Table of Contents

Climate-driven changes in ocean temperatures, currents, or plankton dynamics may disrupt pelagic forage fish recruitment. Being responsive to such impacts enables fisheries management to ensure continued sustainable harvest of forage species. We conducted a management strategy evaluation to assess the robustness of current and alternative Pacific sardine harvest control rules under a variety of recruitment scenarios representing potential projections of future climate conditions in the California Current. The current environmentally informed control rule modifies the harvest rate for the northern sardine subpopulation based on average sea surface temperatures measured during California Cooperative Oceanic Fisheries Investigations field cruises. This rule prioritizes catch at intermediate biomass levels but may increase variability in catch and closure frequency compared to alternative control rules, especially if recruitment is unrelated to ocean temperatures. Fishing at maximum sustainable yield and using dynamically estimated reference points reduced the frequency of biomass falling below 150 000 mt by up to 17%, while using survey index-based biomass estimates resulted in a 14% higher risk of delayed fishery closure during stock declines than when using assessment-based estimates.

Understanding how key environmental factors affect fish communities is necessary for sound environmental management. Accordingly, we studied fish species–environment relationships in Finnish boreal rivers. A self-organizing map (SOM) analysis showed strong relationships between the occurrence of 18 fish species and 10 environmental variables (variance explained: 43.4%). In our logistic regression models run for each fish species, the predictive power varied from poor (AUC = 0.67–0.68) to excellent (AUC = 0.96), indicating that the responses were species-specific. The overall best predictors of the species occurrence were the local variables water depth and water temperature, and the regional variables stream size, altitude and annual mean temperature. Our results on fish assemblage types (clusters), identified by SOM, and co-occurrence of fish species, discovered by a hierarchical cluster analysis, reveal insights into the structure of the river fish assemblages. Moreover, our results suggest that the stream size contributes to thermal ranges in which each species is able to occur, which has relevance to predicting the impacts of climate change on riverine fish.

Diadromous fish populations have incurred precipitous declines across the globe. Among many stressors, these species are threatened by anthropogenic barriers that impede movement, alter riverine habitat, and augment predator communities. In this study, we used acoustic transmitters (n = 220) with predation and temperature sensors to characterize Atlantic salmon (Salmo salar) smolt predation risk in the Penobscot River, Maine, USA. Across two seasons, we documented 79 predation events through a 170 km migratory pathway, which included three hydropower projects and a large estuary. We detected tagged smolts that were predated by fish (n = 42), marine mammals (n = 28), and birds (n = 9). Using a multistate mark-recapture framework, we estimated that 46% of smolts were predated during downstream migration, which accounted for at least 55% of all mortality. Relative predation risk was greatest through impoundments and the lower estuary, where on average, predation rates were 4.8-fold and 9.0-fold greater than free-flowing reaches, respectively. These results suggest that predation pressure on Atlantic salmon smolts is exacerbated by hydropower projects and that predation in the lower estuary may be greater than expected.

In the California Current Ecosystem, the California Undercurrent (CU) is the predominate subsurface current that transports nutrient-rich water from southern California poleward. In this study, we used a large dataset of spatially explicit in situ observations of Pacific hake (Merluccius productus) and the CU (36.5–48.3°N) to estimate relationships between northward undercurrent velocity and hake distribution and determine whether these relationships vary across space or life-history stage. We found that both hake occurrence and density had strong spatially complex relationships with the CU. In areas north of 44°N (central Oregon), the CU effect was spatially consistent and opposite for occurrence (negative) and density (positive), indicating that hake may aggregate in areas of high northward velocity in this region. In areas south of 44°N, the CU effect showed a cross-shelf gradient for both occurrence and density, indicating a more nearshore hake distribution when northward velocity is higher in this region. Together, our results suggest that future changes in the CU due to climate change are likely to impact hake differently in northern and southern areas.

