Jason C. Vokoun

Fine‐scale population structure and riverscape genetics of brook trout (Salvelinus fontinalis) distributed continuously along headwater channel networks

Linear and heterogeneous habitat makes headwater stream networks an ideal ecosystem in which to test the influence of environmental factors on spatial genetic patterns of obligatory aquatic species. We investigated fine‐scale population structure and influence of stream habitat on individual‐level genetic differentiation in brook trout (Salvelinus fontinalis) by genotyping eight microsatellite loci in 740 individuals in two headwater channel networks (7.7 and 4.4 km) in Connecticut, USA. A weak but statistically significant isolation‐by‐distance pattern was common in both sites. In the field, many tagged individuals were recaptured in the same 50‐m reaches within a single field season (summer to fall). One study site was characterized with a hierarchical population structure, where seasonal barriers (natural falls of 1.5–2.5 m in height during summer base‐flow condition) greatly reduced gene flow and perceptible spatial patterns emerged because of the presence of tributaries, each with a group of genetically distinguishable individuals. Genetic differentiation increased when pairs of individuals were separated by high stream gradient (steep channel slope) or warm stream temperature in this site, although the evidence of their influence was equivocal. In a second site, evidence for genetic clusters was weak at best, but genetic differentiation between individuals was positively correlated with number of tributary confluences. We concluded that the population‐level movement of brook trout was limited in the study headwater stream networks, resulting in the fine‐scale population structure (genetic clusters and clines) even at distances of a few kilometres, and gene flow was mitigated by ‘riverscape’ variables, particularly by physical barriers, waterway distance (i.e. isolation‐by‐distance) and the presence of tributaries.

Influence of Rare Species on Electrofishing Distance When Estimating Species Richness of Stream and River Reaches

Abstract The electrofishing distance needed to estimate fish species richness at the stream or river reach scale is an important question in fisheries science. This distance is governed by the shape of the species accumulation curve, which, in turn, is influenced by a combination of factors, including the number of species, their overall abundances, habitat associations, the efficiency of the sampling method, and the occurrence of rare species. In this study we document the influence of rare species on the species accumulation curves from stream and river sites in data sets from five dispersed regions of the USA. Spatial discontinuity (i.e., a noncontinuous distribution within reaches) was observed in four of the five data sets, and the four data sets contained numerically rare species represented by one or two individuals (termed singletons and doubletons, respectively). Numerically rare species were typically proportionately rare (i.e., <1% of the total number of individuals captured), but proportionate...

Earlier Spring Warming of Coastal Streams and Implications for Alewife Migration Timing

Abstract Seasonal temperature increases have been shown to correlate with changes in the migration timing of fish. We looked at existing temperature and fish count data for anadromous alewives Alosa pseudoharengus in several southern New England streams. Run initiation, defined as occurring when the first 5% of the total annual run migrated, was associated with 9°C. A weighted-mean migration temperature, considered an overall indicator of total run timing, revealed that 13°C was a consistent predictor of run timing for one historic and three recent alewife streams over several years. Because historical and recent daily water temperatures with concurrent fish counts were unavailable for any one site, we used the occurrence of 9°C and 13°C stream temperatures to determine the magnitude of any detectable shift in the migration timing of alewives between the 1970s and recent years. Stream temperatures in the spring warmed to 13°C about 12 d earlier in recent years than they did in the 1970s. This implied that...

Using Multimethod Occupancy Estimation Models to Quantify Gear Differences in Detection Probabilities: Is Backpack Electrofishing Missing Occurrences for a Species of Concern?

