Winter Fishery Research Articles

Temperature and Abundance Effects on Spatial Structures of Northern Shrimp (Pandalus borealis) at Different Life Stages in the Oceanographically Variable Gulf of Maine

ABSTRACTThe Gulf of Maine (GOM) northern shrimp, Pandalus borealis, once supported a significant winter fishery, but a moratorium has been placed on the fishery since 2014 because of a population collapse and recruitment failures that have been attributed to unfavorably warm water temperatures. The GOM is at the southernmost end of the northern shrimp's range, suggesting its population dynamics and distribution may be vulnerable to warming water temperatures. In this study, we used survey data to estimate spatial indicators for GOM northern shrimp at four life history stages to identify possible temporal trends and examine relationships between the indicators and northern shrimp abundance and bottom temperature. We observed patchier distributions over time, which were related to declining population abundance, and a distributional shift northward that was associated with warming bottom water temperatures. Northern shrimp habitat distribution was strongly associated with bottom temperature. Shrimp of all life stages were found in bottom waters cooler than the station's average bottom temperature.

Estimating angler effort and catch from a winter recreational fishery using a novel Bayesian methodology to integrate multiple sources of creel survey data

The range of survey methodologies for measuring daily activity, catch and harvest (i.e. creel surveys) of recreational anglers, is increasing with the advent of new technologies and improvements in remote sensing. Individual creel survey types frequently give different insights into a fishery due to their unique sources of methodological bias and coverage, which creates a problem for resource managers since markedly different estimates of important fishery metrics can result. We demonstrate a joint estimation approach using a Bayesian statistical framework that can bring together multiple survey types to derive a single estimate for important metrics. This framework is applied to data collected from a relatively large winter fishery and integrates three traditional creel methodologies (i.e. roving, access and aerial counts), each with very different sources of bias, to derive a common estimate of angler effort. Models integrating two survey types are found to be have lower uncertainty in their estimates. Further, reductions in effort for any one survey type is found to be buffered by the joint estimation approach, such that resource managers will likely find benefits in using more than one survey methodology in an integrated fashion to monitor a fishery.

Petrale sole transboundary connectivity and settlement success: a biophysical approach

Connectivity between inferred spawning areas and potential settlement areas of the petrale sole (Eopsetta jordani) was explored in the California Current System (CCS) using an individual-based model (IBM) coupled with the ROMS hydrodynamic model for the period 1988-2008. The IBM modeled pelagic early life stages, including egg and larval development, growth, natural mortality and settlement into benthos. Eggs were released within discrete spawning grounds identified from the winter fishery logbook data. Potential settlement areas were defined based on bathymetrical criteria and juvenile (2-year old) distribution from a groundfish bottom trawl survey. The influence of cross-shelf and alongshore advection on the transport and connectivity between spawning and benthic settlement areas was explored by identifying the location of juveniles (22 mm length) among the potential settlement areas. The most important spawning regions varied over time with between 4 and 19% of spawned individuals successfully settling, mostly ranging from off northern Washington to northern Oregon. The strong influence of northward alongshore transport resulted in transboundary transport of pelagic life stages from U.S. spawning grounds to inner shelf settlement areas in Canadian waters, with 33.9-70.4% (average 49.7 ± 9.6) of annual successful juveniles settling in Canada. Interannual variability in juvenile settlement success suggests that mesoscale (100-200 km) oceanographic structures play a major role defining pelagic juvenile transport trajectories. While, in some years, the presence of coastal cyclonic eddies can retain juveniles off Oregon, the strong northward transport supplies a large number of juveniles to Moresby and Vancouver island, clearly showing that petrale sole off the west coast of North America are a transboundary stock with important settlement areas off the coast of British Columbia, thus extension of this study into Canadian waters is particularly relevant.

