Research Document - 2013/090
Population viability analysis for the South Newfoundland Atlantic Salmon (Salmo salar) designatable unit
By M.J. Robertson, L.K. Weir, and J.B. Dempson
Abstract
Analyses of recent status and trends as well as a population viability analysis (PVA) were conducted for the South Newfoundland Atlantic Salmon designatable unit (DU 4). Trend analyses were conducted for each South Coast Salmon Fishing Area (SFAs 9-12), four currently monitored rivers (Conne River, Little River, Northeast Brook and Rocky River) and the composite index of these rivers. For individual rivers, only Conne River and Little River in SFA 11 had statistically significant declines in salmon abundance since 1996 (56% and 71% respectively). Population viability analyses were conducted using eight average marine survival values (2% to 9%) and four fishing mortality rates: no angling, catch-and-release only angling, half of current angling and current angling (includes retention and catch-and-release mortality). All possible combinations of marine survival values and fishing mortality rates were assessed to estimate the probability of meeting or exceeding each of three population abundance levels in the next 15 years: current population size, conservation requirement/recovery target and the pre-decline mean. Under current conditions (1996-2010) the probability of DU 4 Atlantic Salmon meeting or exceeding the conservation requirement/recovery target in the next 15 years was 27%. Removing angling mortality increased this probability to 50%. As expected, marine survival has a very strong influence on the potential recovery of DU 4 salmon. An increase in average marine survival from 4% to 5% over the next 15 years improved the probability of achieving the conservation requirement/recovery target from 27% to 66% under current angling rates. This probability reaches 85% with no angling. Given that estimated catch-and-release fishing mortality was relatively low, population projections were generally similar to no angling. The probability of DU 4 Atlantic Salmon remaining at their current population size over the next 15 years was 48% under current angling rates and 72% under no angling. These proportions increase to 87% and 96%, respectively, if average marine survival increased from 4% to 5% over the next 15 years. In general, the probability that DU 4 Atlantic Salmon abundance will increase was greatly improved with higher marine survival rates and management measures to reduce angling mortality.
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