Near resonance acoustic scattering from organized schools of juvenile Atlantic bluefin tuna (Thunnus thynnus)

Schools of Atlantic bluefin tuna (Thunnus thynnus) can exhibit highly organized spatial structure within the school. This structure was quantified for dome shaped schools using both aerial imagery collected from a commercial spotter plane and 400 kHz multibeam echo sounder data collected on a fishing vessel in 2009 in Cape Cod Bay, MA. Observations from one school, containing an estimated 263 fish within an approximately ellipsoidal volume of 1900 m3, were used to seed an acoustic model that estimated the school target strength at frequencies between 10 and 2000 Hz. The fish\u27s swimbladder resonance was estimated to occur at approximately 50 Hz. The acoustic model examined single and multiple scattering solutions and also a completely incoherent summation of scattering responses from the fish. Three levels of structure within the school were examined, starting with fish locations that were constrained by the school boundaries but placed according to a Poisson process, then incorporating a constraint on the distance to the nearest neighbor, and finally adding a constraint on the bearing to the nearest neighbor. Results suggest that both multiple scattering and spatial organization within the school should be considered when estimating the target strength of schools similar to the ones considered here

Decline in condition of northern bluefin tuna (Thunnus thynnus) in the Gulf of Maine

The northern bluefin tuna (Thunnus thynnus) is a highly mobile apex predator in the Gulf of Maine. Despite current stock assessments that indicate historically high abundance of its main prey, Atlantic herring (Clupea harengus), commercial fishermen have observed declines in the somatic condition of northern bluefin tuna during the last decade. We examined this claim by reviewing detailed logbooks of northern bluefin tuna condition from a local fishermen’s cooperative and applying multinomial regression, a robust tool for exploring how a categorical variable may be related to other variables of interest. The data set contained >3082 observations of condition (fat and oil content and fish shape) from fish landed between 1991 and 2004. Energy from stored lipids is used for migration and reproduction; therefore a reduction in energy acquisition on bluefin tuna feeding grounds could diminish allocations to growth and gamete production and have detrimental consequences for rebuilding the western Atlantic population. A decline in northern bluefin tuna somatic condition could indicate substantial changes in the bottom-up transfer of energy in the Gulf of Maine, shifts in their reproductive or migratory patterns, impacts of fishing pressure, or synergistic effects from multiple causes

Changes in the Distribution of Atlantic Bluefin Tuna (Thunnus thynnus) in the Gulf of Maine 1979-2005

The Gulf of Maine, NW Atlantic Ocean, is a productive, seasonal foraging ground for Atlantic bluefin tuna (Thunnus thynnus), but commercial landings of adult size classes were up to 40% below the allocated total allowable catch between 2004 to 2008 for the rod and reel, harpoon, and purse seine categories in the Gulf of Maine. Reduction in Atlantic bluefin tuna catches in the Gulf of Maine could represent a decline in spawning stock biomass, but given wide-ranging, complex migration patterns, and high energetic requirements, an alternative hypothesis is that their dispersal patterns shifted to regions with higher prey abundance or profitability, reducing availability to U.S. fishing fleets. This study fit generalized linear models to Atlantic bluefin tuna landings data collected from fishermen’s logbooks (1979-2005) as well as the distances between bluefin tuna schools and Atlantic herring (Clupea harengus), a primary prey species, to test alternative hypotheses for observed shifts in Atlantic bluefin tuna availability in the Gulf of Maine. For the bluefin model, landings varied by day of year, latitude and longitude. The effect of latitude differed by day of year and the effect of longitude differed by year. The distances between Atlantic bluefin tuna schools and Atlantic herring schools were significantly smaller (p<0.05) than would be expected from a randomly distributed population. A time series of average bluefin tuna school positions was positively correlated with the average number of herring captured per tow on Georges Bank in spring and autumn surveys respectively (p<0.01, r2=0.24, p<0.01, r2=0.42). Fishermen’s logbooks contributed novel spatial and temporal information towards testing these hypotheses for the bluefin tuna fishery

Striped marlin in their Pacific Ocean milieu: Vertical movements and habitats vary with time and place