Intra- and inter-temporal effort allocation and profit-maximizing strategy of trawl fishery

AbstractBottom trawlers are engaged in multi-species fisheries and fish for profit. In quota-regulated fisheries, intra- and inter-temporal substitutions of fishing effort is regarded as a key mechanisms that influences the profitability of the fishing portfolio. The feeding and spawning migration patterns of the available fish species in the fishing portfolio alter the bio-economic conditions of the different fishing areas. In addition, the spatial heterogeneity among different fishing areas in terms of the fuel costs and travel distance, accessibility to other fishing fleets, and sea ice extent affects the relative attractiveness of the fishing areas and further complicates the decisions underlying the effort allocation, such as when and where to fish what and how much to fish to maximize the profit. In this regard, the aim of this article is to identify the key drivers of intra- and inter-temporal effort allocation in a multi-species trawl fishery consisting of 61 Norwegian trawl vessels targeting cod, saithe, and haddock, the aim being to maximize the fishing profit within the quota constraints. We adopted a two-step Heckman estimator that incorporates the relative attractiveness of three heavily trawled areas, the southern and northern parts of the west coast of Norway and the high sea areas of the Arctic. The relative attractiveness is specified by the fish availability, measured using the catch per unit of effort, prices of the target species, fuel cost, intensity of the coastal fleet's participation in winter fishery, and seasonal sea ice extent in the Barents Sea during the period 2011–2016. Our results show that region-specific attributes and spatial margins have a profound impact on the intra-temporal and inter-temporal allocation of fishing effort to maximize the seasonal profit. Furthermore, we found evidence of economically rational behaviour of the Norwegian trawlers in constantly reallocating their fishing effort in response to the changes in the relative attractiveness of the selected fishing areas over the course of a fishing year.

Effects of environmental factors on reproductive potential of the Gulf of Maine northern shrimp (Pandalus borealis)

The northern shrimp (Pandalus borealis) once supported a significant winter fishery in the Gulf of Maine (GOM). However, the population collapsed in 2012 and a fishery moratorium has been in effect since 2014 due to record low levels of spawning stock biomass and persistent recruitment failure. An important parameter in determining population dynamics, fecundity, has not been evaluated for more than 30 years, during which time the GOM has warmed significantly. In this study, we quantified three reproductive characteristics related to fecundity: potential fecundity (PF, number of viable eggs), relative fecundity (RF, number of viable eggs per gram of body weight), and egg size (ES) for GOM northern shrimp. The results showed that PF was strongly related to body size, while RF was independent of body size. Egg size declined with increasing body size for larger females. Egg size is related to size at larval hatch, suggesting that although larger females produced more eggs, those eggs may produce smaller larvae. In contrast with previous studies, PF and RF were positively correlated with bottom temperature in the relatively warm years of our study. We hypothesize that the positive temperature-fecundity relationship we observed may not reflect a direct effect, but possibly a compensatory response relating to decreased population density during the time period of our study. In addition, the environmental effects we observed may to some extent reflect progression of the inshore migration of females. The information derived in this study can help us have a better understanding of environmental effects on reproductive potential for climatically vulnerable species such as the GOM northern shrimp.

Multi-decadal trends in contingent mixing of Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic from otolith stable isotopes

The Atlantic mackerel (Scomber scombrus) in the Northwest Atlantic is comprised of northern and southern components that have distinct spawning sites off Canada (northern contingent) and the US (southern contingent), and seasonally overlap in US fished regions. Thus, assessment and management of this population can be sensitive to levels of mixing between contingents, which remain unknown. Multi-decadal trends in contingent mixing levels within the US fisheries region were assessed, and the contingent composition across seasons, locations, ages, and size classes were characterized using archived otoliths and developing a classification baseline based on juvenile otolith carbon and oxygen stable isotopes (δ13C/δ18O values). Classification of age ≥ 2 adults demonstrated that northern contingent mixing was prevalent within the US continental shelf waters during the past 2 decades (2000–2019), providing an important seasonal subsidy to the US winter fishery despite substantial depletion in spawning stock biomass of the dominant northern contingent. While the majority of older fish were of the northern contingent during the early 2000s, the southern contingent contribution increased with age/size class during the recent period (2013–2019). Spatial mixing was most prevalent during February and March when the northern contingent occurred as far south as the Delmarva Peninsula, but were mostly absent from US waters in May. A positive relationship (albeit not significant; r = 0.60, p = 0.07) occurred between northern contingent mixing and US fisheries landings, which could imply that higher contingent mixing levels might be associated with greater landings for the US winter mackerel fishery. The yield of the Northwest Atlantic mackerel depends upon the status of the northern contingent, with the southern contingent possibly more prone to depletion. Spatially explicit stock assessment models are recommended to conserve both productivity and stability in this two-component population.

