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B. H. Letcher

Publications and source records attributed to B. H. Letcher.

29 records · Page 2Linked to original sources
USGS2005

A field test of the extent of bias in selection estimates after accounting for emigration

Question: To what extent does trait-dependent emigration bias selection estimates in a natural system? Organisms: Two freshwater cohorts of Atlantic salmon (Salmo salar) juveniles. Field site: A 1 km stretch of a small stream (West Brook) in western Massachusetts. USA from which emigration could be detected continuously. Methods: Estimated viability selection differentials for body size either including or ignoring emigration (include = emigrants survived interval, ignore = emigrants did not survive interval) for 12 intervals. Results: Seasonally variable size-related emigration from our study site generated variable levels of bias in selection estimates for body size. The magnitude of this bias was closely related with the extent of size-dependent emigration during each interval. Including or ignoring the effects of emigration changed the significance of selection estimates in 5 of the 12 intervals, and changed the estimated direction of selection in 4 of the 12 intervals. These results indicate the extent to which inferences about selection in a natural system can be biased by failing to account for trait-dependent emigration. ?? 2005 Benjamin H. Letcher.

Evolutionary Ecology Research↗
USGS2003

Effects of life history variation on size and growth in stream-dwelling Atlantic salmon

A large size variation amongst life histories for stream-dwelling Atlantic salmon Salmo salar was found and the relative effect of life histories on size varied over time. As early as December (age 0+ years), fish that later smolted at age 2+ years were significantly larger than fish that did not smolt at age 2+ years. In contrast, there were no mass differences at age 0+ years between fish that would mature or not at age 1+ years (October). The mass differences between smolts and non-smolts persisted until smolting, and differences between mature and immature fish first appeared in May (age 1+ years). Following September (age 1+ years), there was also a significant interaction between smolting and maturity. Previously mature and immature age 2+ year smolts were not significantly different in size, but immature age 2+ year non-smolts were much lighter than mature age 2+ year non-smolts. Based on mass differences, the apparent 'decision' to smolt occurred c. 5 months before (winter, age 0+ years) the decision to mature (late spring, age 1+ years). In addition to strong seasonal growth variation, sizes of freshwater Atlantic salmon were largely structured by the complex interaction between smolt-age and maturity. ?? 2003 The fisheries Society of the British Isles.

Journal of Fish Biology↗
USGS2003

Predation on stocked Atlantic salmon (Salmo salar) fry

We studied predator-prey interactions between juvenile Atlantic salmon (Salmo salar) and trout in three Massachusetts, U.S.A., streams and in artificial streams. We sampled stomach contents of age-1+ and older salmon and trout (Salvelinus fontinalis, Salmo trutta) following salmon fry stocking in the spring of 1997 and 1998. Between 4.3 and 48.6% of the stocked fry were consumed within the first 2 days after stocking, and total fry mortality from predation varied from 4.3 to 60.7%. No significant differences were found between stomach weights of predators (without fry weight) that consumed fry and those that did not. Artificial stream experiments testing effects of habitat complexity and predator species on predator consumption rates revealed that consumption rates were not different between brook (S. fontinalis) and brown (S. trutta) trout (p = 0.59). Predation rate tended to decrease as the percentage of riffle habitat increased but the decrease was not significant (p = 0.22). Our results indicate that predation on stocked Atlantic salmon fry can be substantial (up to 60%), appears to be short lived (2 days), and is not related in a simple way to abiotic and biotic factors.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS2002

Survival of stream-dwelling Atlantic salmon: Effects of life history variation, season, and age

To determine seasonal and age-class variation in the abundance and survival of Atlantic salmon Salmo salar , we conducted multiple samplings of individually tagged juveniles in a small stream (West Brook, Massachusetts). We also estimated the differences in survival and probability of smolting for mature and immature parr. Survival was approximately twofold lower during winter as compared with summer and was higher for fish in their first winter than for fish in their second winter. Parr maturation rates were high (50% of all fish) and peaked in September. The estimated numbers of mature and immature fish were equal for the March samples preceding the smolt run, indicating no overall differences in survival between mature and immature fish during stream residence. Age-2 mature fish were one-third as likely to smolt as immature fish, however, resulting in survival probabilities (from March to smoltification) of 0.22 for mature fish and 0.61 for immature fish. Approximately one-third of the fish captured in the smolt trap were estimated as mature during previous sampling, and virtually all of the age-2 fish remaining in the stream following the smolt run were previously mature. We found no differences in gill Na + , K + ATPase activity between previously mature smolts and immature smolts, but activity was significantly higher in March for fish that later smolted than for those that did not.

