Northern Anchovy Research Articles

Spatial overlap and trophic interactions between pelagic fish and large jellyfish in the northern California Current

Recent studies have indicated that populations of gelatinous zooplankton may be increasing and expanding in geographic coverage, and these increases may in turn affect coastal fish populations. We conducted trawl surveys in the northern California Current and documented a substantial biomass of scyphomedusae consisting primarily of two species (Chrysaora fuscescens and Aurelia labiata). Spatial overlap of these jellyfish with most pelagic fishes, including salmon, was generally low, but there were regions of relatively high overlap where trophic interactions may have been occurring. We compared feeding ecology of jellyfish and pelagic fishes based on diet composition and found that trophic overlap was high with planktivorous species that consume copepods and euphausiid eggs such as Pacific sardines (Sardinops sagax), northern anchovy (Engraulis mordax), Pacific saury (Cololabis saira), and Pacific herring (Clupea pallasi). Moreover, isotope and diet analyses suggest that jellyfish occupy a trophic level similar to that of small pelagic fishes such as herring, sardines and northern anchovy. Thus jellyfish have the potential, given their substantial biomass, of competing with these species, especially in years with low ecosystem productivity where prey resources will be limited.

Contrasting spawning temperature optima: Why are anchovy and sardine regime shifts synchronous across the North Pacific?

Anchovy and sardine are both abundant small pelagic fish that have exhibited out-of-phase population oscillations in both the western boundary current region off Japan and the eastern boundary current upwelling region off California. These species alternations could indicate approximately synchronous patterns (with some variations in timing between ecosystems) despite the reversed temperature regimes for certain periods across the North Pacific, at least until recently. Here we suggest a contrasting pattern of temperature optima for anchovy and sardine spawnings between the opposite sides of the North Pacific as a possible mechanism of the synchronous phases of species alternations. Spawning temperature optima were examined for Japanese anchovy ( Engraulis japonicus) and Japanese sardine ( Sardinops melanostictus), based on occurrence of eggs and larvae in relation to sea surface temperature. The analyses were based on an updated long-term data set of egg and larval surveys from 1978 to 2004 (102,660 net tows) in the western North Pacific. The ratio of relative frequencies of plankton net samples that are positive for eggs or larvae versus all samples was calculated for temperature intervals of 0.1 °C for both species. This spawning temperature index exceeded 1.0 (baseline for optimum) from ca. 15 to 28 °C with a mid-point at 22 °C for anchovy and ca. 13–20 °C with a marked peak at 16–17 °C for sardine. Patterns of spawning temperature clearly show “warm” and “eurythermal” Japanese anchovy and “cool” and “stenothermal” Japanese sardine in the western North Pacific. This relationship between anchovy and sardine showed a marked contrast to earlier published reports on the spawning temperature optima of northern anchovy ( E. mordax) and California sardine ( S. sagax) in the California Current system. The spawning temperature optimum appears to be species-specific rather than genus-specific. The reversed species-specific temperature optima of anchovy and sardine under the reversed temperature regimes could provide a possible theoretical solution to the synchronous anchovy and sardine regime shifts across the North Pacific.

Remotely sensed spawning habitat of Pacific sardine (Sardinops sagax) and Northern anchovy (Engraulis mordax) within the California Current

AbstractWe use trivariate kernel density estimation to define spawning habitat of northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) in the California Current using satellite data and in situ egg samples from the Continuous Underway Fish Egg Sampler (CUFES) deployed during surveys in April by the California Cooperative Oceanic Fisheries Investigations (CalCOFI). Observed egg distributions were compared with monthly composite satellite sea surface temperature (SST) and surface chlorophyll a (chl a) data. Based on the preferred spawning habitat, as defined in SST and chl a space, the satellite data were used to predict potential spawning habitat along two areas of the west coast of North America. Data from the southern area (21.5 to 39°N) were compared to observations from the CUFES data for the period 1998–2005. Northern anchovy and Pacific sardine exhibited distinctly different spawning habitat distributions. A significant relationship was found between satellite‐based spawning area and that measured during surveys for sardine. CUFES area estimated for sardine was similar in magnitude to that estimated from satellite data (∼60 000 km2). In contrast, spawning habitat of anchovy averaged between 1000 and 200 000 km2 for the period 1998–2005, for CUFES and satellite estimates, respectively. Interannual variability in the area (km2) and duration (months) of estimates of suitable habitat varied between species and between the northern (39 to 50.5°N) and southern portions of the California Current. Long‐term monitoring of habitat variability using remote sensing data is possible in the southern portion of the California Current, and could be improved upon in the northern area with the addition of surveys better timed to describe relationships between observed and estimated spawning habitats.

