Nearshore Habitats Research Articles

Particle trajectories in an eastern boundary current using a regional ocean model at two horizontal resolutions

Lagrangian particle tracking (LPT) models are used to study the transport and dispersal of marine organisms. In LPT studies, the accuracy of the circulation is essential for nearshore habitats of Eastern Boundary Current (EBC) regions that are areas of high productivity and economically important fisheries. We used the California Current System as an example of an EBC region, specifically the Oregon coast located in the northern California Current System because it has distinct upwelling and downwelling regimes and variable shelf width. More specifically, we developed and applied a LPT model to compare and contrast particle drift patterns during the spring transition as it is an important period for spawning. We contrasted years (2016–18) using Regional Ocean Modeling System (ROMS) with different horizontal spatial resolutions (2 km, 250 m). Lagrangian particles experience stronger downward velocities and displacements to greater depths in the 250 m ROMS simulations that used a finer resolution bathymetry. Consequently, retention along the Oregon coast increases in the 250 m ROMS compared to the 2 km ROMS. After 10 days, 37%–83% of particles forced with the 2 km ROMS remain in the model domain, compared to 61%–86% of particles remaining when using the 250 m ROMS. Particles in the 250 m ROMS are advected to depth at specific times and locations for each simulated year, coinciding with the location and timing of a strong and shallow alongshore undercurrent that is not present in the 2 km ROMS. Additionally, ageostrophic dynamics close to shore, in the bottom boundary layer, and around headlands emerge in the 250 m resolution model, while they are at best poorly resolved in the 2 km resolution case. We conclude that the higher horizontal model resolution and bathymetry used in the 250 m ROMS generates well-resolved mesoscale and submesoscale features (e.g., surface, subsurface, and nearshore jet) that vary annually. These physical features are significantly different than those modeled by the 2 km model and may be responsible for these differences in particle dispersal. These results have implications for modeling the dispersal, growth, and development of coastal organisms with dispersing early life stages. • We compare ROMS of different horizontal resolutions in particle tracking models. • The higher resolution ROMS (250 m) better resolves mesoscale and submesoscale features. • The resolved mesoscale and submesoscale features may be due to higher resolution and bathymetry. • An increase in particle retention is linked to more resolved mesoscale features.

Habitat preferences of young-of-year spotted gar (Lepisosteus oculatus) in Rondeau Bay, Lake Erie

The young-of-year (YOY) habitat of many fishes listed under the Species at Risk Act (SARA) is poorly described, yet identifying critical habitat is essential to ensure species recovery. Past research on the Endangered spotted gar ( Lepisosteus oculatus Winchell, 1864) in Canada has focused on the habitat use of adults and juveniles, but little is known about the occurrence and habitat use of YOY. Dip net and aquatic habitat sampling were performed in nearshore (lakefront, agricultural drain), mid-channel (agricultural drain), and offshore sites within Rondeau Bay to determine the fine-scale habitat occupancy patterns of age-0 spotted gar. Habitat preference analysis indicated YOY spotted gar strongly preferred shallow (0.5–1.0 m), vegetated, nearshore (lakefront and agricultural drain) habitat and avoided offshore habitat. An association between submerged aquatic vegetation (SAV) and fish size was also found, as dependence on SAV diminished as total length increased. Our study represents the first capture and assessment of habitat associations of early-stage YOY spotted gar in Canada. Given our findings, management efforts should focus on protecting the vegetated nearshore habitat in Rondeau Bay and other occupied locations in Lake Erie to ensure the long-term persistence of spotted gar in Canada.

Plasticity in the morphometrics and movements of an Antarctic apex predator, the leopard seal

