High salinity tolerance of invasive blue catfish suggests potential for further range expansion in the Chesapeake Bay region

In estuaries, salinity is believed to limit the colonization of brackish water habitats by freshwater species. Blue catfish Ictalurus furcatus, recognized as a freshwater species, is an invasive species in tidal rivers of the Chesapeake Bay. Salinity tolerance of this species, though likely to determine its potential range expansion and dispersal in estuarine habitats, is not well-known. To address this issue, we subjected blue catfish to a short-term salinity tolerance experiment and found that this species tolerates salinities higher than most freshwater fishes and that larger blue catfish tolerate elevated salinities for longer periods compared with smaller individuals. Our results are supported by spatially extensive, long-term fisheries surveys in the Chesapeake Bay region, which revealed a gradual (1975–2017) down-estuary range expansion of blue catfish from tidal freshwater areas to habitats exceeding 10 psu [practical salinity units] and that large blue catfish (\u3e 200 mm fork length) occur in salinities greater than 10 psu in Chesapeake Bay tributaries. Habitat suitability predictions based on our laboratory results indicate that blue catfish can use brackish habitats to colonize new river systems, particularly during wet months when salinity decreases throughout the tidal rivers of the Chesapeake Bay

Sublethal effects of salinity and temperature on non-native blue catfish: Implications for establishment in Atlantic slope drainages

The distribution and further range expansion of non-native blue catfish Ictalurus furcatus in coastal waters throughout the United States Atlantic slope depend, in part, on the salinity tolerance of the fish. However, temperature-mediated sublethal effects of increased salinities on blue catfish biology are not yet known. We assessed the effects of salinity and temperature on growth, body condition, body composition and food consumption of juvenile blue catfish in a controlled laboratory experiment. Temperature and salinity had an interactive effect on blue catfish biology, although most fish survived 112 days in salinities up to 10 psu. At salinities 9 psu) likely will not support the full lifecycle of blue catfish, but the fish may use salinities up to 10 psu for foraging, dispersal and even growth. Many oligohaline and mesohaline habitats in U.S. Atlantic slope drainages may thus be vulnerable to establishment of invasive blue catfish, particularly given the increasing temperatures as a result of climate warmin

Reproductive Characteristics Differ in Two Invasive Populations of Blue Catfish

The management of invasive Blue CatfishIctalurus furcatusin Chesapeake Bay tributaries is hindered by the lackof information on its reproductive biology, which is a key component of population models used to forecast abun-dance. We quantified and compared the reproductive traits of female Blue Catfish from two populations from the tidalreaches of the James and York River subestuaries during 2015–2017. In these systems, Blue Catfish matured betweenthe ages of 6 and 10 years and spawned between May and July, with largerfish spawning earlier in the season. Dur-ing spawning events, Blue Catfish produced 2,613–68,356 eggs, with larger and olderfish producing more eggs. Fishin the more densely populated James River matured at a marginally older age but a significantly smaller size thanfishin the York River, but James Riverfish allocated more energy to reproduction. Fish in the James River also hadgreater mean values of the gonadosomatic index, relative fecundity, egg organic content, and proportion of organiccontent in the eggs. Relative fecundity of Blue Catfish decreased withfish size, contrary to observations in most otherfishes. Based on the observed variability in reproductive traits and the size dependence of relative fecundity, we recom-mend incorporation of population-specific reproductive rates into stock assessment models for invasive Blue Catfish

2021 Annual Report Estimating Relative Juvenile Abundance of Ecologically Important Finfish in the Virginia Portion of Chesapeake Bay (1 July 2020 – 30 June 2021)

The Trawl Survey provides crucial data to state, regional, and national fisheries management agencies, including the Virginia Marine Resources Commission (VMRC), the Atlantic States Marine Fisheries Commission (ASMFC), the Mid‐Atlantic Fisheries Management Council (MAFMC), and the National Marine Fisheries Service (NMFS). The MAFMC recognizes the juvenile trawl survey as one of the key predictors of Summer Flounder recruitment. Annual indices of juvenile abundance have been generated from trawl survey data for species of key recreational and ecological importance in the Virginia portion of Chesapeake Bay. These include Spot, Atlantic Croaker, Weakfish, Summer Flounder, Black Sea Bass, Scup, Striped Bass, White Perch, White Catfish, Channel Catfish, Blue Catfish, Silver Perch, American Eel, and Bay Anchovy. We completed most targeted tows this past year and only missed the upper‐river stations in the James and Rappahannock rivers and a few shallow Bay stations during July and August 2020 due to COVID‐19 safety restrictions. As a result, we could not calculate an index for American Eel in the James and Rappahannock rivers. We are also unable to calculate an index for the 2019 year‐class of Black Sea Bass due to the stay‐at‐home order that included May 2020, which was an important index month for this species. A summary of other species affected by COVID‐19 restrictions is shown in the table below. (...

