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908 HAINES AND MODDE TABLE I.-Mean (SD) observed mortality and mark re- tention after 21 and 142 d and final total length (TL) after 142 d for young Colorado squawfish marked by different procedures. For each period, means within a column with- out a letter in common are significantly different (P < 0.05). Mark Final TL (mm) Observed mortality (%) Mark retention (%) Tattoo ink Fin clip Elastic polymer 21 d after marking 10.0 (2.5) z 0.0 (0.0) Y 0.8 (104) y 142 d after marking 92.6 (13.3) z 22.5 (13.9) z 8904 (5.5) z 14.2 (2004) z 89.7 (4.7) z 12.5 (13.9) z 25.7 (4.7) z 33.7 (12.5) z 85.0 (10.6) y 97.8 (3.9) z 100.0 (0.0) z 97.8 (3.8) z Tattoo ink Fin clip Elastic polymer 4 August). On 4 August, 96 fish had recognizable marks, 8 had marks that were difficult to recognize, and 3 had no recognizable marks; no fish died during the period. Vulnerability of Marked Fish to Predation The results of the predation study showed no significant differences among mortality rates from Trial 1 - 15 min. 1.0 0.8 0.6 0.4 CD ~ 0.2 >. "" (ij t:: 0 0 Tatoo-ink Polymer E ., ::I Trial 2 -15 min. 0 CD 1.0 c: a:J 'E a:J ii) 0.8 ~ 0.6 0.4 0.2 0 Tatoo-ink Polymer Fin Clip Control Fin Clip Control predation for the differently marked fish (P = 0.20; Figure 1). However, fish with the 120-min recov- ery period had slightly lower mortality than fish with l5-min recovery (P = 0.028). Significant dif- ferences were also recorded for mortality rates among tanks (P < 0.01) and between trials (P = 0.02). , ~ Field-Marking Evaluation We marked 480 Colorado squawfish with the elastic polymer and released them. We examined 1,027 Colorado squawfish for marks, and recap- tured 45 marked Colorado squawfish, including 5 fish marked in the autumn and recaptured the fol- lowing spring (Table 2). One person was able to mark 25 fish in 10 min; most of this time was spent transferring fish from the holding buckets into MS-222 and then into recovery buckets. On re- capture, the marks were bright and easily detected, including those on the 5 fish marked in the autumn and caught the following spring. Fish survival was comparatively low between mark and release for the first 3 d (22-24 Septem- ber), averaging only 68% (157 of 230 from five backwaters). For the remainder of the study, sur- Trial 1 -120 min. 1.0 0.8 0.6 0.4 0.2 o Tatoo-ink Polymer Trial 2 -120 min. 1.0 Fin Clip Control 0.8 0.6 0.4 0.2 o Tatoo-ink Polymer Fin Clip Control FIGURE I.-Mean instantaneous mortality rates for juvenile Colorado squawfish marked with one of three marks and an unmarked control that were subjected to largemouth bass predation. Error bars represent + I SD.