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Population Biology and Ecology of the North Pacific Giant Octopus in the Eastern Bering Sea

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Population Biology and Ecology of the North Pacific Giant Octopus in the Eastern Bering Sea Population biology and ecology of the North Pacific giant octopus in the eastern Bering Sea Item Type Thesis Authors Brewer, Reid Download date 10/10/2021 20:56:08 Link to Item http://hdl.handle.net/11122/6804 POPULATION BIOLOGY AND ECOLOGY OF THE NORTH PACIFIC GIANT OCTOPUS IN THE EASTERN BERING SEA By Reid S. Brewer, B.S., M.S. A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Marine Biology University of Alaska Fairbanks August 2016 APPROVED: Brenda L. Norcross, Committee Chair Andrew C. Seitz, Committee Member Arny L. Blanchard, Committee Member Olav A. Ormseth, Committee Member Sherry L. Tamone, Committee Member Sarah M. Hardy, Chair Department of Marine Biology Bradley S. Moran, Dean School of Fisheries and Ocean Sciences TBD, Graduate School Dean Abstract 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 incidentally captured and represent an important first step in enhancing octopus management. However, the large iii estimates of biomass suggest the current management is too conservative and the estimates of survival suggest that management estimates of mortality are too low. iv Table of Contents Page Title P ag e.........................................................................................................................................i Abstract.......................................................................................................................................... iii Table of Contents ........................................................................................................................... v List of Figures...............................................................................................................................ix List of Tables................................................................................................................................ xi Acknowledgements .......................................................................................................................xii Chapter 1: Introduction..................................................................................................................1 Literature Cited ................................................................................................................. 4 Chapter 2: Long-term retention of internal elastomer tags in a wild population of North Pacific giant octopus (Enteroctopus dofleini).............................................................................7 Abstract...............................................................................................................................7 Introduction .........................................................................................................................8 Methods .............................................................................................................................10 Results .............................................................................................................................. 12 Discussion .........................................................................................................................13 Acknowledgements...........................................................................................................15 Literature Cited ................................................................................................................18 Chapter 3: Temperature and size-dependent growth and movement of the North Pacific giant octopus (Enteroctopus dofleini) in the Bering Sea ...................................................................21 Abstract............................................................................................................................ 21 Introduction ...................................................................................................................... 22 v Methods ............................................................................................................................25 Results .............................................................................................................................. 28 Discussion .........................................................................................................................30 Acknowledgements ......................................................................................................... 34 Literature Cited ...............................................................................................................43 Chapter 4: Estimates of abundance and survival of the North Pacific giant octopus (Enteroctopus dofleini) in the eastern Bering Sea .................................................................... 47 Abstract.............................................................................................................................47 Introduction .......................................................................................................................48 Methods ............................................................................................................................49 Results .............................................................................................................................. 56 Discussion .........................................................................................................................58 Acknowledgements ......................................................................................................... 63 Literature Cited ...............................................................................................................74 Chapter 5: Seasonal sex-specific reproductive characteristics of the North Pacific giant octopus (Enteroctopus dofleini) in the Bering S ea .................................................................. 77 Abstract.............................................................................................................................77 Introduction .......................................................................................................................78 Methods ............................................................................................................................80 Results .............................................................................................................................. 83 Discussion .........................................................................................................................85 Acknowledgements ......................................................................................................... 91 Literature Cited .............................................................................................................101 vi Chapter 6: Conclusions .............................................................................................................105 Literature Cited ..............................................................................................................111 vii viii List of Figures Page Figure 2.1. Map of Unalaska Island and the study area .........................................................16 Figure 2.2. Visible Implant Elastomers on the ventral surface of an Enteroctopus dofleini........................................................................................................................................... 17 Figure 3.1. The 25 km2 study area where Enteroctopus dofleini growth and movement was examined was located 20 km northeast of Unalaska Island, Alaska...........35 Figure 3.2. Increasing specific growth rate (SGR; % d-1) with increasing temperature
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