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The management and conservation of tuna and other transboundary marine species have to date been limited by an incomplete understanding of the oceanographic, ecological and socioeconomic factors mediating fishery overlap and interactions, and how these factors vary across expansive, open ocean habitats. Despite advances in fisheries monitoring and biologging technology, few attempts have been made to conduct integrated ecological analyses at basin scales relevant to pelagic fisheries and the highly migratory species they target. Here, we use vessel tracking data, archival tags, observer records, and machine learning to examine inter‐ and intra‐annual variability in fisheries overlap (2013–2020) of five pelagic longline fishing fleets with North Pacific albacore tuna (Thunnus alalunga, Scombridae). Although progressive declines in catch and biomass have been observed over the past several decades, the North Pacific albacore is one of the only Pacific tuna stocks primarily targeted by pelagic longlines not currently listed as overfished or experiencing overfishing. We find that fishery overlap varies significantly across time and space as mediated by (1) differences in habitat preferences between juvenile and adult albacore; (2) variation of oceanographic features known to aggregate pelagic biomass; and (3) the different spatial niches targeted by shallow‐set and deep‐set longline fishing gear. These findings may have significant implications for stock assessment in this and other transboundary fishery systems, particularly the reliance on fishery‐dependent data to index abundance. Indeed, we argue that additional consideration of how overlap, catchability, and size selectivity parameters vary over time and space may be required to ensure the development of robust, equitable, and climate‐resilient harvest control rules. [ABSTRACT FROM AUTHOR]

Species distribution models (SDMs) are becoming an important tool for marine conservation and management. Yet while there is an increasing diversity and volume of marine biodiversity data for training SDMs, little practical guidance is available on how to leverage distinct data types to build robust models. We explored the effect of different data types on the fit, performance and predictive ability of SDMs by comparing models trained with four data types for a heavily exploited pelagic fish, the blue shark (Prionace glauca), in the Northwest Atlantic: two fishery dependent (conventional mark‐recapture tags, fisheries observer records) and two fishery independent (satellite‐linked electronic tags, pop‐up archival tags). We found that all four data types can result in robust models, but differences among spatial predictions highlighted the need to consider ecological realism in model selection and interpretation regardless of data type. Differences among models were primarily attributed to biases in how each data type, and the associated representation of absences, sampled the environment and summarized the resulting species distributions. Outputs from model ensembles and a model trained on all pooled data both proved effective for combining inferences across data types and provided more ecologically realistic predictions than individual models. Our results provide valuable guidance for practitioners developing SDMs. With increasing access to diverse data sources, future work should further develop truly integrative modeling approaches that can explicitly leverage the strengths of individual data types while statistically accounting for limitations, such as sampling biases. [ABSTRACT FROM AUTHOR]

Ectothermy and endothermy in extant fishes are defined by distinct integrated suites of characters. Although only ⁓0.1% of fishes are known to have endothermic capacity, recent discoveries suggest that there may still be uncommon pelagic fish species with yet to be discovered endothermic traits. Among the most rarely encountered marine fishes, the louvar Luvarus imperialis is a remarkable example of adaptive evolution as the only extant pelagic species in the order Acanthuriformes (including surgeonfishes, tangs, unicornfishes and Moorish idol). Magnetic resonance imaging and gross necropsy did not yield evidence of cranial or visceral endothermy but revealed a central‐posterior distribution of myotomal red muscle that is a mixture of the character states typifying ectotherms (lateral‐posterior) and red muscle endotherms (central‐anterior). Dissection of a specimen confirmed, and an osteological proxy supported, that L. imperialis has not evolved the vascular rete that is vital to retaining heat in the red muscle. The combination of presumably relying on caudal propulsion while exhibiting internal red muscle without associated retia is unique to L. imperialis among all extant fishes, raising the macroevolutionary question of whether this species – in geologic timescales – will remain an ectotherm or evolve red muscle endothermy. [ABSTRACT FROM AUTHOR]

Salmonid fishes may reside within or migrate between stream and lake habitats, or undergo anadromous migrations between freshwater and the ocean. While the degree of anadromy of salmonids has been thoroughly compared, no analogous review has examined the degree of lake use. To assess the extent of reliance on lake habitat in this family, we considered 16 species of salmon, trout and charr from the genera Oncorhynchus, Salmo and Salvelinus, comparing their (a) use of lakes as spawning habitat, (b) rearing strategies in lakes, and (c) occurrence and diversity of lacustrine trophic polymorphism. In identifying the primary life‐history patterns of each species and exploring the lesser‐known lacustrine behaviours, we found that the extent of reliance on lakes exhibits a negative association with the degree of anadromy. Oncorhynchus rely least on lakes, Salmo to an intermediate level and Salvelinus the most, opposite of the general prevalence of anadromy among these genera. Lakes are critical to adfluvial and lake‐resident salmonids, but they also support anadromous and fluvial life histories by providing spawning, rearing, overwintering and/or summer refuge habitat. Adfluviality, although a non‐anadromous life history, consists of similar migration‐related traits and behaviours as anadromy, including the parr–smolt transformation, sex‐biased patterns of migration and residency, and the presence of precocious males. Lakes support life‐history variants, reproductive ecotypes and trophic morphs unique to lacustrine habitat. Therefore, conservation of salmonids is dependent on maintaining the diversity and quality of their habitats, including lakes. [ABSTRACT FROM AUTHOR]