Animals that display plasticity in behavioral, ecological, and morphological traits are better poised to cope with environmental disturbances. Here, we examined individual plasticity and intraspecific variation in the morphometrics, movement patterns, and dive behavior of an enigmatic apex predator, the leopard seal (Hydrurga leptonyx). Satellite/GPS tags and time-depth recorders were deployed on 22 leopard seals off the Western Antarctic Peninsula. Adult female leopard seals were significantly larger (454±59 kg) and longer (302±11 cm) than adult males (302±22 kg, 276±11 cm). As females were 50% larger than their male counterparts, leopard seals are therefore one of the most extreme examples of female-biased sexual size dimorphism in marine mammals. Female leopard seals also spent more time hauled-out on land and ice than males. In the austral spring/summer, three adult female leopard seals hauled-out on ice for 10+ days, which likely represent the first satellite tracks of parturition and lactation for the species. While we found sex-based differences in morphometrics and haul-out durations, other variables, including maximum distance traveled and dive parameters, did not vary by sex. Regardless of sex, some leopard seals remained in near-shore habitats, traveling less than 50 kilometers, while other leopard seals traveled up to 1,700 kilometers away from the tagging location. Overall, leopard seals were short (3.0±0.7 min) and shallow (29±8 m) divers. However, within this general pattern, some individual leopard seals primarily used short, shallow dives, while others switched between short, shallow dives and long, deep dives. We also recorded the single deepest and longest dive made by any leopard seal—1, 256 meters for 25 minutes. Together, our results showcased high plasticity among leopard seals tagged in a single location. These flexible behaviors and traits may offer leopard seals, an ice-associated apex predator, resilience to the rapidly changing Southern Ocean.

Seventy years of food-web change in South Bay, Lake Huron

Though aquatic ecosystems (and the Laurentian Great Lakes in particular) have faced many stressors over the past century, including fisheries collapses and species invasions, rarely are data available to evaluate the long-term impacts of these stressors on food web structure. Stable isotopes of fish scales from the 1940s to the 2010s in South Bay, Lake Huron were used to quantify trophic position and resource utilization for fishes from offshore (alewife, cisco, lake trout, lake whitefish, rainbow smelt) and nearshore (rock bass, smallmouth bass, white sucker, yellow perch) habitats, providing one of the longest continuous characterizations of food webs in the Laurentian Great Lakes. Mean δ15N and δ13C values for each species were compared across twenty-year time periods. Using directional statistics, no significant community-wide changes were detected between time periods from 1947 to 1999. In contrast, a significant change was detected between 1980-1999 and 2000–2017, with all species showing increased reliance on nearshore resources. The increase in nearshore resource reliance for lake whitefish between these time periods was the greatest in magnitude compared with any other species between any two adjacent time periods. Besides lake whitefish, the increased reliance on nearshore resources was more pronounced for nearshore compared to offshore species. The timing of these shifts coincided with the invasion of dreissenid mussels and round goby, and declines in offshore productivity and prey densities. These results show the unprecedented magnitude of recent food-web change in Lake Huron after 50 years of relative stability.

Spatial and Temporal Distribution and Habitat Selection of Native Yellowstone Cutthroat Trout and Nonnative Utah Chub

AbstractHenrys Lake, Idaho, is a renowned trophy trout fishery that faces an uncertain future following the establishment of Utah Chub (UTC) Gila atraria. Utah Chub were first documented in the lake in 1993 and have become abundant over the past two decades. Little is known about the ecology of UTC, but they typically have negative effects on salmonids in systems where they have been introduced. We sought to fill knowledge gaps in UTC ecology and provide insight on potential interactions with Yellowstone Cutthroat Trout (YCT) Oncorhynchus clarkii bouvieri. Ninety‐four YCT and 95 UTC were radio‐tagged in spring 2019 and 2020 to better understand potential interactions between YCT and UTC in Henrys Lake. Fish were located via mobile tracking and fixed receivers from June to December 2019 and 2020. In June of both years, YCT and UTC were concentrated in nearshore habitats. As water temperatures increased, UTC were documented in deeper water (mean ± SD = 3.6 ± 1.4 m) and YCT became more concentrated in areas with cold water (e.g., mouths of tributaries, in‐lake springs). In July and August, large congregations of UTC were observed. Yellowstone Cutthroat Trout were detected in tributaries from June to August, but no UTC were detected in the tributaries. By late fall (November–December), YCT were located along the shoreline and UTC were detected in the middle of the lake. Both YCT and UTC were observed in areas with dense vegetation. Macrophytes likely provided a food source for UTC and cover from predators for both species. Locations of YCT were negatively related to warm water temperatures, whereas UTC were positively associated with warm water temperatures. Results from this research fill knowledge gaps in UTC and YCT interactions as well as provide valuable insight on the ecology of UTC and adfluvial Cutthroat Trout populations. Furthermore, distribution patterns and habitat selectivity of YCT and UTC in Henrys Lake can be used to inform management decisions for fishery improvement and YCT conservation.

