Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—This paper analyzes historical abundances of spawning stocks of Atlantic sturgeon <em>Acipenser oxyrinchus</em> during the late nineteenth century, when peak United States harvest of Atlantic sturgeon occurred (3,200 metric tons in 1888). The advent of preparation methods for caviar, transportation networks that allowed export of caviar to Europe, improvements in fishing technology, and development of a domestic smoked sturgeon market caused rapid emergence of an Atlantic sturgeon industry after the Civil War. The industry originated and was centered in the Delaware Bay, which supported the most abundant population on the U.S. East Coast. Important fisheries also developed in the Chesapeake Bay, the Carolinas, and Georgia. Caviar was the principal marketable product of the fishery and large females were targeted, resulting in fisheries collapse at the turn of the century. No substantial resurgence of Atlantic sturgeon landings has occurred in the twentieth century. A previous analysis of U.S. Fish Commission catch and effort records for the Delaware Bay fishery provided an estimate of 180,000 females prior to 1890. The Delaware Bay abundance estimate was extrapolated to other states by calculating the mean level of each state’s contribution to U.S. yields during the period 1880–1901. This approach led to abundance estimates of 29,000 for the Southern States (North Carolina, South Carolina, Georgia, Florida), 20,000 for the Chesapeake Bay (Maryland, Virginia), 180,000 for the Delaware Bay, and 6,000 for the Hudson River (New York). Although the approaches used to estimate historical biomass and abundance contain untested assumptions and biases, the dominance of the Delaware Bay population in comparison to others is in part confirmed by the industry that developed there. Given the uncertainty in abundance estimates, conservative benchmarks are proposed of 10,000 females each, for systems that previously supported important fisheries.

Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—The shortnose sturgeon, <em>Acipenser brevirostrum</em>, is a long-lived species that grows slowly, matures at an advanced age, and spawns only intermittently. In the Connecticut River, there are two distinct subpopulations of shortnose sturgeon, which have been separated by the Holyoke Dam for 157 years. My research addressed the viability and persistence for these two separate populations and the effects of dispersal, variation in survival and reproduction, and catastrophes. My risk-based approach used a stage-based metapopulation model that I constructed in RAMAS^® GIS incorporating the available data. Based on the existing data, this population model for the shortnose sturgeon metapopulation in the Connecticut River made several predictions. The observed stability of the two subpopulations was possible either: with reproduction in both upper and lower subpopulations and small to moderate rates of dispersal between them; or with no reproduction in the lower subpopulation, very high reproduction in the upper subpopulation and high rate of net downstream dispersal. My results provided estimates of extinction risk for the shortnose sturgeon metapopulation under various management options and highlighted three key areas for future research, demonstrating the value of a risk-based approach. This approach is particularly useful for management of long-lived aquatic species.

Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—It is difficult to distinguish pallid sturgeon <em>Scaphirhynchus albus</em> from the morphologically similar, congeneric and sympatric shovelnose sturgeon <em>S. platorynchus</em>. This has led some to question whether the pallid sturgeon is indeed a valid species. Another controversy is whether the two species are hybridizing. Indices, based on various morphometric and meristic characters, have been proposed to discriminate among <em>Scaphirhynchus</em> taxa, but they are cumbersome to calculate in the field. We report two mathematical indices developed via multiple regression analysis that use five morphometric ratios and two meristics (Character Index), or the five morphometric ratios alone (Morphometric Character Index) as taxon predictors. Data from a study of pallid sturgeon and shovelnose sturgeon conducted by Carlson and Pflieger (1981) were used to develop the regression models. The consistency of identifications made by the two indices was examined using Discriminant Functions Analysis (DFA) on a collection of 257 <em>Scaphirhynchus</em> specimens from throughout the pallid sturgeon range. Specimens identified via the CI and mCI as pallid sturgeon grouped distinctly from the shovelnose sturgeon cluster; specimens identified as hybrids by the two indices formed an intermediate cluster. The majority (90% and 89.7%, respectively) of the specimens identified as pallid sturgeon by the Character Index (CI) and the Morphometric Character Index (mCI) were classified as pallid sturgeon by DFA. This morphological evidence supports the current status of pallid sturgeon and shovelnose sturgeon as distinct species. Interspecific hybridization, considered by some to be a major threat to the pallid sturgeon, appears to be common. The Pallid Sturgeon Recovery Team has recommended the CI for field identifications throughout the pallid sturgeon’s range.

