Temperate marine reserves enhance targeted but not untargeted fishes in multiple no-take MPAs

Evaluating the influence of marine protected areas on surf zone fish

Marine protected areas (MPAs) globally serve conservation and fisheries management goals, generating positive effects in some marine ecosystems. Surf zones and sandy beaches, critical ecotones bridging land and sea, play a pivotal role in the life cycles of numerous fish species and serve as prime areas for subsistence and recreational fishing. Despite their significance, these areas remain understudied when evaluating the effects of MPAs. We compared surf zone fish assemblages inside and outside MPAs across 3 bioregions in California (USA). Using seines and baited remote underwater videos (BRUVs), we found differences in surf zone fish inside and outside MPAs in one region. Inside south region MPAs, we observed higher abundance (Tukey's honest significant difference [HSD] = 0.83, p = 0.0001) and richness (HSD = 0.22, p = 0.0001) in BRUVs and greater biomass (HSD = 0.32, p = 0.0002) in seine surveys compared with reference sites. Selected live-bearing, fished taxa were positively affected by MPAs. Elasmobranchs displayed greater abundance in BRUV surveys and higher biomass in seine surveys inside south region MPAs (HSD = 0.35, p = 0.0003 and HSD = 0.23, p = 0.008, respectively). Although we observed no overall MPA signal for Embiotocidae, abundances of juvenile and large adult barred surfperch (Amphistichus argenteus), the most abundant fished species, were higher inside MPAs (K-S test D = 0.19, p < 0.0001). Influence of habitat characteristics on MPA performance indicated surf zone width was positively associated with fish abundance and biomass but negatively associated with richness. The south region had the largest positive effect size on all MPA performance metrics. Our findings underscored the variability in species richness and composition across regions and survey methods that significantly affected differences observed inside and outside MPAs. A comprehensive assessment of MPA performance should consider specific taxa, their distribution, and the effects of habitat factors and geography.

Influence of protogynous sex change on recovery of fish populations within marine protected areas

Marine protected areas (MPAs) are increasingly implemented as a conservation tool worldwide. In many cases, they are managed adaptively: the abundance of target species is monitored, and observations are compared to some model-based expectation for the trajectory of population recovery to ensure that the MPA is achieving its goals. Most previous analyses of the transient (short-term) response of populations to the cessation of fishing inside MPAs have dealt only with gonochore (fixed-sex) species. However, many important fishery species are protogynous hermaphrodites (female-to-male sex-changing). Because size-selective harvest will predominantly target males in these species, harvesting not only reduces abundance but also skews the sex ratio toward females. Thus the response to MPA implementation will involve changes in both survival and sex ratio, and ultimately reproductive output. We used an age-structured model of a generic sex-changing fish population to compare transient population dynamics after MPA implementation to those of an otherwise similar gonochore population and examine how different features of sex-changing life history affect those dynamics. We examined both demographically open (most larval recruitment comes from outside the MPA) and demographically closed (most larval recruitment is locally produced) dynamics. Under both scenarios, population recovery of protogynous species takes longer when fishing was more intense pre-MPA (as in gonochores), but also depends heavily on the mating function, the degree to which the sex ratio affects reproduction. If few males are needed and reproduction is not affected by a highly female-biased sex ratio, then population recovery is much faster; if males are a limiting resource, then increases in abundance after MPA implementation are much slower than for gonochores. Unfortunately, the mating function is largely unknown for fishes. In general, we expect that most protogynous species with haremic mating systems will be in the first category (few males needed), though there is at least one example of a fish species (though not a sex-changing species) for which males are limiting. Thus a better understanding of the importance of male fish to population dynamics is needed for the adaptive management of MPAs.

Small-sized and well-enforced Marine Protected Areas provide ecological benefits for piscivorous fish populations worldwide

Many piscivorous fish species are depleted and/or threatened around the world. Marine Protected Areas (MPAs) are tools for conservation and fisheries management, though there is still controversy regarding the best design for increasing their ecological effectiveness. Here, on the basis of a weighted meta-analytical approach, we have assessed the effect of 32 MPAs, distributed worldwide, on the biomass and density of piscivorous fishes. We analysed the MPA features and the biological, commercial and ecological characteristics of fishes that may affect the response of species to protection. We found a positive effect on the biomass and density of piscivores inside MPAs. This effect was stronger for the biomass of medium-sized fishes (in relation to the maximum size reported for the species) and the density of large and gregarious species. The size of the no-take zone had a significant negative impact on both response variables and differed according to the level of enforcement, with smaller no-take zones having higher levels of enforcement. Thus, MPAs help to protect piscivorous fish species, with smaller, but well enforced reserves being more effective for the protection of the local populations of piscivorous fishes throughout the world.

