Evidence of market-driven size-selective fishing and the mediating effects of biological and institutional factors

Climate adaptation in the market squid fishery: fishermen responses to past variability associated with El Niño Southern Oscillation cycles inform our understanding of adaptive capacity in the face of future climate change

Evaluating the strategies fishermen have used to respond to short-term climate variability in the past can help inform our understanding of the adaptive capacity of a fishery in the face of anticipated future change. Using historic fishery landings, climate records, and fishermen surveys, we document how market squid fishermen respond to high seasonal and interannual climate variability associated with the El Niño Southern Oscillation (ENSO) and responses to hypothetical future scenarios of low abundance and range shift. Overall, fishermen have been able to adapt to dramatic shifts in the geographic range of the fishery given their high mobility, with fishermen with larger vessels expressing a willingness to travel greater distances than those with smaller vessels. Nearly half of fishermen stated that they would switch fisheries if market squid decreased dramatically in abundance, although fishermen who were older, had been in the fishery longer, were highly dependent on squid for income, and held only squid and/or coastal pelagic finfish permits were less likely to switch to another fishery in a scenario of lower abundance. While market squid fishermen have exhibited highly adaptive behavior in the face of past climate variability, recent (and likely future) range shifts across state boundaries, as well as closures of other fisheries, constrain fishermen's choices and emphasize the need for flexibility in management systems. Our study highlights the importance of considering connectivity between fisheries and monitoring and anticipating trans-jurisdictional range shifts to facilitate adaptive fishery management.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10584-022-03394-z.

Biodiversity underpins fisheries resilience to exploitation in the Amazon river basin

Inland fisheries feed greater than 150 million people globally, yet their status is rarely assessed due to their socio-ecological complexity and pervasive lack of data. Here, we leverage an unprecedented landings time series from the Amazon, Earth's largest river basin, together with theoretical food web models to examine (i) taxonomic and trait-based signatures of exploitation in inland fish landings and (ii) implications of changing biodiversity for fisheries resilience. In both landings time series and theory, we find that multi-species exploitation of diverse inland fisheries results in a hump-shaped landings evenness curve. Along this trajectory, abundant and large species are sequentially replaced with faster growing and smaller species. Further theoretical analysis indicates that harvests can be maintained for a period of time but that continued biodiversity depletion reduces the pool of compensating species and consequently diminishes fisheries resilience. Critically, higher fisheries biodiversity can delay fishery collapse. Although existing landings data provide an incomplete snapshot of long-term dynamics, our results suggest that multi-species exploitation is affecting freshwater biodiversity and eroding fisheries resilience in the Amazon. More broadly, we conclude that trends in landings evenness could characterize multi-species fisheries development and aid in assessing their sustainability.

Fish provision in a changing environment: The buffering effect of regional trade networks

Local and regional trade networks in small-scale fisheries are important for food security and livelihoods across the world. Such networks consist of both economic flows and social relationships, which connect different production regions to different types of fish demand. The structure of such trade networks, and the actions that take place within them (e.g., people fishing, buying, selling), can influence the capacity of small-scale fisheries to provide sufficient fish in a changing social and ecological context. In this study, we aim to understand the importance of networks between different types of traders that access spatially-distinct fish stocks for the availability and variability of fish provision. We deployed a mixed-methods approach, combining agent-based modelling, network analysis and qualitative data from a small-scale fishery in Baja California Sur, Mexico. The empirical data allowed us to investigate the trade processes that occur within trade networks; and the generation of distinct, empirically-informed network structures. Formalized in an agent-based model, these network structures enable analysis of how different trade networks affect the dynamics of fish provision and the exploitation level of fish stocks. Model results reveal how trade strategies based on social relationships and species diversification can lead to spillover effects between fish species and fishing regions. We found that the proportion of different trader types and their spatial connectivity have the potential to increase fish provision. However, they can also increase overexploitation depending on the specific connectivity patterns and trader types. Moreover, increasing connectivity generally leads to positive outcomes for some individual traders, but this does not necessarily imply better outcomes at the system level. Overall, our model provides an empirically-grounded, stylized representation of a fisheries trading system, and reveals important trade-offs that should be considered when evaluating the potential effect of future changes in regional trade networks.

Predicting potential compliance of small-scale fishers in Brazil: The need to increase trust to achieve fisheries management goals

Many global management and conservation initiatives fail to prevent overfishing either because they do not plan for local engagement, surveillance, and enforcement, and/or because they fail to include alternatives for short-term losses. Thus, these initiatives do not gain support among fishers. In this study, we interviewed fishers to investigate their stated behavior toward fisheries regulations. We assessed possible (non)compliant behavior under scenarios where fishers would face a moratorium on some of their target species. Additionally, we investigated the consequences of such a moratorium on the food web if it were to lead to fishing alternative species. Using data from two Brazilian coastal sites, we found that younger fishers and those who demonstrated a trustworthy relationship with stakeholders were inclined to comply with the rules. The level of potential compliance also varied between the studied places, probably due to unidentified local idiosyncrasies. Fishers tended to trust community actors (e.g., the leader or head of the fishing community) more than institutional actors (e.g., environmental agencies). When fishers were asked why they would choose specific replacement species in the event of a moratorium, they most often cited expected profitability and ease of capture as reasons. Fishers also tended to say that they would replace endangered species with species in the same and/or lower trophic categories. We suggest working toward stronger stakeholder engagement, given that an overall sense of trust in a community appears to be an important asset toward successful management. Higher levels of trust could promote more transparency in the decision-making process, which could facilitate information dissemination, awareness, and the need for compliance. The mixed methods approach used here could help predict responses to new and existing management policies and support adaptive fisheries management.

