California Department of Fish and Wildlife

Abstract Catch inequality—the disproportionate distribution of catch across anglers— is a fundamental but overlooked driver of recreational fisheries dynamics. Here, we use 11 years (2012-2022) of compulsory angler report cards to characterize long-term catch dynamics in the specialized recreational steelhead ( Oncorhynchus mykiss ) fishery in California, U.S.A. Spatialized catch data reveal the fishery is principally supported by wild fish, despite evidence of widespread hatchery straying. California steelhead appear to represent the most catch-unequal recreational fishery studied yet, exhibiting a statewide Gini coefficient of 0.81. Across basins, inequality varies substantially but remains relatively stable over time and flow conditions; high inequality is primarily driven by significant proportions of zero-catch anglers. We find the relationship between sample size and inequality measures is especially influential in fisheries data. Hence, we develop a three-prong approach for identifying minimal sample sizes required for robust Gini estimation. Across basins and years, an average minimum of 77 report cards were required for the present fishery. Collectively, these findings demonstrate the necessity of considering catch inequality in fisheries management, particularly when utilizing angler data. Graphical Abstract N.a.

Abstract Consumptive use of freshwater is of concern in many estuarine ecosystems, and various frameworks have been used to prescribe environmental flows to benefit native species. However, few of these frameworks explicitly examine the potential trade‐offs between socioeconomic and conservation‐oriented values. This is exemplified in California, USA, where freshwater management has been an area of focus and controversy. Operations of numerous reservoirs and water diversion facilities distributed throughout the state, while critical for economic and public health benefits, have contributed to the decline of many native species. The endangered delta smelt ( Hypomesus transpacificus ) is endemic to the Sacramento‐San Joaquin Delta, the heart of California's complex water conveyance system. To aid recovery of delta smelt, fall‐timed freshwater pulse flows were implemented, which require water to be either released from reservoirs, or made unavailable to export for consumptive uses. Previous research has indicated that the effectiveness of the current pulse flow action could be improved by reconsidering the timing and magnitude; however, uncertainties in the predicted fish response to flow pulses may hinder decision‐making about flow management. Using a water resource planning model, different iterations of an individual‐based life cycle model, and decision analysis tools, we assessed the importance of sources of uncertainty to hypothetical flow management decisions, including uncertainty surrounding the predicted responses in delta smelt population growth rates, and variability of decision‐maker's values. We found both the choice of which (if any) flow action to take for delta smelt, and the expected value of further research, depended on how decision‐makers weight the delta smelt and water supply objectives. There was expected value of information (VOI) only if a decision‐maker weighted the delta smelt objective ≥0.59, and within this range, research to improve estimates of changes in delta smelt prey items related to flow actions could be prioritized over other sources of uncertainty to improve outcomes of decision‐making. Our study demonstrates how uncertainty, even if large, may not be equally relevant to different decision‐makers (e.g., with different agency missions), and how VOI analysis can be used to guide management in an overallocated water system such as California.

Disease can threaten endangered species by affecting fitness and survival, suppressing population growth and species recovery. Herein, we investigated three gastrointestinal pathogens-Giardia, Cryptosporidium, and Helicobacter-that could negatively affect the endangered Amargosa vole (Microtus californicus scirpensis). We used PCR testing to determine the presence of the target parasites in 76 fecal samples from 71 Amargosa voles collected during summer 2021 in four marshes in Tecopa, California, USA. Overall, 51 (72%) of 71 voles were PCR positive for Giardia microti, 48 (68%) of 71 for Cryptosporidium spp., and 100% for Helicobacter spp. There were no significant associations between G. microti infection and sex, body condition score, or source marsh. Cryptosporidium sp. infection was significantly more prevalent in smaller marshes. More than half of the individuals sampled (39/71, 55%) were PCR positive for both Giardia and Cryptosporidium spp. upon initial sampling. This study provides foundational information regarding environmentally transmitted parasites in populations of Amargosa voles. Further studies are needed to understand and manage the adverse effects of disease and other threats for the survival of the Amargosa vole.

Climate change mitigation and biodiversity loss are closely linked challenges, yet agricultural strategies often address them separately. Focusing on rice farming, this article shows that widely promoted water-saving practices can reduce greenhouse gas emissions but may also harm freshwater biodiversity that depends on flooded fields. We highlight alternative management approaches and the need for spatially and seasonally targeted strategies that balance climate goals, biodiversity conservation, and food production.

ABSTRACTAccurate information underpins successful ecological science and management. Cryptic species, those that are difficult to differentiate, pose challenges to reliable collection of taxon‐specific information. Blackbirds, including tricolored blackbirds (Agelaius tricolor), a cryptic species of high conservation concern, and red‐winged blackbirds (Agelaius phoeniceus), an abundant congener, are sometimes killed by wind turbines. We used publicly available survey records to evaluate rates at which blackbirds were reported dead at wind energy facilities in California, USA. We then used genetic species identification of carcasses found to estimate true rates of discovery and of misidentification. Of 329 blackbird fatalities in survey records, most were identified as red‐winged (n = 149), “unidentified” (n = 90), or Brewer's (Euphagus cyanocephalus; n = 70); only 13 were identified as tricolored. We also genetically analyzed samples from 40 blackbirds. Of 14 carcasses identified in the field to species, two, including one tricolored, were incorrectly called Brewer's blackbirds (14% misidentification rate). Of the 26 birds called “unidentified blackbird” in the field, 17 (65%) were tricolored, leading to a 19× underestimation of true fatality rate. The state‐wide population of tricolored blackbirds is < 1% the size of that of red‐winged blackbirds. A large proportion of blackbirds found dead were actually tricoloreds, indicating that fatality rates of this state threatened species may be substantially underestimated. The potential for misidentification or nonidentification may create perverse incentives that undermine conservation and have consequences for on‐the‐ground management, mitigation, and operations of high‐priority infrastructure.

