Life history characteristics of the clam<Emphasis Type="Italic"> Mya arenaria</Emphasis> in the White Sea

Dynamics of Mya arenaria beds in two bights of the Chupa Inlet (Kandalaksha Bay, White Sea) were studied on a long-term basis. Observations were carried out at 1– to 3-year intervals from 1979 up to 1999. The studied soft-shell clam beds were characterised by a substantial instability of age structure. Since 1988, only one year-class has dominated in the beds while other generations have been scarce and recruitment was not observed. This pattern of Mya bed dynamics was related neither to interannual environmental changes nor to differential reproduction success or predation effects in the benthic assemblages. Favourable conditions for spat formation in 1988 (low abundance of other M. arenaria generations), as well as for juvenile survival during the following winter, resulted in high abundance of juveniles in both investigated locations in 1989. The mortality rate (μ) in this 1988 generation varied throughout the period of investigation and was related to age. The mortality level decreased for the first 2–4 years of the life cycle, then stabilised for the next 3–4 years, and eventually increased in subsequent years. Overall μ values ranged from 0 to 1.68 year^–1. The oldest specimens observed were 17 years old and had a maximum shell length of 79 mm. Significant differences in average growth rates were observed between molluscs of different locations. Communicated by H.-D. Franke     

Annual reproductive cycle and sexual dimorphism in the dragonet,repomucenus valenciennei, in tokyo bay, japan

The annual reproductive cycle of the dragonet,Repomucenus valenciennei, from Tokyo Bay, Japan, was studied by analysis of seasonal trends in gonadosomatic indices and histological observations of gonads. Sexual dimorphism in the growth of several body parts relative to standard length (SL) and changes in color pattern of the first dorsal fin with growth were also investigated. The spawning season lasted from spring (April [1991] or February [1992]) to autumn (October) with two spawning peaks, in spring and autumn. In spring, only one-year-old (age 1+) fish spawned, age 0+ females not spawning until autumn, at which time they had reached age 1+. Likewise, histological observations of males indicated that testes had reached full maturity by 80 mm SL (age 1+). The minimum mature size of females was estimated as 60 mm SL. In males 45–80 mm SL, the first spine of the first dorsal fin, last ray of the second dorsal fin, last ray of the anal fin, and caudal fin ray showed strongly positive allometry, indicating rapid growth of these structures relative to SL. Subsequently, their growth returned to an isometric pattern in males>80 mm SL. In females, on the other hand, the same body parts showed slightly positive allometry throughout their growth. The color pattern on the first dorsal fin also changed in males 45–80 mm SL.     

Survivorship of penstemon grandiflorus in an oak woodland: combined effects of fire and pocket gophers

Summary The effects of fire and pocket gophers, Geomys bursarius, on the survivorship of Penstemon grandiflorus growing in an oak woodland in Minnesota were studied from 1986 to 1990. Plants growing in sparse vegetation experienced mortality rates twice that of plants growing in dense vegetation. This difference was due partly to pocket gophers whose earth moving activities reduce the density of vegetation and bury and kill individual Penstemon plants. Laboratory feeding trials showed that gophers readily eat Penstemon, particularly the fleshy roots. An experiment involving the removal of 25–75% of the root tissue in 90 plants showed that root loss significantly reduced survivorship, suggesting that gopher herbivory might also kill plants. When gophers were experimentally excluded, plants growing in sparse vegetation exhibited significantly lower mortality rates than those growing in dense vegetation. Plants in the smallest size class exhibited reduced survivorship following a late spring burn; however, overall patterns of survivorship of plants in burned areas did not differ markedly from those in the unburned areas. A longitudenal analysis of plants with different reproductive histories revealed no survivorship cost to reproduction. Mortality rates decreased with increasing plant size. Small plants were more likely to be killed by fire and by being buried under gopher mounds. Differences in underground energy reserves of small and large plants can account for most of the survivorship patterns observed in this study. The study shows that within openings of the oak woodland, fire and gophers reduce the survival of individual Penstemon plants. Nevertheless, since both gophers and fire also serve to perpetuate suitable habitat in the woodland, Penstemon is ultimately dependent on both for its long term persistence in the landscape.     

