Relationship of beaks measurements and body size of Enteroctopus megalocyathus (Cephalopoda: Octopoda)

NICOLÁS ORTIZ; VOGLINO, GIANNINA; CRESPI ABRIL, AUGUSTO CÉSAR

México D.F.

Congreso; Mollusca 2014: encuentro de las américas; 2014

Universidad Autónoma de México

Cephalopods are important fishing resource and represent a valuable prey for higher predators. They are mainly muscular animals and very little of their body mass is indigestible. Between the indigestible body parts, the beaks are the most useful for determining the species and the biomass of cephalopods consumed by predators. Enteroctopus megalocyatus is an endemic species of the southern tip of South America and is part of the diet of several species, including seabirds, marine mammals and elasmobranchs. Besides it is also an important fishing resource targeted by artisanal fisheries. In Argentina, this fishery is unmanaged, in part because fisheries often takes place in remote locations which present difficult access for fishery managers. The aim of this work, is to study the relationship between body size and beaks of E. megalocyathus that can be used in ecological and fishery studies. From each individual total and eviscerated weight and sex were recorded and the following measures of superior and inferior beaks were registered: crest, rostrum, hook and wing lengths. A simple regression analysis was performed between different beak measurements and total and eviscerated weights. The exponential model was the best model fitted to data in all regressions between beaks length and total weight. The relationship between total weight and eviscerated weight was linear. No differences were found between males and females in all cases. The best measure of inferior and superior beaks to estimate total weight was the crest length , whilst rostrum length was the worst. Thus, the biomass of E. megalocyathus consumed by predators could be estimated accurately by using crest length. Also, we propose that beak size would be a useful tool to estimate octopus captures of E. megalocyathus, particularly when it is difficult to access to fishing catches.