Stock identification of neon flying squid (<em>Ommastrephes bartramii</em>) in the North Pacific Ocean on the basis of beak and statolith morphology

Abstract

Summary:Cephalopods are becoming increasingly important in global fisheries as a result of increased landings and are playing an important ecological role in the trophic dynamics of marine ecosystems. Ommastrephes bartramii is a pelagic cephalopod species with two widely distributed spawning stocks in the North Pacific Ocean. It is also a major fishing target for the Chinese squid jigging fleets. Successful separation of these two spawning stocks is critical to fisheries management, but tends to be challenging because of their similar morphology. In this study we attempted to identify the stocks based on discriminant analyses of 9 morphological variables of statolith and 12 variables of beaks measured for O. bartramii samples in the North Pacific. A significant difference was revealed in the standardized beak and statolith variables between sexes in the northeast (NE) stock (P<0.05). The northwest (NW) stock showed significant differences between sexes for all variables (P<0.05) except for upper wing length (P>0.05), whereas the NW stock showed no significant difference in either sex for the statolith variables (P>0.05). The same sex also revealed different patterns with different hard structures between the two stocks. In t-tests females showed significant differences between stocks in statolith morphology (P<0.05) and beak morphology (P<0.05); males also showed this difference between cohorts in statolith variables (P<0.05) except dorsal dome length and wing length (P>0.05), but showed no difference between cohorts (P>0.05) in beak morphometric variables. With the combination of two standardized hard parts, correct classification of stepwise discriminant analysis (SDA) was raised by nearly 20% compared with using only one structure, although overlaps of the NW stock were still found in the scatter-plots. It is concluded that adding more appropriate hard structure variables will effectively increase the success of separating geographic stocks by the SDA method.Keywords: Ommastrephes bartramii; statolith; beaks; morphology; geographic stock; stepwise discriminant analysis.Identificación de las poblaciones de pota saltadora (Ommastrephes bartramii) en el Pacífico Norte a partir de la morfología de estatolitos y mandíbulas Resumen: Los cefalópodos son cada vez más importantes en las pesquerías mundiales como consecuencia de su volumen de capturas, jugando un importante rol en la red trófica de los ecosistemas marinos. Ommastrephes bartramii es una especie de cefalópodo pelágico con dos poblaciones de desove de amplia distribución en el Pacífico Norte. Asímismo, es un importante objetivo de las flotas pesqueras chinas de potera automática. La adecuada identificación de sus dos poblaciones de desove es fundamental para la gestión de esta pesquería, siendo una difícil tarea debido a su morfología similar. En este estudio se pretende identificar los stocks en función de los análisis discriminantes de nueve variables morfológicas del estatolito y doce variables de las mandíbulas, obtenidas en muestras de O. bartramii d...

Morphological Differences and Contour Visualization of Statoliths in Different Geographic Populations of Purpleback Flying Squid (Sthenoteuthis oualaniensis)

“…In the present study, statoliths from three different marine regions were subjected to discriminant analysis using three morphological methods. Classification accuracy is improved by utilizing stepwise discriminant analysis with variables that exhibit significant differences [14,45]. The results indicate that all three methods can successfully discriminate the morphologies of statoliths of the purpleback flying squid from different marine areas.…”

“…Due to its calcified structure, the morphology of the statolith is not easily damaged [7], and it is highly specific [8]. Therefore, they are frequently employed in conjunction with beaks, internal shells, eye lenses, and other hard tissues for studying age and growth [9][10][11], species identification [12], population differentiation [13][14][15], and other purposes [7,8,16].…”

“…Significant progress has been made in the morphological study of statoliths [24][25][26][27][28][29]. Efficient and simple morphological methods can be applied to analyze fish otoliths for individual fish identification, detecting interspecific differences, and population discrimination [14,30,31]. In previous studies, geometric morphometry analysis has also been employed to investigate fish otoliths and other hard tissues in fish.…”

“…The handling of details and local features can be demonstrated by selecting different landmarks [33,35,36]. Statoliths are sometimes combined with other structures (such as the body or the beak) for discriminant analysis [14,37].…”

Stock discrimination of two European squids (Illex coindetii, Loligo forbesii) by statolith shape analysis

“…Fish stocks encompass the living resources within a population used for fishing, typically implying a self‐sustaining population isolated from other stocks of the same species (FAO Fishery Glossary, n.d.). To support effective management, statolith shape analysis is a promising method for defining different stocks of a species, including squids (Fang et al., 2014; Green et al., 2015; Sheerin et al., 2022).…”