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Influence of Carcass‐Derived Nutrients on Sockeye Salmon Productivity of Karluk Lake, Alaska: Importance in the Assessment of an Escapement Goal
Author(s) -
Schmidt Dana C.,
Carlson Stan R.,
Kyle Gary B.,
Finney Bruce P.
Publication year - 1998
Publication title -
north american journal of fisheries management
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.587
H-Index - 72
eISSN - 1548-8675
pISSN - 0275-5947
DOI - 10.1577/1548-8675(1998)018<0743:iocdno>2.0.co;2
Subject(s) - escapement , oncorhynchus , productivity , nutrient , environmental science , abundance (ecology) , otolith , fishery , phosphorus , biomass (ecology) , biology , fish <actinopterygii> , ecology , chemistry , organic chemistry , economics , macroeconomics
The fishery for Karluk Lake (Kodiak Island, Alaska) sockeye salmon Oncorhynchus nerka has undergone a period of high production (1920s to mid‐1940s), decline (mid‐1940s to late 1970s), and recovery (late 1970s to present). We evaluated historical spawner–recruit data and recent (1980–1994) limnological data to develop an escapement goal (EG) to provide maximum sustainable yield for sockeye salmon. Ricker analysis of the spawner–recruit data explained only a small proportion of the total variation ( r 2 = 0.17) in log e recruit/spawner ( R / S ) and exhibited a significant first‐order autocorrelation ( r 1 = 0.68; P < 0.0001). Ricker time–polynomial regression exhibited no significant residual autocorrelation, explained 71% of the variation in log e R / S , and indicated that intrinsic productivity (α parameter) has remained fairly constant, whereas system capacity (β parameter) has been temporally unstable. Markov transition probabilities indicated that escapements between 0.8 and 1.0 million fish maximize yield. In comparison, a graphical assessment of actual spawner abundance versus predicted maximum sustained yield indicated a production threshold (about 0.8 million spawners) and revealed a temporal pattern in production related to spawner abundance. These findings suggest a positive‐feedback mechanism related to the size of the escapement, which we hypothesize is primarily due to nutrients from spawner carcasses. Sockeye salmon carcasses produce an estimated 90% of the phosphorus above baseline loading and have accounted for 40% or more of the total phosphorus in Karluk Lake. The historical trend in sedimentary δ 15 N shows a strong reduction in marine‐derived nutrients since the onset of commercial fishing around 1890, a pattern that roughly corresponds to the decline in sockeye salmon production and system capacity. These findings and other trophic‐level limnological analyses suggest an EG of 0.8–1.0 million fish. Our evaluations also indicated that approximately equal proportions of early‐run (before July 15) and late‐run (after July 15) spawners are needed to optimize sockeye salmon production at Karluk Lake.