Postrelease Hooking Mortality of Rainbow Trout Caught on Scented Artificial Baits

—The postrelease mortality of rainbow trout Oncorhynchus mykiss caught on scented artificial baits was compared with postrelease mortalities of rainbow trout caught on traditional artificial flies. In all, 457 fish were captured on flies, 505 on artificial baits fished actively (ABA), and 511 on artificial baits fished passively (ABP) in five replicate experiments. Water temperature, fish length, lime played, lime out of water, hook location, leader treatment, and bleeding intensity were recorded for each fish captured. Mortalilies were recorded daily over a 3-week holding period. Overall mortalities were 3.9% for fly-caught fish. 21.6% for fish caught on ABA. and 32.1% for fish caught on ABP. Differential mortality among gear types resulted largely from differences in the number of fish hooked in the gill arches or deep in the esophagus (critically hooked) in each group. Overall, critical bookings were 3.9% for ihe fly-caught group, 45.7% for the ABA group, and 78.3% for the ABP group. The Akaike Information Criterion, a model selection procedure, was used to develop a logistical regression model that best fit the mortality data. Parameters that reduced mortality probability include using flies rather than synthetic baits, hooking the fish in a noncritical location, and culling Ihe leader on critically hooked fish. In addilion, as fish length increased, morlalily probabilily decreased. Lengih of lime played and length of lime oul of waler contributed lo morlalily. as did increasing waler temperatures and bleeding intensity. Special regulations such as catch and release and artificial-fly-and-lure-only regulations in trout waters are becoming more important as angling pressure increases and the number of quality trout fishing waters decreases due to habitat loss (Behnke 1980). Many fish stocks no longer can support excessive fishing pressure because of the high demand for quality trout fishing. A high percentage of fish must be returned unharmed by anglers for future recapture lo keep the size and numbers of fish sufficient in quality waters to maintain angler satisfaction. Special regulations are useful in providing for increased demand on trout stocks. Colorado currently has special regulations such as catch and release on 6% of its fishable waters (Powell 1994). Special regulations are useful only if they can be enforced such that the original intent or purpose of the regulations is met. More specifically, special regulations on catch-and-release waters are used to ensure that a single fish can be caught by more than one angler. Fly-and-lure-only fishing in certain waters originally was adopted to reduce mortality of released fish. This regulation was based on overwhelming evidence in studies of hooking mortality that salmonids caught on bait sustain a higher percentage (30-50%) of mortal1 Cooperators are the National Biological Service, ihe Colorado Division of Wildlife, and Colorado State University. ities when released than those caught on flies and lures (5-10%) (Mongillo 1984). Recently, artificial scented baits that fit the Colorado Division of Wildlife's definition of ^artificial fly or lure" have been developed. They are made of a combination of cellulose ether, a polyalkylene glycol, plasticizers, and other chemicals and are impregnated with ami no acids that stimulate active feeding behavior. Fish attack these artificial scented baits ravenously because they are easily detected and are greatly preferred over other substances (Jones 1991). Because fish are strongly attracted to these artificial baits, they may be effectively fished passively, unlike the case with traditional artificial flies and lures. We hypothesized that these scented artificial baits would be swallowed like natural baits, causing fish to be frequently hooked in critical areas such as the gill arches or deep in the esophagus. The relation between deep hooking and mortality of released fish is well documented. In fact, it is the single most important factor in contributing to initial hooking mortality (Wydoski 1977). To test our hypothesis, we initiated a study to quantify mortalities of rainbow trout Oncorhynchus mykiss caught on artificial scented baits and to isolate the causes of mortality. The specific objectives of this study were to determine if active or passive angling with premolded, artificial scented baits resulted in the same mortalities as observed for traditional artificial flies