Age reading of Cabezon (Scorpaenichthys marmoratus): 1) comparison of thin-section and break-and-burn methods and 2) comparison of growth curve fits, Information Reports 2019-04

Identification Information

Citation

Originator: Rasmuson, Leif K., Lisa A. Kautzi, Lindsay Aylesworth, Megan N. Wilson, and Kirsten Grorud-Colvert

Publish Date: April 30, 2019

Online Link: None

BPA Project #:

Contact Information

Agency: Oregon Department of Fish and Wildlife

Name: Leif Rasmuson

Job Position: Marine Fishery Research Project Leader

Telephone: 541-867-0300 x231

E-Mail Address: leif.k.rasmuson@odfw.oregon.gov

Description

Abstract: Ages are a critical component of age-structured stock assessment models. Previous ageing work on Cabezon by the Oregon Department of Fish and Wildlife was completed using the thin-section method because of the small otolith size and a perceived increase in pattern clarity. Recently however, the ODFW marine age reading team elected to try to decrease the amount of time spent on sample preparation while maintaining pattern clarity.In addition to examining how methodological differences in age and growth affect bias and precision of age estimates, we also wanted to examine how these differences ultimately impact parameter estimates obtained when fitting growth functions. Further, previous growth function parameter estimates in Oregon were generated solely from the recreational fishery and with a temporally restricted dataset. Therefore, we reanalyzed the data, examining the effect of port and fishery on the larger dataset while accounting for differences between readers. Therefore, we reassessed parameter estimates for male Cabezon in Oregon to determine whether increasing the size of our dataset affected the growth function parameter estimates. In this study we find that ethanol-soaked otoliths read using the break-and-burn method provide a dramatic increase in the number of structures that can be aged each day. However, our work also demonstrates that there is a large amount of age reading bias and overall lack of precision between otolith preparation methods and readers. The large difference between the ages generated using either thin-sectioning or break-and-burn is a concern because ages from 2005-2008 were read using thin-sectioning and all other years were read using break-and-burn. This work highlights the difficulties of ageing Cabezon and strongly argues for the need to conduct age validation studies for future stock assessments. Future work should be done to compare ages obtained from otoliths, vertebrae and spines. The growth rates during these early stages are likely quite fast, variable, and particularly sensitive to environmental conditions. An increased understanding of the factors that modulate juvenile growth will improve estimates of the steepness of the growth function, with significant impacts on the stock assessment.

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Geographic Extent: Nearshore Oregon Reefs

Status: Final

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Format: pdf

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