Use of multi-source tagging data to estimate regional age-varying striped bass mortality and occupancy

Genetic population structure of anadromous striped bass along the US Atlantic coast was analyzed using 14 neutral nuclear DNA microsatellites. Young-of-the-year and adult striped bass (n = 1114) were sampled from Hudson River, Delaware River, Chesapeake Bay, North Carolina, and South Carolina. Analyses indicated clear population structure with significant genetic differentiation between all regions. Global multilocus F ST was estimated at 0.028 (P < 0.001). Population structure followed an isolation-by-distance model and temporal sampling indicated a stable population structure more than 2 years at all locations. Significant structure was absent within Hudson River, whereas weak but significant genetic differences were observed between northern and southern samples in Chesapeake Bay. The largest and smallest effective striped bass population sizes were found in Chesapeake Bay and South Carolina, respectively. Coalescence analysis indicated that the highest historical gene flow has been between Chesapeake Bay and Hudson River populations, and that exchange has not been unidirectional. Bayesian analysis of contemporary migration indicated that Chesapeake Bay serves as a major source of migrants for Atlantic coastal regions from Albemarle Sound northward. In addition to examining population genetic structure, the data acquired during this project were capable of serving as a baseline for assigning fish with unknown origin to source region.

&lt;em&gt;Abstract&lt;/em&gt;.—Striped bass &lt;em&gt;Morone saxatilis &lt;/em&gt;in inland reservoirs play an important role ecologically and in supporting recreational fishing. To manage these populations, biologists need information about abundance and mortality. Abundance estimates can be used to assess the effectiveness of stocking programs that maintain most reservoir striped bass populations. Mortality estimates can indicate the relative impact of fishing versus natural mortality and the need for harvest regulation. The purpose of this chapter is to evaluate tagging studies as a way of obtaining information about abundance and mortality. These approaches can be grouped into three broad categories: tag recapture, tag return, and telemetry. Tag-recapture methods are typically used to estimate population size and other demographic parameters but are often difficult to apply in large systems. A fishing tournament can be an effective way of generating tagging or recapture effort in large systems, compared to using research sampling only. Tag-return methods that rely on angler harvest and catch and release can be used to estimate fishing (&lt;EM&gt;F&lt;/EM&gt;) and natural (&lt;EM&gt;M&lt;/EM&gt;) mortality rates and are a practical approach in large reservoirs. The key to success in tag-return studies is to build in auxiliary studies to estimate short-term tagging mortality, short- and longterm tag loss, reporting rate, and mortality associated with catch and release. &lt;EM&gt;F &lt;/EM&gt;and &lt;EM&gt;M &lt;/EM&gt;can also be estimated using telemetry tags. Advantages of this approach are that angler nonreporting does not bias estimates and fish with transmitters provide useful ecological data. Cost can be a disadvantage of telemetry studies; thus, combining telemetry tags with conventional tag returns in an integrated analysis is often the optimal approach. In summary, tagging methods can be a powerful tool for assessing the effectiveness of inland striped bass stocking programs and the relative impact of fishing versus natural mortality.

Estimation of summer flounder (Paralichthys dentatus) mortality rates using mark-recapture data from a recreational angler-tagging program

The Chesapeake and Delaware Canal connects upper Chesapeake Bay with the Delaware River. The results of two years of intensive sampling effort in the C&D Canal suggest that this area may be one of the more important spawning grounds of striped bass, Morone saxatilis (Walbaum), in the Chesapeake Bay region. Concentrations of striped bass eggs found during the period of peak spawning may be the highest that have been reported. Limited evidence suggests that the C&D Canal has provided a favorable alternative to now destroyed historical spawning grounds of striped bass in the lower Susquehanna River.

The striped bass (Morone saxatilis) is an economically and ecologically valuable finfish species that inhabits nearshore and estuarine waters of many states along the US Atlantic coast. Chesapeake Bay provides extensive nursery and foraging habitats for striped bass, yet fish in the bay exhibit high prevalence of disease caused by bacteria in the genus Mycobacterium. Detection of population-level impacts associated with mycobacteriosis has been difficult because the disease is chronic and synoptic biological and disease data have been limited. Here, we present modeling analyses of growth data for disease-positive and -negative striped bass in Chesapeake Bay. Three growth relationships were considered, and for each, a single model was parameterized to include several covariates, most notably disease status and severity. Our results indicate that disease-positive and -negative fish have differing growth patterns and that the estimated asymptotic sizes of disease-positive fish are considerably lower than those of disease-negative fish. Compromised growth along with documentation that striped bass in Chesapeake Bay are experiencing disease-associated mortality suggests that disease may be reducing the productivity of this species.

