Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Specimen Collection 

Larval rockfish were collected using a 71cm diameter dual Bongo plankton net system with 505 µm mesh nets and equipped with a small CTD to record depth and physical variables during horizontal net tows at a ship speed of 1.5-2.5 knots down to 28.9-36 m depth.

Collection Location Details

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.  

Specimen Processing and Measurement Methods 

Once the net was retrieved the nets were gently rinsed with saltwater. The content of the cod-ends were concentrated onto a 300 µm mesh sized sieve, transferred into glass jars and preserved in tris-buffered 95% ethanol. Rockfish larvae were sorted from the 505 µm samples. Sagittal otoliths were extracted from 80 larvae selected to represent a range of sample stations and growth stages. Otoliths were mounted with varnish on labeled microscope slide, photographed using a microscope with an oil immersion lens at 100x magnification and rendered via HeliconFocus v8.1.2. The otolith with the clearest resolution from each larva was selected. 

Deployment Details

Each cruise is composed of one or more day trips using one of the two research vessels. The two-three letters indicate the research vessel, the four digits indicates YYMM.

• Winter 2021 sampling took place during cruises BBB2101 and BBB2102
• Spring 2021 sampling took place during cruses BBB2104 and SW2104

Otolith microstructure was measured using the RFishBC package in R. Age (days) and increment widths were measured by two readers. Otoliths were reexamined in cases where measurements varied substantially between readers. Otolith information from larvae 3 days or younger and/or larvae with empty gut contents were excluded. 

Otoliths were mounted with varnish on labeled microscope slide, photographed using a microscope with an oil immersion lens at 100x magnification and rendered via HeliconFocus v8.1.2. The otolith with the clearest resolution from each larva was selected. 

- Data from 2021 and 2022 was merged from two original data files into one data table represented by the primary data file of this dataset. Year data is still retained within the HATCH_OR_CAPTURE_DATE column of this data file.
- Removed units from column names (unit information can be found in the parameters section of the BCO-DMO metadata page).
- Spaces in column names replaced with underscores ("_").

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)