Habitat assessment for Pacific Sardine juveniles

Principal Investigator: Russ Vetter
Co-Principal Investigators: Barbara Javor, Emmanis Dorval, Keith Sakuma

Pacific sardine (Sardinops sagax) is a commercially important, coastal pelagic species that is a major food source for larger fish, sea birds, and marine mammals in the California Current Ecosystem. The US stock is managed under a federal fishery plan that mandates harvest guidelines based on annual assessments. The National Marine Fisheries Service (NMFS) conducts surveys each April off the California coast (when spawning activity is believed to be the greatest) to estimate stock sizes. The stock assessments are based in part on total and brood stock biomass, and daily egg production methods (Hill et al., 2010, 2011, 2012). Sardine spawning habitats usually coincide with areas where sea surface temperature (SST) has reached 14ºC for the northern subpopulation that forms the bulk of the US stock. Egg production falls within relatively narrow environmental parameters (Weber and McClatchie, 2010; Asch and Checkley, 2013). It is generally known that temperature affects growth, particularly in the larval and juvenile stages of fish. The stock assessment model incorporates a SST factor intended to project effects on larval and juvenile survival during cold and warm years. This temperature factor is not necessarily the temperature the young of the year (YOY) endure, but rather a proxy temperature monitored at one site (McClatchie et al., 2010). The actual temperatures of YOY in the Southern California Bight have been inferred from oxygen stable isotopes in otoliths (Dorval et al., 2011; Javor and Dorval, submitted), but no post-spawn surveys (i.e., from May to the following March) have been conducted to assess habitats, abundance, and growth of pre-recruit sardine along the California coast. Such surveys could improve the predictive power of stock assessments for harvest guidelines.

Habitats of spawning adults, larvae, and juvenile sardine are not necessarily the same. During 1983-1998, egg densities were greatest nearshore while larval (<20 mm) densities were greatest in offshore cyclonic eddies (Logerwell and Smith, 2001; Logerwell et al., 2001). During the last two decades, sardine spawning off California has been largely offshore where mature adults are captured (Lo et al., 2005; Reiss et al., 2008; Zwolinski et al., 2011, 2012). Immature juveniles (>20 mm) are primarily caught in nearshore waters off California and in some years off the Pacific Northwest (Emmett et al. 2005; Javor et al., 2011; Javor, 2013; NMFS survey data). The data are sparse on the distribution of young sardine juveniles (~20 mm - ~100 mm) because they are too small and fragile to be captured in commercial seines and in sardine survey trawl nets, and directed surveys (e.g, summer, fall, and winter CalCOFI cruises) do not conduct trawls that would capture such juveniles.

Age-0 juvenile sardine (20 mm to ~140 mm) school and have the potential to swim to their preferred habitats. Elucidating the oceanographic conditions that influence YOY distribution, abundance, survival, and growth could improve stock assessment accuracy by addressing the environmental factors that impact their eventual recruitment. The oceanography of the California Current Ecosystem is complex and influenced by inter-annual variations in the flow of the California Current; the seasonal Davidson Countercurrent; small and mesoscale, cyclonic and anti-cyclonic eddies; geographical features that may entrain water masses (e.g., headlands, bays, bights, and islands); and prevailing and seasonal winds that affect upwelling and surface water movements (Checkley and Barth, 2009). These factors affect the distribution of YOY of other species such as rockfish (Sakuma et al., 2013; Ralston and Stewart, 2013). The primary aim of the proposed research is to characterize YOY (larval and juvenile) sardine abundance and environmental attributes of their preferred habitats in the California Current Ecosystem to provide data on age-0 cohorts for stock assessment.

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Southwest Fisheries Science Center (SWFSC)


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