The Mediterranean spearfish (Tetrapturus belone) is one of the least‐studied istiophorid billfishes, with little known of its biology, ecology, and behavior. To assess the species' movement and thermal niche, we analyzed telemetry data from, to our knowledge, the first and only Mediterranean spearfish ever outfitted with a pop‐up satellite archival transmitting tag. Throughout a 29‐day deployment during July and August 2015, the fish travelled in Italian waters of the Tyrrhenian and Ligurian Seas, spending on average 93% of each 24‐hr period above 30 m and exhibiting a diel activity pattern comprised of daytime vertical movement and nighttime near‐surface residency. The preferred thermal niche was 26–28°C, but the spearfish experienced temperatures as low as 14.2°C during descents. Vertical distribution was limited throughout the deployment with more time spent at depth in areas where the thermocline was comparatively deeper and weaker, consistent with habitat compression experienced by other billfishes. [ABSTRACT FROM AUTHOR]

Migratory behaviour patterns in animals are controlled by a complex genetic architecture. Rainbow trout (Oncorhynchus mykiss) is a salmonid fish that spawns in streams but exhibits three primary life history pathways: stream‐resident (fluvial), lake‐migrant (adfluvial) and ocean‐migrant (anadromous). Previous studies examining fluvial and anadromous O. mykiss have identified several genes associated with life history divergence including the presence of an inversion complex within chromosome 5 (Omy05) that appears to maintain a suite of linked genes controlling migratory behaviour. However, adfluvial trout are migratory without being anadromous, and the genetic basis for this life history has not been investigated from evolutionary perspectives. We sampled wild, native nonanadromous rainbow trout occupying connected stream and lake habitats in a southwest Alaskan watershed to determine whether these fish exhibit genetic divergence between fluvial and adfluvial ecotypes, and whether that divergence parallels that documented in fluvial and anadromous O. mykiss. Data from restriction site‐associated DNA (RAD) sequencing revealed an association between frequencies of both the Omy05 inversion complex and other single nucleotide polymorphisms (SNPs) with habitat type (stream or lake), supporting the genetic divergence of fluvial and adfluvial individuals in sympatry. The presence of a genetic basis for migration into lakes, analogous to that documented for anadromy, indicates that the adfluvial ecotype must be recognized separately from the fluvial form of O. mykiss even though neither is anadromous. These results highlight the genetic architecture underlying migration and the importance of chromosomal inversions in promoting and sustaining intraspecific diversity. [ABSTRACT FROM AUTHOR]

Wild capture fisheries produce 90 million tonnes of food each year and have the potential to provide sustainable livelihoods for nearly 40 million people around the world (http://www.fao.org/3/a-i5555e.pdf). After decades of overfishing since industrialization, many global fish stocks have recovered, a change brought about through effective management. We provide a synthetic overview of three approaches that managers use to sustain stocks: regulating catch and fishing mortality, regulating effort and regulating spatial access. Within each of these approaches, we describe common restrictions, how they alter incentives to change fishing behaviour, and the resultant ecological, economic and community‐level outcomes. For each approach, we present prominent case‐studies that illustrate behaviour and the corresponding performance. These case‐studies show that sustaining target stocks requires a hard limit on fishing mortality under most conditions, but that additional measures are required to generate economic benefits. Different systems for allocation allow stakeholder communities to strike a locally acceptable balance between profitability and employment. [ABSTRACT FROM AUTHOR]

The blue marlin ( Makaira nigricans) is a highly migratory pelagic predator of tropical and subtropical seas. Information on the habitat use of marine species is fundamental to understanding their ecology and population dynamics and is needed to inform responsible management strategies. Using a long-term satellite tagging data set from The International Game Fish Association Great Marlin Race, we examined habitat use and how oxygen and temperature influence the horizontal and vertical distributions of blue marlin in the Central Pacific. Blue marlin primarily occurred in warm waters (26-30°C) and exhibited a diel bimodal depth distribution across the 5-year data record (2009-2013), with fish spending the majority of their time near the surface at night and at deeper depths during the day (25-100 m). The depth distribution of blue marlin was limited in areas where low oxygen and/or temperature conditions occur closer to the surface, with the extent of habitat compression being greatest when both oxygen and temperature were limiting. The migrations of blue marlin appeared restricted during the 2010 La Niña, when increased equatorial upwelling resulted in an extension of the cold, low oxygen waters of the cold tongue into the Central Pacific, creating a barrier to the trans-equatorial migrations that occurred during all other tagging years. If the frequency and intensity of La Niña events increases and the oxygen minimum layer continues to expand as has been predicted under certain climate change scenarios, the migratory behavior and habitat availability of blue marlin may be impacted. [ABSTRACT FROM AUTHOR]