Change in size of deep-sea demersal fish over depth and time

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Deep-sea communities along the continental slope experience a vast environmental gradient, because as depth increases, pressure increases, and temperature, salinity and oxygen decrease. This means that when understanding the effects of fishing or climate change in the deep sea, we must first take account of bathymetric changes. Here we present changes in fish body size over depth and time in the Northeast Atlantic, by accounting for observed size as well as potential maximum size, Lmax. There is an increase in fish size as depth increases, and this effect becomes even more pronounced when we account for the Lmax of the species, implying that individuals are further along in their growth trajectory in deeper waters than they are in the shallows. This may be because of fishing impacts at the shallow end of their range, or due to ontogenetic shifts in species depth ranges. When Lmax is taken into consideration, size has increased over time in shallower waters, possibly due to stricter controls on fishing in the area in recent years. Time trends change depending on the depth range examined, so the “deep sea” cannot be treated as one unvarying system.