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Geology topics

B. H. Letcher

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

At least 37 records · Page 2Linked to original sources
USGS2007

Growth rate differences between resident native brook trout and non-native brown trout

Between species and across season variation in growth was examined by tagging and recapturing individual brook trout Salvelinus fontinalis and brown trout Salmo trutta across seasons in a small stream (West Brook, Massachusetts, U.S.A.). Detailed information on body size and growth are presented to (1) test whether the two species differed in growth within seasons and (2) characterize the seasonal growth patterns for two age classes of each species. Growth differed between species in nearly half of the season- and age-specific comparisons. When growth differed, non-native brown trout grew faster than native brook trout in all but one comparison. Moreover, species differences were most pronounced when overall growth was high during the spring and early summer. These growth differences resulted in size asymmetries that were sustained over the duration of the study. A literature survey also indicated that non-native salmonids typically grow faster than native salmonids when the two occur in sympatry. Taken together, these results suggest that differences in growth are not uncommon for coexisting native and non-native salmonids. ?? 2007 The Authors.

Journal of Fish Biology↗
USGS2006

Diel and seasonal variation in food habits of Atlantic salmon parr in a small stream

The diel and seasonal food habits of young-of-year (YOY) and post-young-of-year (PYOY) Atlantic salmon ( Salmo salar ) parr were assayed over the course of 11 months in the West Brook, Massachusetts USA. Gut fullness of YOY salmon did not vary significantly among months. PYOY salmon exhibited significant seasonal differences in gut fullness, with peak fullness occurring in the spring and late fall. Significant diel differences in PYOY gut fullness occurred in June and April, with peak fullness always occurring at dawn. Prey composition varied substantially among months. Dominant prey items of PYOY salmon were baetid mayflies in June, July, and August, limnephilid caddisflies in October and November, and ephemerellid mayflies in February and April. Few differences in prey composition between PYOY and YOY salmon were observed. Fish growth was unrelated to prey availability, but gut fullness explained up to 97% of growth variation across seasons. Results suggest that spring and fall are critical periods of feeding for PYOY salmon and that diel feeding intensity shifts seasonally.

Journal of Freshwater Ecology↗
USGS2005

Electroshocking and PIT tagging of juvenile Atlantic salmon: Are there interactive effects on growth and survival?

Electroshocking and tagging of fish with passive integrated transponder (PIT) tags are two commonly used methods for conducting mark-recapture studies in freshwater environments and are frequently used in combination. We conducted an experiment to test for the effects of electroshocking, tagging, and a combination of electroshocking plus tagging on the growth and survival of Atlantic salmon Salmo salar parr. We used five treatments that included the presence or absence of PIT tags and electroshocking at 300 or 500 V plus a control group. Fish were measured, weighed, and electroshocked on four occasions separated by approximately 2-month intervals. The average (??1 SD) fork length was 62.1 ?? 1.9 mm and the average weight was 2.5 ?? 0.3 g at the start of the experiment; at the end of the experiment, length averaged 120.5 ?? 11.6 mm and weight averaged 20.9 ?? 6.1 g. We did not detect any significant effects of electroshocking on growth or survival over the course of the experiment. However, there was evidence that tagging negatively influenced survival over the first interval after initial tagging and that survival was positively correlated with fish size. In addition, tagged fish seemed to suffer a minor depression in growth over the first interval, although differences in size among tagged and untagged fish were nonsignificant throughout the course of the experiment. We suggest that the size at tagging may have a greater effect on survival and growth of small (<80-mm) Atlantic salmon parr than the amount of exposure to electroshocking. ?? Copyright by the American Fisheries Society 2005.

North American Journal of Fisheries Management↗
USGS2005

Alternative life histories shape brain gene expression profiles in males of the same population

Atlantic salmon (Salmo salar) undergo spectacular marine migrations before homing to spawn in natal rivers. However, males that grow fastest early in life can adopt an alternative 'sneaker' tactic by maturing earlier at greatly reduced size without leaving freshwater. While the ultimate evolutionary causes have been well studied, virtually nothing is known about the molecular bases of this developmental plasticity. We investigate the nature and extent of coordinated molecular changes that accompany such a fundamental transformation by comparing the brain transcription profiles of wild mature sneaker males to age-matched immature males (future large anadromous males) and immature females. Of the ca. 3000 genes surveyed, 15% are differentially expressed in the brains of the two male types. These genes are involved in a wide range of processes, including growth, reproduction and neural plasticity. Interestingly, despite the potential for wide variation in gene expression profiles among individuals sampled in nature, consistent patterns of gene expression were found for individuals of the same reproductive tactic. Notably, gene expression patterns in immature males were different both from immature females and sneakers, indicating that delayed maturation and sea migration by immature males, the 'default' life cycle, may actually result from an active inhibition of development into a sneaker. ?? 2005 The Royal Society.

