The Pismo clam (Tivela stultorum) has experienced substantial population decline in California over the past century, extinguishing most public participation in a once-iconic recreational fishery before the end of the 20th century. A subsequent decrease in data collection has led to uncertainty about the current population status of this species. We conducted 6 years of intertidal Pismo clam population assessment surveys in Orange, San Diego, and southern Los Angeles Counties to provide a current dataset that could help guide research and management efforts in southern California. Pismo clams were observed at 19 out of 27 study sites during 57 days of surveys. Average clam bed density was low (mean 2.0 ± 1.1 clams/m2, median 0.1 ± 0.7 clams/m2, n = 21 sites), especially when considering larger clams ≥ 35 mm (mean 0.3 ± 0.1 clams/m2, median 0.1 ± 0.4 clams/m2), and varied greatly between sites (0.0–98.5 clams/m2), with Orange County densities approximately one order of magnitude lower than those in San Diego County. Juvenile recruitment was generally low or undetectable, except for consistent recruitment within a < 10 km beach area in San Diego County and a much larger, widespread recruitment event in 2022. Multi-year observations at several sites failed to indicate any consistent seasonal or inter-annual population trends. Densities and abundances were similar to recent historic data (< 30 years old), but are substantially lower than populations prior to the 1980s. We conclude that the Pismo clam persists on many southern California beaches at generally low densities and that recruitment is occurring throughout the southern California region with high spatial and temporal variability. This study provides foundational data to help inform Pismo clam conservation management decisions and to which additional monitoring, ecological research, and fishery data collection should be added.
{"title":"Once-iconic Pismo clams persist in southern California at low intertidal population densities and with variable recruitment","authors":"S. Bignami","doi":"10.51492/cfwj.108.23","DOIUrl":"https://doi.org/10.51492/cfwj.108.23","url":null,"abstract":"The Pismo clam (Tivela stultorum) has experienced substantial population decline in California over the past century, extinguishing most public participation in a once-iconic recreational fishery before the end of the 20th century. A subsequent decrease in data collection has led to uncertainty about the current population status of this species. We conducted 6 years of intertidal Pismo clam population assessment surveys in Orange, San Diego, and southern Los Angeles Counties to provide a current dataset that could help guide research and management efforts in southern California. Pismo clams were observed at 19 out of 27 study sites during 57 days of surveys. Average clam bed density was low (mean 2.0 ± 1.1 clams/m2, median 0.1 ± 0.7 clams/m2, n = 21 sites), especially when considering larger clams ≥ 35 mm (mean 0.3 ± 0.1 clams/m2, median 0.1 ± 0.4 clams/m2), and varied greatly between sites (0.0–98.5 clams/m2), with Orange County densities approximately one order of magnitude lower than those in San Diego County. Juvenile recruitment was generally low or undetectable, except for consistent recruitment within a < 10 km beach area in San Diego County and a much larger, widespread recruitment event in 2022. Multi-year observations at several sites failed to indicate any consistent seasonal or inter-annual population trends. Densities and abundances were similar to recent historic data (< 30 years old), but are substantially lower than populations prior to the 1980s. We conclude that the Pismo clam persists on many southern California beaches at generally low densities and that recruitment is occurring throughout the southern California region with high spatial and temporal variability. This study provides foundational data to help inform Pismo clam conservation management decisions and to which additional monitoring, ecological research, and fishery data collection should be added.","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44817779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zachary A. Cava, Kyla M. Garten, Sarah M. Foster, J. Alvarez
{"title":"Observations of extreme dehydration and rehydration leading to recovery of a threatened California tiger salamander","authors":"Zachary A. Cava, Kyla M. Garten, Sarah M. Foster, J. Alvarez","doi":"10.51492/cfwj.108.9","DOIUrl":"https://doi.org/10.51492/cfwj.108.9","url":null,"abstract":"","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49048819","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
David M. Laabs, Mark L. Allaback, Donald R. Mitchell
The San Joaquin pocket mouse (Perognathus inornatus) is endemic to California and currently includes three subspecies (P. i. inornatus, neglectus, and psammophilus). P. inornatus from the western Mojave Desert have been assigned to the subspecies neglectus based on similar morphology. During the course of live-trapping projects between 1990 and 2017, we captured P. inornatus at several locations in the Mojave Desert and gathered information on habitat associations, relative abundance, seasonal activity, and field identification. P. inornatus was found at elevations ranging from 668–1,109 m above mean sea level in creosote bush scrub, allscale scrub, Joshua tree woodland, rubber rabbitbrush scrub, spinescale scrub, and California juniper woodland. The capture locations and our review of museum specimens indicate that, at a minimum, the species’ range in the Mojave Desert encompasses approximately 7,000 km2 primarily in the Antelope Valley, extending at least as far north as the Rand Mountains, east to the vicinity of Hinkley, south to Palmdale, and west to near Gorman. P. inornatus capture rates were typically low relative to other nocturnal rodents, and it was not found consistently at localities at which it had been captured previously. Adults were sexually dimorphic, with males significantly larger than females. P. inornatus was significantly larger than the sympatric little pocket mouse (P. longimembris) for length of head-body, total length and body mass, and possessed a relatively shorter tail. We collected 15 specimens of P. inornatus from nine localities in the western Mojave Desert for cytogenetic analysis and each possessed the same karyotype, characterized by a diploid complement of 52 chromosomes, which has not been previously described for the genus. We argue that the 52-chromosome form should be considered distinct for conservation purposes, because it occupies a relatively small geographic area that is being subjected to increasing habitat loss and fragmentation due to residential, commercial, and renewable energy development.