Massachusetts↗
USGS2002

Tag retention and survival of Age-0 Atlantic salmon following surgical implantation with passive integrated transponder tags

We evaluated an alternative to using hypodermic needles to implant passive integrated transponder (PIT) tags in the body cavities of juvenile salmonids. We used surgical techniques to place PIT tags into the body cavities of 3,037 age-0 Atlantic salmon Salmo salar and then held fish under hatchery conditions for 9 months. Tag retention was 99.8% (six fish lost tags), and survival was 94.3% (174 fish died) after controlling for initial mortality (0.7%). A single tagger was able to tag 80–100 fish per hour. Surgically implanting PIT tags into the body cavities of age-0 Atlantic salmon proved to be a viable alternative to using hypodermic needles.

North American Journal of Fisheries Management↗
USGS2002

A night seining technique for sampling juvenile Atlantic salmon in streams

For many studies of the population dynamics, growth, and movement of juvenile Atlantic salmon Salmo salar , it is necessary to resample tagged individuals multiple times. However, common sampling techniques such as electrofishing can have negative effects on fish survival and growth, especially when individuals are repeatedly sampled. We describe an alternative to electrofishing that involves sampling at night with small, one-person seines. Juvenile Atlantic salmon in a small brook were tagged with passive integrated transponder tags and sampled 15 times by means of night seining, day electrofishing, and day seining techniques. Capturing juvenile Atlantic salmon by day seining was inefficient, resulting in a capture probability estimate of 0.18. The mean capture probability estimate was 0.45 during night seining samples and 0.78 during electrofishing samples. The total number of age-0 Atlantic salmon captured via night seining increased 4.5 times after fish attained a mean fork length of just over 60 mm. A much greater number of brook trout Salvelinus fontinalis and brown trout Salmo trutta were captured in electrofishing samples than in night seining samples. Night seining may prove useful when electrofishing is impractical, when threatened or endangered species exist, or when multiple recaptures of individuals are desired.

Massachusetts↗
USGS1999

Targeted stock identification using multilocus genotype 'familyprinting'

We present an approach to stock identification of small, targeted populations that uses multilocus microsatellite genotypes of individual mating adults to uniquely identify first- and second-generation offspring in a mixture. We call the approach ‘familyprinting’; unlike DNA fingerprinting where tissue samples of individuals are matched, offspring from various families are assigned to pairs of parents or sets of four grandparents with known genotypes. The basic unit of identification is the family, but families can be nested within a variety of stock units ranging from naturally reproducing groups of fish in a small tributary or pond from which mating adults can be sampled to large or small collections of families produced in hatcheries and stocked in specific locations. We show that, with as few as seven alleles per locus using four loci without error, first-generation offspring can be uniquely assigned to the correct family. For second-generation applications in a hatchery more alleles per locus (10) and loci (10) are required for correct assignment of all offspring to the correct set of grandparents. Using microsatellite DNA variation from an Atlantic salmon ( Salmo solar ) restoration river (Connecticut River, USA), we also show that this population contains sufficient genetic diversity in sea-run returns for 100% correct first-generation assignment and 97% correct second-generation assignment using 14 loci. We are currently using first- and second-generation familyprinting in this population with the ultimate goal of identifying stocking tributary. In addition to within-river familyprinting, there also appears to be sufficient genetic diversity within and between Atlantic salmon populations for identification of ‘familyprinted’ fish in a mixture of multiple populations. We also suggest that second-generation familyprinting with multiple populations may also provide a tool for examining stock structure. Familyprinting with microsatellite DNA markers is a viable method for identification of offspring of randomly mating adults from small, targeted stocks and should provide a useful addition to current mixed stock analyses with genetic markers.

