How does fishing alter marine populations and ecosystems sensitivity to climate?

Abstract

Evidence has accumulated that climate variability influences the state and functioning of marine ecosystems. At the same time increasing pressure from exploitation and other human activities has been shown to impact exploited and non-exploited species and potentially modify ecosystem structure. There has been a tendency among marine scientists to pose the question as a dichotomy, i.e., whether (1) "natural" climate variability or (2) fishery exploitation bears the primary responsibility for population declines in fish populations and the associated ecosystem changes. However, effects of both climate and exploitation are probably substantially involved in most cases. More importantly, climate and exploitation interact in their effects, such that climate may cause failure in a fishery management scheme but that fishery exploitation may also disrupt the ability of a resource population to withstand, or adjust to, climate changes. Here, we review how exploitation, by altering the structure of populations and ecosystems, can modify their ability to respond to climate. The demographic effects of fishing (removal of large-old individuals) can have substantial consequences on the capacity of populations to buffer climate variability through various pathways (direct demographic effects, effects on migration, parental effects). In a similar way, selection of population sub-units within meta-populations may also lead to a reduction in the capacity of populations to withstand climate variability and change. At the ecosystem level, reduced complexity by elimination of species, such as might occur by fishing, may be destabilizing and could lead to reduced resilience to perturbations. Differential exploitation of marine resources could also promote increased turnover rates in marine ecosystems, which would exacerbate the effects of environmental changes. Overall (and despite the specificities of local situations) reduction in marine diversity at the individual, population and ecosystem levels will likely lead to a reduction in the resilience and an increase in the response of populations and ecosystems to future climate variability and change. Future management schemes will have to consider the structure and functioning of populations and ecosystems in a wider sense in order to maximise the ability of marine fauna to adapt to future climates

Synergies between climate and management for Atlantic cod fisheries at high latitudes

“…Prevailing harvesting regimes have also been challenged (7) and contemporary management procedures of many of the world's leading fisheries nations indirectly criticized (8). Assessment tools are unfortunately limited in the amount of complexity (or biological realism) that can be included, even though it is known that stock dynamics result from the interplay of multiple factors acting on the population, each of which can cause fundamentally different responses (9)(10)(11)(12).…”

“…Because of the different ecological responses, a population may react immediately to a climate signal or, because there are often several physical or biological intermediary steps between the forcing and the ecological trait, have a temporally delayed (lagged) response (11,18). These complex interactions may cause unexpected disruptions in the ability of a population to withstand or adjust to climate changes, cause populations to become more sensitive to climate variability at interannual to interdecadal scales (9), or cause fishery management schemes to have unexpected results (10). Hence, it is probably impossible to completely disentangle the effects of fisheries and climate on population.…”

Changing central Pacific El Niños reduce stability of North American salmon survival rates

“…Such increases in coherence among salmon stocks are usually attributed to controllable freshwater influences such as hatcheries and habitat degradation, but the unknown mechanism underlying the ocean climate effect identified here is not directly subject to management actions. U nderstanding the influence of nonstationary climatic shifts on the productivity and persistence of populations is a key challenge to successful management of harvested marine and anadromous resources (1). Management of Pacific salmon fisheries in the United States and Canada exemplifies the challenges posed by climatic shifts; managers must set harvests for some stocks while protecting stocks at risk.…”

Growth and maturation of Korean chum salmon under changing environmental conditions

“…In particular, climate and exploitation (and changes therein) may affect multiple traits simultaneously, and the resulting effects may differ between life stages (Ruggerone et al, 2007;Crozier et al, 2008;Jiao, 2009) and depending on the complex genetic covariance structures between traits (Etterson and Shaw, 2001). Moreover, when multiple life-stage transitions are delicately tuned to conditions in different environments, effects on early life stages are likely to have long-lasting and unpredictable repercussions in subsequent years (Crozier et al, 2008;Planque et al, 2010).…”

“…Finally, although effects of climate and exploitation (and changes therein) are traditionally believed to be additive, evidence suggests that they are predominantly multiplicative and should be treated accordingly (Benson and Trites, 2002;Crozier et al, 2008;Planque et al, 2010).…”