ORCID ID

https://orcid.org/0009-0005-7881-8878

Date Awarded

2023

Document Type

Thesis

Degree Name

Master of Science (M.Sc.)

Department

Virginia Institute of Marine Science

Advisor

David B Rudders

Committee Member

Donna M Bilkovic

Committee Member

Rich W Brill

Committee Member

Mark J.M. Lomeli

Committee Member

Noëlle Yochum

Abstract

Pacific halibut (Hippoglossus stenolepis) is a prohibited species for the U.S. West Coast Bottom Trawl Fishery and in the last decade, there has been a concentrated interest in the use of artificial illumination serving as a potential bycatch reduction device. Previous studies conducted off the coast of Oregon have found that the addition of green light-emitting diodes to the bridles of low-rise, cutback trawls greatly reduced the number of Pacific halibut caught. However, recent regulation changes now permit high-rise trawls, a gear configuration that fishes a very different volume of water than the previously permissible gear profile, in areas where they were once prohibited. No study to date has investigated the efficacy of artificial illumination to reduce Pacific halibut bycatch for this configuration. Field trials for this study were conducted off the Oregon Coast during August of 2022 and were designed to test a high-rise bottom trawl fitted with artificial illumination as a means to potentially reduce Pacific halibut bycatch. Length-dependent catch comparison and catch ratio analyses for trawls with and without illumination were conducted to determine if catches of Pacific halibut and three commercially important groundfish species differ between trawl treatments. Somatic fat content of Pacific halibut and physiological indicators of stress were also assessed via blood plasma samples to determine if there was a difference in physiological condition between Pacific halibut captured in either illuminated or non-illuminated tows. Additionally, an ethogram was constructed to quantify Pacific halibut behavior in response to an approaching high-rise trawl. Analyses were based on a simulated dataset based on previous flatfish behavioral studies and qualitative evidence from video and sonar recordings collected during field trials. While illuminated trawls caught fewer individuals than the non-illuminated trawls for all species in this study, the difference in catch was not statistically significant. Total catch size was found to have a significantly positive effect on glucose and lactate levels for Pacific halibut; however, no statistically significant differences between illuminated and non-illuminated tows were exhibited across all of the physiological parameters assessed in this study. I hypothesize that this lack of difference between treatment groups may have resulted from the change in gear configuration as Pacific halibut are more likely to rise off of the seafloor when responding to an approaching net. The higher headrope orientation used in a high-rise trawl configuration may be presenting too much of a challenge for halibut seeking to avoid the path of the trawl. It is also possible that the location of the lights was insufficient in triggering a change in avoidance behaviors. These findings are contrary to prior evidence and could have potential implications for the industry. Further investigation into Pacific halibut behavior is implored.

DOI

https://dx.doi.org/10.25773/v5-xmxh-jv19

Rights

© The Author

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