Chlorinated hydrocarbons in pelagic forage fishes and squid of the Southern California Bight

Large quantities of DDT and polychlorinated biphenyls (PCBs) have been historically discharged to the Southern California Bight (SCB). While these contaminants have bioaccumulated in sediment-associated fishes, little data exist on concentrations of these compounds in pelagic forage species that are the likely food source for larger predatory mammals and birds. The goal of the present study was to assess the extent and magnitude of DDT and PCB bioaccumulation in the four major pelagic species of the SCB: Pacific sardine (Sardinops sagax), Pacific chub mackerel (Scomber japonicus), northern anchovy (Engraulis mordax), and California market squid (Loligo opalescens). A total of 99 composite samples were collected from commercial landing docks along the southern California coast from July 2003 to February 2004. Whole fish were homogenized and analyzed for total DDT (ortho- and para-isomers of DDT and its degradation products) and 41 PCB congeners. Virtually all of the samples of Pacific sardine, northern anchovy, and Pacific chub mackerel had detectable levels of total DDT. Only 50% of the California market squid samples had detectable total DDT. Northern anchovy had the highest total DDT concentrations (60 +/- 38 microg/kg wet wt), followed by Pacific chub mackerel (41 +/- 40 microg/kg wet wt), Pacific sardine (34 +/- 29 microg/kg wet wt), and California market squid (0.8 +/- 1.2 microg/kg wet wt). In general, concentrations were highest in the central SCB. An estimated 99% of northern anchovy, 83% of Pacific sardine, 33% of Pacific chub mackerel, and 0% of California market squid landings exceeded wildlife risk screening values for total DDT. Virtually none of the landings were estimated to exceed wildlife risk screening values for PCBs.

Exposure assessment of the biotoxin domoic acid in California sea lions: application of a bioenergetic model

The biotoxin domoic acid (DA), produced by diatoms of the genus Pseudo-nitzschia, has caused massive California sea lion Zalophus californianus mortalities and live strandings along the California coast. Since quantifying the field DA dose that causes toxic effects in sea lions is logisti- cally difficult, a bioenergetic model that uses age/sex-specific energy requirements was developed to estimate DA doses, assuming ingestion of 2 important vector species: anchovies Engraulis mordax and sardines Sardinops sagax. In this model, uncertainty and variability were incorporated by assign- ing sampling distributions to each model variable. Variables included: (1) vector energy density and assimilation efficiency of gross fish energy; (2) sea lion weight and energy requirements adjusted for energy expenditures associated with foraging, growth and reproduction; and (3) DA concentration in the vector species. Model outputs were analyzed relative to thresholds that cause adverse effects in other mammal species (1 and 2.71 mg DA kg -1 body weight). Based on DA concentrations measured in fish during a previous Pseudo-nitzschia bloom, consumption of anchovies versus sardines as 20% of the sea lions' daily intake would result in a 4-fold increase in risk of non-lethal toxic effects. Across age classes, the median DA dose in pups (7 to 12 mo old) was twice that estimated for juveniles and was between 2 and 4 times greater than for adults. In DA dose estimates most of the variability resulted from the uncertainty associated with the energy density of the vector species and DA concentration in sardines rather than from the uncertainty associated with sea lions. Finally, we highlight the most relevant areas of research needed for determining a definitive risk of sea lion exposure to DA.

