William E. Pine

Population Viability of the Gulf of Mexico Sturgeon: Inferences from Capture–Recapture and Age-Structured Models

Abstract The Suwannee River, Florida, population of the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi, a subspecies of Atlantic sturgeon A. oxyrinchus oxyrinchus, was evaluated using a capture–recapture approach and an age-structured model to examine population trends from 1986 through 1995. The capture–recapture analysis revealed a positive rate of change (λ) in the adult population, indicating that it was slowly increasing from the mid-1980s through the mid-1990s. The age-structured model revealed that the population was highly sensitive to changes in egg-to-age-1 mortality, the percentage of females that spawn annually, and adult mortality. The model predicted that even slight increases in annual adult mortality (from 16% to 20%) would result in a decline in the Suwannee River Gulf sturgeon population. Population trends were consistent for both modeling procedures and were similar to those in published reports. Although this population is currently expanding, care should be taken to protect adul...

Differential Growth and Survival of Weekly Age-0 Black Crappie Cohorts in a Florida Lake

Abstract Black crappies Pomoxis nigromaculatus exhibit highly variable survival to adulthood because of their varying larval and juvenile abundance, growth, and mortality during early life. We examined how growth and mortality changed with hatch date, prey density, and water temperature for 7-d cohorts of juvenile black crappies in Lake Wauberg, Florida (a 150-ha hypereutrophic natural lake) during spring and summer 1998. Fish were collected once per week from March through June and twice per month during July and August by means of an otter trawl. Based on daily otolith rings, hatching occurred over a 12-week period (1 March−18 May). The mean daily growth rate (DGR) was positively related to water temperature, which increased over the hatching season. Common prey taxa included calanoid copepods, Daphnia and Bosmina spp., and cyclopoid copepods. The total density of these taxa did not differ significantly among collection dates. Mean hatching date shifted from mid-March for fish collected in mid-April to ...

Abundance Trends and Status of the Little Colorado River Population of Humpback Chub

Abstract The abundance of the Little Colorado River population of federally listed humpback chub Gila cypha in Grand Canyon has been monitored since the late 1980s by means of catch rate indices and capture–recapture-based abundance estimators. Analyses of data from all sources using various methods are consistent and indicate that the adult population has declined since monitoring began. Intensive tagging led to a high proportion (>80%) of the adult population being marked by the mid-1990s. Analysis of these data using both closed and open abundance estimation models yields results that agree with catch rate indices about the extent of the decline. Survival rates for age-2 and older fish are age dependent but apparently not time dependent. Back-calculation of recruitment using the apparent 1990s population age structure implies periods of higher recruitment in the late 1970s to early 1980s than is now the case. Our analyses indicate that the U.S. Fish and Wildlife Service recovery criterion of stable abu...

Nonnative Fish Control in the Colorado River in Grand Canyon, Arizona: An Effective Program or Serendipitous Timing?

Abstract The federally endangered humpback chub Gila cypha in the Colorado River within Grand Canyon is currently the focus of a multiyear program of ecosystem-level experimentation designed to improve native fish survival and promote population recovery as part of the Glen Canyon Dam Adaptive Management Program. A key element of this experiment was a 4-year effort to remove nonnative fishes from critical humpback chub habitat, thereby reducing potentially negative interactions between native and nonnative fishes. Over 36,500 fish from 15 species were captured in the mechanical removal reach during 2003–2006. The majority (64%) of the catch consisted of nonnative fish, including rainbow trout Oncorhynchus mykiss (19,020), fathead minnow Pimephales promelas (2,569), common carp Cyprinus carpio (802), and brown trout Salmo trutta (479). Native fish (13,268) constituted 36% of the total catch and included flannelmouth suckers Catostomus latipinnis (7,347), humpback chub (2,606), bluehead suckers Catostomus d...

Counterintuitive Responses of Fish Populations to Management Actions

Abstract Observed ecosystem responses to fisheries management experiments have often been either much smaller or in the opposite direction of the expected responses based on experience or population models. Examples of these responses can be found even for some very simple experimental management manipulations such as predator and prey manipulations in small lakes and ponds to fish population responses to harvest closures. Such counter-intuitive prediction failures offer opportunities to identify key processes and variables that are not widely considered in models used to evaluate ecosystem-based fisheries management policies. A common denominator in the case histories presented are unexpected behavioral responses and strong changes in juvenile survival rates of fish driven by changes in competition, predation, and behavioral responses to predation risk. These factors restructured many of the ecosystems in our simple examples, yet are not widely included in models currently used to evaluate ecosystem-base...