Possible climate-induced environmental impacts on parasite-infection rates of northern shrimp Pandalus borealis eggs in the Gulf of Maine.

The Gulf of Maine northern shrimp Pandalus borealis population once supported a significant commercial winter fishery for the New England states. However, the fishery has been on moratorium since 2014 due to consecutive recruitment failures. The issue of parasite-infected eggs, so-called 'white eggs,' has long been identified for the Gulf of Maine northern shrimp, which makes shrimp eggs nonviable and subsequently hampers the recruitment potential. Furthermore, the proportion of infected females was observed to increase with water temperature. As Gulf of Maine temperatures have been increasing for decades, it is important to re-visit issues related to white eggs to evaluate possible impacts of climate-induced environmental changes on the white egg infection rates. We used biological samples collected by the Northeast Fisheries Science Center in 2012-2016 to evaluate the probability that a female shrimp was infected (Pinf) and the proportion of white eggs in an infected female shrimp (pwe). Although Pinf was high, with an average of 73.81% over the Gulf of Maine, pwe was mostly <5%. The variation in both Pinf and pwe examined in this study was not well explained by environmental factors or female body size. However, the average rates of both Pinf and pwe observed in this study were higher than those observed in the 1960s when the bottom temperatures were cooler. The results can be used to account for egg mortality and provide information on potential impacts of possible climate-induced variability on shrimp population dynamics.

Effects of Fishery‐Related Fight Time and Air Exposure on Prespawn Survival and Reproductive Success of Adult Hatchery Steelhead

AbstractIn recent years, increased scrutiny has been placed on the physiological effects of exhaustive exercise and air exposure on caught‐and‐released fish. Steelhead Oncorhynchus mykiss broodstock in the South Fork Clearwater River, Idaho, were collected by anglers during a winter fishery (water temperatures of 2–5°C); this enabled fight and air exposure times to be recorded to determine their influence on prespawn survival and progeny survival to the fry stage in the hatchery. The average fight time during angling was 164 s. Air exposure was measured when anglers landed fish and again during fish transport from the river to the hatchery vehicle; the longest interval of air exposure averaged 23 s during angling and 28 s during transport. Three‐year average prespawn survival was 97.0% for 1,148 angler‐caught fish, compared to 91.9% for 3,325 swim‐in broodstock collected at the hatchery. The top mixed‐effects logistic regression model estimated that the odds of progeny survival increased by 1.027 times with each additional day of the year until an adult fish spawned; this was likely a reflection of peak spawn time in the hatchery. Fight time and air exposure time did not influence progeny survival or prespawn mortality of adult steelhead captured by anglers.

Зимний промысел рыб семейства Coregonidae в устьевой области дельты р. Лена (бассейн моря Лаптевых)

Зимний промысел рыб семейства Coregonidae в устьевой области дельты р. Лена (бассейн моря Лаптевых)

Industry-Supported Sampling Underpins Temporal Management Policy Change in a Commercial Rock Lobster (Jasus edwardsii) Fishery

