Jasmine Maurer

Life history and population dynamics of four endemic Alaskan skates: determining essential biological information for effective management of bycatch and target species

Jasmine FraurerJasmine R. Maurer

Email address: jfry@mlml.calstate.edu

Graduated – Fall 2009

The four skates species understudy on this project are the commander skate, B. lindbergi (Ishiyama and Ishihara, 1977), whiteblotched skate, B. maculata (Ishiyama and Ishihara, 1977), whitebrow skate, Bathyraja minispinosa (Ishiyama and Ishihara, 1977), and mud skate, Rhinoraja taranetzi (Dolganov, 1985). These skates are common inhabitants around the Aleutian Islands and the eastern Bering Sea continental slope. The whiteblotched skate, which reaches a maximum total length of 120 cm, is most common at depths between 100-650m but has been caught between 73m and 1,110m. The commander skate, which grows to a maximum length of 93 cm, inhabits slightly deeper water at depths of 120m to 950m and possible down to 2,000m. These two differ from each other and the mud skate by their thorn pattern. The whiteblotched skate has strong nuchal thorns but lacks scapular thorns and mid-dorsal thorns. The commander skate has continuous mid-dorsal thorns beginning in the scapular region down to the first dorsal fin. The color pattern of these two skates is distinct and can be used in addition to thorn patterns to distinguish between species. The whiteblotched skate, as the name implies, has dark dorsal color with white to yellow blotches throughout and the ventral surface is gray with darker margins. The commander skate is dark on both dorsal and ventral surfaces, with whitish coloring around the mouth. The whitebrow skate lacks scapular and mid-dorsal thorns, when present nuchal thorns are weak, never more than three; coloration of the dorsal surface is uniformly dark with white “brows” around inner eye. The whitebrow skate is found between 150-1,420m and reached 83cm total length. The key characteristic that differentiates these three skate species from the mud skate is their dark ventral surface, whereas the mud skate has a white ventral side. The mud skate is the smallest of the four skate species with a maximum reported total length of 77cm, and is found at depths of 58-1045m. The dorsal side is grayish brown with small light and dark blotches covered in denticles; the ventral side is white with a mostly brown tail and smooth. The mud skate lacks scapular thorns and mid-dorsal thorns (Mecklenburg et. al., 2002).

There is very little life history information available on any of these four species. Therefore, the main objective of this project is to improve our knowledge of the life history of these four endemic Bering Sea skates. The project can be divided into two segments; age and growth, and reproduction. Below are the specific objectives for each segment of the project starting with the age and growth portion: 1) investigate vertebral centra and caudal thorns as appropriate ageing structures; 2) estimate size-at-age and size at birth; 3) verify age estimates using centrum edge analysis and marginal increment ratio techniques; 4) estimate  maximum age. The objectives for the reproductive portion of this study are to: 1) estimate age at first, 50%, and 100% maturity; 2) estimate fecundity, and investigate the periodicity of reproduction, and potential for sperm storage.

I will be primarily studying three of the four species listed and Shaara Ainsley will be investigating the life history of the whitebrow skate. More information on this species can be found on her webpage.

Bathyraja taranetziM.S. Thesis Project

The project described above encompasses the work I will be doing for my thesis. I plan to focus on two of the species, B. lindbergi and B. maculata. As the project develops more details on my thesis work will be available.

Funding:

Posters and Presentations:

Alaska Marine Science Symposium 2008

Ebert, D.A.*, Fry, J.R., Ainsley, S.M., and Cailliet, G.M. Preliminary results for life history and population dynamics of four endemic Alaskan skates: determining essential biological information for effective management of bycatch and target species.

Western Groundfish Conference 2008

Fry, J.R.*, Ainsley, S.M., Cailliet, G.M., and Ebert, D.A., Preliminary results for life history and population dynamics of four endemic Alaskan skates: determining essential biological information for effective management of bycatch and target species.

* Presenter

Literature cited:

Dolganov, V.N. (1985) Species of Skates of the Family Rajidae from the Northwestern Pacific Ocean. Journal of Ichthyology 25(3):121-132

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.

Mecklenburg C.W., T.A. Mecklenburg, L.K. Thorsteinson (2002). Fishes of Alaska. American Fisheries Society, Bethesda, Md.