BFHP Bass Articles
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BFHP Bass Articles |
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by
Ralph Manns
In 1989, Douglas Carlson of the New York Department of Environmental
Conservation reported* that largemouth bass with unusual dark blotches were
present in the Hudson River Estuary. The markings were a result of an increased
number of pigment cells in the skin and occurred on various body surfaces. Bass
collected by biologists using electro-shocking equipment were more likely to
have these blotches (23 percent) than those caught by bass anglers (11 percent),
that there was no noticeable change in the frequency of these sightings between
1985 and 1988, and that biologists in other states contacted in 1986 had also
seen similarly marked bass. At that time, most of the sightings were in eastern
coastal areas and a few impoundments in the central and southern states.
In 1994, Kathleen Skinner and other biologists at Russell Sage College* *
reported several investigations into these markings. They noted that in 1985,
New York biologist John Schachte found about 33 percent of Hudson River bass
over 12-inches long had blotches, but that 50 percent of bass over 14 inches had
them. Other studies made in that year found parasites were probably not the
cause and that the bass did not show any other specific cellular pathology.
Previous studies of unusual markings on other fish species related abnormal
blotches to environmental contaminants, viruses, heredity, the inflammatory
responses of the skin’s immune system, or changes in hormones that regulated
skin pigment responses. The team noted that another study ruled out a viral
cause. Unmarked bass failed to become blotched when inoculated with sera from
affected bass, there were no associated skin lesions, and other fish species
were not affected.
Skinner’s team checked to see if the Hudson River pollutant, PCB, was a
cause. They found PCBs were high in Hudson River bass, concentrations were
different in male and female fish, and blotched bass contained more PCBs than
unblotched bass from the same areas. But, they noted the blotches occurred in
samples from areas without high PCB concentrations and in bass with the same
concentrations as the unmarked control bass. They concluded that PCBs "may not
be the cause of LMB black blotch syndrome."
Other, as yet unstudied, chemicals might be the cause. Increased pigmentation
in animal tissue is a natural defense mechanism against heavy metals, aromatic
hydrocarbons, acids, and other environmental contaminants.
Clearly, more study is needed to explain what is going on. Before Carson’s
report was published, I’d seen a few bass with the dark blotching. Since then,
the number of blotched fish has seemed to steadily increase and sightings are
now common on most Texas waters I fish. I suspect there is a tie-in with the
increase in catch-and-release bass fishing since the early 1980s. Carson’s
observation that electrofishing produced more blotched bass than angling could
be a result of learned, short-term, lure-avoidance responses by recently
handled, and thus blotched, bass. The increased percentage of blotched bass in
larger sizes could also be associated with catch-and-release, particularly the
forced releases in waters with slot limits.
I moved near a lightly-fished pond 10 years ago. At first, the fish I caught
had no blotches. Since then, I’ve caught and released about 700 bass a year in
this pond, many more than once. I’ve noticed that about a third now show
blotching, often around the mouth. I’ve identified re-caught individuals by
their marks. I’ve also caught fish with distinct and identifiable blotches at
Lake Fork.
Lakes with slot and special limits like Fork that force the release of many
large bass seem to hold more blotched fish. Although contaminants may be
associated with the blotches, I suspect that handling during catch and release
and the hooking and capture process itself are at least related factors. Marks
near mouths are easily attributed to lipping techniques. Those on other parts of
the body are less frequent on my pond bass than on bass at Fork, but seem to be
located at places where bass may have touched a boat, the ground, or have banged
into cover while hooked. The lower tail and anal fins seem to be particularly
vulnerable. One slot-fish at Lake Fork appeared to have the imprint of a hand
across its back.
The marks seem to eventually disappear, suggesting they may be part of a skin
or slime repairing process. I was fish the pond less in December and early
January. The fish I catch in late January seldom have blotches, but the number
of blotches increases over the remainder of a year. I’ve also noted that they
seem to disappear faster from smaller adult bass. The largest fish seem to hold
them for at least two years.
We need a scientific investigation into the possibility that these blotches
are associated with capture and release. They don’t seem to harm bass in any
way, and might even prove useful in the identification of individual fish or
analysis of capture and release rates if anglers are a cause.
* Carlson, D. M. 1989. Unusual pigmentation on largemouth bass. Presentation
to the 45th Annual NE Fish and Wildl. Conf., Ellenville, NY, (Mimeo)
8p.
** Skinner, K. M., L. Pagels, and K. A. Peregrim. 1994. Black blotch
largemouth bass in the Hudson River, New York. Presentation given at the New
York natural History Conference III, April 13-16, 1994. ( Mimeo) 29 p.
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the author’s permission
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