White River Crayfish Research Articles

Is Chemical Control for Crayfish in Hatchery Fish Shipments Practical?

AbstractInvasive crayfish (family Cambaridae) displace native crayfish species and alter aquatic habitat, community structure, and ecosystem function. We evaluated whether chemical control can be a reliable control agent for crayfish to ensure that shipments from fish hatcheries did not result in new infestations of invasive crayfish. A series of acute (≤1 h) toxicity tests were conducted to evaluate the toxicity of cypermethrin and pyrethrin to crayfish, freshwater mussels, and fish; chemical concentrations in test organisms; effectiveness of carbon‐block filters to remove cypermethrin from test waters; and the cost of chemical control relative to extra handling of fish. Cypermethrin dosed at 75 μg/L for 15 min resulted in 100% mortality of adult white river crawfish Procambarus acutus and virile crayfish Faxonius virilis but did not cause >20% mortality in adult pondmussel Ligumia subrostrata, juvenile fatmucket Lampsilis siliquoidea, fingerling Bluegill Lepomis macrochirus, hybrid sunfish (Bluegill × Green Sunfish L. cyanellus), hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), yearling Paddlefish Polyodon spathula, or ready‐to‐eat Bluegill, hybrid sunfish, and Channel Catfish Ictalurus punctatus. Behavioral effects, such as loss of equilibrium or head shaking, were generally limited to 1 h postexposure. Mean concentrations of cypermethrin increased in fish fillets (4–26 μg/g) and whole fish (5–1,770 μg/g); therefore, regulations limiting harvest for up to 7 d following stocking may be required. A carbon‐block filtration system was effective in reducing (<90%) cypermethrin concentrations and thus reducing potential effects to nontarget species in receiving waters. Extra handling of fish was more cost‐effective for all fish tested except for Paddlefish, where the cost of chemical control was half that for extra handling. For all other fish tested, chemical control was 4–10 times more expensive than extra handling. Special use permits or chemical registration are needed before chemical control for crayfish could be routinely used at fish hatcheries.

English

Abstract Freshwater crayfish rank among the most imperilled groups and play several critical roles in freshwater ecosystems, yet survey efforts remain limited throughout much of Canada and North America. Inadequate survey and monitoring efforts render our ecosystems vulnerable to the introduction and spread of harmful invasive species which can be difficult or impossible to control following establishment. During surveys targeting salamander larvae across Pelee Island, Ontario we incidentally captured crayfish and identified them to species. Three species were detected including two native species known only from collections in the 1960s (Creaserinus fodiens, Faxonius immunis) as well as the non-native White River Crayfish (Procambarus acutus) which has not been documented previously in Canada. Our oldest record of P. acutus is from 2015, and the species currently appears to be widespread and well established on Pelee Island and has also recently been recorded in Six Mile Lake on the Canadian Shield. We provide preliminary data on the aquatic habitats where each species was found on Pelee Island and strongly encourage additional monitoring efforts combined with targeted education efforts to prevent the spread of P. acutus to the Ontario mainland.

Intra-and inter-specific competition effects on survival and growth of juvenile Procambarus acutus acutus and Procambarus clarkii

Four similar sizes eastern white river crayfish (Procambarus acutus acutus) and red swamp crayfish (Procambarus clarkii) were stocked separately to determine intra and inter-specific-competition. Three treatment levels were used three treatment levels, with six replicates tanks each with stand green rice (representing a stocking density of approximately 21 individuals per m2). This study was carried out during 90 days to determine growth and survival rate. Results showed that the growth of P. acutus acutus in the interspecific treatment tank was found higher than those grown in the intraspecific-treatment tanks. For P. clarkii, no significant differences in growth (estimated from the mean Total length, TL) were detected between treatments. The survival of the two species was the same up to the first 60 days of the experiment, while the difference in survival was only noticeable at 90 days. The survival rate of P. clarkii in the intraspecific-treatment tanks (55.0%) was higher than in the interspecific tanks (26.7%) treatment, while the survival of P. acutus acutus was found similar in two treatments. It was achieved higher survival, faster growth and larger size in P. a. acutus than P. clarkii when grown in the tank study. Size of body was important in determining competitive interactions between the two species.

