2002 Yellow Perch spawning assessment

Yellow perch spawning and egg deposition survey in Lake Michigan waters near Green Can Reef, Milwaukee - 2002

The Lake Michigan Fisheries unit began its annual yellow perch spawning assessment off of Milwaukee at the Green Can Reef area at the end of May. It has been a very slow warming spring and the water temperature stayed in the mid 40’s in the month of May. We lifted our first gill net set on May 29^th(Lift # 1). Three gangs were set at depths varying from 35 ft. to 65 ft. The bottom temperature was recorded at 48⁰ F. The water temperature was uniform though out most of the water column. The majority of the yellow perch captured in Lift # 1were ripe males, and were captured mainly in the two nets that were set at depths 36-38’ and 42-45’. The deep set net (61-65 ft) produced very few fish. However, this net had more females than males (26 F and 19 M). The majority of the females captured in Lift # 1 were green (54%) followed by 31% spent and 15% ripe. This means that we were right on time when the perch started congregating for spawning on the reef. A total of 1,376 perch were captured (59 F and 1317 M) in three gangs of 450 ft. each with stretch mesh sizes 1", 2", 2 ¼", 2 ½" and 2 ¾". We used a few smaller meshes in Lift # 1 in order to catch any smaller/younger perch that may be in the area. The 1" mesh net caught mainly juvenile alewife. There were no small yellow perch in the smaller mesh panels. All the perch were measured, sexed and released. A sub-sample of 10 perch spines were collected from each mesh size to determine their age. The preliminary data on the ages of these indicated predominantly 4 year-old perch that belonged to 1998 year-class.

Lift # 2 was taken in the same general area and in similar depth ranges on June 5, 2002. The water temperature was 49⁰ F through most of the water column. Since most of the mature females were caught in the larger mesh in Lift #1, we used only 2 ½" and 2 ¾" meshes in the Lift # 2 as it adequately sampled male and female perch. A total of 436 (108 F and 328 M) yellow perch were captured in 3 gangs of 400 ft. each, fished over night at three different depths, 36-38’, 45-45’ and 59-62’. In contrast to Lift #1, the majority of the female perch captured in Lift #2 were spent (68%) followed by 23% green and 9% ripe. It seems that the spawning reached its peak egg deposition at this time in the area.

Overall, a total of 1, 812 (167 F and 1,645 M) yellow perch were captured in the two lifts combined. Of the 167 females, the majority of them were spent (55%) followed by 34% green and 11 % ripe. The bottom temperature has been cooler this year than the previous years during the peak spawning. Maybe the slow warming spring temperature has contributed to the lower peak spawning temperature. The sample on May 29, 2002 consisted of 31% spent females while the sample on June 5, 2002 consisted of 68% spent females. The majority of the spent females were found in the deepest set. We were able to meet the egg collection requirement (12 spawning females) for the Sea Grant research project on the yellow perch early life history to examine causes of poor recruitment in recent years. The WDNR dive team conducted three days of diving from R/V PERCA in the Green Can Reef area to survey and quantify egg deposition.

The following table summarizes the catch per effort (CPE) per 1000 ft. of the gill net for various categories. I have used combined data from mesh sizes 2 ½" and 2 ¾" for this analysis for both the lifts. Only these two mesh sizes were common to both the lifts, and it represented both the sexes adequately.

Sampling date	Sampling depth (ft.)	CPE (all)	CPE (male)	CPE (female)
5/29/2002	Shallow (36-38)	1220	1185	35
	Deep (61-65)	150	55	95
	Intermediate (42-45)	1175	1070	105
6/5/2002	Shallow (36-38)	198	162	35
	Deep (59-62)	228	28	203
	Intermediate (45-45)	665	630	35

2002 yellow perch egg deposition survey: WDNR Dive Team observations

(Based on the input from the Dive Team consisting of Don Beilfuss, Paul Peeters, Tim Kroeff, Brad Eggold and Mike Baumgartner)

In addition to the gill net effort, a diving operation was conducted to assess yellow perch egg deposition in the Green Can Reef area off Milwaukee. In 2002, three days of diving were conducted on 6/5/2002, 6/6/2002 and 6/12/2002. The bottom temperature at this time varied from 46⁰ F to 49⁰ F. Traditionally yellow perch seem to spawn in this area from late May to mid June at depths of 35’ to 55’. The substrate in the reef area ranges from clay to very large size boulders (about the size of a small car), with depressions and peaks, but the vast majority of the substrate is large cobble (golf ball to basketball in size).

