@article{myers_engman_ramirez_torres-molinari_lynch_eaton_cooney_kwak_2024, title={The effects of flow extremes on native and non-native stream fishes in Puerto Rico}, volume={7}, ISSN={["1365-2427"]}, url={https://doi.org/10.1111/fwb.14306}, DOI={10.1111/fwb.14306}, abstractNote={Abstract Globally, freshwater fishes are among the taxa most vulnerable to climate change but are generally understudied in tropical island ecosystems where climate change is predicted to alter the intensity, frequency and duration of extreme flow events. These changes may impact stream ecosystems and native and non‐native biota in complex ways. We compiled an extensive dataset of fish assemblages collected at 119 sites across the Caribbean island of Puerto Rico from 2005 to 2015. We coupled these data with stream flow indices and dam height to understand associations between flow and fish assemblage structure. Sixteen percent of sites contained exclusively non‐native species, 34% contained exclusively native species, and 50% contained native and non‐native species. We built generalised linear models and conducted all subsets model selection to identify extreme flow variables explaining variation in native and non‐native species richness and biomass. We also built models to determine the combined effects of extreme flows and the presence of non‐native species on native species richness and biomass. Extreme flows and dam height were important in explaining variations in native and non‐native species richness and biomass. Model averages showed native biomass decreased by 0.42 kg/ha with a 1‐m increase in dam height, by 0.05 kg/ha with 1 cm/s increase in maximum mean daily high flow and by 3.45 kg/ha with each additional day increase in maximum high flow duration, and increased by 2.06 kg/ha with each additional day increase in mean high flow duration. Model averages predicted that non‐native biomass increased by 1.32 kg/ha with a 1‐m increase in dam height and by 0.01 kg/ha with each additional day increase in mean high flow duration, and decreased by 0.36 kg/ha with each additional day increase in maximum high flow duration. Model averages also predicted an increase in native and non‐native biomass of 0.71 gage and 0.06 kg/ha, respectively, with each additional day increase in maximum low flow duration. The combined effects of non‐native species presence and extreme flows changed the relationship between maximum high and low flow durations and native biomass. Model averages showed that native biomass increased by 1.83 kg/ha with each additional day increase in maximum high flow duration and decreased by 2.52 kg/ha with each additional day increase in maximum low flow duration when non‐native species were present. Native fishes may be able to better cope with longer maximum durations of low flows than expected when non‐native fishes are absent. In mixed fish assemblages, extended maximum durations of high flows may act as a control of non‐native species and dampen their negative effect on native species, but longer maximum durations of low flows may heighten the negative effects of non‐native fishes. Our results are informative for tropical island ecosystems globally and can guide the management and conservation of native fishes, particularly when faced with the dual threats of climate change and non‐native species. Managers may consider increasing efforts to conserve native fishes in Caribbean rivers by maintaining connectivity and habitat complexity while preventing non‐native species introductions.}, journal={FRESHWATER BIOLOGY}, author={Myers, Bonnie J. E. and Engman, Augustin C. and Ramirez, Alonso and Torres-Molinari, Ambar and Lynch, Abigail J. and Eaton, Mitchell J. and Cooney, Patrick B. and Kwak, Thomas J.}, year={2024}, month={Jul} }
