Evidence of Multidecadal Recruitment in the Ocean Quahog, Arctica islandica in the Western Atlantic Ocean

Sara Pace1, Eric Powell1, and Roger Mann2 1Gulf Coast Research Laboratory 2Virginia Institute of Marine Science

Ocean quahogs (Arctica islandica)

• Distribution along both coasts of the North Atlantic basin.

• Tolerates bottom temperatures up to 16° C.

• Shell length up to ~ 130 mm.

• Current estimates age oldest specimen at 507 years (Butler et al. 2013).

Recruitment

• Literature suggests recruitment events are regional and infrequent, occurring once or twice every 20-40 years (Powell & Mann 2005).

• While recruitment appears to be rare in the context of the fishery, as these animals commonly exceed 200 years in age, recruitment is frequent considering their longevity.

• Do not recruit to fishery for 1-3 decades after settlement.

• Any increase in stock productivity anticipated from fishing down the stock would likely be delayed due to time lag between settlement and recruitment to fishery.

25000 Annual OQ Landings

Ocean Quahog Fishery 20000

• Commercially important species 15000 since fishery began in late 1960’s. 10000 • Recent annual landings range EEZ Landings (mt meat) from ~14,000-16,000 mt (meat). 5000

0 • Fishing limits set using information 1975 1980 1985 1990 1995 2000 2005 2010 2015 about biological reference points (BRPs). Year

• Limited information available about OQ stock metrics makes setting BRPs uncertain.

• Updating BRPs is dependent upon the development of a long-term recruitment index.

Objectives

Consensus is that no progress on BRPs can be made without information on long-term recruitment dynamics.

• To utilize imaging software to provide individual ages from analysis of yearly growth bands of selected individuals.

• To develop population age-frequencies for ocean quahogs.

• To use these age frequencies to develop a recruitment time series supporting reference point recommendations for ocean quahogs. Sample Collection Locations

• Clams are collected with a commercial clam dredge.

• 2 collections per site 1. First ~400 clams measured and retained. 2. Every clam is measured but only clams within largest 20th percentile retained.

Sampling Methods

• Full size distribution from each site is split up into 5 mm intervals from 80-120 mm (80 mm fully selected to fishery).

• ~20 clams sampled from each size interval at all sites.

• An additional 20 individuals from one 5 mm size bin at each site have been sampled. • Clams are sectioned along the height axis on a commercial tile saw.

• Clams are ground on increasingly fine sand paper grits and polished using diamond suspension on a wet polishing wheel.

Annual Growth Band Analysis Age-at-Length Plots Long Island 130 New Jersey 130 125 F 125 F F F F 120 120 F F F F F FFF F F F FF F F 115 115 FF F FFFFF FFF F F FFFFF FF F F F FF F F F F F F F 110 F FF F F 110 F FFF F F FFF FFFF F F F FF FF F F F F FF F F FFFF F FFFF 105 F FF F F 105 F F FF FF FF F F FFFFFFF F F FFF F F F 100 F FFFF FF F 100 FFFF F F F F F F F F F F FFF F FFF FF F F F FF FFF F F FFF F F F FF F FF F FF FFFFF F FFFF FFFF F F F FFF F FF FFFF F F F F FF 95 F F Length (mm) Length (mm) 95 F F FF F F F F FF F F FFF F FF FFF F FF FFF F F F F F F F F FF 90 FF F 90 F F FF F F FF FF F FF F FFF FFFF F F FFF 85 FF F 85 FFFFFFF F FFFF F F F FFF F FFFFF F FFFF F FFFFF 80 FFF F F 80 75 75 20 40 60 80 100 120 140 160 180 200 220 240 260 20 40 60 80 100 120 140 160 180 200 220 240 260 Age Age Georges Bank 130 130 Southern New England 125 125 120 120 115 F 115 F F F F F FFFFFFF F F 110 F F F F 110 FF FF F F F F FFF F FF F F FF 105 F F FF F 105 F FFFFFFFFFFF FF F FFFFFFF F F FFFFFF FFFFFFF F F F F FFF F 100 FF F F 100 F FF FF F F F FFF F F F FFF F FFFFFF F F FF F F FFFF 95 F F F 95 F F Length (mm) F FFF F Length (mm) FFF FFFF F F F FFFFFFFF FF F FFFFFFFFFFF F FF F F F F F F 90 FFFF FF FF 90 FFFF F FF F FFFFFF F FFFF F F F FFFFFF F 85 FF FFFF 85 FF F FFF FFFF FF F F FF FF F FF F FF FF FFFFFF 80 F F F 80 FFF F 75 75 20 40 60 80 100 120140160180200 220240260 20 40 60 80 100 120 140 160 180 200 220 240 260 Age Age

GB age frequency 80

70

60

50

40

30 Numbers per 10 minute tow 20

10

0 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 99 102 105 108 111 114 117 120 123 126 129 132 135 138 141 144 147 150 153 156 159 162 165 168 171 174 177 180 183 186 189 192 195 198 Age Conclusions • All 4 sites have old, rarely occurring individuals present in the tail end of the population age-frequency. • Oldest animal at each site: • NJ: 220 y • LI: 248 y • GB: 198 y • SNE: 172 y

• All 4 sites experience a ramp up of recruitment: • NJ: 1855 (~160 y) • LI: 1905 (~110 y) • GB: 1890 (~125 y) • SNE: 1900 (~115 y) • Hypothesis: increase in recruitment co-occurs with ending of the Little Ice Age as the water warmed up.

Conclusions

• The populations at all 4 sites come to an asymptote, indicating that population is at carrying capacity.

• Large year classes not common, recruitment seems to be consistent over a long period of time. • Decrease in young individuals at all 4 sites is due to truncation of data set (only clams > 80 mm aged), not due to a reduction in recruitment. Acknowledgements

• ICES Early career scientist travel award

• Captain and crew of the F/V Christy and F/V Pursuit

• Advisors: Eric Powell, Roger Mann

• Chase Long