Fish larvae in Bahía Sebastián Vizcaíno and the adjacent oceanic region, Baja California, México

The taxonomic composition of the fish larvae assemblage of Bahía Sebastián Vizcaíno and the adjacent oceanic region is presented based on oblique zooplankton hauls made during 12 oceanographic surveys between fall 1997 and fall 2000. In total, 186 taxa representing 71 families were collected. Myctophidae, Phosichthyidae, and Engraulidae were the most abundant during winter and Myctophidae, Merlucciidae, and Bathylagidae during spring. In summer and fall Phosichthyidae and Myctophidae were the most abundant. During 1999 and 2000, seasonal variability was identified in the area by the fish larvae composition, defining winter and fall as a low diversity period and spring and summer as a high diversity period. Interannual variability was detected with an El Niño event, with higher larval abundances of tropical and subtropical taxa, and a La Niña event, with high abundances of larvae of Engraulis mordax.

Spatio-temporal variability in prey harvest and reproductive ecology of a piscivorous seabird, Cerorhinca monocerata, in an upwelling system

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 329:253-265 (2007) - doi:10.3354/meps329253 Spatio-temporal variability in prey harvest and reproductive ecology of a piscivorous seabird, Cerorhinca monocerata, in an upwelling system J. A. Thayer1,2,*, W. J. Sydeman2 1Marine Ecology Division, PRBO Conservation Science, 4990 Shoreline Highway, Stinson Beach, California 94970, USA 2Wildlife, Fish and Conservation Biology, University of California, One Shields Ave., Davis, California 95616, USA *Email: jthayer@prbo.org ABSTRACT: Ocean climate affects the life history and demography of top marine predators through changes in local prey availability. In the California Current System, abundance and distribution of mid trophic-level forage fish may be affected by seasonal and interannual variability in upwelling. We tested the hypothesis that upwelling influences forage fish availability and response of a seabird, but that the effects differ spatially within a region. We examined the availability of multiple forage species and the reproductive ecology of rhinoceros auklets Cerorhinca monocerata relative to ocean climate over 11 yr (1993 to 2003) for 2 colonies off central California: one near the shelf break and another at the coastline. The upwelling index that we used increased through time, while sea surface temperature (SST) generally decreased. Abundance indices of juvenile rockfish Sebastes spp. fluctuated, while northern anchovy Engraulis mordax decreased. Diet of the auklet reflected availability of prey in the environment. Auklet reproduction was affected by both marine climate and prey availability. Seabird breeding as well as harvest of anchovy, rockfish and Pacific saury Cololabis saira were linked to offspring growth, but growth was not necessarily related to offspring survival. Offspring survival was inversely correlated with SST and positively correlated with mass of prey rather than diet composition. Auklet reproduction was more variable offshore than inshore, possibly reflecting variation in the upwelling cells affecting prey availability within the foraging range of birds from each colony. KEY WORDS: Rhinoceros auklet · Northern anchovy · Juvenile rockfish · Pacific saury · Sea surface temperature · Upwelling · Offspring survival · Growth · Timing of breeding · Prey switching Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 329. Online publication date: January 11, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Predicting the vertical profiles of anchovy (Engraulis mordax) and sardine (Sardinops sagax) eggs in the California Current System

AbstractSeveral published models exist for simulating vertical profiles of pelagic fish eggs, but no one has rigorously assessed their capacity to explain observed variability. In this study, we applied a steady‐state model, with four different formulations for vertical diffusivity, to northern anchovy (Engraulis mordax) and Pacific sardine (Sardinops sagax) eggs in the California Current region. Vertical mixing profiles, based on wind speed and hydrography, were combined with estimated terminal ascent velocities of the eggs based on measurements of egg buoyancy and size, to simulate the vertical profiles of the eggs. We evaluated model performance with two data sets: (1) vertically stratified tows for both species and (2) paired samples for sardine eggs from 3‐m depth and in vertically integrated tows. We used two criteria: whether the model predicted individual observed vertical profiles (1) as well as the observed mean and (2) better than the observed mean. Model predictions made with the formulation producing the most gradual profile of vertical diffusivity provided the best match to observations from both data sets and for both species. Addition of a random error term to the terminal ascent velocity further improved prediction for anchovy eggs, but not sardine. For the paired data, model prediction of integrated abundance from abundance at 3‐m depth had significantly lower mean square error than prediction based on a linear regression of 3 m on integrated abundance. Our results support the feasibility of using data from the Continuous Underway Fish Egg Sampler quantitatively as well as qualitatively in stock assessments.

