Aspects of the biology of the sepiolid squid Rossia Pacifica Berry
Date
2020-12-01
Authors
Brocco, Steven L.
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Abstract
Aspects of the biology of the sepiolid squid Rossia pacifica Berry were studied from specimens obtained by otter trawling at Cape Lazo Gully and Saanich Inlet, British Columbia. Temperature, salinity, and sediment size at Cape Lazo Gully varied from 7.18°C to 11.00°C, 28.01 °/oo to 30.21 °/oo, and from less than l00μd to over 250μd respectively. Living specimens in the laboratory exhibited color changes from dark red-brown to opalescent grey-green. They did not mimic the color of the substrate. Comparisons of the morphometric indices of R. pacifica with other species of this genus showed differences in some indices but not in others. The arm formula is inconsistent, the most common being 3>2>4>1 and 3>2=4>1. The lower beak differs from that of R. maarosoma by having a "tooth" on its shoulder. In an aquarium Rossia spent most of its time resting on the bottom either in a horizontal position or with the anterior end elevated. The squid usually formed a depression in the sandy bottom to rest in. In some instances they threw sand onto their backs. Fish were caught with the tentacles and held with the arms while being eaten. Stomach analysis revealed that crustacea were present in 86.6% of the stomachs that contained food, while fish were present in 16.6%. Shrimp formed the largest portion of the crustacea in the diet. Bivalve molluscs, squid, and ostracods were occasionally found. Proportions of crustacea to fish in the diet were higher in smaller squid and decreased in larger animals. Seasonal variations in the diet were correlated with the biomass of shrimp in the area where the squid were collected; when a low biomass of shrimp was present the squid had a higher proportion of fish in their diet. The female R. pacifica are slightly larger than the males of the same age and grow to a larger size than do the males. The male and female reproductive systems are described. Gonad indices show that the ovaries and nidamental glands begin to mature when the females have a dorsal mantle length of approximately 24.0 mm. Spermatophores were not found in males smaller than 22 mm mantle length. The proportion of males containing spermatophores was 9% at 22 mm and increased through 17% at 24 mm, 50% at 26 mm to 90% at 28 mm. During mating the male attaches to the female from below by means of his second, third, and fourth pairs of arms. Spermatophores are transferred into the dorsal region of the female's pallial cavity by his dorsal, hectocotylized arms. The sex ratio of males to females found at Cape Lazo Gully was 1.2:1.0. Spawning occurs in the fall with the most active period occurring from August through October.
This may be correlated with an increase in the water temperature, during this time. The squid have a life span of one year, at the end of which they mate, spawn, and die.
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Keywords
Cape Lazo Gully, Saanich Inlet, sepiolid squid, Rossia pacifica Berry