{"title":"Distribution, morphology, and karyotype of San Joaquin pocket mice from the western Mojave Desert","authors":"David M. Laabs, Mark L. Allaback, Donald R. Mitchell","doi":"10.51492/cfwj.108.10","DOIUrl":"https://doi.org/10.51492/cfwj.108.10","url":null,"abstract":"The San Joaquin pocket mouse (Perognathus inornatus) is endemic to California and currently includes three subspecies (P. i. inornatus, neglectus, and psammophilus). P. inornatus from the western Mojave Desert have been assigned to the subspecies neglectus based on similar morphology. During the course of live-trapping projects between 1990 and 2017, we captured P. inornatus at several locations in the Mojave Desert and gathered information on habitat associations, relative abundance, seasonal activity, and field identification. P. inornatus was found at elevations ranging from 668–1,109 m above mean sea level in creosote bush scrub, allscale scrub, Joshua tree woodland, rubber rabbitbrush scrub, spinescale scrub, and California juniper woodland. The capture locations and our review of museum specimens indicate that, at a minimum, the species’ range in the Mojave Desert encompasses approximately 7,000 km2 primarily in the Antelope Valley, extending at least as far north as the Rand Mountains, east to the vicinity of Hinkley, south to Palmdale, and west to near Gorman. P. inornatus capture rates were typically low relative to other nocturnal rodents, and it was not found consistently at localities at which it had been captured previously. Adults were sexually dimorphic, with males significantly larger than females. P. inornatus was significantly larger than the sympatric little pocket mouse (P. longimembris) for length of head-body, total length and body mass, and possessed a relatively shorter tail. We collected 15 specimens of P. inornatus from nine localities in the western Mojave Desert for cytogenetic analysis and each possessed the same karyotype, characterized by a diploid complement of 52 chromosomes, which has not been previously described for the genus. We argue that the 52-chromosome form should be considered distinct for conservation purposes, because it occupies a relatively small geographic area that is being subjected to increasing habitat loss and fragmentation due to residential, commercial, and renewable energy development.","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"70988565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zair P. Lojkovic Burris, Randall D. Baxter, Christina E. Burdi
The density and quality of zooplankton prey affect the feeding success of larval and juvenile fishes and thus can drive growth, survival, and recruitment. As part of a larger effort investigating potential causes of a pelagic fish decline, we examined regional feeding success (food presence/absence, stomach fullness), diet composition and prey selection of young Longfin Smelt (Spirinchus thaleichthys) in spring and summer as a function of fish size and prey availability in the San Francisco Estuary. We conducted our sampling during two wet and two dry years, because weather and river flow influence prey community composition and location. Larval and juvenile fish showed evidence of food limitation: high proportions of empty stomachs (≤ 70%) and stomach contents totaling <10% of maximum stomach content volume. The total weight of prey consumed increased with fish length, and in most regions and years this resulted from fish consuming larger prey as they grew; however, in many regions during dry years, fish consumed greater numbers of prey instead of larger prey as they grew. Larval fish preferentially consumed Eurytemora spp. except when rotifers or barnacle nauplii occurred in extremely high densities. Juvenile fish consumed a greater diversity of prey yet relied on mysids in most regions and years. Adult calanoid copepods (Pseudodiaptomus spp., Eurytemora spp., and Acartia spp.) were regionally important in juvenile diets and were positively selected when mysids were in low densities, mostly in eastern regions during dry years. This switch from much larger mysids to smaller calanoid copepods explains the increase in prey number (instead of prey size) consumed in these regions. These results, coupled with food limitation in most regions, suggest that the current densities and quality of zooplankton in the San Francisco Estuary are limiting feeding success and potentially growth and survival of young Longfin Smelt.
