Assessment of Red King Crabs Following Offshore Placer Gold Mining in Norton Sound Stephen C. Jewett Reprinted from the Alaska Fishery Research Bulletin Vol. 6 No. 1, Summer 1999 The Alaska Fishery Research Bulletin can found on the World Wide Web at URL: http://www.state.ak.us/adfg/geninfo/pubs/afrb/afrbhome.htm . Alaska Fishery Research Bulletin 6(1):1–18. 1999. Articles Copyright © 1999 by the Alaska Department of Fish and Game Assessment of Red King Crabs Following Offshore Placer Gold Mining in Norton Sound Stephen C. Jewett ABSTRACT: In a 4-year study I assessed impacts of offshore placer gold mining on adult red king crabs Paralithodes camtschaticus in the northeastern Bering Sea near Nome, Alaska. From June to October 1986– 1990, nearshore mining with a bucket-line dredge to depths of 9 to 20 m removed 1.5 km2 and about 5.5 × 106 m3 of substrate. Crabs were offshore of the study area when mining occurred but were in the mining vicinity during the ice-covered months of March and April, which was the primary time data on crab abundance and prey were obtained. Comparisons between mined and unmined stations revealed that mining had a negligible effect on crabs. Crab catches, size, sex, quantity, and contribution of most prey groups in stomachs were similar between mined and unmined areas. However, a few ROV observations indicated that crab abundance was lower in mined areas. Also, plants (mainly eelgrass Zostera marina) and hydroids, which accumulated in mining depressions, were more common in crab stomachs from mined areas. The preponderance of food consumed by crabs throughout the mined and unmined regions was unidentified fishes. Mining effects were analyzed in the context of the small size of the area disturbed, the dynamic nature of the benthic habitat in the region, and the opportunistic feeding habits of the crabs. INTRODUCTION Kenny and Rees 1996). Some investigations utilized large motile epifauna, such as crabs, in their monitor- Small, unregulated placer mining at the turn of the cen- ing studies (Stevens 1981; also see Poling and Ellis tury and more recent (1970s and 1980s) short-term 1993; Ellis et al. 1994; Johnson et al. 1998; Stone and exploratory endeavors have typified coastal marine Johnson 1998 for review of monitoring programs asso- mining activity in Alaskan waters (R. Baer, U.S. De- ciated with submarine tailings disposal). The red king partment of the Interior, Bureau of Mines, Juneau, per- crab Paralithodes camtschaticus (family Lithodidae) sonal communication). Only one Alaskan marine mining supports commercial and noncommercial (subsistence) project on the continental shelf has been environmen- fisheries in Norton Sound that encompass the mining tally monitored. That project, known as the Nome Off- area off Nome. Consequently, this species was the shore Placer Project, assessed the effects of placer choice of regulatory agencies and special interest groups gold mining in the shallow waters of Norton Sound in to evaluate the effects of mining on marine benthos. the northeastern Bering Sea. Mining took place be- Ideally, a long-lived, benthic organism of limited or no tween 1986 and 1990; monitoring occurred between mobility would be most appropriate for monitoring; how- 1986 and 1991. Generally, monitoring of marine mining ever, no such organism inhabits this dynamic nearshore and dredging includes tailing discharge rates, chemical environment. analyses, turbidity, and trace-metal bioaccumulation and This study was designed to evaluate the potential biomagnification (Ellis 1988), and most environmental effect of mining activity on red king crabs in north- monitoring programs include quantification of benthic western Norton Sound near Nome. Specific objectives organisms as an index to assess the effects of mining. were to examine their relative abundance, distribution, Infaunal invertebrates are most frequently sampled and prey. The potential effects of mining on this crab (e.g., Swartz et al. 1980; Jones and Candy 1981; Poiner species are also addressed in Jewett (1997) and Jewett and Kennedy 1984; Ellis and Hoover 1990a, 1990b; et al. (1999). Author: S. C. JEWETT is a research professor with the Institute of Marine Science, School of Fisheries & Ocean Sciences, Univer- sity of Alaska Fairbanks, Fairbanks, AK 99775-7220. Acknowledgments: L. A. Gardner and P. C. Rusanowski — assisted in the planning and sampling; K. McCumby — provided taxonomic assistance; A. Blanchard and C. Chu — assisted with data management and analyses; and A. Blanchard, H. M. Feder, A. S. Naidu, J. B. Reynolds, T. C. Shirley, R. L. Smith — reviewed the manuscript. Project Sponsorship: This investigation was partially funded by now dissolved Western Gold Exploration & Mining Company, Ltd. Partnership (WestGold), 5251 DTC Parkway, Suite 700, Englewood, CO 80111. 