The protozoal parasites Sarcocystis neurona and Toxoplasma gondii are important causes of mortality for threatened southern sea otters (Enhydra lutris nereis) in California. Sarcocystis neurona causes more sea otter deaths than T. gondii and has caused two mortality events, yet S. neurona is comparatively understudied. Little is known about the role of parasite genotype on the outcome of infection (fatal versus non-fatal) for S. neurona-infected sea otters. The objective of this study was to evaluate the effect of parasite genotype in addition to host and environmental factors (animal age, sex, location, and season of stranding) on disease outcome in S. neurona-infected sea otters. A multilocus sequence typing (MLST) approach was used to characterize the S. neurona genotype in fatal (n = 92) and non-fatal (n = 33) sea otter infections. In the northern study region, the IIg/j genotype was more likely to result in fatal infections. In the southern study region, the Ia and Ib/c/d/gg genotypes were the dominant genotypes implicated in fatal infections and were responsible for mortality events that occurred in 2004 (Ib/c/d/gg) and 2021 (Ia). Subadult sea otters were more likely to die from S. neurona than adults. Stranding during the California wet season during peak rainfall events that facilitate land-to-sea flow of infective sporocysts may also play a role in fatal infection outcomes. These findings suggest that parasite genotype, as well as certain host and environmental factors, all contribute to disease outcome following S. neurona infection in southern sea otters.

Human‐induced habitat fragmentation threatens connectivity for populations of wide‐ranging species by compromising long‐distance dispersal. We evaluated movement‐based resource selection of dispersing mountain lions ( Puma concolor ) to identify specific landscape conditions influencing movement decisions and connectivity between populations across the US state of California. Our results elucidate how anthropogenic features inhibit dispersal at the statewide scale, as mountain lions avoided development more strongly as both the area of and building density within developed patches increased. Furthermore, dispersing mountain lions strongly avoided crossing roadways but exhibited relaxed avoidance in areas where vegetative cover was present on both sides of the road. Importantly, mountain lions selected even relatively small patches of natural habitat, which may function as stepping‐stones promoting movement through otherwise unsuitable habitat. We provide empirical evidence linking genetic structure suggestive of reduced connectivity to underlying behavioral mechanisms. Understanding behavior during dispersal is fundamental to conserving connectivity between and viability of populations persisting within fragmented landscapes—and to facilitate recolonization of historical ranges.

ABSTRACTNutria (Myocastor coypus) are semi‐aquatic rodents native to South America, introduced to the USA for fur farming during the early twentieth century. This species' herbivory can cause extensive damage to agriculture and wetland ecosystems. Though declared eradicated from California, USA, in the 1970s, nutria populations were recently discovered in the state's Central Valley and subsequently the Sacramento–San Joaquin Delta, areas of agricultural and conservation significance. We report the use of a combination of nuclear single nucleotide polymorphisms (SNPs) and mitochondrial (mtDNA; cytochrome b locus) markers to characterize the source and demographic history of the current invasion, with the goal of informing eradication efforts. Our study is the first to develop a SNP dataset for nutria, utilizing 6809 loci to characterize genetic diversity in comparison to several potential source populations. Multivariate analysis and Bayesian clustering of the SNP dataset found the greatest similarity to invasive nutria in central Oregon, USA, with minimal genetic differentiation in the Central Valley excluding the leading edges of the invasion. Cytochrome b sequencing resulted in a single contemporary California haplotype shared with nutria in Oregon and Washington but also detected in museum samples from California fur farms predating eradication. Mantel tests found genetic differentiation among nutria in the Central Valley was best explained by ecological distance along rivers, while estimated effective migration surface (eems) analysis indicated gene flow was characterized by infrequent dispersal followed by rapid expansion in large, protected areas of emergent wetland habitat. These combined findings suggest contemporary California nutria represent a recent introduction that underwent rapid expansion. Our data further support treating the Central Valley as a single eradication unit while investing additional resources in targeting dispersal corridors to best achieve management goals. This study presents the first characterization of a regional nutria invasion within the larger context of global population and phylogenetics.

Many North American game animals experienced severe population declines during the 19th century due to market hunting. However, estimates of the timing and magnitude of these declines often rely on anecdotal evidence, which makes it difficult to understand the lasting impacts of hunting pressures versus climate or landscape changes on the genetic diversity of contemporary populations. Historical reports suggest the California quail (Callipepla californica) suffered more significant hunting pressure in the late 19th century relative to either Gambel's (Callipepla gambelii) or mountain quail (Oreortyx pictus). Genomic data can help illuminate the extent to which historical exploitation moulded the genetic health of modern quail populations. We compared whole genome sequences from these three quail species to evaluate whether reported differences in hunting pressure affected contemporary patterns of genetic diversity. Contrary to our expectations, California quail did not exhibit any evidence for population declines until the late 20th century, long after the era of market hunting ended. California quail also exhibited the highest levels of genetic diversity across most analyses with evidence for population expansion over the past 500,000 years. In contrast, the mountain quail exhibited a long-term population decline beginning in the middle of the last ice age 30-40 thousand years ago. The Gambel's quail appears to have suffered a more recent bottleneck in association with a major drought that impacted the desert southwest during the mid-20th century. Gambel's quail also exhibited increased realised genetic load for mild and moderately deleterious genetic variants. Together, our results demonstrate that market hunting had little lasting impact on the genetic diversity of these quail species, whereas landscape and climate changes have led to fluctuations in effective population size (Ne) and the buildup of genetic load.