Northern Distribution Research Articles

Effects of outplanting time on growth, shedding and quality of Saccharina latissima (Phaeophyceae) in its northern distribution range

To reach the goal of large-scale seaweed cultivation in Norway and the rest of Europe, new knowledge about the commercially important kelp species Saccharina latissima is needed. Efforts to maximise biomass by outplanting the seaweed in different seasons can affect seaweed quality. Here, we investigate the effects of outplanting time (February, April, and May) when cultivating S. latissima in the northern range of the species’ distribution. We studied the quantity and quality of the seaweed biomass produced in the autumn following outplanting. Effects on quantity were evaluated as seaweed frond area, relative daily growth rate (DGR) and relative daily shedding rate (DSR). Quality was evaluated by tissue content of carbon and nitrogen compounds and number of fouling epizoans. Cultivation was successful when seedlings were outplanted in both February and April, but not in May. An earlier outplanting, in February, gave a prolonged time for grow-out at sea prior to the main recruitment event of epizoans that occurred in September, thereby earlier outplanting resulted in larger frond areas. The frond area reached in September was doubled when seedlings were outplanted in February compared to April, whereas a later outplanting in April gave a higher DGR and DSR, higher carbon content, and lower amount of fouling epizoans. The outplanting season did not affect tissue nitrate concentration or internally stored nitrate. These results show that outplanting time is an important factor to consider especially for biomass yield, but also for seaweed quality, including epibiosis of the seaweed biomass.

Distribution and structure of Conocarpus erectus L. (Combretaceae) in the northern limit of the Pacific Ocean (Gulf of California)

The distribution of species can expand or retreat following environmental changes. Climate change is driving changes in the distribution of several species. Changes in mangrove distributions have been reported subsequent to an increase in temperature following a tropicalization process. This study documents the presence of Conocarpus erectus above the reported northern limit for the Gulf of California (GC), updating its distribution limit in the Neotropic. The current northern distribution limit of C. erectus in the Pacific Ocean was found at Huatabampo, Sonora (26.69° N, −109.58° W) and San Jose Island, Baja California Sur (25.04° N, −110.63° W), which is different from previous estimates (1970: 23.23° N, −106.32° W; 2011: 23.31° N, −110.17° W). According to the model of the Center for Scientific Research and Higher Education of Ensenada (CICESE), the C. erectus seeds could be potentially dispersed as far north as Tiburon Island, Sonora. The sea surface temperature (SST) tended to increase more than >0.02 °C, which means an important increment on a decadal scale in the GC's SST. The temperature databases (atmospheric and SST) corroborated a temperature increase in this region since the 1980s. The expansion of C. erectus from its northern distribution limit supports the tropicalization process occurring in the GC. The current distribution and dominance of mangrove species in the GC could be changing due to oceanographic (e.g., El Niño-Southern Oscillation) and coastal (e.g., temperature and precipitation) changes. These types of changes have been reported previously in this region and for other mangrove distributional limits. These changes in mangrove distribution are expected to be accompanied by changes in the biota as well as in the provision of ecosystem services. Further and more specific studies are necessary to corroborate the changes in the distribution and the dominance/coverage of other mangrove species. The potential expansion of C. erectus could provide unique ecosystem services in arid and semiarid regions.

High-elevational occurrence of two tick species, Ixodes ricinus and I. trianguliceps, at their northern distribution range

BackgroundDuring the last decades a northward and upward range shift has been observed among many organisms across different taxa. In the northern hemisphere, ticks have been observed to have increased their latitudinal and altitudinal range limit. However, the elevational expansion at its northern distribution range remains largely unstudied. In this study we investigated the altitudinal distribution of the exophilic Ixodes ricinus and endophilic I. trianguliceps on two mountain slopes in Norway by assessing larval infestation rates on bank voles (Myodes glareolus).MethodsDuring 2017 and 2018, 1325 bank voles were captured during the spring, summer and autumn at ten trapping stations ranging from 100 m to 1000 m.a.s.l. in two study areas in southern Norway. We used generalized logistic regression models to estimate the prevalence of infestation of both tick species along gradients of altitude, considering study area, collection year and season, temperature, humidity and altitude interactions as extrinsic variables, and host body mass and sex as intrinsic predictor variables.ResultsWe found that both I. ricinus and I. trianguliceps infested bank voles at altitudes up to 1000 m.a.s.l., which is a substantial increase in altitude compared to previous findings for I. ricinus in this region. The infestation rates declined more rapidly with increasing altitude for I. ricinus compared to I. trianguliceps, indicating that the endophilic ecology of I. trianguliceps may provide shelter from limiting factors tied to altitude. Seasonal effects limited the occurrence of I. ricinus during autumn, but I. trianguliceps was found to infest rodents at all altitudes during all seasons of both years.ConclusionsThis study provides new insights into the altitudinal distribution of two tick species at their northern distribution range, one with the potential to transmit zoonotic pathogens to both humans and livestock. With warming temperatures predicted to increase, and especially so in the northern regions, the risk of tick-borne infections is likely to become a concern at increasingly higher altitudes in the future.Graphical