Hammer it out: shifts in habitat are associated with changes in fin and body shape in the scalloped hammerhead (Sphyrna lewini)

Abstract Major shifts in habitat often occur during life history and can have significant impacts on the morphology and function of an animal; however, little is known about how such ecological changes influence the locomotor system of large aquatic vertebrates. Scalloped hammerheads (Sphyrna lewini) are large sharks found in warm temperate and tropical waters. Smaller scalloped hammerheads are generally found in near-shore habitats, but as they grow larger, individuals spend time in deep-water, pelagic habitats. We measured a number of morphological traits of scalloped hammerheads, ranging from 32 to 130 cm, to determine whether there are allometric changes in morphology in association with this shift in habitat. We found that head morphology, caudal fin area and lateral span scaled with negative allometry, whereas the lengths of their pectoral, dorsal and caudal fins, and their pectoral and caudal fin aspect ratios, scaled with positive allometry. Furthermore, the largest shark in our dataset exhibited an optimal body fineness ratio for locomotor efficiency. This suggests that the changes in ecology have profound influences on the functional morphology of scalloped hammerheads. We discuss how these drastic morphological changes relate to potential changes in scalloped hammerhead swimming function and performance.

Over, Under, Sideways and Down: Patterns of Marine Species Richness in Nearshore Habitats off Santa Catalina Island, California

Santa Catalina Island, located off the southern California coast, is home to the Blue Cavern Onshore State Marine Conservation Area (SMCA), which is recognized as a marine protected area. Here, we provide an updated species inventory of nearshore macroalgae, seagrasses, bony and cartilaginous fishes and invertebrates documented inside the Blue Cavern Onshore SMCA. Species richness data were compiled using scuba-based visual surveys conducted in the field, references from the primary and gray literature, museum records, unpublished species lists and online resources. The current checklist consists of 1091 marine species from 18 different taxonomic groups, which represents an ~43% increase in species diversity compared to the value reported previously. These data are indicative of the high biodiversity known from the Southern California Bight (SCB) region. The total number of intertidal and subtidal taxa reported represent approximately 85% and 45% of the documented macroalgae and plants, 41% and 24% invertebrates, and 62% and 20% of fishes from Catalina Island and the SCB, respectively. Among the marine taxa documented, 39 species either have undergone a geographic range shift or were introduced as the result of human activities, while another 4 species are listed as threatened, endangered or critically endangered. Research findings presented here offer an important baseline of species richness in the California Channel Islands and will help improve the efforts by resource managers and policy makers to conserve and manage similar habitats in the coastal waters off southern California.

Estimating Walleye and Saugeye Gill‐Net Encounter Probability in a Reservoir with Simple Morphometry

AbstractProper interpretation of gill‐net survey data requires knowledge of gill‐net encounter probabilities for target species, including understanding how variation in habitat use and movement rate affects encounter probability. However, few estimates of encounter probability exist. Further, previous studies have hypothesized that gill‐net encounter probability is proportional to swimming speed, which increases with fish size. However, potential swimming speed may not be reflective of movement rates and encounter probability due to species‐specific biology and behaviors. I used a large telemetry data set consisting of 483,169 fine‐scale positions (<5‐m resolution) of Walleye Sander vitreus and saugeye (Walleye × Sauger S. canadensis) to simulate daily North American standard gill‐net surveys. I tagged and tracked 42 fish (340–614 mm) during both 2013 and 2014 and determined whether each fish position from April to November was within 24.8 m of shore (the length of the North American standard net). I also determined fish movement rate (m/h) during simulated gill‐net surveys and whether each fish track during each survey crossed 24.8‐m “virtual” gill nets. I then used Bayesian multi‐level models to evaluate how nearshore habitat use, movement rate, and gill‐net encounter probability varied with fish length, species, and month. Movement rate (m/h) and gill‐net encounter probability were greatest for both Walleye and saugeye during April, May, and June, but neither movement rate nor encounter probability increased with fish length during most months. Walleye used nearshore habitats less frequently than saugeye, especially during September and November, resulting in lower gill‐net encounter probabilities for Walleye. These results show that gill‐net encounter probability varies across species, months, and occasionally fish lengths due to variation in both habitat use and movement rate. These outcomes also indicate that total gill‐net selectivity may change throughout the year due to changes in the relationship between fish length and gill‐net encounter probability.

