Date

2006

Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

Age and growth characteristics of the roughtail skate Bathyraja trachura, a poorly-known deep-water species, were determined from samples collected along the continental slope of the contiguous western United States. A new maximum size was established at 91 cm TL. Age was estimated using a traditional structure (vertebral thin sections) and an alternative non-lethal structure (caudal thorns). Based on poor precision and significantly lower age estimates when compared to age estimates from thin sections, caudal thorns were determined not to be a useful ageing structure for this species. Age estimates from vertebral thin sections were used to model growth. Annual band deposition was found to be a reasonable assumption for this species, but was not validated. Assuming annual band deposition and using length-at-age data, the best model for describing growth of B. trachura was the two parameter VBGF, (L∞ = 101.25, k = 0.09). Although females grew slower and reached a larger maximum size than males, their growth parameters were not statistically different therefore data were pooled (ARSS; p = 0.78). The maximum age determined for B. trachura was 20 yrs for males and 17 yrs for females using vertebral thin sections. First and 50% maturity occurred in males at 58.0 cm TL (~11 yrs) and 72.0 cm TL (~14 yrs). First and 50% maturity occurred in females at 58.0 cm TL (~7 yrs) and 77.0 cm TL (~ 13yrs). Gonosomatic and hepatosomatic indices did not indicate a seasonal trend of the reproductive cycle, suggesting that reproduction may be year round.

Comments

Thesis (M.S.) Division of Science and Environmental Policy. Moss Landing Marine Laboratories

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