Wondering about wandering whiting: Distribution of North Sea whiting between the 1920s and 2000s

The responses of fish populations to anthropogenic and environmental drivers are of growing interest. In commercial fisheries attention is increasingly directed to species historically being of secondary importance and potentially being influenced by these drivers. We present long-term commercial fisheries data of North Sea whiting (Merlangius merlangus), comprising international catches (1903–2010), quotas (1980–2010), and British otter trawler data (landings-per-unit-effort (lpue) for 1923–2009 at the spatial scale of ICES rectangles). Based on lpue data, we tested the possible effects of climate change and fishing pressure on whiting distribution. Results showed no distinct latitudinal and deepening shifts, but a ∼1° westward shift between the late-1940s and 1960s. Relations to climate change and fishing pressure were not strong. The lack of clear latitudinal and deepening shifts contrasts with recent studies on other North Sea species reporting such shifts related to temperature change. The North Sea is at the centre of the distribution range of whiting, and the temperature changes might still fall well within the physiological tolerance limits of this species, hence not affecting the distribution. The drivers for the longitudinal shift remain unclear. However, whiting is also commonly discarded by fisheries; if levels of discarding differ spatially, our results may not represent the true picture of whiting distribution and need to be interpreted with caution. This highlights the challenge in detection and attribution of climate change effects on exploited fish stocks with commercial data only.