Fishers often target multiple species. More diverse harvest portfolios may reduce income risk, increasing resilience to climate-driven changes in target species’ spatial distributions and availability. Moreover, different effects can be observed across vessels in response to the same shocks and stressors, as fishers are heterogeneous. Evaluation of climate risk across different vessel groups within a particular fishery requires consideration of heterogeneous climate impacts on the availability of multiple target species and how such changes may impact substitution behavior. Here we analyze how historical climate-driven changes in forage species distribution and the closure of the Pacific sardine fishery affected landings per vessel of three coastal pelagic species (CPS): Pacific sardine (Sardinops sagax), market squid (Doryteuthis opalescens), and northern anchovy (Engraulis mordax) targeted by the U.S. West Coast CPS fleet from 2000 to 2020. Using cluster analysis, we grouped vessels into different fleet segments and estimated heterogeneous responses by fleet segment and port area. Our results show that considering heterogeneity is essential in the development of equitable and effective adaptation policies designed to mitigate the impact of changes on species availability in these fisheries.

Size-specific body growth responses to warming are common among animal taxa, but sex-specific responses are poorly known. Here we ask if body growth responses to warming are sex-dependent, and if such sex-specific responses vary with size and age. This was tested with sex-specific data of back-calculated individual growth trajectories, in European perch (Perca fluviatilis) from a long-term whole-ecosystem warming experiment (6.3 °C above the surrounding sea). Warming led to both size- and sex-specific differences in growth responses. Warming had a consistent positive effect on body growth of females, but negative effects on male growth at size > 10 cm and age > 2 years. These sex-specific growth responses translate to an increased degree of female-biased sexual size dimorphism (in length-at-age) with warming. Although the exact temperature-mediated effects underlying differential growth responses could not be resolved, results imply global warming may have highly different effects during ontogeny of male and female perch. Such effects should be considered in climate warming scenarios concerning fish growth, population size-structure, and dynamics of aquatic food webs that include fish exhibiting sexual size dimorphism.

The need to transition from traditional single-species fisheries management approaches towards ecosystem-based fisheries management (EBFM), or an ecosystem approach to fisheries, is widely recognised. EBFM is particularly important when considering management actions for economically valuable fisheries for small pelagic forage fish, given their key ecological role. Management strategy evaluation (MSE) is an effective approach to advance the quantitative implementation of EBFM by enabling stakeholders to explore trade-offs among competing ecosystem-related objectives. This paper puts forward six different approaches to advance EBFM with MSE explicity, by taking advantage of data and research already available and by guiding future research. These approaches can be grouped into those which (i) involve the operating model and/or link directly to the operating model while potentially providing additional performance metrics to evaluate ecosystem objectives, (ii) can be incorporated into the performance metrics, and (iii) involve the harvest control rule of the management procedure. This review demonstrates that immediate steps can be taken to implement EBFM targeted at quantitative tactical management, even without a complex, data-rich ecosystem operating model.

Catch per unit effort (CPUE) is used as an index of fish abundance under the premise that changes in CPUE result from changes in true density. However, catchability may also vary based on environmental conditions that affect observed CPUE. We developed a hierarchical model for estimating common carp (Cyprinus carpio) and bigmouth buffalo (Ictiobus cyprinellus) relative abundance with electrofishing survey data from six shallow lakes in northwest Iowa, USA, between 2018 and 2020. Common carp catchability was negatively associated with lake perimeter but unrelated to lake surface area, water depth, Secchi depth, temperature, and month of sampling. Bigmouth buffalo catchability was negatively associated with Secchi depth and water temperature and unrelated to other environmental variables. Hierarchical model posterior distributions of bigmouth buffalo density were less precise than Schnabel estimates, whereas common carp posterior distribution abundance estimates were more precise than Schnabel estimates. Our results indicate that hierarchical models can be a viable substitute for labor-intensive capture–mark–recapture methods to estimate unknown latent variables like relative abundance, and could be applied to other species, sampling gears, and management frameworks.

Unavoidable survey effort reduction has become a reality that must be accounted for in fisheries stock assessment. In addition, negative consequences to survey staff health due to repetitive motion injuries are becoming increasingly costly for managing agencies. In this study, we evaluated the outcomes of reductions in age and length data used in fisheries stock assessment models. The main goal was to determine whether sampling can be reduced to a level that does not excessively increase data uncertainty, yet provides a reduction in repetitive motions that can cause injury to survey staff. We found that reducing length sampling to a maximum of 100–150 fish sampled per haul (either sex-specific or combined sex) provides length composition data for which the uncertainty is not appreciably increased, and it has minimal effect on the uncertainty in age composition data that is subsequently expanded from this subsampled length frequency data. The method employed here, and the results presented, can aid management agencies to balance the magnitude of data collection and subsequent consequences to fisheries stock assessment models.

