Cordell Bank National Marine Sanctuary comprises a diversity of habitats that harbor characteristic fish assemblages. Ocean processes, physical habitat and depth greatly influence the composition and distribution of species that inhabit this area. The habitats in Cordell Bank National Marine Sanctuary support an abundance of fishes, with verified observations of more than 180 species within the sanctuary.
The sanctuary lies within the California Current ecosystem – one of only four major eastern boundary currents in the world. Boundary currents occur over narrow continental shelves in temperate areas of the world and are characterized by surface flow toward the equator, coastal upwelling and high primary productivity. The sanctuary’s temperate fish fauna falls within the Oregonian zoogeographic province, which extends from Point Conception (near Santa Barbara, CA) to Southeast Alaska.
The centerpiece of the sanctuary is Cordell Bank, an elliptically shaped 68-square-kilometer (26-square-mile) submerged island. Manned submersible surveys of the bank community conducted during the fall of 2002 yielded 70 fish species (or species groups) representing 21 families. Rockfishes were the most dominant family, accounting for 27 species and 95 percent of all individuals. Of these, young-of-year (YOY) rockfishes were the most numerous, accounting for 64 percent of all rockfishes.
Fish distribution and abundance on the bank are related to habitat type, depth and location. For example, the shallow, high-relief, rocky pinnacle regions of the central bank are dominated by schooling species such as YOY rockfishes and pygmy, widow and yellowtail rockfishes as well as more solitary species, such as rosy rockfish.
Mid-depth boulder-rock habitats are characterized by the numerically dominant pygmy, squarespot and yellowtail rockfishes as well as rosy and greenspotted rockfishes, lingcod, painted greenling and blackeyed goby. Boulder habitats at the edge of the bank have high densities of large commercially important species, such as bocaccio, yelloweye and canary rockfishes as well as lingcod. Cordell Bank is a significant locus for the recruitment of juvenile rockfishes.
Although the sanctuary is best known for Cordell Bank, the bank actually only occupies approximately 5 percent of the sanctuary’s total area. The remaining habitat is primarily unconsolidated soft bottom containing silty sediments found on the continental shelf and slope.
While limited scientific study has been directly focused on the ichthyofauna of the sanctuary’s soft-bottom habitat, considerable information has been gathered and analyzed on the fish assemblages that inhabit the continental shelf and slope habitats of the Northeastern Pacific Ocean, owing to the value of the fishery resources that exist there.
Along the West Coast of North America, the distribution of marine organisms varies with latitude, generally due to regional changes in water temperature. Fishes that inhabit the continental shelf and upper slope within California have been grouped into four latitudinal regions: 1) northern California; 2) north-central California, 3) south-central California; and 4) southern California. Cordell Bank sanctuary lies within the north-central region, which spans from Cape Mendocino to San Simeon.
In addition to latitudinal changes in fish assemblages, groups can also be defined by depth, since fishes respond to changes in environmental conditions such as light intensity, temperature and oxygen concentration – factors that are depth-dependent. Therefore, fish assemblages in soft-bottom habitats are grouped by both latitude and depth, defined as middle shelf (30 to 100 meters, or 100 to 325 feet), outer shelf (100 to 200 meters) and mesobenthal slope (200 to 500 meters).
While soft-bottom areas are the domain of flatfishes, skates and rays, a number of fusiform (spindle-shaped) fishes such as croakers, rockfishes, sculpins and surfperches also thrive in this habitat. Ecologically significant fishes most commonly found in the middle shelf include big skate, longspine combfish, shortbelly rockfish and pacific sand dab. In the outer shelf, fishes more commonly seen in research collections included the stripetail rockfish, greenstriped rockfish and slender sole. Beyond the shelf break in the mesobenthal slope region, fishes most commonly found include poachers, splitnose rockfish and sablefish. Among the fishes that inhabit all three depth zones are lingcod, spotted cusk eel, plainfin midshipman and Dover sole.
Most of the water column habitat within the sanctuary overlies the continental shelf and makes up the coastal pelagic realm. While few directed studies have been performed at this sanctuary, a considerable amount is known about California’s coastal pelagic fishes.
Fishes that occupy the shallow epipelagic zone (depth to 50 meters) are relatively large, active, fast-growing and long-lived. Fishes commonly placed in this group include sharks (blue, white and thresher), jack mackerel, Pacific mackerel and Pacific hake.
A study of fishes captured in the California/Oregon drift gillnet fishery found that the common mola ranked first in catch, suggesting that this species may be among the most common pelagic fishes in the sanctuary. The commercially important northern anchovy and Pacific sardine have alternated as the most abundant fishes of the coastal pelagic realm off California throughout recent history.
Anadramous fishes, including coho and chinook salmon and steelhead, seasonally occur in the sanctuary. We also know that the early life-history stages of many fishes – such as lingcod, rockfishes and many flatfish species – occupy the epipelagic zone.
Mesopelagic fishes (those found below the epibenthic zone, to depths of 1,000 meters) are relatively small, slow-growing and long-lived. Representatives of this group include the lanternfishes, hatchetfishes and deep-sea smelts. Many mesopelagic fishes make diurnal vertical migrations to feed and often find themselves being taken by larger predators.
The fish communities of this sanctuary respond to both natural and human-caused environmental stresses. Although these stressors are listed separately below, synergies between them obviously exist. Such synergies can be particularly devastating to fish populations and cause steep declines, such as occurred in the California sardine population, which was hit with the combination of cooling ocean temperatures and fishing pressure in the late 1940s.
