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Devries, AL, Checkley DM, Raymond JA.  1972.  Physiology and biochemistry of freezing resistance in Antarctic fishes. Antarctic Journal of the United States. 7:78-79. AbstractWebsite
Checkley, DM.  1980.  The egg production of a marine panktonic copepod in relation to its food supply - Laboratory studies. Limnology and Oceanography. 25:430-446. AbstractWebsite

Egg production by Paracalanus parvus, a particle-grazingcopepod, was investigated in relation to its food supply. The concentration of available food (P) and the rates of ingestion (I) and egg production (B) were measured simultaneously at intervals of 6 h to 2 d for periods of 2-10 d. Concentration, chemical composition (carbon and nitrogen), and species of phytoplankton were experimental variables.Egg production was related to the food ingested during the previous day. For one food type, I and B were rectilinear functions of P. The average maximum rates of ingestion and egg production were 1.1 µg N ∙ female^-1 ∙ d^-1 and 53 eggs ∙ female^-1 ∙d^-1, equivalent to specific rates of 1.5 and 0.37 d^-1. B was proportional to I below a critical ingestion rate, Ic, and independent of I above Ic. For I < Ic, the gross efficiency of egg production (B ∙ I^-1) in terms of nitrogen was 0.37 while in terms of carbon it was a hyperbolic function of the ratio of C:N in the food, ranging between 0.41 (C:Nfood= 4.0) and 0.15 (C:Nfood= 11). For I >Ic, B ∙ I^-1 declined in terms of both carbon and nitrogen.These results, together with the ratio of C:N in particulate matteri n the sea off southern California, suggest that nitrogen (hence protein) potentially limits egg production by adult female Paracalanus and that ingested carbon is used inefficiently.

Checkley, DM.  1980.  Food limitation of egg production by a marine, planktonic copepod in the sea off Southern California. Limnology and Oceanography. 25:991-998. AbstractWebsite

The in situ rate of egg production (B) and female size of Paracalanus parvus, a particle-grazing copepod, water temperature, and the concentrations of chlorophyll a and particulate nitrogen were measured in 31 collections from the euphotic zone of the sea off southern California. B was correlated positively with chlorophyll a and female size and negatively with temperature. A multiple regression of log B on chlorophyll a, particulate nitrogen, female size, and temperature accounts for44% ofthe variationin log B. B was predicted best by an empirical function of food concentration when the food available in nature was considered to be phytoplankton rather than of all types of particulate matter >5 µ.An index of immediate food limitation was derived from laboratory data as a function of food concentration. When applied to extensive measurements of chlorophyll a in the euphotic zone, this index indicates that Paracalanus was often food limited and that food limitation increased along an onshore-offshore transect. Paracalanus was rarely food limited in Santa Monica Bay.

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.

Checkley, DM.  1984.  Relation of growth to ingestion for larvae of Atlantic herring Clupea harengus and other fish. Marine Ecology-Progress Series. 18:215-224.   10.3354/meps018215   AbstractWebsite

Larvae of Atlantic herring Clupea harengus were reared on wild plankton and Artemia salina nauplii in the laboratory at 7 to 9°C for 95 d. Between ages of 20 and 38 d, larvae were fed only Artemia nauplii and the specific rates of ingestion and growth were measured and compared. Relations of rate and efficiency of growth to ingestion were similar in terms of carbon and nitrogen. Growth was linearly related to ingestion (r2= 0.89, n = 9). Starved larvae lost mass at a specific rate of 0.03 d^-1 (3% d^-1) until death at 14 d. A specific ingestion rate of 0.04 d^-1 was required to balance defecation and metabolism. Gross growth efficiency (growth rate/ingestion rate) rose from -1.2 at a low ingestion rate (0.015 d^-1) to 0.4 at the greatest observed ingestion rate (0.11 d^-1) . Condition factor (dry weight length^-3) was significantly related to both ingestion rate and length (r2 = 0.69, n = 20).These results, combined with those for other fish larvae, indicate an asymptotic relation between rates of growth and ingestion such that gross growth efficiency is maximal (0.4) at intermediate ingestion rate. Fish larvae surviving in the sea appear to maximize their ingestion rate and thus grow rapidly but with a reduced efficiency.

