Cordell Bank Habitat Characterization and Biological Monitoring
Principal Investigator(s)
Dale Roberts (Cordell Bank National Marine Sanctuary)
Lisa Etherington (Cordell Bank National Marine Sanctuary)
Tara Anderson (Geoscience Australia)
Start Date 2002-01-01
Funding --
Overview
NOAA proposed National Marine Sanctuary status for Cordell Bank in part because “Cordell Bank supports an extraordinarily diverse and abundant community of marine life.” In 2002, sanctuary staff and collaborators initiated a program to quantify the diversity, distribution and abundance of habitats, fishes and invertebrates on and around Cordell Bank and follow these parameters over time. Underwater surveys of macrofauna (fish and invertebrates) and habitats are conducted using direct observation and video transects from an occupied submersible (Delta). Initially, the data has provided Cordell Bank sanctuary with a species inventory of fishes and benthic invertebrates associated with the Bank. Analyses to date have examined fish-habitat relationships as well as the role of structure-forming invertebrates as habitat for fish in the region of the Bank. Transects have been repeatedly sampled in 2002, 2003, 2004, and 2005. Long term data will be used to evaluate change in population characteristics (e.g., abundance, individual size, distribution) over time. The results of this study illustrate that Cordell Bank includes a diverse array of seafloor habitats that support rich benthic communities. The bank has also been shown to be a locus for rockfish recruitment.
Summary to Date
In 2002, 70 fish species (or species-groups) representing 21 families were enumerated (Anderson et al. In Prep). During this year, rockfishes were the most dominant family, accounting for 27 species and 95% of all individuals. Of these, young-of-year (YOY) rockfishes were the most numerous, accounting for 64% of all rockfishes. It appears that Cordell Bank is a significant locus for the recruitment of juvenile rockfishes. The 2002 data showed that the distribution and abundance of fishes were related to habitat type, depth, and location. In general, fish abundance was highest in the shallowest areas as well as the upper Bank region, with abundance decreasing with distance from the center of the Bank. A variety of habitats were described, including pinnacles, rocky-reefs, boulder-fields, cobbles, sand, and mud.
The shallow, high-relief, rocky pinnacle regions of the central Bank were dominated by schooling species such as YOY rockfish, pygmy (Sebastes wilsoni), widow (S. entomelas), and yellowtail (S. flavidus) rockfishes, along with more solitary species, such as rosy rockfish (S. rosaceus). Mid-depth boulder-rock habitats were characterized by the numerically dominant pygmy, squarespot (S. hopkinsi), and yellowtail rockfishes, as well as rosy (S. rosaceous), and greenspotted (S. chlorostictus) rockfishes, lingcod (Ophiodon elongates), painted greenling (Oxylebius pictus), and blackeye goby (Coryphopterus nicholsi). Boulder habitats at the edge of the Bank also contained higher densities of large commercially important species, such as bocaccio (S. paucispinis), yelloweye (S. ruberrimus), and canary (S. pinniger) rockfishes, and lingcod. Soft sediment habitats also varied in their species assemblages. Coarse sands were characterized by sanddabs (family Bothidae, Citharichthys spp.), poachers (family Agonidae), and combfish (family Zaniolepididae). In contrast, mud habitats (200-300m) were characterized by flatfish, spotted ratfish (Hydrolagus colliei), poachers, combfish, and stripetail rockfish (S. saxicola). In addition to mud-associated species, deep vertical mud walls had high numbers of grotto-dwelling hagfish.
Video transects were also examined to identify the habitat associations of structure-forming invertebrates (including sponges, gorgonian corals, and crinoids) as well as how these organisms may influence the distribution of structure-oriented fish species by acting as biogenic habitat (Pirtle 2005). Structural invertebrates were distributed in distinct physical habitats within three general benthic communities: 1) rock ridge and boulder community; 2) sand community; and 3) mud community. Physical habitat and lifestyle requirements most likely determine the composition and distribution of structure-forming invertebrate communities on Cordell Bank. Several fishes were observed in close proximity with structural invertebrates more than expected by chance occurrence in shared habitats. Fish-structural invertebrate associations were distinguished behaviorally and observed to be important in habitats lacking structural relief or complexity and in open and exposed habitats.
During biological surveys of the Bank, a significant amount of derelict fishing gear was observed. Most of the gear was long line gear that snagged on the bank, while lost gill nets were observed streaming into the water column. In 2002 alone, during surveys conducted on cobble, rock, boulder and high-relief rocky habitat on Cordell Bank, fishing gear was observed on 90% of the transects, with an average density of one piece of gear observed every 670 linear meters. Transects were initially established to sample a variety of habitats with no realization that derelict fishing gear was so prominent on the Bank. Since transects were fixed, we did not document the overall extent and the full impact of this abandoned gear.
Work is in progress to examine temporal variability in fish abundance on Cordell Bank, which will determine the temporal resolution of future sampling needed to detect trends in abundance. Future work will also involve an analysis of spatial patterns and habitat associations of deep water coral and sponge assemblages on the Bank.
Monitoring Trends
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Discussion
Literature Cited
Anderson, T.J., D.A. Roberts, D.F. Howard. In Prep. The distribution, abundance,
and habitat relationships of deep-water groundfishes on Cordell Bank, California. To be submitted to Marine Biology.
Pirtle, J.L. 2005. Habitat-based assessment of structure-forming megafaunal
invertebrates and fishes on Cordell Bank, California. M.S. Thesis, Washington State University. 64 pp.
Collaborators
Dan Howard (Cordell Bank National Marine Sanctuary)
Jodi Pirtle (University of Alaska-Fairbanks, Juneau Center)
Mary Yoklavich (NOAA, National Marine Fisheries Service)
Study Parameters Click here to view the parameters measured in this study.
Study Methods Click here to view the methods and materials used in this study.
Images and Documents Representative structure-forming invertebrates at Cordell Bank: (a) crinoids (Florometra serratissima), (b) the anemone Urticina piscivora, (c) gorgonian (Swiftia sp.), (d) barrel sponges (> 1 m height) and vase sponges, (e) foliose sponges and Stylaster californicus, and (f) brittle stars in sand with arms extended. Photos: CBNMS The combination of complex rocky substrates and large structure-forming invertebrates, such as gorgonians, sponges, and sea anemones, provide habitat for fish on the Bank. Photo: Jodi Pirtle/CBNMS Rockfish, such as yellowtail, widow and blue rockfish, can been found above the pinnacles of Cordell Bank. Photo: Kip Evans Location of derelict fishing gear observed on Cordell Bank during Delta transect surveys. Bathymetric data of Cordell Bank were collected and processed by Rikk Kvitek/CSUMB. Image created by Lisa Etherington Fish density on Cordell Bank as measured by submersible transect surveys in 2002. Rockfish accounted for 95% of fishes recorded and their abundance decreased markedly as you move away from the upper portions of the Bank. Image created by Tara Anderson
Due to the depths and currents on Cordell Bank, the manned submersible, Delta, is used to conduct transect surveys of the Bank community and habitats. Photo: Michael Carver/CBNMS
Fish-habitat relationships poster Fish-habitat relationships at the Cordell Bank National Marine Sanctuary. A poster presented at the 2004 Western Groundfish Conference, Victoria, British Columbia. Pirtle MS thesis Habitat-based assessment of structure-forming megafaunal invertebrates and fishes on Cordell Bank, California. MS thesis by Jodi Pirtle for Washington State University.
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