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A Time Density Model to Estimate Run Size and Entry Timing in a Salmon Fishery
Author(s) -
Springborn Robert Richard,
Lampsakis Nickolas D.,
Gallucci Vincent F.
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<0391:atdmte>2.0.co;2
Subject(s) - catch per unit effort , fishery , oncorhynchus , fisheries management , environmental science , fish <actinopterygii> , statistics , fishing , mathematics , biology
Managers need improved estimates of run size and entry timing for salmon migrating to their natal spawning grounds if they are to improve the biological and economic management of salmon fisheries. A time density model was derived from the inverted exponential model of Mathisen and Berg. During a fishery, this model provides three estimates of run size that are more accurate than the preseason forecast. The result is used to manage fisheries for chum salmon Oncorhynchus keta in the entire Hood Canal area and the Skokomish River of western Washington state. The model uses both daily catches per unit effort (CPUE) by drift gill nets and peak purse‐seine catches from a northern Hood Canal fishery to estimate run size and entry timing. Run size and entry timing estimates are derived from a fitted cumulative time density of daily CPUE; historical data are used to correct for missing daily gill‐net CPUE values. The result is estimates of run size with increased precision and decreased bias. A linear regression model, in which a peak 1‐d purse‐seine catch is an independent variable, is used to correct the time density run size estimate. This correction decreased the run size mean percent error from 18% to 5% and from 27% to 4% on two successive updates. The assumptions are that: (1) the timing and progression of a salmon migration are consistent; (2) there is continuous fish passage in one direction; (3) the gill nets sample passively; (4) estimates of daily CPUE from the fishery can be used to construct the time density; and (5) the cumulative daily CPUE for the season is directly proportional to run size. The accuracy of run size and entry timing estimates obtained during the fishery are likely to be affected by gear competition between the purse‐seine fleet and the drift gill‐net fleet, as well as by data misreporting and time delays in reporting daily drift gill‐net CPUE. This model could be applied to most exploited animal populations where the abundance of individuals over time at a fixed geographic reference frame is approximately normally distributed.