AbstractThe Bridle Shiner Notropis bifrenatus is a small, rare minnow species native to northeastern streams and lakes. It is declining over most of its range and currently is listed as a species of concern in Connecticut. Surveys conducted with seine nets in the 1960s found Bridle Shiners at 56 locations statewide. In contrast, surveys conducted in the 1990s using electrofishing detected Bridle Shiners at 8 locations. Different sampling techniques made it difficult to assess what portion of the observed decline might be a sampling artifact, confounding efforts to assess the actual conservation status. We sampled 18 habitat patches in three Connecticut watersheds in 2012 to determine if seining for Bridle Shiners yielded a higher detection probability than backpack electrofishing. A multimethod occupancy estimation modeling approach, using the program PRESENCE, quantified the probability of correctly detecting Bridle Shiners by gear and as detection covaried with habitat features. Backpack electrofishing ...

Biogeography of Stream Fishes in Connecticut: Defining Faunal Regions and Assemblage Types

Abstract Stream fish survey data were analyzed to describe patterns of fish distributions in wadeable streams (primarily 1st–4th order) in Connecticut. Species occurrence within the United States Geological Survey 8-digit hydrologic unit code watersheds were used to aggregate similar watersheds into stream fish faunal regions. Within each identified region, multivariate analyses were used to identify major fish assemblage types and associate stream habitat with assemblage types. The analyses revealed an eastern and western faunal region defined primarily by distribution of a few native species. Native species associated with the western watersheds were: Semotilus atromaculatus (Creek Chub), Exoglossum maxillingua (Cutlips Minnow), and Cottus cognatus (Slimy Sculpin). Native fishes associated with the eastern watersheds were: Erimyzon oblongus (Creek Chubsucker), Esox niger (Chain Pickerel), and Esox americanus (Redfin Pickerel). Inclusion of non-indigenous species in the analyses resulted in a similar east–west grouping of watersheds. Five and four assemblage types were identified in the eastern and western faunal regions, respectively. Both regions harbored 3 fluvial assemblages defined longitudinally from headwater streams to larger wadeable streams and a macro-habitat generalist assemblage inhabiting streams with proportionately more pool habitat, but taxonomic membership and indicator species rankings among assemblages were not necessarily identical between the regions. A distinct assemblage dominated by Redfin Pickerel was recognized only in the eastern region. Streams in the western region were generally higher in elevation and colder in water temperature. The discovery and description of eastern and western fish faunal regions and their fish assemblage types will be useful in stratifying the biological monitoring of streams and other aquatic resource management actions in Connecticut.

Differences in the Metabolic Rates of Exploited and Unexploited Fish Populations: A Signature of Recreational Fisheries Induced Evolution?

Non-random mortality associated with commercial and recreational fisheries have the potential to cause evolutionary changes in fish populations. Inland recreational fisheries offer unique opportunities for the study of fisheries induced evolution due to the ability to replicate study systems, limited gene flow among populations, and the existence of unexploited reference populations. Experimental research has demonstrated that angling vulnerability is heritable in Largemouth Bass Micropterus salmoides, and is correlated with elevated resting metabolic rates (RMR) and higher fitness. However, whether such differences are present in wild populations is unclear. This study sought to quantify differences in RMR among replicated exploited and unexploited populations of Largemouth Bass. We collected age-0 Largemouth Bass from two Connecticut drinking water reservoirs unexploited by anglers for almost a century, and two exploited lakes, then transported and reared them in the same pond. Field RMR of individuals from each population was quantified using intermittent-flow respirometry. Individuals from unexploited reservoirs had a significantly higher mean RMR (6%) than individuals from exploited populations. These findings are consistent with expectations derived from artificial selection by angling on Largemouth Bass, suggesting that recreational angling may act as an evolutionary force influencing the metabolic rates of fishes in the wild. Reduced RMR as a result of fisheries induced evolution may have ecosystem level effects on energy demand, and be common in exploited recreational populations globally.

Striped Bass Consumption of Blueback Herring during Vernal Riverine Migrations: Does Relaxing Harvest Restrictions on a Predator Help Conserve a Prey Species of Concern?

