Using Harvest Slot Limits to Promote Stock Recovery and Broaden Age Structure in Marine Recreational Fisheries: A Case Study

Fish populations with broad age distributions are expected to have higher reproductive capacity than age-truncated populations because of the disproportionate contributions of older fish. Harvest slot limits, an expected means of ameliorating age truncation, are modeled for Tautog Tautoga onitis in an overfished population subunit that is experiencing overfishing. Tautog, currently managed by a 40 cm minimum size limit (MSL), is a candidate species for slots because it is relatively long-lived, slow-growing, with low discard mortality. We evaluated changes in biomass and abundance-at-age relative to management with the current MSL regulations using a forward population simulation model for four slots: 35–45 (small-wide), 38–42 (small-narrow), 40–50 (large-wide), and 43–47 (large-narrow) cm, inclusive. Angler behavioral responses were evaluated at 0%, 10%, and 20% noncompliance with the upper slot limit. The biomass and number of fish removed are reduced with harvest slot limit management, relative to the MSL, but because the harvest is redirected to smaller fish the reduction in numbers removed is not as large as the reduction in biomass removed. Slot limits broadened the age structure within 10 years by reducing fishing mortality on extant fish. Median spawning stock biomass (SSB) recovered more quickly in three of the slots than with MSL regulation (three to six years to reach SSBThreshold as compared to nine years with MSL management). We concluded that harvest slot limits can broaden age structure and restore biomass in overfished fisheries, but should be evaluated when managing coastal fisheries as a reduction in biomass removed is required

Population Size of Hatchery-Reared and Wild Pallid Sturgeon in the Lower Missouri River

The population size of pallid sturgeon Scaphirhynchus albus is currently unknown throughout much of the Missouri River. Listed as federally endangered in 1990, the pallid sturgeon remains one of the rarest fishes in the Missouri and Mississippi River basins, and little to no natural recruitment occurs. Artificial population supplementation via a hatchery propagation program was initiated, necessitating the collection of sexually mature pallid sturgeon. Therefore, the Nebraska Game and Parks Commission maintained an intensive broodstock collection and mark– recapture effort from 2008 to 2010 to capture reproductively ready adults for the propagation program. Coordinated crews fished baited trotlines from the confluence of the Platte and Missouri rivers at river kilometer (rkm) 957.6 to a point about 80.5 rkm downstream. A total of 438 pallid sturgeon were captured, which amounts to a 7.8% recapture rate. The objectives of the study were to (1) use these data to estimate the annual population sizes of wild-origin and hatchery-reared pallid sturgeon within the above-mentioned 80.5-rkm reach of the lower Missouri River and (2) compare current population levels with the Pallid Sturgeon Recovery Team’s population objective. We used the mark–recapture data in a robust-design analysis to derive population estimates and annual survival, capture, and temporary emigration rates. The annual population estimate for wild pallid sturgeon varied from 5.4 to 8.9 fish/rkm, whereas the estimate for known hatchery-reared fish varied from 28.6 to 32.3 fish/rkm. The robust-design approach to our analysis resulted in useful estimates of population size and other variables important to quantifying species recovery and management targets; the approach may be suitable for other fisheries management data sets