More Information about Finfish and Crustacean  Communities:       

 Data described for the catch of finfish and crustacean taxa collected during 1999 and 2000 were generally based on organisms that were larger than 2-3 centimeters in size, and slow enough to be caught in the trawl net used for this program.   Abundance and biomass values were standardized to the number of individuals per hectare and kilograms per hectare, respectively, and can therefore be compared between habitat types even though trawls were shorter at tidal creek stations compared to the open water stations.   Although the number of species collected per trawl cannot be easily normalized using the same process; tidal creeks trawl tows consistently had a greater number of species than observed at open water sites.  Preliminary summaries of possible values that may be used to classify station condition are provided in this report, but more data are needed before any index of biotic integrity could be developed using finfish and crustacean species.  Species comprising more than 95% of the total catch within each habitat type are listed in Appendix 4.2.

Tidal Creek Stations:

In 1999, trawls were successfully completed at 26 of the 27 tidal creek stations sampled, with 2,979 organisms representing 38 species collected.  The mean density of finfish and crustaceans collected was 830 organisms/hectare with a mean overall biomass of 7.41 kg/hectare.  The mean number of species collected per station was 6.5 species. Diversity and evenness values ranged from 0.61 to 3.11 and from 0.24 to 1.0, respectively.

 During 2000, 30 tidal creek stations were sampled with a total of 3,500 organisms representing 53 species collected.  The mean density and biomass of fish and crustaceans at the stations sampled in 2000 was slightly greater than observed in 1999 (852 individuals/hectare and 9.10 kg/hectare, respectively).  The mean number of species collected per station was 6.8, with diversity values ranging from 0 to 3.61, and evenness values ranging from 0 to 0.95, which was similar to the values observed in 1999.  The overall mean abundance, mean biomass and mean number of species collected per station in 1999 versus 2000 were not significantly different (p > 0.05). 

 Over the two-year period, 27 recreationally important species were captured at tidal creek stations (Table 1, Appendix 4.2). These species comprised 54% of the total abundance.  The four most abundant species, which represented 74% of the total abundance, were white shrimp (Penaeus setiferus), spot (Leiostomus xanthurus), silver perch (Bairdiella chrysoura), and brown shrimp (Penaeus aztecus).  Recreationally important species accounted for 34% of the total biomass collected, with six of these species comprising 72% of the total biomass.  Those species were white shrimp, spot, silver perch, blue crabs (Callinectes sapidus), brown shrimp, and pinfish (Lagodon rhomboides). 

Other recreationally important species collected in tidal creek stations were generally not very abundant.  They included Atlantic croaker (Micropogonias undulatus), weakfish (Cynoscion regalis), Atlantic spadefish (Chaetodipterus faber), mullet (Mugil cephalus), summer flounder (Paralichthys dentatus), ladyfish (Elops saurus), spotted sea trout (Cynoscion nebulosus), pink shrimp (Penaeus duorarum), southern flounder (Paralichthys lethostigma), white catfish (Ictalurus catus), Atlantic sharpnose shark (Rhizoprionodon terranovae), sea catfish (Ariopsis felis), longnose gar (Lepisosteus osseus), Spanish mackerel (Scomberomorus maculatus), crevalle jack (Caranx hippos), gizzard shad (Dorosoma cepedianum), black sea bass (Centropristis striatus), gafftopsail catfish (Bagre marinus), American shad (Alosa sapidissima), and southern kingfish (Menticirrhus americanus).  Some of these species are not commonly harvested recreationally in South Carolina, but they are considered to be recreationally important in other areas and many are kept as incidental catch by fishermen in this state.

The average biomass of white shrimp collected in 1999 was significantly greater than observed in the 2000 catch (p < 0.05), but no other significant differences were found with respect to abundance (organisms/hectare) or biomass (kg/hectare) for catches of spot, silver perch, brown shrimp, blue crab, Atlantic croaker, or pinfish between years.

 Open Water Stations:

The open water stations sampled in 1999 (n = 28) yielded a total catch of 2,541 organisms representing 47 species. The mean abundance per station was 329 organisms/hectare and the mean biomass was 2.45 kg/hectare.  An average of 5.8 species were collected per station that year, with diversity and evenness values ranging from 0.51 to 3.23 and 0.20 to 0.92, respectively.

