Longitudinal Length Back‐Calculations from Otoliths and Scales Differ Systematically in Haddock

Abstract

Parallel macrostructure analysis of otoliths versus scales was conducted on Georges Bank Haddock Melanogrammus aeglefinus sampled in spring 2011 to test whether annuli widths of both structures yield comparable estimates of back‐calculated length at age. While generally similar in number, scale and otolith annuli were found to differ systematically in their relative widths, mainly because initial annuli are deposited closer to the origin in scales than in otoliths. Accounting for the delayed onset of scale versus otolith formation did not remove the systematic bias. To make both structures comparable, we developed an age‐independent correction approach that can adjust cumulative relative annuli widths (RAWs) of Haddock scales to otolith RAWs by the quadratic formula loge(RAWoto) = 0.7244·loge(RAWscale) + 0.0751·loge(RAWscale)2. Our study comprises a necessary step towards extracting and comparing longitudinal growth data over the entire time series of archived Haddock scales (1931–1993) and otoliths (1994–present) to improve understanding of decadal drivers of growth patterns in this fish stock. Historical longitudinal growth data for exploited stocks are currently underutilized despite their high potential value, given that such data do not confound growth and mortality the way population‐based age–length relationships do. Mixed archives consisting of multiple growth structures exist not only for Haddock but for many commercial fish species; hence, prior to mining these valuable time series of longitudinal data the comparability not only of age but also of back‐calculated growth estimates between structures needs to be ascertained.

Age and Growth of the Rio Grande Silvery Minnow, an Endangered, Short‐Lived Cyprinid of the North American Southwest

“…These results are consistent with those of other studies that have investigated the relationship between scale‐based and otolith‐based ages in numerous families of fish, including cyprinids (Vilizzi and Walker ; Simmons and Beckman ), a catostomid (Beckman and Huston ), a gadid (Baumann et al. ), a moronid (Secor et al. ), and salmonids (Zymonas and McMahon ; Schill et al.…”

“…Otoliths generally provide the most accurate and precise record of age (Baumann et al. ), although extraction and analysis of otoliths is more labor intensive than scale analysis and requires sacrifice of the study specimen. Verification of age by direct methods (Beamish and McFarlane ) and subsequent monitoring based on validated indirect estimates may be a cost‐effective and reliable approach for the long‐term management of imperiled species.…”

“…Among direct methods, scalebased ages often have high measurement error due to scale damage, loss and replacement, resorption, and the misinterpretation of false annuli as true annuli (Campana 2001;Sylvester and Berry 2006;Simmons and Beckman 2012). Otoliths generally provide the most accurate and precise record of age (Baumann et al 2013), although extraction and analysis of otoliths is more labor intensive than scale analysis and requires sacrifice of the study specimen. Verification of age by direct methods (Beamish and McFarlane 1983) and subsequent monitoring based on validated indirect estimates may be a cost-effective and reliable approach for the long-term management of imperiled species.…”

Growth‐Increment Formation Using Otoliths and Scales for Age‐0 Chinook Salmon

“…While otolith and scale growth were each proportional to somatic growth of Chinook Salmon, otolith growth was not proportional to scale growth. Baumann et al (2013) suggested that factors influencing otolith increment formation (e.g., metabolic rate) and scale circulus deposition (e.g., somatic growth) are different and that growth of these structures proceeds independently from each other.…”

“…Retrospective analysis is the reconstruction of fish size at an earlier age and is based on size relationships between an aging structure and fish length (Francis 1990). Back-calculation of fish length at a previous age is estimated by aging a hard structure and measuring its radius to a specific growth increment or annulus (Baumann et al 2013). Most fish species deposit regular increments on hard structures (Fisher and Pearcy 1990;Chittaro et al 2015), and increment-deposition frequency may be daily (i.e., otoliths; Bradford and Geen 1992;Bestgen and Bundy 1998) or related to growth rate (i.e., scales; Beamish et al 2004).…”