Fishery Closures Research Articles

The complexity of compliance—Diverse responses to octopus fishery closures in Zanzibar

Abstract Marine protected areas like periodic closures are increasingly used to improve both fisheries management and biodiversity conservation, and often secondarily, human well‐being. Yet rule breaking, whether formal regulations, or community‐agreed norms, continues to negate expected management and conservation outcomes, remaining a major challenge. Although compliance scholarship today is expanding beyond non‐economic explanations of (non)‐compliance behaviour, approaches and theory used fail to show the diversity of perceptions and dispositions that can underpin motivations. A deepening engagement with behavioural sciences like sociology, psychology or behavioural economics is increasingly recognized as key in tackling compliance issues in marine protected areas. In this paper, we contribute to such a strand of compliance scholarship by presenting the responses and positions to (non‐) compliance, rules/regulations and authorities of different people, for example, fishers, traders and others involved in an area‐based fishery management intervention in Zanzibar, Tanzania. We take a qualitative approach aligning with an interpretive research ethic to carry out story circles, photo‐elicitation tasks and focus groups at three sites enacting periodic octopus closures. Theory drawn from sociology, anthropology and cognitive sciences was used to interpret how participants justified were motivated by or dispositioned towards rules, rule makers and rule breakers. Generally, the area‐management intervention was supported by participants, signalling the potential for future compliance most commonly based on the recognition of a degraded marine ecosystem in need of protection. However, the diverse and dynamic responses by different livelihood groups (i.e. traders and fishers) indicated on which basis and through which logics compliance behaviour was condoned or legitimated. This type of insight can help managers gauge or anticipate the potential for non‐compliance in participatory approaches that can impact the health of marine ecosystems. Recommendations include providing discussion spaces for conservation participants' (not just fishermen or fishery organizations) own meanings to be understood and not assumed. Meanings which create and shape relations, actions and concepts in marine protected area processes and thus directly impact the uptake and sustainability of conservation interventions. Read the free Plain Language Summary for this article on the Journal blog.

Characterization of marine heat waves in the Iberia–Biscay–Ireland (IBI) region in 2022

Abstract. Marine heat waves (MHWs) are defined as prolonged periods of anomalously high sea surface temperatures. These events have a profound impact on marine ecosystems, resulting in ecological and economic impacts such as coral bleaching, reduced surface chlorophyll due to increased surface layer stratification, mass mortality of marine invertebrates due to heat stress, rapid species migrations, and fishery closures or quota changes, among others. This research focuses on the study of the MHWs that occurred in the IBI (Iberia–Biscay–Ireland) region during the year 2022, assessing their climatologic properties, analyzing the mean values for the year 2022, and discretizing the events in four subregions representative of the entire domain. Satellite-derived sea surface temperature data were used to detect and characterize the events, revealing that in some areas the year 2022 showed peak anomaly values of (i) 15 MHW events, (ii) 128 d of mean durations, and (iii) 261 total days of MHWs. Through observational and modeling data, the discrete events located in the Bay of Biscay were also examined in the subsurface layers, demonstrating a strong seasonal modulation and heat diffusion through deeper layers, where cold-season events reach higher MHW mean depth values and subsurface positive anomalies of temperature can remain for weeks once an MHW has ended.

Adaptive spatiotemporal management to reduce shark bycatch in tuna fisheries.

Purse-seine tropical tuna fishing in the eastern tropical Pacific Ocean (EPO) results in the bycatch of several sensitive species groups, including elasmobranchs. Effective ecosystem management balances conservation and resource use and requires considering trade-offs and synergies. Seasonal and adaptive spatial measures can reduce fisheries impacts on nontarget species while maintaining or increasing target catches. Identifying persistently high-risk areas in the open ocean, where dynamic environmental conditions drive changes in species' distributions, is essential for exploring the impact of fisheries closures. We used fisheries observer data collected from 1995 to 2021 to explore the spatiotemporal persistence of areas of high bycatch risk for 2 species of oceanic sharks, silky shark (Carcharhinus falciformis) and oceanic whitetip shark (Carcharhinus longimanus), and of low tuna catch rates. We analyzed data collected by fisheries scientific observers onboard approximately 200 large purse-seine vessels operating in the EPO under 10 different flags. Fishing effort, catch, and bycatch data were aggregated spatially and temporally at 1°×1° cells and monthly, respectively. When areas of high fishing inefficiency were closed the entire study period and effort was reallocated proportionally to reflect historical effort patterns, yearly tuna catch appeared to increase by 1-11%, whereas bycatch of silky and oceanic whitetip sharks decreased by 10-19% and 9%, respectively. Prior to fishing effort redistribution, bycatch reductions accrued to 21-41% and 14% for silky and oceanic whitetip sharks, respectively. Our results are consistent with previous findings and demonstrate the high potential for reducing elasmobranch bycatch in the EPO without compromising catch rates of target tuna species. They also highlight the need to consider new dynamic and adaptive management measures to more efficiently fulfill conservation and sustainability objectives for exploited resources in the EPO.