Meeting fisheries, ecosystem function, and biodiversity goals in a human-dominated world

The worldwide decline of coral reefs necessitates targeting management solutions that can sustain reefs and the livelihoods of the people who depend on them. However, little is known about the context in which different reef management tools can help to achieve multiple social and ecological goals. Because of nonlinearities in the likelihood of achieving combined fisheries, ecological function, and biodiversity goals along a gradient of human pressure, relatively small changes in the context in which management is implemented could have substantial impacts on whether these goals are likely to be met. Critically, management can provide substantial conservation benefits to most reefs for fisheries and ecological function, but not biodiversity goals, given their degraded state and the levels of human pressure they face.

Demography of the largest and most endangered Brazilian parrotfish, Scarus trispinosus, reveals overfishing

Many parrotfishes (Labridae: Scarinae) have life history traits, including late maturation and long lifespans, that make them vulnerable to overfishing. The greenbeak parrotfish Scarus trispinosus is the largest Brazilian endemic parrotfish and has been harvested in reef-associated fisheries along the coast. After a sharp population decline, S. trispinosus is now considered by the IUCN to be an Endangered species. We provide an assessment of age-based and reproductive biology for this species and discuss applications for fisheries management. We sampled 95 individuals from inshore and offshore reefs from Rio Grande do Norte state, northeast Brazil, both obtained from artisanal fishing landings and fishery-independent collections. All sampled specimens were females with fork lengths (FL) ranging from 8.1 to 55.9 cm and ages ranging from 0.3 to 7 yr, with estimated median maturity (L50) of 39.2 cm FL and median age (A50) of 4.2 yr. Size class distributions indicate that the inshore reefs are mostly inhabited by juveniles under L50, whereas the offshore reefs are inhabited by mature individuals, suggesting an ontogenetic habitat shift from inshore to offshore reefs around the timing of maturation. The fishing pressure on this species is concentrated in inshore reefs, therefore mostly on immature individuals, which may be severely affecting the reproductive capacity of this species. This information is useful to guide size-based fisheries management, such as regulating minimum capture size and fishing gears that capture individuals smaller than L50. Managing fisheries of endangered species with late maturity and complex reproductive cycles such as S. trispinosus is imperative to aid recovery.

Perceptions and responses of Pacific Island fishers to changing coral reefs

The transformation of coral reefs has profound implications for millions of people. However, the interactive effects of changing reefs and fishing remain poorly resolved. We combine underwater surveys (271 000 fishes), catch data (18 000 fishes), and household surveys (351 households) to evaluate how reef fishes and fishers in Moorea, French Polynesia responded to a landscape-scale loss of coral caused by sequential disturbances (a crown-of-thorns sea star outbreak followed by a category 4 cyclone). Although local communities were aware of the disturbances, less than 20% of households reported altering what fishes they caught or ate. This contrasts with substantial changes in the taxonomic composition in the catch data that mirrored changes in fish communities observed on the reef. Our findings highlight that resource users and scientists may have very different interpretations of what constitutes 'change' in these highly dynamic social-ecological systems, with broad implications for successful co-management of coral reef fisheries.

Sovereign states in the Caribbean have lower social-ecological vulnerability to coral bleaching than overseas territories

Coral reef social-ecological systems worldwide face major impacts from climate change, and spatial variation in vulnerability is driven by differential exposure to climatic threats, ecological and socio-economic sensitivity to those threats, ecological recovery potential, and socio-economic adaptive capacity. We assess variation in social-ecological vulnerability to climate change-induced coral bleaching, specifically for reef-based fisheries and tourism, of islands throughout the insular Caribbean, thus providing the first region-wide quantitative analysis of island-scale social-ecological vulnerability to coral bleaching. We show that different components of vulnerability have distinct spatial patterns and that variability in overall vulnerability is driven more by socio-economic than ecological components. Importantly, we find that sovereign islands are less vulnerable on average than overseas territories and that the presence of fisheries management regulations is a significant predictor of adaptive capacity and socio-economic sensitivity, with important implications for island-level governance and policies to reduce climate vulnerability.

