Paul C. Fiedler

Albacore tuna catch distributions relative to environmental features observed from satellites

Abstract Albacore tuna catch data from the summer of 1981 are displayed on concurrent satellite images of sea surface temperature and phytoplankton pigment concentration, from the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) and the Nimbus-7 Coastal Zone Color Scanner (CZCS), respectively. During 3 week-long periods off California, intense fishing activity and larger catches, indicating aggregations of albacore, were located within pockets of warm, blue oceanic water intruding into the boundary between oceanic and cooler greenish coastal waters. A relatively productive oceanic region, defined by a color front visible in a CZCS image, was the site of albacore aggregation in waters several hundred miles offshore during the first 2 weeks of September 1981.

Tuna aggregation and feeding near fronts observed in satellite imagery

Abstract Stomach contents of albacore ( Thunnus alalunga ) and skipjack ( Katsuwonus pelamis ) caught off California in August 1983 showed they were feeding on juvenile northern anchovy ( Engraulis mordax ), other fishes, and planktonic crustaceans. The distribution and diet of these predators were related to mesoscale frontal features visible in satellite sea surface temperature and phytoplankton pigment imagery. Albacore were caught in the vicinity of a filament of cold, pigment-rich surface water that varied with the intensity of coastal upwelling on time scales of several days. Stomachs of albacore caught closer to the filament contained relatively more juvenile anchovy and fewer pelagic red crabs ( Pleuroncodes planipes ). Skipjack were caught in warm water in the Southern California Bight, north of their normal range due to El Nin˜o warming. They appeared to be feeding most successfully near the strong frontal boundary of a productive, cold water mass south of Pt. Conception, where dense patches of euphausiids were available. Both species were feeding near variable, mesoscale centers of high productivity where prey abundance may be enhanced.

The annual cycle and biological effects of the Costa Rica Dome

The Costa Rica Dome is similar to other tropical thermocline domes in several respects: it is part of an east–west thermocline ridge associated with the equatorial circulation, surface currents flow cyclonically around it, and its seasonal evolution is affected by large-scale wind patterns. The Costa Rica Dome is unique because it is also forced by a coastal wind jet. Monthly climatological fields of thermocline depth and physical forcing variables (wind stress curl and surface current divergence) were analyzed to examine the structure and seasonal evolution of the dome. The annual cycle of the dome can be explained by wind forcingin four stages: (1) coastal shoaling of the thermocline off the Gulf of Papagayo during February–April, forced by Ekman pumping on the equatorward side of the Papagayo wind jet; (2) separation from the coast duringMay–June when the intertropical converg ence zone (ITCZ) moves north to the countercurrent thermocline ridge, the wind jet stops, and the North Equatorial Countercurrent extends toward the coast on the equatorward flank of the ridge; (3) countercurrent thermocline ridging duringJuly–November, when the dome expands to the west as the countercurrent thermocline ridge shoals beneath a band of cyclonic wind stress curl on the poleward side of the ITCZ; and (4) deepening duringDecember–January when the ITCZ moves south and strong trade winds blow over the dome. Coastal eddies may be involved in the coastal shoalingobserved duringFebruary– March. A seasonally predictable, strong, and shallow thermocline makes the Costa Rica Dome a distinct biological habitat where phytoplankton and zooplankton biomass are higher than in surrounding tropical waters. The physical structure and biological productivity of the dome affect the distribution and feeding of whales and dolphins, probably through forage availability. Published by Elsevier Science Ltd.

Blue whale habitat and prey in the California Channel Islands

Abstract Whale Habitat and Prey Studies were conducted off southern California during August 1995 (WHAPS95) and July 1996 (WHAPS96) to (1) study the distribution and activities of blue whales and other large whales, (2) survey the distribution of prey organisms (krill), and (3) measure physical and biological habitat variables that influence the distribution of whales and prey. A total of 1307 cetacean sightings included 460 blue whale, 78 fin whale and 101 humpback whale sightings. Most blue whales were found in cold, well-mixed and productive water that had upwelled along the coast north of Point Conception and then advected south. They were aggregated in this water near San Miguel and Santa Rosa Islands, where they fed on dense, subsurface layers of euphausiids both on the shelf and extending off the shelf edge. Two species of euphausiids were consumed by blue whales, Thysanoessa spinifera and Euphausia pacifica , with evidence of preference for the former, a larger and more coastal species. These krill patches on the Channel Island feeding grounds are a resource exploited during summer–fall by the world’s largest stock of blue whales.

Satellite Observations of the 1982-1983 El Niño Along the U.S. Pacific Coast

Satellite infrared temperature images illustrate several effects of the 1982-1983 El Ni�o: warm sea-surface temperatures with the greatest anomalies near the coast, weakened coastal upwelling, and changes in surface circulation patterns. Phytoplankton pigment images from the Coastal Zone Color Scanner indicate reduced productivity during El Ni�o, apparently related to the weakened coastal upwelling The satellite images provide direct evidence of mesoscale changes associated with the oceanwide El Ni�o event.