Recruitment of European sea bass (Dicentrarchus labrax) in northerly UK estuaries indicates a mismatch between spawning and fisheries closure periods.

European sea bass (Dicentrarchus labrax) is a species of high commercial and recreational value, but it exhibits highly variable recruitment rates and has been subject to recent declines. Emergency management measures put in place to protect spawning stocks include the annual closure of commercial and recreational fisheries over a 2-month, February-March, window. Whether this protection measure is having the desired outcome for this data-poor species remains unclear. Otolith microstructural analyses (counts and widths of daily growth rings and check marks indicative of settlement) were used to estimate (1) spawn timing, (2) pelagic larval duration and settlement timing, (3) growth rate and condition, and (4) the otolith-fish size relationship for juvenile European sea bass caught from two estuaries in Wales (Dwyryd, Y Foryd), located at the northern edge of the species range. We observed a significant mismatch between the timing of fisheries closures and the spawning, with 99.2% of recruits having been spawned after the fishery had reopened (back-calculated median spawn date = May 5 ± 17 days SD), suggesting that the closure may be too early to adequately protect this population. Further, we present the first empirically derived estimates of pelagic larval duration for sea bass recruits settling in UK habitats, which showed a strong negative relationship with spawn date. Finally, we found significant differences in fish condition between the two estuaries, suggesting local variation in habitat quality. The results suggest that the timing of current fisheries closures may not be adequately protecting the spawners supplying these northernmost estuaries, which are likely to become increasingly important as sea bass distributions shift northward in our climate future.

Elucidating the migrations of European seabass from the southern north sea using mark-recapture data, acoustic telemetry and data storage tags

The movement ecology of European seabass, Dicentrarchus labrax, remains poorly understood, especially in the northern ranges of its distribution. To investigate migration patterns of seabass from the southern North Sea, we combined data from different projects from four countries using various tagging techniques. This resulted in 146 recaptures (out of 5598 externally marked seabass), 138 detected animals (out of 162 seabass fitted with an acoustic transmitter) and 76 archived depth and temperature series (out of 323 seabass with an archival tag). Using geolocation modelling, we distinguished different migration strategies, whereby individual fish migrated to the eastern English Channel (15.1%), the western English Channel (28.3%), the Celtic Sea and the norther part of the Bay of Biscay (17.0%), or stayed in the North Sea (39.6%). A high number of seabass exhibited fidelity to the North Sea (90.5% of recaptures, 55.3% for acoustic transmitters and 44.7% of archival tags). Although seabass are generally considered to migrate southwards in winter, a large number of individuals (n = 62) were observed in the southern North Sea, where spawning might potentially occur in a particular deep location along the coast of Norfolk in the UK. Our results highlight the need to consider fine-scaled population structuring in fisheries assessment, and indicate that current seasonal fisheries closures are not aligned with the ecology of seabass in the North Sea.

Impacts of locally managed periodic octopus fishery closures in Comoros and Madagascar: short-term benefits amidst long-term decline

