Cyclical trends in the biomass and mean body weight indices of two Northwest Atlantic squid species and their synchronies with Gulf Stream latitudinal positions

Autoregressive spectral analysis revealed underlying cyclical trends in the highly variable biomass and mean body weight indices of two Northwest Atlantic squid species with opposing life histories. Doryteuthis pealeii attaches its egg masses to the seabed in shallow waters on the Northeast USA shelf. The broader-ranging Illex illecebrosus uses the Gulf Stream (GS) to transport its pelagic egg masses and paralarvae from the Southern (USA shelf) to the Middle (Scotian Shelf) and Northern (Grand Banks) Fishery Regions. We compared significant spectral peaks, or cycles, between the 1993–2016 survey indices, GS latitudinal positions (at 74°, 70°, 65°, 60°, 55° and 50°W) and winter North Atlantic Oscillation (NAO) indices to reveal any synchronicities. Positive NAO anomalies associated with northward GS position shifts were predominant. NAO indices exhibited 2–3-year, 4–5-year, and near-decadal cycles. GS position periodicities included 2–3-year, 3–4-year, and both timescales for west of 65°W (Western Segment), east of 60°W (Eastern), and from 65° to 60°W, respectively. I. illecebrosus indices exhibited stock-wide 3–4-year cycles and 2–3-year cycles for the Middle and Southern Fishery Regions that were synchronous with GS latitudinal positions for the Eastern and Western GS Segments, respectively. D. pealeii biomass cycles varied seasonally. Spring 4–5-year cycles were synchronous with the NAO, and fall near-decadal cycles were synchronous with the NAO and all GS locations analyzed. Our findings of inter-annual biomass and body weight cycles from 2 to 3 years to near-decadal are remarkable given the sub-annual lifespans of both species, but confirm the tight coupling between recruitment, body size, and cyclical environmental forcing factors.