Regulations designed to protect recreational fisheries from overexploitation can fail. Regulations such as size and bag limits restrict harvest by individual anglers but not angler effort and therefore not total harvest. Even when individual harvest limits are set to zero (i.e., catch and release), a combination of hooking mortality and noncompliance may lead to fishing mortality rates that are not sustainable if angling effort is sufficiently high. These assertions were tested and quantified by using simulation experiments on a size‐ and age‐structured model developed for a fishery on an adfluvial bull trout population. The functions and rates describing the biology and fishery were derived from a variety of sources, including published and unpublished information on bull trout and, where such sources were unavailable, from other salmonid species. The model predicts that a 40‐cm minimum size limit for harvest would maintain viable populations at an annual effort up to 4 angler‐hours · ha−1 · year−1, a 65‐cm minimum size limit up to 10 angler‐hours · ha−1 · year−1, and a catch‐and‐release fishery up to 18 angler‐hours · ha−1 · year−1. The quality of the fisheries that developed under these three alternative regulations varied substantially with the amount of angler effort imposed. Uncertainty in the minimum population size necessary to ensure sustainability, recruits per unit stock, catchability, hooking mortality rate, and noncompliance rate modifies quantitative predictions, but the qualitative patterns are general. If anglers respond dynamically to variation in the quality of fishing, then the ability of size limit regulations to sustain fisheries is further compromised. The combination of life history and fishery traits such as slow growth, late age at maturity, low fecundity, longevity, and high catchability render adfluvial bull trout particularly susceptible to overfishing, even within relatively narrow bounds of angler effort.

An exploited bull trout, Salvelinus confluentus, population experienced a 28-fold increase in adult density during a 10-year period from a minimum of 60 individuals. This demonstrates the extent to which this population was overharvested. Its ability to respond in fewer than two generations to the implementation of zero-harvest regulations suggests this population was growth-overfished not recruitment-overfished. Examination of stock–recruitment relationships of various life stages indicates that recovery of this population was regulated by the density-dependent survival of juveniles in the rearing creek. This compensatory response occurred between egg deposition and age-1 and regulated the number of fish recruiting into the adult population. A second population bottleneck became apparent later in the recovery process when density-dependent survival of the adult population resulted in its approach to an asymptote, highlighting the necessity of long-term data sets for examining these compensatory responses. Results from this study demonstrate the importance of understanding the influence of individual life stages on the ability of overexploited populations such as threatened bull trout to recover and for their future management.

Using individual tags combined with a fish fence operated at the mouth of Smith-Dorrien Creek, the primary spawning habitat for Lower Kananaskis Lake bull trout (Salvelinus confluentus), we approximated a complete census of the spawning population from 1996 to 2000 to assess whether timing of upstream and downstream spawning migrations varied with extrinsic and intrinsic factors. The timing of both upstream and downstream migrations varied with sex, previous spawning experience, density, and temperature. Inferred spawning duration based on the predicted upstream and downstream migration dates indicated that experienced female spawners spent the least amount of time upstream and first-time spawners spent the most time upstream. No consistent differences in upstream migration timing were observed between non-repetitive and repetitive spawners. We suggest that variations in spawning migration timing observed in Lower Kananaskis Lake may be linked to environmental factors that influence upstream swimming ability and acquisition and expenditure of energy with respect to reproduction.

Ontogenetic shifts in fish habitat use often occur to reduce the risk of predation or cannibalism. We examined the large‐ and small‐scale spatial behavior of juvenile Bull Trout Salvelinus confluentus during the spawning migration of adfluvial adult Bull Trout into a tributary (Smith‐Dorrien Creek, Alberta) where juveniles rear. We evaluated whether juvenile spatial behavior suggested a direct response to adults that may be interpreted as an attempt to reduce predation risk. Our results showed that the juvenile response to the influx of adults was size dependent, with larger juveniles migrating downstream into Lower Kananaskis Lake and smaller juveniles moving into shallower reaches and margins of the creek. From 1992 to 2002, the downstream migration of juveniles occurred after the upstream migration of spawning adults. Juveniles migrating downstream into the lake were predominantly age 3, with some age‐2 individuals. The lateral movement of juvenile Bull Trout in the creek in response to the presence of adult Bull Trout spawners was also assessed by comparing water depths occupied before, during, and after the spawning period. Median depths of water used by juveniles decreased when adults were present and then shifted to prespawning water depths once spawners had left the creek to return to the lake. These results suggest that behaviorally driven habitat segregation of juvenile and adult Bull Trout occurs at both a small scale (within the creek) and a large scale (within the watershed), likely to reduce cannibalism and to maximize juvenile survival.