Trophic level determination of the roughtail skate, Bathyraja trachura (Gilbert, 1892),employing two techniques: stable isotope analysis and traditional gut content analysis
Mariah Dawson Boyle
Graduated – Fall 2010
My main research interests are fisheries management, ecosystem-based management, deepsea biology, and ichthyology. I earned my B.S. in Marine Biology from Florida Institute of Technology in Melbourne, Florida.
The roughtail skate, Bathyraja trachura (Gilbert 1892) is a medium sized skate with a maximum total length of 910cm, that lives on soft bottom habitat from 200-2,550m, but is more abundant in waters deeper than 600m. These depths on the upper continental slope have recently received attention globally as large commercial fisheries move into these deeper waters from the depleted shelf habitats. A recent paper by Tolimeri and Levin (2006) determined that the six most abundant fishes on the upper continental slope caught in the NMFS/NOAA Fisheries Resource Analysis and Monitoring Division (FRAM) groundfish cruises were: Pacific grenadiers, Coryphaenoides acrolepis; giant grenadiers, Albatrossia pectoralis; deepsea soles, Embassichthys bathybius; longspine thornyheads, Sebastolobus altivelis; California slickheads, Alepocephalus tenebrosus; and B. trachura. Unfortunately, diet and trophic level information for deepwater fishes such as these is often limited by small sample sizes due to the great effort required to collect an adequate sample size. Regurgitation and swim bladder expansion upon ascent often hinder the recovery of viable samples. An alternative to the traditional gut content analysis used to determine trophic level may be necessary due to sampling constraints. My thesis work will attempt to not only quantify the diet of B. trachura, but to investigate the usefulness of carbon and nitrogen stable isotope analysis in this upper continental slope fish assemblage. This study will result in a detailed comparison of trophic levels derived by both gut content analysis and stable isotope analysis of nitrogen and a new revised food web and dual isotope plot for the fishes and invertebrates of the upper continental slope based on stable isotope analysis. My other work at MLML includes a dietary analysis of Raja rhina specimens from Alaska, which is included in a 2008 North Pacific Research Board Technical Report by Ebert et al. on the ecology of skates in the Gulf of Alaska.
Alaska Marine Science Symposium January 2008
Western Groundfish Conference February 2008
Ebert, D.A., J.J. Bizzarro, S.C. Brown, M.D. Boyle, and G.M. Cailliet. 2008. Diet and trophic ecology of skates in the Gulf of Alaska (Raja and Bathyraja spp.): ecological information for ecosystem-based management of demersal resources. North Pacific Research Board Final Report.
Funding has been provided by NOAA NMFS to the National Shark Research Consortium and Pacific Shark Research Center at Moss Landing Marine Laboratories. Funding has also been provided by the International Women’s Fishing Association, Seaspace, PADI Foundation, Earl and Ethel Myers Oceanographic and Marine Biology Trust, Friends of MLML/Packard Foundation Grant, Signe Memorial Scholarship, Xiphias Scholarship and the Yukon & Clemence Chow Scholarship.