Rainfall – Ocean Faunal Interactions, Carteret County, North Carolina

Environmental data has been recorded at the Institute of Marine Sciences (IMS), Morehead City, Carteret County, North Carolina since 1947, rainfall since 1967 (Porter 1985). Porter (1985) analyzed IMS 1979–1981 rainfall noting yearly means of 0.147 inches: 3.73 mm/day/yr. Questions arose: have rainfalls been static during subsequent years 1983–2011; has rainfall at IMS and the adjacent Atlantic Ocean been influenced by storms and hurricanes: and did rainfall and hurricane runoff, flooding and other influences affect shark, finfish and shrimp catches? Answers would shed light on these rainfall/faunal interrelationships.

Rainfall, was collected, during the years 1983–2011, using a rain and snow gauge, U.S. Weather Bureau spec. no. 450-231, Science Associates inc. Model 503 gauge set unobstructed a few meters away from IMS and nearby vegetation. Rainfall was measured as inches/day (1 in.  =  25.4 mm). Yearly, rainfall data was collated and depicted graphically as: means, standard deviations, standard errors of the means and ranges (Fig. 1) using R, ver. 2.15.0 R Development Core Team2012 computer program.

An analysis of variance (ANOVA) tested yearly 1973–2011 rainfall and shark catch trends. Linear regressions, y  =  a + b× were fitted to Onslow Bay 1972–2011 shark longline catch trends (Fig. 2).

Yearly rainfall increased significantly after 1988 (f  =  778, 38 df*) from averages of 705 mm (47.03 in/yr) in pre 1998 to 1,209 mm (51.6 in/yr) during 1999–2011. Yearly IMS rainfall varied 0.51 in/day (12.95 mm/day) during 1983–1999 and 0.75 in: (19.1/day mm) during 2000–2011 (Table 1).

Heaviest rainfalls occurred during August 1999 (Hurricane Dennis, 19 inches, 506 mm), September 1999 (Hurricane Floyd 20 inches (500 mm) and September 2005 (Hurricane Ophelia 17.5 inches (445 mm) Table 1. Yearly, rainfall increased after 1990, ANOVA f  =  7.38, 38 df*.

IMS and adjacent ocean areas were subject to 18 hurricanes between 1983–2011 (Fig. 1). Most occurred in August (7) and September (8) (Table 1). Hurricanes Floyd and Fran caused the most runoff and flooding in eastern North Carolina and influenced water temperatures. Hurricane Fran (September 1996) was the fiercest, arriving at 130 mph (220 km/hr) and caused 10 ft. (3 m) storm surges. Hurricane Floyd (1999) velocity was 197 km/hr and caused 10 ft (3 m) storm surges.

Hurricanes Dennis (September 1984) caused 3 deaths, Fran (September 1996) 14, Floyd (September 1999) 35, and Irene (September 2011) 13 (Table 1).

Yearly shark longline catches between 1973–2011 in Onslow Bay, expressed as catch/unit/effort (CPUE), varied between 0.167 sharks/hook in 1973 and 0.18 in 2003 (Fig. 2). Linear regressions of these variations were : y  =  −0.165× − 1.024, r²  =  0.47 (yrs 1973–1990) f  =  0.0478 and y  =  0.5152× − 2.013, r²  =  0.0804, (years 2000–2011). Long-line catches were greater during pre-1990 and lower post 1990 (when ocean water temperatures shifted significantly f  =  6.40, df 38 (from cooler pre 1990 to warmer 1990 yrs (Schwartz et al. 2010).

Commercial finfish landings varied greatly, similar to shark catches (Table 2): greater during pre 1983–1990 yrs, smaller during post warmer years 1991–2011.

Shrimp catches varied, similar to finfish catches, greater during cooler water years (1973–1999 and smaller during warmer water years (2000–2011) (Table 2).

Most people are oblivious that North Carolina's IMS rainfall and ocean faunas were intricately interrelated as a result of precipitation, storms, and distant El Nino and La Nina influences. Local precipitations cause runoff and flooding that affected river nutrient loads in the adjacent ocean (Drinkwater 1986; Christian et al. 1991; Bales 2003; Boyles et al. 2004; Paerl et al. 2006; Cahoon 2013).

Hurricane precipitation drastically affected Atlantic ocean water temperatures between 1972–1994 vs. 1995–2011; as cooler waters occurred between 1972–1999 vs. warmer waters during 2000–2011 (Goldenberg 2001; Schwartz et al. 2010). Schwartz et al. (2010) noted water temperature shifts and the effects on shark longline catches in Onslow Bay. As ocean water temperatures, increased ice cap melting is occurring and in turn increasing hurricane activity in various parts of the world (Delworth et al. 2007). El Nino events (where Pacific ocean waters are warmer) decreased winter and increased summer precipitation. La Nina reversed these events and increased summer and fall hurricanes (Boyles et al. 2004). Decreased local precipitation affected North Carolina invertebrate faunas (Kirby- Smith and Ustach 1986); Bell and Hall (1999), while sharks (Dogfish and blacknose sharks) simply swam away from hurricane front influences (Gibson 1980; Fiedler and Bernard 1987; Fraser and Shelmerdine 2002; Heupel et al. 2003) and once their skin hair cells sensed hurricane hydrostatic pressure changes. Black tipped sharks vacated an area during heavy rainfalls (Heupel et al. 2003). Pelagic tuna and bottom fishes also responded similarly by swimming away from an affected area (Power and May 1994; Russel 1997; Watterson et al. 1998; Kirby et al. 2000).

Thus, rainfalls are a result of many intricately interrelated events. Rainfall varied at IMS every year. Variations influenced runoff, flooding, while ocean temperature changes influenced shark, finfish, and shrimp populations. Knowledge of these interrelationships would help us better utilize our ocean faunas, on which we depend, and understand the input of rainfall, storms and hurricanes on an area.

Ben Peierls created Figure 1. S. Mclnemy North Carolina Division of Marine Fisheries provided ocean finfish and shrimp landing information. C. McCandless National Marine Fisheries Service Narragansett, RI furnished the Onslow Bay CPUE shark data. Librarians P. Mararo NOAA and J. Miller Duke Marine Lab, Beaufort, NC furnished several important references. To all we owe our thanks.