Date of Award
Winter 1-31-2025
Document Type
Thesis: Open Access
Degree Name
MS Marine Science
Department
Environmental and Ocean Sciences
Committee Chair
Nicholas C. Wegner Ph.D.
Committee Member
Mary Sue Lowery, Ph.D.
Committee Member
John R. Hyde, Ph.D.
Committee Member
Andrew Nosal, Ph.D.
Abstract
In the eastern North Pacific, the oxygen minimum zone naturally shoals seasonally and impacts demersal fish habitat along the continental margins and on offshore seamounts. This hypoxic layer has been shoaling in recent decades, likely affecting the habitat and distribution of commercially-important fish species such as rockfishes (genus Sebastes). Respirometry and shuttle box behavioral experiments were used to determine the hypoxia sensitivities of two rockfish species with contrasting movement patterns and habitat use: cowcod (Sebastes levis) and bocaccio (Sebastes paucispinis). Although both species inhabit similar deep-water, rocky-reef habitat, they have different lifestyles, in which cowcod are mostly benthic, being closely tied to their high-relief rocky habitat, while bocaccio are more pelagic and display more vertical movements above the reef. These species thus serve as excellent models for examining the potential range in hypoxia sensitivity among rockfishes, which comprise the most dominant demersal fish assemblage along the west coast of North America. In this study, the resting metabolic rate (RMR), critical oxygen threshold (Pcrit), and the loss of equilibrium (LOE) were measured for each species at two seasonally relevant temperatures (9 and 12°C). A shuttle box system was used to determine the dissolved oxygen level (% air saturation) that elicited a behavioral avoidance response. Results show that cowcod and bocaccio are both resilient to hypoxic environments, though cowcod generally demonstrated greater tolerance to hypoxia and changes in temperature compared to bocaccio. In particular, cowcod LOEs (0.45% a.s. at 9°C and 2.27% a.s. at 12°C) rank especially low among fishes and likely represent a sit-and-wait approach to episodic exposure to hypoxia, whereas more mobile bocaccio are more likely to behaviorally respond to seek more favorable environmental conditions. Our findings indicate that dissolved oxygen levels typical of depths where bocaccio are commonly found are nearing their critical metabolic limits. As a result, the shoaling of the oxygen minimum zone is likely to push bocaccio into shallower habitats.
Copyright
Copyright held by the author
Digital USD Citation
Chan, Makenna, "Determining the Physiological and Behavioral Tolerance to Hypoxia in Two Species of Rockfish (Sebastes spp.)" (2025). Theses. 68.
https://digital.sandiego.edu/theses/68
Creative Commons License
This work is licensed under a CC BY-NC-ND License.