Octopus fisheries face heightened demand driven by depleted fish stocks and escalating economic value, leading to overextraction of octopus populations and magnifying threats to coastal ecosystems and the livelihoods of fishers who depend on them. Implementation of management strategies such as periodic fishing closures can offer sanctuary for octopus, providing the necessary space and time for the growth and reproduction of this rapidly proliferating species. Despite evidence of positive management outcomes, the role of periodic closures in the long-term sustainability of octopus populations remains uncertain. Here, we examine trends in octopus landings over time and the effects of periodic closures along the Mozambique Channel from Comoros to Madagascar (12°-25°S). Long-term trends in octopus landings varied across three regions: generally stable over a 6-year period in Comoros, increasing over a 4-year period in the Barren Isles and declining over a 17-year period in Atsimo Andrefana, Madagascar. We observed a significant increase in mean catch per unit effort (CPUE, kilograms/fisher-day), and mean total catch (kilograms/day) following periodic closures across villages extracting octopus from closure areas. When evaluating each region independently, we observed this positive effect across Comoros and Atsimo Andrefana, Madagascar while trends in the Barren Isles showed no effect of octopus closures. We applied generalized linear mixed models to examine the influence of 10 covariates on mean daily total catch and CPUE within 7 days and 30 days post-closure. Baseline conditions (quantified by the pre-closure CPUE and daily total catch), closure duration and start month of closure had positive, statistically significant correlations with post-closure CPUE and daily total catch. Additionally, closure duration from 13 to 16 weeks and closure size of approximately 70 hectares were qualitatively associated with net gains in CPUE. Although periodic closures yield positive outcomes for octopus fisheries, the effects may be short-lived, as observed in Atsimo Andrefana, Madagascar, where catch declined over the long-term despite temporary improvements. Our findings underscore a need for a diverse portfolio of management strategies to restore and sustain populations over the long-term.

Rotational fishery closures could enhance coral recovery in systems with alternative states

AbstractRotational closures have potential fisheries benefits, yet their impact on coral cover is unknown. Research has shown that permanent closures can protect herbivorous fish, indirectly benefiting corals, but these observations may not apply when closed periods alternate with fishing. Here, we examine how rotational closures affect coral, focusing on systems with the potential to switch between alternative stable states, a context in which temporary closures may have persistent effects. We show that rotational closures can trigger coral recovery, and in some contexts lead to better coral recovery than fixed closures of similar size. Such benthic effects are only possible if closures last long enough for change to occur. We also note that very large fixed or rotating closures may concentrate fishing effort in areas where fishing remains permitted, leading to lower overall coral cover. Our findings offer crucial guidance to managers regarding rotational closures’ potential advantages and drawbacks.

Decolonising Environmental Risk Assessments of Potentially Polluting Wrecks: a Case Study of the Wreck of the USS Mississinewa in Ulithi Lagoon, Federated States of Micronesia.

Millions of tonnes of oil lie entombed within wrecks from two world wars which, when released, can cause environmental devastation. Wrecks are predominantly risk assessed by the Global North Nations responsible, resulting in an epistemology that separates human from nature. This research aimed to decolonise risk assessments to capture the spatially heterogeneous nature of human vulnerability to oil pollution. Triangulation analysis of interviews and official reports relating to the USS Mississinewa oil spill identified three Global South issues a Eurocentric risk assessment failed to capture: region-specific meteorological conditions causing the leak, remoteness making external resources slow to arrive, and the impact of the fishery closure on traditional subsistence lifestyles. A vulnerability assessment is proposed to prioritise wrecks in susceptible locations. Recommendations are made for a collaborative approach to wreck management by including local voices, resisting the Global North assumption of generality, and recognising the priorities of those living with wrecks.

Evaluating robustness of harvest control rules to climate-driven variability in Pacific sardine recruitment

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.

Evaluating bycatch avoidance in the U.S. Atlantic sea scallop Placopecten magellanicus fishery

AbstractObjectiveThe effectiveness of bycatch avoidance programs relies on changes in fishing behavior in response to spatiotemporal information on bycatch patterns. A voluntary bycatch avoidance program in the U.S. sea scallop Placopecten magellanicus fishery designed to prevent triggering bycatch allocation of Yellowtail Flounder Limanda ferruginea was implemented and maintained concurrently with other management measures. Detecting bycatch avoidance behavior and relative effectiveness for bycatch mitigation presents an analytical challenge.MethodsWe evaluated effectiveness of the bycatch avoidance program over the course of 4 years based on fishing behavior relative to bycatch advisories. Using loglinear models to compare frequencies, we examined the relationship between bycatch reports from participating vessels and bycatch advisories throughout the year in each of the 4 years. We compared results from self‐reported catch to data from a mandatory observer program for participating and nonparticipating vessels in the bycatch avoidance program.ResultSignificant associations between bycatch advisories and fishing locations indicated bycatch avoidance behavior, while accounting for the effect of sea scallop density on fishing location decisions. Evidence of avoidance behavior was stronger in earlier years of the program and varied spatially. Decreasing avoidance behavior coincided with revised bycatch management measures, which appear to have altered the incentives for bycatch avoidance.ConclusionWe found differences in the fishing behavior of fishing captains who participated in the bycatch avoidance program when Yellowtail Flounder bycatch was perceived to threaten economic yield due to fishery closures. Bycatch mitigation program evaluations should consider the program objectives as well as incentives (and disincentives) in interpreting behavior.

