Spatiotemporal variability of rockfish recruitment on California's north coast in relation to habitat availability

Author

Carolyn Belak, Humboldt State UniversityFollow

Graduation Date

Spring 2020

Document Type

Thesis

Program

Master of Science degree with a major in Biology

Committee Chair Name

Brian Tissot

Committee Chair Affiliation

HSU Faculty or Staff

Second Committee Member Name

Eric Bjorkstedt

Second Committee Member Affiliation

HSU Faculty or Staff

Third Committee Member Name

Andre Buchheister

Third Committee Member Affiliation

HSU Faculty or Staff

Fourth Committee Member Name

Mark Carr

Fourth Committee Member Affiliation

Community Member or Outside Professional

Keywords

Rockfish, Recruitment, Nereocystis, Sebastes, Habitat, Settlement

Subject Categories

Fisheries

Abstract

Characterizing primary drivers of temporal and spatial variability in recruitment is imperative to understanding the role of pre- and post-settlement processes influencing marine population dynamics. On benthic reefs, the quality and quantity of suitable settlement habitat can alter post-settlement density-dependent mortality rates and increase chances of survival. The north coast of California has experienced highly unusual oceanographic conditions in recent years, leading to severe loss of highly productive kelp forests and potentially deleterious ecosystem consequences. In the present thesis, I aimed to determine the effects of canopy-forming bull kelp (Nereocystis) and alternative complex habitats on the recruitment of several kelp-associating species of rockfish (genus Sebastes), an ecologically and economically important demersal fish on nearshore rocky reefs. Zero-altered mixed models were employed to analyze the presence and abundance of rockfish recruits seen in two datasets of differing spatiotemporal scales. “Coarse-scale” annual surveys were conducted across 430 km of northern California coastline for five years as part of a long-term Marine Protected Area monitoring effort. To better resolve seasonal recruitment patterns, a “fine-scale” study was also designed, which consisted of one year of monthly surveys concentrated over 10 km in Mendocino County. Rates of settlement, habitat availability, and spatiotemporal factors were explored as effects on rockfish recruitment rates. Model results confirm previously-documented high interannual variability in recruitment but also suggest that rockfish young-of-the-year primarily use complex habitats other than bull kelp as shelter during recruitment. The probability of presence of new recruits was strongly associated with timing of settlement and latitude, indicating that large-scale oceanographic effects likely play a role in predicting the distribution of rockfish. Recruit density was positively related to the abundance of understory algae and negatively correlated with low relief and bull kelp density. Although reliance on surface kelp canopy has been documented elsewhere, rockfish recruit habitat preferences had not been previously described in northern California, and understanding the strength of habitat associations during a period of severe kelp decline will help to anticipate how rockfish populations might respond to environmental variation. While this study spanned a time of unusual oceanographic conditions, my results suggest that young-of-the-year may still be able to find suitable refuge in understory algae and high-relief reefs for survival.

Citation Style

Ecology

Recommended Citation

Belak, Carolyn, "Spatiotemporal variability of rockfish recruitment on California's north coast in relation to habitat availability" (2020). Cal Poly Humboldt theses and projects. 363.
https://digitalcommons.humboldt.edu/etd/363