A winter fishery closure has existed in the northern zone rock lobster fishery of South Australia since 1966. This study describes the process undertaken to review and ultimately change temporal management policy with the aim of providing greater fishing flexibility to the commercial fishing sector. The work was driven by a research subcommittee (RSC) project team consisting of various stakeholder groups that included commercial fishers, fishery research scientists, resource managers, and conservation representatives. The RSC ultimately reported to the South Australian Rock Lobster Fisheries Management Advisory Committee (RLFMAC), an expertise-based, advisory body to the South Australian Government. To inform management discussions and possible policy change, the RSC proposed monthly sampling surveys during the winter fishery closure to examine key aspects of the catch composition. Sampling was underpinned by strong industry support in terms of survey logistics. Results were reviewed by the RSC and indicated that compared with the regular fishing season, closed season surveys identified (1) low catch rates of undersized lobsters; (2) reduced levels of predation mortality; (3) low contribution of female lobsters to the catch; and (4) negligible impacts on key bycatch species. Based on these findings, the RLFMAC recommended that policy changes in relation to the winter fishing closure could be considered. In June 2016, the Department of Primary Industries and Regions South Australia implemented the removal of the winter closure in an offshore region (>80 m depth) of the fishery resulting in a 12-mo fishing season for this area. The winter closure in the remainder of the fishery can be reconsidered after a 3 y period. This work is an example of industry, science, and Government collaboration to deliver management outcomes from industry-supported research.

Movements of a deep-water fish: establishing marine fisheries management boundaries in coastal Arctic waters.

Management boundaries that define populations or stocks of fish form the basis of fisheries planning. In the Arctic, decreasing sea ice extent is driving increasing fisheries development, highlighting the need for ecological data to inform management. In Cumberland Sound, southwest Baffin Island, an indigenous community fishery was established in 1987 targeting Greenland halibut (Reinhardtius hippoglossoides) through the ice. Following its development, the Cumberland Sound Management Boundary (CSMB) was designated and a total allowable catch (TAC) assigned to the fishery. The CSMB was based on a sink population of Greenland halibut resident in the northern section of the Sound. Recent fishing activities south of the CSMB, however, raised concerns over fish residency, the effectiveness of the CSMB and the sustainability of the community-based winter fishery. Through acoustic telemetry monitoring at depths between 400 and 1200m, and environmental and fisheries data, this study examined the movement patterns of Greenland halibut relative to the CSMB, the biotic and abiotic factors driving fish movement and the dynamics of the winter fishery. Greenland halibut undertook clear seasonal movements between the southern and northern regions of the Sound driven by temperature, dissolved oxygen, and sea ice cover with most fish crossing the CSMB on an annual basis. Over the lifespan of the fishery, landfast ice cover initially declined and then became variable, limiting accessibility to favored fisher locations. Concomitantly, catch per unit effort declined, reflecting the effect of changing ice conditions on the location and effort of the fishery. Ultimately, these telemetry data revealed that fishers now target less productive sites outside of their favored areas and, with continued decreases in ice, the winter fishery might cease to exist. In addition, these novel telemetry data revealed that the CSMB is ineffective and led to its relocation to the entrance of the Sound in 2014. The community fishery can now develop an open-water fishery in addition to the winter fishery to exploit the TAC, which will ensure the longevity of the fishery under projected climate-change scenarios. Telemetry shows great promise as a tool for understanding deep-water species and for directly informing fisheries management of these ecosystems that are inherently complex to study.

Depressed resilience of bluefin tuna in the western atlantic and age truncation.

Following intense overfishing in the 1970s, the western stock of Atlantic bluefin tuna (Thunnus thynnus) experienced a long period of depressed abundance, which has been attributed to failure of the population to periodically produce large numbers of juveniles, the western stock mixing with the more highly exploited eastern stock (fisheries in the Northeast Atlantic Ocean and Mediterranean Sea), and regime shift in the population's ecosystem resulting in lower replacement rates. To evaluate the presence of relatively strong years of juvenile production, we analyzed age structure from a recent sample of otoliths (ear stones) collected from the western stock (2011-2013, North Carolina, U.S.A., winter fishery). Mixing levels for the recent sample were analyzed using otolith stable isotopes to test whether age structure might be biased through immigration of eastern stock bluefin tuna. Age structure from historical samples collected from United States and Canadian fisheries (1975-1981) was compared with more recent samples (1996-2007) to examine whether demographic changes had occurred to the western stock that might have disrupted juvenile production. Relatively high juvenile production occurred in 2003, 2005, and 2006. Otolith stable isotope analysis showed that these recruitments were mostly of western stock origin. However, these high recruitments were >2-fold less than historical recruitment. We found substantial age truncation in the sampled fisheries. Half the historical sample was >20 years old (mean age = 20.1 [SD 3.7]; skewness = -0.3), whereas <5% of the recent sample was >20 years old (mean age = 13.4 [SD 3.8]; skewness = 1.3). Loss of age structure is consistent with changes in fishing selectivity and trends in the stock assessment used for management. We propose that fishing, as a forcing variable, brought about a threshold shift in the western stock toward lower biomass and production, a shift that emulates the regime shift hypothesis. An abbreviated reproductive life span compromised resilience by reducing the period over which adults spawn and thereby curtailing the stock's ability to sample year-to-year variability in conditions that favor offspring survival (i.e., storage effect). Because recruitment dynamics by the western stock exhibit threshold dynamics, returning it to a higher production state will entail greater reductions in exploitation rates.