Species of Euryplacidae (Brachyura) in western Mexico

Abstract Two species of Euryplacidae were collected in western Mexico. Trizocarcinus dentatus (12 localities) and Euryplax polita (4 localities) were both found in the Gulf of California. In the case of E. polita 11 specimens (5 males, 5 females, one ovigerous female) were obtained, while in the case of T. dentatus 42 specimens (25 males, 10 females, 7 ovigerous females) were collected. The northern distribution limit of E. polita is extended to the northern Gulf of California (28°16′N 111°36′W). Environmental data for both species are provided, including depth range, temperature, dissolved oxygen, and sediment composition.

The growth responses of Araucaria angustifolia to climate are adjusted both spatially and temporally at its northern distribution limit

Temporal instability and spatial inconsistency in tree growth sensitivity to climate have been reported, but little attention has been given to tropical species. Araucaria angustifolia (Bertol.) Kuntze. (Araucariaceae) is a critically endangered South American subtropical and tropical conifer. It offers the potential to evaluate alterations in tree growth responses as it is climate-sensitive and presents a core zone of distribution in the Brazilian meridional highlands (with small disjunct patches occurring in its most southern and northern ranges). Previous dendrochronological studies in the central and most southern distribution range of A. angustifolia showed different climate-related growth responses, which raises the question of whether the growth responses of A. angustifolia to climate are consistent over space and stable over time at the species' northern distribution limit? We developed well-replicated tree-ring chronologies for A. angustifolia at the species' northern distribution limit, examined its growth dynamics, and evaluated climate-growth relationships. The growth patterns of A. angustifolia allowed the synchronization of its tree ring time-series and the construction of two tree-ring width chronologies (at Brejo da Lapa – BL and Vale das Araucárias – VA) of 55 years and 171 years respectively. The chronologies demonstrated stable and robust signal strengths. Climate-growth response analyses indicated significant positive correlations of the VA chronology with precipitation variables, and with temperature variables in the BL chronology. Different diametric growth patterns were detected between BL and VA. We observed consistent reductions of growth responses to the climate in recent decades. Forest structure and dynamics, disturbance regime, local environmental factors, and climate change could generate physiological alterations and explain variations in A. angustifolia’s growth responses and increments. The species showed different sensitivities to climatic factors both spatially and temporally, and different growth patterns at its northern distribution limit.

First fossil record of Nothotsuga (Pinaceae) in China: implications for palaeobiogeography and palaeoecology

ABSTRACT Nothotsuga is a monotypic genus of Pinaceae endemic to southern China today. Molecular data indicate that Nothotsuga split from Tsuga during the Palaeogene with the earliest fossils from the upper Eocene of North Europe. However, Nothotsuga fossil has not been reported from China. Here, we describe several well-preserved seed cones from the upper Miocene of Tiantai County, Zhejiang Province, China. The fossil cones are characterised by ovate to elliptic shapes, rhombic to suborbicular and auriculate scales, and exserted subspathulate bracts with dentate margin and acute or acuminate apical cusp. These cones are ascribed to a new species Nothotsuga sinogaia sp. nov. based on detailed comparisons with all extant genera of Pinaceae. The present discovery indicate that Nothotsuga had a more northern distribution during the late Miocene and the increased annual range of monthly-mean temperature might have restricted its modern distribution to several scattered and fragmental areas in southern China.