Diversity, Distribution and Habitat Use of Freshwater Crayfish in the Upper Appomattox River Basin, Virginia

The Appomattox River basin in Virginia is a poorly understood system for freshwater crayfish diversity and distribution. We sampled 36 locations in the upper Appomattox basin for crayfish and noted general habitat characteristics. The following 7 species of crayfish were discovered in the system belonging to 4 genera: Cambarus cf. acuminatus, Cambarus bartonii bartonii (Common Crayfish), Cambarus longulus (Atlantic Slope Crayfish), Lacunicambarus diogenes (Devil Crayfish), Procambarus acutus (White River Crayfish), Creaserinus fodiens (Digger Crayfish), and invasive Procambarus clarkii (Red Swamp Crayfish). Native C.cf. acuminatus dominates the upper Appomattox region, having a wider distribution and higher relative abundance compared to other species in the basin. All other taxa demonstrated relatively limited distributions and low abundance. The least encountered species were the 2 primary burrowing species, Devil Crayfish and Digger Crayfish, which exclusively used shallow seasonal pools during the spring breeding season. We report range extensions for C. cf. acuminatus, Atlantic Slope Crayfish, Common Crayfish, Devil Crayfish, Digger Crayfish, and Red Swamp Crayfish, and recommend additional surveys to improve our understanding of the diversity and distribution of crayfish in the Appomattox River basin. Furthermore, we recommend monitoring of the Briery Creek and Sandy River systems to assess the extent and severity of the Red Swamp Crayfish invasion. Additionally, we urge a systematic study to resolve the taxonomic uncertainty of a potentially new Creaserinus species in the Appomattox River basin.

Introduction of Southern White River Crayfish (<i>Procambarus zonangulus</i>) to New Brunswick

Southern White River Crayfish (Procambarus zonangulus), an aquatic, potentially invasive species, is documented from New Brunswick for the first time. It was found in a small, privately owned, lake in the Saint John River system that was apparently stocked for recreational purposes with non-native fish and the crayfish. Procambarus zonangulus has successfully overwintered at the site for at least a year and, more likely, for several years. This is the third species of non-native crayfish recorded in New Brunswick, joining Spiny-cheeked Crayfish (Faxonius limosus) and Virile Crayfish (Faxonius virilis). This is also the first persisting introduction for the genus Procambarus in Canada of which we are aware.

Thermal stress responses of two sympatric crayfishes in Louisiana, Procambarus clarkii Girard, 1852 and Procambarus zonangulus Hobbs & Hobbs, 1990 (Decapoda: Astacoidea: Cambaridae)

Abstract Water temperature is an important abiotic component in farmed and wild crayfish habitats as it influences individual and population characteristics including growth, metabolic activity, and overall population vigor. Thermal limits, however, have not been established for the two commercially important crayfishes in Louisiana, the red swamp crayfish Procambarus clarkii (Girard, 1852) and the southern white river crayfish P. zonangulus (Hobbs & Hobbs, 1990). We aimed to determine the thermal stress responses for the two species. Thermal stress was examined by the critical thermal maxima (CTmax) for crayfish acclimated to 24, 27, or 30 °C for two weeks prior to experimentation. Water temperature in all acclimation trials was increased 1 °C h–1 and the end-point temperature for an individual was determined by the failure of righting response within 30 seconds. CTmax values (±SD) for P. clarkii acclimated at 24, 27, and 30 °C were 39.5 ± 0.5, 39.1 ± 0.3, and 39.4 ± 0.7 °C respectively, and 39.8 ± 0.8, 38.8 ± 0.8, and 39.0 ± 0.6 °C for P. zonangulus. CTmax did not differ significantly between species in any of the acclimation treatments. Thermal stress was also examined by measuring P. clarkii and P. zonangulus hemolymph glucose concentration every two hours for crayfish acclimated at 26 °C for two weeks and water temperature increased 1 °C h–1. Hemolymph glucose concentration began to increase at 36 °C in P. zonangulus and 38 °C in P. clarkii. Large increases in mean hemolymph glucose concentration (±SE) were observed in both P. clarkii (67.19 mg–dl ± 24.55) and P. zonangulus (74.11 mg–dl ± 18.04) at 40 °C.

A Reassessment of the Crayfishes of Pennsylvania's Lake Erie Basin with an Emphasis on Zoogeography, Taxonomy, and Conservation.