Soft-bottom fishes and spatial protection: findings from a temperate marine protected area

Numerous studies over the last decades have focused on marine protected areas (MPAs) and their effects on fish communities. However, there is a knowledge gap regarding how species that live associated with soft-substrates (e.g., sand, mud) respond to spatial protection. We analyzed abundance, biomass and total lengths of the soft-bottom fishes in a multiple-use MPA in the north-eastern Atlantic, the Luiz Saldanha Marine Park (Portugal), during and after the implementation of its management plan. Data were collected by experimental fishing in areas with three different levels of protection, during the implementation period and for three years after full implementation of the MPA. Univariate analysis detected significant biomass increases between the two periods. Fish assemblages were mainly structured by depth and substrate, followed by protection level. Community composition analyses revealed significant differences between protection levels and between the two periods. Species exhibited a broad variation in their response to protection, and we hypothesize that factors such as species habitat preferences, body size and late maturity might be underlying determinants. Overall, this study provides some evidence of protection effectiveness in soft-bottom fish communities, supported by the significant increase in biomass in the protected areas and the positive trends of some species.

Spatial fishing restrictions benefit demersal stocks in the northeastern Mediterranean Sea

The multi-level benefits that marine organisms gain when protected from fishing are well acknowledged. Here, we investigated the effects of a 40-year trawling ban on the status of targeted and non-targeted marine species within a major fishing ground in the northeastern Mediterranean Sea (Thermaikos Gulf, Aegean Sea). Biomass and somatic length of fish and invertebrates (six commercial and three non-commercial demersal species) were measured in three areas of varying fishing pressure, depending on the temporal and spatial operational regimes of fishing vessels. The positive effects of fishing restrictions on the studied demersal stocks were clearly revealed, as the commercial fish species exhibited higher biomass in the intermediate and low pressure areas, as well as increasing maximum and mean total length (and other length indicators) with decreasing fishing effort. The mean total length of non-commercial species generally did not differ among areas, except for species caught and discarded at high rates. The present study shows that fishing does alter the population structure and biomass of commercial demersal species, and that fishing restrictions greatly contribute to improving the status of demersal populations within the restricted areas by providing a refuge for large individuals and their important contribution to the gene pool.

Marine reserves indirectly affect fine-scale habitat associations, but not overall densities, of small benthic fishes

Many large, fishery-targeted predatory species have attained very high relative densities as a direct result of protection by no-take marine reserves. Indirect effects, via interactions with targeted species, may also occur for species that are not themselves targeted by fishing. In some temperate rocky reef ecosystems, indirect effects have caused profound changes in community structure, notably the restoration of predator-urchin-macroalgae trophic cascades. Yet, indirect effects on small benthic reef fishes remain poorly understood, perhaps because of behavioral associations with complex, refuge-providing habitats. Few, if any, studies have evaluated any potential effects of marine reserves on habitat associations in small benthic fishes. We surveyed densities of small benthic fishes, including some endemic species of triplefin (Tripterygiidae), along with fine-scale habitat features in kelp forests on rocky reefs in and around multiple marine reserves in northern New Zealand over 3 years. Bayesian generalized linear mixed models were used to evaluate evidence for (1) main effects of marine reserve protection, (2) associations with habitat gradients, including complexity, and (3) differences in habitat associations inside versus outside reserves. No evidence of overall main effects of marine reserves on species richness or densities of fishes was found. Both richness and densities showed strong associations with gradients in habitat features, particularly habitat complexity. In addition, some species exhibited reserve-by-habitat interactions, having different associations with habitat gradients inside versus outside marine reserves. Two species (Ruanoho whero and Forsterygion flavonigrum) showed stronger positive associations with habitat complexity inside reserves. These results are consistent with the presence of a behavioral risk effect, whereby prey fishes are more strongly attracted to habitats that provide refuge from predation in areas where predators are more abundant. This work highlights the importance of habitat structure and the potential for fishing to affect behavioral interactions and the interspecific dynamic attributes of community structure beyond simple predator-prey consumption and archetypal trophic cascades.

