Browsing College of Fisheries and Ocean Sciences by Author "Hoyt, Zachary N."
Movement and habitat utilization by golden king crab Lithodes aequispinus benedict 1895 in southeastern AlaskaHoyt, Zachary N. (2003-12)Movements and habitat use of golden king crabs (GKC), Lithodes aequispinus, were investigated with a manned submersible and ultrasonic telemetry in Frederick Sound, Alaska. Crabs were collected with commercial crab pots and ultrasonic transmitters were attached to the carapaces of 26 crabs; movements and depth distribution of male and female crabs were monitored bi- monthly from May 11, 2000 to April 12, 2001. Crabs preferred steep, complex habitat with hard substrate; few were on flat, soft substrate. Male and female GKC were not segregated by depth in mid-May. Seventeen pairs of courting crabs were observed during dives; 14 of these pairs were associated with either intermittent or continuous boulder fields and 3 with wall substrates. Crabs did not have seasonal site fidelity. Crabs had seasonal changes in depth distribution, moving to deeper water during late fall and winter and returning to shallower depths during spring. Crabs moved as far as 39 km over one year. No evidence of spatial fidelity was observed; golden king crabs may be moving greater distances or site fidelity maybe on a longer temporal scale than our study, or golden king crabs may be nomadic in nature.
Resource competition, space use and forage ecology of sea otters, Enhydra lutris, in southern southeast AlaskaHoyt, Zachary N.; Eckert, Ginny; Siddon, Chris; Mueter, Franz; Tinker, M. Tim (2015-12)The growing sea otter population in southern Southeast Alaska is impacting commercial shellfish, through foraging and expanding in range and abundance except where hunted for subsistence. Sea otters and their prey have coexisted in the North Pacific Ocean for approximately 750,000 years, but due to exploitation of sea otters from the 1770s until 1911, the species became extinct over much of its range, including southern Southeast Alaska. Subsequently, invertebrate species flourished and were commercially targeted in the late 1900s. Sea otters were relocated (n = 106) to southern Southeast Alaska in 1968. In this dissertation, I evaluated this marine mammal-fisheries conflict through multiple approaches. In Chapter 1, I analyzed geoduck clam and red sea urchin abundance surveys (1994-2012) and catch and effort data from commercial Dungeness crab fisheries (1969-2010) to identify interactions between sea otters and commercial shellfish. In Chapter 2, I collected geo-locations from 30 instrumented sea otters (2011-2014) to identify space use and range expansion. In Chapter 3, I collected sea otter abundance and distribution data from fixed wing aircraft (2010-2014) and observational forage data from sea otters (2010-2013) to determine contemporary population growth and consumption of commercially important shellfish by sea otters. The sea otter population in southern Southeast Alaska has grown from 106 to an estimated 13,139 individuals between 1968 and 2011 with an annual growth rate of 12% and expansion of its range by 117 km2 y-1. Results from a before-after, control-impact analysis indicate that sea otters are rapidly impacting red sea urchin and significantly reducing geoduck clam densities. Further, breakpoints predicted from regression models of Dungeness crab catch are correlated with known sea otter colonization timing. Forty-six percent of the population level diet of sea otters represented commercially important prey. Sea otters targeted commercially important species, specifically red sea urchins and Dungeness crab, when first colonizing an area, after which the diet of sea otters became more diverse as colonization durations increased. Using habitat models based on a bivariate normal probability distribution function, environmental covariates and subsistence hunting pressure on sea otters, I determined that sea otter range expansion was limited by subsistence hunting. Further, female and non-territorial males segregated based on habitat and likely prey preferences. I conclude that sea otter populations will likely continue to grow, and that current shellfisheries cannot coexist with sea otters under existing management. Further, conservation and management of sea otter populations, whether to increase the distribution through translocation efforts or reduce the distribution to avoid human conflicts, could benefit from insights gained from spatially explicit modeling at the landscape level.