Determining relevant variables and quantifiable reference points to establish the maturity stages in Enteroctopus megalocyathus and Illex argentinus using decision tree analysis

CRESPI ABRIL, AUGUSTO CÉSAR; NICOLÁS ORTIZ; GALVÁN, DAVID

México D.F.

Congreso; Mollusca 2014: encuentro de las américas; 2014

Universidad Autónoma de México

Determining the maturity condition of cephalopods is crucial for stock assessment and management, but this task is often difficult to conduct in practice. This study provides observer-independent criteria to classify individuals in maturity stages based on decision tree analysis (DTA). A total of 4551 squids (Illex argentinus) and 1447 octopuses (Enteroctopus megalocyathus) from patagonian coast (Argentina) were sampled. Each individual was sexed and assigned to a macroscopic maturity stage defined by specific maturity scales and validated by histological analysis. Also, for each individual the weight of the gonad, accessory glands/ducts, mantle length and total weight were recorded and Maturity and Hayashi's indexes were calculated. Two different models were fitted, one considering all maturity stages and another considering only intermediate maturity stages since these are the most difficult to determine in practice. For I. argentinus, the weights of nidamental gland and oviducts were the most relevant variables to classified individuals among all female stages (misclassification 23%) whilst spermatophoric complex and testis weights were the key variables for males (misclassification 23%). The second model showed that nidamental gland and spermatophoric complex weights were the most relevant variables to classify females (misclassification 19%) and males (misclassification 21%) respectively. For E. megalocyathus, the oviducts and ovary weights of females and the terminal organ weight of males were the most relevant variables (misclassification 16% and 18%, respectively). The second model, highlighted the same variables, but misclassification improved to 13% for both sexes. In all cases, the frequently used indexes for determining maturity were not relevant. DTA of reproductive system measurements proved to be a useful tool to develop new and simple criteria of maturity stage classification, easy to use in field and independent of observer training. Moreover, the present approach could be easily applied to other cephalopod species using the biological data already existing.