Catch as catch can: markets, availability, and fishery closures drive distinct responses among the U.S. West Coast coastal pelagic species fleet segments

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.

Assessing fish–fishery dynamics from a spatially explicit metapopulation perspective reveals winners and losers in fisheries management

Abstract Sustainable management of living resources must reconcile biodiversity conservation and socioeconomic viability of human activities. In the case of fisheries, sustainable management design is made challenging by the complex spatiotemporal interactions between fish and fisheries. We develop a comprehensive metapopulation framework integrating data on species life‐history traits, connectivity and habitat distribution to identify priority areas for fishing regulation and assess how management impacts are spatially distributed. We trial this approach on European hake fisheries in the north‐western Mediterranean, where we assess area‐based management scenarios in terms of stock status and fishery productivity to prioritize areas for protection. Model simulations show that local fishery closures have the potential to enhance both spawning stock biomass and landings on a regional scale compared to a status quo scenario, but that improving protection is easier than increasing productivity. Moreover, the interaction between metapopulation dynamics and the redistribution of fishing effort following local closures implies that benefits and drawbacks are heterogeneously distributed in space, the former being concentrated in the proximity of the protected site. A network analysis shows that priority areas for protection are those with the highest connectivity (as expressed by network metrics) if the objective is to improve the spawning stock, while no significant relationship emerges between connectivity and potential for increased landings. Synthesis and applications. Our framework provides a tool for (1) assessing area‐based management measures aimed at improving fisheries outcomes in terms of both conservation and socioeconomic viability and (2) describing the spatial distribution of costs and benefits, which can help guide effective management and gain stakeholder support. Adult dispersal remains the main source of uncertainty that needs to be investigated to effectively apply our model to fisheries regulation.

Rapid changes in age structure, mortality, and escapement accompanied stock recovery of the estuarine Red Drum population of Texas

AbstractObjectiveWe analyzed a fishery‐independent catch time series in the context of predicted historical age structure of Red Drum Sciaenops ocellatus for the years 1980–2019. This time series roughly coincided with closure of the commercial fishery in Texas (in 1981) and federal waters (in 1987). Changes in size and age were used to estimate changes in mortality and offshore escapement.MethodsOtoliths collected from Red Drum between 1997 and 2015 in Texas were used to create seasonal length‐at‐age growth functions, which were then used to estimate ages (based on total length) of all Red Drum encountered in fishery‐independent gill‐net samples collected by the Texas Parks and Wildlife Department during 1980–2019 (total n = 311,150). Temporal changes in observed body size and overall catch were used to predict annualized changes in mean age, mortality, and offshore escapement of the estuarine population.ResultThe initial 14‐year period (1980–1993) was characterized by rapid increases in mean catch per hour and mean total length (mm) in fishery‐independent samples, followed by relative stability for the remainder of the time series. There was a 55% increase in estimated mean age of Red Drum when comparing 1980 (mean age = 0.84 year) to 2019 (1.30 years). There were also rapid and significant declines in total mortality (Z; estimated via catch curves) and increases in offshore escapement (estimated indirectly from mortality) in the initial recovery period.ConclusionThe current estuarine population of Red Drum in Texas is significantly larger and older than it was at the onset of fishery management measures, and offshore escapement is annually well above the current target level of 30% set by the federal fisheries management plan. These findings suggest that regulations put into effect starting in the 1980s have succeeded in recovering the estuarine Red Drum population in Texas.

