Contribución al estudio de la Cholga Aulacomya Ater en Putemún (MOLLUSCA, BIVALVIA, MYTILIDAE)

Abstract

Population of Aulacomya ater, Estero de Castro, were studied with monthly samples between May 1965 and June 1966.

The natural bank studied was settled on a muddy bottom, many dead individuals were found there.

Reference is made to taxonomic, synonyms, diagnostic characteristics and habitat.

Aulacomya Ater lives in shallow, in the rather exposed intertidal zones between Peru and the Strait of Magellan throughout the Pacific Coast, and from Southern Brazil, Argentina and Falkland Islands throughout the Atlantic Coast.

The reproductive organs are formed by numerous tubes spread through the visceral mass, especially in the mesosome and the mantle. Sexes are macroscopically differentiated by the colour of the gonads, after they have attained sexual maturity. Males adopt a whitish yellow colour and females, a light brown one, having purple-like parts, its tonality varying according to the quantity of accumulated gametes.

Population sexual cycle is also studied, establishing four sexual maturity states considering the macroscopic morphology of the gonads. It has been determined that the spawning period in the area of Putemún extends from the end of November to February; there is a clear relationship between this and the increase of temperature.

The smallest spawning size corresponded to a mussel 67 mm. in length. The annual average size was 97 mm. 2 periods were confirmed, in which the monthly average decreased: May - July and November - December. In these months the smallest individuals of the whole population were observed, although scarce in number.

A study is made of different mussel population in the Estero de Castro at different depths, observing that samples obtained at a low depth (4.4-4.5 m) present a larger size range than those obtained to lower depths (5.5-9 m). At the last a great number of small-size dead specimens were observed, what is possibly due to mud, depth and place-competition.

The dry weight of soft parts shows its minimum values in November and February coinciding with the largest percentages of spawn individuals.

The size-dry weight of soft part relationship corresponds to the following equation: y = -1.9 + 0.05 x.

Population growth was studied and 3 or 4 age groups were observed. Based on the rings reading, a growth curve was built up, which showed a quick growth in the first period of life, decreasing slowly till the length of 162 mm.

The length-thickness relationship is determined by the equation y = 0.3 + 0.3 x, in which x = size in mm, y = thickness in mm. The length-breadth obeys to the equation y = 8.3 + 0.4 x, in which x = length in mm, y = increasing more quickly in breadth than in thickness, as it grows in length.