Abstract Anadromous blueback herring Alosa aestivalis are declining throughout much of their range, and fishery closures in some systems have failed to produce population recovery. A potential contributing factor is increased predation pressure from sympatric striped bass Morone saxatilis. We integrated data on the predator-prey interaction between striped bass and blueback herring during vernal migrations into the Connecticut River with data on the in-river striped bass fishery to assess the potential for mitigation of blueback herring mortality via increased striped bass harvest. Striped bass abundance, size structure, diets, and angler catches were assessed within a river segment during spring 2005–2008. We estimate that striped bass consumed 400,000 blueback herring (90% confidence interval = 200,000–800,000) annually in our study area during the spring migration season. The predator-prey interaction between striped bass and blueback herring was predator size dependent. Blueback herring were most commonly found in the stomachs of striped bass between 650 and 999 mm total length. Intermediate size-classes (650–799 mm) made the greatest contribution to population-level consumption. Highly abundant small striped bass (400–549 mm) consumed herring infrequently, yet still made substantial contributions to population-level consumption. Anglers caught 17,000 striped bass in our study area during March–June 2008; only 11% of these fish could be harvested under the current 28-in (710-mm) minimum length limit. Allowing anglers to harvest up to 15,000 sublegal striped bass from a “bonus harvest” slot limit would reduce annual predatory losses of blueback herring by up to 10%. Alternatively, a smaller bonus harvest of legal-sized striped bass could achieve reductions in consumption of up to 7%. The recreational fishery in our study area, however, may not be intense enough to realize such harvest levels.

Maximum Daily Consumption and Specific Daily Metabolic Demand of Juvenile Flathead Catfish (Pylodictis olivaris)

ABSTRACT Maximum daily consumption and specific daily metabolic demand were determined for juvenile flathead catfish (Pylodictis olivaris) in the laboratory over a temperature range of 3–32 °C. Maximum daily consumption increased with increasing water temperature, was significantly higher at 19 °C than at colder temperatures, and remained elevated up to 32 °C. Fish rarely ate below 15 °C, most stopped feeding at 11 °C, and no fish consumed anything at 7 °C or below. Specific daily metabolic demand showed a gradual increase with increasing temperature. The quantification of consumption and metabolic demand for juvenile flathead catfish was consistent with descriptions classifying the species as adapted to warmwater conditions.

Loss of Naivety to Angling at Different Rates in Fished and Unfished Populations of Largemouth Bass

AbstractRecreational fishing represents a coupled human and natural system subject to complex feedback processes. Learned lure avoidance represents one feedback process that may influence a fish population’s vulnerability to angling. In the present study, naive Largemouth Bass Micropterus salmoides originating from fished and unfished populations were raised in a pond and subjected to standardized angling. Our objectives were to evaluate the initial angling vulnerability and the rate at which naivety to angling was lost for fished and unfished populations. While no difference in initial angling vulnerability existed among fish from fished and unfished populations of origin, individuals from fished populations learned lure avoidance faster than individuals from unfished populations. Cumulative catch events, a metric that incorporates the number of opportunities individuals had to directly and indirectly experience angling, best predicted declining daily catch rates for both fished and unfished populations,...

Population characteristics of historically unexploited largemouth bass in southern New England water supply reservoirs

Recreational fishing can alter the demography and life history characteristics of fish populations. Unexploited populations are useful references for fisheries managers to place into context the extent of changes in exploited populations and the outcomes of management actions. Our objective is to characterize the largemouth bass Micropterus salmoides populations in two unexploited reservoirs in Connecticut and compare them with an exploited reservoir. Unexploited Hemlock Reservoir was characterized by large proportions of large fish in good condition with relatively low population mortality rates. Unexploited Easton Reservoirs bass proportional size distributions were more similar to exploited Mansfield Hollow Reservoir bass population. However, both unexploited reservoirs had higher catch per effort of stock-size and greater fish than Mansfield Hollow Reservoir indicating greater overall density of large fish. The study of long-term unexploited populations may become more important in the future as managers consider the evolutionary consequences of recreational exploitation.