 @article{torres-molinari_engman_pacifici_dolloff_myers_kwak_2023, title={Patterns in longitudinal distribution of American Eel (Anguilla rostrata) population characteristics in rivers of Puerto Rico}, volume={7}, ISSN={["1365-2400"]}, DOI={10.1111/fme.12645}, abstractNote={AbstractAmerican Eel (Anguilla rostrata) population characteristics and distribution remain drastically understudied in the Caribbean region. We conducted the first island‐wide study to evaluate the distribution of density, length, and sex in relation to distance from the mouth of 23 stream reaches in five rivers in Puerto Rico. We found 287 American Eel at a mean density of 156.7 fish/ha. Sex ratios favored females (52:3) but most of the eel sampled were undifferentiated or undetermined. Generalized linear modeling indicated that upstream habitats with low eel density were optimal environments for production of large and female eel. Our findings indicate that Puerto Rico could significantly contribute to the spawning population and strengthen knowledge of American Eel in the Caribbean. Our findings could be used to guide local and range‐wide conservation efforts to ensure stream connectivity and access to optimal upstream habitat for survival of the population.}, journal={FISHERIES MANAGEMENT AND ECOLOGY}, author={Torres-Molinari, A. and Engman, A. C. and Pacifici, K. and Dolloff, C. A. and Myers, B. J. E. and Kwak, T. J.}, year={2023}, month={Jul} }
 @article{engman_kwak_fischer_2021, title={Big runs of little fish: first estimates of run size and exploitation in an amphidromous postlarvae fishery}, volume={78}, ISSN={["1205-7533"]}, DOI={10.1139/cjfas-2020-0093}, abstractNote={ Amphidromous postlarvae fisheries (APFs) constitute a globally widespread and distinctive class of fishery that is largely unknown to fisheries science. APFs harvest ocean-to-river migrating fishes at smaller sizes and younger ages than any other class of fishery. No quantitative estimates of run size and exploitation exist, which are needed to evaluate APF sustainability. Migrating amphidromous fishes are vectors of marine nutrients to estuaries and rivers, and run size quantification is needed to reveal the magnitude of this ecosystem function. We present a novel adaptation of trapezoidal area under the curve methods, which we apply in a Caribbean case study to yield the first simultaneous estimates of an APF run size and harvest. Run size estimates ranged 7.3–9.4 million postlarvae (926–1184 kg), and exploitation estimates (5.8%–7.0%) indicated low harvest in the Río Grande de Arecibo, Puerto Rico. Our representative run size estimates reveal that amphidromous postlarvae transport hundreds of kilograms of biomass per month to an estuary and river, the first empirical evidence that amphidromous migrations are large-magnitude material subsidies of lotic ecosystems. }, number={7}, journal={CANADIAN JOURNAL OF FISHERIES AND AQUATIC SCIENCES}, author={Engman, Augustin C. and Kwak, Thomas J. and Fischer, Jesse R.}, year={2021}, month={Jul}, pages={905–912} }
 @article{lynch_thompson_beever_cole_engman_hoffman_jackson_krabbenhoft_lawrence_limpinsel_et al._2021, title={Managing for RADical ecosystem change: applying the Resist-Accept-Direct (RAD) framework}, ISSN={["1540-9309"]}, DOI={10.1002/fee.2377}, abstractNote={Ecosystem transformation involves the emergence of persistent ecological or social–ecological systems that diverge, dramatically and irreversibly, from prior ecosystem structure and function. Such transformations are occurring at increasing rates across the planet in response to changes in climate, land use, and other factors. Consequently, a dynamic view of ecosystem processes that accommodates rapid, irreversible change will be critical for effectively conserving fish, wildlife, and other natural resources, and maintaining ecosystem services. However, managing ecosystems toward states with novel structure and function is an inherently unpredictable and difficult task. Managers navigating ecosystem transformation can benefit from considering broader objectives, beyond a traditional focus on resisting ecosystem change, by also considering whether accepting inevitable change or directing it along some desirable pathway is more feasible (that is, practical and appropriate) under some circumstances (the RAD framework). By explicitly acknowledging transformation and implementing an iterative RAD approach, natural resource managers can be deliberate and strategic in addressing profound ecosystem change.}, journal={FRONTIERS IN ECOLOGY AND THE ENVIRONMENT}, author={Lynch, Abigail J. and Thompson, Laura M. and Beever, Erik A. and Cole, David N. and Engman, Augustin C. and Hoffman, Cat Hawkins and Jackson, Stephen T. and Krabbenhoft, Trevor J. and Lawrence, David J. and Limpinsel, Douglas and et al.}, year={2021}, month={Jul} }