Angel, MV, Checkley Jr. DM, Heany SI.  1985.  Chapter One: Plankton migrations. Introduction. Contributions in marine science volume 27 supplement. ( Rankin M, Wohlschlag DE, Eds.).:43-44., Port Aransas, TX: Port Aransas Marine Laboratory, University of Texas Marine Science Institute Abstract
Checkley, DM, Entzeroth LC.  1985.  Elemental and isotopic fractionation of carbon and nitrogen by marine, planktonic copepods and implications to the marine nitrogen cycle . Journal of Plankton Research. 7:553-568.   10.1093/plankt/7.4.553   AbstractWebsite

Particle-grazing copepods, primarily Temora longicornis and T. stylifera, and seawater with natural particles were collected from the northwest Gulf of Mexico. Control and ammonium-enriched aliquots of seawater were incubated in triplicate for 2 days, copepods added and the incubation continued for 2 days. Analyses were made of dissolved nutrients (nitrate, ammonium and phosphate), suspended particles (chlorophyll a and phaeopigments, C, N, τ13C, τ15N), and copepod bodies and feces (C, N, τ13C, τ15N) and the rates of egg and feces production were estimated. Primary production Δchlorophyll a, C, N) was enhanced by N enrichment, indicating its initial N limitation. The rates of egg and feces production were greatest for copepods in N-enriched seawater, indicating food-limited ingestion and egg production. Elemental (C:N) and isotopic (τ13C, τ15N) fractionation by copepods occurred following ingestion of suspended particulate matter (spm) and during the production of tissue (b) and feces (f): C:Nf>C:Nspm >C:Nb, τ13Cb>τ13Cf>τ13Cspm, and τ15Nf>τ15Nb>τ15Nspm. In a second experiment, N-enriched and N-deficient phytoplankton were fed to Acartia tonsa and again C:Nf>C:Nspm>C:Nb. These data indicate that copepods in the present study (i) used nitrogen more efficiently than carbon for tissue production and (ii) produced tissue and feces enriched and excreta depleted in 13C and 15N relative to the suspended particulate matter. The implications of these results to the marine nitrogen cycle are discussed.

Checkley Jr., DM.  1985.  Nitrogen limitation of zooplankton production and its effect on the marine nitrogen cycle. Archiv fuer Hydrobiologie - Beiheft Ergebnisse der Limnologie. 21:103-113. Abstract
Bird, JL, Eppler DT, Checkley DM.  1986.  Comparisons of herring otoliths using Fourier series shape analysis. Canadian Journal of Fisheries and Aquatic Sciences. 43:1228-1234.   10.1139/f86-152   AbstractWebsite

Numeric analysis of otolith morphology provides vital information to commercial fisheries concerning the age distribution, racial origin, and, to some extent, the environmental history of fish stocks. Conventional methods used to retrieve these data, though proven to be effective, are time consuming, susceptible to ambiguous interpretations, and only semiquantitative. Fourier shape descriptors, when used to analyze outlines of otolith silhouettes, represent a rapid, objective, semiautomated means of obtaining much of this information. Analysis of Fourier shape information derived from otoliths of juvenile and adult Alaskan herring and adult Northwest Atlantic herring show that otolith shape reflects differences in fish age and fish race. The shape of otoliths of juvenile fish are significantly different from those of adult fish. Few shape differences can be found, though, between otoliths from adult fish of different age within the same stock. Distinct differences exist between Atlantic and Alaskan adult otolith shapes. For some stocks, minor shape differences occur between left and right otoliths. Differences in otolith shape arising from sexual dimorphism are not apparent.

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.

Hoss, DE, Checkley Jr. DM, Settle LR.  1989.  Diurnal buoyancy changes in larval Atlantic menhaden (Brevoortia tyrannus). Journal du Conseil International pour l'Exploration de la Mer. 191:105-111. Abstract
Checkley, DM, Miller CA.  1989.  Nitrogen isotope fractionation by oceanic zooplankton. Deep-Sea Research Part a-Oceanographic Research Papers. 36:1449-1456.   10.1016/0198-0149(89)90050-2   AbstractWebsite

The ratio of 15N:14N for particulate matter suspended in oceanic, surface waters is high after recent nitrate depletion and low in the stable, oligotrophic ocean. We hypothesize that zooplankters and other pelagic heterotrophs produce 15N-depleted ammonium and 15N-enriched particulate matter that are, respectively, recycled in and exported from the euphotic zone and thus cause the low values of 15N:14N in oligotrophic seas. Heretofore, this pattern was attributed to nitrogen-fixation by the phytoplankton.We measured the ratio of 15N:14N in the bodies and excreted ammonium of zooplankters from the northwest Pacific Ocean and compared these values to the ratio of 15N:14N for subeuphotic, dissolved nitrate. We report that oceanic zooplankton excrete ammonium that is isotopically light relative to their bodies and subeuphotic nitrate. These results are consistent with our hypothesis and the view that the phytoplankton of oligotrophic seas is nourished primarily by nitrogen recycled within the euphotic zone. Nitrate injected into the euphotic zone may be manifest and hence detected by an increase of the ratio 15N:14N for the particulate matter suspended therein.