Exploitation and recovery of a sea urchin predator has implications for the resilience of southern California kelp forests

Size-structured predator-prey interactions can be altered by the history of exploitation, if that exploitation is itself size-selective. For example, selective harvesting of larger sized predators can release prey populations in cases where only large individuals are capable of consuming a particular prey species. In this study, we examined how the history of exploitation and recovery (inside marine reserves and due to fisheries management) of California sheephead (Semicossyphus pulcher) has affected size-structured interactions with sea urchin prey in southern California. We show that fishing changes size structure by reducing sizes and alters life histories of sheephead, while management measures that lessen or remove fishing impacts (e.g. marine reserves, effort restrictions) reverse these effects and result in increases in density, size and biomass. We show that predation on sea urchins is size-dependent, such that the diet of larger sheephead is composed of more and larger sized urchins than the diet of smaller fish. These results have implications for kelp forest resilience, because urchins can overgraze kelp in the absence of top-down control. From surveys in a network of marine reserves, we report negative relationships between the abundance of sheephead and urchins and the abundance of urchins and fleshy macroalgae (including giant kelp), indicating the potential for cascading indirect positive effects of top predators on the abundance of primary producers. Management measures such as increased minimum size limits and marine reserves may serve to restore historical trophic roles of key predators and thereby enhance the resilience of marine ecosystems.

Fishers' behaviour in response to the implementation of a Marine Protected Area

Marine Protected Areas (MPAs) have been widely proposed as a fisheries management tool in addition to their conservation purposes. Despite this, few studies have satisfactorily assessed the dynamics of fishers’ adaptations to the loss of fishing grounds. Here we used data from before, during and after the implementation of the management plan of a temperate Atlantic multiple-use MPA to examine the factors affecting the spatial and temporal distribution of different gears used by the artisanal fishing fleet. The position of vessels and gear types were obtained by visual surveys and related to spatial features of the marine park. A hotspot analysis was conducted to identify heavily utilized patches for each fishing gear and time period. The contribution of individual vessels to each significant cluster was assessed to better understand fishers’ choices. Different fisheries responded differently to the implementation of protection measures, with preferred habitats of target species driving much of the fishers’ choices. Within each fishery, individual fishers showed distinct strategies with some operating in a broader area whereas others kept preferred territories. Our findings are based on reliable methods that can easily be applied in coastal multipurpose MPAs to monitor and assess fisheries and fishers responses to different management rules and protection levels. This paper is the first in-depth empirical study where fishers’ choices from artisanal fisheries were analysed before, during and after the implementation of a MPA, thereby allowing a clearer understanding of the dynamics of local fisheries and providing significant lessons for marine conservation and management of coastal systems.

Lobster and cod benefit from small-scale northern marine protected areas: inference from an empirical before-after control-impact study

Marine protected areas (MPAs) are increasingly implemented as tools to conserve and manage fisheries and target species. Because there are opportunity costs to conservation, there is a need for science-based assessment of MPAs. Here, we present one of the northernmost documentations of MPA effects to date, demonstrated by a replicated before–after control-impact (BACI) approach. In 2006, MPAs were implemented along the Norwegian Skagerrak coast offering complete protection to shellfish and partial protection to fish. By 2010, European lobster (Homarus gammarus) catch-per-unit-effort (CPUE) had increased by 245 per cent in MPAs, whereas CPUE in control areas had increased by 87 per cent. Mean size of lobsters increased by 13 per cent in MPAs, whereas increase in control areas was negligible. Furthermore, MPA-responses and population development in control areas varied significantly among regions. This illustrates the importance of a replicated BACI design for reaching robust conclusions and management decisions. Partial protection of Atlantic cod (Gadus morhua) was followed by an increase in population density and body size compared with control areas. By 2010, MPA cod were on average 5 cm longer than in any of the control areas. MPAs can be useful management tools in rebuilding and conserving portions of depleted lobster populations in northern temperate waters, and even for a mobile temperate fish species such as the Atlantic cod.