Making use of Johan Hjort's “unknown” legacy: reconstruction of a 150-year coastal time-series on northeast Arctic cod (Gadus morhua) liver data reveals long-term trends in energy allocation patterns

Abstract Hidden within the seminal 1914 publication by Johan Hjort, we find what is probably one of the first comprehensive teleost time-series ever published. The series is liver size and fat content of northeast Arctic (NEA) cod measured during the traditional winter fishery in Lofoten, Northern Norway, in 1880–1912 and 1883–1913, respectively. The data were collected well before the advent of the great industrialized fisheries in the 1930s. The raw data used by Hjort originate from annual reports of the Lofoten fishery, initiated by Member of Parliament and pioneer fishery inspector of Northern Norway, Ketil Motzfeldt, in 1859. Based on these reports and following various calibration exercises, we present robust estimates of the hepatosomatic index (HSI) from 1859 to 2012 (except 1863), i.e. over 153 years—extending Hjort's analysis both backwards (1859–1879) and forwards (1913–present). This series of bulk HSI contained five major periods: 1859–1880, 1881–1919, 1920–1974, 1975–2003, and 2004–2012; the highest HSI was recorded 1920–1974, whereas the lowest was from the most recent period. Despite variability, total length was a significant predictor of HSI, 1932–2012. A weak but significant relationship existed with both total-stock biomass and ocean temperature, as well as with the North Atlantic Oscillation winter index under a 1-year lag. The present exceptionally long HSI series will give an excellent opportunity for further research on the “quality of the cod” in a historic perspective.

A novel approach for estimating location and scale specific fishing exploitation rates of eastern Bering Sea walleye pollock (Theragra chalcogramma)

Acoustic data collected opportunistically from eastern Bering Sea (EBS) walleye pollock (Theragra chalcogramma) fishing vessels were used within spatially explicit Leslie depletion models to estimate local exploitation rates. Although stock-wide EBS pollock fishery exploitation rates are generally at or below management objectives (∼6% for the winter fishery), there has been a concern that local fishing may impact forage opportunities needed for the recovery of the endangered Steller sea lion (Eumetopias jubatus). This study used high-resolution fishery information which suggests that on scales from 100km2 to 2500km2 exploitation rates often exceed the area-wide rates. In 2002 through 2005, higher exploitation rates occurred within the area defined as Steller sea lion critical habitat. This study provides a highly resolved quantitative assessment of location-specific fishing impacts, and is an important step in determining a rational approach to monitoring and managing fishing activities while taking into account ecosystem concerns.