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, DM, Uye S, Dagg MJ, Mullin MM, Omori M, Onbe T, Zhu MY.  1992.  Diel variation of the zooplankton and its environment at neritic stations in the Inland Sea of Japan and the north-west Gulf of Mexico. Journal of Plankton Research. 14:1-40.   10.1093/plankt/14.1.1   AbstractWebsite

Diel variations in the zooplankton and its environment were investigated at two, contrasting neritic stations. The first (BG-1), in the Inland Sea of Japan, was mixed and eutrophic, while the second (GM-1), in the north-west Gulf of Mexico, was stratified and oligotrophic. Intensive studies were conducted at each station in late summer for 2-3 days. Dissolved nutrients and the particulate matter were evenly distributed in time and space at BG-1, but were variable, and often maximal at depth in a nepheloid layer, at GM-1. For each station, approximately 20 categories of zooplankton were enumerated in samples collected with a plankton pump and retained on approximately 100-mu-m mesh filters, In general, the zooplankton at BG-1 exhibited little diel variation in abundance and distribution. By contrast, most types of zooplankton at GM-1 performed diel vertical migrations, though primarily within the lower half of the water column between the thermocline and nepheloid layer. Significantly, similar taxa and stages did not always behave similarly in these two, differing environments, nor did the zooplankton at GM-1 tend to aggregate at the depths of maximal particle abundance or primary productivity. We suggest that studies of diel variation of the distribution and abundance of the zooplankton often require more intense sampling, in time and space, in environments which are stratified rather than mixed.

Checkley, DM, Dagg MJ, Uye S.  1992.  Feeding, excretion and egg production by individuals and populations of the marine, planktonic copepods, Acartia spp. and Centropages furcatus. Journal of Plankton Research. 14:71-96.   10.1093/plankt/14.1.71   AbstractWebsite

Diel variations in vertical distribution, gut pigment content, ammonium excretion and egg production were investigated for adult females of Acartia erythraea and A. pacifica in the vertically mixed Inland Sea of Japan and Centropages furcatus in the stratified, neritic Gulf of Mexico. Gut pigment content and egg production rate were maximal at night and ammonium excretion was maximal during the daytime. Neither A. erythraea nor A. pacifica adult females showed an apparent diel migration, but the former were highly concentrated in the sur-face layer during the afternoon. In contrast, C. furcatus adult females showed a clear diel migration, residing immediately above the bottom during the daytime and being concentrated between 10 and 25 m depth during the night-time. Individual-based data on gut content and excretion and egg production rates were combined with vertical-distribution data to calculate population values. In the Inland Sea of Japan, the resultant pattern for Acartia spp. reflected the diel variation in physiological rates and even distribution of adult females, except for the afternoon, surface aggregation of A. erythraea. In the Gulf of Mexico, the pattern for C. furcatus reflected largely the diel variation in each rate process and the heterogeneous distribution of adult females in the water column. Elevated nocturnal feeding activity of these copepods may be due to an endogenous rhythm. The daytime maximum in ammonium excretion and night-time maximum in egg production rate indicated approximate half-day and day time lags, respectively, after the intake of food until its conversion into dissolved excreta and released eggs.

Osgood, KE, Checkley Jr. DM.  1996.  Concentration of Calanus pacificus in the Santa Barbara Basin. EOS Trans. AGU. 76:36. Abstract
Checkley Jr., DM, Cooper T, Lennert C.  1996.  Plankton pattern within and below the surface mixed layer. EOS Trans. AGU. 76:198. Abstract
Osgood, KE, Checkley DM.  1997.  Observations of a deep aggregation of Calanus pacificus in the Santa Barbara Basin. Limnology and Oceanography. 42:997-1001. AbstractWebsite

An optical plankton counter/CTD package was used with zooplankton net samples to map the distribution of fifth copepodid (C5) Calanus pacificus in the Santa Barbara Basin region during two autumn cruises. Diapausing C5 C. pacificus were aggregated in a layer just above the basin's oxygen-deficient bottom waters and below its sill depth. The maximal concentration measured was 6,900 ind. m(-3) from a net sample spanning a depth range double the thickness of the C5 layer Although the C5 concentration varied, the layer was found at all stations of sufficient bottom depth within the basin. During November 1994, C5 C. pacificus accounted for 95-97% of all zooplankton caught in net samples from the layer. Relatively low concentrations of deep-dwelling C5 C. pacificus were observed at nearby stations outside the basin. We hypothesize that C5 C. pacificus descend into the Santa Barbara Basin at diapause, are trapped, and accumulate in a region of relatively low predator abundance. The resultant aggregation is estimated to contain a significant fraction of the regional C. pacificus population and thus assumes an important role in its dynamics.

