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Checkley, DM, Lindegren M.  2014.  Sea surface temperature variability at the Scripps Institution of Oceanography Pier. Journal of Physical Oceanography. 44:2877-2892.   10.1175/jpo-d-13-0237.1   AbstractWebsite

Sea surface temperature (SST) has been measured from near the end of the Scripps Institution of Oceanography (SIO) pier daily since 1916. It is one of the world's longest instrumental time series of SST. It is widely used in studies of climate and marine ecosystems and in fisheries management. The authors hypothesized that a discontinuity exists in 1988, when the old pier was replaced with the present pier. A regression of annual-mean SST at SIO (SSTSIO) on the Pacific decadal oscillation index for 1916-87 was used to predict annual-mean SST (SSTSIO,PDO) for 1916-present. The residual (ResSST(SIO) = SSTSIO - SSTSIO,PDO) time series shows a positive discontinuity in 1988, when the present SIO pier was first used to measure SSTSIO. No discontinuity in 1988 was observed for ResSST at 12 other shore stations or in nearby waters. Use of the first principal component of other shore station time series of annual-mean SST as the predictor yields similar results. SSTSIO measured over 3 days shows a diel cycle and short-term variability consistent with rip current transport of warm surf-zone water to the end of the SIO pier. This study hypothesizes that rip current transport increased with the change from the old to the present pier and contributed to the observed discontinuity in SIO pier SST. The authors estimate an artifact of about +0.45 degrees C due to both rapid (1988 pier change) and gradual processes. Adjusting the SIO pier SST time series for this artifact reduces the long-term trend from +1.1 degrees to +0.6 degrees C century(-1), consistent with the global rate of change of SST over the past century.

Osgood, KE, Checkley DM.  1997.  Seasonal variations in a deep aggregation of Calanus pacificus in the Santa Barbara Basin. Marine Ecology-Progress Series. 148:59-69.   10.3354/meps148059   AbstractWebsite

A deep aggregation of fifth copepodid (C5) Calanus pacificus in the Santa Barbara Basin (SBB) was mapped over 1 1/2 yr with zooplankton net tows, an optical plankton counter, and a moored acoustic Doppler current profiler. High concentrations of diapausing C5 C. pacificus built up in the deep waters of the SBB during the summer and into the fall. During the buildup, the deep aggregation moved up from the bottom as oxygen became depleted in the basin's deep waters. The deep aggregation apparently builds up due to the basin trapping C5s that migrate below the sill depth from water advected over the basin. C5s are retained within the basin until they swim, or are forced, above the sill depth. Possible mechanisms responsible for the dispersal of the deep aggregation are migration to the surface waters with subsequent dispersal by surface currents, advection over the basin's sill due to the buildup of oxygen-deficient water, or flushing of the basin's deep water.

Checkley, DM.  1982.  Selective feeding by Atlantic herring (Clupea harengus) larvae on zooplankton in natural assemblages. Marine Ecology-Progress Series. 9:245-253.   10.3354/meps009245   AbstractWebsite

The hypothesis that larval herring Clupea harenyus select food by type as well as size was tested in laboratory experiments. Herring larvae were reared at 7 to 9°C on wild zooplankton. The percentage of herring larvae with food at day's end increased from 4 % (4 d) to 68 % (9 d) and averaged 83 % for larvae 25 to 74 d old. Larval herring selected particles according to type as well as size; this selectivity varied with larval age and hence size. Copepod nauplii and copepodites were preferred by larvae of all sizes. Among copepodites, Pseudocalanus sp, and Oithona sp. were preferred by smaller and larger larvae, respectively, while Acartia sp. was rarely ingested, even when of acceptable size. Mollusc veligers comprised a significant portion of the diet of young (4 to 24 d) larvae but were actively rejected by older larvae even when perceived and of acceptable size. Particles smaller than the largest acceptable size were consistently preferred, atypical of predation by vertebrates. These results indicate that larval herring select prey according to type as well as size and that this behavior is acquired through experience.

