Growth, mortality, population structure and spawning biology of stocks of the Atlantic smelt Osmerus mordax (Mitchell) in Newfoundland

Nhwani, Lazarus Bundu (1973) Growth, mortality, population structure and spawning biology of stocks of the Atlantic smelt Osmerus mordax (Mitchell) in Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The length (size) and age distributions of spawning smelt are used to determine the existence of different stocks of smelt in Newfoundland. These distributions indicate that the mean size and age of smelt from Norris Arm (Notre Dame Bay) are greater than those of smelt from Port au Port Bay. -- The scale radius-total length relationship of Newfoundland smelt was found to be linear. However, it varies from place and between the sexes. Back-calculated lengths-at-age were therefore computed separately for the sexes and for the different populations studied. -- Growth curves, as constructed from back-calculated lengths, indicated that beyond the first year, females attain a larger size at age than males. The growth curves also show that Norris Arm (Notre Dame Bay) smelt live longer and grow to a larger maximum size than Port au Port Bay smelt. The latter, however, mature at an earlier age. The short life span of Port au Port Bay fish is largely a result of a high spawning mortality. While the Port au Port Bay fish mature at the age of two to three years, their annual mortality rate is between 85% (Port au Port) and over 95% (Piccadilly) between ages 3-5 and 4-5 respectively. The Norris Arm fish mature at the later age of 4 years and have a lower annual mortality rate of 76% between ages 4 and 6. Thus most of the Port au Port Bay fish die at or soon after spawning while many Norris Arm fish survive and spawn more than once. In general, male smelt have a higher mortality rate than females. -- Spawning smelt in the areas studied show a predominance of males over females at all times. Seasonally, the larger and older individuals enter the spawning streams earlier than the smaller and younger individuals. -- The differences in size and age composition as well as in the growth pattern between the Norris Arm (Notre Dame Bay) and Port au Port Bay smelt are indicative of the existence of distinct stocks in these areas. This is supported by the fact that smelt are known to make only limited movements which are close to their spawning sites. It is apparent that Newfoundland smelt consist of different stocks that are possibly delimited by the numerous bays. The importance of this to the management of the fishery are discussed.

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