Methods:

For the purpose of quantifying the number of yellow perch egg skeins deposited in the area, 1000 ft. transects (lead line with flag buoys) were set on the bottom. Three depth ranges were selected to set transects which included shallow water (25-40 ft.), midwater (40-55 ft.) and deep water (55-63 ft.). Two divers dove on each transect scanning approximately 20 to 24 feet on either side on the transect (area covered, for example, is 24 ft. X 1000 ft.). The area scanned varied each dive because of changing water clarity conditions. Each diver counted the number of egg skeins found in their respective scanning area. Whenever there was a large lump of egg masses due to drifting and aggregation, the divers tried to separate and count each skein. The transect line was then lifted and moved to another location. Although the initial search covered a wide depth range, once the divers identified the most intense spawning range, most of the effort was focused in that area. For example, the divers found very few egg masses in water shallower than 30 ft. and deeper than 55 ft.

Observations:

In 2002 a three-day effort with four dives each day were spent on the survey. In general, the distribution of the egg masses was patchy and uneven. Most egg masses were found in the range of 30 – 50 ft. of water. Zebra mussels were colonized on all the hard substrate in the entire area. There were quite a few dead sculpins on the bottom. The visibility was poorer compared to the previous year, although it was still quite clear. The current during the dives was minimal and it did not seem strong enough to cause egg masses to drift much farther than where they were deposited. There were more egg masses in the area with large boulders. It appeared that the south side of the Green Can Reef had more egg masses than the north side, which may be a function of current direction. Also, the bottom was flatter on the north side as opposed to more depressions on the south side. Therefore, the south side may very well be an intense spawning area.

Some suggestions for the future work:

Keep good records of substrate type
Keep records of transect depths and location (GPS), both starting and ending
Obtain a good visual estimate of viewing area on either side of the transect (maybe use a 24 ft. line placed perpendicular to the transect)
Mark the egg mass to see how much drifting occurs due to current
Keep Secchi disc transparency record
Have a debriefing session at the end of the day of diving to record divers input
If possible get good video documentation
If possible, choose two reference dive locations, one in Kenosha area and the other in Sheboygan area, to compare

The following table summarizes the diving effort and the number of yellow perch egg skeins counted along 300 m transects set at various depths in the Green Can Reef area.

2002 Diving for yellow perch egg deposition
Date	Divers	Depth	Location	Area searched	# of egg masses
6/5/2002	Mike B.	63 feet	1 mile SE of Green Can	20 feet	6
	Tim K.			25 feet	5
6/5/2002	Brad E.	40	East of Green Can	20 feet	24
	Paul P.			24 feet	28
6/5/2002	Mike B.	30	North of Green Can	16 feet	14
	Tim K.			12 feet	7
6/5/2002	Brad E.	35 – Only 900 feet of transect	South of Green Can	20 feet	10
	Paul P.			24 feet	12
6/6/2002	Brad E.	35	West/North of Green Can	24 feet	15
	Paul P.			24 feet	12
6/6/2002	Don B.	55	East of Can	25 feet	26
	Tim K.			25 feet	28
6/6/2002	Brad E.	47	South/East of Green Can	24 feet	33
	Paul P.			24 feet	33
6/6/2002	Tim K.	40	South/East of Green Can	25 feet	44
	Don B.			25 feet	30
6/12/2002	Tim K.	32	North of Green Can	20 feet	34
	Brad E.			20 feet	32
6/12/2002	Paul P.	40	South of Green can	24 feet	40
	Mike B.			24 feet	33
6/12/2002	Tim K.	42	North of Green can on outer reef	24 feet	21
	Brad E.			24 feet	12
6/12/2002	Paul P.	40	South of Green Can	24 feet	36
	Mike B.			24 feet	38

Total area searched = 49,701m²

Total eggs found = 573

Egg masses per 1000 m² = 11.53

In 2001, the dive team surveyed 30,600 m²and documented 7.29 egg masses per 1000 m². In comparison to this, the number appear slightly higher in 2002 survey.