To conserve the California Current Ecosystem foodweb, it is important to understand mid-trophic level forage species. Top forage species in this system include Northern anchovy, Pacific sardine and Pacific herring, which are all commercially exploited. They are also influenced by climate, multiple species interactions, and predation. These forage species support predators ranging from seabirds to sea lions, cetaceans to salmon. (See the California Current Predator Diet Database).

Northern anchovy

Northern anchovy are key to ecosystem dynamics in the California Current Ecosystem. Anchovy are prey for >60 species of commercially or recreationally valuable predatory fish, birds, and mammals in this region (see the California Current Predator Diet Database).

Northern anchovy biomass estimates

Long-term biomass estimates for the central stock of northern anchovy (CSNA; Engraulis mordax) in the California Current Ecosystem are estimated from geospatial weighting of egg and larval data from winter/spring California Cooperative Oceanic Fisheries Investigations (CalCOFI) surveys (1951–2021). This is important, to avoid bias due to the nearshore concentration of CalCOFI sampling stations and the anchovy population tendency to contract into that area when abundances are low. While based on the core CalCOFI sampling area, estimates include the entire range of the CSNA, from northwestern Baja California, Mexico, to north of Point Reyes, California, and nearshore waters.

See MacCall et al. (2016) and Thayer et al. (2017) for complete details of methodology and justifications. Biomass estimates have been calculated through 2021 (Thayer et al. 2022), and as new survey data become available estimates are updated regularly (see Anchovy Biomass Estimates).

Northern anchovy population cycles

Famous for its boom/bust population cycles, anchovy in California recently underwent a population collapse (below 20,000 tons) after which estimates have exceeded 2 million tons, similar to dramatic fluctuations in the beginning of anchovy monitoring back in the 1950s (Sydeman et al. 2020). 

No anchovy stock assessment had been conducted for decades, and so initially this extreme decline (2009-2014) went undetected until highlighted by work of FI scientists (MacCall et al. 2016, Davison et al. 2017, Thayer et al. 2017).

This remarkable decline in northern anchovy abundance appeared to occur in the absence of a significant fishery. However during the collapse, while annual fishery catches of a few thousand tons were small by historical comparison, the exploitation rate may have been relatively high given the low stock abundance. The decline in anchovy abundance also coincided with reports of die-offs and reproductive failures of top predators that rely on anchovy for food (brown pelicans, cormorants, sea lions, etc). 

NOAA recently completed a new northern anchovy stock assessment (Kuriyama et al. 2022), the first one since 1995, and is working on a management strategy evaluation (MSE) to try and improve the anchovy stock assessment. An MSE tests and compares management strategies to account for multiple sources of uncertainty. Small pelagic fishes such as anchovy present challenges due to considerable variability in their ecology and life history (such as the boom/bust population dynamics), which leads to substantial uncertainty (Siple et al. 2021).

Indicators of northern anchovy

Predators can be excellent indicators of forage fish, providing information about their abundance, community composition, mortality (see below), length frequencies, etc. We recently integrated data from station-based research trawl surveys and seabird predators that prey upon anchovy to characterize anchovy length distributions in central California for the last several decades (since regular monitoring and stock assessments stopped 1995-2015). Our resulting integrated anchovy indicator reduces the bias individual indices, highlights the use of non-traditional data sources, and provides important information about young-of-the-year anchovy that survive to recruit into the breeding population. Relevant publications are Thayer et al. 2021, 2008, and Thayer and Sydeman 2007.

Mortality by predators

We are collaborating with several institutions to establish rates of anchovy natural mortality caused by predators in the California Current, which can be important to inform a fishery stock assessment. While the anchovy fishery is modest (currently capped at 25,000 metric tons per year), predator populations have increased in recent decades since implementation of federal protections (e.g., Endangered Species Act, Marine Mammal Protection Act). We used the food habits of 42 anchovy predators in the California Current to calculate mean anchovy consumption over a recent 15-year period. Currently, we are focusing on 8 of these predators with more complete timeseries of diet (sea lion, dolphin, large fish, shark, and four seabirds) to estimate variability in annual consumption of anchovy, whose populations can cycle widely (refer to Anchovy Population Cycles).