Jackson, GA, Checkley DM, Dagg M.  2015.  Settling of particles in the upper 100 m of the ocean detected with autonomous profiling floats off California. Deep-Sea Research Part I-Oceanographic Research Papers. 99:75-86.   10.1016/j.dsr.2015.02.001   AbstractWebsite

We have deployed an autonomous profiling float, the SOLOPC, to sample the concentration of particles larger than 100 mu m off the California coast at approximately hourly intervals down to at least 100 m for periods as long as 12 d. We used the data to estimate total aggregate concentrations hourly at 2-m depth intervals, studying the dynamics of particle sedimentation in this difficult-to-sample region. We find that even over time scales of a week, sedimentation is highly variable, with detectable sedimentation events on about one quarter of the days. Most of these observations were along the southwest coast of the United States, a region known for its coastal upwelling and not necessarily representative of more oligotrophic regions. The aggregate settling rates that we estimate, on the order of 50 m d(-1), are consistent with in situ measurements and with rates calculated from coagulation models. The time interval between observations and their vertical resolution constrain the velocities that can be measured. To capture particle settling with velocities less than the 100 m d(-1) that is usually reported for near surface aggregates requires a sampling interval no more than about 0.25 d with a 2 m vertical resolution. This technique provides a powerful new tool to study the dynamics of particles and their sedimentation near the ocean surface, where export starts. (C) 2015 The Authors. Published by Elsevier Ltd.

Shen, SG, Thompson AR, Correa J, Fietzek P, Ayon P, Checkley DM.  2017.  Spatial patterns of Anchoveta (Engraulis ringens) eggs and larvae in relation to pCO(2) in the Peruvian upwelling system. Proceedings of the Royal Society B-Biological Sciences. 284   10.1098/rspb.2017.0509   AbstractWebsite

Large and productive fisheries occur in regions experiencing or projected to experience ocean acidification. Anchoveta (Engraulis ringens) constitute the world's largest single-species fishery and live in one of the ocean's highest pCO(2) regions. We investigated the relationship of the distribution and abundance of Anchoveta eggs and larvae to natural gradients in pCO(2) in the Peruvian upwelling system. Eggs and larvae, zooplankton, and data on temperature, salinity, chlorophyll a and pCO(2) were collected during a cruise off Peru in 2013. pCO(2) ranged from 167-1392 atm and explained variability in egg presence, an index of spawning habitat. Zooplankton abundance explained variability in the abundance of small larvae. Within the main spawning and larva habitats (6-10 degrees S), eggs were found in cool, low-salinity, and both extremely low (less than 200 mu atm) and high (more than 900 mu atm) pCO(2) waters, and larvae were collected in warmer, higher salinity, and moderate (400-600 atm) pCO(2) waters. Our data support the hypothesis that Anchoveta preferentially spawned at high pCO(2) and these eggs had lower survival. Enhanced understanding of the influence of pCO(2) on Anchoveta spawning and larva mortality, together with pCO(2) measurements, may enable predictions of ocean acidification effects on Anchoveta and inform adaptive fisheries management.

Checkley Jr., DM, Ortner PB, Werner FE, Settle LR, Cummings SR.  1999.  Spawning habitat of the Atlantic menhaden in Onslow Bay, North Carolina. Fisheries Oceanography. 8:22-36.: Blackwell Science Ltd   10.1046/j.1365-2419.1999.00019.x   AbstractWebsite

The Continuous, Underway Fish Egg Sampler (CUFES) was used to sample pelagic eggs of the Atlantic menhaden (Brevoortia tyrannus) from 3-m depth off North Carolina in winter 1993–94 and 1994–95. Simultaneous measurements were made of temperature, salinity, and the concentration of chlorophyll a. The maximal concentration of eggs was 346 eggs m−3. Eggs were highly aggregated in patches which occurred between the Gulf Stream and mid-shelf fronts (17–23°C, 36.0–36.4‰). Unexpectedly, eggs were found almost exclusively in water of 20–60 m (mode 20 m) bottom depth. Thus, spawning appears related to bathymetry as well as hydrography. Variograms for egg concentration indicated a mean (± SE) patch scale of 3.6 ± 1.7 km and a high degree of spatial variance explained by CUFES sampling. Lagrangian modelling of particles moving in response to tides, winds, and a prescribed flow from the north indicated that the region of observed, maximal occurrence of eggs is favourable for the retention of eggs and larvae on the shelf adjacent to inlets used to enter nursery areas.

Maillet, GL, Checkley DM.  1991.  Storm-related variation in the growth-rate of otoliths of larval Atlantic menhaden Brevoortia tyrannus: a time series analysis of biological and physical variables and implications for larva growth and mortality. Marine Ecology-Progress Series. 79:1-16.   10.3354/meps079001   AbstractWebsite