Response of anchovies dampens effects of the invasive bivalve Corbula amurensis on the San Francisco Estuary foodweb

Introduced bivalves have suppressed phytoplankton production in many aquatic food- webs, but effects on higher trophic levels have been inconsistent. In the northern San Francisco Estu- ary, the introduced clam Corbula amurensis eliminated summer-long phytoplankton blooms starting in 1987, but responses of mesozooplankton biomass and most fish were somewhat muted. I con- ducted a retrospective analysis of the response of the estuarine foodweb to the decline in phyto- plankton due to clam grazing. When C. amurensis invaded, the distribution of northern anchovy Engraulis mordax shifted toward higher salinity, reducing summer abundance by 94% in the low- salinity region of the estuary. Northern anchovy dominates the biomass of fish in the more saline reaches of the estuary, and is genetically affiliated with the subpopulation on the central California coast, which in turn is strongly influenced by climate variability. However, abundance of northern anchovy within the estuary was not related to available estimates of biomass, catch, or abundance of northern anchovy on the California coast, nor was it related to any of 4 variables describing aspects of climate variability with different time and space scales. The shift in spatial distribution appears to have been a direct behavioral response to reduced food. Bioenergetic calculations showed reduced consumption of zooplankton by all planktivores, including mysids, after C. amurensis became abun- dant and the anchovy left the low-salinity region of the estuary. This reduced consumption appears to have mitigated effects of the loss of phytoplankton productivity, making a greater proportion of the zooplankton productivity available to other fish species. Such behavioral accommodations are likely wherever invasions occur in open systems.

The structure of anchovy outer retinae (Engraulididae, Clupeiformes) — A comparative light‐ and electron‐microscopic study using museum‐stored material

The outer retinal architecture of Engraulididae is uncommon among vertebrates. In some anchovies, e.g., Anchoa, two cone types are arranged alternating in long photoreceptor chains, i.e., polycones. The cones have radially oriented outer segment lamellae in close contact with a complex guanine tapetum, most probably subserving polarization contrast vision. To clarify the distribution of the aberrant polycone architecture within the Engraulididae and to provide indications about polycone evolution, the outer retina morphology of 16 clupeoid species was investigated by light and electron microscopy, predominantly using museum-stored material. The outgroup representatives of four clupeid subfamilies (Clupeonella cultriventris, Dorosoma cepedianum, Ethmalosa fimbriata, Pellonula leonensis) show a row pattern of double cones, partially with single cones at defined positions and a pigment epithelium with lobopodial protrusions containing melanin. The pristigasterid Ilisha africana has double rows of single cones lying between linear curtains of pigment epithelium processes filled with minute crystallites and melanin concentrated near their vitreal tips. Within the Engraulididae, two main architectures are found: Coilia nasus and Thryssa setirostris have linear multiple cones or polycones separated by long pigment epithelium barriers containing tapetal crystallites and melanin in the tips (also found in Setipinna taty), whereas Anchoviella alleni, Encrasicholina heteroloba, Engraulis encrasicolus, Engraulis mordax, Lycengraulis batesii, and Stolephorus indicus exhibit the typical polycone architecture. Cetengraulis mysticetus and Lycothrissa crocodilus show cone patterns and pigment epithelium morphology differing from the other anchovy species. The sets of characters are compared, corroborated with the previous knowledge on clupeoid retinae and discussed in terms of functional morphology and visual ecology. A scenario on polycone evolution is developed that may serve as an aid for the reconstruction of engraulidid phylogeny. Furthermore, this study demonstrates the suitability of museum material for morphological studies, even at the electron microscopic level.