During 1959–61, 8,793 striped, bass,Roccus saxatilis (Walbaum), were tagged and released in the Potomac River, Maryland. Of the 3,344 (37.3%) recaptured, 98.0% were taken in the Maryland part of Chesapeake Bay and its tributaries, 0.5% were recovered in the Virginia part of Chesapeake bay and its tributaries, and 1.5% were taken outside Chesapeake Bay along the Atlantic coast from Delaware to Nova Scotia. In the wintering season (November–March), the tagged fish were concentrated in the lower river and were very active, traveling several miles a day. In the spawning season (April–June), they mostly moved upstream to the spawning grounds where the tagged fish remained for most of the season, and then dispersed downstream to the lower river and into Chesapeake Bay. In the feeding season (July–October), tagged fish were scattered throughout Chesapeake Bay and tributaries. Some striped bass which overwintered in the Potomac were recaptured during the following spawning season in other Chesapeake Bay tributaries, and fish from the Potomac contributed materially to the stocks of striped bass along the northeast Atlantic coast. Spawning striped bass return to the same spawning grounds in successive years. Recaptures of tagged fish by date and location during the wintering, spawning, and feeding seasons, and the miles traveled and days at large by individuals, are tabulated.

Temperature is hypothesized to alter disease dynamics, particularly when species are living at or near their thermal limits. When disease occurs in marine systems, this can go undetected, particularly if the disease is chronic and progresses slowly. As a result, population‐level impacts of diseases can be grossly underestimated. Complex migratory patterns, stochasticity in recruitment, and data and knowledge gaps can hinder collection and analysis of data on marine diseases. New tools enabling quantification of disease impacts in marine environments include coupled biogeochemical hydrodynamic models (to hindcast key environmental data), and multievent, multistate mark–recapture (MMSMR) (to quantify the effects of environmental conditions on disease processes and assess population‐level impacts). We used MMSMR to quantify disease processes and population impacts in an estuarine population of striped bass (Morone saxatilis) in Chesapeake Bay from 2005 to 2013. Our results supported the hypothesis that mycobacteriosis is chronic, progressive, and, frequently, lethal. Yearly disease incidence in fish age three and above was 89%, suggesting that this disease impacts nearly every adult striped bass. Mortality of diseased fish was high, particularly in severe cases, where it approached 80% in typical years. Severely diseased fish also had a 10‐fold higher catchability than healthy fish, which could bias estimates of disease prevalence. For both healthy and diseased fish, mortality increased with the modeled average summer sea surface temperature (SST) at the mouth of the Rappahannock River; in warmer summers (average SST ≥ 29°C), a cohort is predicted to experience >90% mortality in 1 year. Regression of disease signs in mildly and moderately diseased fish was <2%. These results suggest that these fish are living at their maximum thermal tolerance and that this is driving increased disease and mortality. Management of this fishery should account for the effects of temperature and disease on impacted populations.

Catch-and-release fisheries have become very important in the management of overexploited recreational fish stocks. Tag return studies, where the tag is removed regardless of fish disposition, have been used to assess the effectiveness of restoration efforts for these fisheries. We extend the instantaneous rate formulation of tag return models to allow for catch and release as well as harvest. The key point of our methods is that, given an estimate of the tag reporting rate, the fishing mortality rate (F) is separated into two components: the mortality on harvested fish and the “mortality” on tags (because the tags are removed) of fish released alive. The total fishing mortality rate for untagged fish is the sum of the Fs due to harvest and hooking mortality suffered by fish released alive. Natural mortality rates can also be estimated. Both age-independent models and age-dependent models are constructed, and the age-dependent models are illustrated by application to data from a study of striped bass Morone saxatilis in Chesapeake Bay from 1991 to 2003 by the Maryland Department of Natural Resources. By fitting models of the natural mortality rate with limited age and year dependence, we demonstrate an overall decrease in natural mortality rates as fish age and provide evidence of an increase in natural mortality beginning in the late 1990s, when an outbreak of the disease mycobacteriosis is thought to have begun. Our results indicate that fishing mortality is age dependent; selectivity increases up to age 6, when fish appear to be fully recruited to the fishery. There is also evidence of an increase in fishing mortality since 1995, when regulations were relaxed.

First report of Streptococcus parauberis in wild finfish from North America

Management options for the Delaware River population of striped bass Morone saxatilis depend on whether or not the population forms a discrete stock. The recent increase in striped bass in the Delaware River follows decades of scarcity and concern about the possible extinction of the original population. The increase may have resulted from one or more of the following: Expansion of a remnant population, repopulation by migrants from the Chesapeake Bay, or repopulation by migrants from the Hudson River. To determine the origin of the present Delaware River striped bass population, we analyzed mitochondrial DNA (mtDNA) from 191 striped bass collected in the Delaware River between 1990 and 1992. Our results indicate the Delaware River striped bass population is genetically intermediate between the Chesapeake Bay and Hudson River populations; mtDNA major-length genotype frequencies of the Delaware River sample were significantly different (P < 0.05) from those of the Hudson River stock, whereas mtDNA minor-length genotype frequencies of the Delaware River sample differed significantly from those of the Chesapeake Bay stock (P < 0.005). This intermediacy, together with information from historical surveys that suggest the original population did not become extinct, favors the hypothesis that the present Delaware River striped bass stock represents expansion from the original Delaware River stock.

