Spatial management of marine resources can enhance the recovery of predators and avoid local depletion of forage fish

Abstract

The eastern Baltic cod stock has recently started to recover, after two decades of severe depletion, however with unexpected side effects. The stock has not re‐occupied its former wide distribution range, but remains concentrated in a limited area in the southern Baltic Sea. The biomass of forage fish, i.e., sprat and herring, is historic low in this area, which in combination with increasing cod stock results in locally high predation mortality of forage fish and cannibalism of cod. In line with low prey availability, body weight and nutritional condition of cod drastically declined. In the southern Baltic Sea, cod competes with pelagic fisheries for the limited resources of sprat and herring, while the largest biomass of these species is currently found outside the distribution range of cod. Accounting for spatial overlap between species is crucial in developing ecosystem based fisheries management to enhance the recovery of predator stocks.

Regional trade-offs from multi-species maximum sustainable yield (MMSY) management options

“…Our model framework has room for improvements, in particular regarding environmental influences on recruitment (Köster et al 2009), density-dependent growth (Casini et al 2011, Gårdmark et al 2013 and processes accounting for changes in the spatiotemporal overlap of cod and sprat (Eero et al 2012). Nevertheless, we are confident in the range of simulated outcomes.…”

Identifying marine pelagic ecosystem management objectives and indicators

“…Only in special circumstances can dependence of predators on certain preys become limiting, such as in ecosystem with few prey species or predators with a small prey portfolio and localised distribution. Baltic Sea cod feeding on sprat and herring seems to be such a case [23], there are indications that the pelagic prey of cod may have moved spatially further away (north) from the cod populations.…”

How Long Does it Take for Tropical Marine Fish Stocks to Recover after Declines?Case Studies from the Southwest Coast of India

“…In temperate waters, there is only limited evidence for recovery of depleted fisheries based on the present management strategies employed 12,41 . Most severely overfished stocks hence tend to stay depressed or recover only slowly; exceptions to this rule mostly concern particular fast-growing species such as herring and sardines 42 and certain stocks of cod which are well managed 43 . The most important point to be noted is that currently there is no ability to engineer fast recovery of marine resources under the fisheries management regulations in vogue 42 .…”