Species composition, distribution and relative abundance of the inshore fish community off the Argentine Islands, Bellingshausen Sea

In the last three decades, several interdisciplinary studies investigated the marine ecosystems off the West Antarctic Peninsula (WAP), one of the most impacted areas of the Southern Ocean by the global warming. Although the extent of near-shore habitats along the WAP is wider than elsewhere in Antarctica, the coastal fish communities have been rarely studied. Complementing these previous studies, we provide new data on the species composition, population structure and relative abundance of the inshore fish community living off the Argentine Islands (Bellingshausen Sea). Fish samples were caught all the year round during four different periods spread over ten years (from 2006 to 2017). The fish fauna consisted of fourteen high-Antarctic and low-Antarctic species of notothenioids, most of them belonging to the Nototheniidae. Notothenia coriiceps was by far the most abundant species, followed in decreasing abundance by Chaenocephalus aceratus, Notothenia rossii, Trematomus newnesi and Trematomus bernacchii. Our findings provide context for future ecological studies as this area represents either a spawning and nursery area for multiple species in this study. More generally, the inshore waters off the Argentine Islands represent the southern limit of distribution for several low-Antarctic species, and our results provide critical baseline data for assessing possible disruptions in population dynamics driven by the ongoing climate change.

Dynamics of Anthropogenic Wildfire on Babeldaob Island (Palau) as Revealed by Fire History

Wildfire is an understudied threat to biodiversity in many tropical landscapes, including island nations of the Pacific, such as The Republic of Palau—a global biodiversity hotspot with ridge-to-reef resources. Fires are known to occur on Palau’s main island of Babeldaob, where they can result in increased erosion rates and sediment delivery to near-shore areas with impacts to streams and coral reefs. Fire-adapted native plant species are found in savanna habitats, but fires often extend into adjacent forest areas where they kill overstory trees. To assess this serious biodiversity and human health threat, we mapped wildland fires on Babeldaob Island using ground-based surveys and aerial photographs between 2012 and 2015, and satellite imagery between 2012 and 2021. Data on causal factors, vegetation type, and the presence of invasive species were collected between 2012 and 2015, with hunting, arson, and agricultural clearing being the principal causes of ignitions. Wildfires occurred in all months and in all 10 states of Babeldaob, and both numbers of wildfires and total burned area were substantially greater during dry seasons, with the highest totals occurring in the one El Niño drought year in our record. Overall, wildfires appear to have a minor impact on forest vegetation because they are largely confined to savanna systems, but rainfall on burned savanna is a major cause of erosion and the sedimentation of streams and near-shore habitats.

Spatiotemporal Variation in Distribution, Size, and Relative Abundance within a Salish Sea Nearshore Forage Fish Community

AbstractForage fish are schooling species commonly occurring in both offshore pelagic and nearshore coastal habitats. Beyond use by some species for spawning, the dynamics of nearshore habitat use are not well understood. The objective of our study was to evaluate the spring–summer dynamics of forage fish occurrence in nearshore habitats of the Strait of Juan de Fuca, Washington. We suspected that habitat changes resulting from removal of two large dams on the Elwha River (2009–2011) may have altered fish presence and abundance. Monthly beach seine sampling in four regions along 40 km of shoreline was conducted from April to September between 2006 and 2019. We caught nearly 600,000 fish, comprising 82 different species. Nine species of forage fish accounted for 81.7% of all fishes caught; most were classified as postlarvae and juveniles based on size. There were spatial differences in the forage fish assemblage between two of our sites but no discernable year effects and no obvious impact of dam removal on forage community composition. Three species represented 78.8% of the catch: Pacific Herring Clupea pallasii, Pacific Sand Lance Ammodytes hexapterus, and Surf Smelt Hypomesus pretiosus. We used a Bayesian generalized linear mixed model to evaluate spatial and temporal variability in the probability of occurrence of these species. Each species exhibited a unique pattern of intra‐annual, interannual, and regional fluctuations. Pacific Herring occurrence progressively increased monthly, Pacific Sand Lance occurrence decreased, and Surf Smelt probability of occurrence peaked in June. Temporal variations in distribution and abundance of these species are likely driven by life history differences and biological requirements. We speculate that specific characteristics of each region, including proximity to spawning areas, spawn timing, extant current patterns, and ecosystem processes, drove variations in distribution between species.