We examined the physiological performance in the most cosmopolitan coccolithophorid, Emiliania huxleyi and Gephyrocapsa oceanica, which were treated with 8.3 (ambient O₂ (AO)), 4.6 (medium O₂ (MO)), and 2.5 (low O₂ (LO)) mg L^–1 O₂ under 400 ppm (ambient CO₂ (AC)) and 1000 (high CO₂ (HC)) ppm CO₂ conditions. Elevated CO₂ decreased the specific growth rate of cells cultured under AO and LO conditions in both species, but it increased the rate in the MO-grown E. huxleyi. Regardless of the CO₂ levels, diminished O₂ concentration inhibited the growth rate in E. huxleyi while accelerating the rate in G. oceanica. LO reduced the particulate organic carbon (POC) production rate compared to the AO treatment in both species. Additionally, the decrease was higher in the HC cultures than in the AC ones. LO also inhibited the production rate of particulate inorganic carbon (PIC) compared to the AO/AC treatment. Due to a higher reduction in the production rate of PIC than POC, the PIC/POC ratio was decreased in the LO treatment compared to the AO/AC treatment. The current study reveals that low O₂ can, individually or in combination with high CO₂, considerably affect the physiology of marine photoautotrophic organisms.

Mapping the economic value of the ocean is pivotal to understand how marine ecosystems contribute to human well-being and to support fisheries management. We present a framework to analyse fisheries data and map fishing revenues by linking Vessel Monitoring System (VMS) information to logbooks and observer data. We provide a detailed step-by-step methodology and describe different approaches available to fulfill each step, with special notes for the processing of real-world messy data. The framework consists of six processing steps: (1) identifying the target fishery and subsetting VMS data, (2) extracting relevant variables, (3) linking observer and VMS data, (4) identifying fishing activity, (5) linking VMS and logbook data, and (6) extracting derived variables and mapping revenue back to the communities that extracted the resources. Building this framework opens a broad range of applications including marine spatial planning, rapid response analyses, high-resolution stock assessments, and spatially explicit-socioeconomic analyses. We demonstrate the framework in the reef fishery of the Gulf of Mexico, where spatial planning for aquaculture is currently underway.

Temperature modifies the reproductive success of fish, yet, in many species, we lack the information on its role in the early development. In this study, the effect of temperature on the relation between maternal traits (length, age, somatic condition, and muscle lipid and ovarian thyroid hormone concentrations), egg quality (fertilization success, development rate, mortality, and hatching success), and offspring traits (size-at-hatch, yolk sac size, and proportion of malformations) were studied in Baltic herring (Clupea harengus membras) in the northern Baltic Sea. The experiments were conducted at an ambient temperature of 7 °C and at an elevated temperature of 14 °C using 5 to 10 females and 3 replicates per female. The results indicate that elevated temperature may result in a faster developmental rate, a lower early-stage mortality and hatching success, smaller size-at-hatch, a larger yolk sac size, and a higher amount of larval malformations when compared to an ambient temperature. The egg and offspring traits were also associated with the maternal traits, indicating especially that thyroid hormones play a mediating role in the physiological processes.

Successful management of imperilled anadromous salmon stocks requires understanding how salmon will respond to a changing climate across their extensive ranges. Though largely unused for anadromous salmon to date, environmental niche models (ENMs) can provide a strong foundation for estimating where and how much habitat will likely remain favourable. We applied a comprehensive suite of ENM statistical approaches to five Pacific salmon species, focusing on freshwater spawning and natal rearing habitat as not only critical for population survival, but also highly susceptible to a changing climate. We developed ENMs for spawning ranges across British Columbia (BC), Canada, and western US, and projected future scenarios for BC. Projections indicated net expansion of favourable spawning habitat across species in BC, with the most change occurring by 2060. However, shifts in favourable habitat varied greatly geographically and by species, with notable reductions in coastal and southern interior streams. Our results provide a basis for identifying important changes in spawning and natal rearing habitat conditions to help inform priorities for restoration and protection actions.