Evidence that marine reserves enhance resilience to climatic impacts

Establishment of marine protected areas, including fully protected marine reserves, is one of the few management tools available for local communities to combat the deleterious effect of large scale environmental impacts, including global climate change, on ocean ecosystems. Despite the common hope that reserves play this role, empirical evidence of the effectiveness of local protection against global problems is lacking. Here we show that marine reserves increase the resilience of marine populations to a mass mortality event possibly caused by climate-driven hypoxia. Despite high and widespread adult mortality of benthic invertebrates in Baja California, Mexico, that affected populations both within and outside marine reserves, juvenile replenishment of the species that supports local economies, the pink abalone Haliotis corrugata, remained stable within reserves because of large body size and high egg production of the protected adults. Thus, local protection provided resilience through greater resistance and faster recovery of protected populations. Moreover, this benefit extended to adjacent unprotected areas through larval spillover across the edges of the reserves. While climate change mitigation is being debated, coastal communities have few tools to slow down negative impacts of global environmental shifts. These results show that marine protected areas can provide such protection.

Using GIS mapping of the extent of nearshore rocky reefs to estimate the abundance and reproductive output of important fishery species

Kelp Bass (Paralabrax clathratus) and California Sheephead (Semicossyphus pulcher) are economically and ecologically valuable rocky reef fishes in southern California, making them likely indicator species for evaluating resource management actions. Multiple spatial datasets, aerial and satellite photography, underwater observations and expert judgment were used to produce a comprehensive map of nearshore natural rocky reef habitat for the Santa Monica Bay region (California, USA). It was then used to examine the relative contribution of individual reefs to a regional estimate of abundance and reproductive potential of the focal species. For the reefs surveyed for fishes (i.e. 18 out of the 22 in the region, comprising 82% the natural rocky reef habitat <30 m depth, with a total area of 1850 ha), total abundance and annual egg production of California Sheephead were 451 thousand fish (95% CI: 369 to 533 thousand) and 203 billion eggs (95% CI: 135 to 272 billion). For Kelp Bass, estimates were 805 thousand fish (95% CI: 669 to 941thousand) and 512 billion eggs (95% CI: 414 to 610 billion). Size structure and reef area were key factors in reef-specific contributions to the regional egg production. The size structures of both species illustrated impacts from fishing, and results demonstrate the potential that relatively small increases in the proportion of large females on larger reefs could have on regional egg production. For California Sheephead, a substantial proportion of the regional egg production estimate (>30%) was produced from a relatively small proportion of the regional reef area (c. 10%). Natural nearshore rocky reefs make up only 11% of the area in the newly designated MPAs in this region, but results provide some optimism that regional fisheries could benefit through an increase in overall reproductive output, if adequate increases in size structure of targeted species are realized.

Collaborative assessment of California spiny lobster population and fishery responses to a marine reserve network

Assessments of the conservation and fisheries effects of marine reserves typically focus on single reserves where sampling occurs over narrow spatiotemporal scales. A strategy for broadening the collection and interpretation of data is collaborative fisheries research (CFR). Here we report results of a CFR program formed in part to test whether reserves at the Santa Barbara Channel Islands, USA, influenced lobster size and trap yield, and whether abundance changes in reserves led to spillover that influenced trap yield and effort distribution near reserve borders. Industry training of scientists allowed us to sample reserves with fishery relevant metrics that we compared with pre-reserve fishing records, a concurrent port sampling program, fishery effort patterns, the local ecological knowledge (LEK) of fishermen, and fishery-independent visual surveys of lobster abundance. After six years of reserve protection, there was a four- to eightfold increase in trap yield, a 5-10% increase in the mean size (carapace length) of legal sized lobsters, and larger size structure of lobsters trapped inside vs. outside of three replicate reserves. Patterns in trap data were corroborated by visual scuba surveys that indicated a four- to sixfold increase in lobster density inside reserves. Population increases within reserves did not lead to increased trap yields or effort concentrations (fishing the line) immediately outside reserve borders. The absence of these catch and effort trends, which are indicative of spillover, may be due to moderate total mortality (Z = 0.59 for legal sized lobsters outside reserves), which was estimated from analysis of growth and length frequency data collected as part of our CFR program. Spillover at the Channel Islands reserves may be occurring but at levels that are insufficient to influence the fishery dynamics that we measured. Future increases in fishing effort (outside reserves) and lobster biomass (inside reserves) are likely and may lead to increased spillover, and CFR provides an ideal platform for continued assessment of fishery-reserve interactions.