Fishing activity has been conducted at Cordell Bank since the late 1800s. For more than a century, Cordell Bank has been a destination fishing ground for both sport and commercial fishermen.
Due to intensive fishing of deep-water species (particularly groundfishes) in the 1980s, many populations were depleted. A number of rockfish stocks began a precipitous decline caused by fishing pressure and periodic recruitment failure (due to unfavorable oceanographic conditions).
Consequently, some species – including cowcod and canary, yelloweye and darkblotched rockfishes – have been declared overfished by the Pacific Fishery Management Council (PFMC). Current restrictions implemented by the PFMC to rebuild these stocks have greatly limited fishing activity within the sanctuary. It may take decades for some of these stocks to rebuild.
El Niño/Southern Oscillation (ENSO) refers to periodic cycling between anomalously warm (El Niño) and cool (La Niña) ocean water temperatures that spread across the equatorial Pacific Ocean. These temperature anomalies indicate perturbations in the ocean and atmosphere that are manifested over broad scales, including the California Current ecosystem.
An El Niño is signaled at the sanctuary by increases in ocean temperature and sea level, enhanced onshore and northward ocean current flow, and reduced coastal upwelling. Since 1800, there have been approximately 48 El Niño events, with a mean frequency of one event every 4.1 years. Their intensity is variable.
Biological effects from an El Niño include decreased primary productivity, which often cascades to recruitment failures of ecologically important fish species – particularly rockfishes. In addition, fish species with tropical affinities that are naturally associated with warm water (e.g., billfishes) appear further north.
Like an ENSO event, the Pacific Decadal Oscillation (PDO) comprises a warm and a cool interval, but over a longer period of time. PDOs are periods of sustained climate conditions associated with shifts in ecosystem production regimes in cycles of about 50 years.
Biological patterns are related to these climate ‘regime shifts.’ For example, the alternating 20- to 30-year periods of cool and them warm periods in the Pacific track fluctuations in the alternating abundances of anchovies (cool periods) and sardines (warm periods).
As evidence has mounted in recent decades for accelerated global warming, increased attention has been focused on the potential impacts of this change on marine organisms. In the northeastern Pacific, the increase in sea surface temperature has already been documented.
Researchers predict that a monotonic gradual increase in ocean temperature will cause a northward shift in the ranges of at least some species. It is also possible that some fishes will move to deeper, cooler water.
Of course, not all species will shift their ranges in response. If their rate of northward migration is too slow to keep pace with the changes, they will adapt, live under suboptimal conditions or perhaps go locally extinct.
Fishery-independent monitoring is being conducted in the sanctuary in the rocky, pelagic and soft-bottom habitats.
Benthic Community Characterization and Monitoring
The Cordell Bank National Marine Sanctuary, in partnership with the National Oceanic and Atmospheric Administration (NOAA) Fisheries Laboratory in Santa Cruz, the U.S. Geologic Survey (USGS), California Academy of Sciences and the California Department of Fish and Game, conducted a long-term study to classify habitats and monitor fishes and macro-invertebrates on and around Cordell Bank. Benthic transects were monitored annually from 2002 to 2005. The sanctuary plans to continue the monitoring program in the future; however, this is dependent upon funding levels.
Underwater surveys of fishes, invertebrates and their habitats were conducted on and around Cordell Bank using direct observation and video-transect methods from an occupied research submersible (Delta). Transects were distributed over the bank to sample all bank habitats and associated biota.
The data provided sanctuary staff with a species inventory of fishes and benthic invertebrates. Long-term data may be used to identify habitat affinities for species complexes, develop habitat suitability models and provide a foundation to evaluate change over time.
Rockfish Mid-Water Trawl Pre-Recruit Survey
Rockfish productivity is tightly related to recruitment success. During May and June every year since 1983, the NOAA Fisheries Southwest Fisheries Science Center (SWFSC) has performed an annual survey of the distribution and abundance of pelagic juvenile young-of-the-year (YOY) rockfishes. The survey extends from San Diego in the south to the northern boundary at Delgada, just south of Cape Mendocino.
YOY rockfish catches show a large degree of temporal variability. The temporal abundance patterns were found to be similar among many of the different rockfish species. This survey also collects information on marine mammal and seabird distributions
West Coast Bottom-Trawl Survey
The NOAA Fisheries Northwest Fisheries Science Center (NWFSC) conducts annual bottom-trawl surveys of U.S. West Coast groundfish resources. These surveys are designed to provide resource managers with fishery-independent data about the distribution, abundance and biological characteristics of commercially important fish species, particularly Pacific hake, sablefish, and many of the shelf and slope rockfish species.
Survey methodology has changed somewhat since the initiation of studies by the NOAA Fisheries Alaska Fisheries Science Center (AFSC), which conducted studies triennially from 1977 until 2001. Currently, NWFSC conducts annual surveys from the Canadian border to the Mexican border, using chartered commercial fishing vessels towing standardized nets. Separate shelf (55 to 500 meters) and slope (183 to 1,280 meters) surveys are performed.
Cordell Bank Seafloor Mapping
Researchers from California State University Monterey Bay (CSUMB) have collected and processed high-resolution backscatter and bathymetry data of Cordell Bank and surrounding soft-bottom areas. Researchers from CSUMB and the USGS used these data (collected in 2005) to develop a benthic habitat map of Cordell Bank and the surrounding region.
Habitat characteristics such as slope, habitat complexity, depth and substrate type were used to describe the physical habitats that make up Cordell Bank and to relate these seafloor features to benthic community patterns, particularly demersal rockfish populations.
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