The biology of the shorthorn sculpin Myoxocephalus scorpius (L.) in Newfoundland waters

Ennis, G. P. (1969) The biology of the shorthorn sculpin Myoxocephalus scorpius (L.) in Newfoundland waters. Masters thesis, Memorial University of Newfoundland.

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Abstract

The shorthorn sculpin Myoxoaephalus scorpius is not fished commercially in Newfoundland. Its biology, based primarily on year-round monthly samples from Bay Bulls and on direct observations in its natural environment while scuba diving, is presented. -- The nomenclature of the species is reviewed briefly. -- The length frequencies of males were normally distributed but those of the females were more evenly distributed throughout their range of lengths. Females attain larger sizes and, on the average, are larger than the males. -- Various length-weight relationships, including whole, gutted and fillet weights, for each sex are given as well as seasonal changes in the coefficient of condition. -- Average length-at-age data were fitted to the von Bertalanffy equation. Below age 4 the growth rates of males and females were little different but above age 4 the females grew much faster than the males. The difference between average length-at-age for males and females became progressively larger with age. Analysis of the age composition of the populations sampled showed definite year-class dominance. -- Males were found to mature at a younger age and at a smaller size than females. In any age group where there were mature and immature specimens the mature ones, on the average, were larger. -- Ripening ovaries were found to contain 3 generations of ova which were evenly distributed throughout the ovary. Oogenesis takes about 2½ years. Spawning starts in late November to early December and lasts for about one month. The eggs are deposited in clumps in crevices usually in about 20-35 ft of water and after spawning the females move away from the spawning area into deeper water. The mature males remain behind and guard the eggs until they hatch. At temperatures near 0.0°C embryonic development takes over 3 months. Hatching starts about mid-March, reaches a peak towards the end of March and is completed early in April. Newly- hatched larvae were observed to occupy all layers of the water column where the water was about 25-30 ft deep but were concentrated about 2 ft off the bottom. They were observed to swim upwards and to sink downwards in the water column. Mature females produced between 4000 and 61,000 eggs depending on size. -- Shorthorn sculpins are omnivorous carnivores and scavengers. The bulk of their food is benthic invertebrates, mainly crabs, but small, bottom-living fishes form a fairly large part of their diet. Feeding activity changes throughout the year and is considerably reduced before and during the spawning period. They have a rich parasitic fauna, including a variety of trematodes a and nematodes internally and amphipods and hirudineans externally.

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