Proceedings of the Royal Society B: Biological Sci↗
USGS2005

Interaction of rearing environment and reproductive tactic on gene expression profiles in Atlantic salmon

Organisms that share the same genotype can develop into divergent phenotypes, depending on environmental conditions. In Atlantic salmon, young males of the same age can be found either as sneakers or immature males that are future anadromous fish. Just as the organism-level phenotype varies between divergent male developmental trajectories, brain gene expression is expected to vary as well. We hypothesized that rearing environment can also have an important effect on gene expression in the brain and possibly interact with the reproductive tactic adopted. We tested this hypothesis by comparing brain gene expression profiles of the two male tactics in fish from the same population that were reared in either a natural stream or under laboratory conditions. We found that expression of certain genes was affected by rearing environment only, while others varied between male reproductive tactics independent of rearing environment. Finally, more than half of all genes that showed variable expression varied between the two male tactics only in one environment. Thus, in these fish, very different molecular pathways can give rise to similar macro-phenotypes depending on rearing environment. This result gives important insights into the molecular underpinnings of developmental plasticity in relationship to the environment. ?? 2005 The American Genetic Association.

Conference Paper↗
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↗
USGS2004

Comparison of genetic diversity in the recently founded Connecticut River Atlantic salmon population to that of its primary donor stock, Maine's Penobscot River

Anadromous Atlantic salmon returning to the Connecticut River (CR) from 1996 to 1999 were assayed for variability at nine microsatellite DNA loci. Heterozygosity and allele frequencies were compared to the anadromous Atlantic salmon returning to Maine's Penobscot River from 1998 to 2000. The Penobscot River was the primary source of the salmon used to found the previously extirpated population in the Connecticut River. While there were no significant differences in heterozygosity between the source population and the Connecticut River sea-run spawners, microsatellite allele frequencies were significantly different between the populations. Two techniques of estimating effective population size (Ne) suggested a healthy level of genetic variation in the Connecticut River population of anadromous Atlantic salmon. This is significant because the sea-run population is maintained almost entirely through hatchery production. Healthy ratios of Ne to N indicate that hatchery production has not resulted in excessive inbreeding to date. ?? 2003 Elsevier B.V. All rights reserved.

Aquaculture↗
USGS2004

Long-term consequences of variation in timing and manner of fry introduction on juvenile Atlantic salmon (Salmo salar) growth, survival, and life-history expression

We tested the influence of introduction time and the manner of introduction on growth, survival, and life-history expression of Atlantic salmon (Salmo salar). Introduction treatments included three fry stocking times and stream rearing of embryos. Despite poor growth conditions during the early stocking period, early-stocked fish were larger throughout the entire study period, likely the result of prior residence advantage. This interpretation was reinforced by the laboratory study, where early-stocked fish outgrew late-stocked fish when reared together, but not when they were reared separately. In contrast to growth, abundance of stocked fish was greatest for fish stocked during the middle period, and this stocking group produced the greatest number of smolts. Despite smaller size, survival of stream-incubated fish was generally greater than survival of stocked fish. Introduction timing had a pronounced effect on smolt age but a weak effect on extent of parr maturation. Overall, these observations indicate that small differences (???2 weeks) in introduction time can have long-term effects on size, survival, and life-history expression. Results suggest stabilizing selection on introduction times, mediated by the interaction between prior residence (advantage to fish introduced earlier) and habitat suitability (advantage to fish introduced later). ?? 2004 NRC Canada.

