Mahimahi (Coryphaena hippurus) are fast-growing, short-lived pelagic predators that have long supported fisheries and subsistence harvest in tropical regions, particularly Hawai'i, and remain an important component of present-day fisheries. Despite their importance, research on catch patterns and oceanographic associations in the central North Pacific has been limited in recent decades. Here, we integrate multiple decades of data from two central North Pacific pelagic fisheries-a nearly basin-scale longline fishery and Hawai'i's near-island troll fishery-to examine variability in mahimahi catch rates and evaluate whether hypotheses proposed near the turn of the century are supported by the greater spatial and temporal footprint of modern fisheries data. We developed generalized additive mixed models to evaluate the influence of oceanography and fishery dynamics on catch rates, examined nominal and model-derived seasonal patterns, and evaluated whether previously postulated thermal constraints remain relevant to mahimahi availability. Temperature and water clarity played a role in longline catch rates, although fisher effects remained important, whereas near-island troll catch rates were driven primarily by fisher behavior. Across both fisheries, catch rates exhibited persistent seasonality, with peaks in spring and fall shifting toward summer north of Hawai'i and toward winter south of Hawai'i. These findings support a previously hypothesized conceptual model of meridional migration in which mahimahi distribution expands northward in summer and contracts southward in winter. Relative availability indices revealed declining interannual trends in mahimahi availability for both fisheries. The position of the 23 degrees C isotherm, hypothesized in the 1990s to influence mahimahi distribution, was significantly related to interannual variability in mahimahi availability only in the northern domain of the longline fishery in recent decades. This may be due to the poleward shift of the isotherm connected to larger subtropical gyre dynamics. Together, these findings highlight how migration and basin-scale variability shape mahimahi dynamics across the central North Pacific, providing an evaluation of existing hypotheses, and emphasizing the value of multi-scale perspectives for understanding highly migratory pelagic species.
Natural scientists in marine science recognize that social science is useful for studying marine sustainability issues, which often encompass both material and cultural dimensions. That is why natural scientists, especially early career researchers, are transitioning to social science. Shellock et al. have reflected on this transition, identified the challenges involved, and provided tips for the transition. In our reply, we critically engage with this article. We argue that the transition from the natural to the social sciences exhibits a double standard that devalues the social sciences. We outline three reasons why the transition is underestimated: the notion of subjectivity, false familiarity with the social world of social scientists, and acceptance of lower scientific standards. Furthermore, we formulate recommendations on how interdisciplinarity-collaboration or transition-can succeed, including establishing interdisciplinary degree programs, creating dedicated spaces for interdisciplinary collaboration, and actively seeking out social scientists, formal training, and hands-on practice. We aim to contribute to the improvement of marine social science.
Ecosystem-based fisheries management (EBFM) and ecosystem approaches to fisheries management (EAFM), collectively here called "ecosystem-oriented fisheries management" developed three decades ago. They have become firmly embedded in fisheries science and have slowly and variably integrated into fisheries management. Early literature focused on definitions, the components linking ecosystem science to management, and how analogues to single-species reference points and integrated ecosystem assessments to relate ecosystem processes and management objectives. The initial decade primarily reflected principles of EAFM, with the focus on ecosystem attributes affecting the management of individual stocks and complexes. The second decade of literature increases the focus on ecosystems, alongside individual stocks and steps towards EBFM. Linking of climate issues emerges during this period, as do spatial aspects of ecosystem dynamics and management of a broader scope of human impacts. In the (current) third decade, the increasing focus on climate change impacts and spatially explicit management is consistent with emphasis on the evolution towards more broad-based ecosystem-based management (EBM) emphasizing how fisheries relate to other cross-sectoral interests. The next decades will likely see greater emphasis on global change impacts affecting the productivity of species and ecosystems, and the integration of these concepts into ecosystemic management of multiple-use sectors. Climate impacts and the attendant increase in non-stationarity of population and ecosystem processes will perhaps rival ending overfishing (under current stationarity assumptions) as the primary focal areas of fisheries management. Mediation of cross-sectoral conflicts will require new and more spatially resolved data, predictions, and policy instruments with the goal of minimizing conflicts and negotiating the distribution of costs and benefits accruing to the various sectoral interests. Given all of these simultaneous and, in some cases, conflicting management objectives, undoubtedly the future of ecosystem-oriented fisheries management lies not only within the domain of fisheries but in the broader balancing of ecosystem, social, and economic objectives affecting the oceans. Increasingly, the success of fisheries management will be viewed as critically dependent on also addressing social aspects of fisheries, including community well-being, stakeholder involvement (in both management and science), equitable allocation of costs and benefits, and transparency and credibility of management processes.