Doubling the longevity record of the American Three-toed Woodpecker (Picoides dorsalis)

The American Three-toed Woodpecker (Picoides dorsalis) is a relatively poorly known species due to its remote northern distribution, the low density of its populations, and its cryptic behavior. In this article, we report the observation of an 11-year-old individual, nearly 2 times older than the previous record for the species. This longevity is similar to values reported for the closely related Eurasian Three-toed Woodpecker (P. tridactylus). We report on the observation of a male that was captured, aged, color-banded, and photographed in 2010, and photographed again when it was resighted in 2019. This finding has potential implications for the modeling of population viability and the possibility of extinction debt in marginal habitat.

A New Erythrosuchid Archosauriform from the Middle Triassic Yerrapalli Formation of South-Central India

Erythrosuchid archosauriforms are quadrupedal carnivorous reptiles with a proportionally huge skull. They represent one of the first evolutionary radiations of medium to large predatory diapsids after the Permo–Triassic mass extinction. Erythrosuchids are known from Lower–Middle Triassic rocks of South Africa, Russia, and China, and there have been preliminary reports from the Middle Triassic Yerrapalli Formation of south-central India. Here we describe, compare and figure for the first time these Indian erythrosuchid remains. We erect the new genus and species Bharitalasuchus tapani based on a holotype and paratype that preserve tooth-bearing cranial fragments, at least 17 presacral vertebrae, some ribs and probable intercentra, and partial shoulder and pelvic girdles and hindlimb and allow recognizing a series of autapomorphies and unique combination of character states among erythrosuchids. Our phylogenetic analysis recovered Bharitalasuchus tapani most closely related to Shansisuchus shansisuchus and Chalishevia cothurnata from the late Anisian of China and Ladinian of Russia, respectively. The phylogenetic affinities of this new taxon and a revision of the tetrapod assemblage of the Yerrapalli Formation shed light on the age of this unit. The presence of the Wadiasaurus-Rechnisaurus-Bharitalasuchus association in the Yerrapalli Formation closely resembles the Sinokannemeyeria-Shansisuchus dicynodont-erythrosuchid association of late Anisian to early Ladinian Chinese units. This evidence supports a post-early–middle Anisian age, even possibly early Ladinian, for the Yerrapalli Formation. The presence of possibly one of the last erythrosuchids in India would indicate that the clade still retained both a northern and southern Pangean distribution before its extinction.

Genomics helps to predict maladaptation to climate change

The combination of highly resolved climatic and genomic data allows assessment of putative maladaptation of populations to climate change and can identify high-risk populations. Now, a study that accounts for migration and dispersal shows high maladaptation of a North American tree species in the northern and eastern distribution range.

A brief history of the northern quoll (

In response to Australia’s current extinction crisis, substantial research efforts have been targeted towards some of the most imperilled species. One such species is the northern quoll (Dasyurus hallucatus), a marsupial predator that has recently suffered substantial declines in range and is now listed as Endangered. We conducted a systematic review of all literature relevant to the conservation and ecology of northern quolls. We reviewed 143 studies, including research articles, government and industry reports, theses, and books, and quantified research effort in terms of topic, location, and publication period. We then summarised research relevant to northern quoll taxonomy, genetics, distribution, habitat associations, diet, reproduction, movement, threats, management, and Indigenous knowledge. Research effort was higher between 2011 and 2020 than the previous four decades combined. Northern quolls in the Northern Territory were the most studied, followed by the Pilbara, the Kimberley, and Queensland populations. Most studies focused on northern quoll distribution and habitat, management, and threats – primarily cane toads, predation, and fire. We conclude with a non-exhaustive list of ten future research directions. If pursued, these future research directions should provide information critical to managing and conserving northern quolls.

Стрела-змея Psammophis lineolatus (Brandt, 1838) (Serpentes: Lamprophiidae) в Мангистауской и Атырауской областях Республики Казахстан

Materials related to the history of the study of the distribution of the steppe ribbon racer Psammophis lineolatus in Western Kazakhstan are presented in this article. Thus, based on literature and original data, a map was compiled with an inventory of the distribution of the species in the Mangistau and Atyrau oblasts of Kazakhstan through which the northwestern border of the range passes. This border rises from the eastern coast of the Caspian Sea along the left bank of the Urals almost to the border of the West-Kazakhstan oblast before then turning eastwards into the Indersky district of the Atyrau oblast, passing along the northern coast of Lake Inder. Data show that the currently known northern distribution limit for the Steppe Ribbon Racer is on the northwestern edge of the Taisoigan sands, in the Kyzylkoginsky district of the Atyrau oblast (48°49,97′N, 52°55,545′E)

Mitogenome and phylogenetic analyses support rapid diversification among species groups of small-eared shrews genus Cryptotis (Mammalia: Eulipotyphla: Soricidae).