 @article{engman_kwak_fischer_lilyestrom_2019, title={Fish Assemblages and Fisheries Resources in Puerto Rico's Riverine Estuaries}, volume={11}, ISSN={["1942-5120"]}, DOI={10.1002/mcf2.10072}, abstractNote={AbstractTropical estuaries are diverse and productive habitats with respect to their fish assemblages and associated fisheries, but these ecosystems and fisheries are imperiled by multiple anthropogenic threats. Despite the economic, social, and biodiversity value of tropical estuarine fish assemblages, they are poorly understood, especially those on Caribbean islands. We sampled the fish assemblages of four estuaries that were broadly representative of riverine estuaries in Puerto Rico, including the Río Grande de Arecibo, Río Espiritu Santo, Río Mameyes, and Río Sabana. We used a combination of passive (gill nets) and active (seine) gears at locations that spanned the salinity gradient of each estuary during July–October 2013–2014 (rainy season) and March 2015 (dry season). Fish species richness among the riverine estuaries varied from 18 to 29 and was highest in the Río Espiritu Santo estuary. Nonmetric multidimensional scaling differentiated fish assemblages among estuaries but not by season or consistently by location within an estuary. Spearman's rank correlation analysis also revealed dissimilarity among each estuary's fish assemblage, as most pairwise correlations between the species compositions were not significant. We identified common and widespread species among estuaries, including sport fishes, such as the Tarpon Megalops atlanticus and Common Snook Centropomus undecimalis. As the only multi‐river assessment of riverine estuary fish assemblages in Puerto Rico, our results provide the best available information about the spatial variability of assemblages and fisheries resources. This information will benefit future conservation and fisheries management efforts, which are needed due to increasing anthropogenic impacts, such as illegal harvest, invasive species, and water diversions.}, number={2}, journal={MARINE AND COASTAL FISHERIES}, author={Engman, Augustin C. and Kwak, Thomas J. and Fischer, Jesse R. and Lilyestrom, Craig G.}, year={2019}, month={Apr}, pages={189–201} }
 @article{engman_hogue_starnes_raley_kwak_2019, title={Puerto Rico Sicydium goby diversity: species-specific insights on population structures and distributions}, volume={5}, ISSN={["2376-6808"]}, DOI={10.1080/23766808.2019.1606669}, abstractNote={ABSTRACT Sicydiine gobies are major contributors to Caribbean stream fish biodiversity, and ecosystem functions and services. In the Caribbean, Sicydiine gobies are represented by a single genus, Sicydium, but species-level Sicydium taxonomy and distributions remain unresolved in this region. A previous study posited that four species of Sicydium are present in Puerto Rico, including the recently described Sicydium gilberti; however, that study relied solely on morphological characters, and samples from a limited number of locations. Identification of Sicydium to species in studies with more comprehensive sampling has not occurred due to the impracticality of field identification. In our study, we employed morphological data and Mitochondrial Cytochrome C Oxidase I (mtCOI) genetic sequence data, collected from over 500 Sicydium spp. individuals at 16 broadly distributed sites, to provide an inventory of the species of Sicydium that occur in Puerto Rico. Additionally, we reveal new information on the spatial patterns of distribution, relative abundance, population structure, and observed molecular diversity among Sicydium taxa in Puerto Rico’s river systems. This information is essential to advance ecological and evolutionary knowledge of Caribbean fish assemblages, guide stream fish conservation, and to effectively manage fisheries.}, number={1}, journal={NEOTROPICAL BIODIVERSITY}, author={Engman, Augustin C. and Hogue, Gabriela M. and Starnes, Wayne C. and Raley, Morgan E. and Kwak, Thomas J.}, year={2019}, month={Apr}, pages={22–29} }
