Ecology and demographics of Pacific sand lance, Ammodytes hexapterus Pallas, in Lower Cook Inlet, Alaska

Robards, Martin D. (2000) Ecology and demographics of Pacific sand lance, Ammodytes hexapterus Pallas, in Lower Cook Inlet, Alaska. Masters thesis, Memorial University of Newfoundland.

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Abstract

Distinct sand lance populations occur within the relatively small geographic area of Lower Cook Inlet, Alaska. Marked meso-scale differences in abundance, growth, and mortality existed as a consequence of differing oceanographic regimes. Growth rate within populations (between years) was positively correlated with temperature. -- However, this did not extend to inter-population comparisons where differing growth rates were better correlated to marine productivity. Opaque otoliths form in juvenile sand lance during their first summer coinciding with their period of rapid growth. Subsequent opaque zones are deposited during spring, in conjunction with rapidly increasing water temperatures. Areal rather than radial descriptors of otolith size provide the best relation to sand lance length. A single linear regression was insufficient to describe this relationship with separate linear regressions needed for both juveniles and adults. No sexual dimorphism was observed for sand lance in length-at-weight (gonad-free) or length-at-age. Most sand lance reached maturity in their second year. Field observations and indices of maturity, gonad development, and ova-size distribution all indicated that sand lance spawn once each year. Males mature earlier in the season than females, but females (31 %) attain a higher gonadosomatic index than males (21 %). Sand lance spawned intertidally in late September and October on fine gravel/sandy beaches soon after the seasonal peak in water temperatures. Fecundity of females (93-199 mm) was proportional to length, ranging from 1,468 to 16,081 ova. Spawned eggs were 1.02 ± 0.08 mm in diameter, demersal, slightly adhesive, and deposited in the intertidal just below the waterline. Sand lance embryos developed over 67 days through periods of intertidal exposure and sub-freezing air temperatures. Mean dry-weight energy value of sand lance cycles seasonally, peaking in spring and early summer (20.91 klg-1 for males, 21.08 kJg-1 for females), and subsequently declining by about 25 % during late summer and fall (15.91 kJg-1 for males, 15.74 kJg-1 for females). Declines in energy density during late summer paralleled gonadal development, sand lance entering the winter with close to their minimum whole body energy content. Dry weight energy densities of juveniles increased from a minimum 16.67 kJg-1 to a maximum of 19.68 kJg-1 and are higher than adults in late summer.

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