Thomas M. Grothues

Habitat Use, Site Fidelity, and Movement of Adult Striped Bass in a Southern New Jersey Estuary Based on Mobile Acoustic Telemetry

Abstract To determine individual patterns of habitat use, site fidelity, and movement, adult striped bass Morone saxatilis (n = 81; mean fork length = 70.8 cm [range, 48.3-95.3 cm]) were implanted with individually coded acoustic transmitters and tracked with a mobile hydrophone from July 2003 through July 2005 in Mullica River-Great Bay estuary in southern New Jersey. Striped bass in this small coastal bay-estuarine system preferred deeper water near shorelines and were found at the same location 56.6% of the time. In fact, the persistence of individual home ranges at the scale of meters was observed within and among years. When fish were moving, their pattern was characterized by sporadic swimming followed by long periods of little movement. Seasonally, movement in the estuary was highest in April, followed by two secondary peaks in October and December. Daily movement was highest around sunset. Mobile telemetry demonstrated important dynamics in habitat use, site fidelity, and estuarine movements that ...

Long-term response of fishes and other fauna to restoration of former salt hay farms: multiple measures of restoration success

This synthesis brings together published and unpublished data in an evaluation of restoration of former salt hay farms to functioning salt marshes. We compared nine years of field measurements between three restored marshes (Dennis, Commercial, and Maurice River Townships) and a reference marsh (Moores Beach) in the mesohaline portion of Delaware Bay. In the process, we compared channel morphology, geomorphology, vegetation, sediment organic matter, fish assemblages, blue crabs, horseshoe crabs, benthic infauna, and diamondback terrapins. For fishes we compared structural (distribution, abundance) and functional (feeding, growth, survival, reproduction, production) aspects to evaluate the restored marshes in an Essential Fish Habitat context. Marsh vegetation and drainage density responded gradually and positively with restored marshes approximating the state of the reference marsh within the nine-year study period. The fauna responded more quickly and dramatically with most measures equal or greater in the restored marshes within the first one or two years after restoration. Differences in response time between the vegetation and the fauna imply that the faunal response was more dependent on access to the shallow intertidal marsh surface and intertidal and subtidal creeks than on characteristics of the vegetated marsh. The fishes in created subtidal creeks in restored marshes responded immediately and maintained fish assemblages similar to the reference marsh over the study period. The intertidal creek fish assemblages tended to become more like the reference marsh in the last years of the comparison. Overall, these results document the success of the restoration and how marshes function for both resident and transient fauna, especially fishes.

A Review of Acoustic Telemetry Technology and a Perspective on its Diversification Relative to Coastal Tracking Arrays

Automated telemetry systems for tracking ultrasonically tagged marine fauna have diversified in information coding, signal reception, data handling and storage, and deployment architecture in response to niche development among equipment manufacturers. Technologies divide especially along issues of habitat type, spatial scale, and cost. Highly capable designs appropriate to spatial scales from sub-meter resolution to coast-wide migration have emerged. Due to technical constraints (e.g. coding algorithms, frequency) and proprietary interests, tags of one code scheme cannot currently communicate with listening devices from others, sometimes even among devices within a manufacturer’s offering. Large-scale federally funded arrays are being designed as observatories to facilitate discovery and experiments and are committed to single-platform technology. Commitment to a single equipment design unifies such arrays but also contributes to inertia that hinders optimization or further development at the local level. Some solutions for cross-equipment communication exist at both the transmitter and receiver ends of the technology. Un-anticipated movement of tagged marine fauna through these arrays can yield important new insights but can also have negative effects on other users of the array. These possibilities should be considered and coordinated through collaborative administrations and as early as the proposal review process. This paper outlines the needs and constraints to engage scientists with each other and with manufacturers in dialog to mitigate negative effects of diversification without the loss of its benefits. An inability to unify disparate and independent hydrophone arrays risks tremendous lost opportunity to track fish in coastal marine and estuarine settings, as seen in case studies.

