Lake Sturgeon Abundance and Harvest in Black Lake, Michigan, 1975–1999

Abstract

The population of lake sturgeon Acipenser fulvescens in Black Lake, Michigan, has supported a popular winter spear fishery since 1948, but status of the population had not been assessed since the mid-1970s. We sampled the population during May–Jul 1997 with 20.3- and 25.4-cm-stretch-measure gill nets with the objective of estimating population size using the Schnabel method. We also examined harvest data from voluntary registration of speared fish spanning the years 1975–1999 to evaluate the impact that harvest may have had on the population. During 24 sample periods, we tagged and measured 192 lake sturgeon between 75 and 193 cm total length and removed the marginal pectoral fin ray from a subsample of those fish to estimate age. We also recaptured 14 lake sturgeon during the 24 sample periods. Captured fish ranged in age from 9 to 64 years. The estimated size of the 90 cm and larger lake sturgeon population was 1,241 fish. Based on the length frequency of the catch, there were 549 harvestable-size fish (127 cm and larger). This represents a 66% decline from the 1975 estimate of 1,599 harvestable-size fish. Lake sturgeon harvest steadily declined from 1975 to 1999, and regression analysis indicates that if the trend continues, harvest will be near zero by 2011. Average weight and length of harvested lake sturgeon over the same time period has steadily increased, indicating recruitment was not sufficient to keep up with the current harvest. Legal harvest has accounted for 40% of the population decline since 1975. It is likely that illegal harvest, wounding mortality from spearing, and natural mortality account for the remaining 60% of the decline. New restrictive harvest regulations, including a lakewide quota of five fish per year, will be enforced beginning in 2000 to protect the population from extirpation.