Trends and management implications of human‐influenced life‐history changes in marine ectotherms

Abstract

Evidence is accumulating that many marine ectotherms are undergoing rapid changes in their life‐history characteristics. These changes have been variously attributed to fisheries‐induced evolution, inhibited adult growth rate due to oxygen limitation at higher temperatures, and plastic responses to density dependence or changes in ocean productivity. Here, we review the diverse underlying mechanisms by which plastic and evolutionary responses to climate change and fisheries are likely to produce similar life‐history trends in harvested marine ectotherms, leading to faster life‐histories with earlier maturation and smaller adult size‐at‐age. While mechanistically understanding these growth and maturation changes may be difficult, it is becoming clear that changing life‐histories will lead to modified population dynamics, productivity and natural mortality of the affected species. We discuss how the observed and expected life‐history changes could affect the assumptions and uncertainty within single and multispecies models currently used in marine ecosystem management, highlighting that models which allow for dynamic life‐history traits often report significantly different estimates of stock biomass. Given that both climate‐ and harvest‐induced life‐history changes are likely to intensify and possibly amplify each other, there is an urgent need to adequately assess the implications of faster life‐histories for marine ecosystem management. This is especially true for data‐poor stocks, where growth and maturation are not regularly assessed. Targeted monitoring can be used to inform responsive management, but for improved sustainability outcomes, a precautionary approach to management that is robust to life‐history trends is advised.

Fishing constrains phenotypic responses of marine fish to climate variability

“…First, the fish traps used to catch purple wrasse could indirectly select on thermal phenotype and thus cause fisheries‐induced evolution in this trait. It is well documented that fishing gears can be size selective (Law, ) and drive reductions in size and age at maturity and increases in juvenile growth (Audzijonyte et al, ; Swain, ). Our results are, however, counter to theoretical expectations in that it was average adult growth that increased post‐fishing.…”

“…Fishing and climate change are having profound impacts on the trajectory and variability of marine populations (Audzijonyte et al, ; Harley et al, ). However, despite the wealth of work undertaken in marine environments on the causes of longer‐term biological change, the effects of these two drivers have traditionally been considered in isolation, and when in concert only at the population scale (e.g.…”

“…Fishing increases overall mortality rates and can select against certain sized fish, and life‐history theory predicts that this elevated mortality should select for “faster” life histories characterised by rapid juvenile growth, early maturation, smaller body size and reduced life span (Law, ; Roff, ). Fishing can also affect individuals across their lifetime through environmentally sensitive labile traits such as somatic growth (Audzijonyte et al, ; Morrongiello & Thresher, ). Indeed, growth is an ideal candidate with which to explore additive and synergistic impacts of fishing and environmental variability on individuals as it is the phenotypic manifestation of interacting intrinsic (within individual) and extrinsic (environmental or ecological) components that affect the acquisition and allocation of resources (Enberg et al, ).…”

Climate change alters fish community size‐structure, requiring adaptive policy targets

“…Haarr, Sainte‐Marie, Comeau, Tremblay, & Rochette, ) and is manifested through smaller body sizes and increased reproductive investment within populations, which occur as evolutionary responses to long‐term size‐selective fishing pressure (Audzijonyte et al., ). Although FIE has not been reported unambiguously in the North Sea (Audzijonyte et al., ), it may be exacerbating the negative effects of regional ocean warming on fish body sizes (Baudron et al., ), thus contributing to the observed slow recovery of fish size‐structure to pre‐exploitation levels. Such uncertainty in pressure‐state relationships has been recognized as a wider challenge in the use of community‐level indicators around the globe, including size‐based metrics as well as those focusing on other community‐level traits (e.g.…”

Life History of the Gray Snapper at the Warm Edge of Its Distribution Range in the Caribbean

“…Demographic changes may affect community structure and function but also have practical implications for fisheries management and conservation (Gray ; Audzijonyte et al. ).…”