{"title":"Larval and juvenile Longfin Smelt diets as a function of fish size and prey density in the San Francisco Estuary","authors":"Zair P. Lojkovic Burris, Randall D. Baxter, Christina E. Burdi","doi":"10.51492/cfwj.108.11","DOIUrl":"https://doi.org/10.51492/cfwj.108.11","url":null,"abstract":"The density and quality of zooplankton prey affect the feeding success of larval and juvenile fishes and thus can drive growth, survival, and recruitment. As part of a larger effort investigating potential causes of a pelagic fish decline, we examined regional feeding success (food presence/absence, stomach fullness), diet composition and prey selection of young Longfin Smelt (Spirinchus thaleichthys) in spring and summer as a function of fish size and prey availability in the San Francisco Estuary. We conducted our sampling during two wet and two dry years, because weather and river flow influence prey community composition and location. Larval and juvenile fish showed evidence of food limitation: high proportions of empty stomachs (≤ 70%) and stomach contents totaling <10% of maximum stomach content volume. The total weight of prey consumed increased with fish length, and in most regions and years this resulted from fish consuming larger prey as they grew; however, in many regions during dry years, fish consumed greater numbers of prey instead of larger prey as they grew. Larval fish preferentially consumed Eurytemora spp. except when rotifers or barnacle nauplii occurred in extremely high densities. Juvenile fish consumed a greater diversity of prey yet relied on mysids in most regions and years. Adult calanoid copepods (Pseudodiaptomus spp., Eurytemora spp., and Acartia spp.) were regionally important in juvenile diets and were positively selected when mysids were in low densities, mostly in eastern regions during dry years. This switch from much larger mysids to smaller calanoid copepods explains the increase in prey number (instead of prey size) consumed in these regions. These results, coupled with food limitation in most regions, suggest that the current densities and quality of zooplankton in the San Francisco Estuary are limiting feeding success and potentially growth and survival of young Longfin Smelt.","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44153613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Impacts of domesticated ferrets upon wildlife, agriculture, and human health in the USA, compiled from state agency surveys and literature review, with special emphasis upon California","authors":"G. O. Graening","doi":"10.51492/cfwj.108.13","DOIUrl":"https://doi.org/10.51492/cfwj.108.13","url":null,"abstract":"","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":"1 1","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43152081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Aalbers, Michael Wang, L. Bellquist, Kate Kauer, Alexis Jackson, C. Sepulveda
California recreational anglers have recently started using specific deep-drop tackle to target swordfish (Xiphius gladius) below the thermocline during the daytime. Increased rod-and-reel fishing effort stems from promising experimental fishing trials of a recently approved commercial gear type off California (deep-set buoy gear), along with the widespread growth of deep-drop recreational fisheries for swordfish around the world. The rapid development and vast growth potential in this emerging recreational fishery, has outpaced the implementation of sampling programs to accurately quantify swordfish catch, effort, and economic output. We characterized recent sportfishing practices for swordfish and reviewed available California recreational fishery data sources. Findings suggest a sharp increase in estimated catch relative to previous decades and a major shift in the techniques used by local fishers to target swordfish beginning in September 2019. Recent increases in recreational swordfish catches aligned directly with heightened tackle sales for gear specific to deep-drop practices. Given the increased deep-set effort for swordfish within the region and the limited coverage of existing private-vessel catch documentation, additional monitoring efforts are needed to better gauge the potential social, economic, and ecological impacts of this emerging recreational fishery.