Assessing the Risk of Ships Striking Large Whales in Marine Spatial Planning

Marine spatial planning provides a comprehensive framework for managing multiple uses of the marine environment and has the potential to minimize environmental impacts and reduce conflicts among users. Spatially explicit assessments of the risks to key marine species from human activities are a requirement of marine spatial planning. We assessed the risk of ships striking humpback (Megaptera novaeangliae), blue (Balaenoptera musculus), and fin (Balaenoptera physalus) whales in alternative shipping routes derived from patterns of shipping traffic off Southern California (U.S.A.). Specifically, we developed whale-habitat models and assumed ship-strike risk for the alternative shipping routes was proportional to the number of whales predicted by the models to occur within each route. This definition of risk assumes all ships travel within a single route. We also calculated risk assuming ships travel via multiple routes. We estimated the potential for conflict between shipping and other uses (military training and fishing) due to overlap with the routes. We also estimated the overlap between shipping routes and protected areas. The route with the lowest risk for humpback whales had the highest risk for fin whales and vice versa. Risk to both species may be ameliorated by creating a new route south of the northern Channel Islands and spreading traffic between this new route and the existing route in the Santa Barbara Channel. Creating a longer route may reduce the overlap between shipping and other uses by concentrating shipping traffic. Blue whales are distributed more evenly across our study area than humpback and fin whales; thus, risk could not be ameliorated by concentrating shipping traffic in any of the routes we considered. Reducing ship-strike risk for blue whales may be necessary because our estimate of the potential number of strikes suggests that they are likely to exceed allowable levels of anthropogenic impacts established under U.S. laws.

Physical and biological effects of Los Niños in the eastern tropical Pacific, 1986–1989

Abstract The eastern tropical Pacific Ocean was surveyed in August–November 1986, 1987, 1988 and 1989 as part of a long-term program to monitor dolphin stocks. Temperature, salinity, chlorophyll and nutrients were monitored to help interpret variability in dolphin stock estimates. The four surveys reveal major environmental changes during the moderate 1987 El Nino and the cold La Nina episode that followed in 1988. During the “onset” phase of El Nino in fall 1986, surface temperatures were up to 1.5°C above normal in equatorial water, but near normal in tropical water north of the equator. The equatorial thermocline ridge was deepened by 10–30 m. During the “mature” phase of El Nino in fall 1987, surface temperatures anomalies were up to +2.5°C in equatorial water and about +1°C in tropical water. Thermocline topography was anomalously flat. Surface chlorophyll and nutrient concentrations declined by 11–48% compared to 1986, with the greatest declines occurring in coastal and equatorial upwelling systems and along the countercurrent thermocline ridge. During La Nina 1988, equatorial surface temperatures were up to 2.5°C below normal and the equatorial thermocline ridge was 10–50 m more shallow than normal. Chlorophyll and nitrate concentrations increased by 58–65% compared to 1987. In 1989, surface temperature was within ±1°C of normal throughout the study area and chlorophyll concentrations were similar to those observed in 1986. Changes in nutrient availability and biological productivity during the El Nino/La Nina cycle were caused by variations in both the rate of wind-driven upwelling and in the nutrient content of subsurface water entrained by upwelling.

Effects of California El Niiio 1982-1984 on the northern anchovy

El Nitio caused physical and biological changes in the northern anchovy habitat off southern California. Anomalous sea surface temperatures, surface currents, mixed layer depths, and plankton biomass levels began to appear in late 1982 and persisted into 1984. Growth of juvenile and adult anchovy slowed during El Nitio, probably due to reduced availability of zooplankton prey. A decrease in size-at-age in early 1983, with a recovery in late 1984, can be explained by movements of the stock and the latitudinal cline in size-at-age. Spawning range expanded in 1983 due to shifts in sea surface temperature boundaries. Early larval mortality was unusually high in the yolk-sac stage. Fecundity per unit spawning biomass was low in 1983, due primarily to a high proportion of first-year spawners. Size-at-age was very low by spring 1984, but specific fecundity was surprisingly high. Although El Nifio had a variety of significant effects on the northern anchovy, the stock seems to have recovered in 1985.

Variability of the Columbia River plume observed in visible and infrared satellite imagery

Variability of the Columbia River plume in coastal waters off the northwestern United States, 1979-1985, was observed in sea surface temperature and phytoplankton pigment images derived from Advanced Very High Resolution Radiometer and Coastal Zone Colour Scanner data. The orientation, shape, intensity and relative temperature of the plume vary in response to coastal winds and wind-driven surface currents. From October to April, plume water is oriented northward along the coast. Following the spring transition in April or May, the plume is oriented southward, either adjacent to the coast or offshore. Transition between the winter and summer forms can be observed in the satellite imagery. Brief reversals of the prevailing seasonal winds cause rapid changes in the orientation and shape of the plume. Remote sensing of the Columbia River plume offers valuable information for oceanographic studies and fisheries management in the region. Derivation of an appropriate visible-infrared signature for plume waters and tracking of tidal pulses in the plume is suggested as a promising direction for future research.

Seasonal and interannual variability of coastal zone color scanner phytoplankton pigments and winds in the eastern tropical Pacific

Time series of phytoplankton pigment concentration along coastal and oceanic transects in the eastern tropical Pacific Ocean were derived from coastal zone color scanner monthly composite data for November 1978 through June 1986. Seasonal and interannual variability made up about half the total variance of the time series. Seasonal cycles typically consisted of a spring minimum and fall maximum, although many local variations were observed. Interannual variability was as great as seasonal variabillity and was dominated by the 1982-1983 El Nino event