 @article{engman_kwak_cope_2018, title={Do postlarval amphidromous fishes transport marine-derived nutrients and pollutants to Caribbean streams?}, volume={27}, url={https://doi.org/10.1111/eff.12397}, DOI={10.1111/eff.12397}, abstractNote={AbstractDiadromous fishes are known biotransport vectors that can move nutrients, energy and contaminants in an upstream direction in lotic ecosystems. This function has been demonstrated repeatedly in anadromous salmonids, but the role of other diadromous species, especially tropical taxa, as biotransport vectors is less studied. Amphidromous fish species exhibit potential to act as upstream vectors of nutrients and contaminants in their postlarval and juvenile stages, but this role is largely unknown because of limited understanding of larval growth habitats. Moreover, because some species are harvested in artisanal fisheries as postlarvae, and postlarvae are consumed by riverine and estuarine predators, heavy contaminant loads may present a human or wildlife health concern. This research incorporates stable isotope and contaminant analyses to infer larval habitats and contaminant accumulation of amphidromous fishes on the Caribbean island of Puerto Rico. The isotopic signatures of postlarval amphidromous fishes indicated marine basal sources and food web components, rather than those from riverine habitats. Additionally, postlarvae did not contain concentrations of anthropogenic pollutants that would be of ecological or human health concern. These findings are the first and strongest evidence that amphidromous fish postlarvae function as biotransport vectors of marine nutrients into and up river ecosystems without posing a health threat to the receiving food web or human consumers.}, number={3}, journal={Ecology of Freshwater Fish}, publisher={Wiley}, author={Engman, A. C. and Kwak, T. J. and Cope, W. G.}, year={2018}, month={Jul}, pages={847–856} }
 @article{ramírez_gutiérrez-fonseca_kelly_engman_wagner_rosas_rodríguez_2018, title={Drought Facilitates Species Invasions in an Urban Stream: Results From a Long-Term Study of Tropical Island Fish Assemblage Structure}, volume={6}, ISSN={2296-701X}, url={http://dx.doi.org/10.3389/fevo.2018.00115}, DOI={10.3389/fevo.2018.00115}, abstractNote={The natural flow regime is a key regulator of the dynamics of stream communities and ecosystem processes. Native fish assemblages are evolutionarily adapted to their local flow regime. In the Caribbean, streams are vulnerable to changes in climate that will alter their flow regimes. We assessed long-term patterns in fish assemblages (2008-2016) in an urban stream in San Juan, Puerto Rico. We hypothesized that drought periods would result in negative effects on native fish species and positive effects on introduced species. Fish assemblages were sampled annually from 2008 to 2016 by backpack electrofishing, with additional sampling during 2015, which was a drought year. Cumulative dry season discharge was consistently over 300 m3/s from 2008 to 2013, except from 2014 to 2016 when it dropped below 170 m3/s. Thirteen species were found, including most native species reported for Puerto Rico and introduced species (e.g., Cichlids, Poeciliids, and Loracariids). Native species were dominant in abundance during most years, except during drought and post-drought sampling events when introduced species became dominant. Introduced species increased in richness with time from less than two species between 2008 and 2013 to seven in 2015. The increase in introduced species was mostly attributed to the appearance of several species of cichlids towards the end of the study. Cluster analysis divided the data set in two groups: drought and non-drought sampling events. Introduced cichlids and the native A. monticola accounted for more than 60% of assemblage dissimilarity. Fish assemblage abundance and richness were negatively related to several components of stream hydrology (e.g., cumulative daily stream discharge, the number of major floods). A significant change in size over time was found for the native A. monticola, which decreased in size during the drought period. Overall, our study documents drought-facilitated invasions by several aggressive and highly ecologically competitive species, highlights the importance of the natural flow regime as a source of environmental resilience to invasions in tropical island streams, and provides an example of how climate change has and will likely continue to alter Caribbean stream fish assemblages.}, number={AUG}, journal={Frontiers in Ecology and Evolution}, publisher={Frontiers Media SA}, author={Ramírez, Alonso and Gutiérrez-Fonseca, Pablo E. and Kelly, Sean P. and Engman, Augustin C. and Wagner, Karleen and Rosas, Keysa G. and Rodríguez, Natalia}, year={2018}, month={Aug} }