Spearfishing regulation benefits artisanal fisheries: the ReGS indicator and its application to a multiple-use Mediterranean marine protected area

The development of fishing efficiency coupled with an increase of fishing effort led to the overexploitation of numerous natural marine resources. In addition to this commercial pressure, the impact of recreational activities on fish assemblages remains barely known. Here we examined the impact of spearfishing limitation on resources in a marine protected area (MPA) and the benefit it provides for the local artisanal fishery through the use of a novel indicator. We analysed trends in the fish assemblage composition using artisanal fisheries data collected in the Bonifacio Strait Natural Reserve (BSNR), a Mediterranean MPA where the spearfishing activity has been forbidden over 15% of its area. Fish species were pooled into three response groups according to their target level by spearfishing. We developed the new flexible ReGS indicator reflecting shifts in species assemblages according to the relative abundance of each response group facing external pressure. The catch per unit effort (CPUE) increased by ca. 60% in the BSNR between 2000 and 2007, while the MPA was established in 1999. The gain of CPUE strongly depended on the considered response group: for the highly targeted group, the CPUE doubled while the CPUE of the untargeted group increased by only 15.5%. The ReGS value significantly increased from 0.31 to 0.45 (on a scale between 0 and 1) in the general perimeter of this MPA while it has reached a threshold of 0.43, considered as a reference point, in the area protected from spearfishing since 1982. Our results demonstrated that limiting recreational fishing by appropriate zoning in multiple-use MPAs represents a real benefit for artisanal fisheries. More generally we showed how our new indicator may reveal a wide range of impacts on coastal ecosystems such as global change or habitat degradation.

Extensive geographic and ontogenetic variation characterizes the trophic ecology of a temperate reef fish on southern California (USA) rocky reefs

Interactions between predator and prey act to shape the structure of ecological communities, and these interactions can differ across space. California sheephead Semicossyphus pulcher are common predators of benthic invertebrates in kelp beds and rocky reefs in southern California, USA. Through gut content and stable isotope (δ¹³C and †¹⁵N) analyses, we investigated geographic and ontogenetic variation in trophic ecology across 9 populations located at island and mainland sites throughout southern California. We found extensive geographic variation in California sheephead diet composition over small spatial scales. Populations differed in the proportion of sessile filter/suspension feeders or mobile invertebrates in the diet. Spatial variation in diet was highly correlated with other life history and demographic traits (e.g. growth, survivorship, reproductive condition, and energy storage), in addition to proxies of prey availability from community surveys. Multivariate descriptions of the diet from gut contents roughly agreed with the spatial groupings of sites based on stable isotope analysis of both California sheephead and their prey. Ontogenetic changes in diet occurred consistently across populations, despite spatial differences in size structure. As California sheephead increase in size, diets shift from small filter feeders, like bivalves, to larger mobile invertebrates, such as sea urchins. Our results indicate that locations with large California sheephead present, such as many marine reserves, may experience increased predation pressure on sea urchins, which could ultimately affect kelp persistence.

Disentangling trophic interactions inside a Caribbean marine reserve

Recent empirical studies have demonstrated that human activities such as fishing can strongly affect the natural capital and services provided by tropical seascapes. However, policies to mitigate anthropogenic impacts can also alter food web structure and interactions, regardless of whether the regulations are aimed at single or multiple species, with possible unexpected consequences for the ecosystems and their associated services. Complex community response to management interventions have been highlighted in the Caribbean, where, contrary to predictions from linear food chain models, a reduction in fishing intensity through the establishment of a marine reserve has led to greater biomass of herbivorous fish inside the reserve, despite an increased abundance of large predatory piscivores. This positive multi-trophic response, where both predators and prey benefit from protection, highlights the need to take an integrated approach that considers how numerous factors control species coexistence in both fished and unfished systems. In order to understand these complex relationships, we developed a general model to examine the trade-offs between fishing pressure and trophic control on reef fish communities, including an exploration of top-down and bottom-up effects. We then validated the general model predictions by parameterizing the model for a reef system in the Bahamas in order to tease apart the wide range of species responses to reserves in the Caribbean. Combining the development of general theory and site-specific models parameterized with field data reveals the underlying driving forces in these communities and enables us to make better predictions about possible population and community responses to different management schemes.