Comparison of three portable volumetric arrays to localize and identify fish sounds in the wild

We describe three portable volumetric audio/video arrays capable of identifying species-specific fish sounds in the wild. Each array can record fish sounds, acoustically localize the fish in three-dimensions (using linearized or fully non-linear inversion), and record video to identify the species and observe their behavior. The design of each array accommodates specific logistical and financial constraints, covering a range of nearshore habitats and applications. The first platform is composed of six hydrophones, an acoustic recorder, and two video cameras secured to a 2 × 2 × 3 m PVC frame. Hydrophone placement is defined using simulated annealing to maximize localization accuracy. The second platform uses a single video camera, four hydrophones, and an acoustic recorder on a one cubic meter PVC frame. It can be deployed on heterogeneous substrates but has lower localization capabilities. The third platform consists of four hydrophones connected to an acoustic recorder mounted on a tethered underwater drone with built-in video. It allows remote control and real-time positioning in response to observed fish presence but with reduced localization capabilities. The three platforms were deployed off British Columbia, Canada, and used to identify and characterize new sounds from quillback rockfish, copper rockfish, and lingcod.

Mixed‐stock aging analysis reveals variable sea turtle maturity rates in a recovering population

AbstractQuantifying demographic parameters and variable vital rates, such as somatic growth rates, time to maturity, and reproductive longevity, is important for effective management of threatened and endangered populations such as sea turtles (Cheloniidae). To address these knowledge gaps, we applied skeletochronology to analyze and compare somatic growth rates and variation in life‐history traits such as age and size at sexual maturity for 65 green turtles (Chelonia mydas) in the eastern Pacific Ocean (EP), along the west coast of the United States; turtles belonged to ≥2 nesting subpopulations that differed in body size (mean nesting size). Green turtles in the EP spend approximately 5 years in the oceanic stage before recruiting to nearshore habitats, males may be smaller and younger than females at maturation (x̅ = 17.7 ± 5.5 yr vs. 28.0 ± 8.2 yr), and younger age at sexual maturity was associated with smaller size at sexual maturity, suggesting that mean nesting body size may be reflective of maturation timing for subpopulations. Smaller body sizes for females nesting at Michoacán, Mexico (continental) rookeries, yielded a younger predicted age at sexual maturity (x̅ = ~17 yr) compared to females from Revillagigedo Islands, Mexico rookeries, which displayed larger body sizes and older age at sexual maturity (x̅ = ~30 yr). We consider possible mechanisms driving the observed divergence in life‐history traits, including the possibility that earlier maturation (reduced generation length) for turtles in the Michoacán nesting subpopulation may be a response to intense harvesting in the past 50 years, and consideration of such anthropogenic impacts is warranted by population managers. Finally, our results indicate green turtles moved into nearshore neritic habitats at a young age (4–6 yr), emphasize the importance of protecting neritic habitats along the southwestern United States and northwestern Mexican coasts, and encourage the incorporation of variable maturation time in population recovery assessments.

Phenological Variation in Spring Migration Timing of Adult Alewife in Coastal Massachusetts

AbstractThe timing of biological events in plants and animals, such as migration and reproduction, is shifting due to climate change. Anadromous fishes are particularly susceptible to these shifts as they are subject to strong seasonal cycles when transitioning between marine and freshwater habitats to spawn. We used linear models to determine the extent of phenological shifts in adult AlewifeAlosa pseudoharengusas they migrated from ocean to freshwater environments during spring to spawn at 12 sites along the northeastern USA. We also evaluated broadscale oceanic and atmospheric drivers that trigger their movements from offshore to inland habitats, including sea surface temperature, North Atlantic Oscillation index, and Gulf Stream index. Run timing metrics of initiation, median (an indicator of peak run timing), end, and duration were found to vary among sites. Although most sites showed negligible shifts towards earlier timing, statistically significant changes were detected in three systems. Overall, winter sea surface temperature, spring and fall transition dates, and annual run size were the strongest predictors of run initiation and median dates, while a combination of within‐season and seasonal‐lag effects influenced run end and duration timing. Disparate results observed across the 12 spawning runs suggest that regional environmental processes were not consistent drivers of phenology and local environmental and ecological conditions may be more important. Additional years of data to extend time series and monitoring of Alewife timing and movements in nearshore habitats may provide important information about staging behaviors just before adults transition between ocean and freshwater habitats.

