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... \. ~ /IIonII A_aM Journal of Fisherin Manage"",", 6:176-182, 1986 Cl Capyrislu by IIle American FISheries Society 1986 ;\ G, Effects of Repeated EJectroshocking on Instantaneous Growth of Trout1 A. JOHN GATZ, JR.,2 JAMES M. LoAR, AND GLENN F. CADA Environmental Sciences Division, Oak Ridge National Laboratory Oak Ridge. Tennessee 37831, USA Abstract. -Instantaneous growth rates were calculated for age-I, -2, and -3+w:iJd rainbow trout (Salmo gairdnen) and br~wn trout (Salmo trutta) at each of eight stream sites on five streams in western North Carolina and eastern Tennessee. Growth rates of individual trout that had been electroshocked with pulsed DC two to seven times within a 12-month period were lower than the aveqge growth rates for trout of the same age and species at their respective sites. This decrease in growth rate occurred significantly more often among age-l and -2 trout than among those 3 y= and older, and more often among trout that had been electroshocked within the last 2.5 months than among trout that had 3 or more months to recover from electroshocking. These results indicated that fisheries management studies should be designed to avoid repeated electro- shocking, especially at :intervals ofIess than 3 months. Growth studies in which more than a small fraction (e.g., > 20%) of the total population is repeatedly electroshocked at short (< 3-month) intervals are likely to underestimate growth rates. / t~~t Electroshocking is one of the most commonly Methods used methods for collecting stream fishes. Several Eight study sections from five soft-water steams types of fisheries management studies, such as es- in eastern Tennessee and western North Carolina timating annual cycles of growth or production, were sampled between June 1982 and July 1983. multiple 'capture-recapture censusing, and study- The sections were located in third- or fourth-order ing migration, require multiple captures of fish. portions of the streams and had gradients that Nonlethal side effects of repeated exposure to elec- ranged from 2.0 to 26.4 m/km and had mean an- troshockinghave not been studied. Thus, it is not nual flows that ranged from 0.4 to 1.6 m'/s. The known whether or' not 'the use of electroshocking sections were from 107 to 224 m long, and each in multiple-capture studies of the types just men- was divided into two contiguous subsections of tioned causes biases in the results. Single e1ectro- 34-183 m. A complete description of the sites is shocking events cause a variety of short-term given in Lear (1985). physiological responses (Horak and Klein 1967; Trout were e]ectroshocked with two Smith-Root Schreck et al1976; Bouck et al. 1978; Burns and Type XV backpack electroshockers set to deliver Lantz 1978). Repetition of these physiological re- pulsed (120 Hz) DC at 600 V or more. High volt- sponses might alter the behayior or growth offish ages were required to stun the fish even though we even though previous investigators (Ha]sband added two 23-kg salt blocks to the streams to raise 1967; Maxfiddetal. 1971; Ellis 1974; Kynard and conductivities from the typical ambient condi- Lonsdale 1915) reported that a single exposure to tions of 5-10 I'S/cm to ~201'S/cm (monitored electroshocking did not affect subsequent growth. with a Hydrolab Digital 4041 ). Stunned trout were Our research was conducted to determine the ef- placed into 0.64-cm-mesh holding cages prior to iect of repeated electroshocking on the subsequent processing. We measured total lengths and weights growth of brown trout (Sa/mo trutta) and rain bow (Ohaus triple-beam balance), took scale samples, trout (Sa/mo gairdnen) in selected streams in the a!ld marked trout with specific fin clips for each ~uthem Appalachian Mountains. date and subsection. In ] 983 only, we anesthetized ~ the trout with tricaine (MS-222) before processing ~ c::S- and released them after they had fully recovered. <r' \) I Publicati0ll276 I, Environmental Sciences Division, The intervals between e]ectroshockings were set - Oak Ridge NaJionaJ LabOratory. by the need to make four or five Petersen mark- .