Regional Fisheries Oceanography of the California Current System: The CalCOFI program

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Reuben Lasker ed. Fisheries and fishing topic areas.

A Sixteen-year Decline in Dissolved Oxygen in the Central California Current

Aquaculture Diversity of fish Fish diseases and parasites Fish farming Fisheries management Fisheries science Individual fishing quota Sustainable fishery Overfishing Wild fisheries. Artisanal fishing Fisherman Fishing vessel History of fishing. Angling Big-game fishing Catch and release Fishing tournaments Fly fishing. Fish ponds Fishing banks Fishing villages Marine habitats. Glossary Index Outline Category. Categories : Oceanographic organizations Non-profit organizations based in California Oceanographic Time-Series Agriculture in California Fisheries and aquaculture research institutes Fishing in the United States Environmental impact of fishing Environmental issues in California Environmental disasters in the United States Organizations established in establishments in California.

Hidden categories: Webarchive template wayback links All articles with dead external links Articles with dead external links from July Articles with permanently dead external links. Namespaces Article Talk. Views Read Edit View history. Languages Add links. By using this site, you agree to the Terms of Use and Privacy Policy. Paired ringed nets towed obliquely from a depth of approx. Water is filtered through the micron nylon mesh nets with a mouth diameter of 0.

The bongo net is designed to collect mesozooplankton and its samples are critical in determining egg and larval mortality. The data is used in the Daily Egg Production Method for estimating the spawning stock biomass of sardine. Comparisons of different net methodology and potential ramifications have been published. The Pairovet is used to collect ichthyoplankton via vertical tows from 70m to the sea-surface using paired 0.

The smaller nylon mesh is specially designed to retain fish eggs which are found in the upper 70m. Ship pitch and roll, water currents, net clogs, wire angle, and dragging in the neuston layer all are possible sources of variance and error. The manta net was developed to sample the sea-surface over a range of oceanic conditions.

Regional Fisheries Oceanography of the California Current System

The net is able to veer away from the side of the vessel to avoid ship wake and have a mouth unobstructed by a bridle that might cause avoidance by organisms. A variety of fish species have a prolonged transformation between larval and juvenile stages of development during which time the organisms can be found in the surface layer. Trawl aimed to sample and collect pelagic fish.

The net retains juveniles and certain large larval fish. Recently the net has been fastened with a marine mammal excluder device MMEL to decrease the amount of mammalian impact and mortality. Trawl designed to sample juvenile pelagic fish which can avoid other sampling nets by mid-water trawls. The primary target is mid-sized anchovy 15 — 60mm. The net filters about 7,m 3 or times as much water per tow as a standard bongo net.

Trawl designed to capture a multitude of mesopelagic organisms including: krill , late larval and juvenile fishes, and micronekton.

Introduction

Collects juvenile and small fish assemblages in conjunction with multifrequency acoustics to estimate the distribution and biomass of sampled species. The MOHT has a 5. In a few cases, instead of the primary temperature and salinity observations, the temperature and salinity measurements from a secondary CTD with a more realistic profile were used.

To display the variability in dissolved oxygen over time, monthly averages of dissolved oxygen values were used, where data were first binned and averaged for each day if repeat casts were taken , then month. Months without data in the time-series were noted.

Regional Fisheries of the California Current System: The CalCOFI Program | Oceanography

In-situ temperature and salinity were used to calculate alongshore geostrophic velocities. Temperature and salinity observations were binned to 5-meter depth intervals and by station. The reference depth was chosen as a compromise between depth and the availability of temperature and salinity observations. The CalCOFI lines run approximately normal to the coastline, so we considered the cross-transect direction to be alongshore. At Line 67, alongshore phenomena are roughly a coordinate rotation counterclockwise of 30 degrees.

yjoloweqakit.tk Data to plot the bathymetry of Line 67 came from two sources. To more clearly understand ocean mixing processes and to remove the influence of heave, or isopycnal motions with no heat and salinity exchange with the environment as defined in Huang 32 , although the term originates much earlier , oxygen variability was analyzed along potential density surfaces. With regard to transect stations, a chi-squared test for independence was used to determine if the oxygen values for each density were independent of the station number.

