William G. Pearcy

Vertical distribution and migration of oceanic micronekton off Oregon

An Isaacs-Kidd midwater trawl system that opens and closes codend nets and monitors depth and water velocity was used to collect micronekton from 12 contiguous depths in the upper 1000 m. Analysis of variance of the catches of common species indicated significant vertical migrations for five of seven fishes and two of seven shrimp and mysid species. Season bad little effect on the pattern of vertical migrations, average depth distributions, or overall variations in abundance. None of the common species was appreciably more numerous in night than in day catches; thus there was no evidence for day-night differences in avoidance of the trawl. Diel vertical migrations, as evidenced by distinct depth separation of day and night modes of abundance, were evident for only 32% of all the species of fishes, 13% of the shrimps and mysids, and 40% of the cephalopods. The range of diel migrations was generally 200 to 400 m. The four most common migrant fishes and the most abundant migrant shrimp numerically dominated upper mesopelagic waters by day and epipelagic waters by night. Lower mesopelagic waters were inhabited by a larger number of generally less abundant species which exhibited little, if any, diel vertical migration. The population of Stenobrachius leucopsarus, the most common fish, was composed of migratory and non-migratory individuals producing nocturnal peaks of abundance at both mid-depths and in near-surface waters. Both groups included a broad range of individual sizes. Individual fish probably do not migrate into surface waters on every night. The depth range of all species during either day or night was large, extending over several hundred meters and several decades of irradiance. As a result, vertical ranges often overlapped broadly. Common migratory species usually occupied depths of 0 to 50 m at night and 300 to 500 m during daytime. Size segregation by depth was not pronounced.

Food habits of deep-sea macrourid fishes off the Oregon coast

Abstract The abyssal macrourid fishes off Oregon are generalized feeders, as theory predicts for large searchers in an unproductive environment. Analysis of stomach contents revealed that fish feed on a wide variety of foods, but the proportions of different taxa of food vary among and within species, indicating some food selectivity. Broad feeding overlaps occurred between large Coryphaenoides armatus and C. filifer , which fed mainly on squid and fish, and between small C. armatus and C. leptolepis , which fed largely on epifaunal crustaceans. Pelagic crustaceans were numerous in the stomachs of large C. leptolepis . Overlap among the food of these macrourids was more than the overlap among shallow-water, demersal fishes. Most food consisted of epifauna or pelagic animals. It is not known if the squid, shrimp, and fish prey, known to inhabit mesopelagic depths, have vertical distributions extending to 2800 m where they were consumed, or whether macrourids forage far above the bottom. The fact that some squid beaks were from squids larger than the fish which ate them suggests that macrourids are sometimes scavengers and feed on sinking carcasses. The importance of pelagic animals in the diet of large macrourids implies a direct trophic link between abyssobenthic and pelagic animals that may be important in the transport of energy and elements into the deep ocean.

Fish debris in sediments of the upwelling zone off central Peru: a late Quaternary record

Abstract Scales of the anchoveta were abundantly represented among fish remains preserved in partly laminated marine sediments on the upper continental slope of Peru. Hake scales were less common. Sardine scales occurred only sporadically. Recent accumulation rates of scales indicate that prior to exploitation the anchoveta standing stock off Peru was about five times that of northern anchovy off California. During glacial time, however, clupeoids were less abundant off Peru and were more evenly distributed among sardines and anchoveta. Evidence from fish scales and phytoplankton assemblages suggests that the coastal waters off Peru did not respond to continental glacial and neoglacial advances simply by cooling. High accumulation rates of scales from warm-water fishes and tests of cool-water phytoplankton preceded and succeeded an interval containing low numbers of dominantly warm-water taxa. This interval coincided with the second neoglacial advance (2000 to 2700 y B.P.). Similar but less well-defined warm-water and cool-water assemblages coincided with the third neoglacial advance (200 to 400 y B.P.) and the last glacial retreat. Upwelling intensity probably fluctuated more widely during early and late phases of glacial and neoglacial cooling episodes, accounting for the mix of distinctly warm-water and cool-water assemblages and perhaps for an enhanced productivity. A weakened Intertropical Convergence Zone or strengthened coastal countercurrent may explain the warm-water marine faunas and floras and wet climates on the mainland of Peru inferred by others for neoglacial or glacial time.