Distribution and community structure of ichthyoplankton off the coast of Oregon, USA, in 2000 and 2002

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 319:199-213 (2006) - doi:10.3354/meps319199 Distribution and community structure of ichthyoplankton off the coast of Oregon, USA, in 2000 and 2002 Toby D. Auth1,*, Richard D. Brodeur2 1Cooperative Institute for Marine Resources Studies, Oregon State University, Newport, Oregon 97365, USA 2Northwest Fisheries Science Center, NOAA Fisheries, Newport, Oregon 97365, USA *Email: toby.auth@noaa.gov ABSTRACT: The species composition, distribution and concentration of ichthyoplankton off the central Oregon coast in the NE Pacific Ocean were examined during 2000 and 2002 to investigate annual, seasonal, vertical, and cross-shelf variability. Larval concentrations were also analyzed in relation to water temperature and salinity. The 281 samples collected from 5 cruises along a historically sampled transect between April and September in each of the 2 study years yielded 4944 fish larvae comprising 72 taxa in 28 families. The dominant taxa collected were Engraulis mordax, Lyopsetta exilis, Sebastes spp., Stenobrachius leucopsarus and Tarletonbeania crenularis. Total larval concentration increased from 49.3 per 1000 m3 in 2000 to 72.0 per 1000 m3 in 2002, with seasonal concentrations highest in August 2000 (90.3 per 1000 m3) and April 2002 (151.2 per 1000 m3). Relatively few larvae were found at depths >100 m, while highest larval concentrations generally occurred from 0 to 50 m. However, L. exilis concentrations were highest from 50 to 100 m. Larval diversity and concentration were higher offshore (46 to 84 km) than in coastal areas (9 to 28 km). Highest concentrations were normally found at an intermediate station 65 km off the coast. Species designated as either coastal or offshore species by previous studies were predominantly found in their respective shelf regions. With the exception of L. exilis, larval concentrations were positively correlated with temperature and negatively correlated with salinity (p < 0.0001). KEY WORDS: Ichthyoplankton · Fish larvae · Assemblages · Distributions · Multivariate analyses · North Pacific Ocean · Oregon coast Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 319. Online publication date: August 18, 2006 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2006 Inter-Research.

Spatial distribution and species composition of small pelagic fishes in the Gulf of California

Traditional regionalization methods in fisheries based on provinces or major fishing areas, includes large and arbitrary grids in which basic statistics or inferences on distribution or abundance are made. We describe a method for regionalization and analysis of fishing activities for small pelagic fisheries in the Gulf of California based on spatial patterns of landing and catch data in a Geographic Information System (GIS) environment. A fisheries database from logbooks with spatial attributes from October 2002 to June 2007 was analyzed. Landings and catching data were transformed to a Weighted Region Index (WRI) by using fuzzy logic operators. The WRI revealed fishing action centers characterized by areas with the highest WRI values, and a hierarchy for the relative importance of the regions was established. Guaymas, Desemboque de Caborca, Isla Patos, and Bahia San Rafael they were the most prominent ones. An analysis of the relative frequency of species composition showed that the Pacific sardine had an over 80 % abundance in the midriff islands, and remained as the most important in the upper gulf regions, while in the central part of the gulf, relative abundances of Pacific sardine and Northern anchovy were more balanced. Relative abundance of mackerel was significantly larger around Isla Patos than in any other place. Guaymas had the largest relative composition of Northern anchovy and the lowest values for Pacific sardine. Desemboque de Caborca showed the largest homogeneity in species relative composition. It is important to highlight that this results come from in situ data, while the results previously reported come from landing statistics by port. Therefore, the present method acknowledges the spatial differences of species by regions, additional to the traditional time series analysis.