Parameterizing age-structured models from a fisheries management perspective

Age-structured models are widely used in fisheries stock assessments and contain two very important parameters that determine the rate and amount of harvest that can be safely taken: the compensation rate in juvenile survival (κ) and the unfished biomass (Bo). These two parameters are often confounded. It is common for relative abundance indices to lack contrast, and the use of informative priors, or fixing at least one of these parameters, is necessary to develop management advice. Providing management advice proceeds by transforming estimates of biological variables such as Bo and κ into management variables such as the maximum sustainable yield (C*) and the fishing mortality rate that would achieve this yield (F*). There is no analytical solution for the transformation of Bo, κ to C*, or F* for age-structured models with commonly used stock–recruitment functions and therefore must be done numerically. The opposite transition, however, does have an analytical solution for both the Beverton–Holt and Rick...

Age-Structured Mark-Recapture Analysis: A Virtual-Population-Analysis-Based Model for Analyzing Age-Structured Capture-Recapture Data

Abstract We present a new model to estimate capture probabilities, survival, abundance, and recruitment using traditional Jolly–Seber capture–recapture methods within a standard fisheries virtual population analysis framework. This approach compares the numbers of marked and unmarked fish at age captured in each year of sampling with predictions based on estimated vulnerabilities and abundance in a likelihood function. Recruitment to the earliest age at which fish can be tagged is estimated by using a virtual population analysis method to back-calculate the expected numbers of unmarked fish at risk of capture. By using information from both marked and unmarked animals in a standard fisheries age structure framework, this approach is well suited to the sparse data situations common in long-term capture–recapture programs with variable sampling effort.

Comparison of Trap Nets and Otter Trawls for Sampling Black Crappie in Two Florida Lakes

Abstract We compared the effectiveness of a recreational shrimp trawl (used for Penaeus spp.) with that of trap nets for assessing populations of black crappie Pomoxis nigromaculatus. Lakes Griffin and Monroe were sampled with both gears simultaneously during Oct–December 1997. Coefficients of variation (CV = 100 × SD/mean) on mean catch per effort (CPE) values ranged from 105 to 161 for trap nets and from 62 to 96 for trawls. Both trawls and trap nets collected fish less than 150 mm total length (TL), but trawls sampled significantly more adult fish (>250 mm TL). Variable catches in trap nets would require more sampling effort than trawl sampling (up to 4 times as much) to obtain precise estimates of mean CPE. Trawl sampling was preferable to trap nets based on size of fish captured, precision of abundance estimates, cost of the gear, and required sampling effort to estimate mean CPE. However, trawl sampling may be impractical in water bodies with excessive submerged structures, debris, and submersed mac...

Decadal changes in oyster reefs in the Big Bend of Florida's Gulf Coast

Oyster reefs are among the worlds most endangered marine habitats with an estimated 85% loss from historical levels worldwide. Oyster reefs offer diverse ecological and social services for people and natural environments; unfortunately, reefs are also highly sensitive to impairment from natural and human-induced disasters. Understanding the resilience of oyster reef communities to disturbance is key to developing effective conservation and restoration plans. Floridas Big Bend coastline (Gulf of Mexico coast from Crystal River to Apalachee Bay) supports large expanses of oyster reef habitat that have existed for thousands of years in a region that is one of the most pristine coastal zones in the continental US. We assessed trends in oyster habitat along the Big Bend region between 1982 and 2011 by examining changes in areal extent and distance of oyster reefs from shore. During our study period, we found a 66% net loss of oyster reef area (124.05 ha) with losses concentrated on offshore (88%), followed b...

Spawning Site Selection and Potential Implications of Modified Flow Regimes on Viability of Gulf Sturgeon Populations

Abstract Rapid human population growth and an associated increase in consumptive water demands within the ecologically diverse Apalachicola–Chattahoochee–Flint (ACF) River basin of the southeastern United States have led to a series of highly publicized water wars, exacerbated by recent drought conditions, between the states of Alabama, Georgia, and Florida. A key issue is how managing riverine flows to meet human water needs will affect the viability of species that are federally listed as threatened or endangered, including the Gulf of Mexico sturgeon Acipenser oxyrinchus desotoi. Our present understanding of Gulf sturgeon ecology within the Apalachicola River basin indicates that altered riverine flow regimes may affect spawning success and possibly the recruitment patterns of the population. Through intensive field work, we documented Gulf sturgeon spawning site selection in the Apalachicola River and then evaluated the relationship between river stage and the available spawning habitat at these sites...