The age, growth and reproduction of the Bering skate, Bathyraja interrupta (Gill & Townsend, 1897), from the Bering Sea and the Gulf of Alaska

M.S. Thesis Project:   

An increase in skate landings, as well as the development of skate fisheries in the Gulf of Alaska, has amplified interest in the management of skates in the eastern North Pacific. Skates are taken in large numbers as bycatch in Alaskan commercial bottom trawl and long-line fisheries. In recent decades, there has been growing concern over the fishing pressures placed on elasmobranch populations. In general, elasmobranchs are considered to have relatively slow growth, late maturation and a low fecundity, making them susceptible to over fishing (Stevens et al., 2000; Dulvy et al., 2000; Dulvy and Reynolds, 2002).

Accurate estimates of life history parameters are essential to successful fisheries management; as this information is used to set catch limits and gear sizes to protect the fish stocks from depletion. Studies of life history parameters such as age, growth and reproduction, have shown considerable variation among skate species (Gallagher and Nolan, 1999; Mabragaña and Cousseau, 2004; Ebert, 2005; Perez, 2005; Matta, 2006), and appear to be related to latitude, depth, and size that each skate species reaches. Annual stock assessment and fishery evaluation reports (SAFE) are produced for the North Pacific Fishery Management Council (NPFMC), which each year have stressed the importance of estimating parameters for each species in Alaskan skate complex (Gaichas et al., 2005a, 2005b). This essential information can be used to improve current fisheries management and to allow for species-specific management strategies.

The objective of this study is to characterize the life history traits of a common skate species Bering skate in Alaskan waters. The Bering skate, Bathyraja interrupta, is generally found at depths of 55 to 1,372m between the eastern Bering Sea and the Gulf of Alaska. It is characterized by one or two strong scapular thorns on each side, 0 or 1 interdorsal thorns and a continuous (reduced) or interrupted row of mid-dorsal thorns. The dorsal side is dark and covered with denticles, while the ventral side is light with a smooth surface (Mecklenburg et al., 2002). In the age and growth portion of this study the objectives are to: 1) determine whether centra and caudal thorns of B. interrupta have quantifiable growth characteristics with a pattern to the periodicity of the deposition; 2) estimate size-at-age and size at birth 3) to validate age estimates using centrum edge analysis and marginal increment ratio techniques; and 4) calculate theoretical maximum size and longevity. The objectives of the reproductive aspect of the study are to: 1) estimate age at first and 50% maturity; and 2) examine periodicity of reproduction, estimate fecundity and investigate potential for sperm storage.

Additional Projects: The age, growth and reproduction of the whitebrow skate, Bathyraja minispinosa (Ishiyama & Ishihara, 1977), from the Bering Sea

A similar project will focus on the age, growth and reproduction of the whitebrow skate, Bathyraja minispinosa. The whitebrow skate acquired its common name from the distinct white area along the inner edge of the eyes. The scientific name is derived from the minute spines on the dorsal side of the disk. This species is one of 11 known skates of the genus Bathyraja in the eastern Bering Sea continental slope (Ebert, 2005). Hubbs and Ishiyama (1968) elevated the subgenus Bathyraja (Ishiyama, 1958) to generic status, due to exceptional rostral and clasper forms (Ishiyama & Ishihara, 1977). The whitebrow skate has been recorded in the Bering Sea and the Sea of Okhotsk off Hokkaido, Japan. It ranges from 150m to 1,420m in depth (Mecklenburg et al., 2002). As very little is known about this species, it is the aim of this research to help fill gaps life history information.

Publications:

Ebert, D.A., Smith, W.D.,Haas, D.L., Ainsley, S.M. and Cailliet, G.M. North Pacific Research Board Report. 2007. Life history and population dynamics of Alaskan skates: providing essential biological information for effective management of bycatch and target species. North Pacific Research Board Final Report 510, 124 p.

Posters and Presentations:

Ainsley*, S.M., Ebert, D.A., and Cailliet, G.M. The age, growth and reproduction of the Bering skate, Bathyraja interrupta (Gill & Townsend, 1897), from the Gulf of Alaska. Abstract: American Elasmobranch Society 2007 Poster.

Ainsley*, S.M., Ebert, D.A., and Cailliet, G.M. The age, growth and reproduction of the Bering skate, Bathyraja interrupta (Gill & Townsend, 1897), from the Gulf of Alaska. Abstract: American Fisheries Society 2007 Poster.