 @article{kwak_engman_lilyestrom_2019, title={Ecology and conservation of the American eel in the Caribbean region}, volume={26}, ISSN={["1365-2400"]}, DOI={10.1111/fme.12300}, abstractNote={AbstractThe majority of American eel, Anguilla rostrata LeSueur, knowledge is derived from temperate regions in the United States and Canada, with little known from its tropical Caribbean distribution. Findings of original research on American eel distribution, abundance, population biology, habitat ecology and threats from the Caribbean island of Puerto Rico were synthesised. American eel were captured from 48 of 116 sites (41.4%) in 26 of 49 river basins (53.1%) during 2005–2016, and it was extirpated upstream of dams and migration barriers >3.0 m high (38.9% of habitat). Mean density and biomass were 438.9 fish/ha and 23.44 kg/ha, respectively. Upstream habitats favoured larger individuals, and females were larger than males. The swim‐bladder parasite Anguillicoloides crassus Kuwahara, Niimi & Hagaki was not found in 120 eels examined. Realised threats include dams and other migratory barriers, habitat loss and alteration and pollution; exotic species and commercial fishing are impending threats; and the least understood is climate change.}, number={1}, journal={FISHERIES MANAGEMENT AND ECOLOGY}, author={Kwak, Thomas J. and Engman, Augustin C. and Lilyestrom, Craig G.}, year={2019}, month={Feb}, pages={42–52} }
 @article{collazo_terando_engman_fackler_kwak_2019, title={Toward a Resilience-Based Conservation Strategy for Wetlands in Puerto Rico: Meeting Challenges Posed by Environmental Change}, volume={39}, ISSN={["1943-6246"]}, url={https://doi.org/10.1007/s13157-018-1080-z}, DOI={10.1007/s13157-018-1080-z}, number={6}, journal={WETLANDS}, publisher={Springer Science and Business Media LLC}, author={Collazo, Jaime A. and Terando, Adam J. and Engman, Augustin C. and Fackler, Paul F. and Kwak, Thomas J.}, year={2019}, month={Dec}, pages={1255–1269} }
 @article{engman_kwak_fischer_2017, title={Recruitment phenology and pelagic larval duration in Caribbean amphidromous fishes}, volume={36}, ISSN={["2161-9565"]}, DOI={10.1086/694176}, abstractNote={Amphidromous fishes are major components of oceanic tropical island stream ecosystems, such as those of the Caribbean island, Puerto Rico. Fishes with this life history face threats related to the requirement for connectivity between freshwater and marine environments during early life stages. Pelagic larval duration and recruitment phenology are 2 early life-history processes that are crucial for the biology, ecology, conservation, and management of amphidromous fishes. However, these processes are understudied in the Caribbean in general and have never been quantified in Puerto Rico. We quantified recruit abundance, recruitment phenology, and pelagic larval duration of several Caribbean amphidromous fish species in multiple rivers in Puerto Rico and explored the effects of environmental variables on recruit abundances. Two fish taxa—sirajo goby (Sicydium spp.) and River Goby (Awaous banana)—were exceptionally abundant as postlarvae and recruited to Caribbean rivers in pulsed migration episodes that were periodic at annual and lunar scales. Sirajo goby and River Goby recruit abundances varied among rivers, were greater at sunrise than at sunset, and were positively related to river discharge. The pelagic larval duration of 4 fish taxa ranged from a minimum of 28 d to a maximum of 103 d with means between 43 ± 7 d (SD) and 65 ± 11 d. We identified the last-quarter moon phase during the months of June through January as periods of maximum amphidromous fish recruitment to freshwater streams. The results and conclusions of our study can be applied to identify critical times to maintain river–ocean connectivity and stream flow for the benefit of the amphidromous fish population dynamics, stream ecology, and natural resources of the Caribbean.}, number={4}, journal={FRESHWATER SCIENCE}, author={Engman, Augustin C. and Kwak, Thomas J. and Fischer, Jesse R.}, year={2017}, month={Dec}, pages={851–865} }
 @inproceedings{kwak_engman_fischer_lilyestrom_2016, title={Drivers of Caribbean freshwater ecosystems and fisheries}, booktitle={Freshwater, Fish and the Future: Proceedings of the Global Cross-Sectoral Conference}, author={Kwak, T. J. and Engman, A. C. and Fischer, J. R. and Lilyestrom, C. G.}, year={2016}, pages={219–232} }