Striped marlin, Kajikia audax, a top bycatch of the longline fishery, has been designated as being in overfished condition in the Western and Central North Pacific, and overfishing is still occurring. This prompts an urgent need to devise conservation and management measures based on the best, current information on the biology and ecology of this species. Despite decades of conventional tagging around the Hawaiian waters, ecological research on striped marlin in the Central North Pacific has been lacking since 2005, and little is known about striped marlin’s vertical habitat, diving behavior and bycatch vulnerability in this area. To address this knowledge void, 31 popup satellite archival tags (4 X-Tags; Microwave Telemetry, Inc. and 27 MiniPATs; Wildlife Computers Inc.) were deployed on striped marlin (138-192 cm eye fork length) between 2016 and 2019 via the Hawaii-based longline fleet. Transmitted time series records revealed striped marlin spent 38 and 81% of their day and night in the top 5 m, with median daytime and night depths of 44 m and 2 m, respectively. Temperatures experienced were 23.3°C, daytime median, and 24.6°C, nighttime median, to a minimum of 7.6°C at the deepest depth logged, 472 m. Striped marlin exhibited distinct swimming behaviors, including diel depth distributions, excursions around the top of the thermocline, and extended time at the surface, most likely reflecting the dynamic biophysical environment and intrinsic life history of this highly migratory predator. High post-release survivorship (86%) in tagged striped marlin, and their predominant use of the sea surface and mixed layer indicate that live release measures can be a viable bycatch reduction strategy

Predicting trophic position in sharks of the north-west Atlantic Ocean using stable isotope analysis

Author Posting. © Cambridge University Press, 2003. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Journal of the Marine Biological Association of the UK 83 (2003): 1347-1350, doi:10.1017/S0025315403008798.Trophic positions (TP) were estimated for the blue shark (Prionace glauca), shortfin mako (Isurus oxyrinchus), thresher shark (Alopias vulpinus), and basking shark (Cetorhinus maximus) using stable isotope ratios of carbon ([delta]13C) and nitrogen ([delta]15N). The basking shark had the lowest TP (3·1) and [delta]15N value (10·4‰), whereas the thresher shark had the highest values (4·5, 15·2‰). Mako sharks showed considerable variation in TP and isotopic values, possibly due to foraging from both inshore and offshore waters. Thresher sharks were significantly more enriched in [delta]15N than blue sharks and mako sharks, suggesting a different prey base. The [delta]13C values of thresher sharks and mako sharks varied significantly, but neither was significantly different from that of blue sharks. No statistical differences were found between our TP estimations and those derived from published stomach contents analyses, indicating that stable isotope data may be used to estimate the trophic status of sharks.This work was supported by National Marine Fisheries Service Grant NA16MF1323 to M.E.L

Horizontal And Vertical Movements Of Juvenile Bluefin Tuna (Thunnus Thynnus), In Relation To Oceanographic Conditions Of The Western North Atlantic, Determined With Ultrasonic Telemetry

We employed ultrasonic transmitters to follow (for up to 48 h) the horizontal and vertical movements of five juvenile (6.8-18.7 kg estimated body mass) bluefin tuna (Thunnus thynnus) in the western North Atlantic (off the eastern shore of Virginia). Our objective was to document the fishes\u27 behavior and distribution in relation to oceanographic conditions and thus begin to address issues that currently limit population assessments based on aerial surveys. Estimation of the trends in adult and juvenile Atlantic bluefin tuna abundance by aerial surveys, and other fishery-independent measures, is considered a priority. Juvenile bluefin tuna spent the majority of their time over the continental shelf in relatively shallow water (generally less then 40 m deep). Fish used the entire water column in spite of relatively steep vertical thermal gradients (approximate to24degreesC at the surface and approximate to12degreesC at 40 m depth), but spent the majority of their time (approximate to90%) above 15 m and in water warmer then 20degreesC, Mean swimming speeds ranged from 2.8 to 3.3 knots, and total distance covered from 152 to 289 km (82-156 nmi). Because fish generally remained within relatively confined areas, net displacement was only 7.7-52.7 km (4.1-28.4 nmi). Horizontal movements were not correlated with sea surface temperature. We propose that it is unlikely that juvenile bluefin tuna in this area can detect minor horizontal temperature gradients (generally less then 0.5degreesC/km) because of the steep vertical temperature gradients (up to approximate to0.6degreesC/m) they experience during their regular vertical movements. In contrast, water clarity did appear to influence behavior because the fish remained in the intermediate water mass between the turbid and phytoplankton-rich plume exiting Chesapeake Bay (and similar coastal waters) and the clear oligotrophic water east of the continental shelf

Single nucleotide polymorphism discovery in albacore and Atlantic bluefin tuna provides insights into worldwide population structure.