Evaluating Salt Marsh Restoration in Delaware Bay: Analysis of Fish Response at Former Salt Hay Farms

In a continuing effort to monitor the fish response to marsh restoration (resumed tidal flow, creation of creeks), we compared qualitative and quantitative data on species richness, abundance, assemblage structure and growth between pre-restoration and post-restoration conditions at two former salt hay farms relative to a reference marsh in the mesohaline portion of Delaware Bay. The most extensive comparison, during April–November 1998, sampled fish populations in large marsh creeks with otter trawls and in small marsh creeks with weirs. Species richness and abundance increased dramatically after restoration. Subsequent comparisons indicated that fish size, assemblage structure, and growth of one of the dominant species,Micropogonias undulatus, was similar between reference and restored marshes 1 and 2 yr post-restoration. Total fish abundance and abundance of the dominant species was greater, often by an order of magnitude, in one of the older restored sites (2 yr post-restoration), while the other restored site (1 yr post-restoration) had values similar to the reference marsh. The success of the restoration at the time of this study suggests that return of the tidal flow and increased marsh area and edge in intertidal and subtidal creeks relative to the former salt hay farms contributed to the quick response of resident and transient young-of-the-year fishes.

Response of Juvenile Fish Assemblages in Tidal Salt Marsh Creeks Treated for Phragmites Removal

We examined fish assemblages in tidal salt marsh creeks in Delaware Bay in order to evaluate their response to treatment forPhragmites removal following initial treatment in 1996. In Alloway Crrek, a tributary to Delaware Bay, reference creeks draining marsh of untreatedPhragmites or naturally occurringSpartina were compared with creeks in marshes treated forPhragmites removal. These reference and treated creeks occur in close proximity and share many characteristics including salinity, temperature, dissolved oxygen, and turbidity, although creeks inPhragmites sites differed slightly in bathymetry. We analyzed a time series of otter trawl collections (22 monthly sample periods from 1999 to 2001) for differences in juvenile fish assemblage among creeks with different vegetation history. Periodically, young-of-the-year (YOY) and age 1+ white perch (Morone americana), YOY spot (Leiostomus xanthurus), YOY Atlantic menhaden (Brevoortia tyrannus), and other species were relatively more abundant atPhragmites sites, but other dominant species were preiodically abundant at all sites. Among-treatment differences based on principal response curves analysis accounted for about 19% of the total species variation, but differences varied widely among sample periods and there is little or no indication of a trend over the 3-yr period. Larger collections were often associated with subtidal structure, which was more common atPhragmites sites and potentially represents a sampling artifact. Assemblages of creeks with differing vegetation history differ weakly but recognizably, suggesting slow or little response to treatment, at least based on otter trawl collections in subtidal marsh creeks.

Use of a multi-sensored AUV to telemeter tagged Atlantic sturgeon and map their spawning habitat in the Hudson River, USA

An autonomous underwater vehicle (AUV) equipped with a telemetry hydrophone was used to observe Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) in their Hudson River spawning habitat. The positions of two transmitter-tagged fish were repeatedly determined using two methods; probability plots derived from 2-dimensional matrices of received transmitter signal strength calibrated by a reference tag, and by synthetic aperture calculations. Targets thought to be additional, untagged, Atlantic sturgeon were located from sidescan echograms. Positions of tagged and untagged fish were mapped to benthic and hydrographic habitat features by matching the fishs location with the vehicles time and spaced-referenced sensor data. Results were compared to those of surface vessel-based mobile telemetry solutions using bearing and signal strength. This case study demonstrated the usefulness of AUVs to fish telemetry in challenging conditions. The rapid survey provided focus and scaling to further efforts at understanding essential habitat for this Red Listed species.

