Research Document - 2000/37

Status of the Atlantic salmon (Salmo salar L.) stock of Humber River, Newfoundland, 1999.

By Par C.C. Mullins et D. Caines

Abstract

This is the tenth assessment of the Atlantic salmon stock of the Humber River. The results of the mark-recapture study in 1999 indicated that 27,585 (95% CI=20,779 - 37,984) small and 4,433 (95% CI=3,042 - 6,675) large salmon returned to the Humber River during the period of the study. The recapture trap used in 1999 was preferable to angling for tag recaptures because no adjustment is necessary to account for the voluntary tag-reporting rate and the catch did not have to be estimated. A double-tagging experiment indicated no tag loss for salmon recaptured in the recapture trap and by angling. This suggested that calculation methods used in previous years might have resulted in an under-estimate of tag retention rate and possibly, then, a small under-estimate of population size. The recreational fishery retained catch of small salmon was higher than in 1998 but the released catch was lower. The released catch of large salmon was higher than in 1998. Increased retention limits and removal of split season restrictions as well as increased returns may have contributed to improved angling catches. The proportion of large salmon caught in the estuary tagging traps was lower than in 1998 but equal to 1992-98 mean. Egg depositions calculated for 1999 were 201% (95% CI = 144% - 290%) of the conservation requirement. This level of egg deposition had a very high probability of occurrence based on a probability density function incorporating some of the uncertainty associated with the estimate of returns and biological parameters. Potential sources of mortality that could result in additional uncertainty in the estimate of potential egg depositions in 1999 included record low water levels, increased indication of illegal removals and reports of seals on the river. Recruits in 1999 exceeded estimates of the spawners that produced them indicating continued improvement in the stock but fluctuations in returns in recent years create some degree of uncertainty. Returns to the river in 1998 were revised based on updated angling catch data and indicated that the conservation requirement was exceeded in 1998.

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