To investigate spatial patterns of the rate of change in dissolved oxygen, changes in time of oxygen concentration were assessed at observations binned to 0. Station 50 was removed from analysis due to low number of observations. We used anomalies to calculate the correlation and significance, subtracting seasonal averages from monthly averaged observations. To map the calculations back to coordinates for depth and distance offshore, statistics along isopycnals were mapped to the average depth of each isopycnal in the analysis over the data collection period.

To create the vertical profile of rates of decline, rate of decline was calculated with a linear regression model of the oxygen data at each bin of 0. The profile displays the rate of decline as calculated on the average potential density found at each depth. To investigate potential drivers for oxygen dynamics, oxygen time-series on specific potential densities were compared to climate indices important for ocean dynamics in the Pacific Ocean with variations on the timescale of 4—10 years using correlation.

The NPGO is the second mode of sea surface height variability in the North Pacific which is related to the strength of the subtropical gyre circulation The index is calculated from the geostrophic wind stress which is derived from sea level pressure from the U. To compare climate index and dissolved oxygen variability, variation in indices and oxygen time-series were normalized by standard deviations and compared on an annual basis.

The annual means used the average of the normalized monthly anomalies for dissolved oxygen observations and the average of the normalized monthly or seasonal values for the climate indices. In addition, seasonal time-series were defined in three-month intervals with winter as December through February. A major complication in correlation of geophysical and climate phenomena is autocorrelation of time-series data 34 , Consequently, all correlations were tested for lag-1 autocorrelation.

If significant autocorrelation were detected, the true significance of the correlation was corrected by using an effective sample size when calculating the t-statistic and as the sample size to calculate the p-value The effective sample size, n e , is defined according to the lag-1 autocorrelation coefficient r 1 and the original sample size n by:.


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We attempted to better understand why the dissolved oxygen in Central California had declined along Line 67 using a box model to estimate local respiration, source water dissolved oxygen concentration changes, and changes in the magnitude of currents acting in concert. The initial concentrations of oxygen in nearshore and offshore boxes and the initial alongshore geostrophic velocity were taken from Line 67 observations.

Initial concentrations of source waters in dissolved oxygen and salinity were taken from the World Ocean Atlas WOA The gradients in the model were balanced at steady state using salinity; we adjusted the source water salinity by a correction factor and used an empirical relationship between salinity and oxygen 37 to subsequently adjust the source water oxygen. Additional information on the setup of the box model is provided in the supplementary materials. The datasets analyzed during the current study are available from the corresponding author on reasonable request.

Wyrtki, K. The oxygen minima in relation to ocean circulation. Keeling, R. Ocean deoxygenation in a warming world. Annual review of marine science 2 , — Gruber, N. Warming up, turning sour, losing breath: ocean biogeochemistry under global change. The change in oceanic O 2 inventory associated with recent global warming. Deutsch, C. Centennial changes in North Pacific anoxia linked to tropical trade winds. Science , — McClatchie, S.

SearchWorks Catalog

Oxygen in the Southern California Bight: Multidecadal trends and implications for demersal fisheries. Schmidtko, S. Decline in global oceanic oxygen content during the past five decades. Chan, F. Emergence of anoxia in the California Current large marine ecosystem. Grantham, B. Upwelling-driven nearshore hypoxia signals ecosystem and oceanographic changes in the northeast Pacific.

Nature , — Pierce, S. Declining Oxygen in the Northeast Pacific. Journal of Physical Oceanography 42 , — Bograd, S. Changes in source waters to the Southern California Bight. Oxygen declines and the shoaling of the hypoxic boundary in the California Current. Geophysical Research Letters 35 Emerson, S. The biological pump in the subtropical North Pacific Ocean: Nutrient sources, Redfield ratios, and recent changes. Ono, T. Temporal increases of phosphate and apparent oxygen utilization in the subsurface waters of western subarctic Pacific from to Watanabe, Y.

Probability of a reduction in the formation rate of the subsurface water in the North Pacific during the s and s. Mecking, S. Climate variability in the North Pacific thermocline diagnosed from oxygen measurements: An update based on the U. Whitney, F. Persistently declining oxygen levels in the interior waters of the eastern subarctic Pacific.