Fishing, predation, and temperature drive herring decline in a large marine ecosystem

Since 1960, landings of Atlantic herring have been the greatest of any
marine species in Canada, surpassing Atlantic cod and accounting for 24%
of the total seafood harvested in Atlantic Canada. The Scotian Shelf-Bay
of Fundy herring fisheries (NAFO Division 4VWX) is among Canada’s oldest
and drives this productivity, accounting for up to 75% of the total
herring catch in some years. The stocks' productivity and overall
health have declined since 1965. Despite management measures to promote
recovery implemented since 2003, biomass remains low and is declining. The
factors that drive the productivity of 4VWX herring are primarily
unresolved, likely impeding the effectiveness of management actions on
this stock. We evaluated potential drivers of herring variability by
analyzing 52 time-series that describe the temporal and spatial evolution
of the 4VWX herring population and the physical, ecological, and
anthropogenic factors that could affect them using structural equation
models. Variation in herring biomass was best accounted for by the
exploitation rate's negative effect and the geographic distribution
of fishing and recruitment. Thermal phenology and temperature adversely
and egg predation positively impacted the early life stage mortality rate
and, ultimately, adult biomass. These findings are broadly relevant to
fisheries management, but particularly for 4VWX herring, where the current
management approach does not consider their early life stage dynamics or
assess them within the ecosystem or climate change contexts.