An investigation is currently underway to reassess the crayfishes of the Lake Erie basin in northwestern Pennsylvania. A total of 54 stream sites were sampled, with a majority of the streams in the basin sampled at least once. Preliminary data have revealed that the most common crayfish species are Cambarus robustus (Big Water Crayfish), Faxonius propinquus (Northern Clearwater Crayfish), and Cambarus carinirostris (Rock Crayfish) respectively. Faxonius obscurus (Allegheny Crayfish) was discovered in one tributary to Elk Creek and a tributary to Lake Erie, not supporting prior belief that F. obscurus was forcing F. propinquus into smaller tributaries. Three additional species, Faxonius immunis (Calico Crayfish), Creaserinus fodiens (Digger Crayfish), and Cambarus spp. were collected via trapping. Procambarus acutus (White River Crayfish), an invasive crayfish species, was also collected via trapping. The presence of such a diverse crayfish fauna is likely due to the postglacial movement via stream and wetland migrations. The Lake Erie basin represents a range overlap for northern and southern crayfish species, and is a unique location within Pennsylvania’s watersheds.

Distributions of Two Groups of Obligate Crayfish Ectosymbionts—Branchiobdellidans and Entocytherid Ostracods—in New England

North American crayfishes are hosts for 2 major groups of obligate ectosymbionts, namely annelids of the order Branchiobdellida and ostracods of the family Entocytheridae. These symbionts are widely distributed across the continent, coincident with their typical hosts; however, the diversity and distribution of both groups are poorly known in much of the northeastern US. We examined 93 crayfishes collected from 30 sites across New England for the presence of branchiobdellidans and entocytherids. We recovered 4 branchiobdellidan and 3 entocytherid species, with both groups displaying curiously dissimilar distributions. We present here the first published records of the branchiobdellidan Cambarincola vitreus in New England, the first record of the Procambarus acutus (White River Crayfish) from New Hampshire, and begin to fill substantial gaps in the known distribution of 2 major groups of obligate crayfish ectosymbionts.

Comparison of Two Crayfish Trapping Methods in Coastal Plain Seasonal Wetlands

AbstractWe compared crayfish collections from minnow versus microhabitat traps in the Dahomey National Wildlife Refuge, Bolivar County, Mississippi, extending the knowledge of microhabitat trap effectiveness to seasonal bottomland hardwood forest floodplains. Crayfishes were captured in three seasonally flooded habitat types: wooded, trail, and open habitats. The CPUE of vernal crayfish Procambarus viaeviridis and White River crayfish P. acutus was higher in minnow traps, whereas the CPUE of swamp dwarf crayfish Cambarellus puer was higher in microhabitat traps. The CPUE did not differ among habitat types for either trap type. In minnow traps, the CPUE of vernal and White River crayfishes increased steadily during the study, whereas the CPUE of swamp dwarf crayfish did not vary over time. In microhabitat traps, the CPUE did not vary over time for any species. Microhabitat traps were more effective at collecting adult, female vernal crayfish in the winter than in spring, whereas minnow traps were more effective at collecting adult, female vernal crayfish in the spring than in winter. Form I males of all three species were collected in both trap types throughout the study, whereas the only ovigerous females collected were swamp dwarf crayfish. Microhabitat traps caught more small crayfishes, pertinent to studies of population structure and recruitment, and were more effective at collecting adult swamp dwarf crayfish, a species five times smaller than other collected species. Conversely, minnow traps provided a better understanding of abundances and population structures of larger crayfishes. Using both trap types provided data on all size‐classes and life stages and reduced sampling selectivity.

Reassessment of the Crayfishes of the Upper Ohio River Basin in Pennsylvania.

Crayfishes are keystone species and ecosystem engineers in freshwater systems and are considered the third most imperiled taxa on the planet. In 1906, Arnold Ortmann published one of the most complete historic crayfish surveys ever conducted, which has allowed Pennsylvania to assess changes to crayfish fauna over the past century. More recently, waterways have been impacted by anthropogenic stressors such as urbanization and extractive industry. Our primary goal is to determine changes in species distributions and relative abundances of crayfishes in western Pennsylvania by visiting historical and new sites. Surveys in 2015-16 focused on collecting primary burrowers by trapping and burrow excavation. In 2017, efforts shifted to epigean species in the Upper Ohio River drainage, using standardized sampling of 10 seine hauls/site to assess 265 sites. Populations of primary burrowing crayfishes were found at 20% of 61 historical sites and 72% of 57 new collection sites. Of epigean crayfishes, 79% were found at 102 historical sites and 97% of 163 new sites. These collections represent approximately 60% of the survey, with remaining collections to occur in 2018. Important findings were three nonnative species: Faxonius rusticus (Rusty Crayfish), Procambarus clarkii (Red Swamp Crayfish), and Procambarus acutus (White River Crayfish). Preliminary data suggests that crayfish fauna in western Pennsylvania has remained moderately stable over the last century, though the presence of nonnative crayfishes indicates the need for continued monitoring. Efforts in Pennsylvania must focus on prevention and management of the spread of nonnative species to preserve the native crayfish populations that remain.