Biology, Management, and Protection of North American Sturgeon

Abstract.— We use elasticity analyses for three sturgeon species, the shortnose sturgeon <em>Acipenser brevirostrum</em>, Atlantic sturgeon <em>A. oxyrinchus</em>, and white sturgeon <em>A. transmontanus</em>, to calculate the potential to increase population growth rate, λ, by improving survival and fecundity. Elasticity analysis is a means of assessing changes to λ resulting from conservation initiatives. The elasticity of λ to survival has a characteristic profile that includes a plateau of high elasticity values across the young of the year and the juvenile ages. However, survival elasticity falls at maturity and declines rapidly with increasing adult age. Changes to fecundity have relatively little impact; the total of the fecundity elasticities over all ages is equal to the single young-of-the-year survival elasticity. Even though the young-of-the-year survival elasticity is equal to that of any other juvenile age, the overall opportunity for affecting λ; is strongest in the young-of-the-year age-class because of its exceptional potential for increase to survival. The juvenile and adult stages have roughly equal total survival elasticities. These findings are particularly relevant in understanding the contributions of hatcheries, harvest regulations and habitat restoration as strategies for sturgeon conservation. Hatcheries are focused on the young of the year, the demographically most sensitive component of sturgeon life histories, and thus have the potential to make significant increases to λ if the genetic, evolutionary and ecological impacts of hatcheries can be controlled. Harvest, even at low levels, can have a significant negative impact on λ when it affects multiple age classes. Managers can use elasticity analysis to calculate the total impact of harvest and to mathematically evaluate the trade-off in exploiting young versus older individuals. Habitat restoration strategies, usually assessed in terms of survivals of the age classes impacted, would also benefit from using elasticity analysis to interpret their contributions to l. If restoration efforts target the survival of age classes with high elasticities, significant population growth may be achieved.

Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—Gametes of green sturgeon <em>Acipenser medirostris</em> (caught in the Klamath River, California) and farm-reared white sturgeon <em>A. transmontanus</em> were obtained using hormonal induction of ovulation and spermiation. The offspring of one female in each species were reared in the laboratory, to compare their development and growth. Green and white sturgeon embryos had similar rates of development and hatched after 169 h and 176 h, respectively, at incubation temperature 15.7 ± 0.2°C. Embryos of both species exhibited similar holoblastic development and passed through 36 stages characteristic of acipenserids. Green sturgeon fertilization and hatching rates were 41.2% and 28.0%, compared with 95.4% and 82.1% for the white sturgeon. Larval survival to 45 d (metamorphosis) was 93.3% in green and 92.1% in white sturgeon. Newly hatched green sturgeon (length 13.7 ± 0.4 mm, mean ± SD) were larger and less pigmented, compared with white sturgeon. They had large ovoid yolk sacs and did not exhibit pelagic behavior that was observed in white sturgeon. The onset of exogenous feeding in green sturgeon occurred at age 10–15 d and length 24.0 ± 0.5 mm, and metamorphosis was completed at age 45 d and length 74.4 ± 5.9 mm (rearing temperature 18.5 ± 0.2°C). Weight and length of green sturgeon larvae and juveniles were considerably greater than in white sturgeon at each sampling time, but the relative growth rate and weight-length relationship were similar in both species. This suggests an effect of larger egg size and maternal yolk supply on the growth of green sturgeon. We conclude that green sturgeon differs from the white sturgeon in their reproductive strategy and, potentially, reproductive habitat.

Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—Five of the nine populations of white sturgeon <em>Acipenser transmontanus</em>, located between dams on the Middle Snake River, have declined from historical levels and are now at risk of extinction. One step towards more effectively protecting and managing these nine populations is ranking factors that influence recruitment in each of these river segments. We developed a model to suggest which of seven mechanistic factors contribute most to lost recruitment in each river segment: (1) temperature-related mortality during incubation, (2) flow-related mortality during incubation, (3) downstream export of larvae, (4) limitation of juvenile and adult habitat, (5) mortality of all ages during summer episodes of poor water quality in reservoirs, (6) entrainment mortality of juveniles and adults, and (7) angling mortality. We simulated recruitment with, and without, each of the seven factors, over a typical series of hydrologic years. We found a hierarchical pattern of limitation. In the first tier, river segments with severe water quality problems grouped together. Poor water quality during summer had a strong negative effect on recruitment in the river segments between Swan Falls Dam and Hell’s Canyon Dam. In the second tier, river segments with better water quality divided into short river segments and longer river segments. Populations in short river segments were limited by larval export. Populations in longer river segments tended to be less strongly limited by any one factor. We also found that downstream effects could be important, suggesting that linked populations cannot be viewed in isolation. In two cases, the effects of a factor on an upstream population had a significant influence on its downstream neighbors.