Age, Growth, and Functional Gonochorism with a Twist of Diandric Protogyny in Goliath Grouper from the Atlantic Coast of Florida

The lack of data on the age, growth, and reproduction of the Atlantic Goliath Grouper Epinephelus itajara off the coasts of Florida (USA) makes it difficult to estimate the extent of their population recovery following the 1990 fishery closure, as well as the potential effects of the recent (2023) opening of a fishery for juveniles. Goliath Grouper from the Atlantic coast of Florida were non-lethally sampled for size (total length, TL), age (via fin rays), and sex and reproductive stage (via gonad biopsies, milt/egg expression, gonopores) from May to October 2010–2016. Of 653 unique fish captured (not including 118 recaptures), 257 (39.4%) were females (122–228 cm TL; 5–20 years old), 264 (40.0%) were males (104–225 cm TL; 4–22 years old), 100 (15.3%) were unsexed (82–211 cm TL; 3–15 years old), and 32 (4.9%) were protogynous hermaphrodites (108–209 cm TL; 5–20 years old). Protogyny was conclusively determined in two fish recaptured and re-biopsied that had transitioned from female to male. However, an overlap in the age and size of males and females, a 1:1 sex ratio, and the presence of relatively small, young, mature males, in combination with an apparently low functional sex change rate, all indicated that the sexual pattern of Goliath Grouper was functionally gonochoristic with the potential for diandric protogyny. Females > 10 years old were larger-at-age than males, and Goliath Grouper from the Atlantic coast were larger-at-age than fish from the Gulf of Mexico. These differences in age, growth, and reproductive strategy—as well as the nascent fishery for juveniles—need to be monitored closely so that the current and future reproductive capacity of the population continues to ensure growth and sustainability.

The Barents and Norwegian Seas beaked redfish (Sebastes mentella): stock assessment and fishery management

An analytical review of the stock assessment and fishery regulation of the Barents and Norwegian Seas beaked redfish is presented. Model estimates of stock dynamics are characterized by uncertainty associated with incomplete coverage of the beaked redfish distribution in surveys, age determination problems, and assumptions made in the model. The regulation of fishing mortality is based on the precautionary approach, and the main management aim is achievement of the maximum sustainable yield. Technical measures include limiting the minimum mesh size in the trawl, establishing a minimum fish length for fishery, temporal fishery closures and limiting by-catch in multi-species fisheries. The unregulated fishery of the Norwegian-Barents Sea beaked redfish in the 1970s was one of the reasons for the decline in its stock and appearance of poor recruitment, which led to the ban on its targeted fishing in the Norwegian Economic Zone and in the fish protection area of the Svalbard. In 2014, the fishing was reopened. At present, the stock of beaked redfish of the Norwegian-Barents Sea population is in a safe state and further growth of the catch is expected.

Absolute Abundance Estimates of Atlantic Goliath Grouper (Epinephelus itajara) on Spawning Aggregation Sites

Reliable data on Atlantic Goliath Grouper abundance are prerequisite to informed management decisions, particularly as the State of Florida reopened a limited harvest on the species in 2023 after a 32-year moratorium. Limited data exist for this purpose and fisheries data have been unavailable for over three decades due to a fishery closure that began in 1990. The purpose of this study was to compare absolute abundance estimates of Goliath Grouper between two years using an efficient, cost-effective method developed by Koenig. An underwater tagging method was used to collect mark and resight data for use in a Peterson deterministic model. These data were collected at the same spawning aggregation sites off Jupiter, Florida near the time of the new moon in September 2013 and August 2022. We found that Goliath Grouper abundance had declined at all but one of six sites since 2013. Because data were not collected during the intervening years, interannual variability is unknown. However, given the highly age-structured spawning stock of adult Goliath Grouper on the spawning grounds, the lower abundances measured in 2022 may reflect a real decline in the population rather than just representing a weak year of adult recruitment to these spawning sites.

Fishery Closures, More Than Predator Release, Increased Persistence of Nearshore Fishes and Invertebrates to the Deepwater Horizon Oil Spill

Fishery Closures, More Than Predator Release, Increased Persistence of Nearshore Fishes and Invertebrates to the Deepwater Horizon Oil Spill

Filling the data gaps: Transferring models from data-rich to data-poor deep-sea areas to support spatial management