Crayfishes of the Potomac River Basin in West Virginia

The high level of endemism displayed by native crayfish taxa, in addition to the recognized displacement abilities of nonindigenous crayfish such as Faxonius virilis and Procambarus acutus represents a serious threat to indigenous crayfish populations. Other major conservation threats to native crayfish fauna in the eastern portion of West Virginia include land development and land-use practices. The goal of this study was to compare recent and historical species distributions and assess conservation standings of native and nonindigenous crayfishes of the Potomac River Basin in West Virginia. Between June and October of 2007 historical and semi-randomly selected sites were sampled throughout the basin. Abundance was determined by catch per unit effort (CPUE) for ten seine hauls. Morphometric data including total carapace length, propodus length, and palm length were recorded in millimeters for each species. Life history parameters were determined from collections made during the study. Native species collected included Cambarus bartonii, Cambarus carinirostris, and Faxonius obscurus. Introduced species collected included Faxonius virilis and Procambarus zonangulus. C. bartoni was present in the Cacapon, North Branch Potomac, Potomac Direct Drains, and South Branch Potomac. F. obscurus was absent from Potomac Direct Drains, and C. carinirostris was only present in the South Branch Potomac. F. virilis and P. zonangulus were only present in Potomac Direct Drains. Though F. limosus was reported in 1989, no specimens were recovered during over the course of this survey, which indicates possible extirpation from the West Virginia portion of its range.

English

Abstract Invasive crayfish are known to displace native crayfish species, alter aquatic habitat and community structure and function, and are serious pests for fish hatcheries. White River Crawfish (WRC; Procambarus acutus) were inadvertently introduced to a warm-water fish hatchery in Missouri, USA, possibly in an incoming fish shipment. We evaluated the use of chemical control for crayfish to ensure incoming and outgoing fish shipments from hatcheries do not contain live crayfish. We conducted acute (≤ 24 hr) static toxicity tests to determine potency, dose-response, and selectivity of pesticides to WRC, Virile Crayfish (VC; Orconectes virilis), and Fathead Minnow (FHM; Pimephales promelas). Testing identified a formulation of cypermethrin (Cynoff®) as the most potent of five pesticides evaluated for toxicity to crayfish. A 4-hr exposure to a cypermethrin concentration of 100 μg·L-1 was found to kill 100% of juvenile and adult WRC; however, adult VC were not consistently killed. Concentrations of cypermethrin ≤ 100 μg·L-1 did not cause significant (> 10%) mortality in juvenile FHM. Additional testing is needed to examine selectivity between crayfish and hatchery fish species. Biosecurity protocols at hatcheries that use chemical control have the potential to reliably prevent inadvertent transfers of live crayfish in fish shipments.

New Records of Entocytherid Ostracods from New York and New Jersey

Abstract Ostracods of the family Entocytheridae are obligate ectosymbionts, primarily of crayfishes. Although the distribution and diversity of crayfishes is well known in the northeastern US, little is known about entocytherids in this region. In this study, we examined 5 species of crayfishes—Procambarus acutus (White River Crayfish), Orconectes limosus (Spinycheek Crayfish), Orconectes propinquus (Northern Clearwater Crayfish), Cambarus bartonii (Common Crayfish), and Cambarus robustus (Big Water Crayfish)—from 3 counties in New York (Saratoga, Orange, and Tompkins) and 8 counties in New Jersey (Essex, Sussex, Atlantic, Burlington, Camden, Cumberland, Gloucester, and Ocean). We recovered 2 species of entocytherid ostracods: Donnaldsoncythere cayugaensis and Donnaldsoncythere donnaldsonensis. Records from our study expand the known range of D. cayuagensis and fill in gaps in the known range of D. donnaldsonensis.

