Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

This study was carried out within the temperate to subtropical Southern California Bight and surrounding coastal areas between 32° and 35° North, and 117° and 120° West. Specific locations sampled fall within the CalCOFI and CCE-LTER programs' quarterly survey grid from lines 76.7 to 93.4 and stations 26 to 55.

Sampling took place from January to April 2021 on R/V Bob and Betty Beyster cruises BBB2101, BBB2102, and BBB2104 and on R/V Shearwater cruise SW2104. Each cruise number is composed of one or more day trips using one of the two research vessels. The two-three letters indicate the research vessel, and the four digits indicate YYMM.

Larval fish were collected using a 71-centimeter (cm diameter dual Bongo plankton net system equipped with a small CTD to record depth and physical variables during horizontal net tows at a ship speed of 1.5 to 2.5 knots down to 14 to 36 meters (m) depth, depending on bottom depth. The Bongo was equipped with two 505-micrometer (µm) mesh-size nets and a flowmeter mounted in the center of one of them.

Once the net was retrieved the cod-ends were immediately placed in a saltwater ice bath and the nets were gently rinsed with saltwater. The content of the cod-ends was then concentrated onto a 200-300 µm mesh-size sieve, transferred into glass jars, and preserved in Tris-buffered 95% ethanol as quickly as possible. After a few days of storage, the alcohol was exchanged. The samples were sorted under a dissecting microscope and fish larvae were identified based on body shape and pigmentation patterns.

Known Problems/Issues:
The Rockfish data contain some gaps for samples where they were not identified and counted. In those cases, any Rockfish present will be included in the Other / Unidentified category.

Data Processing:
CastAway-CTD software version 1.3 (firmware version v026_r2818) was used for data acquisition and processing using default correction algorithms and binned over 0.3 decibar changes. For more information on data processing, please see the manual at https://www.sontek.com/castaway-ctd.

The flowmeter was calibrated between cruises to accurately calculate the volume of water strained by the net and the abundance of fish larvae. It was assumed the volume would be the same for both the starboard and port side net.

BCO-DMO Processing:
- converted date-time fields to ISO 8601 format;
- renamed fields to comply with BCO-DMO naming conventions;
- corrected typo in dataset: changed "Andhovy" to "Anchovy" in the Common_name column.

NSF Award Abstract:
Like many species of small pelagic marine fish, recruitment and productivity of Northern Anchovy fluctuate by orders of magnitude among years. When abundant, the anchovy support a wide range of marine species, including marine mammals, seabirds and a diverse group of marine fishes. Anchovy, which previously thrived during periods of cool-water temperatures and strong coastal upwelling, are currently booming with abundances far in excess of any historical record, even though the California Current Ecosystem is experiencing an unprecedented marine heat wave. This unexpected occurrence challenges the most basic understanding of the mechanisms driving population dynamics in the species. This project is investigating the effects of trophic relationships on population productivity by capitalizing on the immediate research opportunity afforded by the novel, yet ephemeral, state of a local marine heat wave. Findings from the work are being used to develop a mechanistic model of coastal pelagic fish population dynamics generally, and anchovy dynamics in particular. Funded field and lab work are supporting opportunities for undergraduate training and research, and are generating open-access data that serve the research and teaching/training communities into the future.

This RAPID project augments the scheduled Fall research cruises jointly run by the California Cooperative Oceanic Fisheries Investigation and the California Current Ecosystem Long-Term Ecological Research programs. Together, these programs conduct regional oceanographic surveys that include anchovy spawning grounds and larval nursery areas. The RAPID-augmented sampling is designed to test the emerging hypothesis that anchovy populations are trophodynamically mediated at the larval stage, whereby high recruitment results from increased trophic transfer efficiency from the base of the food web. Larval diets and prey selection analyses are being paired with amino acid compound-specific isotope analysis (δ15N) of the larvae and prey field to generate detailed information on larval trophic ecology. Larval diets and plankton community structure are being related to available data on upwelling and productivity to assess environmental and biological drivers to trophic transfer efficiency. Collectively, these analyses are revealing how food chain length is regulated at the larval level through prey selection, at the prey level through community composition, and at the base of the food chain via coastal upwelling and primary production. Furthermore, this project is establishing whether the current trophic level of anchovy larvae is equal to that of historic population booms and if this is the result of favorable feeding conditions throughout their habitat. Findings from the study are generating a mechanistic understanding of the trophic underpinnings of small pelagic fish population productivity in coastal upwelling systems.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Location Description:
This study is carried out within the temperate to subtropical Southern California Bight and surrounding coastal areas between 32° and 35° N, and 117° and 120° W. Specific locations sampled fall within the CalCOFI and CCE-LTER programs quarterly survey grid from lines 76.7 to 93.4 and stations 26 to 55.

Project Affiliations:
California Current Ecosystem Long-term Ecological Research Program (CCE-LTER)
California Cooperative Oceanic Fisheries Investigations (CalCOFI)