The small-eared shrew genus Cryptotis is the third largest in the family Soricidae and occurs in North, Central, and northern South America. In Mexico and Central and South America, most species inhabit geographically isolated moist, montane habitats at middle and high elevations in a typical sky-island pattern. The 49 recognized species have been partitioned into as many as six species groups based on morphological and molecular phylogenetic studies. The relationships among these species groups are poorly resolved, and their evolutionary histories, including migration patterns and locomotor adaptations, remain unclear. Herein, we provide a new phylogeny incorporating complete mitochondrial genomes (mitogenomes) and supermatrix approach. We compared different evolutionary scenarios using approximately unbiased (AU), Kishino-Hasegawa (KH), and Shimodaira-Hasegawa (SH) statistical tests. The phylogenetic hypothesis based on mitogenomes revealed novel relationships supporting a basal position for the Cryptotis parvus-group in the genus, and a close relationship between C. gracilis and one clade of the C. thomasi-group. The former relationship is consistent with the least derived humerus morphology and northern distribution of the species. The latter relationship implies multiple migrations between Central and South America. The lack of fine resolution for the species group relationships may be due partly to the lack of taxon sampling. In contrast, multi-approach analyses suggest that the unresolved relationships may be a result of rapid diversification during the early stages of Cryptotis evolution.

Revision of occurrence and phytosociology of Ranunculus pedatus Waldst. et Kit. in Slovakia

Ranunculus pedatus is a Eurasian species with a northern distribution edge in southern Slovakia. In the nineties of the 20th century, it was assumed that the species probably occurs only near Štúrovo. Occurrence in the Hron and Ipeľ basins and several localities in the Podunajská nížina lowland between Komárno and Štúrovo was considered historical. Our research was conducted in the field and herbarium collections of 15 herbaria in Austria, the Czech Republic, Hungary, and Slovakia. Except for the well-known occurrence on salt habitats north of Štúrovo, we confirmed the recent occurrence of R. pedatus in Štúrovo town, around Chľaba village and in Ipeľ Basin (Pastovce, Tupá). The new, easternmost Slovak locality was found near the village of Koláre. Recently, 30% of all known sites were confirmed, so we propose reclassifying the species in Slovak Red List from the category critically endangered (CR) to the category endangered (EN). It occurs in salty meadows of the alliance Festucion pseudovinae (class Festuco-Puccinellietea) and in mesic meadows of alliance Arrhenatherion elatioris and Deschampsion cespitosae (class Molinio-Arrhenatheretea).

UPDATED TAXONOMIC LIST OF FISH LARVAE FROM BAHÍA SEBASTIÁN VIZCAÍNO, BAJA CALIFORNIA, MÉXICO

Larvae of 152 fish families were identified in the California Current between 1949-1994 through the CalCOFI Program. Sampling efforts in the southern California Current restarted in 1997 with the ongoing IMECOCAL Program, which includes the transitional area of Bahía Sebastián Vizcaíno (BSV). This work updates the fish larvae taxonomic list of BSV, summarizing the 20-year sampling efforts. Results showed 341 identified taxa (227 to species level, 60 to genus and 54 to family), representing 97 families. The most abundant were Phosichthyidae (37%), Myctophidae (14%) and Synodontidae (9%). Pelagic neritic species Engraulis mordax (Engraulidae) and Sardinops sagax (Clupeidae) showed their maximum larval abundance during spring and winter, respectively. Myctophidae contributed with the highest species richness (39 taxa in 20 genera), followed by the reef-associated Sebastidae (21 taxa in the Sebastes genus). Identified taxa were mostly from southern (tropical) zoogeographic affinity (80%), and a minor component had northern (boreal) affinity (8%) or wide distribution in the northeastern Pacific Ocean (12%). The highest larval abundance and species richness were registered during summer (207 taxa) and fall (219 taxa). In winter and spring, larval abundance and richness decreased almost 50%, however the number of dominant species was higher. The previous ichthyoplankton list for BSV included only samples taken during 1997-2001 and reported larvae of 158 taxa in 71 families, where mesopelagic larvae contributed with most of the bundance and taxonomic richness (˃20%). Seasonal abundance of pelagic neritic species showed a spawning preference for spring and summer conditions. For demersal species, diversity and abundance increased during fall. With this work we increase from 158 to 341 registered taxa, most of them associated to demersal reef habitats with southern distribution. One third of the taxa found (114) could not be identified to species level, highlighting the urgency for more taxonomic studies of ichthyoplankton in the area.