Inhibition of DNA amplification in marine fish larvae preserved in formalin

Recent advances in molecular biology open the possibility to use formalin-preserved specimens stored in ichthyoplankton collections for population genetics studies. Nine DNA extraction techniques were tested on Engraulis mordax larvae preserved in buffered formalin. However, none of the DNA extracts resulted in the positive amplification of mitochondrial DNA (mtDNA) (NADH1, 16srRNA, 12srRNA and control region fractions). An experiment with different length-time exposure to formalin done with Cynoscion parvipinnis larvae allowed us to confirm the difficulty of amplifying mtDNA from larvae preserved in formalin for long time periods and the possibility of DNA extraction and amplification from short-term (less than 48 h) formalin-fixed marine fish larvae preserved in ethanol (70%). We discuss the possible influence of physical–chemical complexes associated with the duration of preservation to inhibition of amplification reactions.

Late Holocene paleofish populations in Effingham Inlet, British Columbia, Canada

Paleontological studies of fish remains in laminated sediments provide a proxy relationship between fish populations and ocean climate. This study examines climate variability from approximately 500 y B.P. to 4000 y B.P. as recorded in fish remain abundances (primarily scales) collected from laminated sediments within Effingham Inlet on the west coast of Vancouver Island, British Columbia. The study also discusses technical issues involving fish remains from laminated sediments, including sampling resolution, sediment volume, identification of remains and appropriate abundance considerations. The dominant species in the assemblage include Northern anchovy and Pacific herring, with lesser percentage-abundances from rockfish, hake, elasmobranches and surfperch. The data indicate that Northern anchovy experienced a shift in scale deposition abundance at approximately 2800 y B.P. with not only a greater total abundance but also a greater consistency of deposition with time. Pacific herring underwent cyclical deposition that changed little through time. Statistical analysis reveals that none of these species is directly responding to climatic signals as indicated in the lithological and palynological record, but that this could have been partially due to the sampling resolution of the piston core. Analysis indicates a lack of correlation between the two dominant species, as might be expected on the basis of their opposing lifestyle strategies with respect to sea surface temperatures. With appropriate sampling strategies, paleohistorical fish remains from laminated sediments reflect changes in population structure and behaviour for some species, illustrate basic secondary trophic information, and provide potential clues to basin-scale oceanographic/climatological variability.

Macrozooplankton and micronekton of the lower San Francisco estuary: Seasonal, interannual, and regional variation in relation to environmental conditions

Macrozooplankton and micronekton are intermediaries linking lower trophic levels (e.g., phytoplankton and mesozooplankton) to higher ones (e.g., fishes and birds). These organisms have not been extensively studied in the San Francisco Estuary (SFE), California. The objective of this study was to determine the distribution and abundance of macrozooplankton and micronekton in the SFE and to describe how these vary seasonally, interannually, and regionally in relation to environmental variables. Water column macrozooplankton and micronekton were sampled monthly from September 1997 to December 2000 at 6 stations spanning North, Central, and South Bays using a Methot Trawl. The macrozooplankton and micronekton in the lower SFE were dominated by 4 fishes and 7 invertebrates that comprised 98% of the total catch. Correspondence analyses revealed 4 groups of species that exhibited similar patterns of distri- bution and abundance. The assemblages changed between the wet and dry seasons and with distance from the coastal ocean. Based on abundance patterns, the dominant taxa in the lower SFE can be classified as: organisms spawned from common members of neritic assemblages that use mostly North Bay and that are abundant during the dry season (Clupea pallasi, Spirinchus thaleichthys, Porichthys notatus); estuarine-dependent organisms with broad distributions in the estuary year-round (Crangon franciscorum, Crangon nigricauda, Engraulis mordax); resident species remaining within the estuary but occurring mostly in South Bay during the wet season (Palaemon macrodactlyus, Synidotea laticauda, Neomysis kadi- akensis); and gelatinous species (Pleurobrachia bachei, Polyorchis spp.) occurring in all three bays with a single peak in abundance in December and January in North and South Bays. The variation in distribution, abundance, and composition of macrozooplankton and micronekton was related to life history strategies, distance from the coastal ocean, and season.