Developing a broader scientific foundation for river restoration: Columbia River food webs

Well-functioning food webs are fundamental for sustaining rivers as ecosystems and maintaining associated aquatic and terrestrial communities. The current emphasis on restoring habitat structure—without explicitly considering food webs—has been less successful than hoped in terms of enhancing the status of targeted species and often overlooks important constraints on ecologically effective restoration. We identify three priority food web-related issues that potentially impede successful river restoration: uncertainty about habitat carrying capacity, proliferation of chemicals and contaminants, and emergence of hybrid food webs containing a mixture of native and invasive species. Additionally, there is the need to place these food web considerations in a broad temporal and spatial framework by understanding the consequences of altered nutrient, organic matter (energy), water, and thermal sources and flows, reconnecting critical habitats and their food webs, and restoring for changing environments. As an illustration, we discuss how the Columbia River Basin, site of one of the largest aquatic/riparian restoration programs in the United States, would benefit from implementing a food web perspective. A food web perspective for the Columbia River would complement ongoing approaches and enhance the ability to meet the vision and legal obligations of the US Endangered Species Act, the Northwest Power Act (Fish and Wildlife Program), and federal treaties with Northwest Indian Tribes while meeting fundamental needs for improved river management.

Aspects of reproduction, early life history, and biology of macrourid fishes off Oregon, U.S.A.

Abstract Egg sizes, fecundities, times of spawning, early benthic life, size frequency, and distribution by sex and size are described for some of the four most common macrourid species off Oregon: Coryphaenoides acrolepis, C. armatus, C. filifer and C. leptolepis . Sizes of eggs at comparable developmental stages from different species were quite different. Average fecundities ranged about 26,000 to 2,500,000 eggs. C. acrolepis and C. filifer may spawn semi-annually. Juveniles of the three sympatric species, C. armatus, C. filifer , and C. leptolepis , become benthic in habit at different sizes. Different mouth size of each species may minimize competition for food. Size frequency distributions were either unimodal ( C. filifer, C. armatus ) or bimodal ( C. acrolepis, C. leptolepis ). However, small C. filifer were rarely collected suggesting that they remain pelagic longer than the young of other species. C. armatus and C. leptolepis were ‘bigger-deeper’, but the trend was not evident in the other two species. Sex ratios also differed: male C. armatus and C. leptolepis were less abundant than females, although their proportion increased with distance offshore. Numbers of males and females were about equal in C. acrolepis and C. filifer . Little evidence for the existence of sexual segregation was found. The liver apparently serves as a buoyancy mechanism in large C. armatus .

Vertical migration and distribution of mesopelagic fishes off Oregon

Abstract Using an Isaacs-Kidd midwater trawl with an opening and closing cod-end device, we collected samples of mesopelagic fishes from depths of 0–150 m, 150–500 m and 500–1000 m during periods of daylight and darkness. The observed day catches per unit volume of all mesopelagic fishes, as well as those of each of the four dominant species, were larger than the night catches at intermediate depths (150–500 m), whereas the opposite was true in the surface layer (0–150 m). These reversed trends in the upper 500 m indicated daily vertical migration, but in all cases the night-time increase in surface waters exceeded the daytime increase at mid-depths. Moreover, the number of fishes in a column of water 1000-m deep was always higher for night than day tows. There was no evidence for day-night differences in catches from the 500–1000 m stratum where catches were uniformly low. The relative importance of avoidance and vertical migration was assessed by assuming (1) that the day-night difference per m2 is a measure of the increased visual avoidance of the trawl in the upper 500 m during daylight periods, and (2) that the daytime increase at mid-depths is the best extimate of vertical migration. Calculations based on these assumptions showed that nearly all the night-time increase in surface water was attributable to vertical migration for one lanternfish. Avoidance alone, however, could explain most of the night-time increase in surface catches for three other common species. The average number of mesopelagic fishes collected in a 0–1000 m column was 1·1/m2 during the day and 1·5/m2 during the night; wet-weight averaged 2·4 and 3·6 g/m2 for day and night collections, respectively.

