Age , Growth, and Reproduction of the roughtail skate Bathyraja trachura (Gilbert, 1892) from the Eastern North Pacific.
Age , Growth, and Reproduction of the roughtail skate Bathyraja trachura (Gilbert, 1892) from the Eastern North Pacific. |
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Purpose:
In California waters, skates are targeted directly by fisheries and also are
taken indirectly as bycatch (Martin and Zorzi 1993). Historically, the value
of skate products has been low, averaging $0.07/lb in the 1981, but has since
increased to the latest available value of $0.16/lb (PacFin 2005). As the value
of skate products increases, fishing effort will grow, raising the level of
fishing mortality. Determining what impact fishing mortality has on individual
populations is further hindered by the lack of species-specific life history
information (Holden 1972, 1974, Martin and Zorzi 1993, Stevens et al. 2000,
Dulvy and Reynolds 2002). Many skates, like most chondrichthyans, have a life
history of slow growth, long lifespan, late reproduction, and low fecundity
making them susceptible to overfishing (Holden 1972, 1974, Stevens et al. 2000,
Dulvy and Reynolds 2002).
Skates are bottom dwelling elasmobranchs with a dorso-ventrally compressed
body and the pectoral fins extending laterally along the body creating a triangular
appearance. Skates have a species specific patterns of thorns covering the tail,
eyes, scapula, pectoral fins, back, and rostrum. Skates are in the order Rajiformes,
and consist of three families: Anacanthobatidae (legged skates), Arhynchobatidae
(soft nosed skates) and Rajidae (hard nosed skates) (Compagno 1999). The genus
Bathyraja is the only representative of the softnosed skates reported from the
California coast (Compagno 1999, Ebert 2003). Information about the genus in
eastern North Pacific waters (California, Oregon and Washington) is limited
to taxonomic descriptions and a few descriptions of egg cases and advanced embryos
(Cox 1963, Ishihara and Ishiyama 1985, Zorzi and Anderson 1988).
The roughtail skate, Bathyraja trachura, occurs in the eastern North Pacific, from the Bering Sea to northern Baja California, inhabiting benthic waters 400 to 2,550 meters (Ishihara and Ishiyama 1985, Ebert 2003). It is described as a medium-sized species (89.0 cm maximum TL) with a dorsal surface that is plum brown or slate gray in color. The tail is covered in prickles and one defined row of 15-34 tail thorns. The ventral surface is also plum brown in color but is smooth, with whitish coloration around the mouth, gill slits, and tip of pelvic lobes (Ishihara and Ishiyama 1985, Mecklenburg et al. 2002).
The purpose of this study is to provide estimates of age, describe growth characteristics and assess reproductive biology for Bathyraja trachura in eastern North Pacific waters. Specifically this study will attempt to: 1) estimate age for B. trachura; 2) compare vertebral to caudal thorn age estimates; 3) validate age estimates using centrum edge and marginal increment analysis (MIA); 4) generate growth models using age and size estimates for both males and females; 5) determine age and size at first, 50% and 100% maturity; and 6) calculate differences in maturity among seasons and between sexes.
Literature cited:
Compagno, L.J.V. 1999. Checklist of living elasmobranchs. In: Hamlett, W.C. (Editor), Sharks, skates, and rays: the biology of elasmobranch fishes. Johns Hopkins University press, Baltimore, Maryland.
Cox, K.W. 1963. Egg-cases of some elasmobranchs and a cyclostome from Californian waters. Calif. Fish and Game. 271-289.
Dulvy, N.K. and J.D. Reynolds. 2002. Predicting extinction vulnerability in skates. Cons. Bio. 16(2):440-450.
Ebert, D.A. 2003. Sharks, Rays, and Chimaeras of California. University of California press. California pp. 284
Holden, M.J. 1972. The growth of Raja brachyura, R. clavata, and R. montagui as determined from tagging data. J. Cons. Int. Explor. Mar. 34(2):161-168.
Holden, M.J. 1974. Problems in the rational exploitation of elasmobranch populations
and some
suggested solutions. Pp. 117-138, In: Sea Fisheries Research. F.R. Harden and
C. Jones, (eds) Logos Press, London.
Ishihara, H. and R. Ishiyama. 1985. Two new North Pacific skates (Rajidae)
and a revised key to
Bathyraja in the area. Jpn. J. of Ichthyol. 32(2):143-179.
Martin, L. and G.D. Zorzi. 1993. Status and review of the California skate fishery. In: Conservation Biology of Elasmobranchs. S. Branstetter (ed). NOAA Tech Rep NMFS 115:39-52.
Mecklenburg, C.W., T.A. Mecklenburg and L.K. Thorsteinson. 2002. Fishes of Alaska. Am. Fish. Soc. Symp. pp. 91-107.
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 J. Mar. Sci. 57:476-494.
Zorzi, G.D. and M.E. Anderson. 1988. Records of the deep-sea skates, Raja (Amblyraja) Badia Garman, 1988 and Bathyjaja abyssicola (Gilbert, 1896) in the eastern north Pacific, with a new key to California skates. Calif. Fish and Game. 74:87-105.
Zorzi, G.D., L.K. Martin and J. Ugoretz. 2001. Skates and Rays. pp. 257-261.
In: California’s living marine resources: a status report. W.S. Leet, C.M. Dewees,
R. Klingbeil, and E.J. Larson (eds) California Department of Fish and Game,
California.
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Last Revision: 5 December 2005