| 1997 | 31:40 | 9 | 18,000 | 0.50 |
| 1998 | 12:48 | 0 | 9,200 | 0.00 |
| 1999 | - | - | - | - |
| 2000 | 1:10 | 8 | 4,225 | 1.89 |
| 2001 | 4.5 | 223 | 30,600 | 7.29 |
| 2002 | 8.0 | 573 | 49,701 | 11.53 |
| 2003 | 6.5 | 246 | 24,526 | 10.04 |
| 2004 | 4.75 | 1 | 21,760 | 0.046 |
| 2005 | 6.0 | 493 | 41,988 | 11.74 |
| 2006 | 5.3 | 339 | 30,065 | 11.27 |
| 2007 | 5.3 | 378 | 34,960 | 10.81 |
| 2008 | 6.3 | 15 | 28,800 | 0.52 |
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 from 2007 show that we captured a total of 2,132 yellow perch comprised of 2,076 males and 56 females.
Wisconsin's Yellow Perch Spawning Assessment
| Year | # of males caught | # of females caught | # of unknowns caught | Total caught | Number tagged |
|---|---|---|---|---|---|
| 1997 | 14,417 | 46 | 11 | 14,474 | 5,163 |
| 1998 | 4,282 | 231 | 0 | 4,514 | 1,328 |
| 1999 | 5,635 | 232 | 0 | 5,867 | 3,142 |
| 2000 | 722 | 133 | 0 | 855 | 0 |
| 2001 | 933 | 438 | 0 | 1,431 | 0 |
| 2002 | 1,645 | 167 | 0 | 1,812 | 0 |
| 2003 | 1,583 | 26 | 0 | 1,609 | 0 |
| 2004 | 997 | 144 | 0 | 1,141 | 0 |
| 2005 | 1,207 | 64 | 0 | 1,271 | 0 |
| 2006 | 1,580 | 161 | 0 | 1,741 | 0 |
| 2007 | 2,076 | 56 | 0 | 2,132 | 0 |
| 2008 | 204 | 122 | 0 | 326 | 0 |
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 a minimum of 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.
Catch Per Unit Effort of Yellow Perch in Wisconsin Beach Seines
| 1989 | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 18.2 | 10.9 | - | 1.0 | 0.8 | 0.0 | 0.7 | 0.03 | 0.05 | 3.02 | 0.0 | 0.02 |
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. It appears that the 2005 year-class is fairly robust and pending over-winter mortality may be a pretty good year-class. However, the full strength of this year-class will not be known until 2008. In 2006, the numbers dropped back down to levels observed throughout most of the 00's at 0.02 yellow perch per seine haul.
In 2007, a total of eighteen species of fish were captured during the survey. The individuals were comprised of both young and adult fish. YOY alewife dominated the catch (117 alewife per 100’ of seine haul), and occurred throughout the survey area. YOY yellow perch also was found in all five harbor sites with an overall CPE (catch per effort) of 34 YOY yellow perch per 100’ of seine haul. This is the second biggest CPE value since the WDNR began the seining survey in 1989. In 2005, we captured 1,934 YOY yellow perch with a CPE of 39 perch per 100’ of seine haul. However, in 2005 survey, most the YOY yellow perch were captured in a single location as opposed to the wide distribution of YOY yellow perch observed in 2007. In 2007, of the fourteen sites sampled, we captured YOY yellow perch in nine different sites.
In addition to the typical seine hauls, the Wisconsin DNR for the sixth time set out monofilament gillnets to increase the sampling area in nearshore waters. 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 2002, we set 18 gill nets in 11 locations for a total of 720 feet of effort. and captured 52 yellow perch. The catch per 100 feet of effort was 7.2 young-of-the-year yellow perch. In 2003, our effort dropped a little to10 gill net sets in 2 locations for a total of 400 feet of effort and captured 51 yellow perch or 12.75 per 100 feet of effort. In 2004 our effort remained at 400 feet of effort with 4 sets at 2 locations capturing 19 YOY perch for a CPE of 4.75. In 2005 we fished exclusively 6 and 10mm bar length gill nets to capture YOY yellow perch. Our catch increased significantly to 780 yellow perch or 195 per 100 feet of effort. This trend is the same observed in our seining effort and indicates a fairly robust 2005 year-class. In 2006, the number of yellow perch in both our seining and gill net surveys decreased. Only 243 yellow perch were caught in our gill net assessment or 61 per 100 feet of effort. In 2007, the number dropped in this assessment to 11 fish per 100 feet of effort.