{"title":"Characterization of a developing recreational deep-drop fishery for swordfish off southern California","authors":"S. Aalbers, Michael Wang, L. Bellquist, Kate Kauer, Alexis Jackson, C. Sepulveda","doi":"10.51492/cfwj.108.12","DOIUrl":"https://doi.org/10.51492/cfwj.108.12","url":null,"abstract":"California recreational anglers have recently started using specific deep-drop tackle to target swordfish (Xiphius gladius) below the thermocline during the daytime. Increased rod-and-reel fishing effort stems from promising experimental fishing trials of a recently approved commercial gear type off California (deep-set buoy gear), along with the widespread growth of deep-drop recreational fisheries for swordfish around the world. The rapid development and vast growth potential in this emerging recreational fishery, has outpaced the implementation of sampling programs to accurately quantify swordfish catch, effort, and economic output. We characterized recent sportfishing practices for swordfish and reviewed available California recreational fishery data sources. Findings suggest a sharp increase in estimated catch relative to previous decades and a major shift in the techniques used by local fishers to target swordfish beginning in September 2019. Recent increases in recreational swordfish catches aligned directly with heightened tackle sales for gear specific to deep-drop practices. Given the increased deep-set effort for swordfish within the region and the limited coverage of existing private-vessel catch documentation, additional monitoring efforts are needed to better gauge the potential social, economic, and ecological impacts of this emerging recreational fishery.","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45545844","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The osprey (Pandion halieatus) declined globally in the mid-late 20th century due primarily to pesticide contamination that reduced reproduction. The species has recovered through much of its range, and its range in California has increased. The species has received limited attention in recent decades, despite recommendations that it be monitored as an environmental indicator. In 2021, we located a sample of 39 osprey occupied nests near the Sacramento River and at reservoirs and small ponds in central interior California and determined habitats used and reproductive success. Nearly one-third of nests were located within 100 m of waterbodies and 88% were within 1000 m. The median distance of nests from roads was 51 m. Thirty-four (87%) of occupied nests were on anthropogenic sites, including utility poles, poles erected for ospreys, transmission towers, light poles, and port structures. Only five nests (13%) were in trees and snags. Nearly half (48%) of nests were on platforms constructed on utility poles and on poles erected for ospreys, both placed to protect electrical systems. Water levels in reservoirs, and some small farm ponds, were lower than average in 2021 due to drought, while the Sacramento River and Port were less affected. Twenty-four (71%) of 34 adequately monitored nests were successful in fledging at least one young. Productivity averaged 1.27 young/occupied nest, suggesting a healthy population. Reproductive success differed significantly among nests at different water body types, with river-port, reservoir, and pond sites exhibiting high, moderate, and low productivity, respectively. Our results document a range expansion into central interior California, presumably in response to reduced pesticide levels, reservoir creation, and availability of anthropogenic nest sites. Results also suggest that drought, and thus predicted warming and drier climate, may disproportionately affect populations nesting at non-riverine habitats by reducing the amount foraging area and increasing the distance from nest sites to foraging areas.
{"title":"Habitat use and reproductive success of ospreys in central interior California","authors":"D. Airola, J. A. Estep","doi":"10.51492/cfwj.108.7","DOIUrl":"https://doi.org/10.51492/cfwj.108.7","url":null,"abstract":"The osprey (Pandion halieatus) declined globally in the mid-late 20th century due primarily to pesticide contamination that reduced reproduction. The species has recovered through much of its range, and its range in California has increased. The species has received limited attention in recent decades, despite recommendations that it be monitored as an environmental indicator. In 2021, we located a sample of 39 osprey occupied nests near the Sacramento River and at reservoirs and small ponds in central interior California and determined habitats used and reproductive success. Nearly one-third of nests were located within 100 m of waterbodies and 88% were within 1000 m. The median distance of nests from roads was 51 m. Thirty-four (87%) of occupied nests were on anthropogenic sites, including utility poles, poles erected for ospreys, transmission towers, light poles, and port structures. Only five nests (13%) were in trees and snags. Nearly half (48%) of nests were on platforms constructed on utility poles and on poles erected for ospreys, both placed to protect electrical systems. Water levels in reservoirs, and some small farm ponds, were lower than average in 2021 due to drought, while the Sacramento River and Port were less affected. Twenty-four (71%) of 34 adequately monitored nests were successful in fledging at least one young. Productivity averaged 1.27 young/occupied nest, suggesting a healthy population. Reproductive success differed significantly among nests at different water body types, with river-port, reservoir, and pond sites exhibiting high, moderate, and low productivity, respectively. Our results document a range expansion into central interior California, presumably in response to reduced pesticide levels, reservoir creation, and availability of anthropogenic nest sites. Results also suggest that drought, and thus predicted warming and drier climate, may disproportionately affect populations nesting at non-riverine habitats by reducing the amount foraging area and increasing the distance from nest sites to foraging areas.","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47237886","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"The current distribution and putative spread of the channeled apple snail in California","authors":"J. Alvarez, Barbara J. Alvarez","doi":"10.51492/cfwj.108.8","DOIUrl":"https://doi.org/10.51492/cfwj.108.8","url":null,"abstract":"","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44546276","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Microhabitat assessment of the Trinity bristle snail (Monadenia setosa), a state threatened species, was conducted at 88 randomly selected sites throughout its known geographic range in northern California. Nineteen abiotic and biotic environmental variables were measured for each site. Results of univariate and multivariate analyses indicate that sample sites were dominated by physical parameters of air and soil temperature, and elevation and exposure in association with habitat structure consisting of the presence, size, and nearness of large woody debris, rocky surface and subsurface structure, and riparian stream corridors, respectively. No individual or small suite of attributes defined microhabitat suitability for the species based on site-specific characteristics. Instead, a robust combination of physical and biological variables was key to the distribution of specimens at the population-level, most of which were allied with structural elements of the sample site.
