• Chemosensory responses and foraging behavior of Pycnopodia helianthoides: predator or scavenger?

      Brewer, Reid; Norcross, Brenda; Highsmith, Raymond; Iken, Katrin (2003-08)
      Chemical cues released by damaged or dead organisms can affect how and where benthic scavengers feed, whether damage or mortality is natural or fishery-related. These cues may also cause predators to act as facultative scavengers. Experiments were performed to determine the role that the seastar Pycnopodia helianthoides plays in the presence of scavengable prey. The results of these experiments suggest that P. helianthoides preferentially scavenge in lieu of its normal predatory role. When given a choice, P. helianthoides choose damaged or decaying food over live prey even when live prey is encountered en route to the damaged animal. The densities and activities of P. helianthoides were compared between areas where food was continually introduced and areas where food was not introduced. Adding scavengable food to areas with P. helianthoides caused a spatial redistribution of the seastar population, a change in the foraging dynamics of the seastars, and in some cases, a change in the densities of the prey that P. helianthoides normally consume. The effects of introducing food appeared to result in a change in the role that P. helianthoides plays in the benthic community. This change in modes could have significant effects on the equilibrium of the benthic community.
    • Population biology and ecology of the North Pacific giant octopus in the eastern Bering Sea

      Brewer, Reid; Norcross, Brenda L.; Seitz, Andrew C.; Blanchard, Arny L.; Ormseth, Olav A.; Tamone, Sherry L. (2016-08)
      The North Pacific giant octopus (Enteroctopus dofleini) is an important member of pan-Pacific coastal ecosystems and represents a large incidental catch in Alaska; however little is known about the biology and ecology of this species, which hinders management. To improve our understanding of E. dofleini biology, I conducted a multiyear tagging study in a 25 km2 study area in the eastern Bering Sea (EBS). I used Visible Implant Elastomers to determine growth and movement patterns for E. dofleini and sacrificed octopus were examined to determine seasonal and sex-specific reproductive characteristics. Using tagging data and Cormack-Jolly-Seber models, I estimated survival and study-area abundance for E. dofleini and expanded the abundance estimates to neighboring areas where most of the incidental catch of octopus occurs. In this three-year study, a total of 1,714 E. dofleini were tagged and 246 were recaptured. In autumn when temperatures were warmest, E. dofleini had higher growth rates, moved more and both sexes were predominantly mature when compared to colder winter months. Size also played a role in E. dofleini ecology, with smaller octopus growing faster than larger octopus and larger, mature octopus moving more than smaller, immature octopus. The abundance estimate for octopus in the study area was 3,180 octopus or 127 octopus per km2, and annual survival was 3.33%. Using 20 years of data from the federal groundfish observer program, I estimated that the biomass for E. dofleini in the area where most of the incident catch occurs was 20,697 mt of octopus, an order of magnitude larger than the current biomass estimate for the entire EBS. Though the study area and the scale of the mark-recapture effort were limited, the survival and abundance estimates are from the same area where most of the octopus are in incidentally captured and represent an important first step in enhancing octopus management. However, the large estimates of biomass suggest the current management is too conservative and the estimates of survival suggest that management estimates of mortality are too low.