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 |
|---|---|---|---|---|
| 2002 | 18 | 720 | 52 | 7.2 |
| 2003 | 10 | 400 | 51 | 12.75 |
| 2004 | 2 | 400 | 19 | 4.75 |
| 2005 | 2 | 400 | 780 | 195 |
| 2006 | 2 | 400 | 243 | 61 |
| 2007 | 2 | 400 | 45 | 11 |
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 (Table 3). 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 2006. In addition, the large numbers of egg masses deposited on spawning reefs in 2001 to 2005 were mostly from these age 3 females. 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 2005 with 226, 7 year-old yellow perch in caught in the assessment nets. However, for the first time, age 3 yellow perch from the 2002 year-class were detected (61) although at much lower levels than the 1998 age 3 fish during the 2001 assessment (243).
During the 2006 graded mesh survey, we again detected that the 1998 year-class dominated the catch. However, the 2002 year-class represented as age 4 were also detected in good numbers, even higher then when the 1998 year-class was age 4. In addition, the 2003 year-class as age 3 fish were also found during this assessment. This is really the first year since 1999 that we have seen multiple year-classes in the winter graded mesh assessment.
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 survey we will find out the strength of the 2005 year-class.
Catch Per Effort and the Percent of Each Sex of Yellow Perch Caught in Graded Mesh Gill Nets
| Age | 1990 | 1991 | 1992 | 1993 | 1994 | 1995 | 1996 | 1997 | 1998 | 1999 | 2000 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2 | 724 | 159 | 49 | 60 | 0 | 0 | 0 | 0 | 0 | 42 | 323 |
| 3 | 1037 | 865 | 276 | 98 | 25 | 0 | 0 | 4 | 2 | 57 | 65 |
| 4 | 938 | 323 | 715 | 402 | 58 | 28 | 0 | 14 | 6 | 215 | 9 |
| 5 | 394 | 327 | 281 | 757 | 218 | 65 | 0 | 11 | 29 | 93 | 27 |
| 6 | 381 | 83 | 181 | 165 | 141 | 120 | 19 | 18 | 35 | 57 | 2 |
| 7 | 90 | 82 | 126 | 49 | 48 | 76 | 51 | 77 | 20 | 45 | 0 |
| 8 | 0 | 32 | 73 | 16 | 11 | 65 | 71 | 251 | 43 | 63 | 8 |
| 9 | 0 | 0 | 14 | 0 | 0 | 24 | 31 | 109 | 110 | 44 | 9 |
| 10 | 0 | 0 | 0 | 0 | 0 | 2 | 12 | 15 | 60 | 33 | 11 |
| 11 | 0 | 0 | 0 | 0 | 0 | 0 | 3 | 0 | 15 | 9 | 1 |
| 12 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 4 | 7 | 0 |
| % Males | 61 | 72 | 82 | 86 | 89 | 90 | 95 | 89 | 80 | 58 | 36 |
| % Females | 39 | 28 | 18 | 14 | 11 | 10 | 5.0 | 11 | 20 | 42 | 64 |
| Age | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 |
|---|---|---|---|---|---|---|---|---|
| 1 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2 | 1 | 0 | 2 | 3 | 0 | 3 | 40 | 3 |
| 3 | 243 | 4 | 0 | 1 | 61 | 29 | 24 | 159 |
| 4 | 20 | 118 | 0 | 0 | 12 | 249 | 60 | 7 |
| 5 | 2 | 4 | 33 | 1 | 0 | 37 | 204 | 46 |
| 6 | 2 | 3 | 0 | 27 | 11 | 0 | 31 | 120 |
| 7 | 1 | 1 | 0 | 1 | 226 | 23 | 4 | 16 |
| 8 | 2 | 0 | 0 | 0 | 6 | 417 | 20 | 7 |
| 9 | 1 | 0 | 0 | 0 | 0 | 7 | 113 | 7 |
| 10 | 1 | 0 | 0 | 0 | 0 | 0 | 0 | 69 |
| 11 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 1 |
| 12 | 0 | 1 | 1 | 1 | 2 | 0 | 0 | 0 |
| % Males | 36 | 38 | 52 | 60 | 64 | 53 | 48 | 51 |
| % Females | 64 | 62 | 48 | 40 | 36 | 47 | 52 | 49 |
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.
These data are currently being analyzed by the Illinois Natural History Survey in conjuncture with the Great Lakes Fishery Commission.
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 purpose of this study was to obtain information on the spawning or reproductive status of yellow perch from Lake Michigan as well as information on the health of the fish and their sex organs (ovaries and testes). Samples of ovaries and testes, blood and liver were taken from yellow perch from Lake Michigan and a reference site, Lake Mendota, Wisconsin, during winter 1996, spawning season in spring 1997 and fall 1997. These samples were then examined to determine the reproductive status and health of the fish.
Statistical analyses are being conducted to look at how the health data varies with sex, age, and reproductive status of the fish in addition to differences between sites. Preliminary analysis of the data indicates that there are some differences in the health of the fish between sites. The ovaries and testes of Lake Michigan fish were generally at earlier stages of development each time they were sampled. Also, abnormalities and differences in the micro-structure (appearance of a cross-section under microscope) were also detected and are being tallied.
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