Date

2005

Document Type

Master's Thesis

Degree Name

Master of Science (M.S.)

Department

Moss Landing Marine Laboratories

Abstract

The sandpaper skate, Bathyraja kincaidii, is commonly taken as bycatch in trawl fisheries off central California although little life history information is known for this species. To assess age, growth and reproduction, 506 Bathyraja kincaidii were collected from commercial samplers, museum collections, and monthly trawl and slope surveys conducted by the National Marine Fisheries Service since January 2002. Sexes were equally represented, with females comprising 48.8% and males 51.2% of samples collected. Females ranged from 199-610 and males from 195-635 mm total length (TL). For age and growth analysis, 188 sectioned vertebrae were read 3 times and APE (0.10), CV (0.09) and D (0.06) precision values calculated. Ages were assigned based on agreement of at least two independent estimates, with an additional read used to establish agreement if necessary. Both marginal increment analysis and centrum edge analysis failed to show significant documentation of growth band formation periodicity. Caudal thorns could not verify age estimates from vertebrae due to within-sample variability of age assignments, variability of caudal thorn growth compared with TL, large bias of age for thorns compared with vertebrae, and unacceptable precision values for APE (14.5), CV (19.70) and D (11.40). Therefore, there were designated unreliable for age and growth analysis of B. kincaidii. Age estimates from vertebral centra indicate a minimum longevity of 17 years for female and 18 years for male B. kincaidii. Females (L = 537.3 mm; k = 0.237; to = -1.629; n = 100) grew faster but males (L = 580.2 mm; k = 0.185; to = -2.530; n = 90) reached a larger size. Maximum likelihood ratio indicated no significant difference (p > 0.05) between male and female von Bertalanffy growth parameters, and combined sexes produced values of L = 557.8 mm and k = 0.207. Females first mature at 450 mm (~4 years), while males first mature 440 mm TL, ~1 year earlier. However, size and estimated age at 50% maturity was similar between sexes: 467 mm and 7.1 years for females and 492 mm and 7.5 years for males. GSI and HSI values indicate a slight, but not statistically significant seasonal increase in reproductive effort and the occurrence of inactive females throughout the year indicates a resting period following parturition.

Comments

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

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