DETERMINING METHODS FOR MONITORING ICHTHYOPLANKTON, FISH COMMUNITIES, SAND SHRIMP, AND CAGED MUSSELS
ICHTHYOPLANKTON
Fish eggs, larvae, and early juveniles may be more sensitive to pollution than adult fish, and can indicate where mature fish are spawning or where there are important nursery habitats. This was the first time that the spatial and temporal distribution of fish eggs and larvae in Saint John Harbour was investigated. Tows of a conical plankton net were used to collect ichthyoplankton at each site from 2011 to 2014 (sampling was done at the same sites as for the invertebrate and sediment studies). Despite Saint John Harbour having been an industrial site for over two centuries it remains a nursery site for a wide variety of fish.
Twenty six species, including five not previously reported from Saint John Harbour were recorded. Fourbeard rockling, a small non-commercial species, was the most abundant fish caught but Atlantic herring, hake species and cunner were also very abundant. Results showed that summer is the optimal time to capture fish eggs and larvae in Saint John Harbour as they are most abundant during this time. Outer harbour sites also have a larger and more consistent community for these organisms. The data were used to develop “baseline reference conditions,” indicating ranges of natural variability in abundance and number of species of fish eggs plus larvae; these conditions can be used as thresholds for assessing future cumulative effects in the Saint John Harbour.
Average number of eggs and larvae caught in plankton net tows at Inner and Outer Saint John Harbour sites. Significantly more eggs and larvae were caught in summer than other seasons and in the Outer- than Inner-Harbour during 11 surveys from 2011-2014
The companion study of invertebrates living in the bottom sediments and of contaminants in Saint John Harbour recommended long term monitoring of these components. Adding fish eggs and larvae to the protocol may increase the ecological range and assessment power of biomonitoring, but, as with the other faunal groups, further study is needed to identify the responses of the ichthyoplankton community to environmental stressors in the SJH, and also to ascertain whether these organisms are good indicators of the health of adult fish populations.
FISH
The project intended to identify an appropriate sentinel species of fish that could be caught relatively easily and consistently in the SJH. Previous research indicated that winter flounder or sculpins (three species) might make good sentinel species. However, sampling with a variety of fishing equipment in several shallow habitats (<15 m depth) did not yield enough fish of the same species at the same sites over time to make meaningful monitoring recommendations.
Dredging in the Saint John Harbour is required to maintain adequate shipping channels
In collaboration with the Saint John Port Authority, fish were studied to determine whether there were differences in the catches and species richness (number of different species) between dredged and un-dredged parts of the harbour. Twenty paired (dredged versus un-dredged) tows (each 0.3 nautical miles long, and approximately 10 minutes in duration) with a small bottom trawl were done at four sites in October 2013 and August 2014. A total of 589 fish representing 14 species were caught with most fish (64%) being taken at un-dredged sites. Species richness was slightly higher at un-dredged sites (12 species) compared to dredged sites (11 species). White flounder, windowpane, gaspereau and white hake were the most abundant species at both sets of sites. Despite these differences, statistical analyses indicate no significant differences in the catches and species richness between dredged and un-dredged sites. Further analyses are underway to determine whether there might be differences in catches between dredged and un-dredged sites for bottom-dwelling species in particular. However, significant differences were observed among the fish assemblages (variety of species) found at each of the four sites. Given that the bottom trawl sampling was effective in detecting differences in fish assemblages among sites, this monitoring may be especially useful in assessing ecological changes in fish distribution throughout the harbour.
Image from Port Saint John.
SAND SHRIMP
Because sand shrimp are widely distributed and easily caught at sites around the harbour, they were identified as a potentially informative and cost-effective sentinel species for nearshore areas. Sampling was conducted to determine whether abundance, growth or reproduction were affected at a nearshore site that receives municipal wastewater effluent, and whether occurrence and growth differed between dredged and undredged areas of the harbour.
Four nearshore sites around the harbour were sampled – three reference sites and one which receives municipal wastewater effluent (MWE). Results showed that shrimp were generally longer and heavier at the MWE site. Results of this nature are often associated with nutrient enrichment from municipal wastewater. Contaminants in the sediments at these sites were also measured. Although there was no clear trend in sediment metals that could explain the differences in shrimp sizes, one relatively pristine site (Musquash Marine Protected Area) had elevated arsenic and nickel concentrations and another site (Digby Ferry Terminal) had high PAHs. Sand shrimp show potential to be used in environmental monitoring programs after further asessments of their ability to reflect local conditions.
BLUE MUSSEL CAGING Experiments
Caged mussels have been successfully used as sentinel species in marine monitoring programs globally. Recent studies show that transplanting bivalves from a reference site to a polluted area can be a feasible strategy for monitoring the effects of contaminants in the water column in both coastal and estuarine zones – especially where native sentinels are not available. For this reason, caged mussels are an ideal sentinel, due to their sessile filter-feeding mechanism, which allows them to rapidly bioaccumulate contaminants in their tissues. The objective of this project was to establish baseline criteria for cumulative effects monitoring in the Saint John Harbour using the common blue mussel as a potential sentinel species. Mortality, growth, energy storage, reproduction, disease diagnostics, and the accumulation of trace metals and organic compounds were measured. Results from other monitoring in the Gulf of Maine (Gulfwatch) and a US national program (National Oceanic Atmospheric Administration) were used for comparison.
Blue mussels pump seawater past their gills to filter out food items and other suspended particles. Assimilated into their tissues or passed through their bodies undigested.
Sites for the mussel study were selected to overlap with the invertebrate and sediment sites in the inner and outer harbour. In addition, some sites in the outer Bay of Fundy were chosen to determine the extent of spatial variability in growth, reproduction, mortality, and the bioaccumulation of contaminants that may exist between harbour and outer bay sites.
Several experimental deployments of caged mussels were done from 2012 to 2014 during different seasons. While mussels caged at the harbour and outer bay sites were consistently higher in some trace metals, there were no significant differences in the biological health of the mussels, as determined by growth, reproduction, or mortality.
References
ENVIRONMENT. 1999. Canadian Sediment Quality Guidelines for the Protection of Aquatic Life.
CANADIAN WATERSHED RESEARCH CONSORTIUM SAINT JOHN HARBOUR NODE: http://www.cwn-rce.ca/initiatives/canadian-watershed-research-consortium/saint-john-harbour-node/
NATIONAL STATUS AND TRENDS MUSSEL WATCH PROGRAM: http://ccma.nos.noaa.gov/about/coast/nsandt/musselwatch.aspx
PIPPY, B. 2015. Understanding variability in sediment contaminants and benthic invertebrate populations in the Saint John Harbour. Master of Science thesis, University of New Brunswick.
POWER, R. 2015. Investigation of sand shrimp (Crangon septemspinosa) as a sentinel species in the Saint John Harbour, Bay of Fundy, Canada. Master of Science thesis, University of New Brunswick.
VAN GEEST, J.L., KIDD, K.A., HUNT, H.L., ABGRALL, M.J., MALTAIS, M.J., AND A. MERCER. 2015. Development of baseline data for long-term monitoring of sediment conditions at reference sites in Saint John Harbour, New Brunswick: benthic infaunal invertebrates and sediment contaminants 2011-2013. Can. Manuscr. Rep. Fish. Aquat. Sci. 3076: v + 97 p.