Otolith shape and size: The importance of age when determining indices for fish-stock separation

Abstract

Stock-separation of highly mobile Clupeids (sprat -Sprattus sprattus and herringClupea harengus) using otolith morphometrics was explored. Analysis focused on three stock discrimination problems with the aim of reassigning individual otoliths to source populations using experiments undertaken using a machine learning environment known as WEKA (Waikato Environment for Knowledge Analysis). Six feature sets encoding combinations of size and shape together with nine learning algorithms were explored. To assess saliency of size/shape features half of the feature sets included size indices, the remainder encoded only shape. Otolith sample sets were partitioned by age so that the impact of age on classification accuracy could be assessed for each method. In total we performed 540 experiments, representing a comprehensive evaluation of otolith morphometrics and learning algorithms. Results show that for juveniles, methods encoding only shape performed well, but those that included size indices held more classification potential. However as fish age, shape encoding methods were more robust than those including size information. This study suggests that methods of stock discrimination based on early incremental growth are likely to be effective, and that automated classification techniques will show little benefit in supplementing early growth information with shape indices derived from mature outlines.

Size-effect, asymmetry, and small-scale spatial variation in otolith shape of juvenile sole in the Southern North Sea

“…Moreover, fish size should always be accounted for because it affects otolith shape even in age-0 fish. Our results are consistent with Mapp et al (2017), who showed that including size information increases the power of stock discrimination based on juvenile otolith shape. The formfactor decreased with increasing size in both nursery grounds and during both sampling years, while ellipticity increased in the Belgian nursery.…”

“…Thus other factors, such as genetic background, spawning location and dispersal may also be important in influencing otolith shape (Cardinale et al, 2004;Capoccioni et al, 2011;Lombarte et al, 2003;Mapp et al, 2017). This observation is supported by the similar levels of variation in otolith shape between nursery grounds and between the two successive sampling years.…”

Relationships between fish and otolith dimensions of Epinephelus summana (Forsskål, 1775) and Cephalopholis argus (Schneider, 1801) from the Egyptian Red Sea coast

“…The study of relationship between otolith size and fish size varied according to the distribution region, the stock and sexes (Sparre et al, 1989;Campana and Casselman, 1993;Reichenbacher et al, 2009;Aneesh et al, 2017), also the change of ontogenetic in the life span or history (Hare and Cowen, 1995). The present work was confirmed with other studies that investigated the correlation between fish length and otolith size (Mahé et al, 2014;Mahé et al, 2016;Mehanna et al, 2016;Jawad, et al, 2017;Mapp 2017;Mahé et al, 2018;Osman et al, 2018).…”

Comparative Analysis of the Otolith Features of Tarek (Alburnus tarichi (Güldenstädt, 1814)) Inhabiting Van Basin (Lake Van, Erçek, Nazik, Aygır) Between Localities

“…However, the right and left otoliths may not provide the same results of prey fish length estimates (Harvey et al 2000;Waessle et al 2003;Kumar et al 2012). The morphological and meristic characteristics of fish and their hard body parts have been shown as useful in stock identification studies (Kumar et al 2017;Bostanci et al 2017;Mapp et al 2017). Otoliths are useful because their growth is related to increase in fish size and generally follow an allometric increase in dimensions (Chilton and Beamish 1982).…”

“…The stock concept is one of the most fundamental in fishery management. The morphological characteristics of fish otoliths have been taken into account in recent years in stock separation studies (Tuset et al 2003;Zengin et al 2015;Renán et al 2016;Bostanci et al 2017;Kumar et al 2017;Mapp et al 2017). The difference in otolith measurement values among the populations will contribute to the stock sorting studies to be performed thereafter.…”