Pathology of Domoic Acid Toxicity in California Sea Lions (Zalophus californianus)

Over 100 free-ranging adult California sea lions (Zalophus californianus) and one Northern fur seal (Callorhinus ursinus), predominantly adult females, were intoxicated by domoic acid (DA) during three harmful algal blooms between 1998 and 2000 in central and northern California coastal waters. The vector prey item was Northern anchovy (Engraulis mordax) and the primary DA-producing algal diatom was Psuedonitzschia australis. Postmortem examination revealed gross and histologic findings that were distinctive and aided in diagnosis. A total of 109 sea lions were examined, dying between 1 day and 10 months after admission to a marine mammal rehabilitation center. Persistent seizures with obtundation were the main clinical findings. Frequent gross findings in animals dying acutely consisted of piriform lobe malacia, myocardial pallor, bronchopneumonia, and complications related to pregnancy. Gross findings in animals dying months after intoxication included bilateral hippocampal atrophy. Histologic observations implicated limbic system seizure injury consistent with excitotoxin exposure. Peracutely, there was microvesicular hydropic degeneration within the neuropil of the hippocampus, amygdala, pyriform lobe, and other limbic structures. Acutely, there was ischemic neuronal necrosis, particularly apparent in the granular cells of the dentate gyrus and the pyramidal cells within the hippocampus cornu ammonis (CA) sectors CA4, CA3, and CA1. Dentate granular cell necrosis has not been reported in human or experimental animal DA toxicity and may be unique to sea lions. Chronically, there was gliosis, mild nonsuppurative inflammation, and loss of laminar organization in affected areas.

Foraging Ecology of Caspian Terns in the Columbia River Estuary, USA

Comparisons were made of the foraging ecology of Caspian Terns (Sterna caspia) nesting on two islands in the Columbia River estuary using radio telemetry and observations of prey fed to chicks and mates at each colony. Early in the chick-rearing period, radio-tagged terns nesting at Rice Island (river km 34) foraged mostly in the freshwater zone of the estuary close to the colony, while terns nesting on East Sand Island (river km 8) foraged in the marine or estuarine mixing zones close to that colony. Late in the chick-rearing period, Rice Island terns moved more of their foraging to the two zones lower in the estuary, while East Sand Island terns continued to forage in these areas. Tern diets at each colony corresponded to the primary foraging zone (freshwater vs. marine/mixing) of radio-tagged individuals: Early in chick-rearing, Rice Island terns relied heavily on juvenile salmonids (Oncorhynchus spp., 71% of identified prey), but this declined late in chick-rearing (46%). East Sand Island terns relied less on salmonids (42% and 16%, early and late in chick-rearing), and instead utilized marine fishes such as Anchovy (Engraulis mordax) and Herring (Clupea pallasi). Throughout chick-rearing, Rice Island terns foraged farther from their colony (median distance: 12.3 km during early chick-rearing and 16.9 km during late chick-rearing) than did East Sand Island terns (9.6 and 7.7 km, respectively). The study leads to the conclusion that Caspian Terns are generalist foragers and make use of the most proximate available forage fish resources when raising young.

Species composition and community structure of pelagic nekton off Oregon and Washington under variable oceanographic conditions

