Michigan Yellow Perch:
traumatic first summer
The following contains elements of a working hypothesis. It has not had
formal peer review-others may disagree with elements.
yellow perch have had poor recruitment since the late 1980’s.
The year classes of 1998 and 2002 were marginal, at best, fair. If the
recruitment trends continue in this manner, the yellow perch populations
in Lake Michigan could become critically low. This has biological implications
within the entire lake food web. Ascertaining the cause for this is
the objective of the Yellow Perch Task Group and the purpose of this
research. We propose that a possible explanation for this population
decline involves zebra mussel-induced habitat change and transport of
pelagic phase yellow perch away from preferred habitat to poor habitat
by strong meso-oceanic currents.
Since the introduction of
zebra mussels into Lake Michigan in the early 1990s, the habitats for
yellow perch have changed dramatically. Zebra mussels have become well
established in rocky areas, predominantly on the west side of the lake,
and have enhanced food resources in these areas by increasing productivity
in the benthos. In areas with soft bottoms, predominantly on the east
side of Lake Michigan, zebra mussels have depleted fish food resources,
particularly the benthic amphipod Diporeia, by filter feeding phytoplankton
upon which the invertebrates had fed. This change in food web structure
may be a major impetus for the decline in the young yellow perch population.
For more information on the effects on fish food resources, please reference
studies by Brandt, Mason et al, and Vanderploeg on the NOAA-GLERL web
The alteration in habitat
value to yellow perch indicates that rocky habitats are improved while
soft habitats are worsened. This does not in itself explain all the
interactions leading to the decline of yellow perch. However, because
Lake Michigan more closely resembles an inland sea, rather than a lake,
the winds generate strong currents and waves. Yellow perch evolved in
much smaller bodies of water and that evolutionary process produced
the current life history in which the tiniest yellow perch, newly hatched,
spend about 40 days or more adrift in the water column. High wind or
current activity, such as is common on Lake Michigan, disperse these
larval fish great distances offshore to potentially unproductive habitats.
Evidence documenting the extent of transport of young yellow perch has
been accumulating, and the most recent material is presented through
this research. Although this is a relatively unknown situation in freshwater,
it is a common problem faced by many marine fishes, including those
from coral reefs. The pelagic phase larval fish are carried away from
their optimal, or preferred, habitats by currents or warm-core rings
(Hare et al 2002, Limnology and Oceanography 47(6): 1774-1789). Some
tropical and subtropical juvenile species end up marooned in the Gulf
In 2002 there was good documentation of transport of pelagic perch.
These collections have been opportunistic, piggybacking with other
cruises. This information is summarized in the adjacent graph (Fig
1). The larval perch were collected by towing for 15 minutes with
a large net (2 m wide and 1 m deep) at the surface of the lake at
night on the dates indicated. The fish in the first graph (June 18,
2002) have been adrift for approximately 3 days and still retain the
majority of their yolk sacs. About a week later (June 24, 2002) the
young perch have drifted and are most abundant about 16 km (10 miles)
offshore. This is about 1/8 of the way to the Michigan shore. These
larvae were inferred to have originated in a rocky area due to the
large amount of Cladophora algae, which is shed from rocks,
associated with them. They may have been farther
off shore, but no more sampling was possible due
to cruise restrictions. A few days later (June 27-29,
2002) the young fish were found in good numbers as far as 41
km (about 25 miles) offshore, or about 1/3 of the way to the Michigan
shore. Note that the larger, and probably older, individuals are farther
offshore, having been adrift and feeding longer. These data indicate
that during early summer when strong winds and currents are not uncommon,
it is feasible that pelagic phase yellow perch can disperse widely
from their hatchery, perhaps even across the lake.
Figure 1: Larval perch transport following hatching. Numbers
along the x-axis indicate distance east or west from the Milwaukee
River mouth (0km) longitude. The y-axis is total length (mm)
for each individual. In each box plot, the box is quartiles,
the lines are 75%, and the dots are outliers. Notice the increase
in distance with time for an 11-day period.
What are, if any, the limitations to drift of these pelagic phase
yellow perch? Can the young perch navigate back to viable habitats
from offshore? These questions remain unanswered and require further
Evidence of the importance of rocky habitat for yellow perch has also
been accumulating. Adults prefer rocky habitat (Wells 1977 J. Fish.
Res. Board Can. 34: 1821-1829) perhaps due to greater food sources
as their stomachs are more filled in these habitats (Wells 1980 Technical
paper). Yellow perch eggs are more abundant in rocky areas (Robillard
and Marsden 2001). Whether this is because the adults are already
primarily on rocky habitat or they actively seek rocks for spawning
is not known. On the west side of Lake Michigan, from the Indiana-Illinois
border north to the Wisconsin border and also from Racine, WI, to
north of Milwaukee, the bottom is rocky, consisting of bedrock fossil
coral reefs and rubble transported by the glaciers long ago. This
provides good feeding and spawning habitat.
In 2002 we documented the first evidence that post-pelagic perch—those
seeking suitable bottom habitat as feeding grounds and shelter—are
also preferentially found on rocks. The preferred habitat, as for
adults, is rocky habitat. We documented a preference for rocky habitat
in newly demersal YOY yellow perch by setting micromesh gill nets
on four different sites with rocky versus sandy habitats (map 1).
The relative catch rate for numbers of juvenile yellow perch captured
in gill nets at rocky sites was approximately four times greater than
at sandy sites in Wisconsin during mid-August through mid-September
Map 1: Map of perch sampling in Lake Michigan.
Cross-hatched areas are rocky habitat, suitable for spawning
and preferred area for yellow perch feeding. Red dots indicate
locations for larval perch collection (Figs 1-3). Blue dots
indicate shore sampling for young perch in rocky and sandy
habitats (Fig 4).
Yellow perch are schooling fish, which causes great variation
in catch from day to day. Despite this, the trend is still apparent.
Diet analysis was conducted on the young fish captured from the rock
and sand habitats. The diet analysis is ongoing, but the preliminary
analysis shows that the young perch on the rocks primarily consumed
amphipods (33%) and isopods (43%), prey associated with rocks. These
rocks are host to abundant yellow perch food, including small crustaceans
and aquatic insects, crayfish, and sculpins. Those fish found on
sand most likely were traveling between rocky areas. This is also
evidenced by the presence of amphipods in their diets, which are associated
only with rocks. Unfortunately, the rocky areas remain relatively
unstudied. Many questions still remain unanswered regarding rocky
habitats and the extent of pelagic phase fish transport by currents
and waves. More study opportunities are needed; as information is
accumulated, it will be included at this site.
Figure 4: Percentage distribution of young
yellow perch on rocky versus sandy habitats. Rock, shown as
the darker bars, is preferred over 4 times than sand, the
lighter bars. The actual numbers found at each location are
above each corresponding bar.