Calibration of VIMS Research Vessel Catch Data to Ensure Continuity of Recruitment Indices for the Chesapeake Bay Region

The VIMS Juvenile Fish Trawl Survey, which has been in operation since 1955, has undergone considerable changes to the sampling gear, location of sampling sites, and the methodology used to select sampling sites. Recently, a new vessel, the R/V Tidewater, replaced the R/V Fish Hawk, which had been in service for 25 years. In addition to the change in vessel, a new net was used; this net design is more robust to deployment methods and performs more consistently under varying environmental conditions. Therefore, a calibration study was conducted whereby the two research vessels with different nets fished in the same area at the same time. This calibration study provides an estimate of the species-specific factors necessary to ‘convert’ the R/V Tidewater catches to those of the R/V Fish Hawk, taking into account the combination of vessel and net. All other protocols (tow duration, scope, vessel speed, and sample processing) remained unchanged. Comparison sampling with the R/V Tidewater and the R/V Fish Hawk began in April 2014 and concluded in May 2015; additional paired tows were completed in August 2016 to provide sufficient samples for Scup, Black Sea Bass, and adult Summer Flounder. We completed a total of 1,141 paired tows during 97 days-at-sea, capturing a total of 327,526 fishes, crabs, and shrimp aboard the R/V Fish Hawk and 323,580 fishes, crabs, and shrimp aboard the R/V Tidewater. From these data, we developed calibration factors for 41 species groups (species-age or species-size combinations). Calibration factors were estimated from the best-fitting model from among four candidate models that accounted for variability in catches between the two vessels. In addition, we examined species composition of the catches from the paired tows using multivariate analysis and found that catches from the two vessels were similar in all months and strata except for shallow stations in Chesapeake Bay. Our ‘whole survey’ approach allowed us to estimate calibration factors for species in all available habitats that are routinely monitored by the VIMS Juvenile Fish Trawl Survey. Further, our consideration of depth, tidal currents, tow direction, water clarity, tow distance, and salinity in the calibration models ensures that the estimates are applicable across the range of estuarine characteristics that are inhabited by these species. The estimated calibration factors will be applied to catches of the R/V Tidewater at the individual-tow level; relative abundance indices will be estimated using the random-stratified survey design in effect since 1988, thus preserving the integrity of the long-term survey data for estimating relative abundance of juvenile fishes and blue crabs in Chesapeake Bay

Estimating Relative Juvenile Abundance of Ecologically Important Finfish and Invertebrates in the Virginia Portion of Chesapeake Bay (Award No. NA03NMF4570378) June 2003-May 2007