Spatial management of the deep sea is challenging due to limited available data on the distribution of species and habitats to support decision making. In the well-studied North Atlantic, predictive models of species distribution and habitat suitability have been used to fill data gaps and support sustainable management. In the South Atlantic and other poorly studied regions, this is not possible due to a massive lack of data. In this study, we investigated whether models constructed in data-rich areas can be used to inform data-poor regions (with otherwise similar environmental conditions). We used a novel model transfer approach to identify to what extent a habitat suitability model for Desmophyllum pertusum reef, built in a data-rich basin (North Atlantic), could be transferred usefully to a data-poor basin (South Atlantic). The transferred model was built using the Maximum Entropy algorithm and constructed with 227 presence and 3064 pseudo-absence points, and 200 m resolution environmental grids. Performance in the transferred region was validated using an independent dataset of D. pertusum presences and absences, with assessments made using both threshold-dependent and -independent metrics. We found that a model for D. pertusum reef fitted to North Atlantic data transferred reasonably well to the South Atlantic basin, with an area under the curve of 0.70. Suitable habitat for D. pertusum reef was predicted on 20 of the assessed 27 features including seamounts. Nationally managed Marine Protected Areas provide significant protection for D. pertusum reef habitat in the region, affording full protection from bottom trawling to 14 of the 20 suitable features. In areas beyond national jurisdiction (ABNJ), we found four seamounts that provided suitable habitat for D. pertusum reef to be at least partially protected from bottom trawling, whilst two did not fall within fisheries closures. There are factors to consider when developing models for transfer including data resolution and predictor type. Nevertheless, the promising results of this application demonstrate that model transfer approaches stand to provide significant contributions to spatial planning processes through provision of new, best available data. This is particularly true for ABNJ and areas that have previously undergone little scientific exploration such as the global south.

Twenty years of monitoring reveal overfishing of bony fish stocks in the coastal national park Banc d’Arguin, in Mauritania

Abstract Along Africa’s western coast, many local communities rely on the ocean for their livelihood. Over the last decades, introductions of new fishing techniques along with globalizing trade have strongly changed local fishing practices. The Parc National du Banc d’Arguin (PNBA) in Mauritania had for centuries been subjected to an artisanal, low‐impact, fishery. This fishing was exclusively oriented towards migratory bony fish species, mullet (Mugil cephalus) and meagre (Argyrosomus regius). Since the 1980s, these species have been replaced by illegal catches of internationally traded elasmobranchs (sharks and rays) and by non‐migratory and relict species (resident) such as tilapias (Sarotherodon melanotheron) and catfishes (Arius sp.). To date, most monitoring and management efforts have been dedicated to evaluating changes in elasmobranch populations and less focus has been on bony fish species. Data from a fishery monitoring programme are used to analyse the trends in effort, catch and catch per unit of effort of bony fish species by fitting non‐parametric generalized additive models to capture changes in the fish community over the last 20 years. Mullet and meagre became overfished early on, and the contribution of resident species (tilapias and catfishes) increased in the catches. Together with a pattern of increased effort on the traditionally targeted species, such a change in the catch could reflect a change in the fish community. These results call for the implementation of sustainable fishing practices within PNBA. We propose the need to implement closures of fisheries during the species’ breeding periods as well as the use of biological reference points such as the size at first capture and maximum sustainable yield targets for resident species.

Disentangling abiotic and biotic controls of age‐0 Pacific herring population stability across the San Francisco Estuary

AbstractPacific herring (Clupea pallasii) is an ecologically and commercially valuable forage fish in the North Pacific Ocean. However, knowledge gaps exist around the abiotic and biotic drivers behind its variable population dynamics—as well as on the ability of the species to show spatially structured trends that stabilize population portfolios in the face of environmental change. Here we examined how historical hydroclimatic variability in the San Francisco Estuary (California) has driven age‐0 Pacific herring population dynamics over 35 years. First, we used wavelet analyses to examine spatiotemporal variation and synchrony in the environment, focusing on two key variables: salinity and temperature. Next, we fitted multivariate autoregressive state‐space models to environmental and abundance time series to test for spatial structure and to parse out abiotic (salinity and temperature) from biotic influences (spawning and density dependence). Finally, we examined the stabilizing effects of spatially asynchronous population fluctuations (i.e., portfolio effects) across the estuary. Our results showed that temperature, but not salinity, fluctuated synchronously across regions on seasonal and decadal timescales. The top‐ranked model showed strong evidence of regional population structure and regional variation in population responses to the environment. As expected, age‐0 herring were generally associated with cooler, saltier conditions in spring. Density dependence was strong in all regions, suggesting that local factors influencing rearing conditions limited juvenile population growth across the estuary. Additionally, age‐0 abundance fluctuations were on average 15% more stable across the estuary than in individual regions, demonstrating that portfolio effects arising from population asynchrony have helped to stabilize recruitment across the estuary over the past four decades. We contend that ecosystem‐based fishery management strategies to restore eelgrass and tidal marsh rearing habitats could increase the carrying capacity of the estuary, further stabilizing the herring population and reducing the risk of fishery closures.