Ebert, D.A., Smith, W.D., Haas, D.L., Ainsley, S.M., and Cailliet, G.M. Life History and Population Dynamics of Alaskan Skates: Providing Essential Biological Information for Effective Management of Bycatch and Target Species. Abstract: North Pacific Research Board Symposium 2007 Poster.

Ebert, D.A., Bizzarro*, J.J., Haas, D.L., Neway, A.L., Ainsley, S.M., Smith, W.D., and Cailliet, G.M. Age, growth, and reproduction of four Alaskan softnose skates (Chondrichthyes: Rajiformes: Arhynchobatidae: Bathyraja). Abstract: North Pacific Research Board Symposium 2006 Poster.

Ebert, D.A., Bizzarro, J.J., Haas, D.L., Neway, A.L., Ainsley, S.M., Smith, W.D., and Cailliet, G.M. Age, growth, and reproduction of six Alaskan skates (Chondrichthyes: Rajiformes: Bathyraja and Raja) Abstract: American Elasmobranch Society 2006.

Ebert, D.A., Bizzarro, J.J., Haas*, D.L., Neway, A.L., Ainsley, S.M., Smith, W.D., and Cailliet, G.M. Age, growth, and reproduction of four Alaskan softnose skates (Chondrichthyes: Rajiformes: Arhynchobatidae: Bathyraja) Abstract: Western Groundfish Conference 2006 Poster.

* Presenter

Funding:

Funding for this project has been provided by the North Pacific Research Board (Project numbers 510 and 715), and NOAA National Marine Fisheries Service through the National Shark Research Consortium’s Pacific Shark Research Center. Additional funding was provided by the Lottery Funds, American Elasmobranch Society and the Dr. Earl H. Myers and Ethel Myers Oceanographic and Marine Biology Trust.

Literature cited:

Dulvy, N.K., J.D. Metcalfe, J. Glanville, M.G. Pawson, and J.D. Reynolds. 2000. Fishery stability, local extinctions, and shifts in community structure in skates. Conservation Biology 14(1): 283-293.

Dulvy, N.K. and J.D. Reynolds. 2002. Predicting extinction vulnerability in skates. Conservation Biology 16(2): 440-450.

Ebert, D. A. (2005) Reproductive biology of skates, Bathyraja (Ishiyama) along the eastern Bering Sea continental slope. Journal of Fish Biology 66: 618-649.

Gaichas, S., B. Matta, D. Stevenson, and J. Hoff. 2005a. 16.3. Bering Sea and Aleutian Islands skates. NPFMC Bering Sea and Aleutian Islands SAFE. p.825-857.

Gaichas, S., N. Sagalkin, C. Gburski, D. Stevenson and R. Swanson. 2005b. 16. Gulf of Alaska Skates. NPRMC Gulf of Alaska SAFE. p. 881-926.

Gallagher, M. and C.P. Nolan. 1999. A novel method for the estimation of age and growth in rajids using caudal thorns. Canadian Journal of Fisheries and Aquatic Science 56: 1590-1599.

Gill, T. and C.H. Townsend. 1897. Diagnosis of new species of fishes found in Bering Sea. Proceedings of the Biological Society of Washington 11: 231-234.

Ishiyama, R. 1958. Studies on the rajid fishes (Rajidae) found in the waters around Japan. Journal of the Shimonoseki College of Fisheries 7(2-3):1-202.

Ishiyama, R and H. Ishihara (1977) Five new species of skates in the Genus Bathyraja from the Western North Pacific, with reference to their interspecific relationships. Japanese Journal of Ichthyology 24(2): 71-89.

Mabragaña, E. and M.B. Cousseau. 2004. Reproductive biology of two sympatric skates in the south-west Atlantic: Psammobatis rudis and Psammobatis normani. Journal of Fish Biology 65: 559-573.

Matta, M.E. 2006. Aspects of the life history of the Alaska skate, Bathyraja parmifera, in the eastern Bering Sea. MS thesis, School of Aquatic and Fisheries Sciences, University of Washington, WA.

Mecklenburg, CW., T.A. Mecklenburg and L.K. Thorsteinson. 2002. Fishes of Alaska. American Fisheries Society, Bethesda, Md. p. 104

Perez, C.R. 2005. Age, growth, and reproduction of the sandpaper skate, Bathyraja kincaidii (Garman, 1908) in the Eastern North Pacific. MS Thesis, California State Univesity, Monterey Bay, CA.

Stevens, J.D., R. Bonfil, N.K. Dulvy, and P.A. Walker. 2000. The effects of fishing on sharks, rays, and chimaeras (chondrichthyans), and the implications for marine ecosystems. ICES Journal of Marine Science 57:476-494.