Population changes

Pacific herring occur throughout the North Pacific Ocean and are vitally important in both pelagic and coastal food webs. Herring are important prey for larger fish, seabirds, and marine mammals. They lay their eggs on coastal seagrasses and algae, and those eggs feed predator species that forage along the shore (e.g., invertebrates, birds, and mammals such as raccoons and black bears). Herring were integral to ancient human cultures, and are still important to native and other modern fisheries. With cooperation from California Audubon scientists, we study trends and variability in herring populations along the west coast of the U.S. and Canada. We are finding that herring abundance in these areas has been declining for the past few decades, which may negatively impact numerous other species, as well as fisheries yield. Results are described in Thompson et al. 2017.

Herring—environmental links

Additionally, we develop indicators of herring as part of the process of implementing ecosystem-based fisheries management. We employ models to describe how annual spawning stock biomass of herring in San Francisco Bay relates to young-of-the-year abundance and environmental conditions in years prior. Understanding population trends and forecasting abundance is important to fisheries managers. See Sydeman et al. 2018 for more information. [Updated data and Table 4 for Sydeman et al. 2018.]

Management

We have developed indicators of herring predator health as well as other forage species, and coupled these with our San Francisco Bay herring abundance forecasting tool. The result is a framework of ecosystem considerations for adjusting herring quotas based on the state of the regional ecosystem. See more information on this subject here.

Predators can be useful indicators of forage fish, providing information about fish abundance, community composition, length frequencies, etc., and may inform fisheries stock assessment parameters such as recruitment indices, cohort strength and natural mortality.  Predator data is often easier and cheaper to obtain than directed fish surveys, particularly for non-commercial fish species that are under-studied.  Moreover, predators target their forage prey while station-based surveys may sometimes miss patchy fish schools.

Alaska puffin diet

Farallon Institute scientists have been analyzing diet data from three puffin species in Alaska. Puffin diet data were collected since the 1970s by the USGS Alaska Science Center, Alaska Maritime National Wildlife Refuge Seabird Monitoring Program, and the Institute for Seabird Research and Conservation. Researchers from these agencies collected data from approximately 40 sites around the Gulf of Alaska and across the Aleutian Islands.  

In order to study puffin diet, field biologists collect samples of the fish and invertebrates (such as squid) that adult puffins bring back to nest burrows to feed to chicks. These diet samples are brought to the lab where they are identified to species, weighed, and measured. For diet analyses, Farallon Institute organized the sample data into the Alaska Puffin Diet Database (APDD), which contains well over 100,000 records of the fish and invertebrate samples collected at the nest burrows, and their sizes. Research and data collection are ongoing, but we have three major analyses of these data, covering temporal variability, geographic variability, and fish condition.

Rhinoceros auklet diet

We have used the diet of rhinoceros auklets to examine forage fish demographics including abundance, community composition, and length frequencies. In central California, auklets’ main prey consists of juvenile rockfish and Northern anchovy (see Anchovy section above). Rhinoceros auklets range around the North Pacific Rim and their diet has been used to characterized forage community composition from Japan to Alaska to Canada and the West Coast of the U.S. Relevant publications include Thayer et al. 2008, 2021, and Thayer and Sydeman 2007.

California sea lion diet

In conjunction with California State Parks, University of California Natural Reserves, and the US Office of Naval Research Marine Mammal and Biology Program, we have studied California sea lion diet in central California (Año Nuevo Island and around Monterey Bay), noting significant shifts in fish species eaten by sea lions between decades. In the 1990s, Pacific sardine and Northern anchovy were dominant, but in the 2010s diet was characterized by rockfish, Pacific hake, and market squid. See Robinson et al. 2018 for more details.

Chinook salmon diet

Chinook salmon in central California rely on anchovy, sardine, herring, juvenile rockfish, market squid and krill. Salmon diet composition was correlated with regional mid-water trawls of prey abundance, and exhibited seasonal shifts in forage communities. Herring in salmon diet also closely tracks changes in the San Francisco Bay herring population. More details are included in Thayer et al. 2014, 2020.