Incorporating biogeography into evaluations of the Channel Islands marine reserve network

Networks of marine reserves are increasingly a major component of many ecosystem-based management plans designed to conserve biodiversity, protect the structure and function of ecosystems, and rebuild and sustain fisheries. There is a growing need for scientific guidance in the design of network-wide monitoring programs to evaluate the efficacy of reserves at meeting their conservation and management goals. Here, we present an evaluation of the Channel Islands reserve network, which was established in 2003 off the coast of southern California. This reserve network spans a major environmental and biogeographic gradient, making it a challenge to assess network-wide responses of many species. Using fish community structure data from a long-term, large-scale monitoring program, we first identified persistent geographic patterns of community structure and the scale at which sites should be grouped for analysis. Fish communities differed most among islands with densities of individual species varying from 3- to 250-fold. Habitat structure differed among islands but not based on reserve status. Across the network, we found that, after 5 years, species targeted by fishing had higher densities (1.5×) and biomass (1.8×) inside reserves, whereas nontargeted species showed no significant differences. Examining trophic groups, piscivore and carnivore biomass was significantly greater inside reserves (1.8× and 1.3× more, respectively), whereas the biomass of planktivores and herbivores was similar inside and out. A framework for incorporating biogeographic variation into reserve network assessments is critical as we move from the evaluation of single reserves to networks of reserves.

Beyond marine reserves: exploring the approach of selecting areas where fishing is permitted, rather than prohibited

BACKGROUND

Marine populations have been declining at a worrying rate, due in large part to fishing pressures. The challenge is to secure a future for marine life while minimizing impacts on fishers and fishing communities.

METHODS AND PRINCIPAL FINDINGS

Rather than selecting areas where fishing is banned -- as is usually the case with spatial management -- we assess the concept of designating areas where fishing is permitted. We use spatial catch statistics for thirteen commercial fisheries on Canada's west coast to determine the minimum area that would be needed to maintain a pre-ascribed target percentage of current catches. We found that small reductions in fisheries yields, if strategically allocated, could result in large unfished areas that are representative of biophysical regions and habitat types, and have the potential to achieve remarkable conservation gains.

CONCLUSIONS

Our approach of selecting fishing areas instead of reserves could help redirect debate about the relative values that society places on conservation and extraction, in a framework that could gain much by losing little. Our ideas are intended to promote discussions about the current status quo in fisheries management, rather than providing a definitive solution.

The impacts of human visitation on mussel bed communities along the California coast: are regulatory marine reserves effective in protecting these communities?

Rocky intertidal habitats frequently are used by humans for recreational, educational, and subsistence-harvesting purposes, with intertidal populations damaged by visitation activities such as extraction, trampling, and handling. California Marine Managed Areas, particularly regulatory marine reserves (MRs), were established to provide legal protection and enhancement of coastal resources and include prohibitions on harvesting intertidal populations. However, the effectiveness of MRs is unclear as enforcement of no-take laws is weak and no regulations protect intertidal species from other detrimental visitor impacts such as trampling. The goal of this study was two-fold: (1) to determine impacts from human visitation on California mussel populations (Mytilus californianus) and mussel bed community diversity; and (2) to investigate the effectiveness of regulatory MRs in reducing visitor impacts on these populations. Surveys of mussel populations and bed-associated diversity were compared: (1) at sites subjected to either high or low levels of human use, and (2) at sites either unprotected or with regulatory protection banning collecting. At sites subjected to higher levels of human visitation, mussel populations were significantly lower than low-use sites. Comparisons of mussel populations inside and outside of regulatory MRs revealed no consistent pattern suggesting that California no-take regulatory reserves may have limited effectiveness in protecting mussel communities. In areas where many people visit intertidal habitats for purposes other than collecting, many organisms will be affected by trampling, turning of rocks, and handling. In these cases, effective protection of rocky intertidal communities requires an approach that goes beyond the singular focus on collecting to reduce the full suite of impacts.