Project: Short-term movements of rockfish between kelp forests in marine reserves

Introduction:

Rockfish (Sebastes spp.) populations have fallen dramatically in recent years and consequently new management strategies are being considered to insure the future of these important species. Some Rockfish stocks have plummeted to as low as 5% of historical (unfished) levels.

Objective:

We are interested in how rockfish dispersal (in the larval and adult phase) affects population persistence given heterogeneous fishing pressure (proposed marine reserves) and oceanographic variability. Our labs integrate field studies with population and bioeconomic models to design and assess ecosystem-based management strategies.

LIFE HISTORY AND MANAGEMENT

There are over 70 rockfish species in the Pacific Northeast and over 100 worldwide. Rockfish are prevalent in every underwater habitat found in California from the subtidal down across the continental shelf and beyond 8,000 feet deep. Individuals of some species live to be over 200 years old.

Presently rockfish populations are in trouble due to over-fishing and recent oceanographic and climate conditions. In California rockfish are broadly managed under two jurisdictions: the offshore (beyond 120 feet deep) and the nearshore, from 120ft to the coast.

RECENT NEARSHORE LEGISLATION

On September 6th, 2002 the Department of Fish and Game announced its plans to adopt the Nearshore Fishery Management Plan (NFMP).

Among the five goals of the NFMP is the goal to "employ science-based decision-making." However, the scientific basis for effective management is far from complete.

The structure of the NFMP legislation therefore mandates that adjustments to the management of the nearshore fishery be made in a "responsible and timely manner" as warranted by new biological and socio-economic information that comes to light. "As knowledge increases, management can become less precautionary."

NEARSHORE ROCKFISH AGE STRUCTURE AND MOVEMENT

In recent field studies myself and fellow graduate student Mike O’farrell have been investigating the movements, age structure, and habitat utilization of the nearshore, semi-pelagic blue rockfish (Sebastes mystinus) at Fort Ross State Park, CA.

BENEFITS

This research has applications for evaluating how proposed marine reserves may conserve the nearshore resource and enhance fisheries. By understanding adult fish movement and predicted transfer rates across reserve boundaries, we plan to investigate the degree to which reserves of various sizes and configurations can be expected to alter overall fishing mortality.

Methods:

We tagged 10 blue rockfish individuals internally with hydro-acoustic pingers and using a system of three equally spaced receiver buoys, to record (via triangulation) the positions of tagged individuals every 5 minutes as they moved about their habitat.

click image to enlarge

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Additionally, we tagged 660 blue rockfish in the same region with external, visible tags. Larger adults (>22 cm) were tagged with Petersen disc tags (pictured below) while smaller rockfish (15-22 cm) were tagged with spaghetti tags.

Tagging location within Fort Ross cove determined the tag color. Externally tagged fish are (and will continue to be) resighted underwater during surveys performed by scuba divers.

click on either image for 148 kb Quicktime movie

By noting the tag color and tag number, we can evaluate blue rockfish movement within Fort Ross cove.

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Progress:

Site fidelity, or centralized, non-random movement, occurs when the area used by an individual is significantly smaller than the area that would be used if an individual’s movement were random. Site fidelity suggests that individual movement and dispersal are linked to spatial features in the environment. Preliminarily, it appears that on a short (one month) time scale, blue rockfish display a form of site fidelity.

Location and setting (click image to enlarge)		The positions of 9 blue rockfish at 20-minute intervals over a three day period. (Click image to enlarge)

Blue rockfish aggregated in a kelp stand (click on image for 202 kb Quicktime movie)

Blue rockfish are not evenly distributed over space but appear to aggregate around kelp stands and underwater pinnacles. We are interested in how movement of adult blue rockfish determines their distribution and abundance in this heterogeneous habitat. Our next challenge is to quantify the degree of site fidelity and the association of blue rockfish with specific habitat features.

Personnel:

Salvador Jorgensen (lead)

A. Peter Klimley, Ph.D.

Louis Botsford, Ph.D.

Department of Wildlife, Fish, & Conservation Biology, University of California, Davis

Acknowledgements:

This project was conducted in conjunction with Mike O'Farrell, a graduate student at Bodega Marine Lab. This research was supported by grants from the Public Service Research Program: "Challenges to California's Natural Resources", from Jastro Shields, the Switzer Foundation, and by a Research Assistantship from the Bodega Marine Laboratory. Equipment and materials were provided courtesy of Drs. Louis Botsford, Peter Klimley, and Steven Morgan.

The physical research itself could not have been performed without the combined efforts of many. In particular, we would like to thank our fish taggers: Clinton Red, Jamie Barlow and Phillip Barlow. Also, we relied heavily on our intrepid divers: Amber Mace, Greg Holzer, Henry Fastenau, Henry Kaiser, Jamie Barlow, Jeremy Downs, Leah Akins and Mark Hodges. Finally, we would like to thank William Walton, Susanna Barlow and the entire staff at Fort Ross State Park for enthusiastically supporting this project.