Responses in growth rate of larval northern anchovy (Engraulis mordax) to anomalous upwelling in the northern California Current

Abstract

We examined variability in growth rate during the larval stage of northern anchovy (Engraulis mordax) in response to physical and biological environmental factors in 2005 and 2006. The onset of spring upwelling was anomalously delayed by 2–3 months until mid‐July in 2005; in contrast, spring upwelling in 2006 began as a normal year in the northern California Current. Larval and early juvenile E. mordax were collected in August, September, and October off the coast of Oregon and Washington. Hatch dates ranged from May to September, with peaks in June and August in 2005 and a peak in July in 2006, based on the number of otolith daily increments. Back‐calculated body length‐at‐age in the June 2005 hatch cohort was significantly smaller than in the August 2005 cohort, which had comparable growth to the July 2006 cohort. Standardized otolith daily increment widths as a proxy for seasonal variability in somatic growth rates in 2005 were negative until late July and then changed to positive with intensification of upwelling. The standardized increment width was a positive function of biomass of chlorophyll a concentration, and neritic cold‐water and oceanic subarctic copepod species sampled biweekly off Newport, Oregon. Our results suggest that delayed upwelling in 2005 resulted in low food availability and, consequently, reduced E. mordax larval growth rate in early summer, but once upwelling began in July, high food availability enhanced larval growth rate to that typical of a normal upwelling year (e.g., 2006) in the northern California Current.

Winter ichthyoplankton biomass as a predictor of early summer prey fields and survival of juvenile salmon in the northern California Current

“…This may have led to fewer larvae surviving or a shift in their distribution off the shelf, potentially rendering them unavailable to juvenile salmon as prey. This delayed upwelling negatively affected larval fish growth and survival as well as seabird breeding success (Sydeman et al 2006, Auth 2008, Takahashi et al 2012. El Niño years may also be character ized by reduced or ineffective upwelling that has been shown to result in dramatic changes in the ichthyoplankton communities in the NCC (Brodeur et al 1985, Doyle 1995, Lenarz et al 1995.…”

Evidence of bottom-up limitations in nearshore marine systems based on otolith proxies of fish growth

“…The positive relationship between chlorophyll and rockfish growth suggests that bottom-up processes limit pelagic-feeding nearshore fish growth rates and provide a potential mechanism underlying positive relationships between fisheries catch data and chlorophyll concentrations (Ware and Thomson 2005; Chassot et al 2007). In places or years of higher chlorophyll concentrations, black rockfish may consume higher quality prey due to within-year increases in the size or energy content of an individual prey item, such as a forage fish (Robards et al 2002;Takahashi et al 2012). Black rockfish growth was not related to the upwelling index despite the finding that cooler, presumably upwelled waters were associated with increased growth.…”

“…As these hypotheses involve conditions in the current year of growth and our focal species tend to consume prey >1 year old, our analyses assume that changing conditions likely influence nearshore fish by controlling the quality, rather than the abundance, of their prey. The condition of key prey groups (forage fish and invertebrates) is already known to respond quickly (within the year) to environmental conditions (Astthorsson and Gislason 1998;Robards et al 2002;Phillips 2005;Blanchette et al 2006;MacFarlane 2010;Takahashi et al 2012). …”

“…Primary production may be maximized at intermediate levels of water column stability with sufficient mixing to replenish nutrients and enough stratification to retain phytoplankton in the photic zone (Sverdrup et al 1942;Gargett 1997). Coastal upwelling indices are correlates for largescale vertical mixing of deeper, nutrient-rich water that promotes production in nutrient-limited systems, or hinders production in light-limited systems that benefit from increased stratification (Barth et al 2007;Demarcq 2009;Takahashi et al 2012). Satellite-based chlorophyll-a indices approximate phytoplankton standing stock biomass available to aquatic food webs; higher values of chlorophyll-a have been associated with increased fish catches (Ware and Thomson 2005; Boyce et al 2010).…”

Influence of Basin‐ and Local‐Scale Environmental Conditions on Nearshore Production in the Northeast Pacific Ocean

“…Cooler conditions and decreased water column stability associated with coastal upwelling indicate greater vertical mixing and nutrient availability to primary producers in the California Current (Chavez and Messié 2009;Demarcq 2009). Increases in nutrient availability cause bottom-up increases in phytoplankton and zooplankton abundances and subsequent increases in forage fish consumption (Peterson and Schwing 2003;Harris et al 2009;Boyce et al 2010;Keister et al 2011), condition (Astthorsson and Gislason 1998;Robards et al 2002;Takahashi et al 2012), and abundance (Hedd et al 2006;Thayer et al 2008;Sydeman et al 2013). Furthermore, cooler conditions can prompt favorable shifts in prey composition (Hedd et al 2006;Mackas et al 2007;Thayer et al 2008;Keister et al 2011;Gladics et al 2015).…”