Variation in Energy Density of Northwest Atlantic Forage Species: Ontogenetic, Seasonal, Annual, and Spatial Patterns.

Wuenschel, Mark¹, Kelcie Bean², Tara Rajaniemi², Kenneth Oliveira², ¹NOAA Fisheries NEFSC, Woods Hole, MA, ²University of Massachusetts, Dartmouth, North Dartmouth, MA

Energy density estimates for marine forage species have been limited, impeding our understanding of this important trophic level. We studied the energy density of eight key forage species; alewife (Alosa pseudoharengus), Atlantic Herring (Clupea harengus), Silver Hake (Merluccius bilinearis), Northern Sand Lance (Ammodytes dubius), Atlantic Mackerel (Scomber scombrus), Butterfish (Peprilus triacanthus), Northern Shortfin Squid (Illex illecebrosus), and Inshore Longfin Squid (Doryteuthis pealeii). Samples were obtained from NOAA NEFSC spring and fall bottom trawl surveys across four regions (Gulf of Maine, Georges Bank, Southern New England, and the Mid-Atlantic Bight) from 2017-2019. In the lab, we developed predictive relations between the percentage dry weight (%DW) and energy density (kJ/g-1) determined by proximate composition analysis (n= 624; r2 0.75 to 0.98). The energy density of additional samples (n=4,670) were estimated from %DW using these relations. For each species, we modeled energy density as a function of fish size, depth, season and year as factors, and location (Latitude, Longitude) using generalized additive models (GAMs). Except for Atlantic Herring, which spawn in fall, species had higher energy density in fall compared to spring. The best fit GAMs included weight, depth by season, and season and year effects for most species. Location (by season) explained significant amounts of variation. Observed variation in energy density across regions, species, seasons, and years provides empirical data to propose and test hypotheses related to ‘upstream’ regulation of energy density (via environmental drivers and productivity) and ‘downstream’ effects on recruitment for these species as well those that prey on them.