Effects of experimental manipulations on the life history pattern of Lymnaea stagnalis appressa say (pulmonata: lymnaeidae)

Field sampling of an Iowa population of Lymnaea stagnalis appressa Say indicated an annual generation pattern, with survivorship to maturity of i percent or less. Estimates of adult fecundity ranged from about 300 to 800 eggs.Density and food manipulations were performed to determine whether density dependent limitation of growth rates, maturation, or fecundity occurs in this fresh water pulmonate snail. Addition of a high quality food resource, spinach, accelerated growth rates, but did not drastically accelerate maturity, nor increase fecundity. Density increments lowered growth rates, delayed maturity, and lowered fecundity, and the addition of spinach did not counteract high densities. Adult densities are fairly low in the field population, and adults are randomly dispersed, indicating little density dependent regulation of fecundity in this population. However, the low survivorship to maturity, response in growth rates with food addition, and increasing survivorship with age and size indicate that juvenile mortality may play an important role in structuring life history patterns in this population.     

Reproduction of wild Japanese macaque females of Yakushima and Kinkazan Islands: A preliminary report

Wild Japanese macaque females of the Yakushima and Kinkazan populations exhibited similar reproductive features. (1) Births/female/year (BR: 0.27–0.35) was lower than those of provisioned troops, but (2) infant mortality (IM: 0.23–0.25) was higher than those of provisioned troops. (3) The interbirth interval (IBI) following the death of infants was 1.5–1.6 years, shorter than that following surviving infants (2.2–2.4 yrs). (4) Birth sex ratio (BSR) did not differ from 1∶1. There was no consistent correlation between (5) female age and IM, (6) maternal rank and offspring BSR, or (7) maternal rank and reproductive success. On the other hand, (8) BR of Yakushima females was significantly lower than that of Kinkazan females. In particular, (9) Yakushima females stopped reproduction earlier than Kinkazan females, although (10) the first birth of Yakushima females was about one year earlier than Kinkazan females. (11) BR exhibited a humped curve against female age in Yakushima, but it was uncertain whether old-aged females of Kinkazan exhibited a post-reproductive life span (PRLS). (12) The survivorship for female juveniles was lower than that for male juveniles in Yakushima, whereas the survivorship for male juveniles was lower than that for female juveniles in Kinkazan. These data may indicate that Yakushima females more severely compete for resources than Kinkazan females, because of high population density, whereas the population density of Kinkazan might be limited by climate (e.g. heavy snow) rather than density dependent ecological effects.     

Age, growth, and reproductive biology of the Waigieu seaperch Psammoperca waigiensis (Perciformes: Latidae) around Okinawa Island, Japan

Age, growth, and reproductive biology of the Waigieu seaperch Psammoperca waigiensis were studied using 291 specimens obtained around Okinawa Island, Japan. Otolith opaque zones that formed every year correlated with spawning activity and were thought to be annual rings. Growth of this species was rapid during the first 2 years, reaching 186.2–270.3 mm in standard length (SL). Females (196.6–334.0 mm SL) were larger than males (186.2–288.6 mm SL), caused by differential growth between sexes, which started before 2 years of age. Most of the specimens were 1–11 years old and accounted for 96% in total. Spawning season was estimated to be from April to October by gonadosomatic index (GSI) and histological observation. The smallest mature female and male were 217.0 mm SL (2 years) and 206.0 mm SL (2 years), respectively. After recruitment in rocky areas up to about 200.0 mm SL and 2 years of age, Psammoperca waigiensis were then found to soon mature.     

Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan

Organisms living in arctic and alpine environments are increasingly impacted by human activities. To evaluate the potential impacts of global change, a better understanding of the demography of organisms in extreme environments is needed. In this study, we compare the age-specific demography of willow ptarmigan (Lagopus lagopus) breeding at arctic and subalpine sites, and white-tailed ptarmigan (L. leucurus) breeding at an alpine site. Rates of egg production improved with age at the alpine and subalpine sites, but the stochastic effects of nest and brood predation led to similar rates of annual fecundity among 1-, 2-, and 3+-year-old females. All populations had short generation times (T<2.7 years) and low net reproductive rates (R ₀<1.2). Stable age distributions were weighted towards 1-year-old females in willow ptarmigan (>59%), and to 3+-year-old females in white-tailed ptarmigan (>47%). High damping ratios (ρ>3.2) indicated that asymptotic estimates were likely to match natural age distributions. Sensitivity and elasticity values indicated that changes in juvenile survival would have the greatest impact on the finite rate of population change (λ) in willow ptarmigan, whereas changes to the survival of 3+-year-old females would have a greater effect in white-tailed ptarmigan. High survivorship buffers white-tailed ptarmigan in alpine environments against the potential effects of climate change on annual fecundity, but may make the species more sensitive to the effects of pollutants or harvesting on adult survival. Conversely, processes that reduce annual fecundity would have a greater impact on the population viability of willow ptarmigan in arctic and subalpine environments. If these same demographic patterns prove to be widespread among organisms in extreme environments, it may be possible to develop general recommendations for conservation of the biological resources of arctic and alpine ecosystems.     