A total of 2,679 organisms representing 44 species were collected at the 30 open water stations sampled in 2000. The mean abundance per station (324 organisms/hectare) was similar to that observed in 1999, but the average catch biomass per station (4.3 kg/hectare) was nearly twice as great.  An average of 5.3 species were collected at each station, with diversity values ranging from zero to 3.24, and evenness values ranging from zero to 0.96.  These values were similar to those observed in 1999.  Statistical comparisons of the mean abundance, biomass, and number of species collected in open water stations between 1999 and 2000 were not significantly different. 

      A total of 26 recreationally important fish and crustacean species were collected over 1999 and 2000 at open water sites.  These taxa represented 57% of the overall abundance and 80% of the overall biomass.  Only one of the four most abundant species collected was a recreationally important species (white shrimp), and comprised 18% of the total abundance.  The other abundant species included star drum (Stellifer lanceolatus), brief squid (Lolliguncula brevis), and bay anchovy (Anchoa mitchilli).  The five species that contributed the most to overall biomass were recreationally important species, and represented 51% of the total biomass.  These species were white shrimp, Atlantic croaker, spot, blue catfish (Ictalurus furcatus), and brown shrimp.    

Other recreationally important species collected in lower abundances in open water stations included longnose gar, northern puffer (Sphoeroides maculatus), southern kingfish, summer flounder, gafftopsail catfish, sea catfish, Spanish mackerel, white catfish, American shad, bluefish (Pomatomus saltatrix), pink shrimp, white perch (Morone americana), Atlantic sharpnose shark, pompano (Trachinotus carolinus), and spotted sea trout. 

Comparisons of the abundance and biomass of the dominant recreationally important species indicated that both the abundance and biomass of Atlantic croaker collected in the 2000 sampling season were significantly greater than observed in 1999 (p < 0.05).  No significant differences in abundance or biomass were found between years with respect to the other dominant recreationally important species (silver perch, spot, pinfish, white shrimp, brown shrimp, or blue crabs). 

Tidal Creek versus Open Water Habitat:

The biological communities sampled by trawls at tidal creek and open water stations displayed a similar array of species (see Table 1 below).  However, the abundance, biomass and diversity of organisms in the two habitat types displayed strong differences (Figure 1 below).  Tidal creek sites had three times the mean faunal density observed at open water sites (p < 0.001).  Mean biomass in tidal creeks was also about triple that observed in open water areas (p < 0.001).  While the difference between habitats in the mean number of species was not as great, it was statistically significant (p = 0.028), and as mentioned earlier, trawls in tidal creeks were shorter than at open water sites.   

Table 1. Abundance and percent of occurrence of the most abundant fish and crustaceans  collected in trawls during 1999 and 2000.  Recreationally important species are in bold text.  Abundance values represent No. of organisms / hectare.

Figure 1.  Mean abundance, biomass, and number of species collected in trawls at open water and tidal creek sites during 1999-2000.

    The lower 25^th percentile of these three metrics (mean abundance, mean biomass, and mean species numbers) in open water habitats fell at or below the 10^th percentile for these metrics in tidal creek habitats (Table 2 below).  Several recreationally important fish and crustacean species (silver perch, spot, pinfish, white shrimp, and blue crabs) also had significantly higher abundance and biomass values (p < 0.05) in tidal creeks compared to open water habitats.  The abundance of two typical species, white shrimp and spot, are presented in Figure 2.  These findings strongly support the need to distinguish between these two habitat types in developing threshold values of concern for these and other measures of species abundance, biomass, and diversity, even though tidal creek habitats comprise only 17% of the state’s overall estuarine habitat.

Table 2. Mean values, and the 10th, 25th, and 50th percentiles for abundance/hectare, biomass/hectare, and number of fish and crustacean species collected in open water and tidal creek habitats.

Figure 2.  Abundance of two recreationally important species, white shrimp (P. setiferus) and spot (L. xanthurus), collected in trawls in open water and tidal creek habitats during 1999-2000.

Three of the stations that fell in the lower 10^th percentile for abundance, biomass, and species numbers (RT00502, RO00010, RO99302) had no catch, although both trawls collected at each station were considered to be valid tows by the field crews.  The other stations with low trawl catch metrics did not display a consistent reduction in each metric, but rather an even distribution among the sites with low values for a single metric (abundance, biomass, or species number) and stations that were low in more than one metric.  