Fisheries Research↗
USGS1998

An individual-based, spatially-explicit simulation model of the population dynamics of the endangered red-cockaded woodpecker, Picoides borealis

Spatially-explicit population models allow a link between demography and the landscape. We developed a spatially-explicit simulation model for the red-cockaded woodpecker, Picoides borealis , an endangered and territorial cooperative breeder endemic to the southeastern United States. This kind of model is especially appropriate for this species because it can incorporate the spatial constraints on dispersal of helpers, and because territory locations are predictable. The model combines demographic data from a long-term study with a description of the spatial location of territories. Sensitivity analysis of demographic parameters revealed that population stability was most sensitive to changes in female breeder mortality, mortality of female dispersers and the number of fledglings produced per brood. Population behavior was insensitive to initial stage distribution; reducing the initial number of birds by one-half had a negligible effect. Most importantly, we found that the spatial distribution of territories had as strong an effect on response to demographic stochasticity as territory number. Populations were stable when territories were highly aggregated, with as few as 49 territories. When territories were highly dispersed, more than 169 territories were required to achieve stability. Model results indicate the importance of considering the spatial distribution of territories in management plans, and suggest that this approach is worthy of further development.

North Carolina↗
USGS1998

Maturation of male age-0 Atlantic salmon following a massive, localized flood

Maturation of male age-0 Atlantic salmon Salmo salar parr in New England, U.S.A. streams is rare (˜5%), but age-0 parr maturation was high (74%) by autumn in the Sawmill River following a massive, localized flood. Maturation was low in two other study streams (3, 7%) in the same year as the flood, and in the Sawmill River (6%) and the other rivers (5%) in the subsequent year, suggesting that high maturation rates were related to the flood. The high age-0 maturation rates appear to have been the result of greater growth opportunity following the flood. Masses of fish in October were two-fold greater in the Sawmill River (13·2 g) than in the other rivers (6·5, 6·9 g). Mechanisms contributing to the fast growth may include community reorganization following the flood and water temperature differences among rivers. The flood caused an age-0 year-class failure for brook trout Salvelinus fontinalis and brown trout Salmo trutta and a large reduction (69%) in the number of salmon compared to the other rivers, possibly reducing competition or agonistic interactions among remaining fish. Average water temperatures were slightly warmer in the Sawmill River (17·0° C) than in the other rivers (15·5, 14·9° C). By influencing community structure and growth of remaining fish, it appears that a strong environmental disturbance can also alter the direction and timing of life histories in Atlantic salmon.

Journal of Fish Biology↗
USGS1998

Effects of a delayed onset of piscivory on the size of age-0 bluefish

Variation in advection or other physical forces may accelerate or delay arrival of young marine fishes into productive nearshore habitats, thereby affecting the length of the available growing season. The bluefish Pomatomus saltatrix is an oceanic spawner whose juvenile stages, upon entry into estuarine waters, become piscivorous and thereby experience greatly increased growth. Size attained during the growing season may therefore be determined by time of arrival into estuarine habitats. We exposed bluefish recently recruited to an estuary to three diet shift treatments in which test fish were fed adult brine shrimp Artemia sp. for 0 , 10, or 20 d before they were switched to piscine prey. Bluefish that had a delayed onset of piscivory were smaller after 40 d of growth, indicating that they did not fully compensate for prior periods of slow growth. These bluefish did exhibit immediate moderate growth compensation (about 6% over 10 d) resulting from increased consumption rates, but relatively low growth efficiencies prevented full recovery of their growth losses. Low growth efficiencies may have resulted from an induced developmental handicap or an energetic penalty for prolonged feeding on an Artemia diet. The timing of age - 0 bluefish recruitment into estuarine environments can have a lasting influence on size attained during the first growing season.

Transactions of the American Fisheries Society↗