Population genetic structure and species delimitation in theCryptanthus zonatuscomplex (Bromeliaceae)

AbstractMorphological variations of individuals and populations of plants have hampered taxonomists from understanding whether such variations are intra- or interspecific. In this research, we study Cryptanthus burle-marxii and C. zonatus, the morphological variations of which overlap, making it difficult to identify them. Both taxa are restricted to the north of the Brazilian Atlantic Forest and are included in the C. zonatus species complex. We applied different methods such as morphological comparison, population genetics using ten nuclear microsatellite markers and ecological niche modelling to study population genetic structure and species delimitation of this species complex. Our analysis revealed that the two genetic clusters were formed possibly because of the presence of a historical geographical barrier in a region called ‘depressão do Abiaí’. The two genetic clusters were concordant with the northern and southern distribution of the complex but incongruent with a morphological variation or current taxonomic delimitation. Thus, we synonymize C. burle-marxii with C. zonatus and re-evaluate its conservation status as endangered.

Distinct intestinal microbial communities of two sympatric anadromous Arctic salmonids and the effects of migration and feeding

Although intestinal microbial communities from anadromous Arctic char (Salvelinus alpinus (Linnaeus, 1758)) in Kitikmeot, Nunavut, Canada, differ depending on the timing and location of capture, determinants of gut microbiota in other wild Arctic salmonids are largely unknown. Using high-throughput 16S rRNA gene sequence data, we compared intestinal microbiota from Arctic char to those from a related and sympatric salmonid, lake whitefish (Coregonus clupeaformis (Mitchill, 1818)). Shifts in lake whitefish gut microbial community composition were observed between brackish water and freshwater, similar to impacts of salinity reported previously for Arctic char. Despite these similarities, gut community profiles for the two salmonids differed, with whitefish having higher diversities and increased proportions of taxa affiliated with potential pathogens. Geography seemed to have a greater impact on freshwater whitefish gut microbiota than on corresponding Arctic char. Additionally, microbiota diversity was significantly more affected by feeding behavior in whitefish compared with sympatric Arctic char. As sampled whitefish were at their northern range limits and grew slowly, we speculate that they, and their microbial consortia, could be more vulnerable to certain abiotic and biotic factors than Arctic char, which are well adapted to conditions found in these high latitude environments and have the most northern distribution of any freshwater fish.

Freezing tolerance of seeds can explain differences in the distribution of two widespread mistletoe subspecies in Europe

The ability of plants to tolerate freezing limits their geographical distribution. Therefore, winter warming may shift a species’ occurrence northwards and/or to higher altitudes. In Europe, the hemiparasitic vascular plant Viscum album (mistletoe) has two common and widespread subspecies: V. a. ssp. album and V. a. ssp. austriacum. The former has a more northern geographic distribution than the latter. Therefore we hypothesised that seeds of V. a. ssp. album are more tolerant to freezing than those of V. a. ssp. austriacum. From these two mistletoe subspecies V. a. ssp. austriacum is, in some managed forest areas, considered a novel threat to tree growth and forest health.Berries of V. a. ssp. album were collected from Sweden, Poland and Switzerland and berries of V. a. ssp. austriacum were collected from Poland, Switzerland and Spain. After storage at −3 °C, seeds were extracted from the pulp of berries and exposed to eight different temperatures between −8 °C and −30 °C, with the storage temperature serving as the control. After freezing treatments, germination of seeds was monitored. In addition, differential thermal analysis was used to measure freeze tolerance of seeds.The seeds of V. a. ssp. album tolerated lower temperatures than seeds of V. a. ssp. austriacum. The temperature at which 50% of seeds lost their ability to germinate (LT50) was −15 °C in V. a. ssp. austriacum and between −15 °C and −19 °C in V. a. ssp. album. The results of differential thermal analysis to determine the freezing point of seeds supported these findings.The freezing tolerance of mistletoe seeds was relatively well coupled with the winter climate at the edge of their current geographic distribution. Based on our results, the warming of winters may eliminate the abiotic barrier that has thus far limited mistletoes’ expansion, opening a window of opportunity for these parasites to increase their abundance and shift their distribution range towards higher latitudes and altitudes.Although mistletoes play important ecological roles in forest ecosystems, their recent increase has raised concern among forest managers, because they may cause a substantial reduction in tree growth in single species dominated stands. Increasing tree species diversity might be an effective method for limiting future mass infestations in homogeneous managed forests.

