Abstract
The understanding of natural variability of harvestable fish stocks is of fundamental interest for their management; however, time series are often biased by the impact of fisheries. Observations show that the mean weight of central Baltic Sea herring (Clupea harengus), a quantity unbiased by fisheries, is indirectly influenced by the Atlantic Multi-decadal Oscillation (AMO) via a complex mediator chain, in which a transition from a marine to a freshwater state plays a major role. This observed trend is also projected for the future in regional climate change scenarios. The consequence of increasing precipitation is a reduction in the marine habitat, a change in the prey community and a decrease in the mean weight of three-year-old central Baltic Sea herring from 50-70 g in the late 1970s to 25-30 g today. The reduction in weight over this period represents a reduction in landings of approximately one million tons of herring and an economic loss of the order of €100 million.
Highlights
Global fish production is under threat from overexploitation and climate change (Jackson et al, 2001; Drinkwater et al, 2003; Brander, 2007, 2010)
In this paper we show that the decrease in the mean weight of 3-year-old central Baltic Sea herring is caused by climate variability via a complex mediator chain described in the following
The observed reduction in the mean weight of central Baltic Sea herring from 50 to 70 g in the late 1970s to 25–30 g today has resulted in a catch deficit in the weight of fish over this period
Summary
Global fish production is under threat from overexploitation and climate change (Jackson et al, 2001; Drinkwater et al, 2003; Brander, 2007, 2010). The strongest impact from climate variability occurs in northern areas like the Barents and Baltic Sea (ACIA, 2015), as well as in enclosed areas, e.g., the Black and Baltic Seas (BACC Author Team, 2008; Philippart et al, 2011). The Baltic Sea is an intra-continental dilution basin with a total area of 415,000 km (including Kattegat, Figure 1) that has a highly productive but low-diversity ecosystem with cod, sprat, and herring as top predators. It is characterized by a closed basin circulation (Voss et al, 2005) and by strong horizontal and vertical gradients in salinity and in ecosystem variables. A local minimum in species numbers occurs in the 5–7 salinity range (Remane, 1934)
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