Indicators of nutrient removal efficiency for riverine wetlands in agricultural landscapes of Argentine Pampas

Main objectives of this study were (a) to assess wetlands contribution to regulation of surface water quality of riverine wetlands in agricultural landscapes through their nutrient removal efficiency (RE), (b) to understand how RE of wetlands is related to hydrological, morphological, chemical and biological attributes, and (c) to identify RE indicators suitable for remote RE assessment. Macrophytes composition, hydrological, chemical, and morphological properties were estimated for 14 riverine wetlands of the Argentinean Pampas, and related to empirically estimated removal-exportation levels of phosphorus (dissolved and total) and nitrogen (inorganic and total). Nutrient inputs and outputs were assessed in four opportunities, two under baseline and two after storm events. A discriminant function based on remotely assessed wetland attributes was able to discriminate three wetland groups according to their contrasting mean RE for total phosphorus and total nitrogen. Descriptors of wetland size (area, length, perimeter) and vegetation (cover of the tall emergent macrophytes) showed the main weights and hence the main value as indicators for conservation and/or management of wetlands according to their nutrient removal capacities.

Comparing fishers' and scientific estimates of size at maturity and maximum body size as indicators for overfishing

We tested whether fishers' local ecological knowledge (LEK) of two fish life-history parameters, size at maturity (SAM) at maximum body size (MS), was comparable to scientific estimates (SEK) of the same parameters, and whether LEK influenced fishers' perceptions of sustainability. Local ecological knowledge was documented for 82 fishers from a small-scale fishery in Samaná Bay, Dominican Republic, whereas SEK was compiled from the scientific literature. Size at maturity estimates derived from LEK and SEK overlapped for most of the 15 commonly harvested species (10 of 15). In contrast, fishers' maximum size estimates were usually lower than (eight species), or overlapped with (five species) scientific estimates. Fishers' size-based estimates of catch composition indicate greater potential for overfishing than estimates based on SEK. Fishers' estimates of size at capture relative to size at maturity suggest routine inclusion of juveniles in the catch (9 of 15 species), and fishers' estimates suggest that harvested fish are substantially smaller than maximum body size for most species (11 of 15 species). Scientific estimates also suggest that harvested fish are generally smaller than maximum body size (13 of 15), but suggest that the catch is dominated by adults for most species (9 of 15 species), and that juveniles are present in the catch for fewer species (6 of 15). Most Samaná fishers characterized the current state of their fishery as poor (73%) and as having changed for the worse over the past 20 yr (60%). Fishers stated that concern about overfishing, catching small fish, and catching immature fish contributed to these perceptions, indicating a possible influence of catch-size composition on their perceptions. Future work should test this link more explicitly because we found no evidence that the minority of fishers with more positive perceptions of their fishery reported systematically different estimates of catch-size composition than those with the more negative majority view. Although fishers' and scientific estimates of size at maturity and maximum size parameters sometimes differed, the fact that fishers make routine quantitative assessments of maturity and body size suggests potential for future collaborative monitoring efforts to generate estimates usable by scientists and meaningful to fishers.

Operationalizing the social-ecological systems framework to assess sustainability

Meeting human needs while sustaining ecosystems and the benefits they provide is a global challenge. Coastal marine systems present a particularly important case, given that >50% of the world’s population lives within 100 km of the coast and fisheries are the primary source of protein for >1 billion people worldwide. Our integrative analysis here yields an understanding of the sustainability of coupled social-ecological systems that is quite distinct from that provided by either the biophysical or the social sciences alone and that illustrates the feasibility and value of operationalizing the social-ecological systems framework for comparative analyses of coupled systems, particularly in data-poor and developing nation settings.

Environmental governance is more effective when the scales of ecological processes are well matched with the human institutions charged with managing human–environment interactions. The social-ecological systems (SESs) framework provides guidance on how to assess the social and ecological dimensions that contribute to sustainable resource use and management, but rarely if ever has been operationalized for multiple localities in a spatially explicit, quantitative manner. Here, we use the case of small-scale fisheries in Baja California Sur, Mexico, to identify distinct SES regions and test key aspects of coupled SESs theory. Regions that exhibit greater potential for social-ecological sustainability in one dimension do not necessarily exhibit it in others, highlighting the importance of integrative, coupled system analyses when implementing spatial planning and other ecosystem-based strategies.

Fish market prices drive overfishing of the 'big ones'

The relationship between fish market price and body size has not been explored much in fisheries science. Here, the mean market prices and fish body size were collected in order to examine the hypothesis that large fish, both among- and within-species, are being selectively targeted by fisheries because they may yield greater profit. Trophic levels, vulnerability to fishing and global landings were also collected because these variables may also be related to the market fish price. These relationships were examined using generalized additive models (GAM), which showed that, among species, fish market price was positively dependent on maximum total length (P = 0.0024) and negatively on landings (P = 0.0006), whereas it was independent of trophic level (P > 0.05) and vulnerability to fishing (P > 0.05). When the fish price vs. size relationship was tested within-species, large individuals were consistently attaining higher market prices compared to their medium and small-sized counterparts. We conclude that the selective removal of the larger fish, which is driven by their market price and to a lesser extent by their availability, may contribute to their overfishing.