Conservation genetics of yellow-bellied toads (Bombina variegata): a matter of geographical scale and isolation

Amphibian populations world-wide are threatened by declines and extinctions mainly due to habitat loss and fragmentation. Habitat fragmentation threatens the yellow-bellied toad Bombina variegata in the northern and western regions of its distribution where it is strictly protected. We studied the genetic structure and diversity of populations at three geographical scales using microsatellite loci to detect potential threats for population persistence. At the local scale, we sampled four neighbouring localities at 1–2.6 km distance to detect effects of short-term (decades) fragmentation on connectivity. At the regional scale, five additional localities in the mountains of the Westerwald (Rhineland-Palatinate, Germany) were studied at up to 50.1 km distance to analyse genetic diversity and population structure. At the continental scale, we included data from regions in the northern distribution with fragmented populations (Hesse and Lower Saxony, Germany) and more continuous populations in the South (Alsace, France; Geneva, Switzerland; Trentino, Italy) to evaluate variation of genetic diversity. At the local scale, short-term fragmentation caused significant genetic differentiation between breeding assemblages only 1.4 km apart from each other. At the regional scale, we found notable genetic distance among localities. At the continental scale, we identified Alsace, Trentino and Geneva in the South as regions with low genetic structuring and high allelic richness, and the northern remaining regions in Germany as deeply structured with reduced allelic richness. We suggest that reduced genetic diversity and habitat fragmentation in northern regions makes these populations particularly vulnerable to decline. In conclusion, informed conservation management of B. variegata should focus on measures maintaining or improving connectivity among neighbouring populations.

Genetic diversity of Rhinogobius delicatus (Perciformes: Gobiidae): origins of the freshwater fish in East Taiwan

Mitochondrial DNA cytochrome b and d-loop sequences (1,984 bp) from 92 specimens of the freshwater goby Rhinogobius delicatus from seven drainages in East Taiwan were identified as two major lineages exhibiting a southern or northern distribution. The existence of low genetic diversity, a pattern of population decline and high population differentiation (F ST=0.711) support the need for the development of management strategies for the conservation of localized populations. The results of a statistical dispersal-vicariance analysis suggested that the ancestral populations of R. delicatus were widely distributed in East Taiwan. Compared with the phylogeographic patterns of the other endemic eastern Taiwan freshwater fishes, Onychostoma alticorpus, Aphyocypris kikuckii and Hemimyzon taitungensis, our study suggests that the freshwater fishes colonized East Taiwan through northeastern and southwestern Taiwan, although the ancestral populations colonized the island before it reached its present shape.

Changes in native lamprey populations in the Great Lakes since the onset of sea lamprey (Petromyzon marinus) control

The control of invasive sea lamprey in the Great Lakes basin has been highly successful, but has deleteriously affected native lamprey species. American brook, northern brook, silver and chestnut lampreys are all susceptible to lampricide treatments. Incidental catch from surveys that targeted sea lamprey were used to determine changes in distributions and catch rates of these native species within the Great Lakes basin since the onset of the sea lamprey control program. Over 2.4 million native lampreys were collected during sea lamprey control operations between 1947 and 2018. Native lampreys were no longer captured from many treated and untreated streams. Silver lamprey and northern brook lamprey distributions were reduced most substantially. These species were no longer found in about three quarters of the number of streams in which they were historically present. The number of streams inhabited by chestnut lamprey has diminished by half. American brook lamprey were still present in the majority of streams previously occupied. Catch rates declined in northern brook lamprey and Ichthyomyzon larvae in some Great Lakes basins, but changes in collection gear and methods made comparisons difficult. Trap and weir data show drastic declines in silver lamprey and chestnut lamprey. Streams that have not been treated with lampricide have suffered similar or greater declines in both the number of streams occupied and catch rates for all four species when compared to untreated streams. Therefore reductions in native lamprey populations were likely due to a number of environmental changes, and not exclusively from lampricide treatments.