Conference Paper↗
USGS2004

Variation in freshwater growth and development among five New England Atlantic salmon (Salmo salar) populations reared in a common environment

We examined phenotypic variation in growth and development from the eyed-egg stage to the age-1+ smolt stage among five New England populations of Atlantic salmon (Salmo salar: East Machias, Narraguagus, Sheepscot, Penobscot, Connecticut) reared in a common laboratory environment. Study populations originated from rivers varying in size, latitude, and level of hatchery supplementation and included one reintroduced population (Connecticut was a recipient of Penobscot origin stock). Phenotypic trait differences were found among populations, and the degree of stock variation depended on ontogeny. Eggs were smaller and hatched sooner in the Penobscot (a northern, intensively managed population), but no stock differences were detected in size or growth efficiency from the onset of exogenous feeding to age 0+ summer. Differences again emerged in age 0+ autumn, with the degree of bimodality in length-frequency distributions differing among stocks; the Connecticut had the highest proportion of upper-mode fish and, ultimately, age-1+ smolts. Although genetic effects could not be entirely separated from maternal effects for egg size variation, it is likely that differences in hatch timing and smolt age had a genetic basis. Early emphasis on age-1+ hatchery-reared smolts in the Connecticut may have led to divergence in smolt age between the Penobscot and Connecticut populations in less than eight generations. ?? 2004 NRC Canada.

Conference Paper↗
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

Life history dependent morphometric variation in stream-dwelling Atlantic salmon

The time course of morphometric variation among life histories for stream-dwelling Atlantic salmon (Salmo salar L.) parr (age-0+ to age-2+) was analyzed. Possible life histories were combinations of parr maturity status in the autumn (mature or immature) and age at outmigration (smolt at age-2+ or later age). Actual life histories expressed with enough fish for analysis in the 1997 cohort were immature/age-2+ smolt, mature/age-2 +smolt, and mature/age-2+ non-smolt. Tagged fish were assigned to one of the three life histories and digital pictures from the field were analyzed using landmark-based geometric morphometrics. Results indicated that successful grouping of fish according to life history varied with fish age, but that fish could be grouped before the actual expression of the life histories. By March (age-1+), fish were successfully grouped using a descriptive discriminant function and successful assignment ranged from 84 to 97% for the remainder of stream residence. A jackknife of the discriminant function revealed an average life history prediction success of 67% from age-1+ summer to smolting. Low sample numbers for one of the life histories may have limited prediction success. A MANOVA on the shape descriptors (relative warps) also indicated significant differences in shape among life histories from age-1+ summer through to smolting. Across all samples, shape varied significantly with size. Within samples, shape did not vary significantly with size for samples from December (age-0+) to May (age-1+). During the age-1+ summer however, shape varied significantly with size, but the relationship between shape and size was not different among life histories. In the autumn (age-1+) and winter (age-2+), life history differences explained a significant portion of the change in shape with size. Life history dependent morphometric variation may be useful to indicate the timing of early expressions of life history variation and as a tool to explore temporal and spatial variation in life history expression.

Oecologia↗
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↗
USGS2001

Effects of developmental stage at stocking on growth and survival of Atlantic salmon fry

Stocked fry are the primary source of fish for the restoration effort for Connecticut River Atlantic salmon Salmo salar , yet it is unknown whether there is a developmental stage at stocking that yields optimal growth and survival or whether good growth and survival can be achieved across a wide range of fry developmental stages. To evaluate the effects of developmental stage on growth and survival, we stocked otolith-marked (thermal-banding patterns) fry from four (1996) or three (1997) developmental stages (thermally delayed, nominal, thermally accelerated-fed, and thermally accelerated-unfed) into three rivers in the spring and sampled the age-0 fish in the fall. There was no difference in 1996 among delayed, nominal, or accelerated-fed developmental stage treatments in the final size or population estimate. Few fish from the accelerated-unfed treatment were recovered. Results from a laboratory starvation study suggested that fish from the accelerated-unfed treatment would die from starvation in about 4 d after release. In 1997, accelerated-fed fish were recaptured at a slightly higher rate than were fish from the delayed or nominal treatment, but final sizes did not differ among treatments. Despite differences in population estimates and sizes among rivers, there was no interaction between treatment and river in either study year, indicating that treatment effects were consistent among rivers. Our results suggest that fry from a fairly wide range of developmental stages will survive equally well and will grow to similar sizes by fall unless the fish have been accelerated without feeding.

Connecticut, Massachusetts, New Hampshire, New Yor↗
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↗