Vertical mixing induced by storms is hypothesized to modify the spatial and temporal availability of food to fish larvae and thus influence their feeding and growth. We investigated the effects of storms on sagitta growth rates of 2 age classes (3 to 15 d and 16 to 50 d, post-hatching) of larval Atlantic menhaden Brevoortia tyrannus during winter 1986 in Onslow Bay, North Carolina, USA. We tested the null hypothesis that sagitta growth rate of 3 to 15 d and 16 to 50 d old larvae is independent of the timing and intensity of storms by using transfer functions to investigate relationships among daily time series of sagitta growth rate and meterological and oceanographic variables. Variation in sagitta increment widith was greatest during the first 1 to 2 wk after hatching. Reduction in sagitta growth rate coincided with storms and corroborated laboratory results that growth increments are formed daily and stressful events are manifest in sagitta microstructure. Age-related trends in sagitta growth rate were observed for both age classes and were removed from the analysis by a standardization procedure. Fluctuation in sagitta growth rate for 3 to 15 d old larvae was inversely cross-correlated with time series of wind speed. Fluctuation in sagitta growth rate for 16 to 50 d old larvae was inversely cross-correlated with time series of wind speed and heat flux. The pattern of cross-correlations for 3 to 15 d old larvae indicated an immediate response of sagitta growth rate to periods of strong winds while sagitta growth rate in 16 to 50 d old larvae lagged strong winds and heat fluxes by 2 to 5 d. Transfer function models incorporating wind speed and heat flux accounted for 40 to 54% of sagitta growth rate variation. Reduction in larval Atlantic menhaden growth rate during early life is consistent with the critical period concept and may be related to dispersion and aggregation mechanisms coupled to wind-induced vertical mixing and its effect on food concentration and availability.

Checkley Jr., DM, Bakun A, Barange M, Castro LR, Freon P, Guevara R, Herrick Jr. SF, McCall AD, Ommer R, Oozeki Y, Roy C, Shannon L, Van der Lingen CD.  2009.  Synthesis and perspective. Climate change and small pelagic fish. ( Checkley Jr. DM, Alheit J, Oozeki Y, Roy C, Eds.).:344-351., Cambridge, UK; New York: Cambridge University Press Abstract
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Lindegren, M, Checkley DM.  2013.  Temperature dependence of Pacific sardine (Sardinops sagax) recruitment in the California Current Ecosystem revisited and revised. Canadian Journal of Fisheries and Aquatic Sciences. 70:245-252.   10.1139/cjfas-2012-0211   AbstractWebsite

Small pelagic fish typically show highly variable population dynamics due, in large part, to climate variability. Despite this sensitivity to climate, few stocks of pelagic species are managed with consideration of the environment. The Pacific sardine (Sardinops sagax) represents a notable exception, for which sea surface temperature (SST) from the Scripps Institution of Oceanography (SIO) pier has been used, until recently, to adjust exploitation pressure under warm (favorable) and cold (unfavorable) climate conditions. Recently, the previously established temperature-recruitment relationship was reassessed using different methods, resulting in abandonment of the temperature-sensitive harvest control rule in 2012. In this study, we revisit the previous temperature-recruitment relationship using the original methodology and an updated data set from 1981 to 2010. In contrast to the recent reassessment, we find temperature explains significant variability in recruitment and recruitment success. We also show that mean annual SST averaged over the present California Cooperative Oceanic Fisheries Investigations area is a better predictor of recruitment variability than SST at the SIO pier. We propose that sustainable management of the Pacific sardine should consider climate variability and that the basis for this be periodically updated and revised to inform management with the best available science.

Mullin, MM, Checkley DM, Thimgan MP.  2003.  Temporal and spatial variation in the sizes of California current macrozooplankton: analysis by optical plankton counter. Progress in Oceanography. 57:299-316.   10.1016/s0079-6611(03)00103-4   AbstractWebsite

Macrozooplankton in the southern California sector of the California Current had been reported to decrease from 1951 to 1998. We analyzed some of the same preserved samples of macrozooplankton taken in non-El Nino years 1955, 1956, 1966, 1981, 1984, 1991, 1995, and 1996, and also 1999, with the optical plankton counter (OPC) to determine whether all size categories changed similarly over time. The results from 1955 to 1996 could be interpreted either as a linearly decreasing trend (total biovolume decreased by 45%) or as a regime shift (decrease of 38% from pre- to post-1975 regimes). The largest zooplankters (>2.7 mm equivalent circular diameter, ecd) were relatively more important, in terms of biovolume, at night than by day, and offshore than onshore. Their biovolume decreased by the greatest relative amount, and biovolume of the smallest zooplankters (0.75-0.80 mm ecd) decreased hardly at all. The decrease in relative importance of large zooplankters was most evident in winter and spring, and was qualitatively similar by day and at night and in nearshore and offshore regions. Total biovolume increased in 1999 to the pre-1975 level, consistent with a possible shift to a new regime. Our results are consistent with (i) a change in biovolume of the large zooplankton over the sampled period; and (ii) a regime shift in the mid-1970s and, possibly, the late 1990s. The laboratory OPC is a useful instrument for the rapid and cost-effective analysis of preserved samples of zooplankton. (C) 2003 Elsevier Ltd. All rights reserved.

