We developed an individual-based, spatially explicit population-dynamics model to explore the effects of temperature, fishing pressure, and reserve size on red abalone (Haliotis rufescens) populations at two of the northern Channel Islands off the coast of California. The model locations represent the “warm” Santa Cruz Island, which has a fishing history of declining abalone stocks, and the “cold” San Miguel Island, which has a history of stable catches. We investigated the effects of three temperature scenarios for 100-year periods on the behavior of each population. In the first scenario we used the real temperature environment (sea surface temperature, SST) from the last 100 years; results showed a decline in both model populations over the last 20 years, with and without fishing. In the second scenario model runs using an SST time series generated from current conditions at the islands showed that in the absence of larval connectivity the warm population would go extinct within 75 years regardless of fishing level. The final SST scenario involved a range of constant, potential SSTs that could occur in the future; abalone populations persisted when the SST was between 11 ̊C and 16 ̊C. The influence of temperature on the model populations and the latitudinal range of suitable SST suggest a northward migration of the real red abalone range as SST increases over the next 100 years. Efforts to rebuild or protect populations for the future should consider which West Coast regions would provide suitable red abalone habitat given rising ocean temperatures. INTRODUCTION Abalone are long-lived, broadcast-spawning coastal gastropods that live in relatively predictable and accessible locations (reviewed by Tegner 1989). They are a valuable fishery resource, yet overexploitation has been a problem in every producing country in the world (e.g., Breen 1986; Tegner 1989). California once supported fisheries for five species of abalones, but all commercial harvesting was halted in 1997 (Tegner 2000). One of these over-exploited species, white abalone (Haliotis sorenseni), recently became the first marine invertebrate in the United States to be listed as an endangered species under the federal Endangered Species Act (Hobday et al. 2001). Recovery efforts for this and other abalone species are underway in California. Abalone fisheries have typically been managed by regulating a minimum size for capture, although quotas now exist in regions where harvesting continues (e.g., Tasmania, South Africa, New Zealand). The size-limit approach was intended to allow several years of reproduction before capture was possible. This approach may succeed if recruitment is frequent, but the combination of abalone life-history characters—specifically, long life span and broadcast spawning—indicate that high recruitment does not occur every year (Hobday et al. 2001). Successful reproduction in broadcast spawning invertebrates also depends on proximity between spawning individuals and their gametes (e.g., Pennington 1985; Babcock and Keesing 1998; Levitan 1998; Claereboudt 1999). Intense fishing can increase the distance between neighbors such that fertilization cannot occur, leading to recruitment failure (e.g., Shepherd and Brown 1993; Hughes and Tanner 1998). Recruitment failure over a period of time is likely to lead to dramatic population decline and loss of the fishery resource (Shepherd et al. 1998). Fishing has often borne the sole blame for stock collapse in many regions. It is important to note that recruitment failure can occur in the absence of fishing, and some investigators suggest that variation in the environment may be a causative factor in irregular recruitment of abalone (e.g., Shepherd et al. 1998). Indeed, the life history characteristics that allow abalone to persist evolved well before human exploitation began, and so irregular recruitment may be a natural process, offset by long-lived adults. The role of the environment has not been clearly demonstrated in the population dynamics of these marine invertebrates, in part because manipulating and monitoring subtidal populations is difficult. Population models are one tool that may improve our understanding of these complex natural patterns (e.g., Claereboudt 1999). Our goal in this study was to develop a model that incorporated abalone population dynamics, environmental variation, and level of fishing to explore production characteristics of abalone populations. The
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