Harvest of crayfish as an ecosystem service of wetlands compared to production systems with planted forage

ABSTRACTCrayfish harvest as an ecosystem service of moist-soil wetlands in the Mississippi Alluvial Valley (MAV) was evaluated using estimates of crayfish yield and operational costs to create enterprise budgets. The average daily yield of crayfish was 2.13 lb/acre (95% CI = 1.19–3.00) and yield did not differ between wetlands dominated with Red Swamp Crayfish or White River Crayfish. Four hypothetical scenarios of harvest operations revealed annual costs associated with harvesting crayfish to be $163.89–370.75/acre. Although these costs were lower than estimated costs currently associated with harvesting crayfish from fields with planted forage in Louisiana ($749.96/acre), a three-fold reduction in crayfish yield (lb/trap/day) from moist-soil wetlands resulted in an increase in the break-even selling price from $1.25/lb in Louisiana to $1.70–$3.86/lb in the MAV. Although this enterprise will likely not compete with the Louisiana rice-crayfish industry, harvesting crayfish from moist-soil wetlands may contribute to ecosystem services provided by wetlands and aid in the reduction of the quantity of crayfish products imported into the U.S. market.

English

Abstract We examined methods for detecting environmental DNA of the invasive white river crayfish Procambarus zonangulus. In a laboratory experiment, we investigated detection capability in benthic sediment samples and in water samples in six flow-through tanks. Additionally we determined whether crayfish density (low = 0.67 or high = 2.69 crayfish·m-2) or crayfish time in tanks influenced DNA detectability (collection of samples on Days 2, 5, 8 and 15). Species-specific primers and probes were designed for P. zonangulus and their specificity was tested against other crayfish species. Limits of detection and quantification were specified for the target DNA sequence by means of quantitative PCR amplifications on dilution series of known amounts of P. zonangulus DNA. We detected crayfish DNA in 14 of the 24 benthic sediment samples and in two of the 24 water samples. DNA detection was found in benthic sediment samples in at least two tanks at every sampling period, while DNA detection was found in water samples only on Day 8. Crayfish DNA was detected in benthic sediment and water samples independently of crayfish density. Crayfish at both densities were observed to ‘explore’ all areas of the tank and move irrespective of diurnal time or conspecific presence. These behavior patterns were observed throughout the 15 day experiment and likely resulted in the positive detections, especially in benthic sediment samples. We believe that these methods could benefit monitoring of invasive crayfish species, although there is no doubt that further optimization and more research is needed to evaluate these techniques in the wild.

The Omnivorous Diet of the Western Chicken Turtle (Deirochelys reticularia miaria)

Chicken Turtles (Deirochelys reticularia) are morphologically adapted for carnivory, and this specialization has been corroborated by diet studies of the eastern and Florida subspecies (D. r. reticularia and D. r. chrysea, respectively). However, the diet of the western subspecies (D. r. miaria) has not been examined. To investigate this important aspect of this subspecies' ecology, we collected 54 fecal samples from 22 adult D. r. miaria and 13 samples from nine juvenile D. r. miaria in southeastern Oklahoma. White River Crayfish (Procambarus acutus) were found in 88.9% of adult samples (mean of 2.3 crayfish per sample), and appeared to be the dominant food source for adults. There was a significant positive relationship between turtle size and crayfish size, and on average the crayfish were 29.8 mm in carapace length. Insects representing six orders (predominantly Hemiptera and Coleoptera) were found in 57.4% of adult fecal samples. Surprisingly, plants were present in 92.6% of adult fecal samples. While most of the plant matter was unidentifiable, Common Rush (mostly seeds; Juncus effusus), Broadleaf Cattail (Typha latifolia), Giant Cutgrass (seeds; Zizaniopsis miliacea), and Purple-fringed Riccia (Ricciocarpus natans) were identified in several fecal samples. There was a significant difference between the diets of juveniles and adults, with juveniles consuming more insects, fewer crayfish, and fewer plants than adults. These results suggest both that there is an ontogenetic shift in the diet of D. r. miaria and that, unlike the other subspecies, D. r. miaria is demonstrably omnivorous.