Discerning Vegetation and Environmental Correlates with Subtidal Marsh Fish Assemblage Dynamics during Phragmites Eradication Efforts: Interannual Trend Measures

We examined the 5-yr (1996–2000) response of subtidal marsh creek fishes (2,793 trawls, 47 species, 30,719 fish) to a large marsh restoration project in the upper Delaware Bay, and found that the salinity gradient covaried along with marsh surface vegetation type among two treated and one untreated reference sites, confounding direct comparison of fish utilization. Examination of environmental correlates with monthly yearly trends highlighted differences between potential mechanism driving assemblage dynamics either intrinsic or extrinsic to the marshes. Within-site and among-site differences in fish assemblage, as described by principal components analysis, correlated poorly with marsh vegetation on both seasonal and interannual scales and appeared to driven by larval supply. Assemblage dynamics could be expalined in part by the occurrence of juveniles of transient marine fishes along a salinity gradient (0–15.2%) range in monthly site mean), but were largely determined by fluctuations in the distribution of two transient species: young-of-the-year bay anchovyAnchoa mitchilli and Atlantic croakerMicropogonias undulatus. A minor mode in variance, driven by locally spawned species, was moderately correlated with environmental parameters. Analysis of marshes on an individual basis did not discern additional important gradients. Our findings are in contrast to those in systems dominated by resident species, probably because transient fishes, which often dominante the system, are more plastic to the nature of ecological services or are affected as much by environment outside of the marsh as by that in the marsh.

Collecting, interpreting, and merging fish telemetry data from an AUV: Remote sensing from an already remote platform

Chemical and hydrological AUV sensors (e.g. C, T, 02, CDOM, Chlorophyll a) collect information about water in contact with or in close proximity to the vehicle. Sonar (e.g. ADCF, side scan, dual beam, and multibeam) collect data about features distant on the scale of tens of meters away and linked to coordinates. In contrast, acoustic tags implanted in fishes or other marine fauna can be detected at distances greater than a kilometer away, which brings special considerations to data treatment and merging. In the case of telemetry systems that log sound pressure levels, relative signal strength can be used to produce proximity maps using regression. For systems with invariant signal timing, a synthetic aperture engine can calculate location of the tag if a suitable AUV path produces a good aperture. In the common case where both of these conditions are lacking, the tag position must be assigned to a place along the vehicles path. The use of tags that broadcast information from their own sensors (e.g. pressure, temperature) can help resolve both the position and environment of the distant tag. An empirically-fashioned hierarchical decision matrix based on numerous AUV-fish telemetry missions in shallow and deep (<3m to 600m) water assists in mission planning, data processing, and displaying AUV-collected data about telemetered fauna and their environment.

Scaling Acoustic Telemetry of Bluefish in an Estuarine Observatory: Detection and Habitat Use Patterns

Abstract We telemetered adult bluefish Pomatomus saltatrix via a fixed estuarine hydrophone array to assess estuarine habitat use and determine the feasibility of using this approach coastwide. Eighteen bluefish (286-622 mm fork length) were surgically implanted with ultrasonic tags transmitting at either 2-s or 5-s intervals. The fish were monitored during their stay within a temperate estuary by hydrophones and associated environmental data loggers at major bottlenecks. They moved quickly through the hydrophone detection ranges, with 3-100 acoustic contacts being recorded within 15-min intervals. Contacts per 15-min interval with fixed hydrophones were similar for fish with 2-s and 5-s transmission interval tags, but mobile tracking proved ineffectual. Bluefish preferred the shallow polyhaline portion of the estuary, but several moved upriver to a salinity as low as 12‰. The latter occurred near the minimum (14°C) of the temperature range utilized (11-27°C). Residence times (0-55 d; mean = 15 d) indicat...

Application of Mobile Dual-frequency Identification Sonar (DIDSON) to Fish in Estuarine Habitats

Abstract Dual-frequency identification sonar (DIDSON) offers important advantages over other sampling tools for observing pelagic and benthic fishes in situ. Because it relies on sound, DIDSON can detect fish in a non-destructive and non-intrusive manner. In our unique application, the equipments small size and low power requirements allow deployment from a kayak for increased maneuverability in complex habitats. Characteristics that typify echograms of different fishes can be extracted using multivariate ordination techniques, such as principal components analysis (PCA), with in situ groundtruthing. Here we present reference images, techniques, and human-observer-error estimates from DIDSON application. Together, these approaches enhance our ability to sample fishes and even observe certain behaviors in complex, turbid environments during a full diel cycle.