A Synthesis of Kootenai River Burbot Stock History and Future Management Goals

AbstractIn Idaho, Burbot Lota lota are endemic only to the Kootenai River, where they once provided an important winter fishery to the indigenous people and European settlers. This fishery and that of Kootenay Lake in British Columbia may have been the most robust Burbot fisheries in North America. However, the fishery in Idaho rapidly declined after the construction of Libby Dam by the U.S. Army Corps of Engineers in 1972, and it closed in 1992. Concomitant to the collapse in Idaho was the collapse of the Burbot fishery in Kootenay Lake and the Kootenay River. The operation of Libby Dam for hydroelectric power generation and flood control created major changes in the river's nutrient concentration, temperature, and seasonal discharge, particularly during the winter when Burbot spawn. Libby Dam operations were implicated as the major limiting factor to Burbot recruitment, giving rise to higher winter temperatures and widely fluctuating flows. Because the Burbot in the Kootenai River are at risk of demographic extinction, a conservation strategy was prepared to outline the measures necessary to rehabilitate the Burbot population to a self‐sustaining level. The strategy indicated that operational discharge changes at Libby Dam are required during winter to provide suitable temperature and discharge conditions for Burbot migration and spawning. Studies recommend that the discharge at Bonners Ferry average 176 m3/s for a minimum of 90 d (mid‐November through mid‐February). Furthermore, preferred Burbot water temperatures of about 6°C are necessary for migration and cooler temperatures of 1–4°C for spawning. With each passing year, Burbot stock limitations increasingly constrain rehabilitation. Thus, coordination of intensive culture, extensive rearing, and pen rearing among the Kootenai Tribe of Idaho, the British Columbia Ministry of Environment, the University of Idaho's Aquatic Research Institute, and the Idaho Department of Fish and Game is important for restoration.

Pseudocollapse and rebuilding of North Sea mackerel (Scomber scombrus)

Abstract Jansen, T. 2014. Pseudocollapse and rebuilding of North Sea mackerel (Scomber scombrus). – ICES Journal of Marine Science, 71: 299–307. The largest observed change in mackerel (Scomber scombrus) abundance in the North Atlantic happened when the so-called “North Sea mackerel” collapsed due to overfishing. Despite protection, it has remained in a depleted state. Central to this interpretation was that the “North Sea mackerel” was considered to be a distinct spawning component. However, a recent study has shown that this is not likely. In the light of this study, a review of the history of mackerel spawning in the North Sea found that the traditional explanation of the collapse did not account for a range of unfavourable environmental changes: high fishing pressure was followed by decreasing temperatures that reduced the spawning migration into the North Sea. This was further supplemented by unfavourable changes in food and wind-induced turbulence. On the population level, this was, therefore, not a local stock collapse, but a southwest shift in spawning distribution combined with a reduction in that portion of the population cline with an affinity for spawning in the northeastern part of the spawning area, including the North Sea. No indication of irreversible genetic or behavioural losses caused by the events was found. The previously unexplained lack of rebuilding of spawning in the North Sea consequently seems related to two environmental factors that have remained unfavourable: (i) zooplankton concentration, and (ii) wind-induced turbulence. Furthermore, the large commercial autumn–winter fishery in the North Sea continues to land unknown quantities of mackerel that have an affinity for spawning in the northeastern part of the spawning area, including the North Sea.

Developing a fine scale system to address river herring (Alosa pseudoharengus, A. aestivalis) and American shad (A. sapidissima) bycatch in the U.S. Northwest Atlantic mid-water trawl fishery

Managers of the Atlantic herring (Clupea harengus) and mackerel (Scomber Scombrus) fisheries have a goal of reducing river herring (Alosa pseudoharengus, Alosa aestivalis) bycatch. Regulations being considered include temporarily closing 30nm×30nm river herring “hotspots” or enacting these measures if a threshold amount of river herring is observed. These closures could be effective at reducing river herring bycatch, but would result in significant economic cost. The uncertainty of the effect of bycatch on river herring populations coupled with potential economic losses due to closed areas suggests a finer scale, voluntary method may be more appropriate. A collaboration between the Sustainable Fisheries Coalition, the Massachusetts Division of Marine Fisheries, and the University of Massachusetts Dartmouth School of Marine Science and Technology seeks to address this issue by implementing near real-time bycatch information systems for this fishery. The first system was implemented during the 2011 winter mid-water trawl fishery (January through March) over an approximate 60nm×70nm area off the coast of New Jersey. Fifty percent of vessels landing in Massachusetts were sampled during this time period. Bycatch information from these vessels was accessed and shared with participating captains using a coded grid of smaller cells approximately 5nm×8nm (10′ longitude×5′ latitude). Industry collaboration and the appearance of small scale spatial and temporal patterns during the 2011 winter fishery suggests this is a plausible approach to reduce river herring and American shad (Alosa sapidissima) bycatch. The comparison of the results of this study to potential management actions displays both advantages and disadvantages of using a larger spatial scale to reduce bycatch while maintaining an active fishery.