The optimal management of the commercially important, but mostly over-exploited, pelagic tunas, albacore (Thunnus alalunga Bonn., 1788) and Atlantic bluefin tuna (BFT; Thunnus thynnus L., 1758), requires a better understanding of population structure than has been provided by previous molecular methods. Despite numerous studies of both species, their population structures remain controversial. This study reports the development of single nucleotide polymorphisms (SNPs) in albacore and BFT and the application of these SNPs to survey genetic variability across the geographic ranges of these tunas. A total of 616 SNPs were discovered in 35 albacore tuna by comparing sequences of 54 nuclear DNA fragments. A panel of 53 SNPs yielded FST values ranging from 0.0 to 0.050 between samples after genotyping 460 albacore collected throughout the distribution of this species. No significant heterogeneity was detected within oceans, but between-ocean comparisons (Atlantic, Pacific and Indian oceans along with Mediterranean Sea) were significant. Additionally, a 17-SNP panel was developed in Atlantic BFT by cross-species amplification in 107 fish. This limited number of SNPs discriminated between samples from the two major spawning areas of Atlantic BFT (FST = 0.116). The SNP markers developed in this study can be used to genotype large numbers of fish without the need for standardizing alleles among laboratories.This work was supported by ATM2010Hegaluze (351BI20090047), ATM2009Hegalabur (351BI20090034) and ATM2008Bonorte (ACM2008BONORTE) projects funded by the Basque Government, and the ACEITUNA (CTM2011-27505) project funded by the Spanish Ministerio de Economía y Competitividad

Dispersal Routes and Habitat Utilization of Juvenile Atlantic Bluefin Tuna, Thunnus thynnus, Tracked with Mini PSAT and Archival Tags

Between 2005 and 2009, we deployed 58 miniature pop-up satellite archival tags (PSAT) and 132 implanted archival tags on juvenile Atlantic bluefin tuna (age 2–5) in the northwest Atlantic Ocean. Data returned from these efforts (n = 26 PSATs, 1 archival tag) revealed their dispersal routes, horizontal and vertical movements and habitat utilization. All of the tagged bluefin tuna remained in the northwest Atlantic for the duration observed, and in summer months exhibited core-use of coastal seas extending from Maryland to Cape Cod, MA, (USA) out to the shelf break. Their winter distributions were more spatially disaggregated, ranging south to the South Atlantic Bight, northern Bahamas and Gulf Stream. Vertical habitat patterns showed that juvenile bluefin tuna mainly occupied shallow depths (mean  = 5–12 m, sd  = 15–23.7 m) and relatively warm water masses in summer (mean  = 17.9–20.9°C, sd  = 4.2–2.6°C) and had deeper and more variable depth patterns in winter (mean  = 41–58 m, sd  = 48.9–62.2 m). Our tagging results reveal annual dispersal patterns, behavior and oceanographic associations of juvenile Atlantic bluefin tuna that were only surmised in earlier studies. Fishery independent profiling from electronic tagging also provide spatially and temporally explicit information for evaluating dispersals rates, population structure and fisheries catch patterns

Spatial dynamics and mixing of bluefin tuna in the Atlantic Ocean and Mediterranean Sea revealed using next generation sequencing

The Atlantic bluefin tuna is a highly migratory species emblematic of the challenges associated with shared fisheries management. In an effort to resolve the species’ stock dynamics, a genomewide search for spatially informative single nucleotide polymorphisms (SNPs) was undertaken, by way of sequencing reduced representation libraries. An allele frequency approach to SNP discovery was used, combining the data of 555 larvae and young-of-the-year (LYOY) into pools representing major geographical areas and mapping against a newly assembled genomic reference. From a set of 184,895 candidate loci, 384 were selected for validation using 167 LYOY. A highly discriminatory genotyping panel of 95 SNPs was ultimately developed by selecting loci with the most pronounced differences between western Atlantic and Mediterranean Sea LYOY. The panel was evaluated by genotyping a different set of LYOY (n = 326), and from these, 77.8% and 82.1% were correctly assigned to western Atlantic and Mediterranean Sea origins, respectively. The panel revealed temporally persistent differentiation among LYOY from the western Atlantic and Mediterranean Sea (FST = 0.008, p = .034). The composition of six mixed feeding aggregations in the Atlantic Ocean and Mediterranean Sea was characterized using genotypes from medium (n = 184) and large (n = 48) adults, applying population assignment and mixture analyses. The results provide evidence of persistent population structuring across broad geographic areas and extensive mixing in the Atlantic Ocean, particularly in the mid-Atlantic Bight and Gulf of St. Lawrence. The genomic reference and genotyping tools presented here constitute novel resources useful for future research and conservation efforts