Joseph E. Hightower

A Review of Tagging Methods for Estimating Fish Population Size and Components of Mortality

Abstract Techniques to improve estimation of animal population size and mortality from tagging studies have received substantial attention from terrestrial biologists and statisticians during the last 20 years. However, these techniques have received little notice from fisheries biologists, despite the widespread applicability to fisheries research, the wide variety of tag types used in fisheries research (from traditional fin clips to telemetry tags), and the development of new computer software to assist with analyses. We present a brief review of population models based on recaptures, returns, or telemetry relocations of tagged fish that can be used to estimate population size, total mortality, and components of mortality (i.e., fishing and natural) that are frequently of interest to fisheries biologists. Recommended strategies include (1) use closed population models (e.g., Lincoln-Peterson) to estimate population size for short term studies where closure assumption can be met, (2) use the robust desi...

Gulf Sturgeon Spawning Migration and Habitat in the Choctawhatchee River System, Alabama-Florida

Abstract Information about spawning migration and spawning habitat is essential to maintain and ultimately restore populations of endangered and threatened species of anadromous fish. We used ultrasonic and radiotelemetry to monitor the movements of 35 adult Gulf sturgeon Acipenser oxyrinchus desotoi (a subspecies of the Atlantic sturgeon A. oxyrinchus) as they moved between Choctawhatchee Bay and the Choctawhatchee River system during the spring of 1996 and 1997. Histological analysis of gonadal biopsies was used to determine the sex and reproductive status of individuals. Telemetry results and egg sampling were used to identify Gulf sturgeon spawning sites and to examine the roles that sex and reproductive status play in migratory behavior. Fertilized Gulf sturgeon eggs were collected in six locations in both the upper Choctawhatchee and Pea rivers. Hard bottom substrate, steep banks, and relatively high flows characterized collection sites. Ripe Gulf sturgeon occupied these spawning areas from late Mar...

Use of Telemetry Methods to Estimate Natural and Fishing Mortality of Striped Bass in Lake Gaston, North Carolina

Abstract Natural mortality can substantially affect fish population dynamics, but the rate is difficult to estimate because natural deaths are rarely observed and it is difficult to separate the effects of natural and fishing mortality on abundance. We developed a new telemetry approach for estimating natural and fishing mortality rates and applied it to the population of striped bass Morone saxatilis in Lake Gaston, North Carolina and Virginia. Our analyses were based on a sample size of 51 telemetered striped bass that were known to be alive and in Lake Gaston at least 1 month after capture and surgery. Relocations of live fish and fish that died of natural causes were used to estimate natural and fishing mortality rates and the probability of relocating telemetered fish. Fishing mortality rates varied seasonally, but few natural deaths were observed, so the best model incorporated a constant annual instantaneous natural mortality rate (M; ±SE) of 0.14 ± 0.02. With the uncertainty in model selection acc...

Effects of a Low-Head Dam on the Distribution and Characteristics of Spawning Habitat Used by Striped Bass and American Shad

Abstract Striped bass Morone saxatilis and American shad Alosa sapidissima in the Neuse River, North Carolina, historically migrated up to 435 km upriver to spawn. However, migration was impeded in 1952 by the construction of Quaker Neck Dam at river kilometer 225 (measured from the point where the Neuse River enters Pamlico Sound). To determine the fraction of tagged fish that migrated upstream of this low-head dam and the characteristics of selected spawning habitat, we implanted sonic transmitters in 25 striped bass and 25 American shad during 1996 and 1997. We determined preferred depth, water velocity, and substrate composition by measuring those characteristics at both randomly selected sites and sites where spawning was observed. Of 13 striped bass and 8 American shad with transmitters that migrated to the base of Quaker Neck Dam, only 3 striped bass passed the structure, indicating that the dam was an impediment to migration. Striped bass spawning was observed only in the area directly below (with...

Distribution of spawning activity by anadromous fishes in an atlantic slope drainage after removal of a low-head dam

Abstract In 1998, the Quaker Neck Dam was removed from the Neuse River near Goldsboro, North Carolina, restoring access to more than 120 km of potential main-stem spawning habitat and 1,488 km of potential tributary spawning habitat to anadromous fishes. We used plankton sampling and standardized electrofishing to examine the extent to which anadromous fishes utilized this restored spawning habitat in 2003 and 2004. Evidence of spawning activity was detected upstream of the former dam site for three anadromous species: American shad Alosa sapidissima, hickory shad A. mediocris, and striped bass Morone saxatilis. The percentages of eggs and larvae collected in the restored upstream habitat were greater in 2003, when spring flows were high, than in 2004. River reaches where spawning occurred were estimated from egg stage and water velocity data. Spawning of American shad and striped bass occurred primarily in main-stem river reaches that were further upstream during the year of higher spring flows. Hickory ...

