Integrating Fishermen's Knowledge with Empirical Data: The Case of Cod (Gadus morhua) Spawning Groups and Alosines

Fishermen’s qualitative observations provide valuable insights, but are notably difficult to integrate with empirical data.  This study examines an approach developed to evaluate biogenic factors associated with the disappearance of cod (Gadus morhua) spawning groups in northern New England where cod are collapsed.  Cod predation of yr0 Atlantic herring (Clupea harengus), and two diadromous prey species, alewives (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) was examined near six rivers in mid-coast Maine to clarify the interaction of cod spawning groups and oil-rich prey. Spatial distribution of yr0 oil-rich prey from recent trawl surveys was used with fishermen’s pre-1960s sites with ripe cod to identify co-occupied sites. Simultaneously displaying yr0 oil-rich prey distribution with pre-1960s sites where ripe cod were caught on a geographic information system (GIS) show ripe cod were caught in the same areas where all three oil-rich prey species are currently found in fall. Fishermen reports from the 1920s confirm that cod were caught at the same fall sites. This procedure identified sites near all six rivers with ripe spawning group cod and the three oil-rich prey until the mid-1960s when yr0 prey abundance dropped precipitously, suggesting nearshore cod spawning groups were linked to yr0 alosids and clupeids.