The demography of Howler Monkeys (Alouatta palliata) on Barro Colorado Island,Panamá

Chronological ages of Alouattaon Barro Colorado Island (BCI) were estimated from longitudinal dental wear. Combining these data with visual censuses, we approximated the study population’s age profile. A stable model was then constructed; from it we derived agespecific mortality rates. Mortality of immature animals is high, with 88% of the males and 65% of the females dying before 5 years. Adult mortality is low until 11 years, when it accelerates. The average adult life span is 16.6 years for males and 15.5 for females. The maximum life span is over 20 years. A pubertal male growth spurt occurs from 3 to 5 years, at which time females are primiparous. Sexual size differences develop primarily during this time. The 1976 age profile had anomalously few animals aged 7 years and males aged 8–9 and 15–16 years. With corroborating evidence, we hypothesize that these deficits resulted from excessive rainfall in 1963 and 1971, which reduced the fall fruit crop and led to a high juvenile mortality. Within half of our study troops, some adult males have nearly identical ages, suggesting an active process of agemate coalition. We hypothesize a form of kin selection, wherein peripheral male cohorts from the same natal troop have greater survival and social success than solitary animals. The stable model suggests an annual growth rate of 1.5% during the 1970s. Estimates of 16.7 and 4% for the previous two decades, following a yellow-fever epidemic, imply that the BCI population is becoming stationary. A very different age structure existed on neighboring Orchid Island in 1976, suggesting general food limitation. By contrast, the lowered, but continuing growth on BCI suggests a less drastic limiting mechanism. We hypothesize that intratroop social competition limits population growth by regulating subadult survival rates during food scarcity cycles.     

Parasite-induced Host Mortality: Indirect Evidence From a Long-term Study

A long-term field study of a perturbed host–helminth system provides indirect evidence that a long-lived swimbladder nematode, Cystidicola farionis, induces mortality of Arctic charr, Salvelinus alpinus. The prevalence and abundance of this parasite has changed little over the period from 1987 to 1999. The cumulative numbers of L₃-stage larvae steadily increased with increasing host age, indicating a continuous exposure to infection throughout the life of the target fish host. Indirect methods, which used data pooled over years and long-term cohort analyses, indicate that parasite-induced host mortality (PIHM) occurs in hosts older than 10 years. Furthermore, using a short-term cohort method adjusted for worm recruitment, we found indications of PIHM occurrence even in younger age groups. These patterns do not seem to be caused by high parasite mortality rates since dead worms are rarely observed inside the swimbladder. Age-related changes in infection rates or in resistance to infection seem to play only a minor role as there were only slight changes in the preference of charr for feeding on amphipods (which are intermediate hosts) and in the acquisition rate of L₃ larvae in older hosts. Mortality of the most heavily infected hosts is the most probable explanation for the observed patterns.     

Rain,prey and predators: climatically driven shifts in frog abundance modify reproductive allometry in a tropical snake

To predict the impacts of climate change on animal populations, we need long-term data sets on the effects of annual climatic variation on the demographic traits (growth, survival, reproductive output) that determine population viability. One frequent complication is that fecundity also depends upon maternal body size, a trait that often spans a wide range within a single population. During an eight-year field study, we measured annual variation in weather conditions, frog abundance and snake reproduction on a floodplain in the Australian wet-dry tropics. Frog numbers varied considerably from year to year, and were highest in years with hotter wetter conditions during the monsoonal season (“wet season”). Mean maternal body sizes, egg sizes and post-partum maternal body conditions of frog-eating snakes (keelback, Tropidonophis mairii, Colubridae) showed no significant annual variation over this period, but mean clutch sizes were higher in years with higher prey abundance. Larger females were more sensitive to frog abundance in this respect than were smaller conspecifics, so that the rate at which fecundity increased with body size varied among years, and was highest when prey availability was greatest. Thus, the link between female body size and reproductive output varied among years, with climatic factors modifying the relative reproductive rates of larger (older) versus smaller (younger) animals within the keelback population.     

