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<br />180
<br />
<br />sta!e are unlikely because first or last capture of
<br />only 4 of the 44 (9%) trout of reproductive age
<br />(age 2 or older) occurred during the spawning sea-
<br />SOD. Seasona] changes in growth rate are known
<br />for salmonids (e.g., Egglishawand Shackley] 977)
<br />but these changes are unlikely to have contributed
<br />to OUT electro shocking results. Rough]y equal
<br />numbers of trout were studied over time periods
<br />spanning predominantly spring and summer
<br />months of expected fast growth (23 fish) as were
<br />studied over predominantly a~tumn and winter
<br />months of expected slow growth (22 fish). The
<br />time intervals for the other ] 8 trout contained
<br />equal numbers of months from each of these two
<br />seasonal periods, including 8 trout that were stud-
<br />ied for 12 months. The previously mentioned pos-
<br />sibilities of stress from handling, marking, or MS-
<br />222 exist, but we considered them to have been
<br />lessimportant than e]ectroshocking for the reasons
<br />indicated above.
<br />Any of several known consequences of eJectro-
<br />shocking could contribute to the results we report.
<br />One minor possibility is the slight decrease in total
<br />benthos and hence in food supply as a result of a
<br />temporary increase in drift following e]ectroshock-
<br />ing (Elliott and Bagenal 1972). A second conse-
<br />quence of e]ectroshocking is an increase in the
<br />level of creatine phosphokinase, an enzyme as-
<br />sociated with tissue pathology (Bouck et aI. 1978).
<br />If tissues are damaged by shocking, so that sub-
<br />stantial portions of the energy budget of the shocked
<br />fish must go to tissue repair or replacement of
<br />depleted stored energy rather than growth for any
<br />.leugth of time, growth rate would, of course, be
<br />reduced. We did not, however, observe any tissue
<br />damage. A third possibility relates to the reduction
<br />in stamina for at least ] d after shocking, as re-
<br />ported by Horak and Klein (1967). Reduced stam-
<br />inacouId make an e]ectroshocked trout unable to
<br />defend a desirable feeding station from an un-
<br />shocked trout of similar size. Given the impor-
<br />tance of prior occupancy on the success of de-
<br />fending a feeding tenitory(Jenkins ] 969), the effect
<br />of even a temporary loss of stamina might have
<br />prolonged effects on feeding position and hence
<br />on growth. This last possibility also could explain
<br />the observed size-age dependency of the reduced
<br />growth rate effect: large (age-3+) fish may be able
<br />to maintain adequate feeding positions, even after
<br />repeated e]ectroshockings, because of their size and
<br />low abundance whereas smaller, more numerous
<br />trout may not. The time effect (Tab]e 2) might best
<br />be explained by the second possibility (i.e., tissue
<br />damap:), if the time required for complete recov-
<br />
<br />GATZ ET AL.
<br />
<br />ery from internal damage were as long as 2.5-3
<br />months.
<br />
<br />Management Implications
<br />
<br />The results reported here are of practical sig-
<br />nificance in fisheries management. Fisheries bi-
<br />o]ogists who estimate growth or production in
<br />streams from a series of collections obtained by
<br />e]ectroshocking should be aware that their results
<br />could be negatively biased if more than a small
<br />fraction (e.g., > 20%) of the total population is
<br />shocked repeatedly. The bias will be especially great
<br />for fish in the younger age classes (ages ] and 2)
<br />and if the interval between shocking is less than 3
<br />months. The likelihood ofa bias will be much less
<br />if only a small proportion of the total population
<br />is repeatedly captured due either to migrations in
<br />and out of the study area or to low overall sampling
<br />efficiency. The bias would be absent in studies that
<br />use electroshocking only to,,pbtain a sample from
<br />which growth orproductioh Is back-calculated (e.g.,
<br />Penczak et al. ] 981; Kraiem ] 982). The chance of
<br />repeated e]ectroshocking affecting the behavior of
<br />fish is sufficiently great that we recommend the
<br />use of other methods of capture for some sampling
<br />occasions in order to minimize the possible neg-
<br />ative effects of electroshocking itself. Finally, it
<br />should be recalled that we used pulsed DC e]ec-
<br />tloshocking, the type that is reported to have the
<br />greatest neurophysiological effect with the mini-
<br />mum possible side effects (Vibert 1967). Studies
<br />employing any other kind of electroshocking
<br />equipment might well show even greater long-term
<br />deleterious effects.
<br />
<br />Acknowledgments
<br />
<br />We thank all those who assisted with the field-
<br />work-D. K. Cox, R. M. Cushman, G. K. Edd]e-
<br />mon, J. L. Elmore, J. W. E]wood, J. V. Flyrin;A.
<br />Go]dsmith, C. T. Hunsaker, M. Kenna, W. C.
<br />Kyker, J. M. Robinson, M. J. Sale, V. R. To]bert,
<br />W. Van Winkle, D. S. Vaughan, and L. L. Wright.
<br />D. K. Cox and R. M. Cushman read the trout
<br />scales. The North Carolina Wildlife Resources
<br />Commission and the U.S. National Park Service
<br />granted us permission to collect fish at the study
<br />sites. We also thank S. M. Adams, E. L. Avery,
<br />and J. E. Breck for challenging comments on an
<br />earlier version of the manuscript.
<br />The research was sponsored by the Division of
<br />Geothermal and Hydropower Technologies, U.S.
<br />Department of Energy, under contract DE-AC05-
<br />
<br />REPEATED ELECTROSHOCKING EFFECT ON GROWTH
<br />
<br />181
<br />
<br />840R21400 with Martin Marietta Energy Sys-
<br />tems, Incorporated.
<br />
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