Dramatic changes in the physical and biological conditions off Washington and Oregon, USA, have occurred since 1998, including extreme El Nino (warm) and La Nina (cool) years, high and low Columbia River flow years, a major intrusion of subarctic water, and a low oxygen event on the shelf. The occurrence of contrasting environmental conditions provided an excellent opportunity to examine pelagic nekton distributions and their abiotic and biotic associations. Pelagic surface trawl surveys conducted during June and September from 1998 to 2002 off northern Washington to central Oregon revealed a nekton community dominated by Pacific herring (33.5% of total catch), Pacific sardines (29.9%), and northern anchovy (12.3%). Between 1998 and 2002, species composition shifted from a community dominated by southern species (mackerels and hake) to one dominated by northern species (squid, smelts, and salmon), but the transition was gradual, and small pelagic spe- cies (sardines, herring, and anchovy) showed no consistent trends in abundance over time. Species diversity/evenness was highest in September 2002. Cluster analysis identified 7 species and 6 station clusters. Subyearling Chinook salmon, market squid, Pacific sardine, yearling coho salmon, and Pacific saury were the strongest indicator species for 5 of these cluster groups. Cluster group distrib- utions differed between both inshore/offshore and north/south. A 3-dimensional ordination ex- plained 55% of the total variance with bottom depth, distance from shore, and sea-surface tempera- ture correlated with the first axis, latitude with the second axis, and surface salinity, surface density and stability with the third axis. Our results suggest that the habitats occupied by pelagic nekton species expand and contract in relation to the dynamic nature of the California Current and are affected by changing ocean conditions at both seasonal and interannual periodicities.

Diel differences in surface trawl fish catches off Oregon and Washington

Abstract Surface rope trawls have recently been used to investigate pelagic fish communities off the west coast of North America. We examined surface rope trawl catches from locations off the Washington and Oregon coast to determine whether they differed day and night. We paired day and night samples from the same location taken within 7 days of each other. Fifty-one sample pairs fit our criteria with 33 of these controlled for tidal state. Samples were taken at 11 different stations during the months of May, June, and September from 1998 to 2002. We used the sign test to compare median densities for nine of the most abundant and commonly occurring fish species: two juvenile salmonids—coho salmon ( Oncorhynchus kisutch ) and yearling Chinook salmon ( O. tshawytscha ); four small pelagics—northern anchovy ( Engraulis mordax ), Pacific herring ( Clupea pallasi ), Pacific sardine ( Sardinops sagax ), and whitebait smelt ( Allosmerus elongatus ); and three larger predatory fishes—Pacific hake ( Merluccius productus ), chub mackerel ( Scomber japonicus ), and jack mackerel ( Trachurus symmetricus ). Both species of salmon were caught at higher densities during the day. The small pelagic and predatory species were caught in higher densities at night. The differences were significant for both salmonids, Pacific hake, chub mackerel, and all small pelagic species. No consistent pattern of correlation existed between the catch differences and differences in temperature or salinity between day and night samples. We believe diel patterns of fish vertical distribution and behavior coupled with the actual depths the net samples are primarily responsible for catch differences.

Fine scale spatial pattern of Pacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax) eggs

AbstractPacific sardine (Sardinops sagax) and northern anchovy (Engraulis mordax) eggs exhibited different spatial structure on the scale of 0.75–2.5 km in two egg patches sampled in the Southern California Bight in April 2000. Plankton samples were collected at 4‐min intervals with a Continuous Underway Fish Egg Sampler (CUFES) on 5 × 5 km grids centered on surface drifters. Variograms were calculated for sardine and anchovy eggs in Lagrangian coordinates, using abundances of individual developmental stages grouped into daily cohorts. Model variograms for sardine eggs have a low nugget effect, about 10% of the total variance, indicating high autocorrelation between adjacent samples. In contrast, model variograms for anchovy eggs have a high nugget effect of 50–100%, indicating that most of the variance at the scales sampled is spatially unstructured. The difference between observed spatial patterns of sardine and anchovy eggs on this scale may reflect the behavior of the spawning adults: larger, faster, more abundant fish may organize into larger schools with greater structure and mobility that create smoother egg distributions. Size and mobility vary with population size in clupeoids. The current high abundance of sardines and low abundance of anchovy off California agree with the greater autocorrelation of sardine egg samples and the observed tendency for locations of anchovy spawning to be more persistent on the temporal scale of days to weeks. Thus the spatial pattern of eggs and the persistence of spawning areas are suggested to depend on species, population size and age structure, spawning intensity and characteristic physical scales of the spawning habitat.