{"title":"Microhabitat Characteristics and Management of the Trinity Bristle Snail in the Greater Trinity Basin of Northern California","authors":"R. M. Sullivan","doi":"10.51492/cfwj.108.3","DOIUrl":"https://doi.org/10.51492/cfwj.108.3","url":null,"abstract":"Microhabitat assessment of the Trinity bristle snail (Monadenia setosa), a state threatened species, was conducted at 88 randomly selected sites throughout its known geographic range in northern California. Nineteen abiotic and biotic environmental variables were measured for each site. Results of univariate and multivariate analyses indicate that sample sites were dominated by physical parameters of air and soil temperature, and elevation and exposure in association with habitat structure consisting of the presence, size, and nearness of large woody debris, rocky surface and subsurface structure, and riparian stream corridors, respectively. No individual or small suite of attributes defined microhabitat suitability for the species based on site-specific characteristics. Instead, a robust combination of physical and biological variables was key to the distribution of specimens at the population-level, most of which were allied with structural elements of the sample site.","PeriodicalId":29697,"journal":{"name":"California Fish and Wildlife Journal","volume":" ","pages":""},"PeriodicalIF":0.5,"publicationDate":"2022-05-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43628395","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
G. Ruiz-Campos, Mariana Solís-Mendoza,, Faustino Camarena-Rosales, A. Andreu-Soler, E. P. Pister, Iván A Meza-Matty
We assessed the population density and habitat selection of the southernmost rainbow trout subspecies, Oncorhynchus mykiss nelsoni, in three stream sites of the Sierra San Pedro Mártir, Baja California, Mexico. Habitat units (sections of the streams visually delimited on the basis of morphological and hydrological features) were sampled between February 2014 and April 2017, along a sample length of 2,980 m corresponding to 105 habitat units, which were classified into ten types. Mean population density (individuals/m2) was similar among the streams sampled (0.035–0.039/m2), as also over time for each stream, except for San Rafael Creek. Low gradient riffle was the habitat unit with the highest mean density of trout (0.151/m2). Of overall manner (dates and sites combined), population density was positively correlated to mean total length (TL), number of trout, and pH levels, and inversely correlated to total of dissolved solids. The total length of the trout was different among sample sites with the lowest and highest values in San Antonio de Murillo Creek and La Grulla Creek, respectively. Also, the total length of individuals among types of habitat units was different, with the highest values for MCP (mid-channel pool) and SRN (step run). Dates and sites pooled, the mean total length of individuals was positively correlated to population density, number of trout, habitat unit area, macrophyte cover, and inversely correlated to temperature. Low population densities (0.011–0.106/m2) combined with its small body size (38–216 mm TL) characterize this endemic trout in the southernmost part of species’ geographic range.
在墨西哥下加利福尼亚州塞拉圣佩德罗Mártir的三个河流站点，对最南端的虹鳟鱼亚种Oncorhynchus mykiss nelsoni的种群密度和生境选择进行了评估。2014年2月至2017年4月，选取了105个生境单元，样本长度为2980 m，共分为10种类型。生境单元是指根据形态和水文特征直观划分的河流断面。平均种群密度(个体/m2)在采样的河流之间相似(0.035-0.039 /m2)，随着时间的推移，除了圣拉斐尔河，每个河流也相似。低梯度沟是鳟鱼平均密度最高的生境单元(0.151只/m2)。总体而言，种群密度与平均总长度(TL)、鳟鱼数量和pH水平呈正相关，与溶解固体总量呈负相关。鳟鱼总长度在不同的采样点之间存在差异，最高值和最小值分别在San Antonio de Murillo Creek和La Grulla Creek。不同生境单元间的个体总长度也存在差异，以中槽池(MCP)和阶跃流(SRN)最大。结果表明，个体平均总长度与种群密度、鳟鱼数量、生境单位面积、植被覆盖度呈正相关，与温度呈负相关。低种群密度(0.011-0.106 /m2)和小体型(38-216 mm TL)是该物种地理分布范围最南端的地方性鳟鱼的特征。
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