Connectivity of Coral Reefs and other Nearshore Habitats: Implications for Marine Resource Management in the Philippines

Marine protected areas (MPAs) have become a mainstay of marine resource management in the Philippines in the past three decades and there is growing advocacy to implement MPA networks — systems of MPAs that effectively protect sufficient proportions of the populations of targeted species. MPA networks aim to reduce fishery-induced mortality of targeted species during critical life stages. Thus, a primary consideration of protecting populations using MPA networks is connectivity — the linking of local populations through the movement of adults or juveniles and the dispersal of larvae. This paper discusses the implications of emerging new knowledge on connectivity for MPA-centric marine resource management in the Philippines, with focus on demersal fishes inhabiting coral reefs, seagrass beds, algal beds, mangroves, and other vital nearshore habitats. The major successes and shortcomings of implementing MPAs are summarized and the evidence for MPA networks improving fisheries via connectivity is assessed. Highlighted are five major challenges for managing marine resources using MPA networks.

Status and Management of the Blue Crab Fishery in the Gulf of Mexico

AbstractManagement of the blue crab Callinectes sapidus fishery in the Gulf of Mexico is the responsibility of the individual states under the purview of a regional management plan. States generally follow the “2‐S” system of management, placing emphasis on size and sex. Despite management policies, harvest and juvenile abundances remain in decline. A significant trend toward decreasing harvest began in the early 2000s, with landings below average in 13 of the 20 years from 2000 to 2019. Since 2010, the fishery has maintained a lower but relatively stable harvest. There have been significant decreases in numbers of late‐stage juveniles in fishery‐independent trawl surveys, while numbers of megalopae and early juveniles have not exhibited declines. Postsettlement mortality is potentially driven by climate‐related hydrological processes that structure the biotic community (predator guild) and nearshore habitats. Diversity of predators, few predation‐free refuges, and a lack of seasonality in predation likely contribute to high regional mortality. Factors that influence quality and quantity of available refuge may ultimately control abundance. Although genetics data describe the population as panmictic, geographic differences in coastal climate and hydrological processes may act to structure populations. Separation of stocks according to ecozones may provide a more suitable approach to population delineation. The 2011 stock assessment divided the population into eastern and western regions based on confounding information on genetics, physiographic features that limit larval transport, variations in climate, and migration of female crabs along the west coast of Florida. There is concern that the population is undergoing Gulf of Mexico‐wide changes in biomass associated with regional climate regime shifts that may alter the resiliency of the stock. Whether the shift to a more favorable climate phase would reverse the declining trends is unknown. Changes in population levels could be rapid given the high juvenile mortality and short generation time as well as the importance of climate in structuring habitat.

Improved Chironomid Barcode Database Enhances Identification of Water Mite Dietary Content

Chironomids are one of the most biodiverse and abundant members of freshwater ecosystems. They are a food source for many organisms, including fish and water mites. The accurate identification of chironomids is essential for many applications in ecological research, including determining which chironomid species are present in the diets of diverse predators. Larval and adult chironomids from diverse habitats, including lakes, rivers, inland gardens, coastal vegetation, and nearshore habitats of the Great Lakes, were collected from 2012 to 2019. After morphological identification of chironomids, DNA was extracted and cytochrome oxidase I (COI) barcodes were PCR amplified and sequenced. Here we describe an analysis of biodiverse adult and larval chironomids in the Great Lakes region of North America based on new collections to improve chironomid identification by curating a chironomid DNA barcode database, thereby expanding the diversity and taxonomic specificity of DNA reference libraries for the Chironomidae family. In addition to reporting many novel chironomid DNA barcodes, we demonstrate here the use of this chironomid COI barcode database to improve the identification of DNA barcodes of prey in the liquefied diets of water mites. The species identifications of the COI barcodes of chironomids ingested by Lebertia davidcooki and L. quinquemaculosa are more diverse for L. davidcooki and include Parachironomus abortivus, Cryptochironomus ponderosus. Parachironomus tenuicaudatus, Glyptotendipes senilis, Dicrotendipes modestus, Chironomus riparius, Chironomus entis/plumosus, Chironomus maturus, Chironomus crassicaudatus, Endochironomus subtendens, Cricotopus sylvestris, Cricotopus festivellus, Orthocladius obumbratus, Tanypus punctipennis, Rheotanytarsus exiguus gr., and Paratanytarsus nr. bituberculatus.

Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State

Tabor RA, Liermann MC, Gearns HA, Moore ZJ, Lynch KD, Kurko K, Crittenden J, Shoemaker ME. 2022. Effectiveness monitoring of juvenile Chinook salmon restoration projects in south Lake Washington, Washington State. Lake Reserv Manage. 38:180–196. We evaluated 4 large restoration projects in south Lake Washington that were designed to improve nearshore habitat for lake-rearing juvenile Chinook salmon (Oncorhynchus tshawytscha). Restoration projects included shoreline modification, substrate enhancement, addition of engineered log jams (ELJs), and nonnatal tributary improvements. For most projects, we used a BACI (before-after-control-impact) study design. Projects were evaluated by determining the nighttime abundance of juvenile Chinook salmon through visual observations (primarily snorkeling with some surface observations in small nonnatal tributaries). Juvenile Chinook salmon are typically concentrated in the south end of the lake near their natal stream, and the project that was the farthest away from the natal stream did not appear to be beneficial, likely because few Chinook salmon were present. The highest observed abundance of juvenile Chinook salmon was associated with ELJs, where the abundance in February to April was typically 2 to 5 times higher than along adjacent, open shorelines. From January to April, juvenile Chinook salmon were usually more abundant in a daylighted nonnatal tributary (i.e., reconfigured from an unusable underground culvert to a more natural stream channel at the surface) than in 2 reference sites. Overall, all 4 project types improved juvenile use of the restored area, with substrate enhancement generally having the weakest response and ELJs the strongest response. Although most restoration projects for salmonids in the Pacific Northwest have focused on lotic systems, our results suggest projects in lentic systems may also be beneficial and should be considered by land-use managers. Supplemental data for this article is available online at https://doi.org/10.1080/10402381.2022.2027054 .

Finding lobsters: investigating a period of unusually low settlement of

Context Spiny lobsters are critically affected by ocean current movements over their long journey from hatching to swimming post-larvae (puerulus). Methods Isolating three different larval stages of the Western rock lobster (Panulirus cygnus), we have applied three-dimensional larval-dispersal modelling techniques Aims To better understand a period of unusually low puerulus settlement in the late 2000s. Key results Model results showed that transport mechanisms assisting pueruli in reaching nearshore habitats may have been inhibited by a strengthening of the southward-flowing Leeuwin Current over the austral summer at the settlement stage. As a result, modelled pueruli were transported significantly less northward, in some cases southward, during and after the period of unusually low settlement. Hatching-stage trajectories also suggest increased dispersal off the coast during 2007 and 2008, transporting modelled larvae further offshore and possibly contributing to decreased recruits into the fishery. Conclusions Our study distinguishes the influence that ocean circulation patterns off Western Australia have on three different larval stages. Implications Larval dispersal modelling of pueruli, therefore, provides a possible explanation for the changes in puerulus settlement over the past two decades and future considerations.

Habitat selection and abundance of West Indian manatees Trichechus manatus at the margins of their expanding range

Habitat selection and abundances at range margins during geographic expansion may influence movement into new areas, shaping the trajectory of climate-driven changes in species distribution. The West Indian manatee is an ideal species to study how habitat selection influences range expansion because its presence has rapidly increased during the past 2 decades in the northern Gulf of Mexico (nGoM), a region outside its historical range. We estimated the habitat selection and abundances of manatees in coastal Alabama waters along the nGoM coast using resource selection functions and N-mixture models, respectively. Warm season (May-Nov) manatee abundances were estimated at 25 and 34 manatees at any given time in coastal Alabama waters in 2010 and 2019, respectively. Manatees primarily used the Mobile-Tensaw River Delta and Dog River areas, selecting nearshore shallow water habitats proximate to submerged aquatic vegetation. Distance to boat ramps and human population density had stronger effects on opportunistic sighting data but remained important for tagged data, indicating that manatee habitat selection overlapped with humans. Temperature strongly predicted manatee sightings; most sightings occurred when temperatures were >20°C. Our data indicate that the key interacting factors likely to moderate manatee range expansion, and therefore be important to management and conservation of this species, include increased sea temperature, availability of nearshore habitat with submerged aquatic vegetation, and regional manatee population dynamics. As environmental conditions at the range margins continue to become more favorable to manatees and areas within the range core decline in quality, areas at the range margins may become increasingly important.