Presentation: State-of-Knowledge Initiative for the Special Committee on Sustainable Aquaculture of the British Columbia Legislature

Delivered November, 2006.

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Biology of Pink Salmon

[A full pdf copy for printing may be downloaded from the WAVES database.]

While pink salmon can be the most abundant species of Pacific salmon, their simple life history results in the species being prone to significant sudden changes in abundance.

Pink salmon have a fixed two-year life cycle (all spawning adults are two-years old) and juveniles emigrate to estuaries very shortly after emergence from stream gravels. Pink salmon enter the coastal marine waters as very small juveniles (28 to 35 mm, and up to 260 mg).

Production of pink salmon is highly dependent on environmental conditions during one spawning year and the subsequent conditions in the ocean the following year. Unlike other Pacific salmon, pink salmon lack the resilience provided by multiple age classes that buffer (protect) a population from conditions in one year.

For example, pink and chum salmon have similar juvenile behaviours but chum salmon return as mature adults at ages 3 to 5 but never at age 2.

Consequently, chum salmon returns observed in any calendar year consist of fish that enter the sea in three different years.

The production dynamics and natural mortality of pink salmon were studied by Parker for populations in central B.C. These early studies established the high natural mortality for pinks during early sea entry (first 40 days) and a lower mortality rate during “ocean” rearing and until return as mature adults after a 410 day period.

Figure A depicts the range of natural mortality rates estimated by Parker over three brood years of pink salmon from the Bella Coola and Atnarko rivers (1961-1963, returns in 1963-1965). Overall survival from juveniles to returning adults ranged from only 1.1% to 10.2% (the same range observed today for Fraser River pink salmon).

However, within the first 40 days, the losses amounted to 59 to 77% of the initial number of juveniles that entered the sea (survival rates of 41% to 23%)

Two important features of Pink salmon population dynamics need to be understood:
    i. life-span mortality is naturally large and variable, and
    ii. total adult return is the outcome of three life phases (freshwater incubation and emergence, early in shore coastal rearing, and growth and survival in the open ocean and return migration).

Within each phase, survival rates may exacerbate or compensate for production in other phases.
 

Within the Broughton Archipelago, both exceptionally poor adult pink salmon returns and exceptionally good returns have been documented in recent years. Returns to specific rivers within the BA may also vary from year to year.

Figure A

References

Beamish, R.J., S. Jones, C. Neville, R. Sweeting, G. Karreman, S. Saksida, and E. Gordon. 2006. Exceptional
    marine survival of pink salmon that entered the marine environment in 2003 suggests that farmed Atlantic
    salmon and Pacific salmon can coexist successfully in a marine ecosystem on the Pacific coast of Canada.
    ICES J. Mar. Sci. 63: 1326-1337.

PFRCC (Pacific Fisheries Resource Conservation Council). 2002. 2002 Advisory: The protection of Broughton
    Archipelago pink salmon stocks. Appendix 2. http://www.fish.bc.ca

Parker, R.R. 1965. Estimation of sea mortality rates for the 1961 brood-year pink salmon of the Bella Coola
    area, British Columbia. J. Fish. Res. Bd. Canada, 22(6): 1523-1554.

Parker, R.R. 1968. Marine mortality schedules of pink salmon of the Bella Coola River, central British Columbia.
    J. Fish. Res. Bd. Canada, 25(4): 757-794.