Eutrophication-induced hypoxia may affect both benthic and pelagic organisms in coastal systems. To evaluate the effect of hypoxia on pelagic striped bass (Morone saxatilis), we quantified the growth rate potential (GRP) of age-2 and age-4 fish in Chesapeake Bay during 1996 and 2000 using observed temperature, dissolved oxygen, and prey abundance information in a spatially explicit bioenergetics modeling framework. Regions of the Bay with bottom hypoxia were generally areas with high quality habitat (i.e., GRP &gt; 0 g·g–1·day–1), primarily because prey fish were forced into warm, oxygenated surface waters suitable for striped bass foraging and growth. In turn, by concentrating fish prey above the oxycline and removing bottom waters as a refuge, hypoxia likely enhanced striped bass predation efficiency and contributed to the recovery of striped bass during the mid-1990s, a time when the striped bass fishery also was closed. This short-term positive effect of hypoxia on striped bass, however, appears to have been counterbalanced by a long-term negative effect of hypoxia in recent years. Ultimately, hypoxia-enhanced predation efficiency, combined with an abundance of striped bass due to restricted harvest, appears to be causing overconsumption of prey fishes in Chesapeake Bay, thus helping to explain poor growth and health of striped bass in recent years.

During a reward program for Atlantic sturgeon (Acipenser oxyrinchus), 40 federally endangered shortnose sturgeon (Acipenser brevirostrum) were captured and reported by commercial fishers between January 1996 and January 2000 from the Chesapeake Bay. Since this is more than double the number of published records of shortnose sturgeon in the Chesapeake Bay between 1876 and 1995, little information has been available on distributions and movement. We used fishery dependent data collected during the reward program to determine the distribution of shortnose sturgeon in the Chesapeake Bay. Sonically-tagged shortnose sturgeon in the Chesapeake Bay and Delaware River were tracked to determine if individuals swim through the Chesapeake and Delaware Canal. Shortnose sturgeon were primarily distributed within the upper Chesapeake Bay. The movements of one individual, tagged within the Chesapeake Bay and later relocated in the canal and Delaware River, indicated that individuals traverse the Chesapeake and Delaware Canal.

Tournament anglers typically possess extensive knowledge of the habitat and seasonal movement of their targeted species. While fish–angler behavioral relationships are critical to understanding fish catchability, few studies have assessed how fish behavior influences their vulnerability to capture by tournament anglers. Our objectives were to determine if Largemouth BassMicropterus salmoidesbehavior, angler behavior, and environmental conditions affect tournament angler catch rate (CPUE) and Largemouth Bass capture probability at fishing tournaments. Forty‐nine Largemouth Bass were tracked weekly using radiotelemetry during a 4‐month period. Five tournament anglers were also selected at weekly tournament events and tracked continuously using a handheldGPSunit. We quantified individual Largemouth Bass behaviors (home range, weekly movement rate, depth use, and spatial overlap with anglers), angler behaviors (depth use, angler movement rate), and environmental conditions (air and water temperature) and used these estimates as covariates in a multiple regression model to assess their effects on tournamentCPUEand then used a multistate mark–recapture model to estimate Largemouth Bass capture probability at tournaments. Our results indicate that Largemouth Bass movement rate, angler fishing depth, and air temperature were highly correlated to tournament anglerCPUE. Mark–recapture models also indicated that air temperature and angler–fish overlap were positively associated with Largemouth Bass capture probability while fish total length, home range, movement rate, and depth use were not successful in characterizing individual variation in capture probability. Our results indicate that Largemouth Bass that are encountered by anglers are more likely to be captured, whereas mismatches between angler and Largemouth Bass behavioral factors, including depth use and movement rates, may result in decreased tournament capture rates. Consideration and continued evaluation of the relationships between Largemouth Bass and angler behaviors and environmental variables is critical to fisheries management as tournament pressure paired with high capture probabilities and selective angling can have large‐scale population‐level impacts.

Societal benefits of floodplains in the Chesapeake Bay and Delaware River watersheds: Sediment, nutrient, and flood regulation ecosystem services

We applied bioenergetics models for dominant Chesapeake Bay piscivores, striped bass (Morone saxatilis), bluefish (Pomatomus saltatrix), and weakfish (Cynoscion regalis), along with site-specific data on diets, growth, and energy density, to examine trophic linkages and the relationship of predatory demand to prey supply. Atlantic menhaden (Brevoortia tyrannus), bay anchovy (Anchoa mitchilli), and spot (Leiostomus xanthurus) accounted for 65–99% of the annual biomass of piscivore diets (excluding age-0 striped bass that ate mostly invertebrates). The diets of young piscivores were dominated by anchovy, but menhaden and spot became increasingly important to older fish. Young (age &lt; 2) striped bass ate mostly benthic prey. Older striped bass fed increasingly on pelagic sources, primarily menhaden, but bluefish and weakfish increased benthic resource use from 10% at age 0 to 50% by age 2. Comparison of consumption (supply) to demand (potential consumption) measured the suitability of Chesapeake Bay for predator production. Bluefish came closest to achieving their demand for prey, suggesting that they are more successful predators than either striped bass or weakfish. Results suggest that Chesapeake Bay may be a better nursery than production area for older fish, and prey supply (not temperature) may account for the movements and use of the estuary by older piscivores.