Combining Telemetry and Fisheries Tagging Models to Estimate Fishing and Natural Mortality Rates

Abstract The traditional multiple-year tag return method is a fundamental approach to estimating fishing and natural mortality rates in fisheries. It can provide reliable and precise estimation of the parameters when the tag reporting rate, λ, is known. However, it is often difficult to estimate λ accurately. An additional disadvantage is that this method has to estimate natural mortality indirectly because natural deaths are not observable. Recently, fisheries biologists have begun to implement telemetry methods to estimate fishing and natural mortality. The advantage of a telemetry method is that it contains direct information about natural mortality and survival. A shortcoming is that there is no direct information on fishing deaths. In this paper, we combine the two methods, using direct information about both fishing and natural mortality to obtain more precise and effectively unbiased parameter estimates, including reporting rate estimates for the regular tags. Using simulation when the telemetry ta...

Spawning Migration of Telemetered Striped Bass in the Roanoke River, North Carolina

Abstract The spring spawning migration is a key period for effective management of anadromous populations of striped bass Morone saxatilis. Information on migratory behavior is needed in order to develop appropriate harvest regulations and to conduct effective surveys while fish are on the spawning grounds. We used ultrasonic telemetry to estimate the timing and duration of the upriver spawning migration for the Roanoke River, North Carolina, population and to evaluate whether a short-term fluctuation in temperature or flow would alter the distribution of telemetered fish on the spawning grounds. Seventy-eight fish implanted with transmitters were released during 1993 and 1994. Twenty-nine telemetered fish migrated upriver in 1994, and 14 telemetered fish entered the river in 1995. Migration of telemetered fish began in mid- to late April when water temperatures in the lower river reached 17–18°C. Males began their spawning migration significantly earlier than females in 1994; the difference was not signi...

Summer Distribution and Condition of Striped Bass within Albemarle Sound, North Carolina

Abstract During 1993–1994, 78 adult striped bass Morone saxatilis captured in the Albemarle Sound–Roanoke River (AR) system were tagged with ultrasonic transmitters to examine summer patterns of distribution, migration, and habitat selection. Additionally, 626 striped bass were collected by electrofishing during 1993 to assess summer condition. Water temperatures within Albemarle Sound rose well above suitable levels for striped bass, but dissolved oxygen remained within tolerance limits. No stratification of temperature or dissolved oxygen occurred and no substantial thermal refuges were located. Telemetered striped bass were found throughout the Albemarle Sound system, selecting for deep water or structure. No evidence of migration to the Atlantic Ocean was found. During summer AR striped bass 325 mm total length or longer were in relatively poor condition, as evidenced by the extensive occurrence of red dermal lesions and ectoparasites. Relative weight (condition based on a standard weight at length) o...

Population Status of North American Green Sturgeon, Acipenser medirostris

North American green sturgeon, Acipenser medirostris, was petitioned for listing under the Endangered Species Act (ESA). The two questions that need to be answered when considering an ESA listing are; (1) Is the entity a species under the ESA and if so (2) is the “species” in danger of extinction or likely to become an endangered species in the foreseeable future throughout all or a significant portion of its range? Green sturgeon genetic analyses showed strong differentiation between northern and southern populations, and therefore, the species was divided into Northern and Southern Distinct Population Segments (DPSs). The Northern DPS includes populations in the Rogue, Klamath-Trinity, and Eel rivers, while the Southern DPS only includes a single population in the Sacramento River. The principal risk factors for green sturgeon include loss of spawning habitat, harvest, and entrainment. The Northern DPS is not considered to be in danger of extinction or likely to become an endangered species in the foreseeable future. The loss of spawning habitat is not large enough to threaten this DPS, although the Eel River has been severely impacted by sedimentation due to poor land use practices and floods. The two main spawning populations in the Rogue and Klamath-Trinity rivers occupy separate basins reducing the potential for loss of the DPS through catastrophic events. Harvest has been substantially reduced and green sturgeon in this DPS do not face substantial entrainment loss. However there are significant concerns due to lack of information, flow and temperature issues, and habitat degradation. The Southern DPS is considered likely to become an endangered species in the foreseeable future. Green sturgeon in this DPS are concentrated into one spawning area outside of their natural habitat in the Sacramento River, making them vulnerable to catastrophic extinction. Green sturgeon spawning areas have been lost from the area above Shasta Dam on the Sacramento River and Oroville Dam on the Feather River. Entrainment of individuals into water diversion projects is an additional source of risk, and the large decline in numbers of green sturgeon entrained since 1986 causes additional concern.

A combined telemetry - tag return approach to estimate fishing and natural mortality rates of an estuarine fish

A joint analysis of tag return and telemetry data should improve estimates of mortality rates for exploited fishes; however, the combined approach has thus far only been tested in terrestrial systems. We tagged subadult red drum (Sciae- nops ocellatus) with conventional tags and ultrasonic transmitters over 3 years in coastal North Carolina, USA, to test the efficacy of the combined telemetry - tag return approach. There was a strong seasonal pattern to monthly fishing mortality rate (F) estimates from both conventional and telemetry tags; highest F values occurred in fall months and lowest levels occurred during winter. Although monthly F values were similar in pattern and magnitude between conventional tagging and telemetry, information on F in the combined model came primarily from conventional tags. The estimated natural mortality rate (M) in the combined model was low (estimated annual rate ± standard error: 0.04 ± 0.04) and was based pri- marily upon the telemetry approach. Using high-reward tagging, we estimated different tag reporting rates for state agency and university tagging programs. The combined telemetry - tag return approach can be an effective approach for estimat- ing F and M as long as several key assumptions of the model are met.