Date

2008

Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The Aleutian skate (Bathyraja aleutica) is a large deep-water species that commonly occurs in bycatch of Alaskan trawl and longline fisheries. Although prominent in the skate biomass of the eastern Bering Sea (EBS) and Gulf of Alaska (GOA) ecosystems, minimal biological information exists. To increase our understanding of this potentially vulnerable species, and address the possibility for two separate populations in Alaskan waters, the age, growth, and reproduction of B. aleutica was studied. Vertebrae and caudal thorns were examined for age determination, and multiple growth models were evaluated to determine growth characteristics. Skates from the EBS attained maximum ages of 17 years for females and 16 years for males, and the two-parameter von Bertalanffy growth functions generated estimates of k = 0.13 yr-l and Lxo = 162.1 cm for females, with similar results for males. Skates from the GOA reached 19 years in females and 18 years in males. Growth parameters of female skates from the GOA were estimated as k = 0.11 yr-l and Loo = 160.0 cm, whereas males grew faster, with estimates of k = 0.15 yr-l and L., = 138.2 cm. In evaluating reproduction, maturity stages were determined using external morphology and histological analyses. Size at maturity was similar among sexes and regions, however, age at maturity was ~3.5 years greater for skates from the GOA (13.7 yrs) than the EBS (l0.4 yrs). Ovarian fecundity reached 60 ova from skates from the EBS skates, and 36 ova for skates from the GOA skates. Both fecundity and ovum diameter increased weakly with size, but not age. The presence of males with mature spermatocysts and gravid females signified reproductive capability during all months sampled. These data indicate B. aleutica is a moderately slow-growing and late-maturing species. Although skates had relatively similar life history characteristics, skates from the GOA had greater longevity, later age at maturity, and lower potential fecundity than skates from the EBS, and may indicate increased vulnerability to fishing pressures.

Comments

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

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