Protected areas buffer against harvest selection and rebuild phenotypic complexity

Abstract

Harvest mortality typically truncates the harvested species' size structure, thereby reducing phenotypic complexity, which can lead to reduced population productivity, increased population variability, and selection on an array of life history traits that can further alter these demographic processes. Marine protected areas (MPAs) are a potential tool to protect older, larger individuals and therefore mitigate such ecological and evolutionary effects of harvest, depending on the degree of connectivity among areas. Such MPA protection relies on a shift in size-dependent mortality, the measurement of which can therefore serve as an early indicator of whether MPAs might achieve the desired longer-term ecological and evolutionary responses. We directly measured MPA effects on size-selective mortality and associated size structure using mark-recapture data on European lobster (Homarus gammarus) collected at three MPA-control area pairs in southern Norway during one decade (n = 5,943). Mark-recapture modeling, accounting for variation in recapture probabilities, revealed (1) that annual mean survival was higher inside MPAs (0.592) vs. control areas (0.298) and (2) that significant negative relationships between survival and body size occurred at the control areas but not in the MPAs, where the effect of body size was predominantly positive. Additionally, we found (3) that mean and maximum body size increased over time inside MPAs but not in control areas. Overall, our results suggest that MPAs can rebuild phenotypic complexity (i.e., size structure) and provide protection from harvest selection.

Protection from fishing improves body growth of an exploited species

“…The competitive environment does seem to differ between the MPAs and fished areas as a recent study found 5.4% of the lobster in the MPA to suffer from claw loss compared to 2.2% in fished areas [32]. Injury inhibit growth and can impact survival [60] and the survival have in fact decreased in these MPAs in the later years relative to the first 3 years after establishment, an effect that was most pronounced in the two smallest MPAs [38]. Contrary to our findings, theoretical work on MPAs has assumed reduced body growth in MPAs due to density dependence, and therefore reduced fisheries yields outside MPAs due to spill-over of slow-growing (and smaller) individuals [35,61].…”

Eco‐evolutionary dynamics of Atlantic cod spatial behavior maintained after the implementation of a marine reserve

“…While survival increased by ~40% right after MPA establishment, it decreased again after just 3 years reaching preprotection levels. In comparison, within the same study region, European lobster experienced a sharp increase in survival up to 3 years after protection followed by a marginal decrease after 9 years, where long‐term survival still remained higher than preprotection levels (Fernández‐Chacón et al, 2020 ). So why did cod not experience a similar survival benefit in the MPA?…”

“…For decades, science on marine protected areas (MPAs) has focused on the demographic effects of protection and the benefit to fisheries. Protection typically increases survival, mean size, and age within the protected populations resulting in a filling‐in of demographic structures (Fernández‐Chacón et al, 2020 ; Moland et al, 2013 , 2021 ; Taylor & McIlwain, 2010 ). Such demographic changes are in turn expected to benefit fisheries beyond MPA boundaries through the net export of pelagic eggs and larvae (the recruitment effect) and spillover of postsettled juveniles and mature fish (Abesamis & Russ, 2005 ; Di Lorenzo et al, 2016 ).…”

Restoration of Abundance and Dynamics of Coastal Fish and Lobster Within Northern Marine Protected Areas Across Two Decades

“…However, in balanced designs with temporally overlapping sampling and standardized effort as used herein, CPUE should yield meaningful information on changes in abundance with time. Spatial heterogeneity in population responses was evident in the studies utilizing the longterm monitoring data collected in the original lobster reserves (Moland et al, 2013a;Fernández-Chacón et al, 2020. This underscores the utility of proper design choices and adequate replication in studies assessing MPA-effects.…”

“…MPAs, in combination with control areas, can also be useful as field laboratories for understanding how fishing can affect mating systems of species. For instance, as lobsters have become more numerous and grown to larger sizes in the MPAs (Fernández-Chacón et al, 2020, the opportunity and scope for mate choice should also increase. In a parental assignment study conducted in Flødevigen, Sørdalen et al (2018) found a female preference for males with larger body sizes, but that the relative size difference between females and males of mated pairs (the size-assortative mating pattern) were significantly larger in the reserve compared to mated pairs in the control area (Figure 3A).…”