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DESCRIPTION
In 2024, USEPA Region 1 Ecology Monitoring Team (EMT) received a request for assistance from the USEPA Atlantic Coastal Environmental Sciences Division (ACESD) to support a preliminary fish population survey of Roger Williams Park in Providence, Rhode Island. The survey was part of ongoing efforts by the Providence Parks Department, Rhode Island Audubon Society, The Nature Conservancy, and Rhode Island Zoological Society to mitigate harmful algae blooms and nutrient loadings to the system. An additional goal of the fish community survey was to assess the biomass of Common Carp (Cyprinus carpio) within the Roger Williams Park waterbodies, as studies suggest carp populations can significantly contribute to the degradation of water quality. Carp feeding behavior disturbs bottom sediments increasing turbidity, resuspending nutrients like phosphorus, and decreasing water clarity. This leads to increased algal bloom occurrences and impacts aquatic ecosystems by degrading habitat conditions for other species (Kloskowski, 2011, Crivelli 1983, Webber & Brown, 2009). Characterization and enumerations of fish species populations in the ponds took place on October 22nd, 23rd and November 20th, 2024. Non-lethal electrofishing by EMT Staff was carried out in the following Roger Williams Park waterbodies: Cunliff Pond, Elm Lake, Edgewood Lake, Pleasure Pond, and Polo Lake. Electrofishing efforts were focused on habitat providing fish cover within the waterbodies. Captured fish were then processed to assess size class and examined for abnormalities.
METHODS
Fish collections were completed by a crew consisting of two netters and a vessel operator on a 16ft Smith-Root electrofishing boat. Fishing was conducted with the assistance of one crew transporting fish to an onshore holding tank where another team processed and identified fish throughout the survey. Fish were identified, measured for total length (compressed tail fin), weighed, and assessed for deformities, fin erosions, lesions, and tumor occurrences (DELT). Data collection and documentation was done using a Survey123 electronic logbook designed by EMT staff.
This processing method allows fish to recover completely from electrical shock, reducing thestress incurred to collected species and the likelihood of mortality. No mortalities were observed during this survey. The water conductivity was measured to be approximately 115 μS at the time of sampling which is optimal for electrical configurations that maximize capture efficiency and minimize mortality: pulsed direct current wave form of 170V, 40% duty cycle and a 60Hz frequency. Netting efficiency was estimated at approximately 60-70% (BPJ). Near-shore littoral area was the targeted habitat, as it is identified to have sufficient fish cover to support populations of the species of interest for this study. The richest habitat for fish was targeted and the majority of fish were captured around dense structures, such as downed trees and boulder fields. Rooted aquatic vegetation was sparse at best, providing little to no refugia for the targeted species.
SUMMARY
Common Carp dominate the fish biomass of the sampled waterbodies. Juvenile and lower age classes of this species appear to be missing. The top-level predator in these ponds is the largemouth bass which is reflected in reasonable numbers concentrated around littoral structures, mostly tree blowdowns. Higher age classes dominated with minimal lower age classes captured. Bluegills were a dominant population and again noticeable in the upper size classes only. There
was not an indication of a highly overpopulated and stunted population of this generalist feeder. Other bottom feeding species such as bullhead and eels are underrepresented due to limited visibility, capture efficiency, and just difficulty collecting stunned fish from greater depths and off the bottom.
These three species made up the majority of fish captured, and all appeared to be in their upper age classes. The lack of almost any juveniles and young of year may allude to the scarcity of refugia for these age classes and the increased vulnerabilities to predation. Carp may be the leading cause of this lack of vegetative refugia due to their abundance, size class, and aggressive bottom feeding behavior. This feeding behavior can not only eliminate important juvenile fish habitat but can exacerbate the resuspension of nutrient laden sediments which can then be readily available to accelerate phytoplankton and or cyanobacteria growth leading to harmful algal
blooms.
These ponds provide an excellent opportunity to study the effects of carp overpopulations on aquatic vegetation, nutrient water column loading and trophic condition, and the subsequent impact they may have on the establishment of a balanced and optimal fish population. There is also an opportunity to look at management strategies that can promote vegetative growth that will sequester nutrients and improve water quality and clarity while providing a more balance fishery population.