viii, 54 leaves : ill. ; 28 cm Notes Typescript Thesis (M.S.)--University of Oregon, 1985 Includes vita and abstract Bibliography: leaves 52-54 Another copy on microfilm is located in Archives

Thesis (M.S.)--Western Washington University, 2010. / Includes bibliographical references (leaves 104-115). Also issued online.

A two part project spanning four and one half years was designed to investigate a number of aspects of the natural history of Octopus dofleini in the Northeast Pacific. The tag-release recapture (Part I) involved weekly SCUBA dives, during daylight hours, at three sites on Southern Vancouver Island, British Columbia, Canada. A total of 320 octopuses were sighted during 616 dives (Part I) and 151 of those octopuses were tagged or recaptured. The ratio of dives per octopus sighted was 1.93:1 and the ratio of dives per octopus tagged or recaptured was 4.08:1. A total of 98 octopuses were tagged (Part I) and 30 of those octopuses were recaptured two or more times for a recapture rate of 30.61%. Statistical analysis of data weighted to provide uniform effort showed Site 1 (Tanner Rock) to have a significantly greater number of large octopuses while Site 2 (Tozier Rock) had a significantly greater number of very small octopuses. An analysis of the data on octopus sex ratios found no significant difference between the number of males and females at each site even though there had been a significant difference in the ratio within Site 2. Analysis of data on annual distribution of octopus body weight combined with the results from the recapture of individual octopuses led to the proposal of a four year lifespan for female Octopus dofleini and an undetermined, but longer, lifespan for males of the species. An examination of the data on octopus movement showed that a peak number of small octopuses (approximately 250 g) appeared at the sites in February. The evidence showed that over the next 19 to 22 months the octopuses grew from approximately 250 grams to a pre adult body weight of 13.8 kg for males (in September) and 14.7 kg for females (in December). No octopuses between 16 and 19.5 kg were captured suggesting a movement of octopuses of that body weight away from the sites. Small numbers of octopuses weighing between 19.5 kg and 28 kg were captured mainly during the first half of the year. An analysis of octopus position data showed that Octopus dofleini does not maintain a constant distance from its nearest neighbour. Nearest neighbour distance was not significantly influenced by the size or sex of the neighbour nor by changes in water temperature. A highly significant correlation was found between estimated den volume and octopus body weight. There were no significant relationships between den surroundings, number of exits, den type and den depth when compared to den usage suggesting that Octopus dofleini is an opportunistic animal using whatever shelter of appropriate volume it discovers. The major food item at all sites as determined by midden heap contents was the Red Rock Crab, Cancer productus. An examination of the physical condition of each octopus captured revealed 21.2% of the animals had either scars or amputated arms or both. Correlations examining the relationships between water temperature and growth rate, body weight, sex and nearest neighbour distance were nonsignificant. Part 11 of the project was the physical measuring and describing of each den at each site. During the 126 SCUBA dives done another 127 octopuses were sighted. As octopuses were captured only when it was necessary to examine the inside of the den there were only 11 octopuses captured during the second part of the project. In total, 447 octopuses were sighted during 742 dives. This results in an effort per octopus sighted of 1.66 dives per octopus. / Graduate

Predators can have large effects on prey populations and on the structure and function of communities. In addition to direct consumption of prey, predators often cause prey to alter their foraging behavior, habitat selection, and morphology. These non-lethal effects of predators can propagate to multiple trophic levels and often exert equal or larger effects upon communities than those of direct consumption. For non-lethal predatory effects to occur, prey must detect and respond to predation risk. While the importance of information transfer in this process has been realized, few studies explore how prey responses are influenced by predator characteristics and environmental conditions that influence the transmission of cues indicative of predation risk. In this dissertation I investigate factors that influence how a single prey species evaluates and responds to predation risk. Here, I examined: 1) the type and nature of cues prey use to evaluate predator risk; 2) how predator identity, predator diet, and the relative risk of predators influence prey response to predation risk; 3) how hydrodynamic conditions influence the delivery of predator cues; 4) how biogeographic trends in predator distribution influence prey response to predation risk; and 5) how genetic structure might vary according to prey geographic location and habitat. To address these questions, I used a common intertidal model system consisting of the rocky intertidal whelk Nucella lapillus (Linnaeus, 1758) and a suite of its predators, the native rock crab Cancer irroratus (Say, 1817), Jonah crab Cancer borealis (Stimpson, 1859), and the invasive green crab Carcinus maenas (Linnaeus, 1758). Nucella use chemical cues emanating from their most common predator (Carcinus maenas) and crushed conspecifics to evaluate predation risk. Nucella from different habitats experience different levels of predation risk, and Nucella from habitats with high levels of predation had larger antipredatory responses to predator risk cues than Nucella that experienced less predation. These chemical cues indicative of predation risk are influenced by hydrodynamic conditions, and Nucella have the strongest anti-predatory response in flow velocities of u= ~4- 8 cm s^-1. Furthermore, Nucella from geographic regions where green crabs are historically absent did not elicit anti-predatory responses, while Nucella from regions where green crabs are common frequently responded. Findings from my dissertation research demonstrate that prey detection and response to predation risk is highly dependent upon predator identity, predator diet, environmental forces, and biogeographic patterns in predator and prey distributions.