1 2 Articles Study Area Numerous storms are prevalent, particularly during the fall months. For example, during October and Novem- This study was conducted from 1986 to 1993 within ber 1989 and 1990, peak easterly winds of over the 88 km2 of State of Alaska offshore mining leases 47 km·h–1 were observed at Nome for 9 and 24 d, re- in northwestern Norton Sound adjacent to the city of spectively (NOAA, Local Climatological Data Monthly Nome. The lease area extends from 64° 26' N north- Summary). A severe storm battered the region on ward to the southern coastline of the Seward Penin- October 5, 1992, with winds to 94 km·h–1 (Nome Nug- sula. The southern boundary generally follows the 20-m get 1992) and disrupted the nearshore habitat to depths depth contour. The eastern boundary is due south, mid- of at least 12 m (personal observation). Surface sedi- way between the mouths of the Snake and Nome Riv- ments in the vicinity of the study area consist of a mo- ers (165° 22' W), and the western boundary is due saic of sediment types including relict gravel and sand south, midway between the mouths of Cripple Creek from residual lag deposits along with modern sediments and Penny River (165° 46' W; Figure 1). The west- of very fine sand- and silt-sized particles from the Yukon ward flow of water along the south coast of the Seward River (Drake et al. 1980; Hess and Nelson 1982; Naidu Peninsula varies in intensity and extent (Hood et al. 1988). The fine sand and silt substrate overlying the 1974; Muench et al. 1981). Surface currents in the more permanent cobble substrate is transient in nature region typically range from 5 to 20 cm·s–1, but current and subject to redistribution by storms, currents, and speeds up to 100 cm·s–1 may occur in the Nome vicin- ice gouging. Wave-induced nearshore currents move ity (Nelson and Hopkins 1972). Bottom current speeds fines both east and west, but the net nearshore sand are generally 10–20 cm ·s–1 (Muench et al. 1981). Tidal transport is to the west approximately 5 × 105 m3·y–1 fluctuations are minimal (Pearson et al. 1981), but major (Drake et al. 1980; Tetra Tech 1980). In the ice-free storms can cause dramatic fluctuation in sea level. months of June through November bottomwater tem- ° ° ° ° ° ° 167 W 166 165 164° 163° 162 161 160 W 65° N STUDY SEWARD PENINSULA AREA NOME SLEDGE ALASKA ISLAND 64° STUDY AREA NORTON SOUND ° 63 N YUKON RIVER CRIPPLE 165o 46' PENNY 165o 22' CREEK RIVER SNAKE RIVER 64o 32' N 64o 32' 10 m C4 R6 02 1986 C3 NOME scale in km LEGEND 1989 R7 MINED AREAS 1987-90 CRAB 20 m STATIONS 1990 S3 NOME 1987 RIVER 1987 1988 1989 1989 1990 1990 1988 MINING LEASE BOUNDARY 165o 22' 64o 26' 64o 26' Figure 1. Map of the Nome Offshore Placer Project showing mining lease boundary, areas mined by year, and 5 stations surveyed for red king crabs. Assessment of Red King Crabs Following Offshore Placer Gold Mining in Norton Sound • Jewett 3 peratures typically range from near 0 to 12°C and sa- ment Council (Natcher et al. 1999). The stock within linities from 21 to 34‰. During ice-covered months of Norton Sound is unique because it: (1) is separate from December through May bottom temperatures range other stocks in the Bering Sea (Seeb et al. 1989), (2) from -1.8 to 1.5°C and salinities from 32 to 34‰ (Hood lives under ice for 5–6 months a year (Dupré 1980), et al. 1974; Muench et al. 1981; Jewett, unpublished). and (3) is confined to waters <31 m in depth. The crab Ice thickness is variable and may approach 1.2 m. The population within the sound is relatively small. A popu- seaward edge of the ice generally extends to the 20-m lation assessment in August 1996 placed the total num- isobath and may be anchored by ice keels especially in ber of legal males (>121 mm carapace width [CW]) at the region from 10 to 20 m (Thor and Nelson 1981). 0.5 million crabs (Lean and Brennan 1997). Migra- Ice gouging takes place sporadically and trends east to tions of the Norton Sound crabs typically follow north– west; gouges normally are <25 m wide and cut <0.5 m south or northeast–southwest patterns (Powell et al. deep into the substrate (Thor and Nelson 1981). 1983). The greatest recorded migration rate in the sound Bioturbation by numerous benthic invertebrates, dem- is 61 km in 46 d (Powell et al. 1983), and the crabs ersal fishes, and occasionally Pacific walrus Odobenus could conceivably traverse the full 250-km length of rosmarus divergens also takes place (Jewett and Feder the sound in a seasonal migration. Adult male red king 1980; Nelson et al. 1981; Klaus et al. 1990). crabs, monitored under ice with ultrasonic biotelem- etry, had an average net movement of approximate- Mining Overview ly 0.26 km·d–1 in the nearshore region near Nome (Rusanowski et al.