Functional and physiological resistance of crayfish to amphibian toxins: tetrodotoxin resistance in the white river crayfish (Procambarus acutus)

Freshwater crayfish are reported to consume early life-history stages of a number of toxic amphibians. Although previous research indicates toxic amphibians are palatable to crayfish, the potential toxicity associated with consumption of toxic prey has been poorly described. We sought to characterise the supposed tetrodotoxin (TTX) resistance of freshwater crayfish, which have been observed to eat the eggs and larvae of toxic Taricha Gray, 1850 newts. White river crayfish (Procambarus acutus (Girard, 1852)) consumed 7.7 ± 4.0 Rough-skinned Newt (Taricha granulosa (Skilton, 1849)) eggs (mean ± SD) when offered 10 eggs in controlled feeding trials. Eggs were determined to contain a concentration of 1239 ± 571 ng (mean ± SD) of TTX. A dose-response assay was then performed to compare ingested doses with physiological TTX resistance. Crayfish were highly susceptible to TTX when administered as an intramuscular injection; TTX doses of 0.1 mass-adjusted mouse units were lethal to 100% of P. acutus crayfish. We established that while crayfish were capable consumers of highly toxic newt eggs, these decapods did not demonstrate physiological resistance to TTX. These findings suggest that crayfish have some functional resistance that renders them capable of consuming TTX-bearing prey despite a lack of physiological resistance to TTX.

Additional Host, Distribution, and Prevalence Records for Alloglossidium caridicolum and Alloglossidium dolandi (Digenea: Macroderoididae), Parasites of Procambarid Crayfish Inhabiting the Coastal Plains of the Southeastern United States

Abstract Examination of antennal glands of 11 specimens of Procambarus zonangulus, from a single locality in Texas and those of 4 specimens of Procambarus blandingii, from a single locality in South Carolina, indicated infections with adult Alloglossidium spp. Prevalence of Alloglossidium caridicolum in P. zonangulus was 18.2%, and that of Alloglossidium dolandi in P. blandingii was 100%. Both collections represented new hosts and distribution records for both digene species.

Evaluation of Baits for Harvesting Procambarid Crawfishes with Emphasis on Bait Type and Bait Quantity

ABSTRACT Two crawfish baits and several bait quantities were evaluated in 2 trials conducted from January through May in four 2.0–2.5-ha experimental earthen crawfish (Procambarus clarkii and Procambarus zonangulus) ponds at the Aquaculture Research Station, Louisiana State University Agricultural Center, Baton Rouge, LA. In the bait-type trial, a freshwater cluepid, gizzard shad (Dorosoma cepedianum), a commercially formulated bait, and a shad + formulated bait combination were evaluated. Highest daily crawfish catch per unit trap effort (CPUE) and bait margin (gross value of crawfish less bait cost) was with gizzard shad at water temperatures less than 20°C (January, February, March), and with formulated bait at 20°C and higher (April, May). The shad + formulated bait combination was effective in attracting crawfish over a wide range of water temperatures from February through May. In the bait quantity trial, both gizzard shad and the formulated bait were evaluated singly at 113 g/trap, 150 g/trap, 227 ...

Response to Long-term Nutrient Deprivation and Recovery in the CrayfishesProcambarus clarkiiandProcambarus zonangulus: Oxygen Consumption and Metabolic Enzymes

Procambarus clarkii (Girard) and Procambarus zonangulus (Hobbs) have adapted to dynamic environments that undergo regular thermal and hydrologic cycles, resulting in extended periods with limited food. To understand the strategy of adaptation to long-term food deprivation, oxygen consumption and activities of several metabolic enzymes were measured over a 5-mo period of starvation and subsequent 1 mo recovery period. There was no significant effect of starvation on oxygen consumption rate for P. clarkii. The oxygen consumption rate for P. zonangulus was significantly lower than fed controls at 4 and 5 mo of starvation. Enzyme activities in both species responded rapidly to starvation. There was a significant decrease in the activity of metabolic enzymes in the hepatopancreas and abdominal muscle of both species at 2 mo, suggesting metabolic rate depression at some level occurs within the first 2 mo of starvation. The decrease in enzyme activities in P. clarkii with starvation lagged slightly behind that of P. zonangulus. The strategy of P. clarkii is better suited to conditions where rapid emergence is required to compete successfully for limited resources; however, survivorship is reduced long-term. P. zonangulus’ ability to reduce metabolic rate may enhance long-term survivorship when emergence is delayed.