Vertical distribution and migration of fishes of the lower mesopelagic zone off Oregon

An exceptionally large midwater trawl (50 m2 mouth area) with 5 opening and closing codends was towed horizontally in the lower mesopelagic zone at depths of 500, 650, 800 and 1000 m off Oregon (USA) from 1–6 September, 1978. In comparison to more conventional trawls, ours collected more fish, including rare species and large individuals of common species. Comparison of collections made by day and by night revealed that 12 of the 15 most common species probably migrated vertically. Bathylagus milleri evidently migrates from 650 m during the day to 500 m at night. Cyclothone acclinidens and C. atraria were more abundant by night than by day at 800 m, possibly due to an upward migration from deeper depths at night. C. pseudopallida, C. signata, Chauliodus macouni, Tactostoma macropus and Stenobrachius leucopsarus were more abundant by day than by night at 500 m, suggesting that they migrated out of this depth horizon at night. Lampanyctus regalis, and large individuals of B. pacificus were more abundant by night than by day at 500 m, possibly because they migrated upward from near 650 m. Many species exhibited trends of increasing or decreasing size with depth, and several species showed changes in migratory behavior with size. For example, only small (<240 mm) T. macropus migrated vertically, whereas only large (>110 mm) B. pacificus appeared to migrate. Depths of maximum abundance of congeneric species were usually separated. B. milleri and B. pacificus had similar distributions by day, but the former was shallower at night. S. leucopsarus tended to live shallower than S. nannochir both day and night. Congeners always occurring at the same depth were Cyclothone pseudopallida and C. signata (both most abundant at 500 m) and C. acclinidens and C. atraria (both most abundant at 800 m).

Marine nekton off Oregon and the 1997-98 El Niño

Abstract Several species of migratory, warm-water, oceanic fishes invaded Oregon waters during the summer of 1997. Also, the jumbo squid (Dosidicus gigas), common in the eastern tropical Pacific, was reported for the first time in 1997 and was caught in large numbers. The occurrence of these oceanic nekton was associated with inshore advection of anomalously warm water. During 1998, after arrival of the main El Nino signal, some warm-water coastal fishes appeared off Oregon. However, unlike observations off California, fewer species of warm-water coastal fishes were noted during the 1997–98 El Nino than during the 1982–83 El Nino.

Comparison of the feeding habits of migratory and non-migratory Stenobrachius leucopsarus (Myctophidae)

Stenobrachius leucopsarus, the most abundant species of myctophid fishes off Oregon, USA, has a bimodal distribution at night, with a peak of abundance in the upper 100 m composed of diel vertical migrants, and another peak at 300 to 500 m composed of fish that did not migrate the night they were caught. We compared the feeding habits of these two groups of fish in an attempt to learn if deep fish migrated to surface waters. Low similarity of diets, differences in the rank order of common prey, and similar states of stomach fullness and digestion of prey suggest that fish captured in deep water at night probably did not feed exclusively in shallow water on previous nights. They probably fed in deep water. The similarity in food habits between deep and shallow fish is most readily explained by daytime feeding by fish in deep water and by broad vertical distributions of prey.

Abundance and Distribution Patterns of Nekton and Micronekton in the Northern California Current Transition Zone

The epipelagic and mesopelagic nekton communities of the northern California Current have been sampled somewhat continuously over the last four decades with bottom and pelagic trawls, small midwater trawls, and purse seines. We review the zoogeography and community and environmental associations of the dominant pelagic micronekton and nekton species in this region with a view to understanding their role in this dynamic marine ecosystem. As is typical of many upwelling eastern boundary current regions, the pelagic biomass is dominated by a few species that fluctuate dramatically through time. The abundance trends of pelagic nekton caught in this region demonstrated large-scale ecosystem changes about the time of the regime shifts of 1976/77 and 1989 and possibly another beginning in 1999. The rapidity of the changes in composition indicates that the response was due to a change in migration or distribution patterns as opposed to recruitment patterns. The 1989 regime shift led to a dramatic increase in sardine and a decrease in anchovy populations. The most pronounced interannual signals were attributed to strong El Niño/Southern Oscillation (ENSO) conditions in 1983 and 1998 that altered the latitudinal ranges and proximity to the coast of many pelagic species. Variations in abundance and cross-shelf distribution patterns were noted for both pelegic nekton and micronektonic from surveys off California, Oregon, and Washington.