All of the stations with trawl catch metrics ranking in the lower 10^th percentile had integrated habitat quality scores greater than 3.5 (see integrated measure section), indicating that they were generally considered to be non-degraded sites with respect to overall water quality, sediment quality and/or benthic condition.  Station locations were almost evenly split between sites located within drainage basins having residential development nearby (< 1 km) and those located well away from residential development; two stations were in areas with no development.  A review of the environmental parameters associated with these stations indicated that one or more parameters at each site showed elevated levels including a toxic microtox or seed clam bioassay, metal contamination exceeding ER-L guidelines, and/or water quality parameters above the 75^th or 90^th percentile for total nitrogen, total phosphorous, chlorophyll-a concentration, fecal coliform bacteria, alkalinity, turbidity, and BOD₅.  In addition, five stations, while falling within the polyhaline range, had salinity values that were below the mean for their respective habitat type.  These lower salinity habitats may support a less dense or less diverse fish and crustacean community, resulting in the low abundance, biomass, and species numbers at RT99037, RO99319 and RT00502, low biomass at RT99531, and low abundance and species numbers at RT99309.  Finally, the mean salinity of 8.2 at station RT99302 classifies the site as mesohaline; in future analyses, trawl catches with mean salinities falling outside the polyhaline range may be analyzed separately.  

Contaminant Levels in Fish Tissue:

Fish, crabs, shrimp and other species can be exposed to contaminants through direct contact and consumption of contaminated sediments and/or prey species.  These contaminants may be stored in the tissue of the fish over long periods of time.  As contaminant levels bioaccumulate, they begin to either have direct effects on the individual animal or are passed on to other species, such as humans, that consume the contaminated organisms.  The SCDHEC has placed consumption advisories on specific fish species or specific areas because of high levels of contaminants in fish flesh.  In cooperation with the EPA National Coastal Assessment Program (NCA), tissue samples were collected from selected target fish species (spot, Atlantic croaker, silver perch and weakfish) beginning in 2000.    

At least one of the target species was collected at 56 of the 60 stations sampled in 2000, with spot being the most common fish collected (38 sites) and Atlantic croaker being the next most common species (10 sites).  Weakfish or silver perch were used as the representative species at the remaining 8 sites (Appendix 4.3).   All of the whole body tissue samples had detectable levels of some contaminant analytes, but only one site (RO00056 in Shipyard Creek, Charleston Harbor) had levels that were elevated for two PAH analytes (Appendix 4.4).  Spot collected from this site had a fluorene wet weight concentration of 15 ng/g and a dry weight concentration of 71 ng/g.  The anthracene concentrations in these spot were 78 ng/g (wet weight) and 383 ng/g (dry weight).  The recovery rate for fluorene was good based on the analysis of standard reference material (SRM) tissue, but anthracene recovery rates were poor (SRM average recovery rate = 42%).  This suggests that the actual anthracene concentration may have been higher than reported.  A corrected concentration would be approximately 186 ng/g (wet weight) and 912 ng/g dry weight. 

When comparisons were made to NCA database for tissue contaminants (unpublished), only anthracene and fluorine at station RO00056 exceeded maximum concentrations observed in other coastal areas of the country.  None of the contaminant analytes exceeded Food and Drug Administration (FDA) criteria for safe consumption.  It should also be noted that these analyses were done on whole fish, rather than just edible tissue that is used for the consumption advisories. 

In order to begin developing criteria on elevated tissue contaminant levels in South Carolina waters, the concentration that represented the 90^th percentile value for each analyte was generated using data from all 56 stations (Appendix 4.3).  The number of analytes measured that exceeded their respective 90^th percentile value was then computed as a measure of chemical enrichment in fish tissue at that site.  The Shipyard Creek site (RO00056) had the maximum number of exceedances (35) out of a total possible score of 87 (number of analytes measured).  Of the stations with the most analyte exceedances, five sites were close to industrial facilities (RO00056, RO00009, RO00015, RO00020, RT00549) and four sites were close to residential development (RO0006, RT00526, RT00549, RT00550). 

Because many of the analytes were below or close to their detection limits, comparisons between the two habitat types (open water and tidal creek) on an analyte by analyte basis would not have provided a meaningful contrast.  Comparisons were therefore made on the sum of all analytes in a class using a Mann-Whitney Rank Sum Test.  The classes were total DDT, total PAH and total PCB.  There were no significant differences between tidal creek and open water habitats for total DDT or total PAH (p = 0.05).  Total PCBs were significantly higher in open water habitats than in tidal creek habitats (p = 0.03). 

The USEPA, in a recent report suggested that southeastern estuaries generally had low tissue contaminant levels compared to the northeast, gulf and west coast regions (USEPA, 2001).  The results from the SCECAP data set, although limited to only one year of data, support this evaluation.