Comparative studies on the biology of nerita atramentosa Reeve, bembicium nanum (Lamarck) and cellana tramoserica (Sowerby) (gastropoda: Prosobranchia) in S.E. Australia

Populations of three coexisting intertidal gastropods, Nerita atramentosa Reeve, Bembicium nanum (Lamarck) and Cellana tramoserica (Sowerby), were sampled from a shore in Botany Bay, New South Wales, from July 1972 to September 1973. The recruitment and growth rates of each species were analysed from size frequency distributions. Mortality of each age cohort, and longevity, were estimated from analyses of the densities of Nerita atramentosa and Bembicium nanum.Nerita atramentosa showed no significant mortality during the first two years on the shore, but high mortality (at an instantaneous rate of 0.084 deaths/individual/month) after reaching the age of reproductive maturity, which was 20 months from settlement and at a mean shell-length of 13.5 mm. No growth could be detected after reproductive maturity was reached. Longevity of N. atramentosa was estimated as 3–5.5 years. Bembicium nanum juveniles showed higher mortality (at an instantaneous rate of 0.233 deaths/individual/month) than reproductively mature animals (0.060 deaths/individual/month). Reproductive maturity was reached at a mean shell-breadth of 11.0mm, i.e., about ten months after settlement on the shore. Longevity was estimated as from 4–8 years. Cellana tramoserica showed different growth patterns depending on the time of settlement.The three species showed different patterns of growth and life history relating to variable recruitment (which was demonstrated in all three species) and different rates of mortality of age cohorts.     

Reproduction, population dynamics, growth and production ofScrobicularia plana da costa (pelecypoda) in the Bidasoa estuary, Spain

The breeding cycle, recruitment, population dynamics, growth and production ofScrobicularia plana were studied at one station in the Bidasoa estuary (SE of the Biscay Bay, Spain) during a period of 3 or 4 years. To complete this study, the reproduction for a period of 1 year was analysed at two other sites of the estuary. At none of the stations important differences in spawning activity were observed between the different years. The animals reproduced for the first time when they reached the age of two years. The histological data and the recruitment analysis showed only one spawning period between June and mid-September, with a peak in July-August. This breeding pattern differs from those shown by other southern European populations. The recruitment of spat (0.25–0.50 mm) occurred from June–July to October–December in different years. The population showed different annual patterns of density and population structure, depending on recruitment success. Growth was most rapid in spring and summer. The bivalves reached a mean length of 21.8 mm at the age of approximately 16 months; in the following year they grew to 30 mm. The growth during the life span fitted the theoretical growth equation of Von Bertalanffy. Annual production was in the range of 59.0–83.4 g AFDW m^–2 year^–1. The P/B ratios of the population varied between 0.84 and 1.48 (1.06 ± 1.36; ¯x ± 95% C.I.).     

Growth and development rates in a riparian spider are altered by asynchrony between the timing and amount of a resource subsidy

Rapid growth in response to increased prey abundance may be induced by environmental variability associated with resource subsidies. Spiders living in riparian areas are subject to frequent, episodic bursts of aquatic prey (subsidies). These periods of high resource abundance may occur at different points in recipient consumers’ development through variation in emergence patterns of prey between years or across a landscape. We examine how variable timing of subsidy abundance intersects with life history scheduling to produce different growth and development outcomes for individuals within a population. Through a series of controlled feeding experiments, we tested the hypotheses that the spider Tetragnatha versicolor: (1) exhibits compensatory growth in response to subsidy variability, (2) that rapid increases in mass may result in a greater risk of mortality, and (3) that the timing of subsidy resources relative to the development schedule of this spider may produce different outcomes for individual growth patterns and adult condition. Spiders fed at very high rates grew fastest but also showed evidence of increased mortality risk during moulting. T. versicolor is capable of exhibiting strong growth compensation—individuals suffering initial growth restriction were able to catch up completely with animals on a constant diet utilising the same amount of food. Spiders that received an early pulse of resources (simulating an early arrival of an aquatic insect subsidy to riparian forests) did worse on all measures of development and fitness than spiders that received either a constant supply of food or a late pulse of resources. Importantly, receiving large amounts of food early in life appears to actually confer relative disadvantages in terms of later performance compared with receiving subsidies later in development. Subsidies may provide greater benefits to individuals or age cohorts encountering this resource abundance closer to the onset of reproductive efforts than subsidies arriving early in development.     