Biology, Management, and Protection of North American Sturgeon

Abstract.<em>—</em>Although most species of anadromous sturgeons worldwide are threatened with extinction, information on the estuarine and marine components of their life history is generally lacking. During March 1997 to July 1999, we used ultrasonic telemetry to examine estuarine and marine habitat use of adult Gulf sturgeon <em>Acipenser oxyrinchus desotoi</em> from the Choctawhatchee Bay/River System, Florida. During winter and spring, telemetered Gulf sturgeon were distributed nonrandomly within Choctawhatchee Bay, with most relocations in nearshore areas 2–4 m deep. Within the bay, Gulf sturgeon occasionally moved long distances but usually remained in localized areas (<1 km²) for several weeks. Areas where Gulf sturgeon remained for prolonged periods were characterized by sandy substrate harboring a benthic community dominated by crustaceans and annelids. A majority of male Gulf sturgeon remained exclusively in Choctawhatchee Bay during the winter and spring. In contrast, a majority of females during this time were either relocated in the Gulf of Mexico or were absent at sampling locations, having last been detected at bay entrances. Declines in habitat quality in Choctawhatchee Bay and the Gulf of Mexico may hinder recovery of this species, since adult Gulf sturgeon rely on these areas for nourishment during periods of gonadal growth.

Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—White sturgeon <em>Acipenser transmontanus</em> in the Hells Canyon reach of the Snake River have been under sport catch-and-release regulations for almost thirty years. Three states, Idaho, Oregon, and Washington bound this river section, and each imposed catchand-release regulations in 1970s. Nez Perce Tribe tribal members can harvest sturgeon throughout the year in this Snake River section. The population structure at the initiation of catch-and-release regulations showed a deficit in the 92–183 cm (TL) length range as white sturgeon within this group were harvested before 1972. The population composition was 86% between 55 and 92 cm, 4% between 92 and 183 cm, and 10% greater than 183 cm. Information collected during 1982–85 and in 1998 shows increasing abundance in the mid-sized length-group (92–183 cm TL). Because of the positive response of this population to a reduction in legal sport harvest, there have been discussions regarding the elimination of catchand-release fishing. Because of the longevity of white sturgeon, it may take another 25–30 years for the older age-class segment (>183 cm TL) to show a response to catch and release. For the interim, I suggest that strong consideration be given for retaining the Hells Canyon population as a conservation research population. This designation would allow for better understanding of population dynamics for future managers, but still allow present activities of catch-and-release sport fishing and tribal harvest.

Biology, Management, and Protection of North American Sturgeon

<em>Abstract.</em>—The Kootenai River ecosystem in Idaho, Montana and British Columbia, Canada has been altered and degraded during the past 75 years. By the mid-1960s, phosphorus concentrations increased 15-fold, and nitrogen doubled from baseline conditions in the Kootenai River due to municipal and industrial development. Pollution abatement beginning in the late 1960s, and subsequent impoundment of the Kootenai River (Libby Dam 1972) reversed this culturally eutrophic condition. By the mid-1990s the Kootenai River was classified as ultraoligotrophic, as it remains today. Reverberating trophic responses to cultural denutrification were temporally correlated with the collapse of the functional Kootenai River ecosystem and its endemic white sturgeon <em>Acipenser transmontanus</em> population. Natural recruitment of white sturgeon in the Kootenai River has been virtually absent during the past 30 years, with several exceptions. In response to consistent natural recruitment failure, the Kootenai River white sturgeon population was listed as endangered on September 6, 1994, under the U.S. Endangered Species Act. Depressed biological productivity, alteration of spawning and rearing habitats, fish species abundance changes, altered predator–prey dynamics, and consistent white sturgeon recruitment failure constituted biological (ecological) responses to Kootenai River Basin development. We propose an integrated hypothesis to explain natural recruitment failure in the Kootenai River white sturgeon population. This hypothesis suggests that, during some years, natural recruitment failure may have been caused by female stock limitation. In other years (those lacking female stock-limitation), we propose that recruitment failure was due to one or more postspawning early life mortality factors.