Jahncke, J, Checkley DM, Hunt GL.  2004.  Trends in carbon flux to seabirds in the Peruvian upwelling system: effects of wind and fisheries on population regulation. Fisheries Oceanography. 13:208-223.   10.1111/j.1365-2419.2004.00283.x   AbstractWebsite

We hypothesized that change in the annual population size of guano-producing seabirds (cormorant, Phalacrocorax bougainvillii; booby, Sula variegata; pelican, Pelecanus thagus) is a response to changes in primary and secondary production of the Peruvian upwelling system. We tested this hypothesis by modeling nitrate input through upwelling to the upper layers of the ocean off Peru between 6degrees and 14degreesS using data on wind stress and sea surface temperature. The model predicted the amount of carbon fixed by primary production each year from 1925 to 2000, which was then apportioned to the Peruvian anchovy (Engraulis ringens) biomass and ultimately to the seabird population and the anchovy fishery, the largest single-species fishery on Earth. The model predicted a marked increase in primary production as a consequence of increasing wind stress. It overestimated the anchovy biomass after the collapse of the fishery in 1972, but closely predicted the growth of seabird populations from 1925 to the mid-1960s, and their decline thereafter, explaining about 94% of the variation in seabird numbers from 1925 to 2000. The model indicates the seabirds consumed 14.4% of the available anchovies and, thus, that seabirds consumed 2.3% of the new production, before the development of the anchovy fishery, and only 2.2% of the available anchovies and 0.3% of the new production after the development of the fishery. The model results clarify the roles that environmental and anthropogenic factors may have had in regulating the guano-producing seabird populations. It indicates that the growth of seabird populations from 1925 to 1955 was likely a response to increased productivity of the Peruvian upwelling system and that the subsequent drastic decline in seabird abundance was likely due to competition for food with the fishery, which caught similar to85% of the anchovies, which otherwise would have been available for the seabirds. This model also shows that an increase in oceanic primary production promotes reproductive success and population growth in higher trophic level organisms.

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Johnson, CL, Checkley DM.  2004.  Vertical distribution of diapausing Calanus pacificus (Copepoda) and implications for transport in the California undercurrent. Progress in Oceanography. 62:1-13.   10.1016/j.pocean.2004.08.001   AbstractWebsite

Migration to deep water during diapause may contribute to the retention of several dominant oceanic calanoid copepod populations in eastern boundary current systems, where the mean flow of poleward undercurrents is in opposition to mean equatorward surface flow. The vertical distributions of Calanus pacificus late copepodid stages were measured at a 1200-m deep, open-ocean station in the Southern California Bight on 13 dates between April 2000 and March 2001 using a MOCNESS (multiple opening and closing net and environmental sensing system). Copepod vertical distribution was compared to the vertical position of the California Undercurrent. Diapausing C pacificus were primarily found between 300 and 400 m at the beginning of the diapause season, in June and July, and between 250 and 350 at the end of the diapause season, in November and January. Depth distributions were broader from August to October, ranging from about 350 m to the maximum depth sampled, 1100 m, and the median depth of diapausing C pacificus was deeper, up to 800-900 m, during this period. Maximal depths of diapausing C. pacificus, 1100-1000 m, were greater than have previously been reported. The mean depth of the California Undercurrent was 250 m, and its approximate depth range was 110-430 m. Diapausing C pacificus CV were abundant in the California Undercurrent at the beginning and end of the diapause season, in June to July and late-November to January, suggesting that poleward transport of diapausing copepods in the California Undercurrent contributes to C pacificus Population retention in the California Current System. (C) 2004 Elsevier Ltd. All rights reserved.

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Checkley, DM, Raman S, Maillet GL, Mason KM.  1988.  Winter Storm Effects on the Spawning and Larval Drift of a Pelagic Fish. Nature. 335:346-348.   10.1038/335346a0   AbstractWebsite

Recruitment for many marine organisms depends on survival and transport of eggs and larvae from spawning grounds to nursery areas1. We investigated the effects of winter storms and the Gulf Stream on the spawning, development and drift of the Atlantic menhaden, Brevoortia tyrannus, which spawns offshore2 and metamorphoses in estuaries3. Spawning was maximal during storms in water upwelled near the western edge of the Gulf Stream. Eggs and larvae drifted shoreward with abundant food in the warm surface stratum of a density-driven circulation maintained by the large sea–air heat flux. We suggest that the Atlantic menhaden and other species have evolved to reproduce in winter near warm boundary currents, including the Gulf Stream and Kuroshio, as a result of physical conditions that permit the rapid development and shoreward drift of their eggs and larvae, with consequent high recruitment and fitness.