Population biology of red abalone, Haliotis rufescens, in northern California.
Robert Leaf Email address: rleaf@mlml.calstate.edu

Abstract. Prospective elasticity analyses have been used to aid in the management of fished species. A size based projection matrix model of red abalone, Haliotis rufescens, in northern California was constructed and elasticity values determined to evaluate the relative contribution of vital rates of each size class (n = 8) to the population growth rate (lambda). Annual growth transitions (gx) were determined from tagged and recaptured individuals (n = 560) from six locations. Fecundity, fx, the number of viable eggs produced per female was determined from a four year reproduction study. Population growth rate (lambda) was set to 1.0 and the first year survival (larval survival through to the first size class) was estimated by iteration. Elasticity values of survivorship and growth (summed px and gx) and fecundity (fx) were determined for each size class. Elasticity values were found to be greatest for the sub-legal red abalone 150 mm to 178 mm (MSL) indicating that changes in the vital rates of this size class are most important to population growth rate. Alteration of size class divisions and vital rates did not result in changes to the relative ranking of elasticity values, suggesting that this model is robust to variations in model structure and vital rate data. These results suggest that the 178 mm (MSL) recreational size limit is set appropriately and that this size limit should not be decreased. This work is an example of how size-based projection matrix models can be used to evaluate the efficacy of fishery management and conservation strategies.

Size-based annual survival probabilities for three size classes of red abalone, Haliotis rufescens, using mark-recapture data from northern and southern California.

Abstract. Size specific mortality rates are currently not available for northern California red abalone, Haliotis rufescens, the only recreational abalone fishery on the west coast. I examined annual survivorship of three size classes (< 100 mm, 100.1 to 178 mm, and > 178.1 mm) of red abalone from five sites in northern California and one site in southern California using capture-mark-recapture data. The number of tagged individuals (n = 273 to 2145), census occasions (n = 3 to 7), and size composition of individuals (41.5 to 227 mm) were variable at each site. Four models were specified for each size class at each site and were analyzed with the Jolly-Seber-Cormack model. The annual survival probabilities of the smallest size class in the study (< 100 mm) at one site in northern California was 0.52 y-1 + (0.05 SE) and was 0.36 y-1 + (0.07 SE) to 0.51 y-1 + (0.08 SE) in southern California. Annual survival probabilities of the median size class (100.1 to 178 mm) from four sites at northern California ranged from 0.37 y-1 + (0.05 SE) to 0.71 y-1 + (0.04 SE) and 0.49 y-1 + (1 SE) to 0.65 y-1 + (0.07 SE) in southern California. The largest size class designated in the study (>178.1 mm) had annual survivorship values of 0.24 y-1 + (0.04 SE) to 0.95 y-1 + (0.08 SE) in northern California and 0.42 y-1 + (0.07 SE) to 0.71 y-1 + (0.01 SE) in southern California. These results indicate that annual survival was variable temporally, spatially, and among size classes. This study is an example of how parsimonious models and conservative use of available data can allow survivorship estimates from previously unutilized capture-mark-recapture data.

Preliminary validation of the age-at-length relationship of red abalone, Haliotis rufescens, by analysis of bomb radiocarbon concentrations in shell carbonate.

Abstract. Current methods to describe age-at-length relationships of red abalone (Haliotis rufescens) are insufficient to determine the ages of large individuals because their shell lengths exceed those predicted by model Linf values. I evaluated the utility of analyzing atomic bomb generated radioisotope 14C concentrations in shell tissue as a method to validate the age-at-length relationship of H. rufescens. Fabens’ method was used to determine von Bertalanffy growth parameters (Linf = 313 mm, k = 0.051 y-1 (0.042 to 0.059, 95% CI)) based on data from a multi-year, multi-site tag-recapture study. Shell carbonate was sampled at four locations on a single shell (251 mm, maximum shell length (MSL)) with the objective to bracket the rise of the radiocarbon signal, known to occur during ~1957 in the NE Pacific. There was close correspondence to the radiocarbon values of extracted shell carbonate and estimated dates of formation based on VBGC estimates. The 251 mm (MSL) red abalone was predicted to be 25.2 to 40.0 years old. This study presents preliminary results from radiocarbon analysis of shell carbonate and demonstrates the utility of validating the age-at-length relationship of red abalone with this method.

Links:

Program MARK

Phi Dot Discussion Forum

Fisheries and Wildlife Science at Virginia Tech

Michael R. Easterling et al. Integral Projection Model

California Department of Fish and Game Red Abalone Information

All Models Are Wrong Some Models Are Useful

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Last Revision: 27 July 2005