The effect of decreasing seasonal sea-ice cover on the winter Bering Sea pollock fishery

Abstract Pfeiffer, L., and Haynie, A. C. 2012. The effect of decreasing seasonal sea-ice cover on the winter Bering Sea pollock fishery. – ICES Journal of Marine Science, 69: . The winter fishing season for eastern Bering Sea pollock (Theragra chalcogramma) is during the period of maximum seasonal sea-ice extent, but harvesters avoid fishing in ice-covered waters. Global climate models predict a 40% reduction in winter ice cover by 2050, with potential implications for the costs incurred by vessels travelling to and around their fishing grounds and the value of their catch. Additionally, it may open entirely new areas to fishing. Using retrospective data from 1999 to 2009, a period of extensive annual climate variation, the variation in important characteristics of the fishery is analysed. When ice is present, it restricts a portion of the fishing grounds, but in general, ice-restricted areas have lower expected profits at the time of restriction than the areas left open. Some areas show a change in effort in warm years relative to cold, but the global redistribution of effort attributable to ice cover is small. This is largely because the winter fishery is driven by the pursuit of roe-bearing fish whose spawning location is stable in the southern part of the fishing grounds.

Survival of Angled Saugers in the Lower Tennessee River

AbstractAn intense winter fishery for sauger Sander canadensis exists in the lower Tennessee River, and the objective of this study was to estimate the survival of angled saugers. In February 2008 and January–March 2009, 81 angled saugers (72 live plus 9 euthanized) were affixed with ultrasonic tags. The movements (or lack thereof) by saugers released alive were compared with those of euthanized fish to assess survival. Sixty‐eight percent of the tagged saugers that were released alive exhibited maximum daily movements exceeding the greatest movement of any euthanized fish (0.5 km/d), and those fish were subsequently classified as survivors. The upstream movements of several euthanized fish indicated that their carcasses were ingested by piscivorous scavengers. In logistic models, the probability of mortality was significantly and inversely related to total length but not to capture depth, water temperature, handling time, or ascent rate. In 2 × 2 contingency tables, the fate of released saugers was not found to be associated with either the presence or absence of bleeding from the hooking wound or whether or not the fish displayed gastric distension. Most released fish survived despite the fact that gastric distension was observed in 72% of the angled saugers.Received August 11, 2010; accepted April 21, 2011

Low prevalence of splenic mycobacteriosis in migratory striped bass Morone saxatilis from North Carolina and Chesapeake Bay, USA

Mycobacteriosis is a chronic bacterial disease causing an ongoing epizootic in striped bass Morone saxatilis in Chesapeake Bay, U.S.A. Prevalence of disease is high in pre-migratory fish, and multiple species of Mycobacterium spp. have been isolated. However, prevalence of mycobacteriosis in the coastal migratory population is unknown and is of concern to multiple coastal states, as disease-related mortality may impact the long-term health of the population. Histological examinations of spleens collected from fish caught by recreational anglers during the winter fishery in coastal North Carolina (2005-2006, n=249) and during the spring fishery in Chesapeake Bay (2006, n=120) indicated a low prevalence of mycobacteriosis (6.8% of all fish examined) in comparison to smaller, pre-migratory Chesapeake Bay fish. Genus-level PCR and subsequent sequencing of the 16-23S intergenic transcribed spacer (ITS) region revealed that all bacteria were phylogenetically related, but species is unknown. Location of survey, gender of fish, and total length of fish had no significant effect on prevalence of mycobacteriosis, parasitic granulomas, or the density of splenic granulomas (p > 0.05). These results may indicate that either granulomas resolve after Chesapeake Bay fish enter the coastal migratory population, or that there is disease-related mortality among pre-migratory Chesapeake Bay fish.