The fisheries trawl survey conducted by the Virginia Institute of Marine Science (VIMS) is the oldest continuing trawl monitoring program (52 years) for marine and estuarine fishes in the United States. This survey provides a monthly baseline assessment of the abundance of juvenile marine and estuarine fishes and some invertebrates in the tidal and mainstem Chesapeake Bay. The survey provides crucial, real time data to various state, regional and national fisheries management agencies, including the Virginia Marine Resources Commission (VMRC), the Atlantic States Marine Fisheries Commission (ASMFC), the Mid-Atlantic Fisheries Management Council (MAFMC), and the National Marine Fisheries Service (NMFS). For example, the VIMS Trawl Survey provided the ASMFC with the only available index for spot, which was the cornerstone for the 2003 ASMFC Spot FMP. The MAFMC recognizes the VIMS Trawl Survey as the only available estimator of summer flounder recruitment, and recently the American eel index was vital to the 2006 ASMFC American Eel Management Plan. Several annual indices of juvenile abundance have been generated from trawl survey data for species of key recreational, commercial, and ecological importance in the Virginia portion of Chesapeake Bay. These include spot, Atlantic croaker, weakfish, summer flounder, black sea bass, scup, striped bass, white perch, white catfish, channel catfish, blue catfish, northern puffer, silver perch, blue crab, American eel, bay anchovy and Atlantic menhaden. Historically, four different estimates of relative abundance have been developed for juvenile finfish collected by this survey. However, only the unconverted indices (random stratified index – RSI, 1988 to present) for the target species discussed are the focus of this report. In recent years, juvenile indices for most species have declined, most often a result of overfishing, degradation of estuarine nursery habitats, and other natural environmental variation. For example, spot RSI indices have declined greatly over the past 50 years.Croaker show the greatest interannual variability of the key species discussed, with fluctuations likely related to weather. There has been an increasing trend in weakfish recruitment indices since 1994, while summer flounder have remained low, perhaps due to overfishing. The scup index has been highly variable and has increased slightly since 2004. Striped bass indices were very low during the 1970\u27s and early 1980\u27s, rebounded in the early 1990\u27s and have decreased and remained low since 2001. White perch YOY and age 1+ indices decreased slightly in 2006 from the previous year. The white catfish YOY index increased in 2006 and the white catfish age 1+ index decreased slightly. The channel catfish YOY and age 1+ indices decreased in 2006. Both blue catfish indices (YOY and age 1+) have increased since 2001. Northern puffer indices have experienced a rapid and continuous decline since 1988. The silver perch index has remained consistently low over the study period. Both age 1+ and adult female blue crab indices exhibited significant declines. American eel and bay anchovy indices have also decreased since the 1980s. The newly created Atlantic menhaden index increased slightly in 2007. The Chesapeake Bay is a major nursery area for many coastal migratory fish species, and the data generated from this survey plays an integral role in management efforts along the Atlantic Coast of the United States

Evaluating Recruitment of American Eel, Anguilla rostrata, to the Potomac River (Spring 2008)

The Atlantic States Marine Fisheries Commission (ASMFC) adopted the Interstate Fishery Management Plan (FMP) for the American eel in November 1999. The FMP focuses on increasing coastal states’ efforts to collect American eel data through both fishery-dependent and fishery-independent studies. Consequently, member jurisdictions agreed to implement an annual survey for young of the year (YOY) American eels. The survey is intended to “…characterize trends in annual recruitment of the YOY eels over time [to produce a] qualitative appraisal of the annual recruitment of American eel to the U.S. Atlantic Coast” (ASMFC, 2000). The development of these surveys began in 2000 with full implementation by 2001. Survey results should provide necessary data on coastal recruitment success and further understanding of American eel population dynamics. A recent American eel stock assessment report (ASMFC, 3 2006) emphasized the importance of the coast-wide survey as an index of sustained recruitment over the historical coastal range and an early warning of potential range contraction of the species. The Virginia Institute of Marine Science continued its spring sampling to estimate relative abundance of YOY American eels in the Potomac River. Funding was provided by the Potomac River Fisheries Commission, which ensured compliance with the 1999 ASMFC Interstate Fishery Management Plan for American Eels

Evaluating Recruitment of American Eel, Anguilla rostrata, in the Potomac River (Spring 2009)

The Atlantic States Marine Fisheries Commission (ASMFC) adopted the Interstate Fishery Management Plan (FMP) for the American eel in November 1999. The FMP focuses on increasing coastal states’ efforts to collect American eel data through both fishery-dependent and fishery-independent studies. Consequently, member jurisdictions agreed to implement an annual survey for young of year (YOY) American eels. The survey is intended to “…characterize trends in annual recruitment of the YOY eels over time [to produce a] qualitative appraisal of the annual recruitment of American eel to the U.S. Atlantic Coast” (ASMFC 2000). The development of these surveys began in 2000 with full implementation by 2001. Survey results should provide necessary data on coastal recruitment success and further understanding of American eel 3 population dynamics. A recent American eel stock assessment report (ASMFC 2006) emphasized the importance of the coast-wide survey for providing data useful in calculating an index of recruitment over the historical coastal range and for serving as an early warning of potential range contraction of the species. Funding for the Virginia Institute of Marine Science’s spring survey in the Potomac River was provided by the Potomac River Fisheries Commission, thereby ensuring compliance with the 1999 ASMFC Interstate Fishery Management Plan for American Eels