Abstract Bio-economic models are widely used to assess the impacts of fisheries management strategies and explore biological, ecological, and economic trade-offs. However, many applications rely on simplified assumptions that limit their ability to inform management under changing climatic and socio-economic conditions. This study presents a tuned and transferable bio-economic framework developed within the European project SEAwise to evaluate fisheries management strategies under the interacting effect of climate change, market dynamics, and policy drivers. The framework integrates climate-driven changes in stock productivity with enhanced representations of fish price dynamics, métier-specific cost structures, and a common set of economic, social, and environmental indicators. It is applied to large-scale and small-scale mixed fisheries across multiple European case studies, including the North Sea, Celtic Seas, Bay of Biscay, and the Mediterranean Sea. The framework also evaluates a range of management strategies, including the fishing mortality corresponding to the maximum sustainable yield (FMSY)- and Pretty Good Yield (PGY), technical measures, and spatial management. Across regions and socio-economic scenarios, results show that management strategies based on FMSY generally provide more robust outcomes under climate and market uncertainty, compared to other strategies, particularly in terms of carbon intensity and distributional effects across small-scale and large-scale fisheries. PGY strategies, instead, can deliver conditional short- to medium-term economic gains under favourable socio-economic scenarios representing alternative future development pathways. The framework also includes behavioural sub-models, illustrated through selected case studies. By jointly assessing economic performance, carbon intensity, and food provision, the framework supports the operationalization of ecosystem-based fisheries management and provides a transparent, replicable approach for evaluating management strategies under climate and socio-economic uncertainty.
Abstract Understanding the mechanisms that underpin ecological stability has traditionally focused on the role of diversity, and particularly through biodiversity and ecosystem functioning (BEF) relationships. Yet, BEF relationships and the drivers of stability remain poorly explored across contrasting systems exposed to multiple pressures, such as exploited marine fish communities. Here, we used bottom trawl surveys from 54 marine demersal communities in the North Atlantic and the Mediterranean Sea to quantify the direction and strength of BEF relationships and to assess the relative importance of community structure, environmental, and anthropogenic pressures for different facets of stability across a broad geographic gradient. We combined linear mixed-effects models to analyze BEF relationships, and structural equation models to evaluate the direct and indirect drivers of stability measured through portfolio effect (PE) metrics that either ignore or account for the mean–variance relationship (Taylor’s power law) of the species within communities. Our results demonstrate how richness and evenness can have both positive and negative effects on demersal fish abundance along a macroecological gradient, with the strength of these relationships varying according to the community properties and the regional context. Stronger PE occurred when species fluctuated more asynchronously, presumably due to the increase in niche differentiation and species’ response diversity to the environment. Moreover, synchrony also channeled the indirect and positive effects of richness and evenness on PE, and all these community properties mediated the indirect effects of environmental conditions and anthropogenic pressures on stability. Accounting for the Taylor’s power law z-value when calculating stability metrics was fundamental because it determined the relationship with diversity and further showed how the PEs related differently with the z-value. Therefore, while biodiversity was linked to stability, the mean–variance scaling should not be ignored in order to better understand the mechanisms that operate the biodiversity–stability–functioning relationships in communities subjected to complex interplays among population dynamics, environmental forcing, and anthropogenic pressures.