Reproductive biology of the fanray, <Emphasis Type="Italic">Platyrhina sinensis</Emphasis> (Batoidea: Platyrhinidae) in Ariake Bay,Japan

The reproductive biology of the fanray, Platyrhina sinensis, was examined in Ariake Bay, Japan, from May 2002 until December 2006. Females reached sexual maturity at a larger size than males [total length (TL) at 50% sexual maturity: male, 393 mm; female, 421 mm]. The present data support a distinct annual reproductive cycle for P. sinensis. The gonadosomatic index (GSI) for mature males showed a clear seasonal trend, declining from August to November. Histological observations showed that mature sperm in the testes occurred from August to November when monthly GSI declined. Concomitantly, pre-ovulatory ova were observed in females collected from August to November. These data indicate that mating, ovulation and fertilization occurred from August to November. Near-term embryos, neonates and recent post-partum females also occurred from August to November. Additionally, all post-partum females possessed large pre-ovulatory ova. Parturition occurred from August to November followed immediately by mating, ovulation and fertilization. Mature females become pregnant every year, and the gestation period is almost 1 year. Fertilized uterine eggs without macroscopic embryonic development were present throughout the annual reproductive cycle, indicating that P. sinensis utilizes embryonic diapause as its reproductive strategy. Both reproductive tracts of females were functional, and fecundity ranged from 1 to 12 with a mean of 6.0, increasing with TL.     

Spatio-temporal variations in biological performances and summer mortality of the Pacific oyster Crassostrea gigas in Normandy (France)

Mortality and biological performances of half-grown Crassostrea gigas were studied from spring 2000 to autumn 2001 at six instrumented stations located in two areas (Gefosse and Grandcamp) of the Bay of Veys (Normandy). Shell and meat growth, condition indexes and a macroscopic maturity index were determined on oysters deployed at the six stations in order to assess spatial variability in the influence of environmental conditions. In addition, histological and biochemical analyses were performed in order to determine the sex and establish the reproductive cycle (at all six sites) and the biochemical composition (at four stations). The data set including monthly mean temperatures and data provided by examination of 2,837 oysters were analysed by Principal Component Analysis and a Hierarchical Ascending Clustering which resulted in the formation of four clusters. The highest station on the shoreline belonged to a cluster characterized notably by low total weight due to a short immersion/feeding period, whereas all other stations belonged to another single cluster. Nevertheless, various biological differences were found between these stations, e.g. the reproductive cycle was generally synchronized throughout the bay but some differences relative to spawning occurrence were observed. In 2000, oyster mortality was higher at Gefosse than at Grandcamp, the latter being a more marine area. In 2001, oyster mortalities were significantly higher and all stations were strongly affected. In the Bay of Veys, oyster biological performances and mortality thus showed spatio-temporal variations which were worthy to be discussed.     

Reproductive biology of the guitarfish <Emphasis Type="Italic">Rhinobatos hynnicephalus</Emphasis> (Batoidea: Rhinobatidae) in Ariake Bay,Japan

Size at sexual maturity, reproductive cycle, and fecundity of the guitarfish, Rhinobatos hynnicephalus, were examined in Ariake Bay, Japan. Females reached sexual maturity at a larger size than males [total length (TL) at 50% sexual maturity: males, 431 mm; females, 476 mm]. Monthly gonadosomatic indices of males decreased abruptly from July to August. Histological examinations confirmed the presence of mature spermatozoa in the testes in July, with semen in seminal vesicles in July and August. Preovulatory ova were observed in females with near-term embryos in August. Parturition occurred in August, immediately followed by mating, ovulation, and fertilization. Gestation period is approximately 1 year. Fertilized uterine eggs without embryonic development were present throughout the annual reproductive cycle. Embryonic development began in June and ended in August, indicating that R. hynnicephalus undergoes embryonic diapause (9 months). Fecundity increased with TL and ranged from 1 to 9 (mean, 4.4) embryos per litter.     

Biological Control ofBemisia argentifolii(Homoptera: Aleyrodidae) on Poinsettia with Inundative Releases ofEncarsia formosa(Hymenoptera: Aphelinidae): Are Higher Release Rates Necessarily Better?

