Frequency of invasive plant occurrence is not a suitable proxy for abundance in the Northeast United States

Measuring and predicting invasive plant abundance is critical for understanding impacts on ecosystems and economies. Although spatial abundance datasets remain rare, occurrence datasets are increasingly available across broad regional scales. We asked whether the frequency of these point occurrences can be used as a proxy for abundance of invasive plants. We compiled both occurrence and abundance data for 13 regionally important invasive plants in the northeast United States from herbarium records and several contributed distribution datasets. We integrated all available abundance information based on infested area, stem count, percent cover, or qualitative descriptions into abundance rankings ranging from 0 (absent) to 4 (highly abundant). Within equal-area grid cells of 800 m, we counted numbers of occurrence points and used ordinal regression to test whether higher densities of occurrence points increased the odds of a higher abundance ranking. We compiled a total of 86,854 occurrence points in 34,596 grid cells, of which 26,114 points (30%) within 11,976 cells (35%) had some form of abundance information. Eleven of the 13 species had a slight but significantly positive odds ratio; that is, more occurrence points of a species increased the odds that the species was abundant within the grid cell. However, the predictive ability of the models was poor (κ \u3c 0.2) for the majority of species. Additionally, most grid cells contained only one or two occurrence points, making it impossible to infer abundance in all but a few locations. These results suggest that currently available occurrence datasets do not effectively represent abundance, which could explain why many distribution models based on occurrence data are poor predictors of abundance. Increased efforts to consistently collect and report invasive species abundance, ideally estimating both infested area and average cover, are strongly needed for regional-scale assessments of potential abundance and associated impact

Movements, connectivity, and space use of immature green turtles within coastal habitats of the Culebra Archipelago, Puerto Rico: implications for conservation

Juvenile green turtles occupy coastal marine habitats important for their ontogeny; however, the details of their movement, connectivity, and space use in these developmental habitats are still poorly understood. Given that these areas are often threatened by human disturbance, additional information on green turtle spatial ecology is needed to meet conservation end- points for this endangered species. For this study, we used fixed passive acoustic telemetry to (1) describe movement patterns and connectivity of immature green turtles within, outside, and across 2 bays, Manglar and Tortuga bays, on Culebra and Culebrita islands, Puerto Rico; and (2) determine spatio-temporal drivers of the presence and absence of turtles within Manglar Bay. Network analysis used to quantify movement patterns showed that turtles in our study exhibited differential space use with little to no connectivity across the 2 bays. In addition, turtles exhibited high site fidelity, with larger turtles leaving on brief trips. We applied a presence−absence Bayesian binomial model on a subset of 9 turtles at an hourly temporal scale and showed that turtles within Manglar Bay occupied areas of lagoon and seagrass habitats at night and were rarely using areas of macroalgae habitat. The parameter estimates from the model enabled us to predict the space use of turtles across Manglar Bay, and the hourly probability distributions highlighted predictive diel movement patterns across the bay. Considering the importance of juvenile and subadult life stages for population viability, we recommend continued protection of these critical juvenile turtle developmental habitats to ensure recruitment into the adult life stage

Seasonal use of a New England estuary by foraging contingents of migratory striped bass

Author Posting. © American Fisheries Society, 2009. This article is posted here by permission of American Fisheries Society for personal use, not for redistribution. The definitive version was published in Transactions of the American Fisheries Society 139 (2010): 257-269, doi:10.1577/T08-222.1.Using acoustic telemetry on migratory striped bass Morone saxatilis in Plum Island Estuary (PIE), Massachusetts, we found that striped bass (335–634 mm total length) tagged in the spring and summer of 2005 (n = 14) and 2006 (n = 46) stayed in the estuary for an average of 66.0 d in 2005 and 72.2 d in 2006. Striped bass spent the most time in two specific reaches: middle Plum Island Sound and lower Rowley River. In both years, three different use-groups of striped bass were observed in PIE. Short-term visitors (n = 24) stayed in the estuary only briefly (range = 5–20 d). Two groups of seasonal residents stayed for more than 30 d, either in the Rowley River (n = 14) or in Plum Island Sound (n = 22). Within PIE, the two seasonal-resident use-groups may be foraging contingents that learn how to feed efficiently in specific parts of the estuary. These distinct within-estuary use patterns could have different implications for striped bass condition and prey impact

Discontinuities Concentrate Mobile Predators: Quantifying Organism-Environment Interactions at a Seascape Scale

Understanding environmental drivers of spatial patterns is an enduring ecological problem that is critical for effective biological conservation. Discontinuities (ecologically meaningful habitat breaks), both naturally occurring (e.g., river confluence, forest edge, drop-off) and anthropogenic (e.g., dams, roads), can influence the distribution of highly mobile organisms that have land- or seascape scale ranges. A geomorphic discontinuity framework, expanded to include ecological patterns, provides a way to incorporate important but irregularly distributed physical features into organism–environment relationships. Here, we test if migratory striped bass (Morone saxatilis) are consistently concentrated by spatial discontinuities and why. We quantified the distribution of 50 acoustically tagged striped bass at 40 sites within Plum Island Estuary, Massachusetts during four-monthly surveys relative to four physical discontinuities (sandbar, confluence, channel network, drop-off), one continuous physical feature (depth variation), and a geographic location variable (region). Despite moving throughout the estuary, striped bass were consistently clustered in the middle geographic region at sites with high sandbar area, close to channel networks, adjacent to complex confluences, with intermediate levels of bottom unevenness, and medium sized drop-offs. In addition, the highest striped bass concentrations occurred at sites with the greatest additive physical heterogeneity (i.e., where multiple discontinuities co-occurred). The need to incorporate irregularly distributed features in organism–environment relationships will increase as high-quality telemetry and GIS data accumulate for mobile organisms. The spatially explicit approach we used to address this challenge can aid both researchers who seek to understand the impact of predators on ecosystems and resource managers who require new approaches for biological conservation

Use of non-natal estuaries by migratory striped bass (Morone saxatilis) in summer

This paper is not subject to U.S. copyright. The definitive version was published in Fishery Bulletin 107 (2009): 329-338.For most migratory fish, little is known about the location and size of foraging areas or how long individuals remain in foraging areas, even though these attributes may affect their growth, survival, and impact on local prey. We tested whether striped bass (Morone saxatilis Walbaum), found in Massachusetts in summer, were migratory, how long they stayed in non-natal estuaries, whether observed spatial patterns differed from random model predictions, whether fish returned to the same area across multiple years, and whether fishing effort could explain recapture patterns. Anchor tags were attached to striped bass that were caught and released in Massachusetts in 1999 and 2000, and recaptured between 1999 and 2007. In fall, tagged striped bass were caught south of where they were released in summer, confirming that fish were coastal migrants. In the first summer, 77% and 100% of the recaptured fish in the Great Marsh and along the Massachusetts coast, respectively, were caught in the same place where they were released. About two thirds of all fish recaptured near where they were released were caught 2–7 years after tagging. Our study shows that smaller (400–500 mm total length) striped bass migrate hundreds of kilometers along the Atlantic Ocean coast, cease their mobile lifestyle in summer when they use a relatively localized area for foraging (<20 km2), and return to these same foraging areas in subsequent years.This project was administered through the Massachusetts Cooperative Fish and Wildlife Research Unit. The Massachusetts Cooperative Fish and Wildlife Research Unit is an association among the U.S. Geological Survey; University of Massachusetts Department of Natural Resources Conservation; Massachusetts Division of Marine Fisheries; Massachusetts Division of Fisheries and Wildlife, and the Wildlife Management Institute