Checkley, DM, Ortner PB, Settle LR, Cummings SR.  1997.  A continuous, underway fish egg sampler. Fisheries Oceanography. 6:58-73.   10.1046/j.1365-2419.1997.00030.x   AbstractWebsite

We describe a method to sample the highly contagious distribution of pelagic fish eggs. CUFES, the continuous, underway fish egg sampler, consists of a submersible pump, concentrator, electronics and sample collector. This system operates continuously and under nearly all sea conditions, providing a real-time estimate of the volumetric abundance of pelagic fish eggs at pump depth, usually 3 m. CUFES-derived estimates of volumetric abundance agree well with those from nets towed at pump depth and with areal abundance estimated from vertically integrated plankton tows. CUFES has been used successfully to sample the eggs of menhaden, pinfish, sardine, and anchovy off the coasts of the eastern and western United States and South Africa. Two large patches of eggs of the Atlantic menhaden were sampled off North Carolina in winter 1993-94, had a linear scale of 5-10 km, and were found in waters between the Gulf Stream and mid-shelf front. Spawning location may he related to bathymetry. CUFES is now being used to estimate spawner biomass by the daily egg production method. An optical plankton counter provided accurate estimates of the number of Atlantic menhaden eggs sample by CUFES.

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.

Iwamoto, I, Trivedi MM, Checkley Jr. DM.  1998.  Real-time detection and classification of objects in flowing water. Machine vision systems for inspection and metrology VII : 4-5 November, 1998, Boston, Massachusetts . 3521( Batchelor BG, Miller JWV, Solomon S, Eds.).:214-220., Bellingham, Wash.: SPIE (International Society for Optical Engineering) Abstract
Van der Lingen, CD, Checkley D, Barange M, Hutchings L, Osgood K.  1998.  Assessing the abundance and distribution of eggs of sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the western Agulhas Bank, South Africa, using a continuous, underway fish egg sampler. Fisheries Oceanography. 7:35-47. AbstractWebsite

A continuous, underway fish egg sampler (CUFES) was employed to assess the abundance and distribution of eggs of both sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the Western Agulhas Bank, South Africa, during September 1996. Samples were collected while underway along six inshore/offshore transects, and at stations along the transects. Volumetric estimates of egg density (eggs m(-3)) from on-station CUFES samples were highly correlated with both volumetric and areal (eggs m(-2)) estimates of egg density from samples collected from CalVET net hauls at these stations, demonstrating the validity of this novel sampling technique. Sardine and round herring eggs were encountered in a band running parallel to the coast and extending from 10 to 33 nautical miles offshore to the shelf edge, and highest egg densities were associated with strong north-west-flowing currents in the region of the shelf edge. Collecting samples while underway increased the precision of the estimate of mean egg density for sardine eggs but not for round herring eggs. The use of CUFES in obtaining a fine-scale resolution of sardine egg distribution, and as a tool for stock assessment, are discussed.

Cambalik, JJ, Checkley DM, Kamykowski D.  1998.  A new method to measure the terminal velocity of small particles: A demonstration using ascending eggs of the Atlantic menhaden (Brevoortia tyrannus). Limnology and Oceanography. 43:1722-1727. AbstractWebsite

A new method, incorporating video, motion analysis, and a novel experimental apparatus, was used to measure the terminal velocity of particles. The method facilitated the investigation of treatment effects and maximized the number of measurements for each replicate, thus improving the statistics for a population of particles. The eggs of the Atlantic menhaden (Brevoortia tyrannus) were used to demonstrate the method by investigating the effects of salinity and stage of development on their ascent rate. Egg ascent rate was greatest at intermediate salinity (36.5 parts per thousand) and decreased in the late stage of embryonic development. We estimate eggs at oceanic salinities (>35.5 parts per thousand) in nature to ascend at 0.19-0.25 cm s(-1).