The effectiveness of inundative releases of the parasitoidEncarsia formosafor control ofBemisia argentifoliion poinsettia was determined in replicated experimental greenhouses. We evaluated two release rates ofE. formosa:a low release rate (1 wasp/plant/week, released in two greenhouses, in spring 1995) and a high release rate (3 wasps/plant/week, released in two greenhouses, in fall 1993), each over a 14-week growing season. Each release trial had one or two control greenhouses in whichB. argentifoliideveloped on poinsettia in the absence ofE. formosa.Life-tables were constructed forB. argentifoliiin the presence and absence ofE. formosaby using a photographic technique to follow cohorts of whiteflies on poinsettia leaves. Weekly population counts of the whitefly were also made. In the absence ofE. formosa,egg to adult survivorship ofB. argentifoliion poinsettia was 75–81%. At the low release rate, egg to survivorship ofB. argentifoliiwas 5% and parasitism was 13%. At the high release rate, egg to adult survivorship forB. argentifoliiwas 8% and parasitism was 23%. The net reproductive rates (R₀) forB. argentifoliipopulations in the absence ofE. formosaranged from 18.01–26.12, indicating a rapidly increasing population. Net reproductive rates for whitefly populations subject to wasp releases were 1.54 for the low release rate greenhouses and 2.11 for the high release rate greenhouses, indicating substantially reducedB. argentifoliipopulation growth. The low release rate provided better control ofB. argentifoliithan the high release rate. This difference was attributed to higher levels of mortality of whiteflies at the low release rate in the first 5–6 weeks of the growing period. We suggest that mutual interference may also have affected observed levels of mortality and parasitism.     

Juvenile settlement,survivorship and in situ growth rates of four species of Caribbean damselfishes in the genusStegastes

Synopsis FourStegastes species were visually censused to determine seasonality and size of juvelines at settlement as well as their survival and growth rates. The census was performed weekly from September 1987 to March 1991 in southwest Puerto Rico. All species had a settlement pulse during September–October. The threespot damselfish,S. planifrons, appeared to have the strongest site fidelity, longest survivorship and slowest growth of the four species. The cocoa damselfish,S. variabilis, and the bicolor damselfish,S. partitus, had similar patterns of site fidelity, life expectancy and growth rates, but these two species differed in being the most and least abundant, respectively. The beaugregory,S. leucostictus, occurred second in abundance but included the least number of new settlers. This species displayed poor site fidelity, a characteristic which probably influenced calculations indicating poor survivorship, life expectancy and growth relative to its congeners. Similarities and differences in these characteristics, as well as in the habitat preferences displayed by these four fishes, may contribute to their abilities to coexist in the same area.     

The New River, Virginia, muskellunge fishery: population dynamics, harvest regulation modeling, and angler attitudes

Although muskellunge, Esox masquinongy, fisheries in northern US states and Canadian provinces are increasingly being managed by introduction of restrictive harvest regulations (e.g. 1370-mm (54′′) minimum length limits), many southern US muskellunge fisheries continue to be managed with comparatively liberal regulations (e.g. 762-mm (30′′) minimum length limits) that are implemented statewide. We studied the population dynamics of the New River, Virginia, muskellunge fishery and used predictive modeling to determine whether restrictive harvest regulations also might prove beneficial for this southern latitude fishery. A creel survey was also conducted to learn more about angler attitudes to the New River muskellunge fishery. Muskellunge grew quickly, with fish reaching harvestable lengths (762 mm, 30′′) in 2–3 years. Muskellunge fishing pressure, harvest rates, and voluntary release rates were low compared with reports for more northern areas. Most anglers, irrespective of how often they fished for muskellunge, defined “trophy” muskellunge to be approximately 1050–1100 mm (41–43′′) in length. Although angler support for restrictive harvest regulations was low, abundance of memorable-length (≥1070 mm, 42′′) muskellunge was predicted to increase under all evaluated length limits. Muskellunge yield would remain static at 914-mm (36′′) and 1016-mm (40′′) length limits, because of the rapid growth of fish, but yield would decline dramatically with a 1143-mm (45′′) length limit, because male muskellunge rarely exceeded 1100 mm (43′′). Because of rapid growth and low release rates, implementation of higher length limits (e.g. 965–1067 mm, 38–42′′) may indeed prove beneficial for augmenting “trophy” muskellunge production on the New River. Angler support for higher minimum length limits might be increased by educating anglers about the rapid growth rates of muskellunge and the expected size structure changes that will result from a length-limit increase. Size structure changes resulting from an increase in the minimum length limit may be difficult to detect because of potential increases in fishing pressure or reduced fish growth as a result of competition for food resources. Long-term monitoring of muskellunge growth and angling pressure may therefore be needed to ensure that new regulations are indeed benefitting the fishery.