\'"\ 2 Present address: Department ofZooJogy, Ohio Wes- recapture population size estimates at each study j r U"'_. """-~. OJrio """. USA. 17:iW. H~re. d,,"~hoclci"ll ore'IT'" 0" p;rin of ... ?;, 071/?f REPEATED ELECTROSHOCKlNG EFFECT ON GROWTH days 1-3 dapartwith timespansofl.5 to 7 months between pairs of collections. Recaptured individ- ual fish, age I or older, could be identified by their unique combinations of fin clips and overall size. Ages of all rainbow trout and brown trout, age 2 and younger, were determined by scale analysis or length-frequency information. Because scales could not be re]iably read for all brown trout age 3 and older, we assigned ages to these fish based on the age-length relationships given by Bachman (1982) for brown trout in a Pennsylvania stream. We chose Bachman's data because the relationship he gave c1ose]y matches our growth information for young brown trout (ages 0-2) and predicts the same ages for larger brown trout that we deter- mined for fish with scales that could be read. A]so, because Bachman (1982) did not use electroshock- ing, his data represented good control values. The short-term effect of a single electroshocking was assessed by comparing the weight of a trout on first capture with its weight on recapture 1-3 d later. No measurable growth was expected over so short a time interval. Hence, any pattern other than equal numbers of weight losses and weight gains was considered to represent a short-term ef- fect of e]ectroshocking. A chi-square test of the null hypothesis of random weight fluctuations was used to de1.ermine statistical significance. The long-term effect of repeated e]ectroshocking was assessed by means of instantaneous growth rates (Ricker ]975). Specifically, the observed in- stantaneous growth rate (G,) of each repeatedly e]ectroshocked trout was compared to the mean instantaneous growth rate (G) of all trout of the same species and age at the site. Instantaneous growth rates for individual trout were calculated as G, = (Iog.,W2 - 10g..wI)/t where W, the weight in grams at first capture, W2 the weight in grams at last capture, and t the time in years between first and last capture. The weight obtained on the penultimate capture was substituted for W2 when the last two captures occurred within a few days of each other to sep- arate short-tenn (as defined above, and see Re- suIts) and ]ong-tenn effects of e]ectroshocking. Species-, age-, and site-specific instantaneous mean growth rates for age-I and age-2 trout were ca]- culated, following Ricker (1975), as 177 G = ]0g..W2 - ]og..w, where w, = the mean weight in grams of trout of the given age and species at the site at the start of the I-year study period, and W2 = is the corresponding mean weight 12 months later. For age-3-8+ brown trout, we used Bachman's (1982) age-length information to obtain annual length increments and our length-weight regres- sions to convert the length increments into weight increments for calculating G. In the absence of data for annual growth increments of rainbow trout in soft-water streams, we used the same G for age-3 trout of both species. Results were again analyzed by chi-square tests. Results Data for brown trout and rainbow trout were corn bined for all analyses because all effects of e]ectroshocking were virtually identical for both species; none of the slight differences between species was statistically significant. The electro- shocking and handling procedure caused an initial weight loss in both species. Of the 213 trout iden- tifiable as individuals both on the date of marking and the date of recapture 1-3 d later, ] 73 had lost weight whereas only 40 had retained the same weight or gained weight over the ]-3 d period (x2 = 81.8; df = I; P < 0.0001 for a null hypothesis of random weight fluctuations). Weight losses var- ied with the size of the fish and ranged from 0.1- 34.1 g. The average weight loss was 5.0% of the initial body weight. The long-term effect of a reduction in instan- taneous growth rate occurred in trout electro- shocked more than once. Sixty-three trout were electro shocked two or more times with a 1.5-] 2- month interval between the last two captures. Of these, 45 (71.4%) showed instantaneous growth rates less than average for all trout of the same species and age at the respective sites (P < 0.005 for a null hypothesis that repeated e]ectroshocking has no effect on growth rate). Three factors were investigated for their importance in causing this pattern of reduced growth rates: (1) number of electroshockings, (2) time since e]ectroshocking, and (3) age ofthe trout. There was only a nonsig- nificant tendency for the number of trout showing reduced growth rates to increase with the number of electroshockings (Table I). Perhaps with a larger sample size, this tendency would have been sig-